UBC Theses and Dissertations

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UBC Theses and Dissertations

Evaluation of the nitrification inhibitors n-serve and atc with urea fertilizer Guthrie, Thomas Flagstad 1981

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EVALUATION OF THE NITRIFICATION INHIBITORS N-SERVE AND ATC WITH UREA FERTILIZER by THOMAS FLAGSTAD GUTHRIE B . S c , C o r n e l l U n i v e r s i t y , 1967 M . S c , C o r n e l l U n i v e r s i t y , 1976 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department o f S o i l S c i e n c e ) We a c c e p t t h i s t h e s i s as co n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1981 (F) Thomas F l a g s t a d G u t h r i e , 1981 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e h e a d o f my d e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f S>O/'/ SdV'&^cJZ^ The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 D a t e D K - f i (2/7<n - i i -ABSTRACT The purpose o f u s i n g c h e m i c a l n i t r i f i c a t i o n i n h i b i t o r s i s t o d e l a y the o x i d a t i o n o f ammoniacal f e r t i l i z e r s d u r i n g the e a r l y p a r t o f the growing season i n o r d e r t o m i n i m i z e N l o s s e s p r i o r t o the p e r i o d o f maximum c r o p uptake. S i n c e NH^ i s e l e c t r o s t a t i c a l l y a t t r a c t e d t o s o i l p a r t i c l e s , l e a c h -i n g l o s s e s would be m i n i m i z e d , and d e n i t r i f i c a t i o n l o s s e s c o u l d not o c c u r i n the absence o f N0 3~. Thus, s m a l l e r amounts o f f e r t i l i z e r N would be r e q u i r e d , r e s u l t i n g i n lower i n p u t s o f money and energy as w e l l as l e s s p o t e n t i a l f o r e n v i r o n m e n t a l p o l l u t i o n . A study ( C h a p t e r Two) was i n i t i a t e d i n the f a l l o f 1977 t o d e t e r m i n e i f ATC c o u l d m i n i m i z e o v e r w i n t e r l o s s e s o f f a l l - a p p l i e d N. Urea (200 kg N/ha) w i t h o r w i t h o u t a 1% c o a t i n g : o f ATC ( 4 - a m i n o - l , 2 , 4 - t r i a z o l e ) was banded or b r o a d c a s t onto a s i l t s o i l on November 8, when the s o i l tempera-t u r e a t 10 cm depth was 1.9°C. The s o i l was sampled t o a depth o f 90 cm a t a p p r o x i m a t e l y one month i n t e r v a l s u n t i l A p r i l , and NH^ + and NO^" were det e r m i n e d . In the banded p l o t s , some n i t r i f i c a t i o n o c c u r r e d p r i o r t o J a n u a r y , but from t h i s date u n t i 1 March t h e r e was v e r y l i t t l e change i n s o i l N H 4 + l e v e l s . O v e r a l l , from December t o A p r i l , t h e r e were 70 and 48% d e c r e a s e s i n the 0-15 cm p l o t s w i t h o u t and w i t h ATC, r e s p e c t i v e l y . In a l l the b r o a d c a s t p l o t s , r e g a r d l e s s o f ATC t r e a t m e n t , n i t r i f i c a t i o n proceeded s t e a d i l y t h r o u g h o u t the s a m p l i n g p e r i o d , w i t h 93 and 85% d e c r e a s e s from the December 0-15 cm NH^1" l e v e l s i n the non-ATC and ATC p l o t s , r e s p e c t i v e l y . I t i s c o n c l u d e d t h a t ATC i s p a r t i a l l y e f f e c t i v e i n m i n i m i z i n g N l o s s e s when a p p l i e d i n the f a l l as a band w i t