UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Effects of repeated fertilization on nitrogen fluxes in a young lodgepole pine stand as measured by an… Whynot, Tim W. 1989

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1989_A6_7 W49.pdf [ 8.81MB ]
Metadata
JSON: 831-1.0097575.json
JSON-LD: 831-1.0097575-ld.json
RDF/XML (Pretty): 831-1.0097575-rdf.xml
RDF/JSON: 831-1.0097575-rdf.json
Turtle: 831-1.0097575-turtle.txt
N-Triples: 831-1.0097575-rdf-ntriples.txt
Original Record: 831-1.0097575-source.json
Full Text
831-1.0097575-fulltext.txt
Citation
831-1.0097575.ris

Full Text

EFFECTS OF REPEATED FERTILIZATION ON NITROGEN FLUXES IN A YOUNG LODGEPOLE PINE STAND AS MEASURED BY AN IN SITU SEQUENTIAL CORING TECHNIQUE By TIM W. WHYNOT Univ e r s i t y of New Brunswick, 1985 SUBMITTED IN PARTIAL FULFILLMENT REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (DEPARTMENT OF FORESTRY) We accept t h i s thesis as conforming to the required standard B.Sc.F., A THESIS OF THE THE UNIVERSITY OF BRITISH COLUMBIA July 4, 1989 c Tim W. Whynot, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Forestry The University of British Columbia Vancouver, Canada DE-6 (2/88) ABSTRACT A young l o d g e p o l e p i n e s t a n d has been f e r t i l i z e d f o u r t imes s i n c e 1982 w i t h f o u r l e v e l s o f n i t r o g e n (N) f e r t i l i z e r w i t h o r w i t h o u t o t h e r macro and m i c r o n u t r i e n t s ("PK") . The e f f e c t o f these r e p e a t e d f e r t i l i z e r a d d i t i o n s on N m i n e r a l i z a t i o n and uptake has been a s s e s s e d u s i n g a s e q u e n t i a l c o r i n g i n s i t u t e c h n i q u e . Both N and PK f e r t i l i z a t i o n appear t o have i n c r e a s e d N m i n e r a l i z a t i o n and uptake (but not s i g n i f i c a n t s t a t i s t i c a l l y ) , w h i l e N a d d i t i o n s have s i g n i f i c a n t l y i n c r e a s e d the i n o r g a n i c N c o n c e n t r a t i o n i n the s o i l . Because N m i n e r a l i z a t i o n has been i n c r e a s e d , i t appears as though r e p e a t e d f e r t i l i z a t i o n has r e s u l t e d i n a s u s t a i n e d i n c r e a s e i n s i t e q u a l i t y as opposed t o a s h o r t t erm i n c r e a s e i n t r e e p r o d u c t i o n . The i n c r e a s e d uptake demand o f the t r e e s on the h e a v i l y f e r t i l i z e d p l o t s can be p a r t i a l l y met by i n c r e a s e d m i n e r a l i z a t i o n ; t h e r e f o r e , f e r t i l i z e r a p p l i c a t i o n on these p l o t s c o u l d t h e o r e t i c a l l y be reduced w i t h o u t r e d u c i n g the r a t e o f u p t a k e . Even though m o i s t u r e appears t o be l i m i t i n g on the s i t e , s i g n i f i c a n t growth responses i n d i c a t e t h a t an improvement i n s i t e n u t r i e n t s t a t u s has i n c r e a s e d t h e degree i i t o which growth p o t e n t i a l f o r the s i t e has been a c h i e v e d . However, r e sponses have p r o b a b l y been reduced by m o i s t u r e l i m i t a t i o n s on the s i t e . The s e q u e n t i a l c o r i n g t e c h n i q u e appears t o o f f e r s e v e r a l advantages over o t h e r f i e l d and l a b t e c h n i q u e s f o r a s s e s s i n g N f l u x e s . Because i t r e s u l t s i n m i n i m a l s o i l d i s t u r b a n c e and i s s e n s i t i v e t o e n v i r o n m e n t a l f a c t o r s which a f f e c t N p r o c e s s e s , i t s h o u l d be u s e f u l f o r t e s t i n g models o f N m i n e r a l i z a t i o n and e v a l u a t i n g more r a p i d indexes o f N a v a i l a b i l i t y . G r o s s m i n e r a l i z a b l e N ( i n c u b a t e d m i n e r a l N c o n c e n t r a t i o n ) e s t i m a t e d by a n a e r o b i c i n c u b a t i o n i n t h e l a b o r a t o r y produced r e s u l t s c o n s i s t e n t w i t h t h o s e o b t a i n e d i n t h e f i e l d . G r o s s m i n e r a l i z a b l e N a l s o c o r r e l a t e d more c l o s e l y w i t h f o l i a r N c o n c e n t r a t i o n and c o n t e n t (on a p e r n e e d l e b a s i s ) t h a n i n s i t u m i n e r a l i z a t i o n . However, ne t m i n e r a l i z a b l e N (gross minus i n i t i a l N m i n e r a l c o n c e n t r a t i o n ) d i d not produce r e s u l t s c o n s i s t e n t w i t h the s e q u e n t i a l c o r i n g d a t a from t h e f i e l d . S e q u e n t i a l c o r i n g a l s o r e q u i r e s v e r y i n t e n s i v e s p a t i a l and t e m p o r a l s a m p l i n g (at l e a s t f o l l o w i n g f e r t i l i z a t i o n ) which w i l l r e s t r i c t i t s use t o r e s e a r c h , and t h e n o n l y t o s t u d i e s which r e q u i r e a c c u r a t e e s t i m a t e s o f i n s i t u N f l u x e s , as opposed t o a s i m p l e index o f N a v a i l a b i l i t y . i i i TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES v i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS x i CHAPTER 1: INTRODUCTION 1 Background 1 O b j e c t i v e s 5 CHAPTER 2: LITERATURE REVIEW 7 Lodgepo le P i n e : Importance and Respons ivenes s t o F e r t i l i z a t i o n 7 "Optimum" N u t r i t i o n T r i a l s 9 I n t r o d u c t i o n 9 R a t i o n a l e 11 F e r t i l i z e r E f f i c i e n c y , F a t e and Response D u r a t i o n . 17 P h y s i o l o g i c a l B a s i s o f Improved N u t r i t i o n 24 M o i s t u r e L i m i t a t i o n s t o Growth P o t e n t i a l and N u t r i e n t - M o i s t u r e - G r a s s I n t e r a c t i o n s 28 N i t r o g e n C y c l i n g 33 M i n e r a l i z a t i o n and F a c t o r s I n f l u e n c i n g I t . . . . . 34 A m m o n i f i c a t i o n and I m m o b i l i z a t i o n 35 N i t r i f i c a t i o n 39 N i t r o g e n Uptake 40 B i o c h e m i c a l N i t r o g e n C y c l i n g 43 Assessment o f N i t r o g e n S t a t u s 45 P l a n t T i s s u e A n a l y s i s 46 S o i l A n a l y s i s 52 L a b o r a t o r y Indexes 54 B i o l o g i c a l Indexes 54 C h e m i c a l Indexes 58 F i e l d Techn iques 60 CHAPTER 3: MATERIALS AND METHODS 66 i v S i t e D e s c r i p t i o n .. 66 The "Optimum" N u t r i t i o n Exper iment 70 Measurement o f N i t r o g e n M i n e r a l i z a t i o n 73 Methodology f o r In S i t u Measurements 73 F i e l d Methods 74 L a b o r a t o r y Methods 77 F o l i a r A n a l y s i s , Biomass and Uptake C a l c u l a t i o n s . . . 78 S t a t i s t i c a l A n a l y s i s 79 CHAPTER 4: RESULTS 82 In S i t u N i t r o g e n F l u x e s 82 Tempora l V a r i a t i o n 82 Growing Season F l u x e s 84 O t h e r A n a l y s e s 94 A n a e r o b i c I n c u b a t i o n 94 F o l i a r A n a l y s i s 94 S o i l M o i s t u r e Content 97 N i t r o g e n Uptake Based on Biomass Increment 101 C o r r e l a t i o n s Between N i t r o g e n Indexes 103 CHAPTER 5: DISCUSSION 108 E f f e c t s o f Repeated F e r t i l i z a t i o n on N i t r o g e n M i n e r a l i z a t i o n and Uptake 108 G r a s s and M o i s t u r e L i m i t a t i o n s t o F e r t i l i z e r Response 119 E v a l u a t i o n o f S e q u e n t i a l C o r i n g T e c h n i q u e 121 CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS 132 LITERATURE CITED 137 APPENDIX 153 v L I S T OF TABLES Page T a b l e 1. T a b l e 2 T a b l e 3 T a b l e 4 T a b l e 5, T a b l e 6, T a b l e 7, T a b l e 8 T a b l e 9, T o t a l p r e c i p i t a t i o n and average d a i l y noon t empera ture f o r each o f t h e s o i l exposure p e r i o d s 67 E i g h t f e r t i l i z e r t r e a t m e n t s as a 2X4 f a c t o r i a l d e s i g n and N and "PK" s p e c i f i c a t i o n s . The n u t r i e n t s a r e added a n n u a l l y depending on f o l i a r N c o n c e n t r a t i o n Amount and t i m i n g o f f e r t i l i z e r m a c r o -n u t r i e n t s a p p l i e d i n exper iment from 1982 t o 1988 Mean monthly ne t m i n e r a l i z a t i o n (net i m m o b i l i z a t i o n i n d i c a t e d by n e g a t i v e v a l u e s ) , u p t a k e , maximum l e a c h i n g , and a v a i l a b l e N v a l u e s by t r e a t m e n t . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n=3 except NOPK where n=2) Growing season ne t m i n e r a l i z a t i o n , u p t a k e , l o s s , and mean exchangeable N f o r each t r e a t m e n t . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n=3 except NOPK where n=2). . . Net a m m o n i f i c a t i o n , ne t n i t r i f i c a t i o n , ammonium- and n i t r a t e - N uptake and l o s s , and mean exchangeable ammonium- and n i t r a t e -N f o r each t r e a t m e n t . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n=3 except NOPK where n=2) 71 73 83 84 91 C o n c e n t r a t i o n o f exchangeable ammonium-N and n i t r a t e - N a t two depths and b u l k samples c o l l e c t e d i n June s e p a r a t e from t h e o t h e r c o r e samples . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s 92 R e q u i r e d sample s i z e t o e s t i m a t e mean s o i l i n o r g a n i c N p o o l w i t h i n t h e s t a t e d a l l o w a b l e e r r o r 90 % o f the t ime (based on a compos i t e o f two cores ) 92 G r o s s and net m i n e r a l i z a b l e N v a l u e s o b t a i n e d by a n a e r o b i c i n c u b a t i o n f o r 7 days a t 40 ° C . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n=3 except NOPK where n=2) 94 v i T a b l e 10. N i t r o g e n c o n c e n t r a t i o n , n e e d l e w e i g h t , and N c o n t e n t f o r c u r r e n t y e a r s f o l i a g e sampled i n September, 1988. S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s 97 T a b l e 11. Mean 1988 need le c o n c e n t r a t i o n o f macro and m i c r o n u t r i e n t s o f c u r r e n t y e a r s f o l i a g e f o r a l l t r e a t m e n t s . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s 100 T a b l e 12. Mean s o i l m o i s t u r e c o n t e n t s f o r growing s e a s o n . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s 100 T a b l e 13. Mean s o i l m o i s t u r e c o n t e n t f o r ambient s o i l , and s o i l i n c u b a t e d i n c o v e r e d and open PVC tubes f o r a l l t r e a t m e n t s . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s 101 T a b l e 14. Mean above-ground biomass e s t i m a t e s and n i t r o g e n uptake e s t i m a t e s based on changes i n above-ground biomass f o r a l l t r e a t m e n t s . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n=3) . . . 104 T a b l e 15. C o r r e l a t i o n c o e f f i c i e n t s between n i t r o g e n a v a i l a b i l i t y indexes o r measurements and f e r t i l i z e r a p p l i c a t i o n . 104 T a b l e 16. Treatment r a n k i n g s from h i g h e s t t o lowes t f o r each o f the parameters measured. . . . 107 v i i L I S T OF FIGURES Page F i g u r e 1. R e s u l t s from an optimum n u t r i t i o n exper iment i n S c o t s p i n e (P inus s y l v e s t r i s L . ) i n Sweden. a) Autumn c o n c e n t r a t i o n s o f n i t r o g e n i n c u r r e n t y e a r s n e e d l e s o f t r e e s f e r t i l i z e d a n n u a l l y from 1971 onwards. b) Y e a r l y stem growth (1972-1979) p l o t t e d a g a i n s t n e e d l e n i t r o g e n c o n c e n t r a t i o n . NI r e f e r s t o an a n n u a l dose o f N i n ammonium n i t r a t e o f 60 k g / h a from 1971-1973, 40 k g / h a from 1974-1976, and 30 k g / h a i n 1977. N2 and N3 a r e two and t h r e e t imes N I , r e s p e c t i v e l y . (From Tamm and A r o n s s o n , 1982) 13 F i g u r e 2. B a s a l a r e a development (a) and annua l volume p r o d u c t i o n (b) o f S c o t s p i n e (P inus s y l v e s t r i s L . ) . The t r e a t m e n t s a r e c o n t r o l (0 ) , i r r i g a t i o n ( I ) , r e p e a t e d f e r t i l i z a t i o n w i t h complete f e r t i l i z e r s ( F ) , and d a i l e y f e r t i g a t i o n w i t h a complete l i q u i d f e r t i l i z e r d i s t r i b u t e d v i a i r r i g a t i o n water (IF) (from I n g e s t a d , 1987) 18 F i g u r e 3. L o c a t i o n o f t h e optimum n u t r i t i o n exper iment i n r e l a t i o n t o Okanagan F a l l s . . 69 F i g u r e 4. S o i l p r o f i l e o f s tudy s i t e from r o a d c u t , showing t y p i c a l depth o f r o o t p e n e t r a t i o n 69 F i g u r e 5. P l o t l a y o u t and e x p e r i m e n t a l d e s i g n o f l o d g e p o l e p i n e optimum n u t r i t i o n exper iment 72 F i g u r e 6. M o n t h l y v a r i a t i o n i n ne t n i t r o g e n m i n e r a l i z a t i o n and uptake f o r c o n t r o l (a) and NOPK (b) t r e a t m e n t s . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f t h e mean 85 F i g u r e 7. M o n t h l y v a r i a t i o n i n ne t n i t r o g e n m i n e r a l i z a t i o n and uptake f o r NI (a) and N1PK (b) t r e a t m e n t s . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f the mean F i g u r e 8. M o n t h l y v a r i a t i o n i n ne t n i t r o g e n v i i i 86 m i n e r a l i z a t i o n and uptake f o r N3 (a) and N3PK (b) t r e a t m e n t s . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f the mean 87 F i g u r e 9. V a r i a t i o n i n growing season net n i t r o g e n m i n e r a l i z a t i o n and uptake f o r t h r e e n i t r o g e n regimes w i t h o u t 1 1 PK" (a) and w i t h "PK" ( b ) . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f t h e mean . . . . 88 F i g u r e 10, V a r i a t i o n i n growing season net a m m o n i f i c a t i o n and n i t r i f i c a t i o n f o r t h r e e n i t r o g e n regimes w i t h o u t "PK" (a) and w i t h "PK" (b) F i g u r e 11. V a r i a t i o n i n growing season ammonium and n i t r a t e uptake f o r t h r e e n i t r o g e n reg imes w i t h o u t "PK" (a) and w i t h "PK" (b) • 89 90 F i g u r e 12. F i g u r e 13 The c o n c e n t r a t i o n o f ammonium and n i t r a t e a t two depths f o r t h r e e n i t r o g e n reg imes w i t h o u t "PK" (a) and w i t h "PK" ( b ) . . . . V a r i a t i o n i n g r o s s and net m i n e r a l i z a b l e N (determined by a n a e r o b i c i n c u b a t i o n i n t h e l a b o r a t o r y ) f o r t h r e e n i t r o g e n reg imes w i t h o u t "PK" (a) and w i t h 1 1 PK" (b) . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f the mean , 93 95 F i g u r e 14. Temporal v a r i a t i o n i n need le n i t r o g e n c o n c e n t r a t i o n (a) and n i t r o g e n c o n t e n t (b) f o r c u r r e n t y e a r s f o l i a g e f o r s i x t r e a t m e n t s from J u l y 20 t o September 25 . . 96 F i g u r e 15. V a r i a t i o n i n c u r r e n t y e a r s f o l i a g e f o r f o u r n i t r o g e n f e r t i l i z e r regimes w i t h and w i t h o u t "PK" a d d i t i o n s : a) n e e d l e N c o n c e n t r a t i o n , b) n e e d l e w e i g h t , and c) n e e d l e N c o n t e n t 98 F i g u r e 16. V a r i a t i o n i n monthly ne t n i t r o g e n m i n e r a l i z a t i o n and uptake f o r v a r y i n g s o i l m o i s t u r e c o n t e n t s : a) c o n t r o l , b) NO+PK, c) N l , d) Nl+PK, e) N3, and f) N3+PK 99 F i g u r e 17. V a r i a t i o n i n s o i l m o i s t u r e c o n t e n t s f o r b u l k s o i l , s o i l i n c u b a t e d i n c o v e r e d c o r e s , and s o i l i n c u b a t e d i n open c o r e s . i x Incubated s o i l s a r e r e p r e s e n t e d a t the end o f t h e exposure p e r i o d s 102 F i g u r e 18. Comparison o f f i v e s o i l n i t r o g e n indexes f o r t h r e e N f e r t i l i z e r regimes w i t h o u t "PK" (a) and w i t h "PK" ( b ) . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f t h e mean 105 F i g u r e 19 a) The change i n g r o s s and ne t m i n e r a l i z a b l e n i t r o g e n (determined by a n a e r o b i c i n c u b a t i o n i n the l a b o r a t o r y ) w i t h v a r i a t i o n i n ne t N m i n e r a l i z a t i o n e s t i m a t e d by i n s i t u s e q u e n t i a l c o r i n g . b) The change i n n e e d l e n i t r o g e n c o n t e n t o f c u r r e n t y e a r s f o l i a g e (sampled i n September) w i t h v a r i a t i o n i n growing season uptake e s imated by i n s i t u s e q u e n t i a l c o r i n g , 106 F i g u r e 20. P i n e g r a s s p r o d u c t i o n i n c o n t r o l (a) and N3+PK (b) p l o t s 113 F i g u r e 21. C a l c u l a t i o n o f N m i n e r a l i z a t i o n and uptake (+ l o s s e s ) r e f l e c t changes i n the b u l k a v a i l a b l e N p o o l d u r i n g the i n c u b a t i o n p e r i o d (from R a i s o n e t a l . . 1987) 127 x ACKNOWLEDGEMENTS I would l i k e t o thank my a d v i s o r , D r . G . F . Weetman, f o r h i s h e l p , i d e a s , and f i n a n c i a l s u p p o r t f o r the f i e l d and l a b work. Thanks a l s o go t o M i n T s z e f o r h i s t e c h n i c a l a s s i s t a n c e and f o r a n a l y s i s o f t h e e n d l e s s number o f samples which I p r o d u c e d f o r him, and R i c k F o u r n i e r f o r h i s h e l p i n g a t h e r i n g equipment and g e t t i n g t h i n g s o r g a n i z e d f o r the f i e l d and l a b work. I a l s o w i sh t o thank my o t h e r committee members, D r . T . M . B a l l a r d , and D r . J . P . Kimmins f o r t h e i r a d v i c e and s u g g e s t i o n s , and r e a d i n g o f the d r a f t s . Mike J u l l a l s o d e s e r v e s s p e c i a l acknowledgement f o r h i s p h y s i c a l endurance i n the f i e l d . F i n a l l y , I am g r e a t l y i n d e b t e d t o my f i a n c e e , L o r r a i n e , f o r t o u g h i n g out t h e heat and b l a c k f l i e s , c o u n t i n g a l l those n e e d l e s , and p r o v i d i n g much needed s u p p o r t d u r i n g t h e w r i t i n g p e r i o d , d e s p i t e the g r e a t p h y s i c a l d i s t a n c e between u s . x i 1 CHAPTER 1 INTRODUCTION BACKGROUND The need f o r f o r e s t p r o d u c t s by an expanding w o r l d p o p u l a t i o n i s expec ted t o grow a t the same t ime as the l a n d base f o r f o r e s t p r o d u c t i o n c o n t i n u e s t o s h r i n k (Thorud , 1983; Kimmins, 1985 and 1987) . A r e c e n t s tudy p r e d i c t e d a 53 p e r c e n t i n c r e a s e i n demand f o r a l l softwood p r o d u c t s between 1976 and 2030 ( F o r d , 1983) . In a d d i t i o n , our f o r e s t c r o p p r o d u c t i o n i s b e i n g c o n f i n e d t o p o o r e r s o i l s and t h o s e t h a t a r e more d i f f i c u l t t o manage (Thorud , 1983) . The i n t e n s i f i c a t i o n o f f o r e s t management p r a c t i c e s t o i n c r e a s e p r o d u c t i v i t y i s an a lmost c e r t a i n r e s u l t o f t h i s i n c r e a s e d need f o r f o r e s t p r o d u c t s (Keeney, 1980) . F e r t i l i z a t i o n i s p o t e n t i a l l y one o f t h e most c o s t e f f e c t i v e t r e a t m e n t s s i n c e s t u d i e s have shown t h a t t r e e growth i s l i m i t e d by n u t r i e n t s h o r t a g e s i n a l l major f o r e s t r e g i o n s o f Canada (Mahendrappa e t a l . . 1986) . I t i s g e n e r a l l y r e c o g n i z e d t h a t t h e a v a i l a b i l i t y o f n i t r o g e n (N) and water a r e two o f t h e main f a c t o r s l i m i t i n g p l a n t growth (Ingestad> 1987) , p a r t i c u l a r l y i n n o r t h e r n c o n i f e r o u s f o r e s t s . The prob lem l i e s no t i n the t o t a l amount o f n i t r o g e n i n an ecosys tem, b u t i n s t e a d i n the r a t e a t which t h e n i t r o g e n i s 2 made a v a i l a b l e t o t h e t r e e s . Gosz (1981) s t a t e d t h a t the u n a v a i l a b i l i t y o f n i t r o g e n i s the most s t r i k i n g c h a r a c t e r i s t i c o f t h e b o u n t i f u l q u a n t i t i e s o f n i t r o g e n s u r r o u n d i n g h i g h e r p l a n t s . A good b a s i s f o r d e t e c t i n g changes i n f o r e s t p r o d u c t i v i t y p o t e n t i a l brought on by management i s not a v a i l a b l e (Thorud , 1983) . The e f f e c t o f f e r t i l i z a t i o n and o t h e r management a c t i v i t i e s i s not a lways easy t o measure, e s p e c i a l l y i f t r e e s a r e not on t h e s i t e , o r a r e j u s t e s t a b l i s h i n g . Even i f t r e e s a r e a v a i l a b l e t o measure, i t i s u s u a l l y d e s i r a b l e t o u n d e r s t a n d why a growth response i s o b t a i n e d i n s t e a d o f s i m p l y d o i n g e m p i r i c a l measurements. F u r t h e r , s c i e n t i s t s i n f o r e s t r y have s t r e s s e d the need t o u n d e r s t a n d t h e i n t e r a c t i o n s between f o r e s t t r e e s and s o i l s as a p r e r e q u i s i t e f o r h i g h and s u s t a i n e d t i m b e r p r o d u c t i o n (Mahendrappa e t a l . , 1 9 8 6 ) . M o r r i s o n (1974) s t a t e d t h a t the aim o f f o r e s t n u t r i t i o n s t u d y i s t o d i s c u s s g e n e r a l s c i e n t i f i c p r i n c i p l e s (or p a t t e r n s ) which can e x p l a i n the p a s t , p r e s e n t and f u t u r e n u t r i e n t r e q u i r e m e n t s o f any f o r e s t . W h i l e n i t r o g e n uptake by p l a n t s i s p r o b a b l y the b e s t measure o f t h e s u p p l y i n g c a p a c i t y o f the s o i l , t h i s approach i s o n l y u s e f u l f o r s t u d y i n g s h o r t term N dynamics and i s d i f f i c u l t t o measure i n f o r e s t communit ies which have s u b s t a n t i a l biomass and t e m p o r a l l y v a r y i n g p r o d u c t i o n o f above and b e l o w - g r o u n d l i t t e r (Raison e t a l . . 1987) . Most o f our knowledge o f N assessment i n c o n i f e r o u s f o r e s t s r e s t s on agronomic p r i n c i p l e s , but agronomic methods 3 f o r a s s e s s i n g N a v a i l a b i l i t y o f t e n a r e i n e f f e c t i v e i n f o r e s t r y (Powers, 1984) . Of t h e many t e c h n i q u e s a t t empted , a l l have s u f f e r e d from one d e f i c i e n c y o r a n o t h e r . N i t r o g e n a v a i l a b i l i t y i s l a r g e l y d e t e r m i n e d by N m i n e r a l i z a t i o n - t h e m i c r o b i a l c o n v e r s i o n o f s o i l o r g a n i c N t o m i n e r a l N . I t has p r o v e n d i f f i c u l t t o measure m i n e r a l i z a t i o n r a t e s i n t h e f i e l d because o f a l a c k o f s u i t a b l e t e c h n i q u e and t h e i n h e r e n t v a r i a b i l i t y i n s o i l s . However, a s e q u e n t i a l c o r i n g i n s i t u t e c h n i q u e has been deve loped i n A u s t r a l i a f o r measur ing n i t r o g e n f l u x e s which may overcome some o f t h e t r a d i t i o n a l s h o r t c o m i n g s o f o t h e r f i e l d t e c h n i q u e s (Ra i son e t a l . , 1987) . C o n v e n t i o n a l f e r t i l i z a t i o n t r i a l s a r e u s e f u l f o r d e t e r m i n i n g growth responses t o f e r t i l i z e r a p p l i c a t i o n , but u s u a l l y do no t m a i n t a i n e l e v a t e d c o n s t a n t f o l i a r c o n c e n t r a t i o n s f o r v e r y l o n g . "Optimum" n u t r i t i o n e x p e r i m e n t s , on t h e o t h e r hand , a r e d e s i g n e d t o m a i n t a i n s e p a r a t e and c o n s t a n t n u t r i e n t l e v e l s ( p a r t i c u l a r l y N) o v e r extended p e r i o d s o f t ime by means o f p e r i o d i c o r annua l f e r t i l i z e r a p p l i c a t i o n s (Tamm and A r o n s s o n , 1982; Weetman and F o u r n i e r , 1984; Holmen e t a l . . 1986) . Optimum n u t r i t i o n exper iments have been w i d e l y used i n Sweden f o r Norway s p r u c e and S c o t s p i n e and a r e v e r y i m p o r t a n t f o r s t u d y i n g the e f f e c t s o f n u t r i e n t s u p p l y and f o l i a g e c o n c e n t r a t i o n s on ecosystem p r o c e s s e s (Tamm, 1969 and 1985; Holmen e t a l . . 1976) . A l s o , the q u e s t i o n o f whether h i g h growth r a t e s can be s u s t a i n e d by r e p e a t e d f e r t i l i z a t i o n i s o f p r a c t i c a l importance t o f o r e s t managers (Weetman and F o u r n i e r , 1984) . 4 These optimum n u t r i t i o n exper iments do no t r e a l l y p r o v i d e t h e t r e e s w i t h optimum n u t r i t i o n i n t h e sense o f b a l a n c e d n u t r i e n t s u p p l i e s (see I n g e s t a d 1979, 1982; I n g e s t a d and K a h r , 1985; I n g e s t a d and L u n d , 1986), but s i n c e they a t tempt t o de termine the optimum f o l i a r n u t r i e n t l e v e l s t h r o u g h r e p e a t e d , v a r y i n g r a t e s o f n u t r i e n t a d d i t i o n s , they have c o n v e n t i o n a l l y been c a l l e d "optimum" n u t r i t i o n exper iments (see Tamm, 1974, 85; Holmen e t a l . f 1976; Tamm and A r o n s s o n , 1982) . T h e r e f o r e , t h i s c o n v e n t i o n w i l l be f o l l o w e d i n t h i s t h e s i s . E s t l i n (1988) r e p o r t e d on the f i v e - y e a r growth r e s p o n s e s f o r an optimum n u t r i t i o n exper iment i n a young l o d g e p o l e p i n e (P inus c o n t o r t a D o u g l . v a r . l a t i f o l i a Engelm.) s t a n d i n S o u t h e r n I n t e r i o r B . C . He found t h a t p i n e growth was s i g n i f i c a n t l y i n c r e a s e d by r e p e a t e d f e r t i l i z a t i o n . P l o t s r e c e i v i n g two a p p l i c a t i o n s o f 150 and one a p p l i c a t i o n o f 75 kg N p e r h e c t a r e between 1982 and 1986, and o t h e r macro and m i c r o n u t r i e n t s (N3PK regime) produced 18, 72, 67, and 41 p e r c e n t more h e i g h t , b a s a l a r e a (stump h e i g h t and b r e a s t h e i g h t ) , and volume growth , r e s p e c t i v e l y , t h a n c o n t r o l p l o t s . The a d d i t i o n o f b o t h N and PK has produced i n t e r a c t i o n s i n growth r e s p o n s e , i n d i c a t i n g a r e q u i r e m e n t f o r b a l a n c e d n u t r i t i o n a t h i g h e r N a p p l i c a t i o n s . These growth responses a r e p r o b a b l y due t o i n c r e a s e d N uptake by t h e t r e e s when the i n o r g a n i c c o n c e n t r a t i o n i n the s o i l i s t e m p o r a r i l y e l e v a t e d by f e r t i l i z a t i o n (Johnson e t a l . , 1980; M i l l e r , 1981) . However, r e p e a t e d f e r t i l i z a t i o n may a l s o 5 s i g n i f i c a n t l y i n c r e a s e m i n e r a l i z a t i o n r a t e s , p a r t i c u l a r l y i f t h e amount o f N added i s l a r g e r e l a t i v e t o s i t e N c a p i t a l ( M i l l e r , 1981; B i n k l e y and R e i d , 1985; C a r l y l e , 1986) . OBJECTIVES The e f f e c t s o f f e r t i l i z a t i o n on N m i n e r a l i z a t i o n and uptake and t h e i n o r g a n i c N c o n c e n t r a t i o n s m a i n t a i n e d i n the s o i l have been i n v e s t i g a t e d u s i n g the s e q u e n t i a l c o r i n g t e c h n i q u e . The change i n p o t e n t i a l m i n e r a l i z a b l e N has a l s o been examined i n t h e l a b o r a t o r y . S i n c e the l o d g e p o l e p i n e optimum n u t r i t i o n t r i a l s i t e appears t o be m o i s t u r e l i m i t e d ( H a s k i n , 1985) , i t i s l i k e l y t h a t m o i s t u r e has l i m i t e d growth response and t h a t f e r t i l i z a t i o n may have r e s u l t e d i n i n c r e a s e d m o i s t u r e use e f f i c i e n c y by the t r e e s . These p o s s i b i l i t i e s have no t been t e s t e d i n the f i e l d , but have been rev iewed t h r o u g h the l i t e r a t u r e . S i n c e the s tudy i n v o l v e s l o d g e p o l e p i n e , t h e g e n e r a l importance and f e r t i l i z e r response c h a r a c t e r i s t i c s o f t h i s s p e c i e s w i l l a l s o be d i s c u s s e d b r i e f l y . I n a d d i t i o n , t h e p r i n c i p l e s o f optimum n u t r i t i o n t r i a l s , t h e p h y s i o l o g i c a l b a s i s o f improved N n u t r i t i o n , N c y c l i n g , and methods o f a s s e s s i n g N a v a i l a b i l i t y w i l l a l s o be r e v i e w e d . The main o b j e c t i v e s o f t h i s s t u d y a r e as f o l l o w s : 1. To e v a l u a t e the m e r i t s o f the s e q u e n t i a l c o r i n g i n s i t u t e c h n i q u e f o r measur ing N f l u x e s and d i s c u s s t h e p o s s i b i l i t y o f i t s use as an index o f the N s u p p l y i n g c a p a c i t y 6 o f s o i l s . 2. To compare the r e s u l t s from s e q u e n t i a l c o r i n g t o t h o s e o b t a i n e d by a n a e r o b i c i n c u b a t i o n i n t h e l a b o r a t o r y . 3 . To de termine i f the growth re sponse ( i n c r e a s e d N uptake) f o l l o w i n g r e p e a t e d f e r t i l i z a t i o n was due t o e i t h e r a ) : t emporary e l e v a t i o n i n the i n o r g a n i c N c o n c e n t r a t i o n as a d i r e c t r e s u l t o f f e r t i l i z e r a p p l i c a t i o n ( i n d i c a t i n g t h a t o n l y a s h o r t t erm c r o p response can be expec ted f o l l o w i n g the f i n a l f e r t i l i z e r a p p l i c a t i o n i n 1991) o r b ) : was due t o an i n c r e a s e i n N m i n e r a l i z a t i o n ( i n d i c a t i n g an i n c r e a s e i n s i t e q u a l i t y p r o d u c e d by f e r t i l i z a t i o n ) , o r due t o a c o m b i n a t i o n o f a) and b) . 4. To de termine the v a r i a b i l i t y o f N f l u x e s and N p o o l s i n s o i l , w i t h and w i t h o u t p r i o r f e r t i l i z a t i o n , and t h e number o f samples r e q u i r e d t o e s t i m a t e N p o o l s w i t h a s p e c i f i c degree o f p r e c i s i o n . 5. To c o r r e l a t e m i n e r a l i z a t i o n and N uptake as c a l c u l a t e d by s o i l d e p l e t i o n t o changes i n f o l i a r N c o n c e n t r a t i o n and c o n t e n t throughout the growing season and t o N uptake c a l c u l a t e d from rough biomass e s t i m a t e s . 7 CHAPTER 2 LITERATURE REVIEW LODGEPOLE PINE: IMPORTANCE AND RESPONSIVENESS TO FERTILIZATION Lodgepo le p i n e account s f o r 15 and 20 p e r c e n t o f the mature t i m b e r i n B r i t i s h Columbia and A l b e r t a , r e s p e c t i v e l y , and from 1977-1982 the average annua l c u t o f l o d g e p o l e p i n e i n Canada was a p p r o x i m a t e l y 15 m i l l i o n m 3 (Kennedy, 1985) . Dermott (1985) s t a t e d t h a t l o d g e p o l e p i n e i s p o t e n t i a l l y the most i m p o r t a n t s p e c i e s i n the f o o t h i l l s and mountain r e g i o n s o f Western Canada. I t i s c o n s i d e r e d by many as t h e second most i m p o r t a n t c o n i f e r s p e c i e s i n t h e r e g i o n next t o s p r u c e . Woodland Resource S e r v i c e s (1985) s t a t e d t h a t i n c r e a s i n g markets and i n c r e a s i n g u t i l i z a t i o n o f l o d g e p o l e p i n e j u s t i f i e s i n t e n s i f i e d management e f f o r t s as an inves tment i n t h e f u t u r e . S i m i l a r l y , Weetman e t a l . (1989) s t a t e d t h a t t h e l i m i t e d s u p p l y o f o l d growth l o d g e p o l e p i n e has c r e a t e d a need f o r i n t e n s i v e management, such as t h i n n i n g and f e r t i l i z a t i o n , t o overcome an impending age c l a s s gap problem i n wood s u p p l y . G i l b e r t (1987) i n d i c a t e d t h a t l o d g e p o l e p i n e has a number o f advantages i n compar i son t o o t h e r t r e e s i n the 8 U n i t e d S t a t e s . I t has a wide e c o l o g i c a l a m p l i t u d e , e x i s t i n g on a wide v a r i e t y o f s i t e s and d o m i n a t i n g n u t r i e n t p o o r s i t e s (Weetman e t a l . . 1989) . As w e l l , i t produces seed a t a v e r y e a r l y age and on a c o n t i n u o u s b a s i s , and i t s wood has good c h a r a c t e r i s t i c s . However, e a r l y seed p r o d u c t i o n may l e a d t o i n c r e a s e d r e g e n e r a t i o n i n g r e s s and t h u s r e s u l t i n t h e e x c e s s i v e l y dense " d o g - h a i r e d " s tands c h a r a c t e r i s t i c o f the s p e c i e s . G i l b e r t l i s t e d d i s a d v a n t a g e s o f l o d g e p o l e p i n e as b e i n g s h o r t - l i v e d , s u b j e c t t o c a t a s t r o p h i c damage by f i r e , mounta in p i n e b e e t l e and w i n d , and r e l a t i v e l y s m a l l s i z e compared t o i t s n e i g h b o r s . Comeau and Kimmins (1985) found f o l i a g e biomass o f l o d g e o p o l e p i n e ranges up t o 14 tonnes h a - 1 and c u r r e n t annua l increment up t o 7.6 m 3 h a - 1 y r - 1 . They i n d i c a t e d t h a t stemwood increment i s l i n e a r l y r e l a t e d t o b o t h f o l i a g e biomass and f o l i a r N c o n t e n t . These l i n e a r r e l a t i o n s h i p s were not i n f l u e n c e d by s i t e c o n d i t i o n s , but s i t e s w i t h x e r i c s o i l m o i s t u r e reg imes s u p p o r t e d lower maximum f o l i a g e biomass and had a lower f o l i a r N c o n t e n t t h a n t h o s e w i t h mes ic s o i l m o i s t u r e r e g i m e s . Lodgepo le p i n e i s o f t e n found growing i n m o i s t u r e and n u t r i e n t p o o r c o n d i t i o n s . As a r e s u l t , a number o f N o r t h A m e r i c a n s t u d i e s have shown i t t o be r e s p o n s i v e t o f e r t i l i z a t i o n w i t h N and o t h e r e lements ( B e l l a , 1978; C o c h r a n , 1979; Weetman e t a l . . 1 9 8 5 ; B r o c k l e y and Y o l e , 1985; and B r o c k l e y , 1989) . However, Weetman e t a l . (1985) i n d i c a t e d t h a t 9 our u n d e r s t a n d i n g o f l o d g e p o l e p i n e n u t r i t i o n i s b e t t e r t h a n i n d i c a t e d by t h e s p a r s e N o r t h Amer ican l i t e r a t u r e . There i s e v i d e n c e t o sugges t t h a t l o d g e p o l e p i n e w i l l r e s p o n d s i m i l a r l y t o f e r t i l i z a t i o n as o t h e r h a r d p i n e s p e c i e s such as j a c k p i n e (P inus b a n k s i a n a L . ) and S c o t s p i n e (P inus s y v e s t r i s L . ) . As w e l l , Weetman e t a l . (1985) s t a t e d t h a t s t u d i e s i n t h e U n i t e d Kingdom and S c a n d i n a v i a have demonstrated d r a m a t i c growth r a t e s f o r l o d g e p o l e p i n e f e r t i l i z e d w i t h b a l a n c e d n u t r i t i o n (mean annua l increments o f 12-15 m 3 h a - 1 y r - 1 a r e a t t a i n a b l e ) . Not o n l y does l o d g e p o l e p i n e r e s p o n d d r a m a t i c a l l y t o b a l a n c e d n u t r i t i o n , S c a n d i n a v i a n s t u d i e s have shown t h a t f o r u n f e r t i l i z e d s o i l s i t grows much f a s t e r t h a n S c o t s p i n e (Weetman e t a l . , 1985) . F o r the same l e v e l o f n u t r i t i o n , i t i s a p p a r e n t l y p h o t o s y n t h e t i c a l l y more e f f i c i e n t t h a n S c o t s p i n e and has a h i g h e r N p r o d u c t i v i t y ( Inges tad and K a h r , 1985) . "OPTIMUM" NUTRITION TRIALS I n t r o d u c t i o n S t u d i e s aimed a t m a i n t a i n i n g v e r y p r o d u c t i v e f o r e s t s o r permanent ly r a i s i n g the p r o d u c t i v i t y o f f o r e s t s t h r o u g h improved n u t r i t i o n a r e not v e r y common o u t s i d e o f Sweden and A u s t r a l i a . T h i s i s l a r g e l y because s o c i o - e c o n o m i c f a c t o r s t e n d t o d e t e r m i n e the d i r e c t i o n and e x t e n t o f r e s e a r c h (Bevege, 1980) . S i m i l a r l y , Boardman and Simpson (1981) s t a t e d t h a t t h e r e a r e two a s p e c t s from which a c c e p t a b l e l e v e l s o f p r o d u c t i o n a r e judged by f o r e s t managers; e i t h e r t h e r e i s a p u r e l y b i o l o g i c a l s t a n d a r d a r b i t r a t e d by t h e concept o f growth 10 l i m i t i n g f a c t o r s o r t h e r e i s an economic s t a n d a r d based on a c o s t - b e n e f i t a n a l y s i s . Because i n t e n s i v e management p r a c t i c e s p l a c e g r e a t demands on s o i l s o f low p r o d u c t i v e p o t e n t i a l , Burgess (1984) s t a t e d t h a t t h e r e i s an u r g e n t need t o d e v e l o p ways o f i n c r e a s i n g f i b r e y i e l d s w i t h o u t harming t h e p r o d u c t i v i t y o f f o r e s t s o i l s . S i m i l a r l y , w i t h the dangers o f n u t r i e n t imbalance from i n i t i a l l u x u r y consumpt ion , War ing (1981) i n d i c a t e d t h a t e x i s t i n g t e c h n o l o g y appears t o be i n a d e q u a t e t o meet t h e c h a l l e n g e o f e f f i c i e n t l y r e p l a c i n g N i n f o r e s t ecosystems and s u s t a i n i n g s i t e p r o d u c t i v i t y . However, as a r e s u l t o f a few s m a l l c a r e f u l l y d e s i g n e d e x p e r i m e n t s , s c i e n t i s t s have d i s c o v e r e d t h a t t h e p r o d u c t i v e c a p a c i t y o f f o r e s t l a n d s , even t h o s e i n h a r s h c l i m a t e s , may be two o r t h r e e t imes h i g h e r t h a n p r e v i o u s l y thought ( A x e l s s o n , 1983a; I n g e s t a d , .1987). These exper iments do not g e n e r a l l y r e s u l t i n "optimum" n u t r i t i o n f o r t h e t r e e s o r s t a n d s , but t h e y do i n d i c a t e t h a t f o r e s t p r o d u c t i v i t y can be d r a m a t i c a l l y improved t h r o u g h improved n u t r i t i o n . In Sweden, a c t u a l annua l f o r e s t p r o d u c t i o n i s 80 m i l l i o n m 3 w h i l e the p o t e n t i a l annua l f o r e s t p r o d u c t i o n appears t o be 400 m i l l i o n m 3 ( A x e l s s o n , 1983b) . Ecosys tem n u t r i e n t c y c l i n g i s t h e major c o n s t r a i n t c o n t r o l l i n g a c t u a l p r o d u c t i v i t y . Because n u t r i e n t s l i m i t f o r e s t p r o d u c t i o n i n many p l a c e s o f the w o r l d , the p r i n c i p l e s a p p l i e d and r e l a t i v e i n c r e a s e s observed i n Sweden s h o u l d be a p p l i c a b l e t o most managed f o r e s t s ( A x e l s s o n , 1985) . I n v iew o f the wide d i f f e r e n c e i n s i t e p r o p e r t i e s , i t 11 i s s u r p r i s i n g t h a t the a c t u a l annua l d r y m a t t e r p r o d u c t i o n by t r e e and most a g r i c u l t u r e c r o p s a r e o f t e n s i m i l a r ( A x e l s s o n , 1983a) . However, A x e l s s o n i n d i c a t e d t h a t the p o t e n t i a l d r y m a t t e r p r o d u c t i o n o f f o r e s t s exceeds t h a t o f most a g r i c u l t u r e c r o p s . R a t i o n a l e Tamm (1968) s t a t e d t h a t f i e l d optimum n u t r i t i o n exper iments form a b r i d g e between b a s i c p h y s i o l o g y work and c o n v e n t i o n a l s i l v i c u l t u r e f e r t i l i z a t i o n e x p e r i m e n t s , which a r e u s u a l l y more a p p l i e d i n c h a r a c t e r . Tamm (1985) l i s t e d the o b j e c t i v e s o f optimum n u t r i t i o n exper iments as f o l l o w s : 1. To de termine t h e b i o l o g i c a l p r i m a r y p r o d u c t i v i t y o f f o r e s t ecosystems a t optimum n u t r i e n t l e v e l s . 2. To de termine the impact o f n u t r i e n t s , water s u p p l y , and canopy d e n s i t y on a c t u a l and p o t e n t i a l p r o d u c t i v i t y a t s e l e c t e d s i t e s . 3. To de termine the between-year v a r i a t i o n i n growth and f o l i a r n u t r i e n t c o n c e n t r a t i o n s o f t r e e s a t d i f f e r e n t n u t r i e n t r e g i m e s . 4. To de termine the e f f e c t o f i n t e r r u p t e d f e r t i l i z a t i o n on f o r e s t p l o t s which have been exposed t o e l e v a t e d n u t r i e n t l e v e l s , p a r t i c u l a r l y N , o v e r l o n g p e r i o d s . 5. To de termine the l o n g - t e r m e f f e c t o f c o n t i n u o u s s m a l l N a d d i t i o n s , comparable w i t h t h o s e i n a c i d d e p o s i t i o n i n some r e g i o n s . 