h u r e a , but when b r o a d c a s t t h e r e i s no e f f e c t on n i t r i f i c a t i o n . L e a c h i n g o f the w a t e r - s o l u b l e ATC was the l i k e l y cause o f i t s poor e f f e c t i v e n e s s . S i g n i f i c a n t l e a c h i n g o f urea from the zone o f a p p l i c a t i o n was a l s o found t o o c c u r d u r i n g the f i r s t month f o l l o w i n g i t s a p p l i c a t i o n . A l a b o r a t o r y s t u d y ( C h a p t e r T h r e e ) was c o n d u c t e d t o d e t e r m i n e the i n f l u e n c e o f the n i t r i f i c a t i o n i n h i b i t o r s ATC and N-Serve [ 2 - c h l o r o - 6 -( t r i c h l o r o m e t h y l ) - p y r i d i n e ] on urea h y d r o l y s i s i n a s i l t s o i l a t 2 and 12°C. There was no d e l a y o f u r e o l y s i s caused by the p r e s e n c e o f t h e s e c h e m i c a l s , even a t 20 times the recommended a p p l i c a t i o n r a t e . At 2°C the r a t e o f h y d r o l y s i s was about h a l f t h a t a t 12°C, w i t h 21 and 7 days b e i n g r e q u i r e d f o r complete h y d r o l y s i s a t 2 and 12°C, r e s p e c t i v e l y . These r e s u l t s s u g g e s t t h a t l e a c h i n g o f u r e a may o c c u r f o l l o w i n g i t s a p p l i c a t i o n t o a c o l d s o i l d u r i n g p e r i o d s o f heavy p r e c i p i t a t i o n as was found i n the w i n t e r n i t r i f i c a -t i o n study ( C h a p t e r Two). A s e r i e s o f f i e l d e x p e r i m e n t s ( C h a p t e r Four) was c o n d u c t e d w i t h s i l a g e c o r n (Zea mays L.) t o compare the e f f e c t i v e n e s s o f the n i t r i f i c a t i o n i n h i b i -t o r s ATC and N-Serve i n a loamy sand and a s i l t . Urea was c o a t e d w i t h the i n h i b i t o r s a t a r a t e o f 1% o f a c t i v e i n g r e d i e n t per w e i g h t o f N and a p p l i e d as a band o r b r o a d c a s t i n the s p r i n g o f 1977 and 1978. N e i t h e r i n h i b i t o r s i g n i f i c a n t l y a f f e c t e d n i t r i f i c a t i o n when a p p l i e d as a b r o a d c a s t t r e a t m e n t t o e i t h e r s o i l . In the s i l t , both i n h i b i t o r s were e q u a l l y e f f e c t i v e i n d e l a y i n g n i t r i f i c a t i o n when banded, whereas i n the loamy sand ATC was much more e f f e c -t i v e than N-Serve. The e f f e c t i v e n e s s o f N-Serve p e r s i s t e d much l o n g e r i n t h e s i l t (86 days) than i n the loamy sand (23 d a y s ) . T h i s s u g g e s t e d t h a t v o l a t i - . l i z a t i o n o f N-Serve s e v e r e l y l i m i t e d i t s e f f e c t i v e n e s s i n the loamy sand. There was no s i g n i f i c a n t improvement i n c r o p y i e l d s o r N c o n t e n t due t o i n h i b i t o r t r e a t m e n t i n e i t h e r s o i l . - i v -TABLE OF CONTENTS Page INTRODUCTION (C h a p t e r One) 1 L i t e r a t u r e C i t e d 13 EFFECTS OF 4-AMIN0-1,2,4-TRIAZOLE ON TRANSFORMATIONS OF FALL- 17 APPLIED UREA-N ( C h a p t e r Two) A b s t r a c t 17 I n t r o d u c t i o n 19 Methods and M a t e r i a l s 21 R e s u l t s and D i s c u s s i o n 26 Banded f e r t i l i z e r a p p l i c a t i o n 26 B r o a d c a s t f e r t i l i z e r a p p l i c a t i o n 30 C o n c l u s i o n s 35 L i t e r a t u r e C i t e d 37 EFFECTS OF LOW TEMPERATURES AND NITRIFICATION INHIBITORS ON UREA 39 HYDROLYSIS ( C h a p t e r Three) A b s t r a c t 39 I n t r o d u c t i o n 40 Methods and M a t e r i a l s 41 R e s u l t s and D i s c u s s i o n 42 L i t e r a t u r e C i t e d 46 NITRIFICATION INHIBITION BY N-SERVE AND ATC IN SOILS OF VARYING 47 TEXTURE (C h a p t e r Four) A b s t r a c t 47 I n t r o d u c t i o n 49 Methods and M a t e r i a l s 51 - v -Page R e s u l t s and D i s c u s s i o n 57 1977 s i l t s o i l r e s u l t s (Experiment 1) 57 1978 s i l t s o i l r e s u l t s (Experiment 2) 63 1978 cropped loamy sand s o i l r e s u l t s ( E xperiment 3) 65 1978 f a l l o w loamy sand s o i l r e s u l t s ( E x p e r i m e n t 4) 69 Crop r e s u l t s 71 C o n c l u s i o n s 75 L i t e r a t u r e C i t e d 76 SUMMARY AND CONCLUSIONS ( C h a p t e r F i v e ) 78 APPENDIX 1.1. F i e l d d e s c r i p t i o n o f s i l t s o i l used i n study 82 1.2. F i e l d d e s c r i p t i o n o f loamy sand s o i l used i n st u d y 83 2.1. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1977 s i l t 85 (Exp e r i m e n t 1) on v a r i o u s sampling dates 2.2. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1978 s i l t 86 (Experiment 2) on v a r i o u s s a m p l i n g d a t e s 2.3. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1978 cropped 87 loamy sand (Experiment 3) on v a r i o u s sampling d a t e s 2.4. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1978 f a l l o w 88. loamy sand ( E x p e r i m e n t 4) on v a r i o u s s a m p l i n g d a t e s 3. S e l e c t e d p h y s i c a l and c h e m i c a l p r o p e r t i e s o f s o i l s 89 used i n t h e s i s r e s e a r c h , 1977-1978 - v i -LIST OF TABLES T a b l e Page 2.1 S e l e c t e d p h y s i c a l and che m i c a l p r o p e r t i e s a t d i f f e r e n t depths o f s o i l used i n w i n t e r n i t r i f i c a t i o n s t u d y 22 2.2 S o i l m o i s t u r e , p r e c i p i t a t i o n , and average s o i l tempera-t u r e s between sampling d a t e s , 1977-1978 25 2.3 Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n banded and c o n t r o l p l o t s on v a r i o u s sampling dates as a f f e c t e d by urea-N and ATC n i t r i f i c a t i o n i n h i b i t o r , 1977-1978 27 2.4 Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n b r o a d c a s t and c o n t r o l p l o t s on v a r i o u s sampling d a t e s as a f f e c t e d by urea-N and ATC n i t r i f i c a t i o n i n h i b i t o r , 1977-1978 31 3.1 E f f e c t s o f te m p e r a t u r e , N-Serve and ATC on urea hydro-l y s i s i n a s o i l 43 4.1 E x p e r i m e n t a l c o n d i t i o n s p r e v a i l i n g d u r i n g s t u d i e s o f the e f f e c t s o f ATC and N-Serve on n i t r i f i c a t i o n and c o r n p r o d u c t i o n 53 4.2 S o i l m o i s t u r e t e n s i o n (0-15 and 15-30 cm), average s o i l t emperature (10 cm depth) and c u m u l a t i v e p r e c i -p i t a t i o n between sampling dates a t S i t e s 1 and 2, 1977 and 1978 56 4.3 Y i e l d o f s i l a g e d r y m a t t e r , % t o t a l N i n h a r v e s t and s i l k l e a v e s i n Experiments 1, 2, and 3 as a f f e c t e d by r a t e o f N, typ e o f NI and placement o f N 72 - v i i -LIST OF FIGURES F i g u r e Page 1.1 