6. To de termine the a l l o c a t i o n o f growth t o d i f f e r e n t 12 p a r t s o f t r e e s under d i f f e r e n t n u t r i e n t reg imes (Tamm e t a l . , 1980) . The c r e a t i o n o f c u r v e s w i t h s e p a r a t e i n t e r n a l n u t r i e n t l e v e l s f o r d i f f e r e n t t r e a t m e n t s i s the most i m p o r t a n t p r e r e q u i s i t e f o r a q u a n t i t a t i v e assessment o f d e f i c i e n t and optimum f o l i a r l e v e l s i n a f o r e s t e d s t a n d (Tamm and A r o n s s o n , 1982) . The c u r v e s have t o be e s t a b l i s h e d f o r each s p e c i e s and n u t r i e n t and have l i t t l e p h y s i o l o g i c a l meaning u n l e s s b o t h p l a n t growth and i n t e r n a l n u t r i e n t l e v e l a r e kept r e a s o n a b l y c o n s t a n t d u r i n g the e x p e r i m e n t a l p e r i o d (Tamm and A r o n s s o n , 1982) . When such a s t a t e i s e s t a b l i s h e d , c o n c l u s i o n s can be drawn on the o p p o r t u n i t i e s f o r a s u s t a i n e d re sponse t o f e r t i l i z a t i o n , and d e f i c i e n t , adequate and optimum f o l i a r n u t r i e n t c o n c e n t r a t i o n s (see F i g u r e 1 ) . An e m p i r i c a l a p p r o a c h , based on r e p e a t e d N a d d i t i o n s , i s n e c e s s a r y because we s t i l l l a c k t h o s e e l u s i v e measures o f s o i l o r s t a n d N s t a t u s t h a t w i l l p r e d i c t re sponse t o N a d d i t i o n (Tamm and A r o n s s o n , 1982; Weetman, 1983) . T h e r e i s a d i f f i c u l t y i n i n t e r p r e t i n g growth response c u r v e s i n r e l a t i o n t o f o l i a r N c o n c e n t r a t i o n o b t a i n e d from c o n v e n t i o n a l f i e l d exper iments because t h e r e s p o n s e s o b t a i n e d f o r growth and f o l i a r l e v e l s a r e not s i m u l t a n e o u s (Tamm, 1968) . Growth i s a r e s u l t o f i n t e g r a t e d p r o c e s s e s over t i m e , b u t the measured i n t e r n a l n u t r i e n t c o n c e n t r a t i o n r e p r e s e n t s o n l y one p o i n t on the t ime s c a l e . Exper iment s w i t h e n t i r e f o r e s t ecosystems n e c e s s i t a t e 13 o b s e r v a t i o n s over extended p e r i o d s , because growth i n any one y e a r i s de termined b o t h by e n v i r o n m e n t a l i n f l u e n c e s i n t h a t y e a r and by p r e v i o u s s t a n d development (Tamm, 1974). There i s u s u a l l y a l a g p e r i o d b e f o r e t h e ecosystem can be c o n s i d e r e d to have a d j u s t e d t o a change i n c o n d i t i o n s . I t appears as though t e n y e a r s i s the minimum p e r i o d o f t ime r e q u i r e d t o o b t a i n a s t eady s t a t e growth response o f t r e e s t o changed n u t r i e n t a v a i l a b i l i t y (Weetman and F o u r n i e r , 1984) . M i l l e r e t a l . (1981) a l s o found t h a t t h e optimum N . E55 N o r r l i d e n ( A N ) N96 3-E 5 5 N o r r l i d e n ( A N ) 1970 72 74 76 78 Stsm volume growth m3«ha" 1 .year" ' ' 15H 10' — o P0K0 - - • » P2K2 •if—r- —r i— 2.0 2.5 N \ 1»71 - 78 F i g u r e 1. R e s u l t s from an optimum n u t r i t i o n exper iment i n S c o t s p i n e (P inus s y l v e s t r i s L . ) i n Sweden. a) Autumn c o n c e n t r a t i o n s o f n i t r o g e n i n c u r r e n t y e a r s need le s o f t r e e s f e r t i l i z e d a n n u a l l y from 1971 onwards. b) Y e a r l y stem growth (1972-1979) p l o t t e d a g a i n s t need le n i t r o g e n c o n c e n t r a t i o n . N l r e f e r s t o an annua l dose o f N i n ammonium n i t r a t e o f 60 k g / h a from 1971-1973, 40 k g / h a from 1974-1976, and 30 kg i n 1977. N2 and N3 are two and t h r e e t imes N l , r e s p e c t i v e l y (Adapted from Tamm and A r o n s s o n , 1982) . 14 c o n c e n t r a t i o n d i f f e r s w i t h growth parameter measured, v a r i e s w i t h age u n t i l canopy c l o s e s , and t ends t o be c l i m a t i c a l l y i n d e p e n d e n t . They c o n c l u d e d t h a t c r i t i c a l f o l i a r l e v e l s r e q u i r e s t a n d a r d i z a t i o n by age o r development s t a g e o f the t r e e s . The concept o f l i m i t i n g f a c t o r s d a t e s back t o L i e b i g ' s work o f 1840 (Tamm, 1975) . L i e b i g ' s law s t a t e s t h a t y i e l d i s p r o p o r t i o n a l t o t h e most d e f i c i e n t e lement up t o a l i m i t , as l o n g as t h i s e lement i s i n "minimum". Tamm (1975) s t a t e d t h a t e x p e r i e n c e has shown t h a t " L i e b i g ' s law o f t h e minimum" i s an o v e r s i m p l i f i c a t i o n , but t h e i r a r e cases where t h i s t h e o r y d e s c r i b e s what w i l l happen. The next s t e p was M i t s c h e r l i c h ' s e x p o n e n t i a l e q u a t i o n f o r the r e l a t i o n s h i p between added f e r t i l i z e r and p r o d u c t i o n - the law o f d i m i n i s h i n g r e t u r n s : Y = A (1 - e _ c x ) where Y = a c t u a l y i e l d c = f a c t o r o f e f f i c i e n c y A = maximum y i e l d o b t a i n a b l e x = r a t e l e v e l o f f a c t o r v a r i e d M i t s c h e r l i c h ' s c u r v e a c c o u n t s o n l y f o r growth up t o a c e r t a i n maximum o r optimum. L i e b i g ' s Law o f t h e Minimum and M i t s c h e r l i c h ' s E q u a t i o n b o t h r e f e r t o t h e d e c l i n i n g s e c t i o n o f t h e growth c u r v e and b o t h r e c o g n i z e the asymptote as the c a r r y i n g c a p a c i t y o f a s i t e (Boardman and Simpson, 1981) . Both r e l a t i o n s h i p s d i s p l a y a r a p i d i n c r e a s e i n e n v i r o n m e n t a l r e s i s t a n c e as c a r r y i n g c a p a c i t y i s r e a c h e d . Boardman and Simpson (1981) s t a t e d t h a t t h e s e r e l a t i o n s h i p s have too o f t e n 15 p r e v e n t e d t h e e x p l o r a t i o n o f e n v i r o n m e n t a l f a c t o r s a t d i f f e r e n t l e v e l s a g a i n s t a background managed so t h a t n o n -v a r y i n g f a c t o r s o p e r a t e i n a s e r i e s a t d i f f e r e n t l e v e l s but i n u n i s o n . Boardman and Simpson c o n c l u d e d t h a t a t r u e measure o f a gene p o o l 1 s p o t e n t i a l a t a s i t e can o n l y be o b t a i n e d from s t u d i e s which r a i s e the l e v e l a t which t h e n o n - v a r y i n g f a c t o r s ( o t h e r n u t r i e n t s ) o p e r a t e . In a system where a b i o t i c f a c t o r s a p p l y a minimum c o n s t r a i n t , growth i s e x p o n e n t i a l i n t ime a t a r a t e de termined by the genotype and i n t e n s i t y o f n u t r i t i o n (Boardman and Simpson, 1981) . The d i f f e r e n c e between the e x p o n e n t i a l growth o f t h e u n r e s t r a i n e d b i o t i c component and t h e a c t u a l growth e q u a t i o n , which shows e x p o n e n t i a l decay w i t h t i m e , i s s i t e e n v i r o n m e n t a l r e s i s t a n c e . In o r d e r t o i n c r e a s e p r o d u c t i v i t y e n v i r o n m e n t a l r e s i s t a n c e must be r e d u c e d . I n g e s t a d (1977, 1982) q u e s t i o n e d the use o f optimum c u r v e s o b t a i n e d from optimum n u t r i t i o n e x p e r i m e n t s . He a d j u s t e d t h e s u p p l y o f n u t r i e n t s t o the a c t u a l uptake o f the p l a n t i n s t e a d o f work ing w i t h n u t r i e n t s o l u t i o n s o f d i f f e r e n t c o n c e n t r a t i o n s , exchanged a t i n t e r v a l s (or a d d i n g f e r t i l i z e r a n n u a l l y ) . Optimum n u t r i t i o n exper iments w i t h s e e d l i n g s have shown t h e s e e d l i n g ' s f r e s h weight t o be an e x p o n e n t i a l f u n c t i o n o f the i n t e r n a l N c o n c e n t r a t i o n up t o an optimum where t h e i n c r e a s e i s s topped a b r u p t l y : Y= 0.7 e 8 - 9 x where x = N c o n c e n t r a t i o n (% o f f r e s h weight) y = s e e d l i n g f r e s h we ight (% o f maximum) 16 T h u s , t h e optimum n u t r i e n t s t a t u s i s i d e n t i f i e d as a d i s c r e t e v a l u e r a t h e r t h a n a c o n c e n t r a t i o n range ( I n g e s t a d , 1987) . T h i s i s q u i t e c o n t r a d i c t o r y t o the t r a d i t i o n a l optimum c u r v e which i s d e s c r i b e d as a l o g a r i t h m i c f u n c t i o n i m p l y i n g d i m i n i s h i n g r e t u r n w i t h i n c r e a s e d N c o n c e n t r a t i o n (Tamm and A r o n s s o n , 1982) . S i n c e young s e e d l i n g s grow e x p o n e n t i a l l y , n u t r i e n t s u p p l y a l s o has t o be e x p o n e n t i a l t o m a i n t a i n an optimum n u t r i e n t s t a t u s . I f t o t a l growth i s p l o t t e d a g a i n s t t o t a l N added, an a lmost l i n e a r r e l a t i o n s h i p i s o b t a i n e d ( s l i g h t l y convex towards the x - a x i s ) . I n g e s t a d (1987) i n d i c a t e d t h a t the r e l a t i v e growth r a t e i s a l s o l i n e a r l y c o r r e l a t e d w i t h the n u t r i e n t amount o f the s e e d l i n g s : dW/dt = P n n where W = p l a n t weight n = n u t r i e n t amount i n p l a n t P n = n u t r i e n t p r o d u c t i v i t y However, t r e e s tands d i f f e r from s e e d l i n g s growing under l a b c o n d i t i o n s i n s e v e r a l r e s p e c t s , such as s e l f - s h a d i n g i n canopy , i n t e r n a l r e d i s t r i b u t i o n o f n u t r i e n t s , and c o m p e t i t i o n f o r n u t r i e n t s among t r e e s , l e s s e r v e g e t a t i o n and m i c r o o r g a n i s m s ( Inges tad and L u n d , 1986) . S e l f - s h a d i n g changes t h e e x p o n e n t i a l growth c u r v e t o a s i g r a o i d a l one (Tamm and A r o n s s o n , 1982). Bowen (1981) s t a t e d t h a t s t u d i e s on i o n uptake and p l a n t growth i n s o l u t i o n c u l t u r e a r e o f t e n i r r e l e v a n t t o the s o i l s i t u a t i o n because t h e i o n a b s o r p t i o n by r o o t s i n s o l u t i o n c u l t u r e i s v e r y d i f f e r e n t from i o n 17 a b s o r p t i o n o f r o o t s i n s o i l . In s o i l t h e l i m i t i n g s t e p i s not u s u a l l y t h e r e l a t i v e a b s o r b i n g a b i l i t y o f r o o t s , b u t i s i n s t e a d t h e t r a n s f e r o f i o n s from s o i l t o r o o t , making r o o t abundance v e r y i m p o r t a n t . However, because a young p l a n t grows e x p o n e n t i a l l y b o t h above and below g r o u n d , t h e a c c e s s t o n u t r i e n t s may thus i n c r e a s e e x p o n e n t i a l l y w i t h t ime (Tamm and A r o n s s o n , 1982) . A l s o , n a t u r a l s e l e c t i o n between p l a n t s has o f t e n f a v o r e d those a b l e t o s u r v i v e and propagate where a more o r l e s s c o n t i n u o u s rep lacement o f n u t r i e n t s t a k e s p l a c e by o r g a n i c m a t t e r m i n e r a l i z a t i o n . T h e r e f o r e , some o f I n g e s t a d ' s i d e a s on p l a n t n u t r i t i o n have d i r e c t i m p l i c a t i o n s i n the f i e l d . An i n t e r e s t i n g f i n d i n g from I n g e s t a d ' s exper iments i s t h a t d e f i c i e n c y symptoms appear when the n u t r i e n t s t a t u s i s r a p i d l y c h a n g i n g from one l e v e l t o a n o t h e r , b u t d i s a p p e a r when t h e p l a n t i s adapted t o the new n u t r i e n t s u p p l y . The appearance o f d e f i c i e n c y symptoms i s e v i d e n c e o f an u n s t a b l e n u t r i e n t s i t u a t i o n and not o f a s p e c i f i c low l e v e l o f the n u t r i e n t i n q u e s t i o n , which agrees w e l l w i t h t h e n a t u r a l b e h a v i o r o f p l a n t s . Where l a c k o f N s t r o n g l y l i m i t s growth , c l e a r d e f i e n c y symptoms a r e seldom seen ( I n g e s t a d , 1987) . F e r t i l i z e r E f f i c i e n c y , Fate and Response Duration C o n v e n t i o n a l f e r t i l i z a t i o n ( u s u a l l y s i n g l e a p p l i c a t i o n ) i s q u i t e i n e f f i c i e n t i n t h a t the t r e e s t y p i c a l l y r e c o v e r l e s s t h a n 30 p e r c e n t o f a p p l i e d N (Johnson and T o d d , 1988) . However, on an ecosystem l e v e l N r e t e n t i o n i s u s u a l l y 18 much b e t t e r (70-90 p e r c e n t ) . War ing (1981) s t a t e d t h a t r e c o v e r y o f N f e r t i l i z e r by t r e e s i s w e l l below t h a t r e p o r t e d f o r a g r i c u l t u r a l c r o p s . I f f e r t i l i z a t i o n c o u l d be done f r e q u e n t l y (eg. v i a i r r i g a t i o n ) o r w i t h s low r e l e a s e f e r t i l i z e r so c o n s t r u c t e d t h a t the n u t r i e n t s become a v a i l a b l e a t the same r a t e they a r e used by c r o p s , the s o l u b l e N amounts i n s o i l c o u l d be kept low and s t i l l a c h i e v e h i g h uptake r a t e s ( I n g e s t a d , 1977). I n g e s t a d (1982, 1987) s t a t e d t h a t l ower N a p p l i c a t i o n s r e s u l t i n much i n c r e a s e d f e r t i l i z e r use e f f i c i e n c y , d r a m a t i c growth and s u s t a i n e d i n c r e a s e s i n p i n e p r o d u c t i v i t y ( F i g u r e 2 ) . S i m i l a r l y , Tamm (1985) c o n c l u d e d t h a t r e g u l a r and c a r e f u l l y a d j u s t e d n u t r i e n t a p p l i c a t i o n s produce a much b e t t e r re sponse t h a n c o n v e n t i o n a l a p p l i c a t i o n s . m2 h a - > m 3 h a ' 1 y e a r " 1 F i g u r e 2. B a s a l a r e a development (a) and annua l volume p r o d u c t i o n (b) o f S c o t s p i n e (P inus s y l v e s t r i s L . ) . The t r e a t m e n t s a r e c o n t r o l (0 ) , i r r i g a t i o n ( I ) , r e p e a t e d f e r t i l i z a t i o n w i t h comple te f e r t i l i z e r s ( F ) , and d a i l y f e r t i g a t i o n w i t h a complete l i q u i d f e r t i l i z e r d i s t r i b u t e d v i a i r r i g a t i o n water (IF) (from I n g e s t a d , 1987) . 19 In a j a c k p i n e optimum n u t r i t i o n exper iment i n Quebec, Weetman and F o u r n i e r (1984) o b t a i n e d t h e h i g h e s t volume r e s p o n s e s w i t h low annua l a p p l i c a t i o n s a t h i g h l y e f f i c i e n t growth i n c r e a s e s p e r u n i t N a p p l i e d . S i x a p p l i c a t i o n s o f 56 kg N p e r h e c t a r e o v e r a 10 -year p e r i o d were e f f i c i e n t i n t h e u t i l i z a t i o n o f N , but not e f f i c i e n t i n terms o f c o s t . They s t a t e d t h a t t h e r e i s a t r a d e o f f between e f f i c i e n c y o f N use , a p p l i c a t i o n c o s t and response p r o d u c e d . They c o n c l u d e d t h a t t h e e c o n o m i c a l l y optimum a p p l i c a t i o n i s an economic dosage r a t e r e a p p l i e d as the response peak d e c l i n e s , but t h a t t h i s w i l l produce l e s s volume p e r h e c t a r e t h a n t h e b i o l o g i c a l l y optimum l e v e l o f N n u t r i t i o n . However, Johnson and Todd (1988) d i d no t c o n f i r m t h a t t r e e growth i s o p t i m i z e d by f r e q u e n t f e r t i l i z a t i o n , b u t i n s t e a d o b t a i n e d b e t t e r growth re sponses from one a p p l i c a t i o n p e r y e a r t h a t from q u a r t e r l y a p p l i c a t i o n s i n l o b l o l l y p i n e (P inus t a e d a L . ) . L o n g - t e r m growth responses t o s i n g l e a p p l i c a t i o n s o f N f e r t i l i z e r a r e u s u a l l y a t t r i b u t e d p r i m a r i l y t o e f f i c i e n t c o n s e r v a t i o n o f f e r t i l i z e r N t a k e n up by t r e e s d u r i n g the b r i e f p e r i o d i m m e di a te l y f o l l o w i n g f e r t i l i z a t i o n when s o i l m i n e r a l N l e v e l s a r e e l e v a t e d (Johnson and T o d d , 1988; M i l l e r , 1981) . Johnson and Todd (1988) found p r o l o n g e d t r e e growth responses due t o c o n s e r v a t i o n o f N by i n t e r n a l t r a n s l o c a t i o n w i t h i n t r e e s . W i t h l o b l o l l y p i n e , a p p r o x i m a t e l y h a l f o f the c a l c u l a t e d f e r t i l i z e r r e c o v e r y was i n f o l i a g e and t r a n s l o c a t i o n s t u d i e s i n d i c a t e t h a t t h i s N i n f o l i a g e was 20 e f f i c i e n t l y c o n s e r v e d . A x e l s s o n and A x e l s s o n (1986) a l s o found t h a t t h e r e l a t i v e w i t h d r a w a l o f n u t r i e n t s from n e e d l e s p r i o r t o s h e d d i n g was independent o f f e r t i l i z e r t r e a t m e n t , so t h a t t h e a b s o l u t e amounts o f n u t r i e n t r e d i s t r i b u t i o n w i t h i n crowns were h i g h e r i n f e r t i l i z e d p l o t s . I n a s tudy o f Douglas f i r , i t was found t h a t excess N s t o r e d i n t r e e s t h a t i n i t i a l l y appeared t o be e x c e s s i v e l y f e r t i l i z e d g r a d u a l l y was expended i n enhanc ing t r e e growth and b u i l d i n g o f N i n the f o r e s t f l o o r (Weetman and F o u r n i e r , 1984) . W i t h no N a p p l i e d , c o n t i n u o u s i m m o b i l i z a t i o n o f N i n t r e e s o c c u r r e d , r e s u l t i n g i n d i e i n g o f o l d e r t i s s u e s and u t i l i z a t i o n o f N thus r e l e a s e d f o r new growth . T h e r e f o r e , l u x u r y consumpt ion p r o l o n g e d t h e d u r a t i o n o f growth r e s p o n s e . T h e r e f o r e , N f e r t i l i z e r a p p l i e d a t normal o p e r a t i o n a l r a t e s i s a p p l i e d t o t h e t r e e s r a t h e r t h a n t o the s i t e ( M i l l e r , 1981) . T h i s i s a l s o s u p p o r t e d by the f a c t t h a t growth r e s p o n s e s a r e commonly o b t a i n e d w i t h N a p p l i c a t i o n s t h a t a r e q u i t e s m a l l r e l a t i v e t o t o t a l ecosystem N c a p i t a l and t h a t l a r g e i n c r e a s e s i n s o i l i n o r g a n i c N f o l l o w i n g f e r t i l i z a t i o n a r e s h o r t - l i v e d , t y p i c a l l y d e c l i n i n g t o background l e v e l s w i t h i n two y e a r s o r l e s s (Johnson e t a l . , 1980; M i l l e r , 1981; Johnson and T o d d , 1988) . S i m i l a r l y , He i lman and G e s s e l (1963) s t a t e d t h a t i t i s p r o b a b l y not l o n g b e f o r e a v a i l a b l e N i n the s o i l approaches former l e v e l s because o f r a p i d u t i l i z a t i o n o f excess a v a i l a b l e N by p l a n t s and s o i l m i c r o o r g a n i s m s . O v e r r e i n (1967) s t a t e d t h a t t h e a d d i t i o n o f f e r t i l i z e r t o raw humus immedia te ly g i v e s r i s e t o a s e r i e s o f p h y s i c a l , 21 c h e m i c a l , and b i o l o g i c a l r e a c t i o n s , which g r e a t l y a f f e c t i t s a v a i l a b i l i t y t o p l a n t s . When N i s a p p l i e d t o t h e f o r e s t f l o o r i n an i n o r g a n i c form such as ammonium n i t r a t e , t h e N i s q u i c k l y i n c o r p o r a t e d i n t o the s o i l s o l u t i o n o r exchange complex i n which form i t i s immedia te ly a v a i l a b l e t o p l a n t s and s o i l organisms (Kumi, 1984) . P a r t o f the added N can be absorbed o r f i x e d by o r g a n i c m a t t e r ( c h i e f l y l i g n i n ) and c l a y s ( A l l i s o n , 1973) . Ammonium can a l s o be p h y s i c a l l y absorbed by o r g a n i c m a t t e r , b u t i t i s a v e r y weak bond which can be removed when t h e ammonium c o n c e n t r a t i o n i s l o w e r e d . The ammonium can a l s o r e a c t c h e m i c a l l y w i t h o r g a n i c m a t t e r t o form i n s o l u b l e compounds r e s i s t a n t t o d e c o m p o s i t i o n ( M o r t l a n d and W o l c o t t , 1965) . Broadbent (1966) s t a t e d t h a t an a p p r e c i a b l e f r a c t i o n o f the ammonium N can be f i x e d w i t h i n t h e c r y s t a l l a t t i c e o f m i n e r a l s which can c o n t r i b u t e t o d e c r e a s e d a v a i l a b i l i t y o f N . S i m i l a r l y , Kudeyarov (1981) s t a t e d t h a t some f e r t i l i z e r N may be f i x e d i n a g r i c u l t u r e s o i l s , depending on s o i l p r o p e r t i e s , form o f f e r t i l i z e r a p p l i e d , and a p p l i c a t i o n r a t e . He i n d i c a t e d t h a t t h i s form o f N i s not as m o b i l e as exchangeable N H 4 + , but t h a t f i x e d N H 4 4 " may be c o n s i d e r e d as k i n d o f a r e s e r v e form o f m i n e r a l N i n t h e s o i l . T h e r e i s e v i d e n c e f o r l o n g e r term enr i chment o f n o n -m i n e r a l , b u t l a b i l e N i n s o i l s by f e r t i l i z a t i o n . However, a permanent i n c r e a s e i n s i t e p r o d u c t i v i t y , as d i s t i n c t from a s h o r t t erm i n c r e a s e i n c r o p p r o d u c t i o n , w i l l o c c u r o n l y where N a d d i t i o n s a r e l a r g e r e l a t i v e t o t h e e x i s t i n g c a p i t a l o f the 22 s i t e ( M i l l e r , 1981; C a r l y l e , 1986) . Kudeyarov (1981) s t a t e d t h a t the i n c o r p o r a t i o n o f f e r t i l i z e r i n t o the o r g a n i c f r a c t i o n may a l s o be q u i t e r a p i d , b u t once i n the o r g a n i c f r a c t i o n i t i s no t r e a d i l y r e l e a s e d a g a i n . Much o f the o r g a n i c N d e r i v e d from an i n o r g a n i c source may be a c c o u n t e d f o r i n the amino form and as such may be r e m i n e r a l i z e d . However, Broadbent (1966) s t a t e d t h a t some o f i t may a l s o undergo p r o g r e s s i v e s t a b i l i z a t i o n . W i l l i a m s (1972) f e r t i l i z e d S c o t s p i n e w i t h u r e a and ammonium s a l t s and found t h a t ne t m i n e r a l i z a t i o n was about t w i c e as h i g h as the c o n t r o l , i n d i c a t i n g t h a t i m m o b i l i z e d f e r t i l i z e r N was i n a more a c t i v e p o o l t h a n n a t i v e o r g a n i c N . In c o n t r a s t , Hauck (1981) found the m i n e r a l i z a t i o n o f i m m o b i l i z e d f e r t i l i z e r N ranged from 2 t o 10 % d u r i n g t h e growing season i n which i t was i m m o b i l i z e d and 1 t o 3 % p e r y e a r t h e r e a f t e r , i n d i c a t i n g t h a t f e r t i l i z e r N i m m o b i l i z e d i n humus subs tances i s v e r y s t a b l e . S i n c e t h e a d d i t i o n o f N a l s o r e s u l t s i n i n c r e a s e d n e e d l e c o n c e n t r a t i o n i n t r e e s ( M o r r i s o n , 1974, van den D r i e s c h e , 1974; M i l l e r , 1981; Johnson and T o d d , 1988; and o t h e r s ) i t can a l s o r e s u l t i n i n c r e a s e d N c o n c e n t r a t i o n i n l i t t e r . I n c r e a s e d n e e d l e N c o n c e n t r a t i o n can r e s u l t i n a d e c r e a s e i n p o l y p h e n o l c o n t e n t o f t i s s u e s and i n c r e a s e d d e c o m p o s i t i o n . Gosz (1981) i n d i c a t e d t h a t i n c r e a s e d N uptake f o r a number o f y e a r s a f t e r f e r t i l i z a t i o n as w e l l as a r e d u c t i o n i n f o r e s t f l o o r i n d i c a t e t h a t i m m o b i l i z a t i o n r a t e s d e c r e a s e and m i n e r a l i z a t i o n r a t e s i n c r e a s e . S i m i l a r l y , the 23 e f f e c t o f r e p e a t e d s m a l l doses t h a t i n d i v i d u a l l y have l i t t l e o r no e f f e c t can o n l y be u n d e r s t o o d i f v i r t u a l l y a l l o f the n u t r i e n t s a r e t a k e n up and r e c y c l e d w i t h i n t h e s t a n d ( I n g e s t a d , 1987) . However, t h e r e a r e i n d i c a t i o n s t h a t f e r t i l i z e r may i n c r e a s e t h e l i g n i n l e v e l i n l i t t e r . I f t h i s i s t r u e , f e r t i l i z a t i o n may r e s u l t i n a s u b s t r a t e l e s s s u i t a b l e f o r l i t t e r decomposing organisms (Berg , 1986) and a lower a c t i v i t y o f decomposing m i c r o b e s . However, i t appears t o be g e n e r a l l y t r u e t h a t l i t t e r from w e l l f ed t r e e s appears t o r e l e a s e N more r e a d i l y t h a n does t h a t from N d e f i c i e n t t r e e s ( M i l l e r , 1981; I n g e s t a d , 1987) . ' A n o t h e r f a c t o r a f f e c t i n g l o n g - t e r m growth response i s t h a t growth responses advance the s tage o f s t a n d development , e f f e c t i v e l y moving the s t a n d ahead c h r o n o l o g i c a l l y ( M i l l e r , 1981) . T h i s means t h a t , even a f t e r response has ceased and t r e e s r e t u r n t o the growth c u r v e f o r the s i t e , t r e e s may e i t h e r appear t o be growing f a s t e r o r s l o w e r t h a n u n f e r t i l i z e d t r e e s , depending which s i d e o f the growth c u r v e they a r e on . T h i s can be e s p e c i a l l y s i g n i f i c a n t i n young p l a n t a t i o n s when t h e t ime t a k e n t o r e a c h crown c l o s u r e may be s u b s t a n t i a l l y d e c r e a s e d by f e r t i l i z a t i o n . N o t w i t h s t a n d i n g an advance i n s t a n d deve lopment , the p e r s i s t e n c e o f growth response depends on how l o n g i n c r e a s e d n u t r i e n t a v a i l a b i l i t y and n u t r i e n t use e f f i c i e n c y can s u s t a i n i n c r e a s e s i n l e a f a r e a and growth p e r u n i t l e a f a r e a ( B i n k l e y and R e i d , 1985) . A l o n g term i n c r e a s e i n n u t r i e n t a v a i l a b i l i t y 24 may e i t h e r r e s u l t from g r e a t e r i n t e r n a l c y c l i n g w i t h i n the t r e e o r a s u s t a i n e d i n c r e a s e i n m i n e r a l i z a t i o n from r e m i n e r a l i z a t i o n o f i m m o b i l i z e d N i n the s o i l a n d / o r an i n c r e a s e i n l i t t e r q u a n t i t y and q u a l i t y . PHYSIOLOGICAL BASIS OF IMPROVED NUTRITION Most n u t r i t i o n s t u d i e s o f f o r e s t t r e e s have been concerned w i t h the c o n c e n t r a t i o n o f n u t r i e n t s w i t h i n one t i s s u e o r a n o t h e r , r a t h e r t h a n w i t h p h y s i o l o g i c a l p r o c e s s e s ( A t t i w i l l , 1986) . An u n d e r s t a n d i n g o f p l a n t p r o d u c t i v i t y s h o u l d be based on q u a n t i t a t i v e d a t a d e s c r i b i n g the dynamics o f p r o c e s s e s such as water , n u t r i e n t , and c a r b o n f l u x e s i n t e g r a t e d i n t o ne t biomass increments ( A x e l s s o n , 1986) . Fundamental p r o c e s s e s a r e c a r b o n f i x a t i o n , r e s p i r a t i o n r a t e , c a r b o n p a r t i t i o n i n g , and the whole ecosystem r e t e n t i o n and d e l i v e r y c a p a c i t y o f water and n u t r i e n t s . W h i l e the p e n a l t i e s o f l u x u r y a p p l i c a t i o n o f N i n a g r i c u l t u r e may not a p p l y t o f o r e s t s and t h e r e may be l o n g term b e n e f i t s i n terms o f N a c c u m u l a t i o n and c y c l i n g , i t i s i m p o r t a n t t o ensure t h a t d e f i c i e n c i e s o f o t h e r e lements a r e no t i n d u c e d . The b a l a n c e between n u t r i e n t s i s e s s e n t i a l f o r t h e p h y s i o l o g i c a l s t a t u s and growth a b i l i t y o f v a r i o u s p l a n t s p e c i e s (Aronsson e t a l . . 1977) . In f a c t , the b a l a n c e appears t o be even more i m p o r t a n t than the a b s o l u t e l e v e l w i t h i n a r a t h e r wide r a n g e . As i n d i c a t e d e a r l i e r , n u t r i e n t s need t o be added w i t h r e g a r d t o t h e law o f the l i m i t i n g and s i m u l t a n e o u s l y w i t h r e g a r d t o maintenance o f b a l a n c e d 25 n u t r i t i o n (Turner, 1981). The most common mechanism by which nutrients l i m i t production i s probably by l i m i t i n g the amount of photosynthetically active organs (Tamm, 1975). Energy interception for photosynthesis and t o t a l CO2 uptake rate depend on the l e a f area of a tree or canopy (Landsberg, 1986). In Swedish t r i a l s , increased l e a f area index owed to repeated N additions has been c l o s e l y related to above ground biomass production. I t i s well known that a needle's l i f e span i s strongly influenced by the N status and the amount of needles formed strongly increases a f t e r f e r t i l i z a t i o n (Aronsson et a l . . 1977). Weetman and Fournier (1984) suggested that, i n boreal forests, l e a f area or number rather than photosynthetic e f f i c i e n c y are the primary controls on productivity. However, an increase i n l e a f biomass i s a useful strategy up to a maximum value only. Therefore, an increase i n photosynthetic a c t i v i t y per unit needle i s to be expected when nutrient and water a v a i l a b i l i t y i s improved (Aronsson et a l . f 1977). Nitrogen concentration i s p o s i t i v e l y correlated with s p e c i f i c l e a f area, chlorophyll content, and maximim CO2 a s s i m i l a t i o n rate per unit dry weight (Matyssek, 1986). M i l l e r and M i l l e r (1976) stated that the increase i n stem growth as a r e s u l t of f e r t i l i z e r a p p l i c a t i o n seemed to be due to increased photosynthetic area (up to 70 percent) and an increase i n net a s s i m i l a t i o n rate (up to 60 percent) as well as a s h i f t i n t o t a l net primary production to stem wood. 26 However, Tamm and A r o n s s o n (1982) s t a t e d t h a t i n c r e a s e d p h o t o s y n t h e t i c a c t i v i t y might i n c r e a s e y i e l d f u r t h e r , b u t o n l y 10 t o 20 p e r c e n t p e r y e a r i n p i n e , w h i l e l e a f a r e a might i n c r e a s e 100 p e r c e n t o r more over c o n t r o l . Because i n c r e a s e d n u t r i e n t s t a t u s appears t o i n c r e a s e t h e r a t e o f p h o t o s y n t h e s i s o n l y s l i g h t l y , much o f t h e s t r o n g i n c r e a s e i n y i e l d i n optimum n u t r i t i o n c o n d i t i o n s i s a t t r i b u t e d t o a change i n r e s o u r c e a l l o c a t i o n i n t h e t r e e s where new f o l i a g e i s f a v o r e d and l e s s i s d i r e c t e d i n t o f i n e r o o t p r o d u c t i o n (Tamm and A r o n s s o n , 1982; A x e l s s o n and A x e l s s o n , 1986) . A x e l s s o n and A x e l s s o n s t a t e d t h a t t h e r e i s growing e v i d e n c e t h a t reduced d r y m a t t e r a l l o c a t i o n t o f i n e r o o t s i s one o f the most i m p o r t a n t mechanisms by which i n c r e a s e d n u t r i t i o n i n c r e a s e s above g r o u n d - p r o d u c t i o n . S i m i l a r l y , C a r l y l e (1986) i n d i c a t e d t h a t t r e e s may a l l o c a t e a g r e a t e r p r o p o r t i o n o f r e s o u r c e s t o f i n e r o o t p r o d u c t i o n on p o o r s i t e s and t h a t f i n e r o o t s a r e c a r b o n s i n k s and must r e c e i v e c a r b o h y d r a t e s from p h o t o s y n t h e s i s . I n g e s t a d and Kahr (1985) s t a t e d t h a t under n u t r i e n t s t r e s s , comparatively l a r g e r o o t systems t a k e up s m a l l amounts o f n u t r i e n t s , whereas c l o s e t o the optimum, comparatively s m a l l r o o t systems t a k e up l a r g e amounts o f n u t r i e n t s . Enhanced r o o t growth w i l l c o u n t e r a c t the low n u t r i e n t uptake under n u t r i e n t s t r e s s c o n d i t i o n s , b u t a t a h i g h energy c o s t . Root growth and c a r b o n p a r t i t i o n i n g a r e m a i n l y r e g u l a t e d by t h e n u t r i e n t s t a t u s o f the p l a n t ( Inges tad and L u n d , 1986) . S i m i l a r l y , Agren and I n g e s t a d (1987) s t a t e d t h a t 27 p a r t i t i o n i n g f o l l o w s an a b s o l u t e r e q u i r e m e n t from t h e b a l a n c e between c a r b o n a s s i m i l a t i n g s t r u c t u r e s (shoots) and c a r b o n u t i l i z a t i o n de termined by N n u t r i t i o n . The b a l a n c e between s h o o t s and r o o t s i s a r e s u l t o f an e q u i l i b r i u m between an i n t e r n a l s i n k f o r c a r b o n s u b s t r a t e , the s t r e n g t h o f which i s d e t e r m i n e d by the amount o f N ( p r o t e i n ) i n t h e p l a n t , and the c a p a c i t y t o s u p p l y c a r b o n s u b s t r a t e s s e t by t h e amount o f s h o o t . T h e r e f o r e , the shoot t o r o o t p l a n t r a t i o i s a p p r o x i m a t e l y a l i n e a r f u n c t i o n o f the i n t e r n a l N c o n c e n t r a t i o n . In s o i l (as opposed t o s o l u t i o n c u l t u r e ) , r o o t growth has a d o m i n a t i n g i n f l u e n c e on uptake r a t e ( Inges tad and K a h r , 1985) . The l e v e l o f uptake i s de termined by t h e amount o f n u t r i e n t made a v a i l a b l e t o t h e r o o t s p e r u n i t o f s o i l a r e a p e r u n i t o f t i m e . T h i s n u t r i e n t f l u x d e n s i t y de termines the uptake r a t e , n u t r i e n t s t a t u s and shoot growth r a t e as w e l l as r o o t growth r a t e w h i c h , i n t u r n , i n f l u e n c e s uptake r a t e . T h i s f eedback w i l l l e v e l out t o a s t a b l e e q u i l i b r i u m between s o i l f e r t i l i t y and growth , where n u t r i t i o n and growth a r e c o n t r o l l e d by r o o t growth r a t e (a p l a n t p r o p e r t y ) and n u t r i e n t f l u x d e n s i t y (a s o i l p r o p e r t y ) . S i m i l a r l y , Running and Dunner (1987) s t a t e d t h a t stem growth i s t h e l a s t p r i o r i t y i n c a r b o n a l l o c a t i o n by a t r e e , coming a f t e r r e s p i r a t i o n , r o o t and canopy growth demands a r e met. In c o a s t a l D o u g l a s - f i r (Pseudotsuqa m e n z i e s i i ( M i r b . ) Franco) s t a n d s , K u r t z and Kimmins (1987) found a n e g a t i v e (but not s i g n i f i c a n t ) r e l a t i o n s h i p between s i t e index and b o t h f i n e 28 r o o t p r o d u c t i o n and m o r t a l i t y . However, t h e y s t a t e d t h a t i f o v e r a l l p r o d u c t i o n i n c r e a s e s , f i n e r o o t p r o d u c t i o n and biomass may a l s o i n c r e a s e , even i f the a l l o c a t i o n t o f i n e r o o t s g e n e r a l l y becomes p r o p o r t i o n a l l y l e s s . They f u r t h e r i n d i c a t e t h a t f e r t i l i z a t i o n can r e s u l t i n an o v e r a l l d e c l i n e i n f i n e r o o t p r o d u c t i o n and reduce r o o t m o r t a l i t y . O t h e r s have sugges ted t h a t f i n e r o o t t u r n o v e r on r i c h s i t e s may be g r e a t e r t h a n on p o o r e r s i t e s , thus o f f s e t t i n g the lower be low-ground biomass v a l u e s commonly r e p o r t e d f o r r i c h s i t e s ( N a d e l h o f f e r e t a l . . 1985) . MOISTURE LIMITATIONS TO GROWTH POTENTIAL AND NUTRIENT-MOISTURE-GRASS INTERACTIONS I t has been sugges ted t h a t water a v a i l a b i l i t y may d e f i n e t h e upper l i m i t o f p r o d u c t i v i t y and n u t r i t i o n , and the r a t e a t which p r o c e s s e s p r o c e e d t o t h a t end (Bevege, 1980) . Gho lz (1982) found a s t r o n g r e l a t i o n s h i p between l e a f a r e a index and net p r i m a r y p r o d u c t i v i t y t o growing season water b a l a n c e i n t h e P a c i f i c Northwes t . S i m i l a r l y , Kimmins e t a l . (1989) s t a t e d t h a t m o i s t u r e de termines the f o l i a g e biomass c a r r y i n g c a p a c i t y ( F C C ) , w h i l e n u t r i e n t a v a i l a b i l i t y d e t e r m i n e s t h e degree t o which FCC i s a c h i e v e d . As ment ioned e a r l i e r , f e r t i l i z a t i o n i n c r e a s e s a c h i e v e d f o l i a r b iomass . When N a v a i l a b i l i t y i n c r e a s e s , o t h e r n u t r i e n t s , as w e l l as water t e n d t o be growth d e t e r m i n i n g f a c t o r s (Aronsson e t a l . , 1977) . T r e e growth i s reduced t o a c e r t a i n e x t e n t by water d e f i c i t s , b o t h i n d i r e c t l y , t h r o u g h i n t e r f e r e n c e s w i t h 29 p h y s i o l o g i c a l p r o c e s s e s such as p h o t o s y n t h e s i s , n i t r o g e n m e t a b o l i s m , s a l t a b s o r p t i o n and t r a n s l o c a t i o n , and d i r e c t l y by r e d u c e d c e l l t u r g o r o r enlargement and o t h e r p r o c e s s e s i n v o l v e d i n growth ( P r i t c h e t t and F i s h e r , 1987; L a n d s b e r g , 1986) . A number o f s t u d i e s have shown a c o r r e l a t i o n between p h o t o s y n t h e s i s and t r a n s p i r a t i o n r a t e s ( G i l e s e t a l . , 1984) . On f o r e s t e d s i t e s where a t m o s p h e r i c e v a p o r a t i v e demand d u r i n g the growing season i s g r e a t e r t h a n a v a i l a b l e w a t e r , t r e e s must s t r i k e a b a l a n c e between maximum p h o t o s y n t h e s i s and m a i n t a i n i n g a s u i t a b l e i n t e r n a l water s t a t u s . I n c r e a s e d l e a f a r e a would i n c r e a s e p h o t o s y n t h e t i c p o t e n t i a l , but a t a c o s t o f i n c r e a s e d t r a n s p i r a t i o n water l o s s . To a c e r t a i n e x t e n t , t r e e s can c o n t r o l water l o s s t h r o u g h p h y s i o l o g i c a l c o n t r o l o f s t o m a t a l a p e r t u r e , but s t o m a t a l c l o s u r e r e s t r i c t s CO2 uptake and t h u s reduces p r o d u c t i v i t y . I n g e s t a d (1979) s t a t e d t h a t i t has been shown t h a t a r e l a t i v e l y h i g h p o t a s s i u m c o n t e n t means a b e t t e r water economy. P l a n t s w i t h a good n u t r i e n t s t a t u s have been shown t o t a k e up l e s s water p e r u n i t o f d r y m a t t e r produced t h a n p l a n t s w i t h a n u t r i e n t d e f i c i e n c y ( H i l l e r d a l - H a g s t r o m e r e t a l . , 1987) . An i n c r e a s e i n l e a f a r e a r e s u l t s i n a h i g h e r t r a n s p i r a t i o n r a t e and hence would l e a d t o lower v a l u e s o f mean n e e d l e water p o t e n t i a l , u n l e s s t h e r e a r e c o r r e s p o n d i n g r e d u c t i o n s i n f low r e s i s t a n c e o f t h e water pathway between s o i l and l e a v e s . A l t h o u g h n u t r i t i o n and water a b s o r p t i o n a r e i n d i v i d u a l 30 p r o c e s s e s i n the r o o t , the n e c e s s i t y f o r a v a i l a b l e water i n b o t h p l a n t and s o i l f o r growth and n u t r i e n t t r a n s p o r t makes them i n t i m a t e l y r e l a t e d ( V i e t s , 1972; Kimmins e t a l . , 1989) . T h i s makes i t d i f f i c u l t t o c l e a r l y d e f i n e t h e e f f e c t s o f d r o u g h t on n u t r i t i o n . O n l y c o n s i d e r i n g the s o i l s o l u t i o n as a s t r i c t l y c h e m i c a l sys tem, and i g n o r i n g i o n a b s o r p t i o n by r o o t s and the e f f e c t s o f water on m i c r o o r g a n i s m s , V i e t s (1972) i n d i c a t e d t h a t v e r y l i t t l e i n f o r m a t i o n e x i s t s on the changes i n n u t r i e n t c o n c e n t r a t i o n i n the s o i l s o l u t i o n as the s o i l d r i e s from f i e l d c a p a c i t y t o the w i l t i n g p o i n t . Ions v e r y weakly adsorbed by m i n e r a l o r o r g a n i c s o i l f r a c t i o n s such as N03~ s h o u l d t h e o r e t i c a l l y doub le i n c o n c e n t r a t i o n as water volume d e c r e a s e s by 50 p e r c e n t . The q u a n t i t y o f water i n the s o i l a f f e c t s not o n l y t h e amount o f n u t r i e n t s i n the s o i l s o l u t i o n , b u t a l s o the r a t e o f movement t o the r o o t by d i f f u s i o n and mass f l o w . F u r t h e r , a l t h o u g h s o i l water c o n t e n t appears t o be v e r y i m p o r t a n t i n n u t r i e n t t r a n s p o r t t o the r o o t , i t s e f f e c t on r a t e o f r o o t e x t e n s i o n and m y c o r r h i z a l hypha e x t e n s i o n may be j u s t as i m p o r t a n t . Rates o f r o o t e x t e n s i o n may be 5 cm p e r d a y , but d i s t a n c e s o f i o n d i f f u s i o n a r e o n l y 1 t o 5 mm. However, d i f f u s i o n toward the r o o t i s m o s t l y r a d i a l whereas r o o t e x t e n s i o n i s l i n e a r . Root e x t e n s i o n i s a l s o i m p o r t a n t f o r k e e p i n g t h e r o o t t i p p h y s i o l o g i c a l l y e f f e c t i v e . The r a t e o f r o o t e l o n g a t i o n i s v e r y dependent on a v a i l a b l e w a t e r , because r o o t growth i s i n p a r t a h y d r a t i o n p r o c e s s ( V i e t s , 1972) , 31 V i e t s (1972) a l s o s t a t e d t h a t much o f t h e n u t r i e n t uptake may o c c u r soon a f t e r the s o i l i s w e t t e d ; p l a n t s may be a b l e t o meet a l l o f t h e i r n u t r i e n t r e q u i r e m e n t s p r o v i d e d the s o i l n u t r i e n t p o o l i s adequate . T h i s may be v e r y i m p o r t a n t i n t r e e s which have a w e l l - e s t a b l i s h e d c a p a c i t y t o s t o r e n u t r i e n t s f o r f u t u r e u s e . The abundance and dominance o f p i n e g r a s s ( C a l a m a o r o s t i s rubescens Buck . ) i n s o u t h and c e n t r a l i n t e r i o r B r i t i s h Columbia makes i t o f major importance as a c o m p e t i t o r w i t h c r o p t r e e s ( H a e u s s l e r and C o a t e s , 1986) . P i n e g r a s s i s v e r y common i n the Southern I n t e r i o r B . C . and o f t e n seeds i n a l o n g w i t h l o d g e p o l e p i n e on c l e a r c u t s , where i t may compete s t r o n g l y f o r l i m i t e d s o i l m o i s t u r e . Most s t u d i e s i n d i c a t e t h a t p i n e g r a s s responds v e r y w e l l t o n u t r i e n t i n p u t s . Freyman and van Ryswyk (1969) found s i g n i f i c a n t herbage y i e l d re sponses t o ammonium n i t r a t e and s u l p h u r i n t h e p r e s e n c e o f i n c r e a s e d N, but n e g l i g i b l e r e s p o n s e s t o phosphorous , p o t a s s i u m , and m i c r o n u t r i e n t s . S i m i l a r l y , Fober and G i e r t y c h (1971), S q u i r e (1977), and Cochran (1979) a l s o i n d i c a t e d t h a t the growth o f g r a s s i s g r e a t l y s t i m i l a t e d by f e r t i l i z e r . Nords trom (1984) c i t e d a s t u d y i n which N and P a p p l i c a t i o n d i d no t i n c r e a s e the h e i g h t growth o f D o u g l a s - f i r , b u t caused a d j a c e n t g r a s s t o f l o u r i s h . He s t a t e d t h a t a g e n e r a l o b s e r v a t i o n from s t u d i e s has been t h a t g r a s s e s t e n d t o r e s p o n d more t o n u t r i e n t a d d i t i o n s t h a n do a s s o c i a t e d t r e e s . B l a c k e t a l . (1988) s t u d i e d s i t e p r e p a r a t i o n 32 p r o c e d u r e s t o m i n i m i z e s e e d l i n g water and t e m p e r a t u r e s t r e s s i n t h e Montane Spruce zone i n the s o u t h e r n i n t e r i o r o f B . C . F o r l o d g e p l e p i n e they found no major d i f f e r e n c e s i n stem growth o r s u r v i v a l between t r e a t m e n t s where g r a s s was removed and c o n t r o l s , b u t shoot d r y m a t t e r p r o d u c t i o n was g r e a t e r where t h e g r a s s was removed, and v o l u m e t r i c water c o n t e n t and s o i l water s t o r a g e were much lower on c o n t r o l t r e a t m e n t s . Nords trom (1984) s t a t e d t h a t t h e i n f l u e n c e o f r o o t c o m p e t i t i o n between t r e e s and shrubs can be v e r y s i g n i f i c a n t , b u t t h a t n a t i v e herbage y i e l d s t e n d t o d e c l i n e a f t e r t e n y e a r s i n l o d g e p o l e p i n e c l e a r c u t s , even though crown c l o s u r e may be low. T h i s sugges t s t h a t t r e e r o o t s have d e v e l o p e d s u f f i c i e n t l y by t e n y e a r s o f age t o g a i n a c o m p e t i t i v e advantage o v e r g r a s s c o m p e t i t i o n f o r a v a i l a b l e m o i s t u r e ( B a s i l e and J e n s o n , 1971; N o r d s t r o m , 1984) . I n c o n t r a s t , B a r r e t t and Youngberg (1965) s t a t e d t h a t t h e growth o f dominant ponderosa p i n e t r e e s i n c e n t r a l Oregon was s i g n i f i c a n t l y a f f e c t e d by woody and herbaceous c o m p e t i t i o n . They found t h a t the u n d e r s t o r y v e g e t a t i o n consumed s i g n i f i c a n t amounts o f w a t e r . S i m i l a r l y , O l i v e r (1984) and Powers and J a c k s o n (1978) found t h a t c o m p e t i t i o n from u n d e r s t o r y v e g e t a t i o n s i g n i f i c a n t l y a f f e c t e d t r e e growth i n ponderosa p i n e . However, i t s h o u l d be noted t h a t the u n d e r s t o r y v e g e t a t i o n i n some o f t h e s e s t u d i e s i n c l u d e d b o t h shrubs and g r a s s and t h a t the ecosystems a r e l i k e l y more m o i s t u r e l i m i t e d t h a n t h o s e i n t h e Montane Spruce b i o g e o c l i m a t i c zone i n B . C . 