Chemical s t r u c t u r e and p r o p e r t i e s o f ATC and N-Serve 10 2.1 NH^-N i n 0-15 cm h o r i z o n e x p r e s s e d as % o f NH^-N p r e s e n t i n Dec. 5 samples v s . t i m e , 1977-1978 34 4.1 R a t i o o f ppm NH4-N/ppm N0 3-N i n 0-15 cm depth o f 1977 s i l t as a f f e c t e d by method o f N a p p l i c a t i o n , p r e s e n c e o f n i t r i f i c a t i o n i n h i b i t o r , and time. In t h i s and subsequent f i g u r e s d a t a p o i n t s f o r each sampling d a t e accompanied by the same number are 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 . 0 5 ) 58 4.2 C o n c e n t r a t i o n o f NhL-N (ppm) i n 0-15 cm depth o f 1977 s i l t as a f f e c t e d by method o f N a p p l i c a t i o n , p r e s e n c e o f n i t r i -f i c a t i o n i n h i b i t o r , and time 60 4.3 Sum o f exchangeable (ppm NH 4 + ppm N0 3)-N i n 0-15 cm depth o f 1977 s i l t as a f f e c t e d by method o f N a p p l i c a t i o n , p r e s e n c e o f n i t r i f i c a t i o n i n h i b i t o r , and time 61 4.4 R a t i o o f ppm NH4-N/ppm N0 3~N i n 0-15 cm depth o f 1978 s i l t as a f f e c t e d by^me-tJaod o f N a p p l i c a t i o n , _ type o f n i t r i f i c a t i o n i n h i b i t o r , and time 64 4.5 , R a t i o o f ppm NH4-N/ppm N0 3-N i n 0-15 cm depth o f 1978 cropped loamy sand as a f f e c t e d by method o f N a p p l i c a -t i o n , type o f n i t r i f i c a t i o n i n h i b i t o r , and time 66 4.6 R a t i o o f ppm NH4-N/ppm N0 3~N i n 0-15 cm depth o f 1978 f a l l o w loamy sand as a f f e c t e d by method o f N a p p l i c a t i o n , t y p e o f n i t r i f i c a t i o n i n h i b i t o r , and time 70 - v i i i -ACKNOWLEDGEMENTS The a u t h o r wishes t o thank Dr. A.A. Bomke f o r h i s h e l p f u l s u p e r -v i s i o n t h r o u g h o u t t h i s p r o j e c t . O t h e r members o f the S o i l S c i e n c e Department who a i d e d me i n my r e s e a r c h o r p r e p a r a t i o n o f t h i s t h e s i s were: V a l e r i e M a r s h a l l ( t y p i n g ) , Anne Macadam ( f i e l d work and l a b o r a t o r y a n a l y s i s ) , J u l i e L a n s i q u o t ( d r a f t i n g ) , Dr. T.A. B l a c k (equipment f o r m o n i t o r i n g s o i l t e m p e r a t u r e ) . I am a l s o g r a t e f u l t o S a n n i f e r L o u i e f o r t y p i n g the f i n a l d r a f t and t o Ron K i t z e l f o r p r o v i d i n g the s i t e f o r much o f my f i e l d work. I a l s o w i s h t o thank my w i f e , Mary, f o r her s u p p o r t and p a t i e n c e d u r i n g my degree program. F i n a n c i a l a s s i s t a n c e f o r t h i s p r o j e c t was s u p p l i e d by Western C o o p e r a t i v e s F e r t i l i z e r s L t d . and the Western Canada F e r t i l i z e r A s s o c i a t i o n . - 1 -Chapter One INTRODUCTION Importance o f N F e r t i l i z e r P l a n t s , l i k e a l l o r ganisms, r e q u i r e n i t r o g e n (N) f o r t h e i r growth and r e p r o d u c t i o n . N i t r o g e n i s a c o n s t i t u e n t o f a l l p r o t e i n , a l l enzymes, many o f the m e t a b o l i c i n t e r m e d i a t e s i n v o l v e d i n s y n t h e s i s and energy t r a n s f e r , and even o f the d e o x y r i b o n u c l e i c a c i d s making up the g e n e t i c code i t s e l f . Of the elements n e c e s s a r y f o r h i g h e r p l a n t growth, N i s u s u a l l y r e q u i r e d i n l a r g e r q u a n t i t i e s than any o t h e r element absorbed from the s o i l . F o r a 9400. kg/ha y i e l d o f c o r n g r a i n (Zea mays L . ) , 146 kg N, 28 kg P, 39 kg K, 17 kg Ca, and 24 kg Mg a r e removed per h e c t a r e ( M a r t i n e t aj_., 1976).. Some s o i l s can s t i l l s u p p l y a l l o f the N needs o f the c r o p . T h i s i s most p r o b a b l e where m o i s t u r e d e f i c i t l i m i t s c r o p y i e l d s , and l o s s e s o f N a r e m i n i m a l , such as the steppe and p r a i r i e r e g i o n s o f the w o r l d . Areas o f h i g h e r r a i n f a l l , such as the c o a s t a l r e g i o n s o f North America, g e n e r a l l y r e q u i r e N a p p l i c a t i o n s f o r optimum y i e l d s s i n c e c r o p growth i s not l i m i t e d by l a c k o f m o i s t u r e , and N l o s s e s by l e a c h i n g and d e n i t r i f i c a t i o n a r e s i g n i f i c a n t . Under f a v o r a b l e c o n d i t i o n s , 80% o r more o f the f e r t i l i z e r N may be r e c o v e r e d by the crop to which i t was a p p l i e d . However, under many s o i l and c r o p p i n g c o n d i t i o n s , e f f i c i e n c i e s o f 50% o r l e s s a r e not uncommon ( A l l i s o n , 1955; Prasad e t a l _ . , 1971). Loss Mechanisms f o r N F e r t i l i z e r Most N f e r t i l i z e r s a r e s u b j e c t t o c e r t a i n c h e m i c a l , p h y s i c a l and b i o c h e m i c a l e v e n t s which can r e s u l t i n s i g n i f i c a n t l o s s e s o f N from the s o i l -- 2 -r o o t zone a f t e r a p p l i c a t i o n . L o s s e s o c c u r p r i n c i p a l l y t h r o u g h ( i ) l e a c h i n g o f n i t r i t e (NO^ -) and n i t r a t e ( N 0 3 + ) ; ( i i ) b i o l o g i c a l d e n i t r i f i c a t i o n o f both N02~ and NO^ -; ( i i i ) v o l a t i l i z a t i o n o f ammonia (NH3) f o l l o w i n g improper a p p l i c a t i o n o f anhydrous o r aqua NH^ and s u r f a c e a p p l i c a t i o n o f urea and o t h e r ammoniacal N s o u r c e s t o n e u t r a l o r a l k a l i n e s o i l s ; and ( i v ) c h e m i c a l d e n i t r i -f i c a t i o n a c c o r d i n g t o mechanisms proposed by A l l i s o n (1963). F e r t i l i z e r N can a l s o be l o s t t h r o u g h (v) s u r f a c e r u n o f f and e r o s i o n , ( v i ) i n t e r l a t t i c e f i x a t i o n o f ammonium ( N H 4 + ) by c l a y m i n e r a l s , ( v i i ) m i c r o b i o l o g i c a l i m m o b i l i z a -t i o n , and ( v i i i ) c h e m i c a l i m m o b i l i z a t i o n i n v o l v i n g r e a c t i o n s o f f e r t i l i z e r N w i t h s o i l o r g a n i c components. The l a t t e r t h r e e mechanisms r e p r e s e n t temp-o r a r y l o s s e s , s i n c e f i x e d o r i m m o b i l i z e d N i s g r a d u a l l y r e l e a s e d o v e r t i m e . Reasons f o r I n c r e a s i n g F e r t i l i z e r N E f f i c i e n c y A t l e a s t t h r e e good r e a s o n s e x i s t f o r i m p r o v i n g the e f f i c i e n c y o f N f e r -t i l i z e r a p p l i c a t i o n s . I n c r e a s e d e f f i c i e n c y would ( i ) save money due t o lower a p p l i c a t i o n r a t e