33 T h e r e a r e a l s o b e n e f i t s from g r a s s c o m p e t i t i o n . H a e u s s l e r and Coates (1986) s t a t e d t h a t a c o v e r o f g r a s s i n c o r p o r a t e s v a l u a b l e , n u t r i e n t r i c h o r g a n i c m a t t e r i n t o s u r f a c e s o i l l a y e r s . T h e r e f o r e , an i n c r e a s e i n g r a s s d e n s i t y i s l i k e l y t o r e s u l t i n a more r a p i d b u i l d up o f o r g a n i c m a t t e r and t h u s i n c r e a s e m o i s t u r e and n u t r i e n t r e t e n t i o n on t h e s i t e . NITROGEN CYCLING N i t r o g e n c y c l i n g has r e c e i v e d more a t t e n t i o n i n f o r e s t r e s e a r c h t h a n any o t h e r n u t r i e n t . B i n k l e y (1986) summarized s i x major p r o c e s s e s which form the N c y c l e : 1. N i t r o g e n F i x a t i o n which uses energy d e r i v e d from p h o t o s y n t h e s i s t o reduce a t m o s p h e r i c N t o ammonia which can t h e n be used and r e c y c l e d w i t h i n the ecosys tem. 2. A m m o n i f i c a t i o n i s the r e l e a s e o f ammonia from decomposing o r g a n i c m a t t e r . A t pH l e v e l s common i n f o r e s t s o i l s , t h e ammonia immedia te ly absorbs one H + from the s o i l s o l u t i o n t o become ammonium. Example: CH 2 NH 2 C00H + 1.5 0 2 — C 0 2 + H 2 0 + N H 3 3. N i t r i f i c a t i o n i s the m i c r o b i a l o x i d a t i o n o f ammonium t o form n i t r a t e : NH.4+ + 2 0 2 — N03~ + H 2 0 + 2 H + E l e c t r o n s a r e donated from the N atom t o t h e oxygen m o l e c u l e , r e l e a s i n g energy f o r use by t h e m i c r o b e s . 4. D e n i t r i f i c a t i o n i s a form o f n i t r a t e r e d u c t i o n where t h e n i t r a t e a n i o n i s used as a t e r m i n a l e l e c t r o n a c c e p t o r i n the absense o f oxygen. N i t r a t e i s r e d u c e d t o N 2 34 (or N2O) and l o s t from the ecosystem: 2 N 0 3 " + 12 H + + 10 e" — N 2 + 6 H 2 0 5. N i t r a t e r e d u c t i o n i s t h e r e d u c t i o n o f n i t r a t e t o ammonia and must precede the use o f n i t r a t e by p l a n t s and m i c r o b e s : N 0 3 " + 9 H + + 8 e" — N H 3 + 3H 2 0 6. Ammonium a s s i m i l a t i o n f o l l o w s N f i x a t i o n o r ammonium u p t a k e . Ammonia i s combined w i t h an o r g a n i c m o l e c u l e such as g lu tamate t o produce g l u t a m i n e . These v a r i o u s o x i d a t i o n and r e d u c t i o n r e a c t i o n s can be c o n f u s i n g , e s p e c i a l l y because terms such as n i t r i f i c a t i o n and d e n i t r i f i c a t i o n do not r e f e r t o o p p o s i t e r e a c t i o n s . M i n e r a l i z a t i o n ( a m m o n i f i c a t i o n and n i t r i f i c a t i o n ) , u p t a k e , and t r e e i n t e r n a l c y c l i n g w i l l be d i s c u s s e d i n the f o l l o w i n g s e c t i o n s . M i n e r a l i z a t i o n and F a c t o r s I n f l u e n c i n g I t The s t u d y o f the g e n e r a l c o u r s e o f m i n e r a l i z a t i o n o f o r g a n i c N i n s o i l was p r a c t i c a l l y comple ted b e f o r e 1935 (Paul and Juma, 1981) . However, P a u l and Juma s t a t e d t h a t the r e l a t i o n s h i p s between C and N and t h e e f f e c t s o f e n v i r o n m e n t a l f a c t o r s have t o be de termined f o r each s o i l t y p e , i n d i c a t i n g t h a t t h e u n d e r l y i n g p r i n c i p l e s a r e not u n d e r s t o o d . S i m i l a r l y , Weetman (1983) s t a t e d t h a t humus N a v a i l a b i l i t y t h e o r y goes back a lmos t 100 y e a r s , but i t s o r g a n i c c h e m i s t r y i s no t v e r y w e l l u n d e r s t o o d . 35 Ammonification and Immobilization The d e c o m p o s i t i o n p r o c e s s may be d e f i n e d as the b i o l o g i c a l l y media ted breakdown o f an o r g a n i c s u b s t r a t e ( C a r l y l e , 1986) . Carbon and o t h e r e lements r e l e a s e d from the s u b s t r a t e a r e used t o s u p p o r t m i c r o b i a l r e s p i r a t i o n and s y n t h e s i s o f m i c r o b i a l t i s s u e . S i m i l a r l y , N m i n e r a l i z a t i o n i s the b i o l o g i c a l l y mediated r e l e a s e o f o r g a n i c bound N from a s u b s t r a t e and i t s c o n v e r s i o n t o i n o r g a n i c forms . The r e l e a s e o f o r g a n i c a l l y bound amino N may be termed p r o t e o l y s i s ( C a r l y l e , 1986) , but p r o t e o l y s i s i s u s u a l l y r e s t r i c t e d t o h y d r o l y s i s o f p o l y p e p t i d e s . I t s subsequent r e d u c t i o n t o ammonium i s c a l l e d a m m o n i f i c a t i o n , a l t h o u g h a m m o n i f i c a t i o n may be used f o r b o t h s t e p s . Berg and S t a a f (1981) proposed t h r e e s t a g e s i n the ne t l o s s o f N d u r i n g l i t t e r d e c o m p o s i t i o n : 1. L e a c h i n g o f S o l u b l e Compounds i s t h e r a p i d r e l e a s e o f i n i t i a l l y s o l u b l e N i n l i t t e r . T h i s s tage i s s h o r t and runs from t h e b e g i n n i n g o f we ight l o s s u n t i l the end o f i n i t i a l ne t r e l e a s e . T h i s l e a c h i n g o f water s o l u b l e s u b s t a n c e s can remove s i g n i f i c a n t amounts o f N and g i v e s t h e p o s s i b i l i t y o f r a p i d r e c y c l i n g t o p l a n t s . I n f o r m a t i o n on the s i z e and t u r n o v e r o f t h e s o l u b l e o r g a n i c N p o o l s i s s p a r s e , b u t van C l e v e and White (1980) found i t t o be 40 kg h a - 1 , composing n e a r l y 10 p e r c e n t o f t o t a l N , and much l a r g e r t h a n the i n o r g a n i c p o o l s . 1 5 N l a b e l l i n g i n d i c a t e d the t u r n o v e r o f t h i s p o o l t o be the major pathway, d e m o n s t r a t i n g t h a t a c o n s i d e r a b l e p o r t i o n o f 36 m o b i l i z e d N may not pass t h r o u g h the i n o r g a n i c f r a c t i o n s . The a b i l i t y o f e c t o m y c o r r h i z a l f u n g i t o u t i l i z e s o l u b l e N p r o v i d e s a mechanism o f N uptake by t r e e s t h a t does no t i n v o l v e t h e i n o r g a n i c p o o l (Heal e t a l . . 1982) . 2. Net A c c u m u l a t i o n o f N ( I m m o b i l i z a t i o n ) b e g i n s as soon as a ne t a b s o l u t e i n c r e a s e i n N t a k e s p l a c e a f t e r the l e a c h i n g phase o r from t h e b e g i n n i n g o f we ight l o s s i f l e a c h i n g does no t o c c u r . I t r e s u l t s from a l o s s o f c a r b o n t h r o u g h r e s p i r a t i o n w h i l e N i s r e t a i n e d by m i c r o b e s ( C a r l y l e , 1986) . N i s r e t a i n e d by the m i c r o o r g a n i s m s u n t i l C:N reaches 25-35 ( C a r l y l e , 1986) a t which t ime N c o n c e n t r a t i o n i s a t a maximum. In a p e r i o d o f low demand by p l a n t s , i m m o b i l i z a t i o n i s no t u n f a v o r a b l e s i n c e i t may h e l p p r e v e n t l e a c h i n g and l o s s o f N from t h e s i t e ( B e r n i e r , 1965) . H e a l e t a l . (1982) s t a t e d t h a t an i n i t i a l i n c r e a s e i n the a b s o l u t e amount o f N i n the r e s o u r c e i s o f t e n observed as a r e s u l t o f N 2 f i x a t i o n , i m m i g r a t i o n by organisms o r i n p u t o f l e a c h a t e s . H e n d r i c k s o n and R o b i n s o n (1984) sugges ted t h a t N accumulates i n f r e s h l i t t e r i n p r o p o r t i o n t o i t s i n c r e a s e i n f u n g a l b iomass , s u g g e s t i n g t h a t i t i s t r a n s l o c a t e d from o l d e r l i t t e r v i a f u n g a l hyphae. 3 . Net N L o s s i s t h e ne t r e l e a s e o f N a f t e r a maximum amount has been accumulated i n l i t t e r , more o r l e s s p r o p o r t i o n a l t o r a t e o f C l o s s . In f i e l d s i t u a t i o n s , c o n s i d e r a t i o n o f t h e s e t h r e e s t a g e s may be academic because , a t any one t i m e , t h e f o r e s t 3 7 f l o o r w i l l c o n s i s t o f l a y e r s o f o r g a n i c d e b r i s i n v a r y i n g s t a t e s o f d e c o m p o s i t i o n (Keeney, 1980) . However, knowledge o f t h e s e s t a g e s adds t o our u n d e r s t a n d i n g o f the p r o c e s s and thus t h e p r e d i c t i o n o f m i n e r a l i z a t i o n r a t e s . A m m o n i f i c a t i o n and i m m o b i l i z a t i o n t a k e p l a c e c o n t i n u o u s l y and s i m u l t a n e o u s l y w i t h t h e d r i v i n g f o r c e b e h i n d t h e c y c l e b e i n g t h e h e t e r o t r o p h i c s o i l p o p u l a t i o n (Kumi, 1984; C a r l y l e , 1986) . A ne t change i n t h i s p o o l , ne t a m m o n i f i c a t i o n o r ne t i m m o b i l i z a t i o n , depends on a b a l a n c e between the s i m u l t a n e o u s p r o c e s s e s o f g r o s s a m m o n i f i c a t i o n and g r o s s i m m o b i l i z a t i o n . Net a m m o n i f i c a t i o n w i l l u s u a l l y o n l y o c c u r when N r e l e a s e d from the decomposing s u b s t r a t e exceeds t h a t r e q u i r e d by m i c r o f l o r a ( C a r l y l e , 1986) . T h i s b e g i n s t o o c c u r b e f o r e the s u b s t r a t e C : N r a t i o f a l l s below t h a t o f the m i c r o b i a l b iomass . More N i s t h e n r e l e a s e d p e r u n i t o f s u b s t r a t e C t h a n can be used i n the s y n t h e s i s o f m i c r o b i a l b iomass . However, ne t a m m o n i f i c a t i o n can be s u b s t a n t i a l when the C:N o f t h e s u b s t r a t e i s g r e a t e r than the C:N o f the m i c r o b i a l biomass (Heal e t a l . . 1982) . V i t o u s e k and Matson (1985) s t a t e d t h a t t h e ne t m i n e r a l i z a t i o n i n t h e f i e l d s h o u l d be p r e d i c t a b l e from s o i l m o i s t u r e , s o i l t e m p e r a t u r e , and t h e q u a n t i t y and q u a l i t y ( i n h e r e n t m i n e r a l i z a b i l i t y ) o f s o i l o r g a n i c N . A l t h o u g h not s p e c i f i c a l l y d e f i n e d , t h e term l i t t e r q u a l i t y means the s u s c e p t i b i l i t y t o a t t a c k and d e c o m p o s i t i o n by m i c r o o r g a n i s m s and a n i m a l s ( S t a a f and B e r g , 1981) . I t i s u s u a l l y g i v e n by 38 v a r i o u s i n d i c e s r e l a t e d t o c h e m i c a l c o m p o s i t i o n , such as l i g n i n and N c o n c e n t r a t i o n , o r C:N and C : P r a t i o s . The l i t t e r produced by f o r e s t t r e e s c o n t a i n s a p r o p o r t i o n o f r e l a t i v e l y r e s i s t a n t compounds (eg. l i g n i n ) and i s c h a r a c t e r i z e d by h i g h r a t i o s o f C:N and C : P . P a s t o r e t a l . (1984) s t a t e d t h a t t h e r e a r e complex r e l a t i o n s h i p s among N a m m o n i f i c a t i o n , n i t r i f i c a t i o n , p r o d u c t i v i t y , s p e c i e s c o m p o s i t i o n , P s u p p l y and s i t e m o i s t u r e s t a t u s . V e g e t a t i o n i n f l u e n c e s N m i n e r a l i z a t i o n t h r o u g h i t s c o m p e t i t i o n w i t h m i c r o b e s f o r n u t r i e n t s and t h r o u g h l i t t e r q u a l i t y and q u a n t i t y . Berg (1986) s t a t e d t h a t s u b s t r a t e q u a l i t y and s o i l c l i m a t e a r e t h e most i m p o r t a n t f a c t o r s i n f l u e n c i n g d e c o m p o s i t i o n r a t e s . S i m i l a r l y , A t t i w i l l (1986) s t a t e d t h a t t h e r a t e o f d e c o m p o s i t i o n o f f o r e s t l i t t e r i s m a i n l y c o n t r o l l e d by c l i m a t e as measured by a c t u a l e v o p o t r a n s p i r a t i o n ( A E T ) . He i n d i c a t e d t h a t c l i m a t e was s e v e r a l o r d e r s o f magnitude more i m p o r t a n t t h a n l i t t e r q u a l i t y (as measured by l i g n i n conten t ) as AET i n c r e a s e d . S i m i l a r l y , V i t o u s e k and Matson (1985) found t h a t the s e a s o n a l c o u r s e o f ne t N m i n e r a l i z a t i o n i n s i t u was p r i m a r i l y c o n t r o l l e d by s o i l t e m p e r a t u r e and m o i s t u r e , r a t h e r t h a n s e a s o n a l d i f f e r e n c e s i n s u b s t r a t e q u a l i t y . However, Theodorou and Bowen (1983) c o n c l u d e d t h a t the m i c r o b i a l p o p u l a t i o n i n the f i e l d , i n f l u e n c e d by f a c t o r s such as t empera ture and m o i s t u r e , a r e as i m p o r t a n t i n t h e r e l e a s e o f N as a r e s o i l t e m p e r a t u r e and m o i s t u r e p e r s e . 39 A m m o n i f i c a t i o n i s enhanced by c y c l e s o f d r y i n g and w e t t i n g . D r y i n g c y c l e s f o l l o w e d by r a i n f a l l may be accompanied by b u r s t s o f i n s i t u m i n e r a l i z a t i o n ( C a r l y l e , 1986) . However, P a s t o r e t a l . (1984) i n d i c a t e d t h a t t h e t o t a l amount o f N m i n e r a l i z e d a f t e r one month under s t a b l e c o n d i t i o n s was e q u a l t o t h a t under f l u c t u a t i n g c o n d i t i o n s . F o r a wide range o f s o i l s , t h e optimum m o i s t u r e c o n t e n t f o r a m m o n i f i c a t i o n i s between 50 and 75 % o f the water h o l d i n g c a p a c i t y ( C a r l y l e , 1986) . O r g a n i c m a t t e r d e c o m p o s i t i o n , h u m i f i c a t i o n and m i n e r a l i z a t i o n may a l s o be a f f e c t e d by a c t i v i t i e s o f s o i l fauna (Anderson e t a l . , 1985) . S o i l fauna e x c r e t e N i n the form o f ammonia, u r e a , amino a c i d s , o r u r i c a c i d s (Heal e t a l . , 1982) . Because the C:N r a t i o o f fauna i s h i g h e r t h a n , o r a t l e a s t s i m i l a r t o t h o s e o f m i c r o f l o r a consumed, N i s m i n e r a l i s e d . S o i l fauna a l s o m e c h a n i c a l l y p r o c e s s l i t t e r and d e t r i t u s , t h u s i n f l u e n c i n g o r g a n i c m a t t e r d i s t r i b u t i o n , t e m p o r a l homogeneity o f s i t e s and d e c o m p o s i t i o n p r o c e s s e s and g e n e r a l l y i n c r e a s i n g m i n e r a l i z a t i o n (Heal e t a l . , 1982; C a r l y l e , 1986) . N i t r i f i c a t i o n Even though some f o r e s t s o i l s can have s u b s t a n t i a l a n i o n exchange c a p a c i t i e s a t low pHs, most f o r e s t s o i l s g e n e r a l l y have low exchange c a p a c i t i e s f o r a n i o n s . N i t r a t e i s t h e r e f o r e much more m o b i l e t h a n ammonium, and i s prone t o l e a c h i n g i f no t t a k e n up by p l a n t s ( B i n k l e y , 1986) . T h i s , p l u s 40 t h e f a c t t h a t n i t r a t e can l e a v e the ecosystem v i a d e n i t r i f i c a t i o n , makes n i t r i f i c a t i o n p o t e n t i a l l y v e r y i m p o r t a n t i n an ecosys tem. N i t r i f i c a t i o n i s a r e a c t i o n i n which c e r t a i n "chemo-a u t o t r o p h i c " organisms and some h e t e r o t r o p h s o x i d i z e ammonium i o n s t o n i t r i t e and t h e n t o n i t r a t e (Kumi, 1984) . Each s tage i s c a r r i e d out by s p e c i f i c o r g a n i s m s , w i t h a u t o t r o p h i c b a c t e r i a r e s p o n s i b l e f o r most n i t r a t e p r o d u c t i o n . In c e r t a i n c o n i f e r o u s f o r e s t ecosystems , h e t e r o t r o p h i c n i t r i f y i n g f u n g i may be more i m p o r t a n t due t o a s h o r t a g e o f a u t o t r o p h i c n i t r i f i e r s (Keeney and G a r d n e r , 1970) . Under c o n d i t i o n s which p r e v a i l i n many f o r e s t s o i l s ( a c i d i c c o n d i t i o n s and s t r o n g m i c r o b i a l c o m p e t i t i o n f o r i n o r g a n i c N) n i t r i f i c a t i o n i s g e n e r a l l y low ( C a r l y l e , 1986) because n i t r i f i e r s a r e poor c o m p e t i t o r s w i t h h e t e r o t r o p h s when ammonium c o n c e n t r a t i o n i s low. Ammonium may t h u s be the end p r o d u c t o f m i n e r a l i z a t i o n . Keeney (1980) sugges ted t h a t the o f t e n o b s e r v e d low n i t r i f i c a t i o n r a t e i n f o r e s t s i s due t o the low p o p u l a t i o n o f n i t r i f i e r s and t h a t , g i v e n f a v o r a b l e c o n d i t i o n s by p e r t u r b a t i o n s , n i t r i f i c a t i o n w i l l commence f o l l o w i n g a l a g p e r i o d , e s p e c i a l l y where an i n i t i a l l a r g e i n o r g a n i c p o o l i s t u r n e d o v e r r a p i d l y . N i t r o g e n Uptake T h e r e a r e s e v e r a l i n t e r d e p e n d e n t f a c t o r s which r e g u l a t e N uptake i n an ecosystem ( C o l e , 1981): 1. S o i l and s o l u t i o n p r o c e s s e s , i n c l u d i n g mass f low 41 and d i f f u s i o n o f N03~ and NH4 + i o n s , r a t e o f N a m m o n i f i c a t i o n , i m m o b i l i z a t i o n , n i t r i f i c a t i o n , and d e n i t r i f i c a t i o n . 2. S i z e , l o c a t i o n , r a t e o f r o o t e l o n g a t i o n , and p r e s e n c e o f m y c o r r h i z a l a s s o c i a t i o n s . 3 . S p e c i f i c c h e m i c a l and b i o c h e m i c a l r e a c t i o n s a t the s o i l s o l u t i o n r o o t i n t e r f a c e , r e g u l a t i n g t h e a s s i m i l a t o r y p r o c e s s . 4. The N r e q u i r e m e n t o f p l a n t s , i n c l u d i n g t h e r a t e o f p r i m a r y p r o d u c t i o n . I t has been shown t h a t the most d e c i s i v e f a c t o r f o r t r e e n u t r i e n t uptake i s i t s growth energy o r u t i l i z a t i o n c a p a c i t y under p r e v a i l i n g c o n d i t i o n s (Tamm, 1969 and 1975; I n g e s t a d , 1987) . The a b i l i t y o f t r e e s t o compete w i t h s a p r o p h y t i c m i c r o f l o r a f o r N , even d u r i n g p e r i o d s o f v e r y low N a v a i l a b i l i t y (Heal e t _ a l . , 1982) s h o u l d p r o b a b l y a l s o be i n c l u d e d w i t h t h i s l i s t . The f a c t t h a t f o r e s t s t y p i c a l l y t a k e up r e l a t i v e l y low q u a n t i t i e s o f N does not mean t h a t they cannot u t i l i z e more, s h o u l d more become a v a i l a b l e ( C o l e , 1981) . T h e r e a r e many reasons f o r t h e wide range o f uptake i n f o r e s t s i n c l u d i n g the r a t e o f p r o d u c t i o n , N a v a i l a b i l i t y , d u r a t i o n o f n e e d l e r e t e n t i o n , i n t e r n a l t r a n s l o c a t i o n and s t a n d age . Between 25 and 125 kg N h a - 1 a r e i n c o r p o r a t e d a n n u a l l y i n t o t r e e biomass (Keeney, 1980) . However, most o f t h i s N i s r e c y c l e d by l i t t e r f a l l , t h r o u g h f a l l and i n t e r n a l r e d i s t r i b u t i o n , so t h a t ne t uptake i s a p p r o x i m a t e l y 5 t o 25 kg h a - 1 (Keeney, 1980) . However, such e s t i m a t e s a r e v e r y 42 m i s l e a d i n g s i n c e N r e q u i r e m e n t v a r i e s w i t h s p e c i e s , s i t e c o n d i t i o n s , and s t a n d age ( C a r l y l e , 1986) and the n u t r i e n t uptake r e q u i r e m e n t s o f f i n e r o o t p r o d u c t i o n have no t been q u a n t i f i e d f o r many f o r e s t s (Kimmins, 1987) . Most l i k e l y , N a v a i l a b i l i t y d u r i n g t h e maximum growth s tage i s the most c r i t i c a l t o p r o d u c t i v i t y ( C a r l y l e , 1986; Kimmins, 1977) . C a r l y l e (1986) d e s c r i b e d the v a r i a t i o n o f N uptake w i t h s t a n d age . In young s t a n d s , N uptake i s v e r y dominant , which must c o n t i n u a l l y i n c r e a s e t o meet the demands o f growth and deve lopment . S i n c e crowns a r e s m a l l and do not f u l l y occupy t h e s i t e , the c a p t u r e o f a t m o s p h e r i c i n p u t i s low as i s i t s r e t e n t i o n i n t r e e biomass because o f l i m i t e d r o o t system deve lopment . V i r t u a l l y , a l l the t r e e ' s uptake demand must be met by the s o i l , and N c o n c e n t r a t i o n and r e p l e n i s h m e n t i n s o i l s o l u t i o n a r e c r i t i c a l t o s t a n d development a t t h i s s t a g e . T h i s i s a s tage when response t o a wide range o f n u t r i e n t a d d i t i o n s can be expec ted ( M i l l e r , 1981) . Maximum l e a f a r e a i s a c h i e v e d j u s t p r i o r t o canopy c l o s u r e a t which t ime i t d e c l i n e s s l i g h t l y and s t a b i l i z e s . F o l l o w i n g canopy c l o s u r e , ne t uptake remains f a i r l y c o n s t a n t s i n c e t h e o n l y i n c r e a s e i n N i s i m m o b i l i z e d i n woody components . A t t h i s t i m e , a l a r g e p r o p o r t i o n o f n u t r i e n t r e q u i r e m e n t can be met by i n t e r n a l r e c y c l i n g and t h e m i n e r a l s o i l i s r e p l a c e d by the f o r e s t f l o o r as t h e main zone o f u p t a k e . Decreased i m m o b i l i z a t i o n i n t r e e biomass and enhanced i n p u t mean t h a t N demand may be v e r y low ( M i l l e r , 1981) . The i o n i c form o f N p r e f e r r e d by t r e e s f o r uptake has 43 not been as e x t e n s i v e l y s t u d i e d f o r t r e e s as f o r a g r i c u l t u r e c r o p s . However, a p p a r e n t l y t r e e s t h a t have e v o l v e d i n h i g h ammonium, low n i t r a t e environments p r e f e r t o t a k e up t h e ammonium i o n ( C o l e , 1981) . B i o c h e m i c a l N C y c l i n g N i t r o g e n c y c l i n g w i t h i n a t r e e i n v o l v e s t h e m o b i l i z a t i o n and t r a n s l o c a t i o n o f N from o l d e r f o l i a g e t o younger f o l i a g e , s tems, b r a n c h e s , and r o o t s ( C a r l y l e , 1986) . The t r a n s l o c a t i o n o f N from a g i n g t i s s u e a l l o w s a t r e e a s l i g h t degree o f n u t r i e n t independance from the s o i l when N a v a i l a b i l i t y i s low. In c o n i f e r s , most r e t r a n s l o c a t i o n i s not a s s o c i a t e d w i t h t i s s u e d e a t h , but i s the t r a n s l o c a t i o n and r e u s e o f N accumulated d u r i n g p e r i o d s o f i n a c t i v e growth . A heavy removal o f N from senescent p l a n t organs i n e v i t a b l y means low c o n c e n t r a t i o n s o f N i n l i t t e r and i t s w i t h d r a w a l from the b i o g e o c h e m i c a l c y c l e ( i n t e r n a l N c y c l e o f e c o s y s t e m s ) . As l o n g as the t r a n s l o c a t e d N remains s t o r e d i n o r g a n i c form, the p l a n t g a i n s an energy advantage (Berg and S t a a f , 1981) . Gosz (1981) s t a t e d t h a t i f a s p e c i e s i s grown under d i f f e r e n t s i t e c o n d i t i o n s t h e r e w i l l be a l a r g e d i f f e r e n c e i n i n t e r n a l c y c l i n g o f N , i n d i c a t i n g t h a t a c o n i f e r s p e c i e s has t h e a b i l i t y t o modi fy v a r i o u s p h y s i o l o g i c a l p r o c e s s e s , t i s s u e c h a r a c t e r i s t i c s ( l i g n i n and p o l y p h e n o l c o n c e n t r a t i o n ) and f o l i a g e p e r s i s t e n c e i n response t o N a v a i l a b i l i t y . Berg and S t a a f (1981) sugges ted t h a t p l a n t s growing on N poor s o i l s are 44 more l i k e l y t o be e f f i c i e n t i n N c o n s e r v a t i o n w h i l e the same s p e c i e s growing on an N r i c h s i t e t ends t o r e d i s t r i b u t e a lower p e r c e n t a g e o f l e a f N b e f o r e s h e d d i n g . S i n c e N c o n c e n t r a t i o n s a r e g e n e r a l l y lowes t on i n f e r t i l e s i t e s , such a mechanism would magnify t h e d i f f e r e n c e s i n c o n c e n t r a t i o n i n l i t t e r f a l l between s i t e s compared w i t h t h a t o f l i v i n g t i s s u e a l o n g a f e r t i l i t y g r a d i e n t . T h e r e f o r e , d i f f e r e n c e s i n a v a i l a b i l i t y o f N s h o u l d be r e f l e c t e d i n t h e N c o n c e n t r a t i o n o f o l d e r f o l i a g e (Gosz, 1981) . T h i s a l s o r e s u l t s i n a h i g h l i t t e r C:N r a t i o on poor s i t e s and a p o s i t i v e feedback which lowers N a v a i l a b i l i t y even f u r t h e r . A l s o , s p e c i e s adapted t o poor s i t e s (such as l o d g e p o l e p i n e ) g e n e r a l l y r e t a i n f o l i a g e f o r l o n g e r p e r i o d s ( C a r l y l e , 1986) . However, i n managed s t a n d s , the onse t o f N d e f i c i e n c y i s commonly a s s o c i a t e d w i t h pronounced N w i t h d r a w a l and s a c r i f i c i a l a b s c i s s i o n o f o l d e r n e e d l e s , d e c r e a s i n g f o l i a g e l o n g e v i t y . T u r n e r (1977) s t u d i e d t h e e f f e c t o f f e r t i l i z a t i o n on N c y c l i n g i n a D o u g l a s - f i r s t a n d and found t h a t i n c r e a s e d N uptake l e d t o d e c r e a s e d r e d i s t r i b u t i o n w i t h i n the t r e e and l o n g e r n e e d l e r e t e n t i o n . However, A x e l s s o n and A x e l s s o n (1986) and B i n k l e y and R i e d (1985) found t h a t the a b s o l u t e amounts o f n u t r i e n t r e d i s t r i b u t i o n w i t h i n crowns were h i g h e r i n f e r t i l i z e d p l o t s . Kimmins (1987) s t a t e d t h a t the i n t e r a c t i o n o f m o i s t u r e and n u t r i e n t s may e x p l a i n some o f the i n c o n s i s t e n c i e s i n the l i t e r a t u r e on i n t e r n a l c y c l i n g . I n t e r n a l c y c l i n g o f a s p e c i e s i s a f f e c t e d by any f a c t o r t h a t i n f l u e n c e s p l a n t growth and uptake demand such as s o i l m o i s t u r e . 45 ASSESSMENT OF NITROGEN STATUS Because o f the c o m p l e x i t y o f the N c y c l e , t h e r e have been many a t tempts t o d e v e l o p a method which a c c u r a t e l y r e f l e c t s N a v a i l a b i l i t y i n f o r e s t s o i l s . There can be a c o n s i d e r a b l e l a c k o f agreement among N a v a i l a b i l i t y i n d e x e s , stemming from d i f f e r e n c e s i n t h e r e l a t i v e s e n s i t i v i t i e s o f each method t o e n v i r o n m e n t a l f a c t o r s i n f l u e n c i n g s o i l N t r a n s f o r m a t i o n s , as w e l l as from d i f f e r e n c e s i n the components o f the N c y c l e a s s e s s e d by each method (Hart and F i r e s t o n e , 1989) . The c h o i c e o f method depends upon o b j e c t i v e s . S c i e n t i f i c a l l y r i g o r o u s p r o o f o f n u t r i e n t d e f i c e n c i e s i s t oo t ime consuming and e x p e n s i v e f o r r o u t i n e d i a g n o s t i c use i n f e r t i l i z e r p r e s c r i p t i o n s ( B a l l a r d and C a r t e r , 1986) , but i s n e c e s s a r y as a b a s i s f o r d e v e l o p i n g more r a p i d t e c h n i q u e s . M o r r i s o n (1974) i n d i c a t e d t h a t t e c h n i q u e s a r e needed f o r b o t h d i a g n o s t i c and p r e d i c t i v e u s e . D i a g n o s i s i s the i d e n t i f i c a t i o n o f f a c t o r s i n f l u e n c i n g growth w h i l e p r e d i c t i o n i s t h e f o r e c a s t o f growth responses t o a l t e r a t i o n o f c o n d i t i o n s . The most commonly used methods o f d i a g n o s i s a r e v i s u a l symptoms, p l a n t t i s s u e a n a l y s i s , s o i l a n a l y s i s , p o t c u l t u r e s , b i o a s s a y s , f i e l d t r i a l s , and i n d i c a t o r p l a n t s ( P r i t c h e t t and F i s h e r , 1987) . A l l o f t h e s e methods have i n h e r e n t advantages and d i s a d v a n t a g e s . D e t a i l e d d e s c r i p t i o n s o f t h e s e methods can be found i n P r i t c h e t t and F i s h e r (1987) 46 and B i n k l e y (1986). Methods o f p l a n t t i s s u e and s o i l a n a l y s i s w i l l be d i s c u s s e d f u r t h e r i n the f o l l o w i n g pages . P l a n t T i s s u e A n a l y s i s On c u r r e n t l y f o r e s t e d s i t e s , d i r e c t e x a m i n a t i o n o f t r e e t i s s u e s i s commonly used t o a s s e s s f o r e s t n u t r i t i o n ( B i n k l e y , 1986) . T r a d i t i o n a l l y , s t u d i e s o f f o r e s t t r e e n u t r i t i o n have r e v o l v e d around the c o n c e n t r a t i o n o f d i f f e r e n t n u t r i e n t s i n t h e o r g a n s . However, Weetman and W e l l s (1989) l i s t e d two main problems o f f o l i a r a n a l y s i s o f t r e e s : 1. L a c k o f a c l e a r r e l a t i o n s h i p between s o i l c h e m i c a l a n a l y s i s and f o l i a r a n a l y s i s which may a l s o r e f l e c t problems w i t h s o i l a n a l y s i s ( t h i s w i l l be d i s c u s s e d l a t e r ) . However, more i m p o r t a n t t h a n t h i s may be the l a c k o f a c l e a r r e l a t i o n s h i p between f o l i a r a n a l y s i s and t r e e growth o r v i g o r . 2. The i n a b i l i t y t o a p p l y s e e d l i n g based f o l i a r c o n c e n t r a t i o n s t a n d a r d s t o o l d e r t r e e s . However, o t h e r o p t i o n s w i l l be d i s c u s s e d l a t e r . R e c y c l i n g o f l i t t e r f a l l i n o l d e r s tands t ends t o mask c o n v e n t i o n a l m i n e r a l s o i l - f o l i a r a n a l y s i s - growth r a t e r e l a t i o n s h i p s as seen i n young s tands p r i o r t o canopy c l o s u r e (Weetman and W e l l s , 1989) . However, M i l l e r and M i l l e r (1976) s t a t e d t h a t t h e N c o n c e n t r a t i o n i n n e e d l e f a l l may s e r v e as a good i n d i c a t o r o f N s t a t u s because the t r a n s f e r o f m o b i l e e lements p r i o r t o senescence may make f r e s h l i t t e r a b e t t e r i n d i c a t o r o f n u t r i e n t s t a t u s t h a n c u r r e n t y e a r s f o l i a g e . 47 Because o f a l a c k o f c l e a r r e l a t i o n s h i p between f o l i a r a n a l y s i s and growth response t o f e r t i l i z e r , t w i g s , phloem, xy l em, sap and r o o t m a t e r i a l have a l s o been used w i t h v a r y i n g s u c c e s s as assay t i s s u e s (Weetman and W e l l s , 1989) . O n l y t w i g s approach f o l i a g e i n d i a g n o s t i c v a l u e (Powers, 1984) . Weetman and W e l l s (1989) l i s t e d t h r e e i m p o r t a n t c r i t e r i a f o r sample m a t e r i a l i n p l a n t t i s s u e t e s t s : 1. The t i s s u e chosen must p r o v i d e a c l e a r s e p a r a t i o n o f t r e e s o f d i f f e r e n t n u t r i e n t s t a t u s . 2. The t i s s u e s h o u l d have a r e l a t i v e l y s t a b l e n u t r i e n t c o n c e n t r a t i o n among t r e e s a t a s p e c i f i c t i m e . 3 . Samples must be r e l a t i v e l y easy t o c o l l e c t . The d i f f i c u l t y o f o b t a i n i n g r e p r e s e n t a t i v e samples from n e a r the t o p o f l a r g e t r e e s r e s t r i c t s use o f f o l i a r s a m p l i n g . B e f o r e d i s c u s s i n g s p e c i f i c t e c h n i q u e s i t s h o u l d be ment ioned t h a t n u t r i e n t v a r i a t i o n i n f o l i a g e between y e a r , s eason , t r e e h e i g h t , age, e t c . can c r e a t e huge s a m p l i n g problems t h a t can be overcome somewhat by s t a n d a r d i z a t i o n o f t e c h n i q u e . T u r n e r e t a l . (1978) p r o v i d e d a good r e v i e w o f n u t r i e n t v a r i a t i o n i n f o l i a g e . There a r e f i v e main approaches t o i n t e r p r e t f o l i a r a n a l y s i s d a t a from f o r e s t s t a n d s : 1. C r i t i c a l V a l u e s T h i s i s the o l d e s t approach based on t h e as sumpt ion t h a t compar ing v a l u e s w i t h p r e v i o u s l y p u b l i s h e d " c r i t i c a l l e v e l s " f o r a p a r t i c u l a r t r e e s p e c i e s w i l l r e s u l t i n response 48 t o f e r t i l i z e r a d d i t i o n i f v a l u e s a r e c l o s e t o c r i t i c a l . The c r i t i c a l l e v e l i s the c o n c e n t r a t i o n above which l i t t l e p o s i t i v e growth response can be o b t a i n e d when the s u p p l y o f t h e n u t r i e n t i s i n c r e a s e d ( B a l l a r d and C a r t e r , 1986) o r the c o n c e n t r a t i o n c o r r e s p o n d i n g t o 90 p e r c e n t o f maximum growth when t h a t n u t r i e n t a l o n e i s l i m i t i n g (Powers, 1984) . A n a l y s i s o f f o l i a g e from s tands o f d i f f e r e n t growth r a t e s , o f t e n i n c l u d i n g f e r t i l i z e r t r i a l s , e n a b l e d the f o r e s t department o f many c o u n t r i e s t o e s t a b l i s h c r i t i c a l v a l u e s by t h e e a r l y 1960's ( M i l l e r e t a l . . 1981) . Such c r i t i c a l v a l u e s a r e assumed t o be s t a b l e f o r s p e c i e s and age and t r e e s i z e , b u t t h i s i s u s u a l l y no t the case ( M i l l e r e t a l . , 1981) . T h e r e f o r e , i t i s i m p o r t a n t t h a t c r i t i c a l f o l i a g e l e v e l s be s t a n d a r d i z e d by age o r development s tage o f the t r e e s . C r i t i c a l v a l u e s overcome some problems o f v a r i a t i o n i n u s i n g optimum r a t i o s , l a c k o f p r e c i s i o n i n s u f f i c i e n c y r a n g e s , t h e r e q u i r e m e n t f o r f i e l d t r i a l s , and the absence o f d a t a f o r DRIS, which w i l l be d i s c u s s e d l a t e r . However, d e f i c i e n c y v a l u e s a r e o f t e n v e r y b r o a d and l a c k r e q u i r e d f i e l d v e r i f i c a t i o n (Powers, 1984) . Swan (1967) i n d i c a t e d t h a t t h e r e a r e so many s o i l , g e n e t i c , c l i m a t i c , and o t h e r f a c t o r s i n t r y i n g t o de termine response t o f e r t i l i z e r , t h a t i t i s i n a d v i s a b l e t o t r y t o d e f i n e response ranges too r i g i d l y . A x e l s s o n (1983a) s t a t e d t h a t the main prob lem w i t h c r i t i c a l v a l u e s i s t h a t c o n c e n t r a t i o n cannot be thought o f as an independent v a r i a b l e i n t h e sys tem, b u t o n l y as a dependent one, d e r i v e d from biomass and amounts o f n u t r i e n t s . 49 N u t r i e n t c o n c e n t r a t i o n can be reduced when an e lement i s d i l u t e d by an i n c r e a s e i n f o l i a r mass ( B a l l a r d and C a r t e r , 1986) . T h e r e f o r e , i t might be b e s t t o expres s v a l u e s as c o n c e n t r a t i o n t imes t i s s u e , o r expres s a c t u a l amounts o f n u t r i e n t i n s t e a d o f c o n c e n t r a t i o n (Agren , 1983) . However, t h i s can be p r o b l e m a t i c because i t may be d o m i n a n t l y a r e f l e c t i o n o f growth , i n f l u e n c e d by f a c t o r s o t h e r t h a n n u t r i t i o n . 2. N i t r o g e n Content and P r o d u c t i v i t y N u t r i e n t c o n t e n t can be e x p r e s s e d on a n e e d l e number, l e a f a r e a , o r shoot b a s i s ( B a l l a r d and C a r t e r , 1986) . I t i s argued t h a t the n u t r i e n t f l u x d u r i n g t h e p e r i o d o f f a s t growth i s the key v a r i a b l e f o r u n d e r s t a n d i n g and p r e d i c t i n g f o r e s t p r o d u c t i v i t y (Weetman and W e l l s , 1989) . Because i t i s the amount o f n u t r i e n t i n c o r p o r a t e d i n t o d i f f e r e n t organs t h a t i s c r i t i c a l , not the c o n c e n t r a t i o n , the N p r o d u c t i v i t y concept has been d e v e l o p e d . T h i s concept a l l o w s the growth o f a f o r e s t s t a n d t o be p r e d i c t e d r a t h e r t h a n the growth o f i n d i v i d u a l t r e e s (Agren , 1983; A x e l s s o n , 1983a) . 