s , ( i i ) c o n s e r v e some o f t h e energy which i s c u r r e n t l y used f o r N f e r t i l i z e r p r o d u c t i o n , and ( i i i ) r e d u ce t h e e n v i r o n m e n t a l p o l l u t i o n w h ich sometimes r e s u l t s from N f e r t i l i z e r s . From t h e f a r m e r ' s v i e w p o i n t , s a v i n g money i s o f g r e a t e s t importance. The c o s t o f N f e r t i l i z e r has i n c r e a s e d g r e a t l y d u r i n g r e c e n t y e a r s , from $105 per m e t r i c t o n o f urea (23<£/kg N) i n 1975 t o $270 p e r m e t r i c t o n (60<£/kg N) i n 1980 ( p r i c e s i n B r i t i s h C o l u m b i a ) . In t h e p a s t , N f e r t i l i z e r was r e l a t i v e l y i n e x p e n s i v e , so f a r m e r s o f t e n used an e x c e s s t o e n s u r e optimum y i e l d s . But the g r e a t l y i n c r e a s e d c o s t o f N f e r t i l i z e r has caused f a r m e r s t o be more c o n s e r v a t i v e i n t h e i r a p p l i c a t i o n r a t e s , which may l e a d t o reduced y i e l d s u n l e s s the e f f i c i e n c y can be improved. - 3 -The manufacture o f N f e r t i l i z e r s r e q u i r e s a g r e a t d e a l o f e nergy, g e n e r a l l y i n the form o f n a t u r a l gas. T h i s i s one reason f o r the r a p i d i n c r e a s e i n p r i c e . D u r i n g 1972 i n the U n i t e d S t a t e s , 10.4 m i l l i o n m e t r i c tons o f anhydrous ammonia was produced f o r N f e r t i l i z e r , r e q u i r i n g 12.8 3 b i l l i o n m o f n a t u r a l gas. T h i s usage ac c o u n t e d f o r 2 p e r c e n t o f the 3 600 b i l l i o n m o f gas consumed t h a t y e a r ( J o n e s , 1979). The s i n g l e l a r g e s t energy i n p u t f o r c o r n p r o d u c t i o n i s the energy r e q u i r e d t o p r o -duce f e r t i l i z e r N. T h i s energy amounts t o over 30 p e r c e n t o f the e s t i -mated t o t a l 2.9 m i l l i o n k i l o c a l o r i e s r e q u i r e d t o produce 9400 kg/ha o f c o r n , u s i n g 125 kg/ha o f N f e r t i l i z e r ( P i m e n t e l e t a_l_., 1973). Thus, r e d u c t i o n o f N f e r t i l i z e r r a t e s would s i g n i f i c a n t l y d e c r e a s e the energy r e q u i r e m e n t f o r a g r i c u l t u r e . However, N f e r t i l i z e r e f f i c i e n c y would have t o be i n c r e a s e d i n o r d e r t h a t c r o p y i e l d s would not be lowered by u s i n g lower N f e r t i l i z e r r a t e s . R e d u c t i o n o f e n v i r o n m e n t a l c o n t a m i n a t i o n i s a n o t h e r i m p o r t a n t r e a s o n f o r d e c r e a s i n g N a p p l i c a t i o n r a t e s . N o r m a l l y , a l l forms o f N f e r t i l i z e r are c o n v e r t e d t o n i t r a t e s , p r i m a r i l y by the s o i l b a c t e r i a Nitrosomonas sp. ( o x i d i z e s N H 4 + t o NO,,-), and N i t r o b a c t e r sp. ( o x i d i z e s N0 2~ t o N 0 3 ~ ) . N i t r a t e s a r e v e r y s o l u b l e i n w a t e r , and s i n c e they are n e g a t i v e l y c h a r g e d , they a r e not e l e c t r o s t a t i c a l l y a t t r a c t e d t o the n e g a t i v e l y charged s o i l c o l l o i d s . Thus, NO^ i s v e r y s u s c e p t i b l e to l e a c h i n g i n the e v e n t o f p r e c i p i t a t i o n o r i r r i g a t i