3. N u t r i e n t R a t i o s Many b i o c h e m i c a l and p h y s i c a l p r o c e s s e s w i t h i n the t r e e a r e o p t i m i z e d not by m a i n t a i n i n g o p t i m a l n u t r i e n t c o n c e n t r a t i o n s , but by m a i n t a i n i n g c e r t a i n n u t r i e n t e lement r a t i o s w i t h i n c r i t i c a l ranges ( B a l l a r d and C a r t e r , 1986) . I n g e s t a d has d e v e l o p e d m i n e r a l n u t r i t i o n r a t i o s r e q u i r e d f o r optimum p r o d u c t i o n f o r a range o f p l a n t s p e c i e s (Weetman and W e l l s , 1989) . Exper iment s have shown t h a t a p p r o x i m a t e l y the same r a t i o s a r e r e q u i r e d by most s p e c i e s and do not v a r y w i t h 50 age . T h i s approach t o t i s s u e a n a l y s i s sugges t s t h a t a t t empts s h o u l d be made t o m a i n t a i n optimum f o l i a r p r o p o r t i o n s by v a r y i n g the N a d d i t i o n r a t e o f b a l a n c e d n u t r i e n t s u p p l i e s t o s e a r c h f o r maximum f e r t i l i z e r r e s p o n s e . 4. The D i a g n o s i s and Recommendation I n t e g r a t e d System (DRIS) Because o f the dynamic n a t u r e o f f o l i a r c o m p o s i t i o n , which i s s t r o n g l y i n f l u e n c e d by a g i n g p r o c e s s e s as w e l l as o t h e r f a c t o r s , f o l i a r d i a g n o s i s can become v e r y complex (Walworth and Sumner, 1987). DRIS was d e v e l o p e d by B e a u f i l s (1973) as an o b j e c t i v e means o f c o p i n g w i t h t h e d i f f i c u l t y i n h e r e n t i n d i a g n o s t i c p r o c e d u r e s (Weetman and W e l l s , 1989) . DRIS p r o v i d e s a means o f o r d e r i n g n u t r i e n t r a t i o s i n t o m e a n i n g f u l e x p r e s s i o n s which a r e c a l l e d DRIS i n d i c e s . These g i v e an i n d i c a t i o n o f the r e l a t i v e s t a t u s o f n u t r i e n t s i n p l a n t m a t e r i a l r e l a t i v e t o o t h e r n u t r i e n t s . One o f the main advantages o f DRIS i s t h a t n u t r i e n t r a t i o s and p r o d u c t s appear t o be r e l a t i v e l y c o n s t a n t w i t h age . Jones (1981), c i t e d i n Weetman and W e l l s (1989), l i s t e d f i v e assumpt ions o f DRIS: 1. R a t i o s o f n u t r i e n t e lement c o n c e n t r a t i o n s a r e o f t e n b e t t e r i n d i c a t o r s o f n u t r i e n t d e f i c i e n c i e s t h a n a r e s i n g l e n u t r i e n t e lement c o n c e n t r a t i o n s . 2. Some n u t r i e n t e lement c o n c e n t r a t i o n r a t i o s a r e more i m p o r t a n t t h a n o t h e r s . 3 . Maximum c r o p y i e l d s a r e a t t a i n a b l e o n l y when v a l u e s o f i m p o r t a n t r a t i o s approach optimum v a l u e s . 51 4. DRIS i n d i c e s can be c a l c u l a t e d f o r each e lement . 5. S i n c e i m p o r t a n t r a t i o s must approach optimum v a l u e s t o o b t a i n h i g h y i e l d s , the v a r i a n c e o f an i m p o r t a n t r a t i o i s s m a l l e r i n a h i g h y i e l d i n g p o p u l a t i o n t h a n i n a low y i e l d i n g p o p u l a t i o n . T h e r e f o r e , t h e r a t i o o f a h i g h y i e l d i n g p o p u l a t i o n v a r i a n c e t o a low y i e l d i n g p o p u l a t i o n v a r i a n c e can be used t o s e l e c t i m p o r t a n t r a t i o s . The f i r s t s t e p i n the i m p l e m e n t a t i o n o f DRIS i s the e s t a b l i s h m e n t o f s t a n d a r d v a l u e s o r norms f o r i m p o r t a n t s p e c i e s (Walworth and Sumner, 1987) . However, a prob lem f o r DRIS i s t h a t when norms a r e d e v e l o p e d f o r v a r i o u s a r e a s , r e g i o n a l d i f f e r e n c e s become a p p a r e n t . The main prob lem w i t h t h i s system i s the absense o f adequate d a t a on n u t r i e n t c o n c e n t r a t i o n r a t i o s i n h i g h y i e l d i n g f o r e s t c r o p s . 5 . G r a p h i c a l F o l i a r D i a g n o s i s Timmer and Stone (1978) d e v e l o p e d a s i m p l e and r a p i d approach f o r i d e n t i f y i n g n u t r i e n t l i m i t a t i o n s under f i e l d c o n d i t i o n s which t a k e s advantage o f t h e d e t e r m i n a t e growth h a b i t o f many c o n i f e r s ( B i n k l e y , 1986) . T h i s g r a p h i c a l t e c h n i q u e has been used t o p l o t the s h i f t s i n e lement need le c o n c e n t r a t i o n , e lement c o n t e n t , and u n i t n e e d l e we ight o f f e r t i l i z e d t r e e s from u n t r e a t e d t r e e s which a r e compared on one graph (Weetman and W e l l s , 1989) . The magnitude and d i r e c t i o n o f s h i f t s have been o f v a l u e i n a s s e s s i n g s t a n d n u t r i e n t s t a t u s and the p r o b a b l e response t o f e r t i l i z a t i o n . T h i s t e c h n i q u e i s a good approach f o r i d e n t i f y i n g 52 which n u t r i e n t ( i f any) l i m i t s growth i n a r e g i o n where l i t t l e p r e v i o u s work has been done. However, because i t s v a l i d i t y i s c o n f i n e d t o f i r s t y e a r response e v a l u a t i o n , i t can be p r o b l e m a t i c where response i s e i t h e r d e l a y e d o r v e r y t r a n s i e n t . S o i l A n a l y s i s Powers (1984) s t a t e d t h a t the p r i n c i p l e o f s o i l N t e s t i n g i s t h a t the f r a c t i o n o f N produced by t h e t e s t i s a measure o f t h a t a v a i l a b l e f o r p l a n t u p t a k e . He i n d i c a t e d t h a t t h e aim o f t e s t i n g i s not t o show the p r e c i s e amount o f N r e l e a s e d i n a s eason , but s i m p l y t o p r o v i d e a u s e f u l index o f a v a i l a b i l i t y . I t s advantage i s t h a t i t can be conducted whether s u i t a b l e v e g e t a t i o n i s p r e s e n t o r n o t . Armson (1973) s t a t e d t h a t a t tempts t o r e l a t e p l a n t growth t o s o i l n u t r i e n t a n a l y s i s have been g e n e r a l l y l e s s p r o d u c t i v e i n terms o f d i a g n o s t i c use t h a n p l a n t t i s s u e a n a l y s i s . Armson s t a t e d t h a t one o f the reasons f o r t h i s i s t h a t any method o f e x t r a c t i n g an element from s o i l i s a r b i t r a r y and i t s a p p l i c a b i l i t y t o t r e e s must be p r e v i o u s l y e s t a b l i s h e d , even though t h i s i s a l s o t r u e f o r t i s s u e a n a l y s i s . S i m i l a r l y , Khanna (1981) s t a t e d t h a t t h e d i f f i c u l t i e s a s s o c i a t e d w i t h s o i l c h e m i c a l a n a l y s i s a r e b o t h t e c h n i c a l ( a s s o c i a t e d w i t h s a m p l i n g , p r e p a r a t i o n , and a n a l y s i s o f s o i l samples) and c o n c e p t u a l ( d e f i n i n g m o b i l i z a b l e forms o f n u t r i e n t s ) . D i a g n o s t i c use o f s o i l a n a l y s i s can be p r o b l e m a t i c 53 because o f s o i l v a r i a b i l i t y and d i s s i m i l a r i t y o f s o i l h o r i z o n s and because o f i n s u f f i c i e n t l y s t r o n g r e l a t i o n s h i p s between measured s o i l v a r i a b l e s and t r e e n u t r i e n t s t a t u s ( B a l l a r d , 1986) . L i k e f e r t i l i z e r p o t t r i a l s , s o i l a n a l y s i s i s e s s e n t i a l l y d i a g n o s t i c and d e r i v e s i t s p r e d i c t i v e a b i l i t y from e m p i r i c a l t e s t i n g ( M o r r i s o n , 1974) . Khanna (1981) s t a t e d t h a t up t o the p r e s e n t t i m e , s o i l a n a l y s i s used f o r d e t e c t i o n and p r e d i c t i o n o f growth responses have been m o s t l y o f a s t a t i c n a t u r e w i t h one a n a l y s i s d u r i n g the r o t a t i o n . Khanna i n d i c a t e d t h a t t h i s approach o v e r l o o k s t h e f a c t t h a t b o t h the r a t e o f t r e e growth and t h e n u t r i e n t r e q u i r e m e n t o f f o r e s t s tands a r e dynamic p r o c e s s e s v a r y i n g w i t h t h e age o f the s t a n d . However, as t r e e demand i n c r e a s e s , t h e volume o f s o i l e x p l o r e d by r o o t s i n c r e a s e s , p o s s i b l y i -r e d u c i n g a p e r c i e v e d d i f f e r e n c e i n n u t r i e n t r e q u i r e m e n t p e r u n i t s o i l . Kimmins (1977) c r i t i c i z e d the use o f c u r r e n t a n a l y t i c a l methods because most o f the a v a i l a b l e n u t r i e n t methods were d e v e l o p e d f o r annua l c r o p s on a g r i c u l t u r a l s o i l and t h e b i o l o g i c a l i n t e r p r e t a t i o n o f the r e s u l t s t h e y g i v e i s sometimes q u e s t i o n a b l e f o r f o r e s t s o i l and t r e e c r o p s . Because t r e e s a r e l o n g - l i v e d , s o l u t i o n s t h a t e x t r a c t the r e a d i l y a v a i l a b l e ( g e n e r a l l y q u i t e s o l u b l e ) n u t r i e n t s a r e o f l e s s v a l u e i n p r e d i c t i n g n u t r i e n t needs o f t r e e s t h a n o f a g r i c u l t u r e c r o p s . A g r i c u l t u r e c r o p s r e q u i r e r e l a t i v e l y h i g h l e v e l s o f a v a i l a b l e n u t r i e n t s i n a more r e s t r i c t e d s o i l vo lume, w h i l e the n u t r i e n t s u p p l y i n g power may be more 5 4 i m p o r t a n t f o r t r e e c r o p s ( P r i t c h e t t and F i s h e r , 1987) . L a b o r a t o r y Indexes N i t r o g e n m i n e r a l i z a t i o n indexes have p r o v e n u s e f u l f o r p r e d i c t i n g b o t h s i t e p r o d u c t i v i t y and f e r t i l i z e r r e s p o n s e . M i n e r a l i z a b l e N i s a measure o f the p o t e n t i a l o f a s o i l t o s u p p l y N t o p l a n t s (Dahnke and Vasey , 1973) . As w i t h any s o i l a n a l y s i s , t h e i n t e r p r e t a t i o n o f N a v a i l a b i l i t y indexes must be based e m p i r i c a l l y on p r e v i o u s l y e s t a b l i s h e d r e l a t i o n s h i p s o f p l a n t uptake from the s o i l o r on p l a n t re sponses t o N f e r t i l i z e r a p p l i c a t i o n ( S t a n f o r d e t a l . . 1973) . U n f o r t u n a t e l y , optimum o r t h r e s h o l d v a l u e s f o r m i n e r a l i z a b l e N have no t been e s t a b l i s h e d f o r d i f f e r e n t s p e c i e s , s i t e t y p e s , o r s t o c k i n g l e v e l s ( B a l l a r d and C a r t e r , 1986) . L a b o r a t o r y i n d i c e s o f N a v a i l a b i l i t y can be broken i n t o c h e m i c a l methods and b i o l o g i c a l methods (Keeney, 1980). C h e m i c a l methods a r e based on the d e t e r m i n a t i o n o f N H 4 - N o r t o t a l N r e l e a s e d on t r e a t m e n t o f a s o i l sample w i t h a c i d i c o r b a s i c s o l u t i o n s o r w i t h d i s t i l l e d water f o r v a r y i n g t imes and t e m p e r a t u r e s . B i o l o g i c a l methods i n v o l v e the d e t e r m i n a t i o n o f i n o r g a n i c N produced on i n c u b a t i o n o f a s o i l sample f o r one t o t h r e e weeks under a e r o b i c o r a n a e r o b i c c o n d i t i o n s (Keeney, 1980) . B i o l o g i c a l Indexes . Keeney (1980) s t a t e d t h a t i n c u b a t i o n methods have , i n g e n e r a l , g i v e n r e s u l t s h i g h l y c o r r e l a t e d t o N uptake by p l a n t s grown i n t h e greenhouse , and e v i d e n c e now seems c o n c l u s i v e t h a t they p r o v i d e a v a l i d 55 measure o f a s o i l ' s a b i l i t y t o r e l e a s e N . A e r o b i c methods c o n s i s t o f i n c u b a t i o n o f a s o i l sample f o r a p e r i o d o f two t o f o u r weeks under n e a r optimum c o n d i t i o n s f o r b a c t e r i a l d e c o m p o s i t i o n o f o r g a n i c m a t t e r and N m i n e r a l i z a t i o n (Dahnke and Vasey , 1973) . I n c u b a t e d samples a r e t h e n t e s t e d f o r ammonium and n i t r a t e . Some i n v e s t i g a t o r s p r e l e a c h t h e s o i l t o remove ammonium and n i t r a t e (Keeney, 1980) . A p r a c t i c a l advantage o f p r e l e a c h i n g i s t h a t a s e p a r a t e e x t r a c t i o n i s no t r e q u i r e d t o de termine m i n e r a l N i n i t i a l l y p r e s e n t i n the u n i n c u b a t e d s o i l . However, i t has been s p e c u l a t e d t h a t p r e l e a c h i n g o f s o i l s w i t h water might remove s i g n i f i c a n t amounts o f r e a d i l y m i n e r a l i z a b l e , water s o l u b l e o r g a n i c N compounds (Macduff and W h i t e , 1985) . The a e r o b i c t e s t o f S t a n f o r d and Smith (1972) and has been proposed as the u l t i m a t e method o f d e f i n i n g t h e m i n e r a l i z a b l e s o i l N p o o l f o r a g r i c u l t u r a l s o i l s . They d e t e r m i n e d t h e N m i n e r a l i z e d over t ime (up t o 30 weeks) and c a l c u l a t e d t h e N m i n e r a l i z a t i o n p o t e n t i a l which i s c h a r a c t e r i s i t c o f the s o i l . T h i s method i s u s e f u l as a r e s e a r c h t o o l f o r examining the l o n g term m i n e r a l i z a t i o n c h a r a c t e r i s t i c s o f s o i l , but i s t oo l a b o r i o u s f o r r o u t i n e use . However, i t s e r v e s as a r e l i a b l e b a s i s f o r d e v e l o p i n g and s e l e c t i n g more r a p i d mehods f o r a s s e s s i n g s o i l N a v a i l a b i l i t y ( S t a n f o r d , 1980) . The a n a e r o b i c i n c u b a t i o n method d e v e l o p e d by Waring and Bremner (1964) i s a t t r a c t i v e because o f i t s s i m p l i c i t y ( S t a n f o r d , 1980) and has s e v e r a l advantages o v e r a e r o b i c 56 i n c u b a t i o n (Keeney, 1980, 1982): 1. O n l y ammonium needs t o be measured. 2. T h e r e a r e no problems w i t h m a i n t a i n i n g o p t i m a l water c o n t e n t . 3. H i g h e r t empera tures can be used t h a n i n a e r o b i c t e s t s s i n c e t h e optimum tempera ture f o r n i t r i f i c a t i o n i s o f no c o n c e r n . 4. More N i s m i n e r a l i z e d i n a g i v e n p e r i o d d u r i n g a n a e r o b i c c o n d i t i o n s , a l l o w i n g f o r a s h o r t e r p e r i o d o f i n c u b a t i o n . Under a n a e r o b i c c o n d i t i o n s more ammonium may accumulate s i n c e m i c r o b i a l growth i s d e p r e s s e d , w i t h o u t n e c e s s a r i l y r e d u c i n g m i n e r a l i z a t i o n ( C a r l y l e , 1986) . B i n k l e y and H a r t (1989) sugges ted t h a t a n a e r o b i c i n c u b a t i o n p r i m a r i l y measures m i c r o b i a l b iomass . However, McNabb e t a l . (1978) found t h a t , due t o l a r g e w i t h i n s i t e v a r i a b i l i t y , a n a e r o b i c i n c u b a t i o n c o u l d no t d i s t i n g u i s h between h a b i t a t t y p e s . S i m i l a r l y , Powers e t a l . (1978) sugges ted t h a t e i t h e r m o d i f y i n g t h e l a b t e m p e r a t u r e t o r e f l e c t f i e l d c o n d i t i o n s , o r c a l i b r a t i n g t h e t e s t t o s p e c i f i c f o r e s t t y p e s , would be n e c e s s a r y t o ge t good c o r r e l a t i o n s w i t h i n s i t u m i n e r a l i z a t i o n . T h i s may be because t h e a n a e r o b i c method i s s e n s i t i v e t o o n l y a few components o f the N c y c l e (see B i n k l e y and H a r t , 1989) . However, Powers (1980) s t a t e d t h a t the c o r r e l a t i o n found between m i n e r a l i z a b l e s o i l N and f o l i a r N shows t h a t the a n a e r o b i c s o i l t e s t may be u s e f u l i n s u p p l e m e n t i n g f o l i a r a n a l y s i s and o f f e r s an a l t e r n a t i v e t o f o l i a r s a m p l i n g i n v e r y t a l l t r e e s . 57 Powers (1984) i n d i c a t e d t h a t a e r o b i c i n c u b a t i o n s a r e f a v o r e d i n a g r i c u l t u r e because they i n c l u d e n i t r a t e p r o d u c t i o n , b u t a n a e r o b i c i n c u b a t i o n s a r e s u i t a b l e f o r f o r e s t r y because n i t r a t e p r o d u c t i o n i s u s u a l l y q u i t e low. Bevege (1980) s t a t e d t h a t i n c u b a t i o n s t u d i e s can p r o v i d e some q u a l i t a t i v e i n d i c a t i o n o f i n s i t u m i n e r a l i z a t i o n i n some s o i l s , but not o t h e r s . He i n d i c a t e d t h a t i n c u b a t i o n s t u d i e s a r e v a l u a b l e f o r comparing t r e a t m e n t and s e a s o n a l e f f e c t s on m i n e r a l i z a b l e N , but a r e l e s s u s e f u l f o r d e t e r m i n i n g m i n e r a l i z a t i o n i n the f i e l d . Keeney (1980) c o n c l u d e d t h a t the a n a e r o b i c i n c u b a t i o n method i s t h e most s a t i s f a c t o r y t o d a t e ; however, the r e s u l t s o f any s h o r t - t e r m i n c u b a t i o n method w i l l be a f f e c t e d by sample p r e t r e a t m e n t and h a n d l i n g (Keeney, 1982) . S i m i l a r l y , Bremner (1965) s t a t e d t h a t the r e s u l t s o b t a i n e d by i n c u b a t i o n methods a r e p o i n t l e s s u n l e s s methods o f s a m p l i n g , d r y i n g , g r i n d i n g , s i e v i n g , s t o r i n g and i n c u b a t i o n a r e r i g o r o u s l y s t a n d a r d i z e d . However, Powers (1980) i n d i c a t e d t h a t combin ing e x t r a c t a b l e NH4 + w i t h t h a t m i n e r a l i z e d d u r i n g i n c u b a t i o n c o u n t e r s the s t o r a g e e f f e c t s . Carbon d i o x i d e p r o d u c t i o n may a l s o be used t o e s t i m a t e a v a i l a b l e N . The p r i n c i p l e o f t h i s p r o c e d u r e i s t h a t the amount o f CO2 produced when a s o i l sample i s i n c u b a t e d w i t h an excess o f e a s i l y decomposable o r g a n i c m a t t e r w i l l be p r o p o r t i o n a l t o the amount o f m i n e r a l N i n i t i a l l y p r e s e n t i n s o i l p l u s the amount made a v a i l a b l e d u r i n g i n c u b a t i o n (Dahnke and V a s e y , 1973) . T h i s i s a c t u a l l y a measure o f g r o s s m i n e r a l i z a t i o n (Heal e t a l . . 1982) . The main advantage o f t h i s 58 p r o c e d u r e i s t h a t t h e r e i s no need t o e x t r a c t the s o i l t o d e t e r m i n e the amount o f a v a i l a b l e N s i n c e i t i s r e l a t e d t o the amount o f CO2 g i v e n o f f d u r i n g i n c u b a t i o n , b u t t h e approach can be p r o b l e m a t i c . C h e m i c a l Indexes . F o r many y e a r s , s o i l s c i e n t i s t s have a t tempted t o d e v e l o p r a p i d c h e m i c a l e x t r a c t i o n methods t h a t would p r o v i d e s u i t a b l e i n d i c e s o f s o i l N a v a i l a b i l i t y . U s u a l l y , t h e g o a l has been t o e x t r a c t a f r a c t i o n o f o r g a n i c N t h a t i s w e l l c o r r e l a t e d w i t h m i n e r a l i z a b l e N . The p o t e n t i a l u s e f u l n e s s o f a p a r t i c u l a r c h e m i c a l index f o r s o i l N a v a i l a b i l i t y i s de termined by i t s r e l i a b i l i t y as a b a s i s f o r p r e d i c t i n g t h e c a p a c i t y o f s o i l s t o m i n e r a l i z e N i n t h e f i e l d ( S t a n f o r d , 1980) . T h e r e f o r e , a c h e m i c a l index i s u s u a l l y not worthy o f f u r t h e r a t t e n t i o n i f r e s u l t s do no t c o r r e l a t e h i g h l y w i t h amounts o f N r e l e a s e d b i o l o g i c a l l y i n c o n t r o l l e d l a b i n c u b a t i o n s . Dahnke and Vasey (1973) l i s t e d t h r e e c h e m i c a l indexes f o r N a v a i l a b i l i t y : 1. T o t a l N i t r o g e n , O r g a n i c M a t t e r , and O r g a n i c C a r b o n . T o t a l N has no t proven t o be a good index o f s i t e p r o d u c t i v i t y o r re sponse t o N a d d i t i o n s ( P r i t c h e t t and F i s h e r , 1987) . T h i s i s because i t r e p r e s e n t s l a r g e q u a n t i t i e s o f N t h a t a r e u n a v a i l a b l e f o r p l a n t growth . However, Powers (1984) i n d i c a t e d t h a t r e c e n t work has c e n t e r e d on t o t a l s o i l N as a s t a b l e measure o f f e r t i l i t y and S t a n f o r d (1980) s t a t e d t h a t t h e t o t a l N c o n t e n t o f s o i l s s h o u l d not be i g n o r e d as a p o s s i b l e means o f d i s t i n g u i s h i n g among s o i l s w i t h r e s p e c t t o N 59 s u p p l y i n g a b i l i t y . Powers i n d i c a t e d t h a t r e s u l t s a r e b e s t when t o t a l N i s e x p r e s s e d as amount p e r u n i t a r e a by s p e c i f i c h o r i z o n s o r by t h e whole p r o f i l e , and a r e g e n e r a l l y p o o r when t o t a l N i s e x p r e s s e d as a s i m p l e c o n c e n t r a t i o n . Keeney (1982) s t a t e d t h a t d e t e r m i n i n g t o t a l s o i l N by K j e l d a h l i s t oo c o s t l y f o r r o u t i n e s o i l t e s t i n g , b u t o r g a n i c m a t t e r c o n t e n t can be r e a d i l y de termined by o x i d a t i o n p r o c e d u r e s . However, because o f the wide range o f C : N r a t i o s t h i s t e c h n i q u e i s not v e r y p r e c i s e . 2. The A l k a l i n e Permanganate T e s t c o n s i s t s o f measur ing t h e amount o f N H 3 l i b e r a t e d when a s o i l sample i s b o i l e d i n a s o l u t i o n c o n t a i n i n g p o t a s s i u m permanganate (KMnG"4) and sodium c a r b o n a t e (Na2CC>3) . 3 . A c i d and A l k a l i n e H y d r o l y s i s . Most o r g a n i c s u b s t a n c e s i n s o i l a r e h i g h l y r e s i s t a n t t o d e c o m p o s i t i o n , but a p o r t i o n i s p r e s e n t i n the p r o t e i n form and may be c o n v e r t e d t o N H 3 by a c i d o r a l k a l i n e h y d r o l y s i s . Few s t u d i e s which use c h e m i c a l e x t r a c t i o n t e c h n i q u e s have been r e p o r t e d f o r f o r e s t systems (Keeney, 1980) . Webster (1978) found t h a t ammonium produced by a u t o c l a v i n g was h i g h l y r e l a t e d t o t o t a l s o i l N but not w e l l c o r r e l a t e d t o m i n e r a l i z a b l e N i n a D o u g l a s - f i r s t a n d . Lea and B a l l a r d (1982) found weak, i n v e r s e c o r r e l a t i o n s between s o i l N r e l e a s e d by a u t o c l a v i n g and s i t e index o f l o b l o l l y p i n e . However, Nommik (1976) found a r e a s o n a b l y good r e l a t i o n s h i p between m i n e r a l i z a b l e N produced by a n a e r o b i c i n c u b a t i o n and the ammomium r e l e a s e d on hot a c i d chromate t r e a t m e n t o f a c i d 60 f o r e s t s o i l s . Bremner (1965) s t a t e d t h a t t h e c h i e f o b j e c t i o n t o the use o f c h e m i c a l methods i s t h a t t h e y a r e c o m p l e t e l y e m p i r i c a l and make no a l l o w a n c e f o r the f a c t t h a t t h e N m i n e r a l i z a t i o n -i m m o b i l i z a t i o n c y c l e i n s o i l i s c o n t r o l l e d by t h e s u p p l y o f energy m a t e r i a l f o r m i c r o b i a l p r o c e s s e s . Tamm and P e t t e r s o n (1969) c o n c l u d e d t h a t i t i s v e r y d i f f i c u l t t o c h a r a c t e r i z e the a v a i l a b i l i t y o f o r g a n i c a l l y bound N by c h e m i c a l means. F i e l d T e c h n i q u e s Because l a b o r a t o r y e s t i m a t e s o f N a v a i l a b i l i t y a r e i n s e n s i t i v e t o s i t e e n v i r o n m e n t a l f a c t o r s t h a t a r e known t o i n f l u e n c e the N s u p p l y i n g power o f s o i l , s e v e r a l i n s i t u t e c h n i q u e s have been t r i e d (Hart and F i r e s t o n e , 1989) . These i n c l u d e t h e f o l l o w i n g : 1. B u r i e d Bags i n v o l v e i n c u b a t i o n o f d i s t u r b e d ( s i eved) s o i l i n p l a s t i c bags b u r i e d i n the f i e l d . T h i s method i s e q u i v a l e n t t o l a b o r a t o r y i n c u b a t i o n , except t h a t t e m p e r a t u r e s a r e v a r y i n g . 2. Bagged U n s i e v e d S o i l Columns i n v o l v e i n c u b a t i o n o f r e l a t i v e l y u n d i s t u r b e d s o i l columns e n c l o s e d i n p l a s t i c bags i n the f i e l d . S o i l columns can be i s o l a t e d w i t h t h i n m e t a l cans o r capped PVC t u b e s . 3 . Ion Exchange R e s i n s (IER) i n v o l v e measurement o f m i n e r a l N c o l l e c t e d by i o n exchange r e s i n s p l a c e d i n f i e l d f o r extended p e r i o d s . 4. C o r e - I E R ( r e s i n cores ) i n v o l v e i n c u b a t i o n o f 61 u n d i s t u r b e d s o i l columns e n c l o s e d i n tubes capped a t b o t h ends by IER bags (DiStephano and G h o l z , 1986; H a r t and F i r e s t o n e , 1989) . 5. C l o s e d - T o p Tube S e q u e n t i a l C o r i n g i n v o l v e s the i n c u b a t i o n o f u n d i s t u r b e d s o i l i n capped P o l y v i n y l C h l o r i d e (PVC) tubes which p r e v e n t uptake and d i r e c t l e a c h i n g o f n u t r i e n t s by r a i n f a l l (see page 73 f o r methodology f o r t h i s method) . 6. B u r i e d , S o i l - F i l l e d Chambers which a r e l i n k e d t o t h e s u r r o u n d i n g s o i l by h i g h - f l o w r a t e c e r a m i c p l a t e s (Powers e t a l . . 1978) . 7. M o d e l l i n g Approach which i n v o l v e s d e t e r m i n i n g the e f f e c t s o f v a r y i n g t emperature and m o i s t u r e on N m i n e r a l i z a t i o n i n d i s t u r b e d s o i l s . A l l o f t h e methods d e s c r i b e d above have one o r more p o t e n t i a l d i f f i c u l t i e s (Raison e t a l . . 1987): 1. Changes i n d u c e d by r o o t s e v e r i n g . 2. S o i l d i s t u r b a n c e ( s i e v i n g ) which can markedly a f f e c t m i n e r a l i z a t i o n r a t e s . S i e v i n g b r e a k s down s o i l a g g r e g a t i o n and reduces the s p a t i a l c o m p a r t m e n t a l i z a t i o n between a c t i v e m i c r o o r g a n i s m s and l a b i l e s u b s t r a t e s ( B i n k l e y and H a r t , 1989) . 3 . N o n - v a r y i n g s o i l m o i s t u r e c o n t e n t s . 4. F o r the m o d e l l i n g approach t o be u s e f u l , t e m p e r a t u r e and m o i s t u r e response s u r f a c e s must be de termined f o r u n d i s t u r b e d s o i l s and account needs t o be t a k e n f o r s e a s o n a l v a r i a t i o n i n m i n e r a l i z a b l e N p o o l s . 62 The b u r i e d bag t e c h n i q u e , o r i g i n a l l y d e v e l o p e d by Eno (1960), has been w i d e l y used and c o n s i s t s o f e n c l o s i n g a s o i l sample i n a gas permeable p o l y e t h y l e n e bag and i n c u b a t i n g i n t h e f i e l d (DiStephano and G h o l z , 1986) . D i s a d v a n t a g e s o f t h e t e c h n i q u e i n c l u d e n o n - v a r y i n g m o i s t u r e c o n t e n t and no p r o v i s i o n f o r normal l e a c h i n g p r o c e s s e s t o o c c u r , n e c e s s i t a t i n g a s h o r t i n c u b a t i o n p e r i o d . However, t h i s method does account f o r the e f f e c t s o f d a i l y and s e a s o n a l t emperature f l u c t u a t i o n s on m i c r o b i a l p r o c e s s e s . N a d e l h o f f e r e t a l . (1984) used the second t e c h n i q u e l i s t e d above which i n v o l v e d the i n c u b a t i o n o f r e l a t i v e l y u n d i s t u r b e d s o i l (unsieved) i n p o l y e t h y l e n e bags i n t h e f i e l d and found t h a t the d i f f e r e n c e i n ammonium exchangeable N between s t a r t and f i n i s h i n s u r r o u n d i n g u n d i s t u r b e d s o i l s was a p p r o x i m a t e l y e q u a l t o the change i n ammonium-N i n i n c u b a t e d s o i l s . T h u s , they s t a t e d t h a t t h e r e was a s t r o n g o v e r a l l c o r r e l a t i o n between net a m m o n i f i c a t i o n measured i n i n c u b a t e d s o i l s and t h e change i n ambient s o i l ammonium o v e r i n c u b a t i o n i n t e r v a l s . However, t h i s c o n c l u s i o n does no t c o n s i d e r the e f f e c t s o f uptake on ambient s o i l ammonium. N a d e l h o f f e r e t a l . (1985) p o i n t e d t o the f o l l o w i n g a d d i t i o n a l e v i d e n c e which sugges t s t h a t t h i s t e c h n i q u e a c c u r a t e l y e s t i m a t e d a c t u a l r a t e s o f m i n e r a l i z a t i o n i n the s u r r o u n d i n g s o i l : 1. L i n e a r c o r r e l a t i o n s were found between net N m i n e r a l i z a t i o n r a t e s and b o t h above-ground p r o d u c t i o n and N a l l o c a t i o n t o l i t t e r . 63 2. Westermann and C r o t h e r s (1980) found t h a t v i r t u a l l y a l l N u p t a k e , as p r e d i c t e d u s i n g ne t N m i n e r a l i z a t i o n c a l c u l a t i o n s , c o u l d be accounted f o r i n h a r v e s t e d above- and be low-ground b iomass . However, Westerman and C r o t h e r s used s i e v e d s o i l . 3 . A b e r e t a l . (1983) found t h a t t o t a l l i t t e r N i n p u t s t o s o i l c l o s e l y matched independent measures o f ne t N m i n e r a l i z a t i o n o u t p u t s from s o i l s . The use o f r e s i n bags b u r i e d i n s o i l i s assumed t o s i m u l a t e p l a n t r o o t s o r n a t u r a l exchange s i t e s by a b s o r b i n g c a t i o n and a n i o n s . The q u a n t i t y o f n u t r i e n t i o n s accumulated i n r e s i n s i s c o n s i d e r e d t o be an i n t e g r a t e d measure i n t h a t s o i l o v e r t h e t ime p e r i o d t e s t e d (Mahendrappa e t a l . . 1986; G i b s o n , 1986) and w i l l be a f f e c t e d by m i n e r a l i z a t i o n , uptake by compet ing microbes and p l a n t s , i o n m o b i l i t y and t r a n s p o r t , and t h e water regime o f the s o i l ( B i n k l e y , 1984) . N i t r a t e m o b i l i t y g e n e r a l l y exceeds t h a t o f ammonium by 3 0 - f o l d , because o f a much h i g h e r c a t i o n exchange c a p a c i t y t h a n a n i o n exchange c a p a c i t y i n s o i l s ( B i n k l e y , 1984) . Because o f t h e importance o f i o n m o b i l i t y and t r a n s p o r t i n r e g u l a t i n g i o n c a p t u r e by r e s i n bags , t h i s would s e v e r e l y b i a s the sample towards n i t r a t e and the method i s u n l i k e l y t o p r o v i d e a good q u a n t i t a t i v e e s t i m a t e o f N m i n e r a l i z a t i o n b u d g e t s . A n o t h e r prob lem w i t h IER bags i s d e t e r m i n i n g the o p t i m a l depth a t which t o p l a c e them (Hart and F i r e s t o n e , 1989) . However, B i n k l e y i n d i c a t e d t h a t r e s i n bags appeared t o r e s p o n d t o s o i l m o r p h o l o g i c a l and microenv ironment c o n d i t i o n s 64 i n t h e f i e l d t h a t c o u l d not a p p l y i n c o n t r o l l e d l a b c o n d i t i o n s . S i m i l a r l y , H a r t and B i n k l e y (1985) found t h a t o n -s i t e IER bags were b e t t e r a b l e t o d i s t i n g u i s h between f e r t i l i z e d and u n f e r t i l i z e d s i t e s 3 .5 y e a r s f o l l o w i n g f e r t i l i z a t i o n t h a n l a b o r a t o r y a n a l y s i s . The c o r e - I E R method r e l i e s on i o n exchange r e s i n s t o t r a p ammonium and n i t r a t e e n t e r i n g and l e a v i n g u n d i s t u r b e d c o r e s , b u t i t a l s o p r o v i d e s a measure o f N a v a i l a b i l i t y t h a t can be e x p r e s s e d on a s o i l mass o r volume b a s i s (DiStephano and G h o l z , 1986; H a r t and F i r e s t o n e , 1989) . An advantage o f the c o r e - I E R method i s t h a t i t m a i n t a i n s an open system t o water f l o w , t h u s a l l o w i n g a f l u c t u a t i n g m o i s t u r e c o n t e n t as w e l l as a l l o w i n g l e a c h i n g l o s s e s t o o c c u r . The major d i s a d v a n t a g e o f t h i s t e c h n i q u e i s t h a t i t i s v e r y l a b o r i n t e n s i v e which may be v e r y i m p o r t a n t on s i t e s where a l o t o f r e p l i c a t i o n i s needed (Hart and F i r e s t o n e , 1989) . Lemee (1967), c i t e d i n B i n k l e y and H a r t (1989), o r i g i n a l l y d e v e l o p e d a t e c h n i q u e f o r i n c u b a t i n g s o i l samples i n aluminum cans t h a t were p e r f o r a t e d on t h e s i d e s , c l o s e d on t o p , and open on the bot tom. Adams and A t t i w i l l (1986) m o d i f i e d t h i s t e c h n i q u e by u s i n g p l a s t i c PVC tubes capped w i t h i n v e r t e d p e t r i d i s h e s . R a i s o n e t a l . (1987, 1989) f u r t h e r m o d i f i e d t h e t e c h n i q u e by u s i n g open c o r e s and c a l c u l a t i n g l e a c h i n g l o s s e s as t h e d i f f e r e n c e between open and c l o s e d c o r e s . An advantage o f the b u r i e d bag , bagged c o r e , c o r e - I E R , and capped PVC tube s e q u e n t i a l c o r i n g t e c h n i q u e s i s t h a t they 65 e s t i m a t e r e l a t i v e n i t r i f i c a t i o n (the p r o p o r t i o n o f m i n e r a l N t h a t i s n i t r a t e a t the end o f an i n c u b a t i o n p e r i o d ) ( R o b e r t s o n , 1982) . R e l a t i v e n i t r i f i c a t i o n p r o v i d e s an independant means o f e v a l u a t i n g t h e g e n e r a l importance o f f a c t o r s thought t o r e g u l a t e n i t r i f i c a t i o n i n the f i e l d . D e s p i t e t h e a v a i l a b i l i t y o f t h e s e t e c h n i q u e s , R a i s o n e t a l . (1987) s t a t e d t h a t i t has been i m p o s s i b l e t o a s s e s s the r e l i a b i l i t y o f r e s u l t s from t h e s e methods because o f the unknown e f f e c t o f a s say c o n d i t i o n s on r a t e s o f m i n e r a l i z a t i o n i n d i f f e r e n t s o i l s . There i s no s t a n d a r d method which i s known t o measure m i n e r a l i z a t i o n r a t e s a c c u r a t e l y under f i e l d c o n d i t i o n s s i n c e a l l methods r e l y on measur ing the a c c u m u l a t i o n o f m i n e r a l N i n the absense o f a c t i v e r o o t s which r e s u l t s i n some a l t e r a t i o n t o the p h y s i c a l s t r u c t u r e . S i m i l a r l y , W i l l i a m s (1983) s t a t e d t h a t i n s i t u measurements o f N m i n e r a l i z a t i o n a r e confounded by t h e s i m u l t a n e o u s p r o c e s s e s o f u p t a k e , a s s i m i l a t i o n by m i c r o o r g a n i s m s and l e a c h i n g , and d e a t h and decay o f r o o t s . The o b j e c t i v e then must be t o f i n d methods which m i n i m i z e these e f f e c t s (Ra i son et__al. , 1987) . 66 CHAPTER 3 MATERIALS AND METHODS SITE DESCRIPTION The s tudy s i t e i s s i t u a t e d i n Southern I n t e r i o r B r i t i s h Co lumbia a t 4 9 ° N o r t h l a t i t u d e and 1 1 9 ° West l o n g i t u d e . S p e c i f i c a l l y , i t i s i n the Okanagan H i g h l a n d s , 26 km e a s t o f Okanagan F a l l s on Weyerhaeuser Canada L t d . F i s h Lake Road (R250). The s i t e i s p a r t o f the S o l c o Creek watershed , bounded on the southwest by B o u l d e r Creek and on t h e n o r t h e a s t by F i s h C r e e k , i n t r e e Farm L i c e n s e # 15 ( F i g u r e 3 ) . The s i t e i s i n the d r y Montane Spruce (MSbl) b i o g e o c l i m a t i c subzone (Phase I a - Thompson P l a t e a u ) ( M i t c h e l l and G r e e n , 1981) . I t l i e s on the mid t o upper p o r t i o n o f a concave s l o p e a t an e l e v a t i o n o f 1520 m. I t c o n s i s t s o f a hummocky t e r r a c e o f g l a c i o f l u v i a l o r i g i n w i t h a s l i g h t l y mounded m i c r o topography (mounds l e s s t h a n one meter i n h e i g h t ) . The p a r e n t m a t e r i a l i s m o d e r a t e l y s t o n y , u n s o r t e d sandy g r a v e l , p r e d o m i n a n t l y o f g r a n i t e s , q u a r t z i t e s , and g r a n o d i o r i t e (Weetman and F o u r n i e r , 1982) . The s i t e i s z o n a l w i t h r e s p e c t t o c l i m a t e , s l o p e g r a d i e n t and p o s i t i o n , but i s a z o n a l w i t h r e s p e c t t o s o i l due t o t h e s h a l l o w r o o t i n g zone (see P o j a r e t a l . , 1986 f o r c h a r a c t e r i s t i c s o f z o n a l e c o s y s t e m s ) . 67 Temperature and r a i n f a l l were m o n i t e r e d a t a l o c a l f i r e weather s t a t i o n ( se t up by Weyerhaeuser) 6 km e a s t o f the s t u d y s i t e a t an e l e v a t i o n o f 1700 m. The s t a t i o n i n d i c a t e d a d e c l i n e i n r a i n f a l l throughout the growing season and a peak o f average d a i l y noon t emperature i n August (Tab le 1 ) . There i s g e n e r a l l y l i t t l e r a i n i n J u l y and August and t h e s o i l t emperature c l a s s i s c o l d w i t h an average o f 140-220 growing days above 5 ° C (Weetman and F o u r n i e r , 1982) . The r e l a t i v e b i o g e o c l i m a t i c s o i l m o i s t u r e regime i s x e r i c t o s u b x e r i c ( M i t c h e l l and G r e e n , 1981) and t h e s o i l m o i s t u r e s u b c l a s s i s s e m i a r i d (see A g r i c u l t u r e Canada, 1987) . The water d e f i c i t f o r t h e growing season i s a p p r o x i m a t e l y 130 mm and l a s t s seven t o e i g h t weeks ( H a s k i n , 1985) . The c l i m a t i c m o i s t u r e index i s a p p r o x i m a t e l y 40. The a c t u a l s o i l n u t r i e n t regime i s medium t o poor (net m i n e r a l i z a b l e N i s 33 kg p e r h e c t a r e - see T a b l e 9 ) . T a b l e 1. T o t a l p r e c i p i t a t i o n and average d a i l y noon t emperature f o r each o f the s o i l exposure p e r i o d s . PERIOD PRECIPITATION (mm) AVERAGE DAILY NOON TEMP. ° C May 20 - June 20 62.3 10.9 June 21 - J u l y 20 35.7 13.6 J u l y 21 - Aug . 18 26 .1 17.5 A u g . 18 - S e p t . 25 15.3 15.2 The s o i l i s an O r t h i c D y s t r i c B r u n i s o l (see A g r i c u l t u r e Canada, 1987) w i t h a r a p i d l y d r a i n e d sandy t o c o a r s e loamy t e x t u r e and an e f f e c t i v e r o o t i n g depth o f 20 t o 30 cm ( F i g u r e 4 ) . 68 The s o i l has a pH o f 4.67 i n 0.01 M C a C l 2 / c o a r s e f r a c t i o n c o n t e n t o f 18 p e r c e n t , an o r g a n i c m a t e r i a l c o n t e n t o f 7 .1 p e r c e n t , and a m i n e r a l s o i l b u l k d e n s i t y o f 1.19 g / c m 3 ( H a s k i n , 1985) . The f o r e s t f l o o r i s a hemimor (see K l i n k a e t a l . , 1981) w i t h an average t h i c k n e s s o f 1.2 cm and a b u l k d e n s i t y o f 0.355 g / c m 3 ( H a s k i n , 1985) . The s t a n d a d j a c e n t t o the exper iment a r e a ( a c r o s s s lope) i s a mature l o d g e p o l e p i n e s t a n d (85 t o 100 y e a r s o ld ) w i t h l e s s t h a n 50 p e r c e n t crown c l o s u r e . Common ground v e g e t a t i o n noted i n t h i s s t a n d were K i n n i k i n n i k ( A r c t o s t a p h y l o s u v a - u r s i L . S p r e n g . ) , p i n e g r a s s ( C a l a m a g r o s t i s rubescens B u c k . ) , common j u n i p e r ( J u n i p e r u s communis L . ) , g l a n d u l a r - l e a v e d L a b r a d o r t e a (Ledum  g landu losum N u t t . ) , A r c t i c l u p i n e (Lupinus a r c t i c u s S. W a t t s . ) , and g r o u s e b e r r y (Vacc in ium scopar ium L e i b e r g . ) . See Angrove and B a n c r o f t (1983) f o r s p e c i e s d e s c r i p t i o n s . P r i o r t o 1971, t h e e x p e r i m e n t a l a r e a was c o v e r e d w i t h a dense mature l o d g e p o l e p i n e s t a n d , 11 t o 20 m i n h e i g h t . I t was l o g g e d t r e e l e n g t h i n 1971, w i t h any s l a s h s u b s e q u e n t l y windrowed and burned t o ge t r i d o f dwarf m i s t l e t o e (Arceuthobum americanum) which i s common i n the a r e a and had i n f e s t e d t h e s t a n d . F o l l o w i n g t h e s e t r e a t m e n t s , the s t a n d was l e f t t o r e g e n e r a t e n a t u r a l l y , f i l l i n g i n from 1974 t o the p r e s e n t t i m e . In 1979, a survey i n d i c a t e d t h a t 67 p e r c e n t o f the a r e a was s u f f i c i e n t l y r e s t o c k e d , and i n t h e f a l l o f 1980, t h e s t a n d was p r e c o m m e r c i a l l y t h i n n e d from 5900 t o 1100 stems p e r h e c t a r e (3 m s p a c i n g ) . In 1981, need le e x a m i n a t i o n r e v e a l e d t h a t 80 p e r c e n t o f F i g u r e 4. S o i l p r o f i l e o f s t u d y s i t e f r o m r o a d c u t , showi t y p i c a l d e p t h of r o o t p e n e t r a t i o n . the t r e e s were m i l d l y c h l o r o t i c . In 1982, t h r e e p e r c e n t o f the t r e e s had s u f f e r r e d p i n e w e e v i l (Rhyacconia s p . ) damage (Weetman and F o u r n i e r , 1982) . These d i s t u r b a n c e s have l e a d t o changes i n the ground v e g e t a t i o n , c h a r a c t e r i s t i c o f a more s e r a i s tage o f development . P i n e g r a s s i s now the dominant ground v e g e t a t i o n s p e c i e s on the s i t e . O t h e r common s p e c i e s p r e s e n t which a r e a l s o found i n the a d j a c e n t mature s t a n d i n c l u d e common j u n i p e r , K i n n i k i n n i k , A r c t i c l u p i n e , and g r o u s e b e r r y . S p e c i e s noted which were not found i n a d j a c e n t s t a n d i n c l u d e s p r e a d i n g dogbane (Apocynum  a n d r o s a e m i f o l i u m L . ) , s o a p b e r r y (Shepherd ia c a n a d e n s i s ( L . ) N u t t . ) , v e l v e t - l e a v e d b l u e b e r r y (Vacc in ium m y r t i l l o i d e s M i c h x . ) , * f i r e w e e d ( E p i l o b i u m a n c r u s t i f o l i u m L . ) , t w i n f l o w e r ( L i n n a e a  b o r e a l i s L . ) , and Saskatoon b e r r y (Amelanch ier a l n i f o l i a ( N u t t . ) N u t t . ) . "OPTIMUM" NUTRITION EXPERIMENT In t h e s p r i n g o f 1982, f o u r l e v e l s o f n i t r o g e n (N) a p p l i c a t i o n s w i t h o r w i t h o u t a p p l i c a t i o n s o f o t h e r n u t r i e n t s were randomly a s s i g n e d t o e i g h t p l o t s i n each o f t h r e e b l o c k s (Table 2 ) . The a d d i t i o n o f o t h e r m a c r o n u t r i e n t s and m i c r o n u t r i e n t s has been l a b e l l e d as "PK". The r e s u l t i s a 2X4 f a c t o r i a l exper iment e s t a b l i s h e d i n a randomized complete b l o c k d e s i g n ( F i g u r e 5 ) . F e r t i l i z e r has been a p p l i e d i n May o r e a r l y June i n 1982, 1983, 1985, and 1988 (Table 3 ) . N i t r o g e n has been a p p l i e d as ammonium n i t r a t e ; "PK" has been a p p l i e d i n a s p e c i a l f o r m u l a o f 71 t r i p l e superphosphate and m u r i a t e p o t a s h . Treatments w i l l c o n t i n u e u n t i l 1991 which s h o u l d p r o v i d e s u f f i c i e n t t ime t o s t a b i l i z e N c o n c e n t r a t i o n s i n the f o l i a g e and e s t a b l i s h r e l i a b l e growth t r e n d s f o r s p e c i f i c f o l i a r c o n c e n t r a t i o n s (Tamm, 1968; Tamm and A r o n s s o n , 1982; Weetman and F o u r n i e r , 1984; and o t h e r s ) . The f e r t i l i z e d p l o t s a r e c i r c u l a r w i t h an o u t e r g r o s s a r e a o f .087 ha and i n n e r ne t a r e a o f .05 h a . Each i n n e r p l o t c o n t a i n s 50 t o 70 t r e e s . F o l i a g e has been c o l l e c t e d each f a l l ; c u r r e n t y e a r shoot s a r e c l i p p e d from t e n t r e e s p e r p l o t and combined t o produce p e r p l o t samples . Three and f i v e - y e a r growth measurements have been completed t o date and r e p o r t e d on by Webber (1985) and E s t l i n (1988). T a b l e 2. E i g h t f e r t i l i z e r t r e a t m e n t s as a 2X4 f a c t o r i a l d e s i g n and N and "PK" s p e c i f i c a t i o n s . The n u t r i e n t s a r e added a n n u a l l y depending on f o l i a r N c o n c e n t r a t i o n . NITROGEN # REPLICATIONS D e s i r e d F o l i a r N regime kg N / h a N C o n c e n t r a t i o n s +PK - P K NO 0 _ 3 3 N l 50 1.2% 3 3 N2 100 1.6% 3 3 N3 150 2.0% 3 3 NUTRIENTS ADDED IN "PK" TREATMENT (KG/HA) Macro M i c r o K CA MG P S FE MN ZN BO CU MO 91 56 48 38 31 1.8 0.75 0.7 0.3 0.3 0.2 7 2 5. P l o t l a y o u t and e x p e r i m e n t a l d e s i g n o f l o d g e p o l e p i optimum n u t r i t i o n e x p e r i m e n t . 73 MEASUREMENT OF NITROGEN MINERALIZATION Methodology f o r In S i t u Measurements The ne t m i n e r a l i z a t i o n (or i m m o b i l i z a t i o n ) o f N i n s o i l s has been c a l c u l a t e d from the measured changes i n m i n e r a l - N c o n t e n t o f l a r g e l y u n d i s t u r b e d s o i l i s o l a t e d i n s i d e tubes i n s i t u (Ra i son e t a l . , 1987) . The tubes p r e v e n t e d t h e uptake o f m i n e r a l -N by r o o t s , and s o i l columns were e i t h e r c o v e r e d t o p r e v e n t l e a c h i n g , o r l e f t open and s u b j e c t e d t o a more v a r y i n g m o i s t u r e T a b l e 3. Amount and t i m i n g o f f e r t i l i z e r m a c r o n u t r i e n t s a p p l i e d i n exper iment from 1982 t o 1988. FERTILIZER NUTRIENT APPLICATION (KG/HA) ACCUMULATED APPLICATION (KG/HA) TREATMENT 1982 1983 1984 1985 1986 1987 1988 N Regime NO N l 50 50 — 25 — — 50 175 N2 100 100 — 50 — — 100 350 N3 150 150 — 75 — — 150 525 "+PK" P 38 38 — 19 — — 38 135 K 91 91 — 45.5 — — 91 318.5 Ca 56 56 — 28 — — 56 196 Mg 48 48 — 24 — — 48 168 S 31 31 — — 15.5 — ""* 31 108.5 r e g i m e . Net m i n e r a l i z a t i o n (or i m m o b i l i z a t i o n ) was c a l c u l a t e d as t h e sum o f changes i n N H 4 - N (net ammoni f i ca t ion ) and N O 3 - N (net n i t r i f i c a t i o n ) . A l l v a l u e s r e p r e s e n t means based on i n t e n s i v e s p a t i a l s a m p l i n g and have been e x p r e s s e d b o t h as a c o n c e n t r a t i o n (mg N / k g s o i l ) and on an a r e a b a s i s (kg N / h a s o i l l a y e r ) . Net N m i n e r a l i z a t i o n = N e ( t + i ) c - N ^ t ) N uptake = N e ( t + i ) c " N b( t+1) - ( l o s s e s ) 74 Maximum L e a c h i n g ( l o s se s ) = N e ( t + i ) c _ N e ( t + l ) o where N e ( t + i ) C = m i n e r a l N c o n t e n t i n exposed , c o v e r e d c o r e a t end o f p e r i o d N b ( t ) = m i n e r a l N c o n t e n t o f b u l k , u n c o n f i n e d s o i l a t b e g i n n i n g o f exposure p e r i o d N b( t+1) = m i n e r a l N c o n t e n t o f b u l k , u n c o n f i n e d s o i l a t end o f exposure p e r i o d . N e ( t + l ) o = m i n e r a l N c o n t e n t o f exposed , open c o r e s a t end o f p e r i o d N m i n e r a l i z a t i o n , uptake and l o s s were c a l c u l a t e d f o r f o u r p e r i o d s from May t o September as shown and f l u x e s summed t o produce a t o t a l f o r the growing season . Because a p a i r e d d i f f e r e n c e t e s t r e v e a l e d no s i g n i f i c a n t d i f f e r e n c e between open and c o v e r e d c o r e m i n e r a l - N c o n c e n t r a t i o n s , l o s s e s were no t i n c l u d e d i n the c a l c u l a t i o n o f u p t a k e . F i e l d Methods Due t o t ime and c o s t c o n s t r a i n t s , the s t u d y o f N f l u x e s has been done o n l y on s i x t r e a t m e n t s ; the N2 t r e a t m e n t s were e x c l u d e d . I n a d d i t i o n , p l o t 13 (see F i g u r e 5) was dropped from t h e s a m p l i n g i n June due t o s u r f a c e s t o n i n e s s which made i t v e r y 75 d i f f i c u l t t o i n s e r t the PVC tubes i n t o the s o i l t o the d e s i r e d d e p t h . Ten groups o f 20 cm l e n g t h PVC tubes were d i s t r i b u t e d randomly i n each i n n e r p l o t . Each group i n c l u d e d one b u l k , one c o v e r e d , and one open t u b e . A r e a s d i s t u r b e d by ground s q u i r r e l s were a v o i d e d . Cores were c o v e r e d w i t h two l a y e r s o f p a r a f f i n . The samples were b u l k e d two i n t o one f o r the months o f J u n e , J u l y , A u g u s t , and September t o reduce the number o f l a b a n a l y s e s . A 15-20 cm depth was chosen because i t has been shown i n o t h e r s t u d i e s t h a t maximum m i n e r a l i z a t i o n r a t e s g e n e r a l l y o c c u r i n t h e s u r f a c e h o r i z o n s (Powers, 1980, 1984; R a i s o n e t a l . . 1987; and o t h e r s ) , the e f f e c t i v e r o o t i n g depth i s q u i t e s h a l l o w on the s t u d y s i t e (see F i g u r e 4 ) , and o t h e r s t u d i e s have found m i n e r a l i z a b l e N produced a t s i m i l a r depths t o be h i g h l y c o r r e l a t e d t o t r e e growth (eg. Shumway and A t k i n s o n , 1977) . T h i s depth s h o u l d a l s o p r o v i d e a good average v a l u e t o d i s t i n g u i s h between t r e a t m e n t s . C o r e s were pounded d i r e c t l y i n t o the s o i l w i t h a f o u r pound hammer. S o i l columns were e x t r a c t e d from the s o i l i n t h e PVC tubes w i t h the a i d o f a s l i v e r o f broken tube p l a c e d i n s i d e t h e c o r e t o h o l d the s o i l i n p l a c e u n t i l i t c o u l d be bagged. Samples were c o l l e c t e d a p p r o x i m a t e l y e v e r y 30 days from May t o September, w i t h t h e e x c e p t i o n o f the September sample which was c o l l e c t e d a f t e r 38 days o f i n c u b a t i o n (see T a b l e 1 ) . Sampl ing p e r i o d was m a i n t a i n e d a t a p p r o x i m a t e l y 30 days f o r two main r e a s o n s : l . T o a l l o w s i g n i f i c a n t a c c u m u l a t i o n o f NH4 + but a t t h e same t ime a v o i d a l a r g e a c c u m u l a t i o n o f NH4 + which c o u l d o x i d i z e t o produce more NG"3~ t h a n under normal c o n d i t i o n s : 2. Not 76 l o n g enough t o a l l o w s e v e r e d r o o t d e c o m p o s i t i o n t o a f f e c t m i n e r a l i z a t i o n r a t e s . An a p p r o p r i a t e p e r i o d c o u l d o n l y be guessed a t because t h e r e were no p r e v i o u s r e s u l t s upon which t o base the t ime p e r i o d s . As w e l l , i t was expec ted t h a t the d i f f e r e n t t r e a t m e n t s would accumulate ammonium and n i t r a t e a t d i f f e r e n t r a t e s , t h e r e b y l i k e l y making d i f f e r e n t exposure p e r i o d s a p p r o p r i a t e f o r each t r e a t m e n t . Deep s o i l columns were c o l l e c t e d i n June t o e s t i m a t e the amount o f a v a i l a b l e m i n e r a l - N a t a g r e a t e r d e p t h . These b u l k samples were s e p a r a t e d i n t o two s e c t i o n s (0-15 cm and 15-25 cm) f o r d e t e r m i n a t i o n o f exchangeable NH4 - N and NO3 - N . E x t r a s o i l columns were c o l l e c t e d i n September t o e s t i m a t e b u l k d e n s i t y f o r each column t o an approx imate 15 cm d e p t h ; b o t h f o r e s t f l o o r and m i n e r a l s o i l were measured t o g e t h e r as i n i n c u b a t e d s o i l s . The volume o f s o i l columns i n s i d e c o r e s was d e t e r m i n e d and the e n t i r e s o i l column was o v e n - d r i e d and weighed t o e s t i m a t e b u l k d e n s i t y f o r the s i t e . Based on the 15 cm d e p t h , the c o n v e r s i o n f a c t o r from mg N-kg s o i l - 1 t o k g - h a - 1 was c a l c u l a t e d as 0.996 so t h e two v a l u e s a r e e s s e n t i a l l y the same. In J u l y , A u g u s t , and September, f o l i a g e samples were c o l l e c t e d from t e n t r e e s p e r p l o t and b u l k e d t o produce p e r p l o t samples . C u r r e n t y e a r s shoots were c o l l e c t e d i n t h e upper two-t h i r d s o f the crowns w i t h p o l e p r u n e r s . The n e e d l e s were s t r i p p e d from the shoot s d u r i n g the same day they were c o l l e c t e d t o a v o i d any n u t r i e n t l o s s e s due t o t r a n s l o c a t i o n . In J u l y and A u g u s t , f o l i a g e was c o l l e c t e d o n l y from those p l o t s from which s o i l samples had been c o l l e c t e d . In September, f o l i a g e was c o l l e c t e d from a l l 24 p l o t s . 77 L a b o r a t o r y Methods S o i l columns were s i e v e d through a 4 mm s i e v e and s t o r e d a t 4 ° C p r i o r t o d o i n g KCL e x t r a c t i o n s . They were t h e n p r e p a r e d f o r a n a l y s i s u s i n g t h e e q u i l i b r i u m method (Keeney and N e l s o n , 1982) . To de termine exchangeable ammonium-N and n i t r a t e - N one hundred ml o f 2M KC1 was added t o t e n grams o f s i e v e d s o i l i n widemouth p l a s t i c b o t t l e s . The samples were t h e n shaken on a m e c h a n i c a l s h a k e r f o r a minimum o f one h o u r . Next , the s o l u t i o n s were f i l t e r e d i n t o 40 ml c o n t a i n e r s and s t o r e d a t 4 ° C u n t i l c o l o r i m e t r i c a n a l y s i s w i t h a T e c h n i c o n A u t o a n a l y s e r . S o i l wetness (percent d r y mat ter ) was d e t e r m i n e d f o r each sample by d r y i n g a s m a l l sample f o r 24 hours a t 105 ° C and c a l c u l a t i n g weight l o s s ( R a w l i n s , 1976) . Twelve a b n o r m a l l y h i g h v a l u e s o b t a i n e d from t h e auto a n a l y s e r were d e l e t e d from the a n a l y s i s . T h i s amounted t o l e s s t h a n h a l f o f one p e r c e n t o f the t o t a l number o f samples a n a l y s e d . To de termine the g r o s s and net p o t e n t i a l m i n e r a l i z a b l e N o f each t r e a t m e n t , b u l k June samples were a n a e r o b i c a l l y i n c u b a t e d f o r 7 days a t 40 ° C (Waring and Bremner, 1964) . Keeney (1980) i n d i c a t e d t h a t t h i s method o f f e r s the g r e a t e s t promise o f the b i o l o g i c a l methods because i t i s s i m p l e and q u i c k . Net p o t e n t i a l m i n e r a l i z a b l e N was t a k e n as t h e d i f f e r e n c e between i n c u b a t e d m i n e r a l - N and i n i t i a l m i n e r a l - N c o n c e n t r a t i o n s . G r o s s p o t e n t i a l m i n e r a l i z a b l e N was t a k e n as the i n c u b a t e d m i n e r a l - N c o n c e n t r a t i o n (Powers, 1980) . 78 F i v e grams o f s i e v e d , a i r - d r i e d s o i l were p l a c e d i n 20 x 125 mm b o r o s i l i c a t e g l a s s tubes w i t h 25 ml d i s t i l l e d water . Sample water volumes were chosen (by t r i a l and e r r o r ) such t h a t water v i r t u a l l y f i l l e d t h e tubes a f t e r sample a b s o r p t i o n , but a l l o w e d c o n s t a n t water volumes t o be used f o r a l l samples . Each tube was t i g h t l y s e a l e d by a c o m b i n a t i o n o f T e f l o n t h r e a d tape and p h e n o l i c screw c a p . Samples were t h e n p l a c e d i n a P r e c i s i o n S c i e n t i f i c T h e l c o Model 4 g r a v i t y c o n v e c t i o n i n c u b a t o r ; i n c u b a t i o n was i n i t i a t e d immedia te ly a f t e r t h e samples were p r e p a r e d . Temperature was m o n i t e r e d u s i n g a m e r c u r y - i n - g l a s s thermometer and was checked d a i l y . F o l l o w i n g i n c u b a t i o n , c o n t e n t s were poured i n t o w i d e -mouthed p l a s t i c b o t t l e s . S e v e n t y - f i v e ml o f 2.66 M KC1 was t h e n added, and f o l l o w e d by one hour o f m e c h a n i c a l s h a k i n g . Then , the samples were f i l t e r e d t h r o u g h Whatman No. 41 f i l t e r paper and s t o r e d a t 4 ° C u n t i l a n a l y s i s . FOLIAR ANALYSIS, BIOMASS AND NITROGEN UPTAKE CALCULATIONS F i v e hundred f a s c i c l e s o f f o l i a g e f o r each p l o t were d r i e d a t 7 0 ° C f o r 24 hours and weighed b e f o r e s e n d i n g t o t h e l a b f o r a n a l y s i s . In J u l y and A u g u s t , o n l y N c o n c e n t r a t i o n was d e t e r m i n e d . A complete n u t r i e n t a n a l y s i s was per formed f o r September samples . T r e e biomass was c a l c u l a t e d from h e i g h t and b r e a s t h e i g h t d i a m e t e r measurements made i n 1981 ( p r i o r t o i n i t i a l f e r t i l i z a t i o n ) , 1984, and 1986, based on g e n e r a l biomass formulas d e v e l o p e d by S t a n d i s h e t a l . (1985) o f the form: v = a + b d 2 h where v = k g / h a d r y weight d = d i a m e t e r a t b r e a s t h e i g h t h = t o t a l h e i g h t a and b v a r y , depending on component b e i n g e s t i m a t e d I n d i v i d u a l t r e e e s t i m a t e s were summmed t o ge t p e r p l o t e s t i m a t e s o f b iomass . S i n c e d a t a was not a v a i l a b l e f o r l o d g e p o l e p i n e , c o n c e n t r a t i o n o f N i n above-ground j a c k p i n e components p r e s e n t e d by M o r r i s o n (1973) were used t o e s t i m a t e t h e N c o n t e n t i n above -ground b iomass . The N c o n c e n t r a t i o n s o f each o f t h e components were m u l t i p l i e d by an adjustment f a c t o r f o r each t r e a t m e n t based on 1988 September f o l i a r N c o n c e n t r a t i o n s ( f a c t o r = t r e a t m e n t f o l i a r c o n c e n t r a t i o n / c o n t r o l f o l i a r c o n c e n t r a t i o n ) (Tamm, 1960; M i l l e r e t a l . . 1981; Johnson and T o d d , 1988) . These f o r m u l a s p r o v i d e an e s t i m a t e o f the d r y weight o f wood, b a r k , b r a n c h e s , and f o l i a g e , but they a r e u n l i k e l y t o y i e l d a c c u r a t e r e s u l t s f o r a s i t e - s p e c i f i c s tudy such as t h i s one. As w e l l , t h e s m a l l t r e e s i z e i n t h i s s t u d y put them on the lower end o f t h e range o f t h e biomass e q u a t i o n s . The e s t i m a t e s a l s o do not c o n s i d e r be low-ground biomass o r the uptake o f ground v e g e t a t i o n . T h e r e f o r e , t h e r e l i a b i l i t y o f t h e s e e s t i m a t e s can be q u e s t i o n e d and t h e y have o n l y s e r v e d as an index f o r compar i son p u r p o s e s . STATISTICAL ANALYSIS A n a l y s i s o f v a r i a n c e was used t o de termine i f t h e r e were any s i g n i f i c a n t d i f f e r e n c e s between t r e a t m e n t s f o r the f o l l o w i n g 80 p a r a m e t e r s : 1. T o t a l growing season m i n e r a l i z a t i o n , m i n e r a l - N u p t a k e 1 and l o s s e s . M o d e l : F l u x = C o n s t a n t + B l o c k + N + PK + N•PK 2. M o n t h l y m i n e r a l i z a t i o n , m i n e r a l - N u p t a k e 1 , l o s s e s and exchangeable N c o n c e n t r a t i o n . M o d e l : F l u x = C o n s t a n t + B l o c k + N + PK + P e r i o d + N'PK + N * P e r i o d + N - P K * P e r i o d 3. S o i l wetness . Model s i m i l a r t o #2. 4. F o l i a g e N c o n c e n t r a t i o n , N c o n t e n t p e r u n i t n e e d l e and n e e d l e w e i g h t . Model s i m i l a r t o #1. In a l l cases the ANOVAs were checked ( v i s u a l l y ) t o ensure n o r m a l i t y and homogeneity o f v a r i a n c e s . In cases where t h e s e assumpt ions were v i o l a t e d a p p r o p r i a t e t r a n s f o r m a t i o n s were done and t h e assumpt ions r e c h e c k e d . A n a l y s i s o f c o v a r i a n c e was used t o t e s t f o r d i f f e r e n c e s between t r e a t m e n t s f o r biomass uptake e s t i m a t e s w i t h the i n i t i a l 1981 biomass as the c o v a r i a t e . M o d e l : N uptake = C o n s t a n t + B l o c k + B + N + PK + B-N + B-PK + N'PK + B ' N - P K where B = i n i t i a l biomass i n 1981 I f i n t e r a c t i o n terms were found t o be s i g n i f i c a n t , t h e f a c t o r s c o u l d not be a n a l y s e d s e p a r a t e l y . I f s i g n i f i c a n t d i f f e r e n c e s were f o u n d , d i f f e r e n c e s between i n d i v i d u a l t r e a t m e n t s were s e p a r a t e d by u s i n g c o n t r a s t s . Pearson c o r r e l a t i o n c o e f f i c i e n t s were c a l c u l a t e d t o compare t h e v a r i o u s p a r a m e n t e r s . A l l s t a t i s i c a l a n a l y s i s were c a r r i e d out u s i n g SYSTAT ( W i l k i n s o n , 1988). R e g a r d l e s s o f s t a t i s t i c a l s i g n i f i c a n c e , summary s t a t i s t i c s were c a l c u l a t e d f o r each parameter and t h e mean v a l u e s 81 compared and r a n k e d . Because the f l u x e s were c a l c u l a t e d as d i f f e r e n c e s between means, w i t h i n - p l o t s t a n d a r d e r r o r s were c a l c u l a t e d by summing the p o o l s t a n d a r d e r r o r s ( Z a r , 1974; R a i s o n e t a l . . 1987) . However, b e t w e e n - p l o t s t a n d a r d e r r o r ( treatment s t a n d a r d e r r o r ) has been c a l c u l a t e d from t h e v a r i a n c e between t h e t h r e e p l o t v a l u e s (one o b s e r v a t i o n p e r p l o t ) on the assumpt ion t h a t t h i s would account f o r the w i t h i n - p l o t e r r o r . A l t e r n a t i v e l y , i t i s p o s s i b l e t o c a l c u l a t e t h e s t a n d a r d e r r o r from a n a l y s i s o f v a r i a n c e based on the f o l l o w i n g f o r m u l a : 2 M S E - n 0 / n = S 1 2 / n 1 + S 2 2 / n 2 where n D = number o f samples averaged p e r p l o t n = number o f o b s e r v a t i o n s p e r t r e a t m e n t However, h e t e r o g e n e i t y o f v a r i a n c e s between t r e a t m e n t s made d a t a t r a n s f o r m a t i o n s n e c e s s a r y , making c a l c u l a t i o n o f v a r i a n c e s i n r e a l space d i f f i c u l t . I t i s a l s o p o s s i b l e t o e s t i m a t e the s t a n d a r d e r r o r by p o o l i n g the t h r e e p l o t s p e r t rea tment t o g e t h e r t o produce one e s t i m a t e based on 15 r e p l i c a t i o n s . However, t h i s would r e s u l t i n p s e u d o r e p l i c a t i o n (see H u r l b e r t , 1984) . The sample s i z e s r e q u i r e d t o e s t i m a t e exchangeable N p o o l s w i t h i n a 10 o r 2 0 p e r c e n t s t a n d a r d e r r o r o f t h e mean on a p e r p l o t b a s i s were c a l c u l a t e d f o r each t r e a t m e n t based on the f o l l o w i n g f o r m u l a (Powers, 1980, 1984): n = t 2 • S 2 / E 2 where N = # o f samples p e r p l o t , E = p r e c i s i o n d e s i r e d S = v a r i a n c e , t = s t u d e n t t f o r a g i v e n p r o b a b i l i t y 82 CHAPTER 4 RESULTS IN SITU NITROGEN FLUXES Due t o v e r y h i g h v a r i a b i l i t y , p a r t i c u l a r l y f o l l o w i n g f e r t i l i z a t i o n , no s i g n i f i c a n t N o r "PK" e f f e c t s c o u l d be found f o r e i t h e r ne t m i n e r a l i z a t i o n , u p t a k e , o r l o s s , e i t h e r by month o r f o r the t o t a l growing season . However, N f e r t i l i z a t i o n s i g n i f i c a n t l y i n c r e a s e d m i n e r a l - N c o n c e n t r a t i o n i n t h e s o i l , (see Appendix f o r a n a l y s i s o f v a r i a n c e t a b l e s ) . Temporal V a r i a t i o n D e s p i t e not f i n d i n g s i g n i f i c a n t N o r "PK" e f f e c t s , d e f i n i t e t r e n d s can be seen by examining mean f l u x r a t e s ( T a b l e 4, F i g u r e s 6 - 8 ) . Both N and "PK" f e r t i l i z a t i o n appear t o have i n c r e a s e d m i n e r a l i z a t i o n and uptake r a t e s . V a r i a b i l i t y o f l o s s r a t e s i n c r e a s e d w i t h i n c r e a s i n g f e r t i l i z e r a p p l i c a t i o n , but the l o s s e s were b o t h p o s i t i v e and n e g a t i v e (a s a m p l i n g a r t i f a c t ) , t h u s r e v e a l i n g no d e f i n i t e t r e n d s . N e g a t i v e uptake r a t e s were a l s o o b t a i n e d f o r a few p l o t s and some p e r i o d s , but t h e s e a r e a l s o s a m p l i n g a r t i f a c t s and have no b i o l o g i c a l meaning. 83 T a b l e 4. Mean m o n t h l y n e t m i n e r a l i z a t i o n ( n e t i m m o b i l i z a t i o n i n d i c a t e d by n e g a t i v e v a l u e s ) , u p t a k e , maximum l e a c h i n g a n d a v a i l a b l e N v a l u e s b y t r e a t m e n t . S t a n d a r d e r r o r s o f mean i n p a r e n t h e s e s (n=3 e x c e p t NOPK where n=2). TREATMENT PERIOD May - J u n e J u n e - J u l y J u l y - Aug Aug - S e p t (32 d a y s ) (30 da y s ) (29 d a y s ) (38 d a y s ) N e t m i n e r a l i z a t i o n (mg N/kg s o i l ) NO 1. 5 (1.1) 3.3 (0.4) -1.0 (1.3) 5. 1 (3.9) NOPK 22 . 0 (7.1) 0.9 (5.8) -0.2 (2.6) 0. 0 (5.8) N l 9. 9 (15.1) 7.5 (7.4) 4.3 (4.1) 21. 2 (1.5) N1PK 35. 6 (22.6) 4.5 (3.2) 24.3 (26.9) 67. 7 (58.8) N3 36. 6 (35.9) 21.1 (42.6) 52.8 (13.0) •33. 7 (10.8) N3PK 61. 6 (74.5) 11.5 (56.1) 31.6 (27.1) •11. 6 (21.2) • U p t a k e (mg N/kg s o i l ) NO 1. 0 (0.1) 3.6 (0.2) 0.1 (2.3) 0. 0 (0.2) NOPK 22. 6 (1.2) 4.3 (0.0) 1.3 (2.5) 0. 5 (0.4) N l 14. 5 (7.2) 24.1 (9.1) 9.1 (7.7) 13. 5 (4.5) N1PK 49. 9 (23.3) 21.6 (5.6) 26.4 (19.4) 54. 4 (57.2) N3 0. 0 (8.4) 29.7 (39.7) 11.9 (12.6) 4. 5 (35.3) N3PK 79. 2 (66.5) 37.1 (34.1) 71.9 (46.9) 5. 3 (12.6) Maximum L e a c h i n g (mg N/kg s o i l ) NO -3 . 4 (1.7) 0.0 (1.1) -0.6 (0.2) 3. 6 (4.2) NOPK -4. 3 (19.3) -7.0 (10.2) 15.1 (14.1) -1. 3 (1.5) N l 6. 3 (19.1) 15.4 (10.1) 8.1 (7.0) 6. 2 (10.8) N1PK -31. 0 (37.3) -2.1 (3.9) 1.3 (12.8) 61. 9 (65.0) N3 -6. 0 (23.9) -23.7 (52.5) -28.9 (38.3) -6. 1 (4.6) N3PK 101. 4 (43.5) -40.2 (34.6) 39.6 (7.5) -9. 6 (11.5) • • E x c h a n g e a b l e N (mg N/kg s o i l ) May 20 J u n e 21 J u l y 21 Aug 18 S e p t 25 NO a 10 (1.4) 10 (0.2) 10 (0.7) 9 (2.9) 16 (1.5) NOPKa 13 (2.0) 12 (3.9) 9 (1.8) 7 (1.7) 7 (4.5) N l b 49 (9.9) 44 (8.6) 28 (8.0) 23 (6.8) 30 (9.0) NIPKb 56 (13.6) 42 (13.2) 25 (8.6) 23 (16.2) 36 (18.0) N3 c 82 (28.3) 119 (21.4) 110 (14.9) 151 (23.5) 113 (42.6) N3PKC150 (34.0) 132 (46.3) 77 (44.6) 32 (18.4) 31 (18.0) * n e g a t i v e v a l u e s a r e i n d i c a t e d a s z e r o s f o r u p t a k e . ** t r e a t m e n t s f o l l o w e d b y t h e same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t (p < . 0 5 ) . 84 S e a s o n a l t r e n d s v a r i e d w i t h t r e a t m e n t f o r the f l u x e s , and few c o n s i s t e n t t r e n d s were observed ( F i g u r e s 6 - 8 ) . However, ne t m i n e r a l i z a t i o n was n e g l i g i b l e f o r p e r i o d t h r e e i n b o t h NO t r e a t m e n t s w h i l e ne t i m m o b i l i z a t i o n o c c u r r e d f o r p e r i o d f o u r f o r b o t h N3 t r e a t m e n t s . T h e r e i s a s t r o n g r e l a t i o n s h i p between t h e monthly m i n e r a l i z a t i o n and uptake r a t e s as c a l c u l a t e d by s o i l d e p l e t i o n ( r= .796 ) . Month ly uptake i s l e s s s t r o n g l y c o r r e l a t e d w i t h exchangeable N p r e s e n t a t the b e g i n n i n g o f each p e r i o d ( r= .286 ) . Growing Season F l u x e s S i m i l a r t o monthly f l u x e s , growing season f l u x e s g e n e r a l l y i n c r e a s e d w i t h i n c r e a s i n g N a n d / o r "PK" f e r t i l i z e r a p p l i c a t i o n s (Tab le 5, F i g u r e 9 ) . N i t r i f i c a t i o n and n i t r a t e uptake appear t o be prominent i n the c o n t r o l p l o t s (Tab le 6, F i g u r e s 10 -11) . The T a b l e 5. Growing season net m i n e r a l i z a t i o n , u p t a k e , l o s s , and mean exchangeable N f o r each t r e a t m e n t . S t a n d a r d e r r o r s o f mean i n p a r e n t h e s e s (n=3 except f o r NOPK where n=2). TREATMENT GROWING SEASON NITROGEN FLUX EXCHANGEABLE (mg N / kg s o i l ) NITROGEN M i n e r a l i z a t i o n Uptake Loss (mg N / k g s o i l ) "NO 9.0 (4.0) 4.8 (4.8) - 0 . 5 (6.9) 11.2 (0.4) NOPK 22.8 (9.8) 26.4 (6.4) - 2 7 . 7 (45.0) 9.7 (0.6) NI 42.9 (24.8) 62.8 (13.4) 19.9 (11.5) 34.8 (6.9) N1PK 132.1 (106.9) 150.4 (100.1) 30.2 (93.5) 36.2 (13.7) N3 76.8 (76.4) 34.4 (19.9) - 6 4 . 7 (65.9) 115.2 (15.1) N3PK 93.6 (152.9) 183.8 (123.5) 91.2 (27.0) 101.1 (29.7) TEMPORAL VARIATION in N MINERALIZATION and U P T A K E 85 c o E \ o CO O) . * \ z OS E X 3 100 50 -50 • UPT. • MIN • I " t .Vi 150 c o E \ o (0 OS \ E F i g u r e 6 100 -50 -0 --50 Period M o n t h l y v a r i a t i o n i n n e t n i t r o g e n m i n e r a l i z a t i o n and u p t a k e f o r c o n t r o l (a) and NO+PK (b) t r e a t m e n t s . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f t h e mean. TEMPORAL VARIATION in N MINERALIZATION and U P T A K E 86 100 50 -50 • UPT. • MIN • 150 100 r Period Monthly v a r i a t i o n i n net nitrogen mineralization and uptake for NI (a) and Nl+PK (b) treatments. V e r t i c a l bars represent + or - 1 standard error the mean. T E M P O R A L VARIATION in N MINERALIZATION and UPTAKE 87 100 50 -0 --50 150 100 -Period . Monthly v a r i a t i o n i n net nitrogen mineralization and uptake for N3 (a) and N3+PK (b) treatments. V e r t i c a l bars represent + or - 1 the mean. standard error N MINERALIZATION and UPTAKE o tn O) \ z D) JE K 3 C O cn CQ e W o> c i o 300 200 100 -100 • UPT. • MIN. 8 8 300 o CB D) J£ \ z DJ K 3 i l c o CO CB O co O) c 1 o C 200 -100 --100 NO N1 N3 Nitrogen Regime F i g u r e 9 . V a r i a t i o n i n growing season net n i t r o g e n m i n e r a l i z a t i o n and uptake f o r t h r e e n i t r o g e n regimes w i t h o u t "PK" (a) and w i t h "PK" ( b ) . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f the mean. Nitrogen Regime Figure 10. Va r i a t i o n i n growing season net ammonification and n i t r i f i c a t i o n for three nitrogen regimes without "PK" (a) and with "PK" (b). AMMONIUM and NITRATE UPTAKE 90 F i g u r e 11. V a r i a t i o n i n growing season ammonium and n i t r a t e uptake f o r t h r e e n i t r o g e n regimes w i t h o u t "PK" (a) and w i t h "PK" ( b ) . 91 T a b l e 6. Net a m m o n i f i c a t i o n , ne t n i t r i f i c a t i o n , ammonium- and n i t r a t e - N uptake and l o s s , and mean exchangeable ammonium- and n i t r a t e - N f o r each t r e a t m e n t . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n=3, except NOPK where n=2). TREATMENT GROWING SEASON NITROGEN FLUX (mg N / k g s o i l ) * A m m o n i f i c a t i o n N i t r i f i c a t i o n NH4 + Uptake N03~ Uptake NO 4 . 9 (6.5) 4 .1 (5.5) 1. 0 (2.6) 3.8 (7.3) NOPK 24. 7 (8.0) - 1 . 9 (1.8) 29. 0 (3.6) 0 (2.7) N l 36. 9 (18.3) 6.0 (7.2) 43. 0 (14.1) 19.8 (1.0) N1PK 111. 0 (86.2) 21 .1 (20.7) 122. 3 (75.4) 28.0 (24.7) N3 54. 6 (54.6) 22.2 (27.3) 46. 6 (30.7) 0 (7.8) N3PK 78. 9 (142.2) 14.7 (13.0) 163. 3 (114.9) 20.5 (10.1) N H 4 - N Loss N 0 3 - -N Loss E x c h . NH 4 + E x c h . N03~ NO 0. 6 (6.2) - 1 . 0 (1.7) 5. 3 (0.9) 5.9 (1.4) NOPK - 2 7 . 9 (46.2) 0.2 (1.2) 5. 5 (0.1) 4.2 (0.5) N l 18. 3 (14.5) 1.6 (9.3) 18. 6 (5.7) 16.2 (1.3) N1PK 36. 2 (91.4) - 6 . 0 (3.6) 28 . 0 (9.6) 8.2 (4.2) N3 - 4 2 . 3 (34.0) -22 .4 (32.1) 57. 1 (14.8) 58 .1 (4.4) N3PK 81. 7 (22.8) 9 .5 (4.5) 84 . 1 (23.8) 17.0 (9.8) * N e g a t i v e v a l u e s a r e p r e s e n t e d as zeros f o r u p t a k e . p r o p o r t i o n o f n i t r i f i c a t i o n and n i t r a t e uptake i s g r e a t e s t i n t h e c o n t r o l p l o t s , but the a b s o l u t e v a l u e s o f n i t r i f i c a t i o n , and N03~ uptake g e n e r a l l y i n c r e a s e w i t h f e r t i l i z a t i o n w i t h the e x c e p t i o n o f t h e NOPK and the N3 t r e a t m e n t s where N03~ uptake appears t o be z e r o . C o n c e n t r a t i o n s o f i n o r g a n i c N g e n e r a l l y d e c r e a s e d w i t h d e p t h , w i t h the e x c e p t i o n o f the NO t r e a t m e n t s (Tab le 7, F i g u r e 12 ) . However, the a b s o l u t e v a l u e s o f i n o r g a n i c N i n the o t h e r t r e a t m e n t s a r e g r e a t e r a t g r e a t e r d e p t h s . N i t r a t e - N i s g e n e r a l l y a g r e a t e r p r o p o r t i o n o f t o t a l m i n e r a l - N a t the i n c r e a s e d d e p t h . 92 T a b l e 7. C o n c e n t r a t i o n o f e x c h a n g e a b l e ammonium-N a n d n i t r a t e - N a t two d e p t h s i n b u l k s a m p l e s c o l l e c t e d i n J u n e s e p a r a t e f r o m t h e o t h e r s e q u e n t i a l c o r i n g s a m p l e s . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s . TREATMENT EXCHANGEABLE N (mg N / k g s o i l ) Ammonium-N N i t r a t e - N M i n e r a l - N D e p t h (cm) 0-15 15-25 0-15 15-25 0-15 15-25 NO 2.6 2.5 7.4 9.4 10.0 11.9 (0.9) (0.8) (3.0) (4.6) (2.3) (4.4) NOPK 10.1 2.9 4.1 8.1 14.3 11.0 (16.7) (1.6) (1.2) (4.5) (16.2) (5.8) NI 45.1 13.0 27.9 13.9 73.0 26.9 (48.1) (14.4) (24.7) (10.6) (67.6) (23.4) N1PK 40.7 6.1 12.4 15.0 53 .1 21.1 (52.4) (8.8) (21.1) (21.6) (71.1) (30.3) N3 109.9 22.4 65.1 34.6 175.0 57.0 (113.0) (32.9) (35.3) (30.2) (140.1) (62.5) N3PK 156.8 50.0 19.9 16.1 176.7 66.1 (155.2) (99.2) (15.8) (13.6) (164.0) (109.2) Sample s i z e c a l c u l a t i o n s i n d i c a t e a n e e d t o sample more i n t e n s i v e l y i n t h e f e r t i l i z e d p l o t s ( T a b l e 8 ) , a t l e a s t i n t h e s e a s o n i m m e d i a t e l y f o l l o w i n g f e r t i l i z a t i o n . The N1PK t r e a t m e n t a p p e a r s t o r e q u i r e t h e most s a m p l e s . T a b l e 8. R e q u i r e d sample s i z e t o e s t i m a t e mean s o i l i n o r g a n i c N p o o l w i t h i n t h e s t a t e d a l l o w a b l e e r r o r 90 % o f t h e t i m e ( b a s e d on a c o m p o s i t e o f two c o r e s ) . TREATMENT REQUIRED NUMBER OF SAMPLES PER PLOT E = 0.2 X E = 0.1 X NO 4 13 NOPK 12 40 NI 26 96 N1PK 42 164 N3 32 122 N3PK 16 56 X e q u a l s t h e mean e x c h a n g e a b l e p o o l by t r e a t m e n t . PROFILE of INORGANIC N 9 3 200 1 1 1 1 1 1 r 200 I 1 i 1 1 r tfoVP^6 * ^ V ^ tf^V^6 Nitrogen Regime and Depth (cm) F i g u r e 12. The c o n c e n t r a t i o n o f ammonium and n i t r a t e a t two depths f o r t h r e e n i t r o g e n reg imes w i t h o u t "PK" (a) and w i t h "PK" ( b ) . 94 OTHER ANALYSES A n a e r o b i c I n c u b a t i o n G r o s s m i n e r a l i z a b l e N de termined by a n a e r o b i c i n c u b a t i o n was s i g n i f i c a n t l y i n c r e a s e d by N f e r t i l i z a t i o n but no t by PK f e r t i l i z a t i o n (Tab le 9, F i g u r e 13 ) . However, ne t m i n e r a l i z a b l e N was not s i g n i f i c a n t l y a f f e c t e d by f e r t i l i z a t i o n and d i d not r e v e a l any s i g n i f i c a n t t r e n d s . F o l i a r A n a l y s i s F o l i a r N c o n t e n t p e r u n i t need le o f c u r r e n t y e a r s f o l i a g e i n c r e a s e d over the growing season ( F i g u r e 14b) w h i l e n i t r o g e n c o n c e n t r a t i o n d e c l i n e d from J u l y 20 t o August 18 and i n c r e a s e d s l i g h t l y u n t i l September 25 f o r a l l t r e a t m e n t s ( F i g u r e 14a) . T a b l e 9. G r o s s and net m i n e r a l i z a b l e N v a l u e s o b t a i n e d by a n a e r o b i c i n c u b a t i o n f o r 7 days a t 4 0 ° C . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n=3 except NOPK where n=2). TREATMENT GROSS MINERALIZABLE N NET MINERALIZABLE N (mg N / kg s o i l ) NO 42 .1 ( 2 . 9 ) a 33.2 ( 3 . 2 ) a NOPK 40. 0 ( 1 . 5 ) a 29.8 ( 3 . 4 ) a NI 53 . 3 ( 5 . 1 ) a 20.5 ( 3 . 3 ) a N1PK 62.9 ( 8 . 7 ) a 28.2 (0. 4) a N3 112.0 (15 .5)b 11.5 (11 .8 )a N3PK 191.6 (29 .0)b 31.2 (18 .8 )a V a l u e s i n t h e same v e r t i c a l column f o l l o w e d by the same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r (p < . 0 5 ) . G R O S S and NET M I N E R A L I Z A B L E N o 03 TO \ z o> 5 Z e 2 CO N e c o CD TO \ z z 0 S CB N CP c 200 150 100 50 O NETMIN. • GROSSMIN. 200 150 -100 -50 -95 NO N1 N3 Nitrogen Regime F i g u r e 13. V a r i a t i o n i n g r o s s and net m i n e r a l i z a b l e N (determined by a n a e r o b i c i n c u b a t i o n i n the l a b o r a t o r y ) f o r t h r e e n i t r o g e n reg imes w i t h o u t "PK" (a) and w i t h "PK" ( b ) . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f t h e mean. TEMPORAL FOLIAR N VARIATION 2.5 J? © > •o c o c o c o U •o © e Z 2.0 -1.5 -1.0 -0.5 e •o e e c \ Z O) S c o O •D © © z F i g u r e 14 0.6 0.5 0.4 0.3 0.2 0.1 , N3PK b / JULY 20 AUG 18 SEPT 25 Sampling Date Temporal v a r i a t i o n i n need le n i t r o g e n c o n c e n t r a t i o n (a) and n i t r o g e n c o n t e n t (b) f o r c u r r e n t y e a r s f o l i a g e f o r s i x t r e a t m e n t s from J u l y 2 0 t o September 25. 97 September N c o n c e n t r a t i o n was s i g n i f i c a n t l y i n c r e a s e d by N a p p l i c a t i o n (Tab le 10, F i g u r e 15a) . Both N and 1 1 PK" a p p l i c a t i o n s i g n i f i c a n t l y i n c r e a s e d N c o n t e n t ( F i g u r e 15c) but t h e r e was a s i g n i f i c a n t N-PK i n t e r a c t i o n . Needle we ight was s i g n i f i c a n t l y i n c r e a s e d o n l y by "PK" a p p l i c a t i o n ( F i g u r e 15b) . T a b l e 10. N i t r o g e n c o n c e n t r a t i o n , n e e d l e w e i g h t , and N c o n t e n t f o r c u r r e n t y e a r s f o l i a g e sampled i n September, 1988. S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s . TREATMENT N CONCENTRATION NEEDLE WEIGHT N CONTENT (% d r y weight) (g/1000 need les ) (mg/needle) NO 1.1 ( 0 . 2 ) a 22.3 ( 1 . 7 ) a 0.27 ( .02) NOPK 1.1 ( 0 . 0 ) a 26.0 (1 .4 )b 0.28 ( .02) NI 1.4 (0 .1 )b 21.5 ( 1 . 3 ) a 0.29 (.01) N1PK 1.3 (0 .1 )b 26.5 (2 .5 )b 0.34 (.02) N2 1.5 ( 0 . 1 ) c 18.5 ( 1 . 3 ) a 0.27 ( • 01) N2PK 1.5 ( 0 . 0 ) c 25.9 (3 . l ) b 0.40 ( .04) N3 1.5 ( 0 . 1 ) c 19.8 ( 3 . 2 ) a 0.31 (.03) N3PK 1.7 ( 0 . 2 ) d 33.8 (6 .8 )b 0.60 (• 18) V a l u e s i n the same v e r t i c a l column f o l l o w e d by the same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t (p < . 0 5 ) . O t h e r macro and m i c r o n u t r i e n t c o n c e n t r a t i o n s a r e g i v e n i n T a b l e 11. V e r y few t r e n d s a r e e v i d e n t , but s u l p h u r and s u l p h a t e c o n c e n t r a t i o n s appear t o have been i n c r e a s e d by "PK" a d d i t i o n s , w h i l e manganese c o n c e n t r a t i o n appears t o be d e c r e a s e d by "PK". S o i l M o i s t u r e Content No r e l a t i o n s h i p was found between ne t N m i n e r a l i z a t i o n o r uptake and s o i l wetness ( F i g u r e 16) . There was a s t r o n g d e c l i n e i n s o i l wetness throughout the growing season FOLIAGE VARIATION e e c \ Z 0> Z o N1 N2 Nitrogan Regime F i g u r e 15. V a r i a t i o n i n c u r r e n t y e a r s f o l i a g e f o r f o u r n i t r o g e n f e r t i l i z e r regimes w i t h and w i t h o u t "PK" a d d i t i o n s : a) n e e d l e N c o n c e n t r a t i o n , b) n e e d l e w e i g h t , and c) need le N c o n t e n t . 0.0 100 -0.0 N I T R O G E N F L U X V E R S U S S O I L M O I S T U R E C O N T E N T U P T . O M I N . 1 1 A o o o A o o o • o A o o 0.1 0.2 30 20 10 1 1 e A o _ o 0 a. 0 0 O a - a A -O A A A o o o 1 -100 99 ° b £ U P T . O M I N . 0.1 0.2 0.3 0.2 0.3 16, 0.0 0.1 Soil Moisture Content (portion of dry weight) V a r i a t i o n i n monthly ne t n i t r o g e n m i n e r a l i z a t i o n and uptake f o r v a r y i n g s o i l m o i s t u r e c o n t e n t s : a) c o n t r o l , b) N0+PK, c) NI, d) Nl+PK, e) N3, and f) N3+PK. 0.4 100 T a b l e 11. Mean 1988 need le c o n c e n t r a t i o n o f macro and m i c r o n u t r i e n t s o f c u r r e n t y e a r s f o l i a g e f o r a l l t r e a t m e n t s . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s . TREATMENT MACRO NUTRIENT CONCENTRATION (%) P K Ca Mg S NO . 14 (.02) .76 (.07) .12 (.02) . 10 (.01) .08 (.01) NOPK . 15 ( .02) .72 (.07) . 12 (.01) .11 (.02) .09 (.02) N l . 16 ( .01) .69 (.04) .13 (.04) . 10 (.01) . 06 ( .00) N1PK .16 (.01) .74 (.07) . 13 (.02) . 11 ( .02) .10 ( .00) N2 . 17 (.02) .77 (.08) . 14 (.01) . 11 (.01) .05 (.01) N2PK . 16 (.02) .70 (.09) .11 ( • 02) .09 (.01) .10 (.01) N3 .16 ( .03) .68 (.14) . 14 ( .01) . 11 (• o i ) .06 (.00) N3PK .16 ( .01) .75 ( • 08) . 12 (.02) . 10 ( .01) . 11 ( .00) MICRO NUTRIENT CONCENTRATION (PPM) Mn Fe Cu Zn S O 4 B NO 155 (45) 69 (33) 4 .7 (1. 5) 48 (4) 32 (9) 20 (2) NOPK 141 (28) 63 (36) 4 .7 (0. 6) 46 (6) 102 (53) 26 (5) N l 193 (85) 108 (102) 5 .7 (2. 5) 54 (5) 14 (3) 21 (1) N1PK 166 (40) 55 (33) 4 .0 (1. 7) 37 (10) 46 (14) 29 (5) N2 226 (68) 55 (26) 4 .3 (1 . 2) 46 (4) 14 (3) 21 (1) N2PK 122 (57) 73 (37) 4 .7 (1. 5) 38 (6) 54 (30) 21 (4) N3 171 (113) 62 (19) 4 .7 (1. 5) 41 (16) 16 (3) 20 (3) N3PK 133 (24) 63 (26) 7 .0 (2. 6) 49 (15) 42 (16) 22 (1) T a b l e 12. Mean s o i l m o i s t u r e c o n t e n t s f o r growing s e a s o n . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s . TREATMENT SOIL MOISTURE CONTENT (% d r y weight) NO 12.8 (7.2) a NOPK 13.7 (6.3) b N l 9.6 (5.6) c N1PK 12.8 (6.6) a N3 12.4 (7.8) a N3PK 14.1 (6.2) b V a l u e s i n the same v e r t i c a l column f o l l o w e d by the same l e t t e r a r e no t s i g n i f i c a n t l y d i f f e r e n t (p < . 0 5 ) . 101 ( T a b l e 13, F i g u r e 17) , but no c o r r e s p o n d i n g d e c l i n e i n m i n e r a l i z a t i o n o r u p t a k e . M o i s t u r e c o n t e n t s i n s o i l s i n c u b a t e d i n c o r e s were c o n s i s t e n t l y s i g n i f i c a n t l y ( p a i r e d d i f f e r e n c e t e s t ) h i g h e r t h a n m o i s t u r e c o n t e n t s i n t h e b u l k s o i l s w i t h the e x c e p t i o n o f the s o i l s i n c u b a t e d i n t h e c o v e r e d c o r e s d u r i n g t h e f i n a l i n c u b a t i o n p e r i o d (Tab le 13, F i g u r e 17) . S o i l wetness was s i g n i f i c a n t l y a f f e c t e d by N a p p l i c a t i o n (NI < NO and N3) and was s i g n i f i c a n t l y i n c r e a s e d by "PK" ( T a b l e 12) . Nitrogen Uptake Based on Biomass Increment Based on changes i n above ground b iomass , a n a l y s i s o f c o v a r i a n c e r e v e a l e d no s i g n i f i c a n t e f f e c t o f e i t h e r N o r PK a p p l i c a t i o n on N uptake but mean uptake i n c r e a s e d w i t h N a p p l i c a t i o n (Tab le 14) . However, t h e i n i t i a l b iomass i n 1981 s i g n i f i c a n t l y a f f e c t e d biomass increment and N u p t a k e . T a b l e 13. Mean s o i l m o i s t u r e c o n t e n t f o r ambient s o i l , and s o i l i n c u b a t e d i n c o v e r e d and open PVC tubes f o r a l l t r e a t m e n t s . S t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s . SAMPLING DATE SOIL MOISTURE CONTENT (% d r y weight) (end o f i n c u b a t i o n p e r i o d ) b u l k c o v e r e d open June 20 18.3 ( 4 . 5 ) a 20.3 (5 .6 )b 20.3 (4 .5 )b J u l y 20 13.2 ( 6 . 0 ) a 16.1 ( 4 .4 )b 16.3 (4 .4 )b A u g . 18 5.8 ( 4 . 2 ) a 8.8 (3 .2 )b 7.8 (3 .3 )b Sep . 25 12.5 ( 5 . 6 ) a 6.6 (3 .3 )b 14.0 ( 3 . 2 ) a A v g . f o r Season 12.5 ( 6 . 8 ) a 12.9 ( 6 . 9 ) a 14.6 (6 .0 )b V a l u e s i n t h e same row f o l l o w e d by t h e same l e t t e r a r e not s i g n i f i c a n t l y d i f f e r e n t (p < . 0 5 ) . 102 MOISTURE FLUCTUATIONS 30 I 1 1 1 1 1 0 I 1 1 1 1 L S a m p l i n g D a t e F i g u r e 17. V a r i a t i o n i n s o i l m o i s t u r e c o n t e n t s f o r b u l k s o i l , s o i l i n c u b a t e d i n c o v e r e d c o r e s and s o i l i n c u b a t e d i n open c o r e s . Incubated s o i l s a r e r e p r e s e n t e d a t the end o f the exposure p e r i o d s . 103 CORRELATIONS BETWEEN NITROGEN INDEXES The c o r r e l a t i o n c o e f f i c i e n t s between v a r i o u s N indexes a r e g i v e n i n T a b l e 15 and the indexes a r e g r a p h i c a l l y compared i n F i g u r e 18. Important c o r r e l a t i o n s can be summarized as f o l l o w s . G r o s s m i n e r a l i z a b l e N was s t r o n g l y c o r r e l a t e d w i t h N f e r t i l i z a t i o n ( r= .749) , b u t o n l y weakly c o r r e l a t e d w i t h t o t a l season ne t m i n e r a l i z a t i o n (r=.354) ( F i g u r e 19a) (see pages 72 and 75 f o r d e f i n i t i o n s ) . Net m i n e r a l i z a b l e N was n e g a t i v e l y c o r r e l a t e d w i t h N a p p l i c a t i o n (r=- .217) and weakly p o s i t i v e l y c o r r e l a t e d w i t h ne t N m i n e r a l i z a t i o n ( r= .214 ) . Net N m i n e r a l i z a t i o n was o n l y weakly c o r r e l a t e d w i t h N f e r t i l i z e r a p p l i c a t i o n (r=.214) and n e g a t i v e l y c o r r e l a t e d w i t h n e e d l e we ight and f o l i a r N c o n t e n t . F o l i a r N c o n t e n t was o n l y weakly c o r r e l a t e d w i t h N uptake (r=.194) ( F i g u r e 19b) , but more s t r o n g l y c o r r e l a t e d w i t h g r o s s m i n e r a l i z a b l e N ( r= .576 ) . Needle we ight was s t r o n g l y c o r r e l a t e d w i t h "PK" f e r t i l i z a t i o n (r=.742) and f o l i a r N c o n c e n t r a t i o n was s t r o n g l y c o r r e l a t e d w i t h N f e r t i l i z a t i o n ( . 8 7 5 ) . N u p t a k e , as measured by s o i l d e p l e t i o n , i s v e r y s t r o n g l y c o r r e l a t e d w i t h ne t m i n e r a l i z a t i o n ( r= .908 ) . The t r e a t m e n t s were ranked from h i g h e s t t o lowes t f o r t h e v a r i o u s n i t r o g e n a v a i l a b i l i t y indexes and measurements ( T a b l e 16 ) . Net m i n e r a l i z a b l e N was the o n l y index which p r o v i d e d s u b s t a n t i a l l y d i f f e r e n t r a n k i n g s from t h e o t h e r s , a l t h o u g h no two indexes were i n t o t a l agreement. The two uptake c a l c u l a t i o n s a l s o produced s l i g h t l y d i f f e r e n t r a n k i n g s . 104 T a b l e 14. Mean a b o v e - g r o u n d b i o m a s s e s t i m a t e s and n i t r o g e n u p t a k e b a s e d on c h a n g e s i n a b o v e - g r o u n d b i o m a s s f o r a l l t r e a t m e n t s . S t a n d a r d e r r o r s i n p a r e n t h e s e s (n = 3 ) . TREATMENT ABOVE--GROUND BIOMASS (kg/ha) N UPTAKE (kg N/ha) 1981 1984 1986 1986 NO 27. 3 (4.6) 294 (89) 77 441 (15 218) 57 (11) NOPK 15. 2 (7.0) 244 (59) 64 377 (10 676) 47 (8) NI 55. 4 (13.8) 477 (65) 107 560 (11 452) 102 (11) N1PK 32. 6 (12.1) 413 (99) 100 153 (19 912) 96 (19) N2 22. 8 (15.0) 328 (178) 79 557 (38 290) 82 (39) N2PK 40. 1 (17.4) 533 (186) 130 709 (50 693) 134 (52) N3 62. 4 (29.1) 487 (179) 107 490 (36 869) 118 (41) N3PK 33 . 8 (10.8) 515 (100) 143 750 (20 363) 158 (22) T a b l e 15. C o r r e l a t i o n c o e f f i c i e n t s b etween n i t r o g e n a v a i l a b i l i t y i n d e x e s o r measurements and f e r t i l i z e r a p p l i c a t i o n . N "PK 1 N e e d l e F o l i a r F o l i a r N e t N F e r t . F e r t . W e i g h t N Cone. N C o n t M i n . N F e r t 1.00 "PK" F e r t 0.00 1. 00 N e e d l e Wt. .2 67 .742 1. 00 F. N Cone. .875 .123 .409 1.00 F. N C o n t . .589 .531 .890 .767 1.00 N e t N M i n . .214 . 185 -.232 . 122 -.147 1.00 1-N U p t a k e .318 .417 .124 .296 .194 .908 N L o s s .105 .305 .345 .203 .356 .409 G r o s s M i n N .749 . 300 .377 .685 .576 .354 N e t M i n N -.217 .208 -.014 . 359 -.208 .214 2 N U p t a k e .73 0 .081 .398 . 525 .529 -.159 I n o r g a n i c N .847 .002 .237 .836 .567 .252 IN N G r o s s N e t 2 N I n o r g a n i c U p t a k e L o s s M i n . N M i n . N U p t a k e N !N U p t a k e 1.00 N L o s s .604 1.00 G r o s s M i n N .528 .217 1.00 N e t M i n N .297 .131 .461 1. 00 2 N U p t a k e .071 . 182 .631 .270 1.00 I n o r g a n i c N .312 .089 .621 -.401 .334 1.00 1 c a l c u l a t e d b a s e d on s o i l d e p l e t i o n . 2 c a l c u l a t e d b a s e d on a b o v e - g r o u n d b i o m a s s i n c r e m e n t . SOIL N INDEX COMPARISONS 105 300 a o m W \ z tn 5 x 9 o CO 200 2 100 -m EXCH. • NETMIN. • GROSSMIN. • OPT. • MIN. o CO OD X \ z O) 5 X « C o -100 300 200 -£ 100 -0 --100 NO N1 N3 Nitrogen Regime F i g u r e 18. Comparison o f f i v e s o i l n i t r o g e n i n d e x e s f o r t h r e e N f e r t i l i z e r reg imes w i t h o u t "PK" (a) and w i t h "PK" ( b ) . V e r t i c a l b a r s r e p r e s e n t + o r - 1 s t a n d a r d e r r o r o f t h e mean. o a a x \ z t» 2 c o m Si 3 O c o o (0 c < •o a a c \ z O) E c c o u o u. F i g u r e 19. L A B 300 200 100 V E R S U S F I E L D M I N E R A L I Z A T I O N -100 1— - NET 6 GROSS c £ t. 106 -400 -200 0 200 400 Field Net Mineralization (mg N/kg soil for Growing Season) FOLIAR N CONTENT VERSUS UPTAKE 0.8 0.6 -0.4 -0.2 -0.0 -100 0 100 200 300 400 Growing Season Uptake (Mg N/kg soil) a) The change i n g r o s s and n e t m i n e r a l i z a b l e n i t r o g e n (determined by a n a e r o b i c i n c u b a t i o n i n t h e l a b o r a t o r y ) w i t h v a r i a t i o n i n ne t N m i n e r a l i z a t i o n e s t i m a t e d by i n s i t u s e q u e n t i a l c o r i n g . b) The change i n n e e d l e n i t r o g e n c o n t e n t o f c u r r e n t y e a r s f o l i a g e (sampled i n September) w i t h v a r i a t i o n i n growing season u p t a k e e s t i m a t e d by i n s i t u s e q u e n t i a l c o r i n g . 107 A l t h o u g h uptake ( c a l c u l a t e d from s o i l d e p l e t i o n ) and f o l i a r N c o n t e n t a r e no t c l o s e l y c o r r e l a t e d , they p r o d u c e d s i m i l a r r a n k i n g s . T a b l e 16. Treatment r a n k i n g s from h i g h e s t t o l owes t f o r each o f the parameters measured. N INDEX OR MEASUREMENT Rank Net N i t r o g e n U p t a k e 1 U p t a k e 2 Net M i n e r a l i z a b l e M i n e r a l i z a t i o n N i t r o g e n H i g h e s t N1PK N3PK N3PK NO N3PK N1PK N3 N3PK N3 NI NI NOPK NI N3 N1PK N1PK NOPK NOPK NO NI Lowest NO NO NOPK N3 G r o s s M i n e r a l - I n o r g a n i c F o l i a r N F o l i a r N i z a b l e N N Concent . Concent . Content H i g h e s t N3PK N3 N3PK N3PK N3 N3PK N3 N1PK N1PK N1PK NI N3 NI NI N1PK NI NO NO NO NOPK Lowest NOPK NOPK NOPK NO 1 c a l c u l a t e d based on s o i l d e p l e t i o n . 2 c a l c u l a t e d based on above-ground biomass i n c r e m e n t . 108 CHAPTER 5 DISCUSSION EFFECTS OF REPEATED FERTILIZATION ON NITROGEN MINERALIZATION AND UPTAKE Repeated a p p l i c a t i o n s o f b o t h n i t r o g e n and "PK" f e r t i l i z e r have i n c r e a s e d ne t m i n e r a l i z a t i o n and u p t a k e , b u t no t s i g n i f i c a n t l y (Tab le 5, F i g u r e 9 ) . N i t r o g e n f e r t i l i z a t i o n has s i g n i f i c a n t l y i n c r e a s e d the i n o r g a n i c N p o o l s i n the s o i l . One N3PK p l o t (24) e x p e r i e n c e d ne t i m m o b i l i z a t i o n t h r o u g h o u t the growing season which may be t h e r e a s o n t h a t s i g n i f i c a n t d i f f e r e n c e s i n m i n e r a l i z a t i o n were not f o u n d . T h i s p l o t had a l o t o f s l a s h on the f o r e s t f l o o r , p r o v i d i n g an abundant s o u r c e o f c a r b o n which can r e s u l t i n i m m o b i l i z a t i o n o f f e r t i l i z e r N ( C a r l y l e , 1986; R a i s o n e t a l . . 1989) . However, s i n c e t h i s s l a s h remains r e l a t i v e l y i n t a c t , i t would be e x c l u d e d from i n s i d e t h e c o r e s . D e s p i t e t h i s , i n c r e a s e d net m i n e r a l i z a t i o n g e n e r a l l y o c c u r r e d on the f e r t i l i z e d p l o t s even though they had been r e c e n t l y f e r t i l i z e d w i t h i n o r g a n i c f e r t i l i z e r (ammonium n i t r a t e ) . I n o r g a n i c f e r t i l i z e r N can be r a p i d l y i m m o b i l i z e d i n t o m i c r o b i a l b iomass . Even d u r i n g the p e r i o d immedia te ly 109 f o l l o w i n g f e r t i l i z a t i o n , ne t m i n e r a l i z a t i o n o c c u r r e d on a l l t h e f e r t i l i z e d p l o t s . T h i s i s i n c o n t r a s t t o t h e f i n d i n g s o f R a i s o n e t a l . (1989) who found a marked and s u s t a i n e d ne t i m m o b i l i z a t i o n o f f e r t i l i z e r N H 4 - N d u r i n g the i n i t i a l 135 days a f t e r N f e r t i l i z e r a d d i t i o n w h i l e ne t m i n e r a l i z a t i o n was o c c u r r i n g on u n f e r t i l i z e d s o i l . However, the R a i s o n e t a l . s t u d y o n l y d e a l t w i t h s i n g l e a p p l i c a t i o n s o f n u t r i e n t s . Net m i n e r a l i z a t i o n g e n e r a l l y d i d no t r e v e a l any d e f i n i t e t r e n d s o v e r the growing season w i t h t h e e x c e p t i o n o f t h e N3 t r e a t m e n t s which e x p e r i e n c e d net i m m o b i l i z a t i o n d u r i n g August and September (Tab le 4 , F i g u r e s 6 - 8 ) . An e x p l a n a t i o n f o r t h e ne t i m m o b i l i z a t i o n w i t h these t r e a t m e n t s and not o t h e r s l a t e i n the season has not been f o u n d . S i n c e i t appears t h a t m i n e r a l i z a t i o n has been i n c r e a s e d by f e r t i l i z a t i o n , t r e e growth re sponses ( i n c r e a s e d uptake) o b s e r v e d a r e l i k e l y the r e s u l t o f b o t h t e m p o r a r i l y e l e v a t e d i n o r g a n i c N c o n c e n t r a t i o n s i n the s o i l due d i r e c t l y t o N f e r t i l i z e r a p p l i c a t i o n and i n c r e a s e d m i n e r a l i z a t i o n , i n d i r e c t l y caused by f e r t i l i z a t i o n . T h i s i s s u p p o r t e d by two main o b s e r v a t i o n s . F i r s t , uptake was g e n e r a l l y h i g h e r than m i n e r a l i z a t i o n , i n d i c a t i n g some dependence o f the t r e e s on the i n c r e a s e d a v a i l a b l e N i n t h e s o i l as a r e s u l t o f f e r t i l i z a t i o n . Second, ne t N m i n e r a l i z a t i o n d i d not c o r r e l a t e w e l l w i t h n e e d l e N c o n t e n t i n t h e f o l i a g e (Tab le 15) which s h o u l d be a r e l a t i v e i n d i c a t o r o f uptake ( A x e l s s o n , 1983; A g r e n , 1983; R a i s o n e t a l . . 1989) . N uptake c a l c u l a t e d from s o i l d e p l e t i o n a l s o d i d not 110 c o r r e l a t e w e l l w i t h f o l i a r N c o n t e n t . P o s s i b l e r easons f o r t h i s i n c l u d e v a r y i n g need le number o f c u r r e n t y e a r s f o l i a g e between t r e a t m e n t s and h i g h e r r e l a t i v e N t r a n s l o c a t i o n on p l o t s w i t h lower N a v a i l a b i l i t y , thus m a i n t a i n i n g h i g h N c o n c e n t r a t i o n s i n c u r r e n t y e a r s f o l i a g e d e s p i t e low N a v a i l a b i l i t y ( T u r n e r , 1977; Gosz , 1981; S t a a f a n d B e r g , 1981) . Even though the importance o f b i o c h e m i c a l c y c l i n g i s no t w e l l e s t a b l i s h e d i n s a p l i n g - s i z e d t r e e s , a 5 t o 10 y e a r growth response would be expec ted as a r e s u l t o f N c o n s e r v a t i o n and i n c r e a s e d a b s o l u t e r e d i s t r i b u t i o n o f N w i t h i n t h e t r e e s even w i t h o u t i n c r e a s e d m i n e r a l i z a t i o n ( M i l l e r , 1981; Johnson and T o d d , 1988) . I n c r e a s e d m i n e r a l i z a t i o n , on t h e o t h e r hand , r e p r e s e n t s more o f a permanent i n c r e a s e i n s i t e q u a l i t y as opposed t o a s h o r t term i n c r e a s e i n c r o p p r o d u c t i o n . S i m i l a r l y , M i l l e r (1981) s t a t e d t h a t h e a v i l y f e r t i l i z e d C o r s i c a n p i n e e s t a b l i s h e d a new growth p a t t e r n c o n s i s t e n t l y f a s t e r t h a n i n o t h e r t r e a t m e n t s . The mechanisms by which f e r t i l i z a t i o n has i n c r e a s e d m i n e r a l i z a t i o n have not been i n v e s t i g a t e d i n t h i s s t u d y , but some p o s s i b i l i t i e s a r e d i s c u s s e d below. F i r s t , i n c r e a s e d N a v a i l a b i l i t y can r e s u l t i n l e s s r e l a t i v e i n t e r n a l r e d i s t r i b u t i o n b e f o r e l e a f f a l l (but i n c r e a s e d a b s o l u t e N w i t h d r a w e l from a b s c i s s i n g t i s s u e s ) and d e c r e a s e d l e a f p e r s i s t e n c e (Gosz, 1981; C a r l y l e , 1986) . T h i s can l e a d t o i n c r e a s e d l i t t e r f a l l w i t h a h i g h e r N c o n c e n t r a t i o n , r e s u l t i n g i n h i g h e r d e c o m p o s i t i o n and m i n e r a l i z a t i o n r a t e s ( M i l l e r , 1981; I n g e s t a d , 1987) , o r a t I l l l e a s t enhanced N r e l e a s e from l i t t e r (Berg e t a l . . 1987) . The t r e e s have responded t o i n c r e a s e d n u t r i e n t a d d i t i o n s by s i g n i f i c a n t l y i n c r e a s i n g need le s i z e (wi th the e x c e p t i o n o f the N3 t r e a t m e n t - see page 115 f o r d e s c r i p t i o n o f n u t r i e n t imbalance i n N3 trea tment ) and N c o n c e n t r a t i o n . However, i t i s u n l i k e l y t h a t f e r t i l i z a t i o n would r e s u l t i n i n c r e a s e d f o l i a g e l o s s u n t i l f o l l o w i n g crown c l o s u r e ( M i l l e r and M i l l e r , 1976) . As w e l l , mean m i n e r a l i z a t i o n r a t e s a r e e l e v a t e d on the N3 p l o t s d e s p i t e the s m a l l n e e d l e s i z e o f the N3 t r e e s . However, i n c r e a s e d g r a s s v i g o r and t u r n o v e r on the f e r t i l i z e d p l o t s ( F i g u r e 20) c o u l d produce e f f e c t s s i m i l a r t o i n c r e a s e d f o l i a g e b iomass . Second, i n c r e a s e d N a v a i l a b i l i t y can a l s o r e s u l t i n i n c r e a s e d f i n e r o o t p r o d u c t i o n even i f the a l l o c a t i o n t o f i n e r o o t s g e n e r a l l y becomes p r o p o r t i o n a l l y l e s s ( N a d e l h o f f e r e t  a l . . 1985; K u r t z and Kimmins, 1987) . F i n e r o o t t u r n o v e r can g r e a t l y a f f e c t m i n e r a l i z a t i o n r a t e s (Powers', 1984) . However, i n c r e a s e d f i n e r o o t biomass does no t n e c e s s a r i l y i m p l y i n c r e a s e d t u r n o v e r r a t e s and K u r t z and Kimmins s t a t e d t h a t compar i sons w i t h i n one s p e c i e s have shown a g r e a t e r f i n e r o o t b iomass on p o o r and d r y s i t e s t h a n on r i c h and m o i s t s i t e s . However, i n c r e a s e d g r a s s p r o d u c t i o n on the f e r t i l i z e d p l o t s has p r o b a b l y had a major impact on t h i s . The most l i k e l y r e a s o n f o r the i n c r e a s e i n ne t m i n e r a l i z a t i o n i s the r e m i n e r a l i z a t i o n o f f e r t i l i z e r N which was i m m o b i l i z e d f o l l o w i n g e a r l i e r a p p l i c a t i o n s . F e r t i l i z e r N can be r a p i d l y i m m o b i l i z e d i n m i c r o b i a l b iomass , p a r t i c u l a r l y 112 i f r e a d i l y a v a i l a b l e s o u r c e s o f C a r e a v a i l a b l e t o s u s t a i n h i g h m i c r o b i a l a c t i v i t y ( C a r l y l e , 1986) . R a i s o n e t a l . (1989) found t h a t p a r t o f i m m o b i l i z e d f e r t i l i z e r N remained i n m i n e r a l i z a b l e o r g a n i c forms , which was r e f l e c t e d i n s i g n i f i c a n t l y i n c r e a s e d ne t m i n e r a l i z a t i o n r a t e s i n f e r t i l i z e d p l o t s a f t e r an i n i t i a l p e r i o d o f i m m o b i l i z a t i o n . S i m i l a r l y , M i l l e r (1981) i n d i c a t e d t h a t i f the amount o f f e r t i l i z e r n u t r i e n t r e t a i n e d i s l a r g e i n r e l a t i o n t o t h e o r i g i n a l s i t e c a p i t a l , l o n g term i n c r e a s e s i n m i n e r a l i z a t i o n can r e s u l t . He based t h i s on t h e assumpt ion t h a t t h e i m m o b i l i z e d f e r t i l i z e r N r e m i n e r a l i z e s a t the same r a t e as the n a t i v e o r g a n i c N , but o t h e r s have i n d i c a t e d t h a t i m m o b i l i z e d f e r t i l i z e r N may be i n a s l i g h t l y more a c t i v e p o o l t h a n n a t i v e o r g a n i c N ( W i l l i a m s , 1972; Hauck, 1981) . Based on c a l c u l a t e d mean r a t e s , ne t m i n e r a l i z a t i o n i n t h e N3PK t r e a t m e n t has i n c r e a s e d a p p r o x i m a t e l y 84 kg N p e r h e c t a r e over the c o n t r o l (Tab le 5 ) . Assuming 50 p e r c e n t (see M i l l e r , 1981) o f the accumulated a p p l i c a t i o n o f 525 kg N p e r h e c t a r e remains i m m o b i l i z e d i n s i t e o r g a n i c m a t t e r , t h i s means t h a t a p p r o x i m a t e l y 32 p e r c e n t o f i m m o b i l i z e d N f e r t i l i z e r i s r e m i n e r a l i z i n g a n n u a l l y which i s c o n s i d e r a b l y h i g h e r than the t y p i c a l v a l u e f o r n a t i v e N ( W i l l i a m s , 1972; Hauck, 1981; M i l l e r , 1981; B i n k l e y and H a r t , 1989) . T h i s e s t i m a t e would have t o be v e r i f i e d by measur ing t o t a l N accumulated on the s i t e f o r each t r e a t m e n t . R e s e a r c h has a l s o shown t h a t c h e m i c a l f e r t i l i z e r s can have an e f f e c t on n u t r i e n t t u r n o v e r r a t e s o f humus (Roberge F i g u r e 20. P i n e g r a s s p r o d u c t i o n i n c o n t r o l (a) a n d N3+PK (b) p l o t s . 114 and Knowles , 1966; Mahendrappa, 1978) - a " p r i m i n g " e f f e c t o f f e r t i l i z e r N on n a t i v e N ( B a l l a r d , 1987) . S i m i l a r l y , W i l l i a m s (1972) i n d i c a t e d t h a t added n u t r i e n t s can s t i m u l a t e m i c r o b i a l a c t i v i t y d i r e c t l y by a d d i n g n u t r i e n t s t h a t a r e i n s h o r t s u p p l y , o r i n d i r e c t l y by a m e l i o r a t i n g t h e i r env i ronment . Thus , the n a t i v e N i s p r o b a b l y r e c y c l i n g a t a f a s t e r r a t e . T h i s c o u l d be the mechanism by which 1 1 PK" f e r t i l i z e r has i n c r e a s e d ne t m i n e r a l i z a t i o n . I n c r e a s e d phosphorus (P) c o n c e n t r a t i o n i n the f o r e s t f l o o r , r e s u l t i n g i n a h i g h e r C : P r a t i o , can i n c r e a s e N m i n e r a l i z a t i o n ( P a s t o r e t a l . . 1984; Kumi , 1984) . N i t r o g e n a v a i l a b i l i t y can be improved by P a p p l i c a t i o n , but the l i n k a g e between N and P i s not v e r y w e l l u n d e r s t o o d (Kumi, 1984) . In a j a c k p i n e optimum n u t r i t i o n exper iment Kumi found t h a t the a d d i t i o n o f PK appeared t o i n c r e a s e t o t a l N by more t h a n 100 k g . S i m i l a r l y , PK may have a l s o r e s u l t e d i n a b u i l d up o f the f o r e s t f l o o r by i n c r e a s i n g g r a s s p r o d u c t i o n , but t h i s has no t been v e r i f i e d . Needle we ight has been s i g n i f i c a n t l y i n c r e a s e d by "PK" i n 1988 (Tab le 10, F i g u r e 15b) , but a s i m i l a r i n c r e a s e p r o d u c e d by "PK" was no t no ted i n e a r l i e r y e a r s (Webber, 1985; E s t l i n , 1988) . The a d d i t i o n o f "PK" has a l s o s i g n i f i c a n t l y i n c r e a s e d m o i s t u r e c o n t e n t s (Tab le 12) , p o s s i b l y by m a i n t a i n i n g a h i g h e r p o t a s s i u m (K) c o n c e n t r a t i o n i n t h e f o l i a g e , which p l a y s an i m p o r t a n t r o l e i n s t o m a t a l r e g u l a t i o n ( I n g e s t a d , 1979; H i l l e r d a l - H a g s t r o m e r e t a l . . 1987) . However, 1988 f o l i a r a n a l y s i s d i d not i n d i c a t e an i n c r e a s e d K c o n c e n t r a t i o n i n the "PK" f e r t i l i z e d p l o t s (Tab le 11 ) . 115 I n c r e a s e d m o i s t u r e c o n t e n t s c o u l d i n c r e a s e m i n e r a l i z a t i o n r a t e s by a f f e c t i n g m i c r o b i a l a c t i v i t y , but no r e l a t i o n s h i p was found between m i n e r a l i z a t i o n and s o i l wetness ( F i g u r e 16 ) . A p o s s i b l e e x p l a n a t i o n f o r t h i s c o u l d be t h e i n t e r a c t i o n o f m o i s t u r e and t e m p e r a t u r e , w i t h i n c r e a s e d m i n e r a l i z a t i o n due t o an i n c r e a s e i n t e m p e r a t u r e o f f s e t t i n g t h e e f f e c t s o f r educed m o i s t u r e (Theodorou and Bowen, 1983) . S i m i l a r l y , P a s t o r e t a l . (1984) found t h a t m i n e r a l i z a t i o n was not c o r r e l a t e d w i t h s o i l m o i s t u r e c o n t e n t , b u t s o i l m o i s t u r e c o n t e n t s were h i g h ( g r e a t e r t h a n 50 p e r c e n t by mass) i n t h e i r s t u d y . However, Matson and V i t o u s e k (1981) found m o i s t u r e c o n t e n t s between 10 and 3 0 p e r c e n t t o be l i m i t i n g t o m i c r o o r g a n i s m s i n m i n e r a l s o i l s and F i s h e r ( i n l i t t . f 20 Dec. 1988) found t h a t m o i s t u r e l i m i t e d n i t r o g e n m i n e r a l i z a t i o n i n a l o d g e p o l e p i n e s t a n d . The i n c r e a s e d m i n e r a l i z a t i o n observed i n t h i s s t u d y would appear t o i n d i c a t e t h a t m o i s t u r e does not l i m i t m i n e r a l i z a t i o n i n x e r i c s i t e s i n the montane s p r u c e zone . I n g e s t a d (1987) p r e s e n t e d a model i n which t h e n u t r i e n t f l u x i s d i v i d e d i n t o two p a r t s , one d e l i v e r e d by m i n e r a l i z a t i o n and the o t h e r by f e r t i l i z a t i o n . The model can be used t o a n a l y s e t h e dynamic e f f e c t s o f b o t h n u t r i e n t s o u r c e s as w e l l as t h e i n t e r a c t i o n between f e r t i l i z a t i o n and t h e n a t u r a l n u t r i e n t f low upon the f e r t i l i t y l e v e l o f the ecosys tem. A l t h o u g h t h i s model i s based on c o n t i n u o u s n u t r i e n t a d d i t i o n i n f e r t i g a t i o n ( f e r t i l i z e r a p p l i e d i n l i q u i d form) exper iments which improve the s o i l m o i s t u r e reg ime , s i m i l a r 116 p r i n c i p l e s s h o u l d a p p l y i n t h i s e x p e r i m e n t . U s i n g N3PK uptake as an uptake a s s o c i a t e d w i t h a d e s i r a b l e a t t a i n a b l e y i e l d , i t s h o u l d be p o s s i b l e t o de termine t h e f e r t i l i z e r r e q u i r e m e n t f o r each t r e a t m e n t t o meet t h i s need ( S t a n f o r d , 1980; I n g e s t a d , 1987) . To o b t a i n t h i s uptake demand, a b a l a n c e d f e r t i l i z e r a p p l i c a t i o n would be r e q u i r e d t o supplement t h e N a p p l i c a t i o n ( I n g e s t a d , 1987) . A l s o , the uptake demand c o u l d not immedia te ly be r e a l i z e d f o r some o f t h e t r e a t m e n t s due t o the s m a l l e r average s i z e o f t h e t r e e s (Holmen e t a l . . 1976) . I n g e s t a d (1987) i n d i c a t e d t h a t f e r t i l i z e r a d d i t i o n s s h o u l d be low a t f i r s t t o a v o i d l o s s e s because o f t h e low uptake c a p a c i t y o f the t r e e s . The c a l c u l a t e d uptake has i n c r e a s e d t o a p p r o x i m a t e l y 185 kg N p e r h e c t a r e f o r the N3PK t r e a t m e n t ( T a b l e 5) w h i l e annua l m i n e r a l i z a t i o n has r e a c h e d a p p r o x i m a t e l y 95 kg N p e r h a , a p p r o x i m a t e l y h a l f o f the uptake demand. The d e f i c i t o f 90 kg N p e r ha has been s u p p l i e d by i n i t i a l a v a i l a b l e N i n the s o i l , t h e r e s u l t o f the s p r i n g 1988 f e r t i l i z a t i o n . Based on t h i s , a p p r o x i m a t e l y 90 kg N p e r ha must be added i n 1989 i n t h i s t r e a t m e n t t o make up the d e f i c i t . T h u s , an i n c r e a s e i n m i n e r a l i z a t i o n has r e s u l t e d i n a s m a l l e r r e q u i r e m e n t f o r f e r t i l i z e r a d d i t i o n . As l i t t e r f a l l becomes more prominent i n the N3PK p l o t s , m i n e r a l i z a t i o n s h o u l d i n c r e a s e even f u r t h e r , r e s u l t i n g i n s m a l l e r f e r t i l i z e r r e q u i r e m e n t s u n t i l the uptake demand can be t o t a l l y s u p p l i e d by m i n e r a l i z a t i o n ( I n g e s t a d , 1987). T h i s appears t o f i t the t h e o r y b e h i n d optimum n u t r i t i o n s t a t u s which i s t h a t t h e whole 117 s t a n d - s o i l system becomes s a t u r a t e d w i t h n u t r i e n t s w i t h i n 10 y e a r s and t h e system t h e n c y c l e s the n u t r i e n t s n e c e s s a r y f o r h i g h p r o d u c t i v i t y throughout the r o t a t i o n ( A x e l s s o n , 1985). These uptake and m i n e r a l i z a t i o n r a t e s r e p r e s e n t s u b s t a n t i a l i n c r e a s e s o f 180 and 85 kg p e r h e c t a r e , r e s p e c t i v e l y , o v e r c o n t r o l f l u x e s , b u t s i g n i f i c a n t c o n c e n t r a t i o n s o f exchangeable N found i n t h e lower h o r i z o n s ( p a r t i c u l a r l y i n the c o n t r o l ) i n d i c a t e s t h a t the a c t u a l f l u x e s r e p o r t e d on an a r e a b a s i s a r e l i k e l y u n d e r e s t i m a t e d . Uptake f o r the N3 p l o t s was v e r y low compared t o ne t m i n e r a l i z a t i o n (Tab le 5, F i g u r e 9 ) . N3 p l o t s m a i n t a i n e d h i g h a v a i l a b l e N p o o l s throughout t h e growing season ( T a b l e 4 ) , i n d i c a t i n g t h a t s o i l N a v a i l a b i l i t y exceeded t r e e N r e q u i r e m e n t (Ra i son e t a l . , 1989) . I t appears t h a t t h e r e may have been an a c t i v e d i s c r i m i n a t i o n a g a i n s t N uptake e x e r t e d by t h e s e t r e e s i n response t o h i g h t i s s u e N c o n c e n t r a t i o n . Uptake by r o o t s i s m e t a b o l i c a l l y c o n t r o l l e d and a c t i v e feedback mechanisms can l i m i t f u r t h e r N uptake when h i g h l e v e l s o f N accumulate i n the p l a n t (Ra i son e t a l . , 1989) . In f a c t , low growth r a t e s ( E s t l i n , 1988) , deformed growth and a g e n e r a l poor v i g o r o f N3 t r e e s i n d i c a t e t h a t t h e r e i s a s e v e r e n u t r i e n t imbalance due t o t h e heavy N a p p l i c a t i o n s . T h i s may be due t o h i g h amino a c i d and n i t r a t e c o n c e n t r a t i o n s and low l i g n i n c o n c e n t r a t i o n s , r e s u l t i n g i n weakly l i g n i f i e d shoots (Waring e t a l . , 1985) . The d i s t o r t i o n c o u l d a l s o be the r e s u l t o f boron d e f i c i e n c y i n d u c e d by n i t r o g e n f e r t i l i z a t i o n (Mannerkoski and Miyazawa, 1983; 118 M o l l e r , 1983; A r o n s s o n , 1983; B r o c k l e y and Y o l e , 1985, B r o c k l e y , 1989) , but t h i s was no t s u b s t a n t i a t e d by 1988 f o l i a r a n a l y s i s ( T a b l e 11) s i n c e b o r o n c o n c e n t r a t i o n s were w e l l above the d e f i c i e n c y l e v e l o f 10 ppm sugges ted by B a l l a r d and C a r t e r (1986) . Premature n e e d l e shed was a l s o no ted on some N 3 p l o t s . A r o n s s o n (1985) r e p o r t e d t h a t h i g h a p p l i c a t i o n s o f N promoted premature n e e d l e f a l l due t o an imbalance i n t h e N:P r a t i o i n n e e d l e s b u t N 3 and N3PK f o l i a g e appear t o have s i m i l a r N:P r a t i o s ( T a b l e s 10 and 11) , a t l e a s t i n c u r r e n t y e a r s f o l i a g e . S o i l N H 4 - N p o o l s were g e n e r a l l y l a r g e r and more v a r i a b l e t h a n N O 3 - N p o o l s w i t h the e x c e p t i o n o f t h e c o n t r o l p l o t s ( T a b l e 7 ) . N i t r i f i c a t i o n and n i t r a t e uptake as a p r o p o r t i o n o f t o t a l f l u x r a t e s were g r e a t e s t on t h e c o n t r o l p l o t s , but t h e a b s o l u t e v a l u e s were much l e s s t h a n f o r t h e o t h e r t r e a t m e n t s ( F i g u r e s 10 -11) . T h u s , i t appears as though t h e s e N d e f i c i e n t s i t e s may n i t r i f y s i g n i f i c a n t l y d e s p i t e the low c o n c e n t r a t i o n o f ammonium-N i n the s o i l . I n c o n t r a s t , R a i s o n e t a l . (1989) and o t h e r s have found n i t r i f i c a t i o n t o be n e g l i g i b l e i n u n f e r t i l i z e d c o n i f e r o u s f o r e s t s and s i g n i f i c a n t l y i n c r e a s e d by f e r t i l i z a t i o n (Johnson and T o d d , 1988) . N i t r i f i c a t i o n was h i g h e s t i n t h e N3 t r e a t m e n t w h i l e n i t r a t e - N uptake was v e r y low. T r e n d s may i n d i c a t e t h a t NO3 - N was p r e f e r r e d by t r e e s where N i s d e f i c i e n t w h i l e N H 4 - N was p r e f e r r e d where N was more p l e n t i f u l . N a d e l h o f f e r e t a l . (1984) s t a t e d t h a t l o d g e p o l e p i n e appears t o grow b e s t w i t h ammonium which would e x p l a i n t h e i r apparent p r e f e r e n c e f o r 119 ammonium a t h i g h N a v a i l a b i l i t i e s , w h i l e t h e t r e e s may be more o p p o r t u n i s t i c i n o b t a i n i n g a v a i l a b l e N where N i s l i m i t i n g ( C a r l y l e , 1986) . N i t r a t e l o s s e s as a p e r c e n t a g e o f t o t a l l o s s e s v a r i e d s u b s t a n t i a l l y , b u t i n g e n e r a l t h e y were n e g l i g i b l e ( T a b l e 6 ) . However, as ment ioned e a r l i e r , t h e v a l i d i t y o f t h e l o s s c a l c u l a t i o n s i s d e b a t a b l e because o f the f l u c t u a t i o n o f t h e v a l u e s around zero and r e q u i r e s f u r t h e r s t u d y . Based on the d e c r e a s e i n i n o r g a n i c c o n c e n t r a t i o n w i t h depth ( F i g u r e 12) i t appears as though most o f t h e a v a i l a b l e f e r t i l i z e r N has remained i n the s u r f a c e h o r i z o n s . S i m i l a r l y , He i lman and G e s s e l (1963) s t a t e d t h a t t h e c o n c e n t r a t i o n o f N i n the 0-15 cm l a y e r was s i g n i f i c a n t l y h i g h e r on f e r t i l i z e d p l o t s w i t h t h e f e r t i l i z e r h a v i n g l i t t l e e f f e c t below 3 0 cm. However, h i g h e r c o n c e n t r a t i o n s o f i n o r g a n i c N a t t h e lower depth i n t h e f e r t i l i z e d p l o t s t h a n t h e c o n t r o l p l o t s i n d i c a t e s some downward movement. The p r o p o r t i o n o f NO3-N i n c r e a s e d s l i g h t l y w i t h d e p t h , i n d i c a t i n g more downward movement o f n i t r a t e t h a n ammonium. GRASS AND MOISTURE LIMITATIONS TO FERTILIZER RESPONSE Because m o i s t u r e appears t o l i m i t t h e p o t e n t i a l p r o d u c t i v i t y o f ecosystems (Bevege, 1981; Kimmins e t a l . , 1989) , growth response t o f e r t i l i z a t i o n i s p r o b a b l y l e s s on t h i s x e r i c s i t e t h a n i t would be on a more mes ic s i t e . Most s t u d i e s i n d i c a t e t h a t p i n e g r a s s responds w e l l t o f e r t i l i z a t i o n (Freyman and Ryswyk, 1969; C o c h r a n , 1979; 120 N o r d s t r o m , 1984; e t c ) . T h e r e f o r e , f o l l o w i n g f e r t i l i z a t i o n more v i g o r o u s g r a s s ( F i g u r e 20) would p r o b a b l y use more a v a i l a b l e m o i s t u r e , f u r t h e r r e d u c i n g s o i l m o i s t u r e c o n t e n t , and t h e r e f o r e reduce t r e e growth p o t e n t i a l . Even though f e r t i l i z a t i o n may i n c r e a s e water use e f f i c i e n c y i n t r e e s ( H i l l e r d a l - H a g s t r o m e r e t a l . , 1982) , an i n c r e a s e i n g r a s s c o m p e t i t i o n can t h e r e f o r e be expec ted t o reduce a c t u a l t r e e growth . The e f f e c t s o f g r a s s on N m i n e r a l i z a t i o n have not been a c t i v e l y i n v e s t i g a t e d i n t h i s s t u d y , but two g e n e r a l i z a t i o n s can be made. F i r s t , i f i n c r e a s e d g r a s s v i g o r reduces s o i l wetness , i t c o u l d have a n e g a t i v e e f f e c t on m i n e r a l i z a t i o n s i n c e m o i s t u r e i s thought t o l i m i t m i n e r a l i z a t i o n (Matson and V i t o u s e k , 1981; Theodorou and Bowen, 1983) . T h i s was not s u b s t a n t i a t e d by m i n e r a l i z a t i o n - s o i l wetness r e l a t i o n s h i p s o b t a i n e d i n t h i s s tudy ( F i g u r e 16) . Second, as ment ioned e a r l i e r , i n c r e a s e d g r a s s v i g o r c o u l d r e s u l t i n a h i g h e r annual t u r n o v e r o f g r a s s and f i n e r o o t s , a b u i l d up o f the f o r e s t f l o o r , and t h e r e f o r e i n c r e a s e d m i n e r a l i z a t i o n r a t e s . T h u s , d e s p i t e compet ing f o r m o i s t u r e w i t h t r e e s and s o i l m i c r o f l o r a , g r a s s re sponse t o f e r t i l i z a t i o n has p r o b a b l y had a b e n e f i c i a l e f f e c t on n u t r i e n t r e t e n t i o n , m o i s t u r e h o l d i n g c a p a c i t y , and N m i n e r a l i z a t i o n . I t i s a l s o l i k e l y t h a t g r a s s c o m p e t i t i o n w i l l be l e s s i m p o r t a n t f o l l o w i n g crown c l o s u r e by which t i m e t r e e r o o t s s h o u l d be d e v e l o p e d s u f f i c i e n t l y t o reduce i t s e f f e c t s (Nordstrom, 1984) . Crown c l o s u r e s h o u l d be r e a c h e d sooner on t h e f e r t i l i z e d p l o t s . 121 EVALUATION OF SEQUENTIAL CORING TECHNIQUE The s e q u e n t i a l c o r i n g i n s i t u t e c h n i q u e r e s u l t s i n l e s s s o i l d i s t u r b a n c e t h a n o t h e r f i e l d and l a b t e c h n i q u e s used f o r a s s e s s i n g N a v a i l a b i l i t y ; t h u s i t s h o u l d t h e o r e t i c a l l y a c c u r a t e l y r e p r e s e n t N f l u x e s as they a r e o c c u r r i n g i n t h e s u r r o u n d i n g u n d i s t u r b e d s o i l . However, because o f t h e methodology used w i t h the t e c h n i q u e , t h e r e a r e a l s o some drawbacks i n v o l v e d i n i t s u s e . S o i l wetness measurements c o n f i r m e d t h a t m o i s t u r e c o n t e n t s i n s o i l s i n c u b a t e d i n tubes f l u c t u a t e d i n re sponse t o l o c a l c o n d i t i o n s . Even though s o i l wetness was c o n s i s t e n t l y h i g h e r i n t h e i n c u b a t e d c o r e s t h a n i n the b u l k s o i l ( e x c e p t i n g t h e c o v e r e d c o r e s i n the f i n a l p e r i o d ) , the changes i n the i n c u b a t e d s o i l s g e n e r a l l y r e f l e c t e d changes i n the s u r r o u n d i n g b u l k s o i l ( F i g u r e 17) . H a r t and F i r e s t o n e (1989) found t h a t s o i l s i n c u b a t e d i n I E R - c o r e s had s i g n i f i c a n t l y h i g h e r m o i s t u r e c o n t e n t s t h a n b u l k s o i l s , and d i d not r e f l e c t changes i n b u l k s o i l . They s p e c u l a t e d t h a t t h i s was because o f t h e c o a r s e r t e x t u r e o f r e s i n r e l a t i v e t o t h e s o i l around i t . T h i s would impede water movement because o f the t e x t u r a l d i s c o n t i n u i t y between t h e r e s i n and s o i l . T h i s i s not a problem w i t h t h e s e q u e n t i a l c o r i n g t e c h n i q u e because the c o n t a c t between the i n c u b a t e d and b u l k s o i l i s no t b r o k e n . The wide d i f f e r e n c e i n s o i l m o i s t u r e c o n t e n t i n t h e 122 c o v e r e d c o r e i n September c o u l d i n d i c a t e t h a t c o v e r e d c o r e s may not be a b l e t o a c c u r a t e l y r e f l e c t i n c r e a s e s i n s o i l m o i s t u r e i n t h e s u r r o u n d i n g s o i l . T h u s , s o i l i n open c o r e s may b e t t e r r e f l e c t i n c r e a s e s i n s o i l m o i s t u r e due t o r a i n f a l l t h a n s o i l i n c o v e r e d c o r e s . However, because m o i s t u r e and n u t r i e n t s a r e a b l e t o f low f r e e l y between the s o i l i n c u b a t e d i n t h e c o r e s and b u l k s o i l , l e a c h i n g can o c c u r i n t h e open c o r e s and t h e r e f o r e must be e s t i m a t e d . D e s p i t e t h i s , the assumpt ion t h a t l o s s e s a r e s m a l l compared t o u p t a k e , upon which t h i s method i s b a s e d , appeared t o be met. T h i s i s s u p p o r t e d by s e v e r a l f a c t o r s . F i r s t , c a l c u l a t e d l e a c h i n g l o s s e s f l u c t u a t e d w i d e l y around z e r o ( T a b l e s 4 and 5) and a p a i r e d d i f f e r e n c e t e s t r e v e a l e d no s i g n i f i c a n t d i f f e r e n c e s i n i n o r g a n i c N c o n c e n t r a t i o n s between t h e open and c o v e r e d t u b e s . T h u s , the f l u c t u a t i o n s a r e p r o b a b l y t h e r e s u l t o f s a m p l i n g e r r o r , e s p e c i a l l y s i n c e n e g a t i v e l o s s e s have no b i o l o g i c a l meaning. Second, any c a l c u l a t e d l o s s e s would r e p r e s e n t a maximum because o f no uptake from t h e i n c u b a t e d s o i l s (Raison e t a l . . 1987) . T h i r d , d e s p i t e m a i n t a i n i n g h i g h i n o r g a n i c N c o n c e n t r a t i o n s i n the s o i l due t o low u p t a k e , c a l c u l a t e d l o s s e s on N3 p l o t s were n e g a t i v e ( T a b l e s 4 and 5 ) . F o u r t h , even though l a r g e q u a n t i t i e s o f N have been added i n t h i s e x p e r i m e n t , t h e t o t a l a p p l i c a t i o n has been s p r e a d o v e r seven y e a r s . T h u s , where r a i n f a l l i s low i t may be s a t i s f a c t o r y t o a v o i d u s i n g c o v e r e d c o r e s t o save on d u p l i c a t i o n o f work 123 ( R a i s o n , i n l i t t . 19 J u l y , 1988) . However, t h i s c o u l d cause problems on s i t e s r e c i e v i n g more r a i n f a l l , p a r t i c u l a r l y i n young , h e a v i l y f e r t i l i z e d s tands and i t i s p o s s i b l e t h a t s i g n i f i c a n t l e a c h i n g c o u l d o c c u r e a r l y i n t h e s p r i n g when the s o i l i s m o i s t and uptake i s low. Time c o u l d a l s o be saved by not u s i n g open c o r e s as w e l l ( B i n k l e y and H a r t , 1989) , but t h i s c o u l d o v e r e s t i m a t e uptake i f l e a c h i n g l o s s e s were l a r g e . S e q u e n t i a l c o r i n g a l s o measures s e v e r a l p r o c e s s e s s i m u l t a n e o u s l y , g i v i n g i n f o r m a t i o n on r e l a t i v e n i t r i f i c a t i o n and n i t r a t e - N uptake r a t e s as w e l l as a m m o n i f i c a t i o n and ammonium-N uptake r a t e s ( F i g u r e s 10 -11) . I f t h i s i n f o r m a t i o n i s r e l i a b l e , the t e c h n i q u e can be used t o enhance our knowledge o f p l a n t p r e f e r e n c e f o r e i t h e r ammonium o r n i t r a t e as w e l l as c o n d i t i o n s c o n d u c i v e t o n i t r i f i c a t i o n . The t e c h n i q u e i s u s e f u l f o r d e t e r m i n i n g a rough b a l a n c e shee t between m i n e r a l i z a t i o n and u p t a k e . I t can be used t o de termine what p o r t i o n o f uptake demand can be met by m i n e r a l i z a t i o n , and t h u s how much f e r t i l i z e r i s r e q u i r e d t o make up the d e f i c i t between the uptake and m i n e r a l i z a t i o n (see e a r l i e r d i s c u s s i o n ) . As w i t h o t h e r f i e l d t e c h n i q u e s , d e t e r m i n i n g the a p p r o p r i a t e exposure p e r i o d can be p r o b l e m a t i c , e s p e c i a l l y when d e a l i n g w i t h d i f f e r e n t t r e a t m e n t s as i n t h i s s t u d y . S e v e r a l f a c t o r s need t o be c o n s i d e r e d when s e l e c t i n g an a p p r o p r i a t e p e r i o d f o r f i e l d exposure (Ra i son e t a l . , 1987) . F i r s t , t h e p e r i o d s h o u l d be s u f f i c i e n t l y l o n g t o produce a s i g n i f i c a n t change i n p o o l s o f m i n e r a l - N . T h i s 124 v a r i e d by t r e a t m e n t as f l u x e s v a r i e d by an o r d e r o f magnitude ( T a b l e s 4 and 5 ) . However, because p o o l s i z e s a l s o v a r i e d by an o r d e r o f magni tude , i t was p o s s i b l e t o d e t e c t s m a l l e r r a t e s o f m i n e r a l i z a t i o n and uptake i n c o n t r o l p l o t s . However, l o n g e r p e r i o d s o f exposure would have been more a p p r o p r i a t e f o r t h e NO t r e a t m e n t s . Second, the e f f e c t s o f r o o t s e v e r i n g and subsequent r o o t d e c o m p o s i t i o n need t o be m i n i m i z e d . These e f f e c t s were not examined i n t h i s s t u d y . T h i r d , t h e r e i s a need t o v a r y the l e n g t h o f exposure p e r i o d s t o c o i n c i d e w i t h major changes i n e n v i r o n m e n t a l v a r i a b l e s which a f f e c t m i n e r a l i z a t i o n r a t e s , such as s o i l w e t t i n g and d r y i n g p e r i o d s , o r f e r t i l i z e r a d d i t i o n s . In t h i s s t u d y , t h e f i r s t i n c u b a t i o n p e r i o d was s t a r t e d immed ia t e ly f o l l o w i n g f e r t i l i z a t i o n . I t might have been b e t t e r t o w a i t a few days u n t i l the f e r t i l i z e r had c o m p l e t e l y d i s s o l v e d o r have comple ted t h e f i r s t i n c u b a t i o n p e r i o d s h o r t l y f o l l o w i n g f e r t i l i z a t i o n . F o u r t h , the exposure p e r i o d s h o u l d no t be so l o n g t h a t a c c u m u l a t i o n o f ammonium may i n d u c e n i t r i f i c a t i o n i n systems t h a t do not n o r m a l l y n i t r i f y s i g n i f i c a n t l y . N i t r i f i c a t i o n o c c u r r e d i n t h i s s t u d y , but i t d i d not appear t o be i n d u c e d by a b n o r m a l l y h i g h ammonium c o n c e n t r a t i o n s i n t h e i n c u b a t e d s o i l s , s i n c e s i g n i f i c a n t q u a n t i t i e s o f n i t r a t e were found i n u n i n c u b a t e d s o i l (Tab le 6 ) . H a r t and F i r e s t o n e (1989) i n d i c a t e d t h a t i n c u b a t i o n p e r i o d s can be extended i f a method a l l o w s l e a c h i n g l o s s e s t o o c c u r , but t h i s may not be 125 a p p r o p r i a t e i n a r e a s o f low r a i n f a l l o r w i t h c o v e r e d c o r e s . T h i s may be an advantage o f r e s i n c o r e s o v e r c o v e r e d c o r e s ( B i n k l e y and H a r t , 1989) . A l t h o u g h t h i s s tudy o n l y d e a l t w i t h one s i t e , t h e r e s u l t s o b t a i n e d w i t h s e q u e n t i a l c o r i n g s h o u l d be d i r e c t l y comparable t o r e s u l t s o b t a i n e d from o t h e r s i t e s s i n c e a c t u a l f l u x e s a r e b e i n g c a l c u l a t e d (or a t l e a s t an e s t i m a t e o f them) as opposed t o indexes i n the case o f most o t h e r t e c h n i q u e s (Hart and F i r e s t o n e , 1989) . B i n k l e y and H a r t (1989) argued t h a t l a b o r a t o r y i n c u b a t i o n s p r o v i d e an o p p o r t u n i t y f o r compar i son a c r o s s s i t e s t h a t would not be p o s s i b l e under v a r y i n g c o n d i t i o n s , but t h i s i s o n l y u s e f u l f o r comparing s u b s t r a t e q u a l i t y , not a c t u a l m i n e r a l i z a t i o n r a t e s . L a b o r a t o r y i n c u b a t i o n s must be m o d i f i e d t o r e f l e c t f i e l d c o n d i t i o n s o r c a l i b r a t e d f o r s p e c i f i c f o r e s t t y p e s (Powers e t a l . . 1 9 7 8 ; Powers, 1984) . S t a n f o r d and Smith (1972) s t a t e d t h a t an i m p o r t a n t c r i t e r i o n o f t h e u s e f u l n e s s o f any method i s i t s a d a p t a b i l i t y f o r use under v a r i o u s s o i l c o n d i t i o n s . However, i t may be d i f f i c u l t t o f i n d s i g n i f i c a n t d i f f e r e n c e s i n f l u x e s between s i t e s because o f the huge s t a n d a r d e r r o r s which can o c c u r w i t h t h i s t e c h n i q u e ( T a b l e s 4 and 5, F i g u r e s 6-9 and 18) . W i t h i n - p l o t s t a n d a r d e r r o r can be c a l c u l a t e d as d e s c r i b e d on page 78 but cannot be e x p l i c i t l y i n c l u d e d i n a n a l y s i s o f v a r i a n c e ; t h i s i s i n c o r p o r a t e d i n the mean square e r r o r d u r i n g the ANOVA. Due t o h i g h s p a t i a l v a r i a b i l i t y i n i n o r g a n i c p o o l s f o l l o w i n g f e r t i l i z a t i o n (see T a b l e 8 f o r s a m p l i n g r e q u i r e m e n t s ) , s i g n i f i c a n t d i f f e r e n c e s 126 were no t found between the c a l c u l a t e d f l u x r a t e s . In t h i s r e g a r d g r o s s m i n e r a l i z a b l e N produced by a n a e r o b i c i n c u b a t i o n was s u p e r i o r . T h u s , s e q u e n t i a l c o r i n g may not be a p p r o p r i a t e f o r d e t e r m i n i n g s t a t i s t i c a l l y s i g n i f i c a n t t r e a t m e n t a f f e c t s w i t h i n a p a r t i c u l a r s i t e w i t h o u t v e r y i n t e n s i v e s a m p l i n g . Because e s t i m a t e s o f f l u x r a t e s a r e based on d i f f e r e n c e s between means, t h e t e c h n i q u e i s t oo l a b o r i o u s f o r r o u t i n e use as an index o f N a v a i l a b i l i t y f o r f e r t i l i z e r p r e s c r i p t i o n s . Woods e t a l . (1980) s t a t e d t h a t N f l u x e s a r e l i k e l y t o be l e s s v a r i a b l e than N p o o l s and t h a t management i n d u c e d changes i n t r a n s f e r r a t e s o f N may be e a s i e r t o d e t e c t t h a n changes i n N p o o l s . I f t h i s were the c a s e , i t would reduce t h e e f f o r t r e q u i r e d f o r t h i s t e c h n i q u e , b u t t h i s was not v e r i f i e d i n t h i s s t u d y . U s i n g u n d i s t u r b e d s o i l columns, i n c u b a t e d i n p o l y e t h y l e n e bags , N a d e l h o f f e r e t a l . (1984) found the d i f f e r e n c e s i n exchangeable ammonium-N between the s t a r t and f i n i s h o f t h e i n c u b a t i o n p e r i o d were a p p r o x i m a t e l y e q u a l t o changes i n ammonium-N i n i n c u b a t e d s o i l s , i n d i c a t i n g t h a t uptake o f ammonium d i d no t g r e a t l y a f f e c t ammonium-N p o o l s . T h i s was no t v e r i f i e d i n t h i s s tudy s i n c e ammonium uptake was s u b s t a n t i a l ( F i g u r e 11 ) . The c a l c u l a t i o n o f m i n e r a l i z a t i o n and uptake i s based on changes i n b u l k exchangeable v a l u e s ( F i g u r e 2 1 ) . T h u s , m i n e r a l i z a t i o n minus uptake e q u a l s t h e change i n b u l k exchangeable N (assuming z e r o l o s s e s ) . Some d e f i n i t e advantages o f the t e c h n i q u e over o t h e r t e c h n i q u e s l i s t e d by R a i s o n e t a l . (1987) were s u b s t a n t i a t e d 127 i n t h i s s t u d y . F i r s t , t h e r e appears t o be m i n i m a l s o i l d i s t u r b a n c e w i t h o n l y s l i g h t compact ion due t o f o r c i n g the PVC tubes i n t o the s o i l . S o i l s a r e not l i f t e d p r i o r t o i n c u b a t i o n as i n the c o r e - I E R and bagged c o r e methods (see N a d e l h o f f e r e t  a l . , 1984 and H a r t and F i r e s t o n e , 1989) . toil mineral-N itart (o) * n d (°) exposure (days) N m i n - Ne(t+l)c - N^,) - 16-7 • 9 N„ - N e( t +0 C - Nb( t +i) - (loues) „ 16-3-(2) - 11 Maximum leaching - N^t+i^ - N g ^ i ^ - 16-14- 2 F i g u r e 21. C a l c u l a t i o n o f N m i n e r a l i z a t i o n and uptake (•flosses) r e f l e c t changes i n t h e a v a i l a b l e N p o o l d u r i n g the i n c u b a t i o n p e r i o d (from R a i s o n e t a l . , 1987) . Second , o r g a n i c N p o o l s a r e r e p l e n i s h a b l e from i n p u t s o f o r g a n i c N from r o o t s i n c o v e r e d c o r e s , and from i n p u t s o f o r g a n i c N from b o t h r o o t s and above-ground l i t t e r i n open c o r e s . However, i t i s u n l i k e l y t h a t l o d g e p o l e p i n e f a s c i c l e s would f a l l i n t o the open c o r e s , o r a t l e a s t f a l l f l a t on the f o r e s t f l o o r w i t h i n the c o r e s . T h i r d , the method i s a p p l i c a b l e t o f o r e s t s o i l s i n which t h e r e i s a marked 128 development o f o r g a n i c m a t t e r g r a d i e n t s above and w i t h i n the s u r f a c e m i n e r a l s o i l h o r i z o n s . A few c l e a r d i s a d v a n t a g e s o f the t e c h n i q u e have become a p p a r e n t as w e l l . F i r s t , even though b o t h uptake and m i n e r a l i z a t i o n a r e e s t i m a t e d , these two f l u x e s a r e c a l c u l a t e d based on t h e same i n c u b a t e d v a l u e s . T h u s , t h e y a r e no t independent and c o r r e l a t i o n s between them can be m i s l e a d i n g . F o l l o w i n g h i g h N f e r t i l i z e r a p p l i c a t i o n s when m i n e r a l - N c o n c e n t r a t i o n s i n t h e s o i l a r e e l e v a t e d , uptake i s no t g e n e r a l l y dependent on m i n e r a l i z a t i o n (Johnson and T o d d , 1988; R a i s o n e t a l . , 1989) , but t h e two f l u x e s were s t i l l h i g h l y c o r r e l a t e d (Tab le 15) . Mean i n o r g a n i c N c o n c e n t r a t i o n and g r o s s m i n e r a l i z a b l e N de termined i n the l a b o r a t o r y were more h i g h l y c o r r e l a t e d t o need le N c o n t e n t t h a n e i t h e r N m i n e r a l i z a t i o n o r uptake ( c a l c u l a t e d from s o i l d e p l e t i o n ) . S i m i l a r l y , R a i s o n e t a l . (1989) d i d no t f i n d a good r e l a t i o n s h i p between annua l N uptake and the c o n c e n t r a t i o n o f N i n n e e d l e f a l l f o r the f i r s t y e a r f o l l o w i n g f e r t i l i z a t i o n , but t h e y o b t a i n e d b e t t e r c o r r e l a t i o n s i n l a t e r y e a r s . However, the t e c h n i q u e i s c a p a b l e o f d e t e c t i n g s i g n i f i c a n t d i f f e r e n c e s between m i n e r a l i z a t i o n and u p t a k e . F o r i n s t a n c e , N uptake was v e r y low f o r t h e N3 t r e a t m e n t , d e s p i t e h a v i n g h i g h m i n e r a l i z a t i o n r a t e s ( F i g u r e 9) ( a l s o see R a i s o n e t a l . . 1987) . Second, as w i t h o t h e r s i m i l a r t e c h n i q u e s , v a l u e s may not r e f l e c t a c t u a l uptake i f p l a n t s can take up c e r t a i n s o l u b l e forms o f o r g a n i c N , t h u s s h o r t - c i r c u i t i n g t h e 129 m i n e r a l i z a t i o n p r o c e s s (Van C l e v e and W h i t e , 1980; H e a l e t  a l . . 1982) . F i n a l l y , t h e method c o u l d pose problems i n s tony s o i l s o r s o i l s w i t h an abundance o f c o a r s e r o o t s which may make i n s e r t i o n o f the c o r e s i n t o the s o i l d i f f i c u l t . The l a c k o f c o r r e l a t i o n between t h e v a r i o u s N indexes ( T a b l e 15) p r o b a b l y stems from d i f f e r e n c e s i n the component o f t h e N c y c l e a s s e s s e d by each method (Hart and F i r e s t o n e , 1989) as w e l l as the t e m p o r a l and s p a t i a l v a r i a t i o n i n t h e s o i l . D e s p i t e not c o r r e l a t i n g s t r o n g l y w i t h t h e o t h e r i n d e x e s , ne t N m i n e r a l i z a t i o n and N uptake produced s i m i l a r t r e a t m e n t r a n k i n g s t o the o t h e r i n d e x e s , e x c l u d i n g ne t m i n e r a l i z a b l e N which was h i g h e s t i n the c o n t r o l p l o t s (Tab le 16, F i g u r e 13) (see pages 72 and 75 f o r e x p l a n a t i o n s o f ne t N m i n e r a l i z a t i o n and ne t m i n e r a l i z a b l e N) . R a i s o n e t a l . (1987) w i t h s i m i l a r f i n d i n g s , s p e c u l a t e d t h a t l a b i n c u b a t i o n s were no t s e n s i t i v e t o i n c r e a s e s i n l a b i l e p o o l s produced by f e r t i l i z a t i o n . N uptake c a l c u l a t e d from biomass e s t i m a t e s showed s i m i l a r t r e n d s and r a n k i n g s among t r e a t m e n t s as uptake c a l c u l a t e d from s o i l d e p l e t i o n , b u t the a b s o l u t e r a t e s a r e s u b s t a n t i a l l y h i g h e r f o r t h e NO t r e a t m e n t s , d e s p i t e b e i n g based on o n l y above ground biomass e s t i m a t e s . The g e n e r a l agreement i n r a n k i n g among the v a r i o u s indexes i s p r o b a b l y a r e f l e c t i o n o f t h e wide d i f f e r e n c e s i n N a v a i l a b i l i t y between t r e a t m e n t s , d e s p i t e not f i n d i n g s i g n i f i c a n t d i f f e r e n c e s w i t h the i n s i t u t e c h n i q u e . F o l i a r N c o n c e n t r a t i o n s were g e n e r a l l y a t a minimum around August 18 f o r most o f t h e t r e a t m e n t s ( F i g u r e 14 ) . T h i s 130 s u p p o r t s t h e i d e a t h a t the b e s t t ime t o sample f o l i a g e i s d u r i n g p e r i o d s o f r a p i d growth when demands f o r N a r e l a r g e (Waring and Youngberg , 1972; A x e l s s o n , 1983a) . I t appears as though l a b o r a t o r y i n c u b a t i o n s may be ana logous t o t a k i n g f o l i a r samples i n the f a l l as opposed t o e a r l i e r i n the growing season - v a r i a b i l i t y i s r e d u c e d , b u t v a l u a b l e i n f o r m a t i o n may be l o s t (Waring and Youngberg , 1972; A x e l s s o n , 1983a; Powers, 1984) . Thus , g r o s s m i n e r a l i z a b l e N may be b e t t e r f o r d i s t i n g u i s h i n g between t r e a t m e n t s w i t h i n one s i t e , b u t does no t measure a c t u a l m i n e r a l i z a t i o n r a t e s . T h u s , the b e n e f i t s o f one t e c h n i q u e over a n o t h e r depend on t h e o b j e c t i v e s o f the s t u d y . There a r e s e v e r a l ways i n which the t e c h n i q u e as used i n t h i s s t u d y can be improved upon. F i r s t , the use o f s t u r d y and s h a r p g a l v a n i z e d o r s t a i n l e s s s t e e l t u b e s , i n s t e a d o f p o l y v i n y l c h l o r i d e t u b e s , would make i n s e r t i o n o f the c o r e s i n the s o i l l e s s p r o b l e m a t i c and may r e s u l t i n l e s s compact ion o f t h e s o i l co lumn. R a i s o n e t a l . (1987) found t h a t g a l v a n i z e d s t e e l tubes have l i t t l e e f f e c t on N m i n e r a l i z a t i o n o r s o i l t e m p e r a t u r e . Second, v a r i a b i l i t y may be reduced by s t r a t i f y i n g by d e p t h ( R a i s o n , i n l i t t . 14 J u l y , 1988) and i n c r e a s e d b u l k i n g (Powers, 1984) . F i n a l l y , s a m p l i n g s h o u l d w a i t a t l e a s t one y e a r f o l l o w i n g t h e most r e c e n t f e r t i l i z e r a p p l i c a t i o n , t o a l l o w the N p o o l s and f l u x r a t e s t o s t a b i l i z e (Broadbent , 1966; Johnson e t a l . . 1980; R a i s o n , i n l i t t . 14 J u l y , 1988; and o t h e r s ) . The s e q u e n t i a l c o r i n g t e c h n i q u e overcomes some 131 problems o f t e m p o r a l v a r i a b i l i t y i n N m i n e r a l i z a t i o n p o t e n t i a l i n h e r e n t i n l a b i n c u b a t i o n s ( P o p o v i c , 1971; Powers, 1984) , but because o f h i g h s p a t i a l v a r i a b i l i t y i n m i n e r a l N p o o l s , v e r y i n t e n s i v e s a m p l i n g i s r e q u i r e d t o e s t i m a t e N f l u x e s a c c u r a t e l y , e s p e c i a l l y f o l l o w i n g f e r t i l i z a t i o n . T h e r e f o r e , the t e c h n i q u e i s i n a p p r o p r i a t e f o r s t u d i e s where o n l y an index o f N a v a i l a b i l i t y i s r e q u i r e d (eg. r o u t i n e f e r t i l i z e r p r e s r i p t i o n s o r s i t e c l a s s i f i c a t i o n ) . However, s e q u e n t i a l c o r i n g s h o u l d be p a r t i c u l a r l y u s e f u l when more d e t a i l e d i n f o r m a t i o n on N f l u x e s i s d e s i r e d , o r f o r t e s t i n g m i n e r a l i z a t i o n models under v a r y i n g c o n d i t i o n s and d e t e r m i n i n g the r e l i a b i l i t y o f more r a p i d indexes o f N a v a i l a b i l i t y . 132 CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS Repeated a p p l i c a t i o n s o f f e r t i l i z e r have p r o v i d e d a good o p p o r t u n i t y b o t h t o e v a l u a t e t h e m e r i t s o f the s e q u e n t i a l c o r i n g i n s i t u t e c h n i q u e f o r measur ing N f l u x e s and t o s tudy changes i n t h e n i t r o g e n c y c l e caused by f r e q u e n t f e r t i l i z a t i o n , b u t h i g h v a r i a b i l i t y o f m i n e r a l N p o o l s caused by r e c e n t f e r t i l i z a t i o n has c r e a t e d d i f f i c u l t i e s . E v a l u a t i n g the a c c u r a c y o f a t e c h n i q u e i s p r o b l e m a t i c because no method p r o v i d e s an u n e q u i v o c a l index o f N a v a i l a b i l i t y i n f o r e s t s o i l s (Hart and B i n k l e y , 1985) , but the s e q u e n t i a l c o r i n g method appears t o o f f e r s e v e r a l advantages and a few d i s a d v a n t a g e s o v e r o t h e r f i e l d and l a b o r a t o r y t e c h n i q u e s f o r e v a l u a t i n g the N s u p p l y i n g c a p a c i t y o f a s o i l . Because i t i s v e r y l a b o u r i n t e n s i v e , i t s a p p l i c a t i o n w i l l be l i m i t e d t o r e s e a r c h and i t w i l l never be a p p r o p r i a t e as a t o o l f o r r o u t i n e f e r t i l i z e r p r e s c r i p t i o n s o r s i t e c l a s s i f i c a t i o n . However, because i t i s s e n s i t i v e t o e n v i r o n m e n t a l f a c t o r s which a f f e c t N p r o c e s s e s and r e s u l t s i n m i n i m a l s o i l d i s t u r b a n c e , i t s h o u l d i n c r e a s e our u n d e r s t a n d i n g o f t h e dynamic c o n t r o l s on N a v a i l a b i l i t y t o t r e e s and u l t i m a t e l y l e a d t o an i n c r e a s e d u n d e r s t a n d i n g o f ecosystem N p r o c e s s e s . I t s h o u l d a l s o be u s e f u l f o r v e r i f y i n g models and 133 e v a l u a t i n g more r a p i d N indexes f o r p r e d i c t i n g f e r t i l i z e r r e s p o n s e . The a p p r o p r i a t e n e s s o f t h i s t e c h n i q u e f o r a p a r t i c u l a r s t u d y w i l l s t r o n g l y depend on t h e o b j e c t i v e s o f the s t u d y . A n a e r o b i c i n c u b a t i o n may be more s u i t a b l e f o r comparing t r e a t m e n t s w i t h i n the same system s i n c e e n v i r o n m e n t a l f a c t o r s do no t v a r y , o r f o r s i m p l y comparing s u b s t r a t e q u a l i t y . The f o l l o w i n g c o n c l u s i o n s have been r e a c h e d from t h e optimum n u t r i t i o n exper iment : 1. The i n c r e a s e d t r e e growth r e p o r t e d by E s t l i n (1988) i s p r o b a b l y the r e s u l t o f b o t h i n c r e a s e d N a v a i l a b i l i t y due t o e l e v a t e d i n o r g a n i c N c o n c e n t r a t i o n s i n t h e s o i l as a d i r e c t r e s u l t o f N f e r t i l i z a t i o n and i n c r e a s e d m i n e r a l i z a t i o n r a t e s s t i m u l a t e d by b o t h N and PK f e r t i l i z a t i o n . 2. Because N m i n e r a l i z a t i o n appears t o have been i n c r e a s e d by f e r t i l i z a t i o n , s i t e q u a l i t y has been improved and a h i g h e r p r o p o r t i o n o f uptake demand can be met by m i n e r a l i z a t i o n on t h e t r e a t e d p l o t s . 3 . F e r t i l i z a t i o n o f x e r i c s i t e s i n t h e Montane spruce zone can s i g n i f i c a n t l y i n c r e a s e the the degree t o which growth p o t e n t i a l d e t e r m i n e d by m o i s t u r e i s r e a l i z e d . F e r t i l i z a t i o n p r i o r t o crown c l o s u r e s t i m u l a t e s g r a s s c o m p e t i t i o n which may b e n e f i c i a l l y b u i l d up o r g a n i c m a t t e r , d e s p i t e compet ing w i t h t h e t r e e s f o r l i m i t e d m o i s t u r e . 4. Repeated heavy a p p l i c a t i o n s o f N w i t h o u t t h e 134 a d d i t i o n o f o t h e r n u t r i e n t s can cause n u t r i e n t imbalances and a subsequent r e d u c t i o n i n t r e e v i g o r . 5. L e a c h i n g does not appear t o be s i g n i f i c a n t on x e r i c s i t e s i n t h e Montane Spruce b i o g e o c l i m a t i c zone (at l e a s t not a f t e r v e g e t a t i o n has d e v e l o p e d s u f f i c i e n t uptake c a p a c i t y t o u t i l i z e t h e added n u t r i e n t s ) . Because t h i s i s a p r e l i m i n a r y s tudy t o e v a l u a t e the e f f e c t s o f r e p e a t e d f e r t i l i z e r a p p l i c a t i o n s on N c y c l i n g w i t h an e s s e n t i a l l y u n t e s t e d t e c h n i q u e , some recommendations f o r f u r t h e r s t u d y w i l l be made. F i r s t , t o i n c r e a s e our u n d e r s t a n d i n g o f t h e f a c t o r s r e g u l a t i n g N m i n e r a l i z a t i o n and u p t a k e , t o improve use o f the s e q u e n t i a l c o r i n g t e c h n i q u e , t o e x p l a i n i n c r e a s e d m i n e r a l i z a t i o n r a t e s , and t o e v a l u a t e o t h e r indexes o f N a v a i l a b i l i t y , i t i s recommended t h a t : 1. T o t a l N c o n c e n t r a t i o n i n the s o i l and on an a r e a b a s i s be measured t o e s t i m a t e any i n c r e a s e s o v e r c o n t r o l v a l u e s . 2. Carbon t o n i t r o g e n and c a r b o n t o phosphorus r a t i o s and o t h e r indexes o f N a v a i l a b i l i t y be e s t i m a t e d i n the s o i l and f o r e s t f l o o r . 3 . N m i n e r a l i z a t i o n be remeasured a t l e a s t one y e a r f o l l o w i n g the l a s t a p p l i c a t i o n o f f e r t i l i z e r , p o s s i b l y a t two depths t o reduce v a r i a b i l i t y , t o ge t a b e t t e r e s t i m a t e o f N f l u x e s on an a r e a b a s i s . T h i s s h o u l d be done w i t h s t a i n l e s s s t e e l o r g a l v a n i z e d meta l t u b i n g . Some c o r e s s h o u l d a l s o be 135 i n c u b a t e d on s i t e throughout the September-May p e r i o d t o d e t e r m i n e i f s i g n i f i c a n t m i n e r a l i z a t i o n o c c u r s d u r i n g t h e w i n t e r months. 4. To improve c o n f i d e n c e o f l e a c h i n g e s t i m a t e s , i t may be a p p r o p r i a t e t o use t h e r e s i n - c o r e method d e v e l o p e d by DiStephano and Gholz (1986) t o e s t i m a t e m i n e r a l i z a t i o n and l e a c h i n g , o r p o s s i b l y use l y s i m e t e r s below t h e r o o t i n g zone t o c o l l e c t l e a c h a t e s . Second, i n l i n e w i t h the o b j e c t i v e s o f optimum n u t r i t i o n s t u d i e s , the f o l l o w i n g recommendations a r e made: 1. Long term growth responses s h o u l d be m o n i t e r e d . 2. To e x p l a i n the mechanisms r e s u l t i n g i n i n c r e a s e d growth re sponses as a r e s u l t o f s u s t a i n e d i n c r e a s e s i n n u t r i e n t s u p p l y the f o l l o w i n g s h o u l d be examined: a . A l l o c a t i o n o f biomass t o stem, b r a n c h e s , f o l i a g e and r o o t s . Above-ground biomass can be de termined by d i r e c t s a m p l i n g o f a l i m i t e d number o f t r e e s per p l o t . See K u r t z and Kimmins (1987) f o r r o o t s a m p l i n g methods. b . Determine changes i n l e a f a r e a index i n t h e t r e a t e d p l o t s as w e l l as any i n c r e a s e i n p h o t o s y n t h e s i s r a t e p e r u n i t l e a f a r e a (Landsberg , 1986) . 3. Sample o l d e r f o l i a g e t o de termine i f i n c r e a s e d N s u p p l y has a f f e c t e d t h e i n t e r n a l c y c l i n g s t r a t e g i e s o f the t r e e s and t h e p r o d u c t i o n o f l i t t e r . Measure f o r e s t f l o o r depth t o d e t e r m i n e any e f f e c t s o f i n c r e a s e d n e e d l e l i t t e r and g r a s s 136 p r o d u c t i o n . 4. Measure changes i n pH produced by r e p e a t e d f e r t i l i z a t i o n t o de termine i f f e r t i l i z a t i o n has a d v e r s e l y a f f e c t e d s o i l p H . 5. C o r r e l a t e growth t r e n d s t o f o l i a r n u t r i e n t c o n c e n t r a t i o n s and r a t i o s t o de termine optimum and c r i t i c a l c o n c e n t r a t i o n s and r a t i o s f o r l o d g e p o l e p i n e . 137 LITERATURE CITED A b e r , J . D . , J . M . M e l i l l o , C A . M c C l a u g h e r t y , and K . N . Eshe lman. 1983. P o t e n t i a l s i n k s f o r m i n e r a l i z e d n i t r o g e n f o l l o w i n g d i s t u r b a n c e i n f o r e s t ecosys tems , i n R. H a l l b e r g (ed.) E n v i r o n m e n t a l B i o g e o c h e m i s t r y . E c o l o g i c a l B u l l e t o n s - N F R 35:179-192. M. and P. A t t i w i l l . 1986. N u t r i e n t c y c l i n g and n i t r o g e n m i n e r a l i z a t i o n i n e u c a l y p t f o r e s t s o f s o u t h - e a s t e r n A u s t r a l i a . I I . I n d i c e s o f n i t r o g e n m i n e r a l i z a t i o n . P l a n t and S o i l 92: 341-362. G . I . 1983. N i t r o g e n p r o d u c t i v i t y o f some c o n i f e r s . Can . J . F o r . Res . 13:494-500. G . I . and T . I n g e s t a d . 1987. Root and shoot r a t i o s as a b a l a n c e between n i t r o g e n p r o d u c t i v i t y and p h o t o s y n t h e s i s . P l a n t , C e l l E n v i r o n . 10:579-588. A g r i c u l t u r e Canada. E x p e r t Committee on S o i l S u r v e y . 1987. The C a n a d i a n System o f S o i l C l a s s i f i c a t i o n . Second E d i t i o n . A g r i . Can . P u b l . 1646. 164 p p . A l l i s o n , F . E . 1973. S o i l O r g a n i c M a t t e r and I t s R o l e i n Crop P r o d u c t i o n . U . S . D . A . New Y o r k . A n d e r s o n , J . M . , M . A . L e o r n a r d , P. Ineson and S. H u i s h . 1985. F a u n a l b iomass : a key component o f a g e n e r a l model o f n i t r o g e n m i n e r a l i z a t i o n . S o i l B i o l . Biochem. 17(5) : 735-735. A n g r o v e , K . and B . B a n c r o f t . 1983. A g u i d e t o some common p l a n t s o f the Southern I n t e r i o r o f B r i t i s h C o l u m b i a . Land Management Handbook Number 2, V o l 2. Dry and S u b c o n t i n e n t a l C l i m a t i c r e g i o n s . B . C . M i n i s t r y o f F o r e s t s . Armson, K . A . 1973. S o i l and p l a n t a n a l y s i s t e c h n i q u e s as d i a g n o s t i c c r i t e r i a f o r e v a l u a t i n g f e r t i l i z e r needs and t r e a t m e n t r e s p o n s e . Pp. 155-166 i n Symposium on F o r e s t F e r t i l i z a t i o n i n an E n v i r o n m e n t a l S e t t i n g . S t a t e U n i v . o f New Y o r k . S y r a c u s e 22-25 , A u g . 1972. A r o n s s o n , A . 1983. Growth d i s t u r b a n c e s caused by b o r o n d e f i c i e n c y i n some f e r t i l i z e d p i n e and s p r u c e s tands on m i n e r a l s o i l s . Pp 116-121 i n K . K K o l a r i (ed.) Growth D i s t u r b a n c e s o f F o r e s t T r e e s . P r o c . o f M e e t i n g Adams, A g r e n , A g r e n , 138 i n J y v a s k y l a and K i v i s u o , F i n l a n d , 10-13 O c t . 1982. Commun. I n s t . F o r . Fenn . 116. A r o n s s o n , A . 1985. I n d i c a t i o n s o f s t r e s s a t u n b a l a n c e d n u t r i e n t c o n t e n t s o f s p r u c e and p i n e . K . Skogs . o . L a n t b r . akad . t i d s k r . Supp. (Stockholm) 17:40-51 . A r o n s s o n , A . , S. Elowson and T . I n g e s t a d . 1977. E l i m i n a t i o n o f water and m i n e r a l n u t r i t i o n as l i m i t i n g f a c t o r s i n a young S c o t s P i n e s t a n d . I . E x p e r i m e n t a l d e s i g n and some p r e l i m i n a r y r e s u l t s . Swedish C o n i f e r o u s f o r e s t P r o j e c t . T e c h n i c a l R e p o r t 10. A t t i w i l l , P . M . 1986. I n t e r a c t i o n s between c a r b o n and n u t r i e n t s i n f o r e s t ecosystems. T r e e P h y s i o l . 2 :389-399. A x e l s s o n , B . 1983a. U l t i m a t e f o r e s t p r o d u c t i v i t y : What i s p o s s i b l e ? Pp 61-69 i n F o r e s t S i t e and C o n t i n u o u s P r o d u c t i v i t y . IUFRO M e e t i n g , Aug 22-28,1982 i n S e a t t l e . U . S . D . A . F o r . S e r v . Gen. T e c h . Rep. PNW 163. A x e l s s o n , B . 1983b. Methods f o r maintenance and improvement o f f o r e s t p r o d u c t i v i t y i n Nor thwes tern E u r o p e . Pp 305-311 i n F o r e s t S i t e and Cont inuous P r o d u c t i v i t y . IUFRO M e e t i n g , Aug 22-28,1982 i n S e a t t l e . U . S . D . A . Gen. T e c h . Rep. PNW 163. A x e l s s o n , B . 1985. I n c r e a s i n g f o r e s t p r o d u c t i v i t y and v a l u e by m a n i p u l a t i n g n u t r i e n t a v a i l a b i l i t y . Pp . 5-37 i n R. B a l l a r d , P . Farnum, G . A . R i t c h i e , J . K . Winjum (eds . ) F o r e s t P o t e n t i a l s , P r o d u c t i v i t y and V a l u e . 20-24 Aug. 1984. Tacoma, Washington . Weyerhaeuser S c i e n c e Symposium No. 4. A x e l s s o n , B . 1986. D i f f e r e n c e s i n y i e l d on d i f f e r e n t s i t e s : an i r r i g a t i o n - f e r t i l i z a t i o n s tudy o f n u t r i e n t f l u x d u r i n g f a s t growth , i n S . P . G e s s e l (ed.) F o r e s t S i t e and P r o d u c t i v i t y . A x e l s s o n , E . and B . A x e l s s o n . 1986. Changes i n c a r b o n a l l o c a t i o n p a t t e r n s i n s p r u c e and p i n e t r e e s f o l l o w i n g i r r i g a t i o n and f e r t i l i z a t i o n . T r e e Phys . 2: 189-204. B a l l a r d , T . M . 1986. Overview o f f o r e s t n u t r i t i o n a l problems i n the B . C . i n t e r i o r and methods o f d i a g n o s i s . Pp 1-10 i n P r o c . o f the I n t e r i o r F o r e s t F e r t i l i z a t i o n Workshop. Kamloops. 4-5 F e b . ,1986. B . C . M i n . F o r e s t s . Mimeo. B a l l a r d , T . M . 1987. F o r e s t S o i l s Manual ( S o i l S c i e n c e 303 and F o r e s t r y 312) . Dept . o f S o i l S c i e n c e , U . B . C . B a l l a r d , T . M . and R . E . C a r t e r . 1986. E v a l u a t i n g f o r e s t s t a n d n u t r i e n t s t a t u s . B . C . M i n . F o r . L a n d . Mgt . Rep. No. 139 20. B a r r e t t , J . W . and C . T . Youngberg . 1965. E f f e c t o f t r e e s p a c i n g and u n d e r s t o r y v e g e t a t i o n on water use i n pumice s o i l . S o i l S c i . S o c . P r o c . 472-475. B a s i l e , J . V . and C . E . J e n s o n . 1971. G r a z i n g p o t e n t i a l on l o d g e p o l e p i n e c l e a r c u t s i n Montana. U . S . F . S . Res . Pap. I N T - 9 8 . B e a u f i l s , E . R . 1973. D i a g n o s i s and recommendation i n t e g r a t e d system (DRIS) . S o i l S c i . B u l l . No. 1. U n i v e r s i t y o f N a t a l , South A f r i c a . B e l l a , I . E . 1978. F e r t i l i z i n g a f t e r t h i n n i n g 7 0 - y e a r o l d l o d g e p o l e p i n e (Pinus c o n t o r t a D o u g l . v a r . l a t i f o l i a Engelm.) i n A l b e r t a . E n v i r o n . C a n . , C a n . F o r . S e r v . B i - m o n t h Res . N o t e s . 34 (4 ) :22 -23 . B e r g , B . 1986. N u t r i e n t r e l e a s s e from l i t t e r and humus i n c o n i f e r o u s f o r e s t s o i l s - a m i n i r e v i e w . Scand J . F o r . Res . 1:359-369. B e r g , B . and H . S t a a f . 1981. L e a c h i n g , a c c u m u l a t i o n , and r e l e a s e o f n i t r o g e n i n decomposing f o r e s t l i t t e r . Pp. 163-178. i n F . E . C l a r k and T . R o s s w a l l ( e d s ) . T e r r e s t r i a l N i t r o g e n C y c l e s . P r o c e s s e s , Ecosys tem S t r a t e g i e s and Management. P r o c . o f SCOPE/UNEP. Roy. Swed. A c a d . S c i . Sweden. 16-22 S e p t . , 1979. B e r g , B . , H . S t a a f , and B . Wessen. 1987. Decompos i t i on and n u t r i e n t r e l e a s e i n need le l i t t e r from N i t r o g e n -f e r t i l i z e d S c o t s p i n e (Pinus s y l v e s t r i s ) s t a n d s . Scand . j . F o r . Res . 2:399-415. B e r n i e r , B . 1965. N i t r o g e n t r a n s f o r m a t i o n s , p . 71 i n P r o c . F i f t h Can . S o c . M i c r o . B i o l . M e e t i n g . Quebec. J u n e . 1965. Bevege, D . I . 1981. N i t r o g e n i n f o r e s t ecosystems: assessment and s y n t h e s i s . Pp. i n Rummery, R . A . and F . J . H i n g s t o n . ( e d s . ) Managing N i t r o g e n Economies o f N a t u r a l o f N a t u r a l and Man Made F o r e s t Ecosys tems . P r o c . CSIRO Workshop, A u s t r a l i a . 5-9 O c t . , 1980. B i n k l e y , D. 1986. F o r e s t N u t r i t i o n Management. John W i l e y and Sons . 290 p p . B i n k l e y , D. 1984. Ion exchange r e s i n bags: f a c t o r s a f f e c t i n g e s t i m a t e o f n i t r o g e n a v a i l a b i l i t y . S o i l S c i . S o c . Am. J . 48:1181-1184. B i n k l e y , D. and S . C . H a r t . 1989. The components o f n i t r o g e n a v a i l a b i l i t y assessments i n f o r e s t s s o i l s . A d v . i n 140 S o i l S c i . 10: 57-112. B i n k l e y , D. and P. R e i d . 1985. L o n g - t e r m i n c r e a s e o f n i t r o g e n a v a i l a b i l i t y from f e r t i l i z a t i o n o f D o u g l a s - f i r . Can J . F o r . Res . 15:723-724. B l a c k , T . A . , M . D . Novak. R . L . F l e m i n g , R . S . Adams, and N . E l d r i d g e . 1988. S i t e p r e p a r a t i o n p r o c e d u r e s t o m i n i m i z e s e e d l i n g water and t empera ture s t r e s s i n b a c k l o g a r e a s i n the Southern I n t e r i o r . 1987-88 Annual r e p o r t t o the Southern I n t e r i o r FRDA T e c h . Adv . Com. B . C . M i n . o f F o r . ( u n p u b l i s h e d ) . Boardman, R. and J . A . Simpson. 1981. F e r t i l i z a t i o n t o o p t i m i z e p r o d u c t i v i t y . Pp. 303-317 i n P r o c e e d i n g s A u s t r a l i a n F o r e s t N u t r i t i o n Workshop. P r o d u c t i v i t y i n P e r p e t u i t y . C a n b e r r a , A u s t r a l i a . August 10-14, 1981. Boomsma D . B . and J . A . B u r g e r . 1981. F a c t o r s a f f e c t i n g n i t r o g e n m i n e r a l i z a t i o n i n an a c i d sandy f o r e s t s o i l . Pp . 250 -258 i n Rummery, R . A . and F . J . H i n g s t o n . ( e d s . ) Managing N i t r o g e n Economies o f N a t u r a l o f N a t u r a l and Man Made F o r e s t Ecosys tems . P r o c . CSIRO Workshop, A u s t r a l i a . 5-9 O c t . , 1980. Bowen, G.D.<1981. Approaches t o n u t r i t i o n a l p h y s i o l o g y . Pp. 79-92 i n P r o c e e d i n g s A u s t r a l i a n F o r e s t N u t r i t i o n Workshop. P r o d u c t i v i t y i n P e r p e t u i t y . C a n b e r r a , A u s t r a l i a . August 10-14, 1981. Bremner, J . M . 1965. N i t r o g e n a v a i l a b i l i t y i n d e x e s . Pp . 1324-1345 i n C A . B l a c k (ed.) Methods o f S o i l A n a l y s i s , p a r t 2. C h e m i c a l and M i c r o b i o l o g i c a l p r o p e r t i e s . Am. S o c . A g r o n . I n c . Monogr. 10. M a d i s o n , W i s c o n s i n . B r o a d b e n t , F . E . 1966. In terchange between i n o r g a n i c and o r g a n i c n i t r o g e n i n s o i l s . H i l g a r d i a . 37(6) :165-180 . B r o c k l e y , R . P . 1989. Response o f t h i n n e d , immature l o d g e p o l e p i n e t o n i t r o g e n f e r t i l i z a t i o n : t h r e e - y e a r growth r e s p o n s e . B . C . M i n . F o r . F . R . D . A . R e p o r t 036. B r o c k l e y , R . P . and D. Y o l e . 1985. Growth re sponse o f l o d g e p o l e p i n e t o o p e r a t i o n a l f e r t i l i z e r a p p l i c a t i o n near Burns L a k e , B . C . B . C M i n i s t r y o f F o r e s t s Res . Rep. 85005-HQ. B u r g e s s , D. 1984. The r o l e o f c h e m i c a l f e r t i l i z e r s i n i n t e n s i v e f o r e s t r y . I E A / F E - ENFOR C a n . F o f . S e r v . R e p o r t 1984:3 46 pp and a p p e n d i c e s . C a r l y l e , J . C . 1986. N i t r o g e n c y c l i n g i n f o r e s t e d ecosys tems , f o r e s t r y A b s t r a c t s . 47 (5) :307-330 . C o l e , D.W. 1981. N i t r o g e n uptake and t r a n s l o c a t i o n by f o r e s t 141 ecosys tems . Pp. 163-178 i n F . E . C l a r k and T . R o s s w a l l ( e d s ) . T e r r e s t r i a l N i t r o g e n C y c l e s . P r o c e s s e s , Ecosystem S t r a t e g i e s and Management. P r o c . o f SCOPE/UNEP. Roy. Swed. A c a d . S c i . Sweden. 16-22 S e p t . , 1979. Comeau, P . G . and J . P . Kimmins. 1985. Stemwood p r o d u c t i o n o f l o d g e p o l e p i n e and r e l a t i o n s h i p t o f o l i a r n i t r o g e n c o n t e n t and s i t e . P o s t e r a b s t r a c t i n D . M . Baumgartner , R . G . K r e b i l l , J . T . A r n o t t , and G . F . Weetman (eds . ) Lodgepo le p i n e . The S p e c i e s and I t s Management. P r o c . Spokane, Wash. 8-10 May, and V a n c o u v e r , B . C . 14-16 May, 1984. C o c h r a n , P . H . 1979 Response o f t h i n n e d l o d g e p o l e p i n e t o f e r t i l i z a t i o n . U . S . D . A . F o r . S e r v . Res . Note . PNW-335. Dahnke, W . C . and E . H . V a c e y . 1973. T e s t i n g s o i l s f o r n i t r o g e n . Pp. 97-114 i n L . M . Walsh , and J . D . b e a t o n , ( eds . ) S o i l T e s t i n g and P l a n t A n a l y s i s . S o i l S c i . S o c . o f Am. Dermot, C A . 1985. F u t u r e o f l o d g e p o l e p i n e f o r e s t r y : a p u b l i c manager 's p e r s p e c t i v e i n Canada. Pp. 3 59-366 i n Lodgepo le P i n e . The S p e c i e s and i t s Management. Symp. p r o c . May 8-10, 1984, Spokane, Wash, and May 14-16, 1984, V a n c o u v e r , B . C . D i S t e f a n o , J . F . and H . L . G h o l z . 1986. A p r o p o s e d use o f i o n exchange r e s i n s t o measure n i t r o g e n m i n e r a l i z a t i o n and n i t r i f i c a t i o n i n i n t a c t s o i l c o r e s , commun. S o i l . S c i . P l a n t . A n a l . 17:989-998. E n o , C F . 1960. N i t r a t e p r o d u c t i o n i n the f i e l d by i n c u b a t i n g t h e s o i l i n p o l y e t h y l e n e bags . S o i l . S c i . Amer. P r o c . 24:277-279. E s t l i n , M . R . 1988. F i v e y e a r growth response o f l o d g e p o l e p i n e i n an optimum n u t r i t i o n exper iment near Okanagan F a l l s , B . C . BSF T h e s i s , F a c . F o r e s t r y . U . B . C . 88 p p . F o b e r , H . and M. G i e r t y c h . 1971. E f f e c t o f g r a s s c o m p e t i t i o n on t h e growth and m i n e r a l n u t r i t i o n o f s p r u c e ( P i c e a a b i e s K a r s t . ) . Arboretum K o r n i c h i e . 16: 81-105. F o r d , E . D . 1983. What do we need t o know about f o r e s t p r o d u c t i v i t y and how can we measure i t ? Pp 2-12 i n F o r e s t S i t e and Cont inuous P r o d u c t i v i t y . IUFRO M e e t i n g , Aug 22-28,1982 i n S e a t t l e . U . S . D . A . F o r . S e r v . Gen. T e c h . Rep. PNW 163. Freyman, S. and A . L . van Ryswyk. 1969. E f f e c t o f f e r t i l i z e r on p i n e g r a s s i n Southern B r i t i s h C o l u m b i a . J . Range Mgmt 22:390-395. 142 G i l e s , D . G . , B l a c k , T . A . and D . L . S p i t t l e h o u s e . 1985. D e t e r m i n a t i o n o f growing season water d e f i c i t s on a f o r e s t e d s l o p e u s i n g water b a l a n c e a n a l y s i s . Can J . F o r . Res . 15: 107-114. G i b s o n , D . J . 1986. S p a t i a l and t e m p o r a l h e t e r o g e n e i t y i n s o i l n u t r i e n t s u p p l y measured u s i n g i n s i t u i o n exchange r e s i n bags . P l a n t and S o i l 96:445-450. G i l b e r t , A . S . 1987. Resource management i s s u e s and d i r e c t i o n f o r l o d g e p o l e p i n e f o r e s t l a n d s - N o r t h e r n Rockey M o u n t a i n s . Pp 7-9 i n Management o f S m a l l Stem Stands o f Lodgepo le P i n e - Workshop P r o c . June 3 0 - J u l y 2 , 1986. F a i r m o n t Hot S p r i n g s . U . S . D . A . F o r . S e r v . Gen. T e c h . Rep. INT-237 . G h o l z , H . L . 1982. E n v i r o n m e n t a l l i m i t s on above ground net p r i m a r y p r o d u c t i o n , l e a f a r e a , and biomass i n v e g e t a t i o n zones o f the P a c i f i c Northwes t , e c o l o g y 63(2 ) :469-481 . Gordon , A . M . and K. Van C l e v e . 1982. S e a s o n a l p a t t e r n s o f n i t r o g e n m i n e r a l i z a t i o n f o l l o w i n g h a r v e s t i n g i n the w h i t e s p r u c e f o r e s t s o f i n t e r i o r A l a s k a . Pp . 119-130 i n R.W. Wein , R . R . R i e v e and I R. Methven (eds . ) Resources and Dynamics o f B o r e a l Zone. Thunderbay , O n t a r i o . Aug . 1982. G o s z . J . R . 1981. N i t r o g e n c y c l i n g i n c o n i f e r o u s ecosys tems . Pp. 405-426 i n F . E . C l a r k and T . R o s s w a l l ( e d s ) . T e r r e s t r i a l N i t r o g e n C y c l e s . P r o c e s s e s , Ecosys tem S t r a t e g i e s and Management. P r o c . o f SCOPE/UNEP. Roy. Swed. A c a d . S c i . Sweden. 16-2 2 S e p t . , 1979. H a e u s s l e r , S . a n d D. C o a t e s . 1986. A u t e c o l o g i c a l c h a r a c t e r i s t i c s o f s e l e c t e d s p e c i e s t h a t compete w i t h c o n i f e r s i n B r i t i s h C o l u m b i a : A L i t e r a t u r e Review. B . C . M i n . F o r . FRDA R e p o r t 001. 180 p p . H a r t , S . C . and D. B i n k l e y . 1985. C o r r e l a t i o n s among i n d i c e s o f f o r e s t n u t r i e n t a v a i l a b i l i t y i n f e r t i l i z e d and u n f e r t i l i z e d l o b l o l l y p i n e p l a n t a t i o n s . P l a n t and S o i l . 85 :11-21 . H a r t , S . C . and M . K . F i r e s t o n e . 1989. E v a l u a t i o n o f t h r e e i n s i t u s o i l n i t r o g e n a v a i l a b i l i t y a s s a y s . C a n . J . F o r . Res . 19:185-191. H a s k i n , C M . 1985. N i t r o g e n a v a i l a b i l i t y and s o i l m i c r o c l i m a t e a f t e r c l e a r c u t t i n g l o d g e p o l e p i n e . M a s t e r ' s T h e s i s . U . B . C . 71 p p . Hauck, R . D . 1981. N i t r o g e n f e r t i l i z e r e f f e c t s on n i t r o g e n c y c l e p r o c e s s e s . Pp. 551-560 i n F . E . C l a r k and T . 143 R o s s w a l l ( e d s ) . T e r r e s t r i a l N i t r o g e n C y c l e s . P r o c e s s e s , Ecosystem S t r a t e g i e s and Management. P r o c . o f SCOPE/UNEP. Roy. Swed. A c a d . S c i . Sweden. 16-22 S e p t . , 1979. H e a l , O . W . , M . J . S w i f t , and J . M . A n d e r s o n . 1982. N i t r o g e n c y c l i n g i n U n i t e d Kingdom f o r e s t s : t h e r e l e v a n c e o f b a s i c e c o l o g i c a l r e s e a r c h . P h i l . T r a n s . R. S o c . L o n d . B . 296:427-444. H e i l m a n , P . E . and S . P . G e s s e l . 1963. N i t r o g e n r e q u i r e m e n t s and t h e b i o l o g i c a l c y c l i n g o f n i t r o g e n i n D o u g l a s - f i r s t a n d s i n r e l a t i o n s h i p t o the e f f e c t s o f n i t r o g e n f e r t i l i z a t i o n . P l a n t and S o i l 18 (3 ) :386-401 . H e n d r i c k s o n , O . Q . and J . B . R o b i n s o n . 1984. E f f e c t s o f r o o t s and l i t t e r on m i n e r a l i z a t i o n p r o c e s s e s i n f o r e s t s o i l . P l a n t and S o i l 80:391-405. H i l l e r d a l - H a g s t r o m e r , K . , E . M a t t s o n - D j o s and J . H e l l k v i s t . 1982. F i e l d s t u d i e s o f water r e l a t i o n s and p h o t o s y n t h e s i s i n S c o t s P i n e . I I . I n f l u e n c e o f i r r i g a t i o n and f e r t i l i z a t i o n on n e e d l e water p o t e n t i a l o f young p i n e t r e e s . P h y s i o l . P l a n t 50:353-364. Holmen, H . , A . N i l s s o n , B . P o p o v i c and G . W i k l a n d e r . 1976. The optimum n u t r i t i o n exper iment . N o r r l i n d e n . A b r i e f d e s c r i p t i o n o f an exper iment i n a young s t a n d o f S c o t s p i n e (P inus s y l v e s t r i s L . ) Roy. C o l . o f F o r . S tockholm No .26 . H u r l b e r t , S . H . 1984. P s e u d o r e p l i c a t i o n and the d e s i g n o f e c o l o g i c a l f i e l d e x p e r i m e n t s . E c o l . Monog. 54 (2 ) :187 -211. I n g e s t a d , T . 1977. N i t r o g e n and p l a n t growth; maximum e f f i c i e n c y o f n i t r o g e n f e r t i l i z e r s . Ambio 6 ( 2 - 3 ) : 1 4 6 -151. I n g e s t a d , T . 1979. N i t r o g e n s t r e s s i n b i r c h s e e d l i n g s . I I . N . P, K, C a , and Mg n u t r t i o n . P h y s i o l . P l a n t 50:353-364. I n g e s t a d , T . 1982. R e l a t i v e a d d i t i o n r a t e and e x t e r n a l c o n c e n t r a t i o n : d r i v i n g v a r i a b l e s used i n f o r e s t n u t r i t i o n r e s e a r c h . P l a n t C e l l E n v i r o n . 5:443-453. I n g e s t a d , T . 1987. New concept s on s o i l f e r t i l i t y and p l a n t n u t r i t i o n as i l l u s t r a t e d by r e s e a r c h on f o r e s t t r e e s and s t a n d s . Geoderma 40:237-252. I n g e s t a d , T . and M. K a h r . 1985. N u t r i t i o n and growth o f c o n i f e r o u s s e e d l i n g s a t v a r i e d r e l a t i v e n i t r o g e n a d d i t i o n r a t e s . P h y s i o l . P l a n t . 65:109-116. 144 I n g e s t a d , T . and A . L u n d . 1986. Theory and t e c h n i q u e s f o r s t e a d y m i n e r a l n u t r i t i o n and growth o f p l a n t s . S c a n . J . F o r . Res . 1:439-453. J o h n s o n , D . W . , N . T . Edwards and D . E . T o d d . 1980. N i t r o g e n m i n e r a l i z a t i o n , i m m o b i l i z a t i o n , and n i t r i f i c a t i o n f o l l o w i n g U r e a f e r t i l i z a t i o n o f a f o r e s t s o i l under f i e l d and l a b o r a t o r y c o n d i t i o n s . S o i l S c i . S o c . Am. J . 44:610-616. J o h n s o n , D.W. and D . E . T o d d . 1988. N i t r o g e n f e r t i l i z a t i o n o f young y e l l o w - p o p l a r and l o b l o l l y p i n e p l a n t a t i o n s a t d i f f e r e n t f r e q u e n c i e s . S o i l S c i . S o c . Am. J . 52:1468-1477. D . R . 1980. P r e d i c t i o n o f s o i l N a v a i l a b i l i t y i n f o r e s t ecosystems: a l i t e r a t u r e r e v i e w . F o r . S c i . 26 (1 ) :159 -171. D . R . 1982. N i t r o g e n - a v a i l a b i l i t y i n d i c e s . Pp . 711-733 i n Methods o f S o i l A n a l y s i s . P a r t 2. A . L . Page ( e d . ) . S o i l S c i . Soc . A m e r . , M a d i s o n , D . R . and W.R. G a r d n e r . 1970. The dynamics o f n i t r o g e n t r a n s f o r m a t i o n i n s o i l . Pp. 192-194 i n G l o b a l E f f e c t s o f E n v i r o n m e n t a l P o l l u t i o n . S p r i n g e r V e r l a g , New Y o r k . D . R . and D.W. N e l s o n . 1982. N i t r o g e n - i n o r g a n i c forms . Pp . 643-693 i n Methods o f S o i l A n a l y s i s . P a r t 2. A . L . Page ( e d . ) . S o i l S c i . Soc . A m e r . , M a d i s o n , W . I . Kennedy, R.W. 1985. Lodgepole p i n e as a commerc ia l r e s o u r c e i n Canada. Pp. 21-24 i n D . M . Baumgartner , R . G . K r e b i l l , J . T . A r n o t t , and G . F . Weetman (eds . ) Lodgepo le p i n e . The S p e c i e s and I t s Management. P r o c . Spokane, Wash. 8-10 May, and V a n c o u v e r , B . C . 14-16 May, 1984. Khanna, P . K . 1981. S o i l a n a l y s i s f o r e v a l u a t i o n o f f o r e s t n u t r i e n t s u p p l y . Pp 231-238 i n P r o c e e d i n g s A u s t r a l i a n F o r e s t N u t r i t i o n Workshop. P r o d u c t i v i t y i n P e r p e t u i t y . C a n b e r r a , A u s t r a l i a . August 10-14, 1981. Kimmins , J . P . . 1 9 7 7 . E v a l u a t i o n o f the consequences f o r f u t u r e t r e e p r o d u c t i v i t y o f the l o s s o f n u t r i e n t s i n who le -t r e e h a r v e s t i n g . F o r . E c o l . Manage. 1:169-183. Kimmins, J . P . 1985. F u t u r e shock i n y i e l d f o r e c a s t i n g : the need f o r a new a p p r o a c h . F o r . C h r o n . 61(6) :503-512 . Kimmins , J . P . 1987. F o r e s t E c o l o g y . M a c m i l l a n , New Y o r k . 533 p p . Keeney, Keeney, Keeney, Keeney, Kimmins , J . P . , P . G . Comeau, and W.A. K u r t z . 1989. M o d e l l i n g t h e i n t e r a c t i o n s between m o i s t u r e and n u t r i e n t s i n the 145 c o n t r o l o f f o r e s t growth . F o r . E c o l . and Mgmt. In P r e s s . K l i n k a , K . , R . N . G r e e n . , R . L . T r o w b r i d g e and L . E . Lowe. 1981. Taxonomic c l a s s i f i c a t i o n o f humus forms i n ecosystems o f B r i t i s h C o l u m b i a . B . C . M i n . F o r . Land Mgt . R e p o r t No. 8, 54 p p . Kudeyarov , V . N . 1981. m o b i l i t y o f f i x e d ammonium i n s o i l s . Pp 281-290 i n F . E . C l a r k and T . R o s s w a l l ( e d s ) . T e r r e s t r i a l N i t r o g e n C y c l e s . P r o c e s s e s , Ecosys tem S t r a t e g i e s and Management. P r o c . o f SCOPE/UNEP. Roy. Swed. A c a d . S c i . Sweden. 16-22 S e p t . , 1979. Kumi , J . W . 1984. E f f e c t s o f r e p e a t e d f e r t i l i z a t i o n and a s traw a p p l i c a t i o n t o the o r g a n i c l a y e r s under j a c k p i n e and s e e d l i n g r e s p o n s e . M a s t e r ' s T h e s i s . U . B . C . I l l p p . K u r t z , W.A. and J . P . Kimmins. 1987. The i n f l u e n c e o f s i t e q u a l i t y on t r e e r e s o u r c e a l l o c a t i o n t o f i n e r o o t s and i t s e f f e c t on h a r v e s t a b l e p r o d u c t i v i t y o f C o a s t a l * D o u g l a s - f i r S t a n d s . B . C . m i n . F o r . FRDA Rep. 034. L a n d s b e r g . J . J . 1986. E x p e r i m e n t a l approaches t o t h e s t u d y o f the e f f e c t s o f n u t r i e n t s and water on c a r b o n a s s i m i l a t i o n by t r e e s . T r e e Phys . 2:427-444. L e a , R. and R. B a l l a r d . 1982. P r e d i c t i n g l o b l o l l y p i n e growth re sponse from N f e r t i l i z e r , u s i n g s o i l N a v a i l a b i l i t y i n d i c e s . S o i l S c i . Soc . Am. J . 46:1096-1099. M a c d u f f , J . H . and R . E . W h i t e . 1985. Net m i n e r a l i z a t i o n and n i t r i f i c a t i o n r a t e s i n a c l a y s o i l measured and p r e d i c t e d i n permanent g r a s s l a n d from s o i l t empera ture and m o i s t u r e c o n t e n t s . P l a n t and S o i l . 86:151-172. Mahendrappa, M . K . , N.W. F o s t e r , G . F . Weetman, and H . H . K r a u s e . 1986. N u t r i e n t c y c l i n g and a v a i l a b i l i t y i n f o r e s t s o i l s . Can . J . S o i l S c i . 66:547-572. M a n n e r k o s k i , H . and T . Miyazawa. 1983. Growth d i s t u r b a n c e s and n e e d l e and s o i l n u t r i e n t c o n t e n t s i n a N P K - f e r t i l i z e d s c o t s p i n e p l a n t a t i o n on a d r a i n e d s m a l l sedge bog . Pp. 85-90 i n K . K K o l a r i (ed.) Growth D i s t u r b a n c e s o f F o r e s t T r e e s . P r o c . o f M e e t i n g i n J y v a s k y l a and K i v i s u o , F i n l a n d , 10-13 O c t . 1982. Commun. I n s t . F o r . Fenn . 116. M a t s o n , P . A . and P . M . V i t o u s e k . 1981. N i t r i f i c a t i o n p o t e n t i a l f o l l o w i n g c l e a r c u t t i n g i n the H o o s i e r N a t i o n a l F o r e s t , I n d i a n a . F o r . S c i . 27:781-791. M a t y s s e k , R. 1986. C a r b o n , water , and n i t r o g e n r e l a t i o n s i n e v e r g r e e n and dec iduous c o n i f e r s . T r e e P h y s i o l . 2:177-146 187, McNabb, D . H . , R . L . F r e d r i k s o n , and K. Cromack, J r . 1978. M i n e r a l i z a b l e s o i l n i t r o g e n i n some f o r e s t h a b i t a t t y p e s o f the Oregon c a s c a d e s . A g r o n . A b s t r . p 190. M i l l e r , H . G . 1981. F o r e s t f e r t i l i z a t i o n : some g u i d i n g c o n c e p t s . F o r e s t r y 54(2) :157-167 . M i l l e r , H . G . and J . M . Cooper . 1973. Changes i n amount and d i s t r i b u t i o n o f stem growth i n p o l e - s t a g e c o r s i c a n p i n e f o l l o w i n g a p p l i c a t i o n o f n i t r o g e n f e r t i l i z a t i o n . F o r e s t r y 46(2) :157-187 . M i l l e r , H . G . and J . D . M i l l e r . 1976. E f f e c t o f n i t r o g e n s u p p l y on ne t p r i m a r y p r o d u c t i o n i n C o r s i c a n P i n e . J . A p p l i e d E c o l . 13:249-256. M i l l e r , H . G . , J . D . M i l l e r , and J . M . Cooper . 1981. Optimum f o l i a r n i t r o g e n c o n c e n t r a t i o n i n p i n e and i t s change w i t h s t a n d age . Can J . f o r . Res . 11:563-572. M i l l e r , H . G . , J . M . Cooper , J . D . M i l l e r and O . J . L . P a u l i n e . 1979. N u t r i e n t c y c l e s i n p i n e and t h e i r a d a p t a t i o n t o p o o r s o i l s . Can . J . F o r . Res . 9 :19-26 . M i t c h e l l , W.R. and R . E . G r e e n . 1981. I d e n t i f i c a t i o n and i n t e r p r e t a t i o n o f ecosystems o f t h e Western Kamloops F o r e s t R e g i o n , F i r s t A p p r o x . Land Management Handbook No. 2, V o l 2. Dry and s u b c o n t i n e n t a l C l i m a t i c R e g i o n s . B . C . M i n i s t r y o f F o r e s t s . M o l l e r , G . 1983. V a r i a t i o n o f boron c o n c e n t r a t i o n i n p i n e n e e d l e s from t r e e s growing on m i n e r a l s o i l i n Sweden and re sponse t o n i t r o g e n f e r t i l i z a t i o n . Pp. 111-115 i n K . K K o l a r i (ed.) Growth D i s t u r b a n c e s o f F o r e s t T r e e s . P r o c . o f M e e t i n g i n J y v a s k y l a and K i v i s u o , F i n l a n d , 10-13 O c t . 1982. Commun. I n s t . F o r . Fenn . 116. M o r r i s o n , I . K . 1973. D i s t r i b u t i o n o f e lements i n a e r i a l components o f s e v e r a l n a t u r a l j a c k p i n e s tands i n N o r t h e r n O n t a r i o . Can . J . F o r . Res . 3:170-179. M o r r i s o n , I . K . 1974. M i n e r a l n u t r i t i o n o f c o n i f e r s w i t h s p e c i a l r e f e r e n c e t o n u t r i e n t s t a t u s i n t e r p r e t a t i o n : a r e v i e w o f the l i t e r a t u r e . Can . F o r . S e r v . C a n . Dept . E n v i r . P u b l . No. 1343. M o r t l a n d , M . M . and A . R . W o l c o t t . 1965. S o r p t i o n o f i n o r g a n i c n i t r o g e n compunds by s o i l m a t e r i a l s . Pp. 150-197 i n W.V. Bartholemew and F . E . C l a r k (eds . ) S o i l N i t r o g e n . N a d e l h o f f e r , K . J . , J . D . Aber and J . M . M e l i l l o . 1984. S e a s o n a l p a t t e r n s o f ammonium and n i t r a t e uptake i n n i n e 147 temperate f o r e s t ecosys tems . P l a n t and S o i l 80:321-335. N a d e l h o f f e r , K . J . , J . D . Aber and J . M . M e l i l l o . 1985. F i n e r o o t s , ne t p r i m a r y p r o d u c t i o n , and s o i l n i t r o g e n a v a i l a b i l i t y : a new h y p o t h e s i s . E c o l o g y 66:1377-1390. N o r d s t r o m , L . O . 1984. The e c o l o g y and management o f f o r e s t range i n B r i t i s h C o l u m b i a : A rev i ew and a n a l y s i s . B . C . M i n . F o r . Land Manage. Rep. No. 19. O l i v e r , W.V. 1984. Brush reduces growth o f t h i n n e d ponderosa p i n e i n N o r t h e r n C a l i f o r n i a . USDA F o r . S e r v . P a c i f i c Southwest F o r e s t and Range E x p . S t a . Res . Pap. PSW-172. O v e r r e i n , L . N . 1967. I m m o b i l i z a t i o n and m i n e r a l i z a t i o n o f t r a c e r n i t r o g e n i n f o r e s t raw humus. I . E f f e c t o f t empera ture on the i n t e r c h a n g e o f n i t r o g e n a f t e r a d d i t i o n o f u r e a - , ammonium-, and n i t r a t e - N 1 5 . P l a n t and S o i l 2 7 ( 1 ) : 1 - 1 9 . P a s t o r , J . , J . D . A b e r , and C A . M c C l a u g h e r t y . 1984. Above ground p r o d u c t i o n and N and P c y c l i n g a l o n g a n i t r o g e n m i n e r a l i z a t i o n g r a d i e n t on Blackhawk I s l a n d , W i s c o n s i n . E c o l o g y 65(1) :256-268 . P a u l , E . A . and N . G . Juma. 1981. M i n e r a l i z a t i o n and i m m o b i l i z a t i o n o f s o i l N by m i c r o o r g a n i s m s . Pp. 179-195 i n F . E . C l a r k and T . R o s s w a l l ( e d s ) . T e r r e s t r i a l N i t r o g e n C y c l e s . P r o c e s s e s , Ecosys tem S t r a t e g i e s and Management. P r o c . o f SCOPE/UNEP. Roy. Swed. A c a d . S c i . Sweden. 16-22 S e p t . , 1979. P o j a r , J . , K . K l i n k a , and D . V . M e i d i n g e r . 1986. B i o g e o c l i m a t i c ecosystem c l a s s i f i c a t i o n i n B r i t i s h C o l u m b i a . F o r . E c o l . Manage. 22:119-154. P o p o v i c , B . 1971. E f f e c t o f s a m p l i n g d a t e on n i t r o g e n m o b i l i z a t i o n d u r i n g i n c u b a t i o n e x p e r i m e n t s . P l a n t and S o i l 34:381-392. Powers, R . F . 1980. M i n e r a l i z a b l e s o i l n i t r o g e n as an index o f n i t r o g e n a v a i l a b i l i t y t o f o r e s t t r e e s . S o i l S c i . Soc . Am. J . 44:1314-1320. Powers, R . F . 1984. E s t i m a t i n g s o i l n i t r o g e n a v a i l a b i l i t y t h r o u g h s o i l and f o l i a r a n a l y s i s . Pp 353-379 i n E . Stone (ed.) F o r e s t S o i l s and Treatment Impacts . P r o c . S i x t h N . Am. F o r . S o i l s C o n f . Dept . F o r e s t r y , W i l d l i f e and F i s h e r i e s , U n i v . o f Tennessee . Powers, R . F . and G . D . J a c k s o n . 1978. Ponderosa p i n e response t o f e r t i l i z a t i o n : i n f l u e n c e o f b r u s h removal and s o i l 148 t y p e . USDA F o r . S e r v . P a c i f i c S o u t h w e s t F o r e s t and Range Exp. S t a . Res. Pap. PSW-132. 9 pp. Powers, R.F., R.F. Townsend, and R . J . L a a c k e , J r . 1978. A s s e s s i n g s o i l n i t r o g e n a v a i l a b i l i t y u n d e r f o r e s t c o n d i t i o n s . A g r o n . A b s t r . p.192. P r i t c h e t t , W.L. and R.F. F i s h e r . 1987. P r o p e r t i e s a n d Management o f F o r e s t S o i l s . S e c o n d E d i t i o n . J o h n W i l e y a n d Sons. 494 pp. R a i s o n , R . J . , M.J. C o n n e l l and P.K. Khanna. 1987. M e t h o d o l o g y f o r s t u d y i n g f l u x e s o f s o i l m i n e r a l - N i n s i t u . S o i l B i o l . B i o c h e m . 1 9 ( 5 ) : 5 2 1 - 5 3 0 . R a i s o n , R . J . , M.J. C o n n e l l , P.K. Khanna, and R.A. F a u l k i n e r . 1989. E f f e c t s o f i r r i g a t i o n and N - f e r t i l i z a t i o n on f l u x e s o f s o i l m i n e r a l - N i n a s t u d y o f P i n u s r a d i a t a . F o r . E c o l . Manage. ( I n P r e s s ) . R a w l i n s , S.L. 1976. Measurement o f w a t e r c o n t e n t and t h e s t a t e o f w a t e r i n s o i l s , i n K o z l o w s k i , T T . ( e d . ) Water D e f i c i t s and P l a n t Growth. 4: 1-55. R o b e r g e , M.R. and R. K n o w l e s . 1966. U r e a l y s i s , i m m o b i l i z a t i o n , and n i t r i f i c a t i o n i n B l a c k s p r u c e ( P i c e a m a r i a n a M i l l . ) humus. P r o c . S o i l S c i . S o c . Amer. 3 0 ( 2 ) : 2 1 0 - 2 0 4 . R o b e r t s o n , G.P. 1982. N i t r i f i c a t i o n i n f o r e s t e d e c o s y s t e m s . P h i l . T r a n s . R. S o c . L o n d . B296:445-457. R u n n i n g , S.W. a n d B.L. C o n n e r , 1987. Water s t r e s s r e s p o n s e a f t e r t h i n n i n g l o d g e p o l e p i n e s t a n d s i n Montana. Pp. 111-117 i n Management o f S m a l l - S t e m S t a n d s o f L o d g e p o l e P i n e - w o r k s h o p P r o c . J u n e 3 0 - J u l y 2, 1986. F a i r m o n t H o t S p r i n g s . U.S.D.A. F o r . S e r v . Gen. T e c h . Rep. INT-237. Shumway, J . S . and W.A. A t k i n s o n . 1977. M e a s u r i n g and p r e d i c t i n g g r o w t h r e s p o n s e i n u n t h i n n e d s t a n d s o f D o u g l a s - f i r by p a i r e d t r e e a n a l y s i s a n d s o i l t e s t i n g . Wash. S t a t e D ept. N a t . R e s . N o t e 15, 10pp. S t a a f , H. and B. B e r g . 1981. P l a n t l i t t e r i n p u t t o s o i l . Pp. 147-162 i n F.E. C l a r k and T. R o s s w a l l ( e d s ) . T e r r e s t r i a l N i t r o g e n C y c l e s . P r o c e s s e s , E c o s y s t e m S t r a t e g i e s and Management. P r o c . o f SCOPE/UNEP. Roy. Swed. A c a d . S c i . Sweden. 16-22 S e p t . , 1979. S t a n d i s h , J . T . , G.H. M a n n i n g and J . P . D e m a e r s c h a l k . 1985. D e v e l o p m e n t o f b i o m a s s e q u a t i o n s f o r B r i t i s h C o l u m b i a t r e e s p e c i e s . Can. F o r . S e r v . BC-X-264. 149 S t a n f o r d , G . 1980. E v a l u a t i o n o f n i t r o g e n r e q u i r e m e n t s and s o i l n i t r o g e n a v a i l a b i l i t y i n a g r i c u l t u r e and f o r e s t r y . Pp. 205-228 i n R u n n i n g , R . A . and F . J . H i n g s t o n . ( e d s ) . Managing N i t r o g e n Economies o f N a t u r a l o f N a t u r a l and Man Made F o r e s t Ecosys tems . P r o c . CSIRO Workshop. A u s t r a l i a . 5-9 O c t . , 1980. S t a n f o r d , G . , J . O . Legg , and S . J . S m i t h . 1973. S o i l n i t r o g e n a v a i l a b i t y e v a l u a t i o n s based on n i t r o g e n m i n e r a l i z a t i o n p o t e n t i a l s o f s o i l a n d uptake o f l a b e l l e d and u n l a b e l l e d n i t r o g e n by p l a n b t s . P l a n t and S o i l 39:113-124. S t a n f o r d , G . and S . J . S m i t h . 1972. N i t r o g e n m i n e r a l i z a t i o n p o t e n t i a l o f s o i l s . S o i l S c i . Soc o f Am. P r o c . 36: 465-472. S q u i r e , R . 0 . 1 9 7 7 . I n t e r a c t i n g e f f e c t s o f g r a s s c o m p e t i t i o n , f e r t i l i z i n g , and c u l t i v a t i o n on t h e e a r l y growth o f P i n u s r a d i a t a D. Don. A u s t . F o r . Res . 7:247-252. Tamm. C . O . 1968. An at tempt t o a s s e s s the optimum n i t r o g e n l e v e l i n Norway Spruce under f i e l d c o n d i t i o n s . R o y a l C o l l . F o r . S tockho lm. No. 61. Tamm, C . O . 1969. F e r t i l i z a t i o n i n f o r e s t s t a n d s from the p o i n t o f v i ew o f n u t r i t i o n o f f o r e s t t r e e s p e c i e s . T h i r d I n t e r . Conf . on F o r e s t y i e l d F o r e s t F e r t i l i z a t i o n , Prague , June 23-26, 1969. Tamm, C . O . 1974. Exper iments t o a n a l y s e the b e h a v i o i r o f young s p r u c e f o r e s t a t d i f f e r e n t n u t r i e n t l e v e l s . Paper r e a d a t t h e f i r s t I n t e r n a t i o n a l Congress o f E c o l o g y . 1974. Tamm, C . O . 1975. P l a n t n u t r i e n t s as l i m i t i n g f a c t o r s i n ecosystem d y n a m i c s . P p . 1 2 3-132 i n P r o d u c t i v i t y o f Wor ld Ecosys t ems . F i f t h Gen. Assembly o f the S p e c i a l Committee f o r the I n t e r n . B i o l . P r o g . A u g . 31 - S e p t . , 1972. Tamm, C . O . 1985. The Swedish optimum n u t r i t i o n exper iments i n f o r e s t s t a n d s - a ims , methods, y i e l d r e s u l t s . K . Skogs . o. L a n t b r . a k a d . t i d s k r . S u p p l . 17:30-39 . Tamm, C . O . and A . A r o n s s o n . 1982. Optimum n u t r i t i o n o f some n o n - f o o d p l a n t s . Paper p r e s e n t d a t t h e c o n g r e s s : O p t i m i z a t i o n o f y i e l d s - the r o l e o f f e r t i l i z e r s . 1 2 t n I n t e r n a t i o n a l Potash I n s t i t u t e Congress a t G o s l a r , f e d e r a l R e p u b l i c o f Germany. June 21-25 , 1982. Tamm, C . O . and A . A r o n s s o n and H . B u r g t o r f . 1980. Above ground p r o d u c t i o n o f Norway s p r u c e a t optimum n u t r i e n t s u p p l y on a low p o t e n t i a l s i t e . P o s t e r p r e s e n t e d a t I n t e r n . UNESCO-MAB/IUFRO Symposium s t a b i l i t y o f Spruce F o r e s t 150 ecosys tems . BRNO/Czech. O c t . 29-Nov. 2, 1979. Tamm, C O . and A . P e t t e r s s o n . 1969. S t u d i e s o f n i t r o g e n m o b i l i z a t i o n i n f o r e s t s o i l s . S t u d i a F o r e s t a l i a S u e c i c a . No. 75. Theodorou , C . and G . D . Bowen. 1983. E f f e c t s o f t e m p e r a t u r e , m o i s t u r e , and l i t t e r on n i t r o g e n m i n e r a l i z a t i o n i n P i n u s r a d i a t a F o r e s t S o i l s . A u s t . J . F o r . Res . 13:113-119. T h o r u d , D . B . 1983. Opening remarks , p . 1 i n F o r e s t S i t e and C o n t i n u o u s P r o d u c t i v i t y . IUFRO M e e t i n g , Aug 22-28, 1982, S e a t t l e . U . S . D . A . F o r . S e r v . Gen. T e c h . Rep. PNW 163. Timmer, V . R . and E . L . S t o n e . 1978. Comparat ive f o l i a r a n a l y s i s o f young balsam f i r f e r t i l i z e d w i t h n i t r o g e n , phosphorous , p o t a s s i u m and l i m e . S o i l S c i . S o c . o f Am. J . :125-130. T u r n e r , J . 1977. E f f e c t o f n i t r o g e n a v a i l a b i l i t y on n i t r o g e n c y c l i n g i n a D o u g l a s - f i r s t a n d . F o r . S c i . 2 3 ( 3 ) : 3 0 7 -316. T u r n e r , J . 1981. I n t e r a c t i o n s o f n i t r o g e n w i t h o t h e r n u t r i e n t s i n c o n i f e r o u s s t a n d s . Pp. 311-326 i n R u n n i n g , R . A . and F . J . H i n g s t o n . ( e d s ) . Managing N i t r o g e n Economies o f N a t u r a l o f N a t u r a l and Man Made F o r e s t Ecosys t ems . P r o c . CSIRO Workshop. A u s t r a l i a . 5-9 O c t . , 1980. T u r n e r , J . , S . F . D i c e , D.W. C o l e , and S . P . G e s s e l . 1978. V a r i a t i o n o f n u t r i e n t s i n f o r e s t t r e e f o l i a g e - a r e v i e w . C o l l e g e o f F o r e s t R e s o u r c e s . U n i v e r s i t y o f Wash ington . I n s t i t u t e o f F o r e s t P r o d u c t s C o n t r i b u t i o n Number 35. 33 p p . Van C l e v e , K . and R. W h i t e . 1980. F o r e s t - f l o o r dynamics i n a 6 0 - y e a r o l d paper b i r c h ecosystem i n i n t e r i o r A l a s k a , P l a n t and S o i l 54:359-381. van den D r i e s c h e , R .1974 . P r e d i c t i o n o f m i n e r a l n u t r i e n t s t a t u s o f t r e e s by f o l i a r a n a l y s i s . B o t . Rev . 40:347-394. V i e t s J r , F . C 1972. Water d e f i c i t s and n u t r i e n t a v a i l a b i l i t y i n K o z l o w s k i , T . T . ( e d . ) Water D e f i c i t s and P l a n t Growth. Academic P r e s s . 3:217-239. V i t o u s e k , P . 1982. N u t r i e n t c y c l i n g and n u t r i e n t use e f f i c i e n c y . The Amer ican N a t u r a l i s t 119(4) :553-571 . V i t o u s e k , P . M . and P . A . Matson . 1985. D i s t u r b a n c e , n i t r o g e n a v a i l a b i l i t y , and n i t r o g e n l o s s e s i n an i n t e n s i v e l y 151 m a n a g e d l o b l o l l y p i n e p l a n t a t i o n . E c o l o g y 66(4) :1360-1376. V l a s s a k , K. 1970. T o t a l s o i l n i t r o g e n and n i t r o g e n m i n e r a l i z a t i o n . P l a n t and S o i l 32:27-32 . Walworth , J . L . and M . E . Sumner. 1987. The d i a g n o s i s and recommendation i n t e g r a t e d system (DRIS) . Advances i n S o i l S c i e n c e 6:149-188. W a r i n g , H . D . 1981. S i l v i c u l t u r a l and management problems i n s u p p l y i n g n i t r o g e n f o r p r o d u c t i o n f o r e s t r y . Pp. 83-123 i n R u n n i n g , R . A . and F . J . H i n g s t o n . ( e d s ) . Managing N i t r o g e n Economies o f N a t u r a l o f N a t u r a l and Man Made F o r e s t Ecosys tems . P r o c . CSIRO Workshop. A u s t r a l i a . 5-9 O c t . , 1980. W a r i n g , R . H . and C . T . Youngberg . 1972. E v a l u a t i n g f o r e s t s i t e s f o r p o t e n t i a l growth response o f t r e e s t o f e r t i l i z e r . Northwest S c i . 46:67-75 . W a r i n g , S . A . and J . M . Bremner. 1964. Ammonium p r o d u c t i o n i n s o i l under w a t e r l o g g e d c o n d i t i o n s as an index o f n i t r o g e n a v a i l a b i l i t y . Nature 201:951-952. W a r i n g , R . H . , A . J . S . Mcdona ld , S. L a r s s o n , T . E r i c s s o n , A . W i r e n , E . A r w i d s s o n , A . E r r i c s s o n , and T . Lohammer. 1985. D i f f e r e n c e s i n c h e m i c a l c o m p o s i t i o n o f p l a n t s grown a t c o n s t a n t r e l a t i v e growth r a t e s w i t h s t a b l e m i n e r a l n u t r i t i o n . O e c o l o g i a ( B e r l i n ) 66:157-160. Webber. G . E . 1985. T h r e e - y e a r growth and f o l i a r re sponse i n a l o d g e p o l e optimum n u t r i t i o n e x p e r i m e n t . BSF T h e s i s . F a c . F o r e s t r y . U . B . C . (unpubl i shed) 77 p p . Webster , S . R . 1978. Comparison o f a v a i l a b l e n i t r o g e n p r o c e d u r e s f o r D o u g l a s - f i r (Pseudotsuga m e n z i e s i i ) s o i l s . A g r o n . A b s t r . p . 1 9 4 . Weetman, G . F . 1983. U l t i m a t e f o r e s t p r o d u c t i v i t y i n N . A m e r i c a . Pp . 70-80 i n F o r e s t S i t e and C o n t i n u o u s P r o d u c t i v i t y . IUFRO M e e t i n g , Aug 22-28, 1982, S e a t t l e . Gen. T e c h . Rep. PNW 163. Weetman, G . F and R . F . F o u r n i e r . 1982. Okanagan F a l l s , B . C . -Optimum n u i t r i t i o n E x p e r i m e n t . E s t a b l i s h m e n t R e p o r t , u n p u b l i s h e d . Weetman, G . F and R . F . F o u r n i e r . 1984. T e n - y e a r growth and n u t r i t i o n e f f e c t s o f a s traw t r e a t e m n t and o f r e p e a t e d f e r t i l i z a t i o n on j a c k p i n e . Can . J . F o r . Res . 14:416-423. Weetman, G . F . , R . F . F o u r n i e r , E . Panazzo , and R. B r o c k l e y . 152 1989. The r e l a t i o n between s o i l n i t r o g e n m i n e r a l i z a t i o n r a t e s , f i r s t season n e e d l e w e i g h t , f o l i a r n i t r o g e n c o n t e n t and f e r t i l i z e r response o f young l o d g e p o l e p i n e . U n p u b l i s h e d . Weetman, G . F . and C . W e l l s . 1989. P l a n t a n a l y s i s as an a i d i n f e r t i l i z i n g f o r e s t s , i n S o i l T e s t i n g and P l a n t A n a l y s i s . S o i l S c i . S o c . o f Am. In p r e s s . Weetman, G . F . , R . C . Y a n g and I . E . B e l l a . 1985. N u t r i t i o n and f e r t i l i z a t i o n o f l o d g e p o l e p i n e . Pp. 225-230 i n Lodgepo le P i n e - the s p e c i e s and I t s Management. Symp. P r o c . May 8-10, Spokane, Wash, and May 14-16, 1984, V a n c o u v e r , B . C . Westermann, D . T . and S . E . C r o t h e r s . 1980. M e a s u r i n g s o i l n i t r o g e n m i n e r a l i z a t i o n under f i e l d c o n d i t i o n s . A g r o n . J . 72:1009-1011. Whitehead D. and P . G . J a r v i s . 1981. C o n i f e r o u s f o r e s t s and p l a n t a t i o n s i n T . T . K o z l o w s k i (ed.) Water D e f i c i t s and P l a n t Growth. Academic P r e s s . 6 :49-151. W i l k i n s o n , L . 1988. SYSTAT: The System f o r S t a t i s t i c s . E v a n s t o n , I L : S y s t a t , I n c . W i l l i a m s , B . L . 1972. N i t r o g e n m i n e r a l i z a t i o n and o r g a n i c m a t t e r d e c o m p o s i t i o n i n S c o t s p i n e humus. F o r e s t r y 45 (2 ) : 177-188. W i l l i a m s . B . L . 1983. N i t r o g e n t r a n s f o r m a t i o n s and d e c o m p o s i t i o n i n l i t t e r and humus from beneath c l o s e d -canopy S i t k a S p r u c e . F o r e s t r y 5 6 ( l ) : 1 7 - 3 2 . Woodland Resources S e r v i c e s . 1985. V a l u e added o p p o r t u n i t i e s f o r a l b e r t a l o d g e p o l e p i n e s o l i d wood p r o d u c t s . C a n -A l b e r t a FRDA r e p o r t . 15 p p . Woods, P . V . , R. J . R a i s o n and P . K . Khanna. 1980. S p a t i a l v a r i a t i o n i n some n i t r o g e n p o o l s and f l u x e s i n t h r e e e u c a l y p t f o r e s t s . Pp. 62-73 i n R u n n i n g , R . A . and F . J . H i n g s t o n . ( e d s ) . Managing N i t r o g e n Economies o f N a t u r a l and Man Made F o r e s t Ecosys t ems . P r o c . CSIRO Workshop. A u s t r a l i a . 5-9 O c t . , 1980. Z a r , J . H . 1974. B i o s t a t i s t i c a l A n a l y s i s . P r e n t i c e - H a l l , I n c . 620 p p . APPENDIX 154 ANALYSIS OF VARIANCES TABLES GROWING SEASON NET MINERALIZATION (SQUARE ROOT + 210) N = 17 MULTIPLE R = .270 SQUARED MULTIPLE R = .073 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO P BLOCK 2.135 2 1. 068 0. 028 0. 972 N 10.607 2 5.304 0.142 0. 870 PK 0.294 1 0.294 0.008 0. 931 N*PK 12.651 2 6. 326 0.169 0. 847 ERROR 337.286 9 37.476 GROWING SEASON UPTAKE (SQUARE ROOT + 55) N = 17 MULTIPLE R = .477 SQUARED MULTIPLE R = .228 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO P BLOCK 0.132 2 0.066 0. 002 0. 998 N 39.248 2 19.624 0.621 0. 559 PK 30.499 1 30.499 0.965 0. 351 N*PK 5.228 2 2.614 0.083 0. 921 ERROR 284.304 9 31.589 1 5 5 MONTHLY NET MINERALIZATION ( S Q U A R E R O O T + 1 0 0 ) N = 6 8 M U L T I P L E R = . 4 7 5 S Q U A R E D M U L T I P L E R = . 2 2 6 A N A L Y S I S O F V A R I A N C E S O U R C E S U M - O F - S Q U A R E S D F M E A N S Q U A R E F - R A T I O P B L O C K 0 . 6 5 4 2 0 . 3 2 7 0 . 0 5 5 0 . 9 4 7 N 6 . 1 5 3 2 3 . 0 7 7 0 . 5 1 3 0 . 6 0 2 P K 1 . 0 2 0 1 1 . 0 2 0 0 . 1 7 0 0 . 6 8 2 P E R I O D 1 2 . 0 8 2 3 4 . 0 2 7 0 . 6 7 2 0 . 5 7 4 N * P K 3 . 5 0 4 2 1 . 7 5 2 0 . 2 9 2 0 . 7 4 8 N * P E R I O D 3 7 . 8 6 0 6 6 . 3 1 0 1 . 0 5 3 0 . 4 0 6 P K * P E R I O D 6 . 4 3 0 3 2 . 1 4 3 0 . 3 5 8 0 . 7 8 4 N * P K * P E R I O D 3 . 6 6 7 6 0 . 6 1 1 0 . 1 0 2 0 . 9 9 6 E R R O R 2 5 1 . 7 9 5 4 2 5 . 9 9 5 MONTHLY UPTAKE ( S Q U A R E R O O T + 5 5 ) N = 6 8 M U L T I P L E R = . 5 0 0 S Q U A R E D M U L T I P L E R = . 2 5 0 A N A L Y S I S O F V A R I A N C E S O U R C E S U M - O F - S Q U A R E S D F M E A N S Q U A R E F - R A T I O P B L O C K 0 . 4 5 8 2 0 . 2 2 9 0 . 0 3 8 0 . 9 6 3 N 1 7 . 1 8 4 2 8 . 5 9 2 1 . 4 3 0 0 . 2 5 1 P K 1 9 . 9 0 1 1 1 9 . 9 0 1 3 . 3 1 1 0 . 0 7 6 P E R I O D 7 . 9 3 6 3 2 . 6 4 5 0 . 4 4 0 0 . 7 2 5 N * P K 6 . 2 6 1 2 3 . 1 3 1 0 . 5 2 1 0 . 5 9 8 N * P E R I O D 1 4 . 8 4 9 6 2 . 4 7 5 0 . 4 1 2 0 . 8 6 7 P K * P E R I O D 8 . 7 8 6 3 2 . 9 2 9 0 . 4 8 7 0 . 6 9 3 N * P K * P E R I O D 3 . 6 1 4 6 0 . 6 0 2 0 . 1 0 0 0 . 9 9 6 E R R O R 2 5 2 . 4 1 2 4 2 6 . 0 1 0 ) MONTHLY EXCHANGEABLE NITROGEN 156 N = 85 MULTIPLE R = .890 SQUARED MULTIPLE R = .792 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO P BLOCK 14044. 236 2 7022. .118 7. 297 0. .002 N 139319. 189 2 69659. .594 72. 390 <0. .001 PK 307. 364 1 307. .364 0. 319 0. .574 PERIOD 4456. 854 4 1114. .213 1. 158 0. ,340 N*PK 1130. 243 2 565. .121 0. 587 0. .559 N*PERIOD 5032. 561 8 629. .070 0. 654 0. .729 PK*PERIOD 7926. 093 4 1981. .523 2. 059 0. .099 N*PK*PERIOD 13537. 957 8 1692. .245 1. 759 0. .106 ERROR 51001. 018 53 962. .283 CONTRASTS: NITROGEN EFFECT HYPOTHESIS NO N l N3 F P 1 2 -1 -1 62 . 511 <0. .001 2 0 1 -1 82 .269 <0. .001 GROSS MINERALIZABLE NITROGEN N = 85 MULTIPLE R = 0.551 SQUARED MULTIPLE R = 0.304 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO P BLOCK 1605.427 2 802.713 0.061 0.941 N 197667.693 2 98833.847 7.493 0.001 PK 17980.703 1 17980.703 1.363 0.247 N*PK 26757.590 2 13378.795 1.014 0.367 ERROR 1015588.173 77 13189.457 CONTRASTS: NITROGEN EFFECT HYPOTHESIS NO N l N3 1 2 - 1 - 1 2 1 - 1 0 3 1 0 - 1 4 0 - 1 1 F 5.009 0.257 11.921 9.978 P 0.028 0.614 0.001 0. 002 157 NET MINERALIZABLE NITROGEN N = 85 MULTIPLE R = 0.196 SQUARED MULTIPLE R = 0.038 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO P BLOCK N PK N*PK ERROR 4897.543 1805.002 1618.587 1393.631 247150.723 2 2 1 2 77 2448.772 902.501 1618.587 696.816 3209.750 0.763 0.470 0.281 0.756 0.504 0.480 0.217 0.805 FOLIAR NITROGEN CONCENTRATION N = 24 MULTIPLE R = 0.956 SQUARED MULTIPLE R = 0.914 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO P~~ BLOCK 0.106 2 0. 053 7. 036 0.008 N 0.942 3 0. 314 41. 683 <0.0001 PK 0.015 1 0. 015 1. 99 0.180 N*PK 0.063 3 0. 021 2. 805 0.078 ERROR 0.1055 14 0. 008 CONTRASTS: NITROGEN EFFECT HYPOTHESIS NO NI N2 N3 F P 1 3 -1 -1 -1 85 .204 <0.0001 2 1 -1 0 0 17 .832 0.0009 3 0 1 -1 0 13 .378 0.0026 4 0 0 1 -1 6 .900 0.0199 158 FOLIAR WEIGHT N = 24 MULTIPLE R = 0.871 SQUARED MULTIPLE R = 0.759 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO BLOCK N PK N*PK ERROR 3.002 65.042 338.250 93.594 158.982 2 3 1 3 14 1.501 21.681 338.250 31.198 11.356 0.132 0.877 1.909 0.174 29.786 0.0001 2.747 0.082 FOLIAR NITROGEN CONTENT N = 24 MULTIPLE R = 0.900 SQUARED MULTIPLE R = 0.811 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO BLOCK N PK N*PK ERROR 0.006 0.106 0. 098 0.061 0.064 2 3 1 3 14 0.003 0. 035 0. 098 0.020 0.004 0.704 0.512 7.805 0.003 21.567 0.0004 4.504 0.021 159 SOIL WETNESS N = 336 MULTIPLE R = .714 SQUARED MULTIPLE R = .509 ANALYSIS OF VARIANCE SOURCE SUM-OF--SQUARES DF MEAN SQUARE F-RATIO P BLOCK 86. .956 2 43. .478 1. 774 0. , 171 N 325. .647 2 162. .823 6. 645 0. .002 PK 319. .554 1 319. ,554 13. 042 <0. ,001 PERIOD 6691. .907 3 2230. .636 91. 040 <0. ,001 N*PK 69. .101 2 34. .551 1. 41 0. ,245 N*PERIOD 123. .460 6 20. .577 0. 840 0. .540 PK*PERIOD 75. ,516 3 25, , 172 1. 027 0. ,381 N*PK*PERIOD 150. .828 6 25. , 138 1. 026 0. ,408 ERROR 7595. .549 310 24. ,502 CONTRASTS: NITROGEN EFFECT HYPOTHESIS NO N l N2 F P 1 2 - 1 - 1 3.104 0.079 2 1 - 1 0 9.283 0.003 3 1 0 - 1 0.006 0.937 4 0 1 - 1 10.122 0.002 N UPTAKE CALCULATED FROM BIOMASS ESTIMATES N = 24 MULTIPLE R = . 986 SQUARED MULTIPLE R = .972 ANALYSIS OF VARIANCE SOURCE SUM-OF-SQUARES DF MEAN SQUARE F-RATIO P BLOCK 14.317 2 7.158 2.855 0. 135 B81 16.506 1 16.506 6. 583 0. 043 N 15.244 3 5.081 2 . 027 0. 212 PK 0.473 1 0.473 0.189 0. 679 B81*N 23.033 3 7.678 3 . 062 0. 113 B81*PK 0.861 1 0.861 0.343 0. 579 N*PK 5.927 3 1.976 0.788 0. 543 B81*N*PK 1.293 3 0.431 0.172 0. 912 ERROR 15.043 6 2.507 Where B81 = i n i t i a l b i o m a s s i n 1981. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0097575/manifest

Comment

Related Items