o n . . L e a c h i n g o f N0g~ can l e a d t o c o n t a m i n a t i o n .of d r i n k i n g water su p p l i e s . , and an a l l o w a b l e l i m i t f o r N0g~-N i n d r i n k i n g , water o f 10 m g / l i t e r has been adopted by - 4 -many a g e n c i e s . Enrichment o f l a k e s w i t h NO^ can l e a d t o i n c r e a s e d e u t r o -p h i c a t i o n r a t e s as w e l l as more r a p i d growth o f a l g a e and weeds. S e v e r a l s o u r c e s o f d r i n k i n g water i n C a l i f o r n i a (Ward, 1970) and I l l i n o i s (Harmeson e t al_, 1971) have been found t o be contaminated w i t h NO^" . o r i g i n a t i n g from f e r t i l i z e r a p p l i c a t i o n s . Under p a r t i a l l y a n a e r o b i c c o n d i t i o n s , c e r t a i n s o i l b a c t e r i a can use NO^" as an e l e c t r o n a c c e p t o r i n p l a c e o f oxygen which l e a d s t o the reduc-t i o n o f NO^" t o n i t r o g e n {H^) o r n i t r o u s o x i d e ( ^ 0 ) . As ^ 0 r i s e s t o the s t r a t o s p h e r e i t i s p h o t o c h e m i c a l l y o x i d i z e d t o form n i t r i c o x i d e (NO), which i n t u r n may r e a c t w i t h the ozone l a y e r . D e s t r u c t i o n o f the ozone l a y e r c o u l d l e a d t o i n c r e a s e d u l t r a v i o l e t r a d i a t i o n on the e a r t h ' s s u r f a c e , and thus a h i g h e r i n c i d e n c e o f human s k i n c a n c e r ( M c E l r o y e t _al_, 1977). Approaches t o Improving N F e r t i l i z e r E f f i c i e n c y An e f f i c i e n t means o f u s i n g N f e r t i l i z e r s i s t o a p p l y a p o r t i o n o f the N s h o r t l y b e f o r e the c r o p i s p l a n t e d and then a p p l y s i d e d r e s s i n g s o f N d u r i n g the growing season. T h i s m i n i m i z e s N l o s s e s , s i m p l y because the c r o p i s a b l e t o absorb t he N b e f o r e i t can be l e a c h e d o r d e n i t r i f i e d . However, i t i s c o s t l y i n terms o f l a b o r and equipment f o r the farmer t o make s e v e r a l N a p p l i c a t i o n s , and s o i l compaction would a l s o be i n c r e a s e d . T h i s p r a c t i c e i s g e n e r a l l y more a p p r o p r i a t e f o r home ga r d e n e r s o r vege-t a b l e f a r m e r s . S p r i n g o r summer N f e r t i l i z e r a p p l i c a t i o n s a re almost always more e f f i c i e n t than f a l l a p p l i c a t i o n s , s i n c e l e s s time i s a v a i l a b l e f o r l o s s e s o f N t o o c c u r . Stevenson and Baldwin (1969) found t h a t f a l l - a p p l i e d " 5 " ammonium n i t r a t e , u r e a , and anhydrous ammonia a l l r e s u l t e d i n s i g n i f i -c a n t l y lower c o r n g r a i n y i e l d s than s p r i n g - a p p l i e d N on c l a y , c l a y loam and s i l t loam s o i l s i n s o u t h e r n O n t a r i o o v e r a p e r i o d o f f o u r y e a r s . R e l a t i v e e f f i c i e n c i e s o f f a l l - a p p l i e d vs., s p r i n g - a p p l i e d N ranged from 0.30 t o 0.87 a t the v a r i o u s l o c a t i o n s , w i t h t h e lower e f f i c i e n c i e s b e i n g f o u n d i n t h e c l a y . s o i I s , presumably due t o g r e a t e r d e n i t r i f i c a t i o n l o s s e s . S i m i l a r r e s u l t s have been found by numerous o t h e r r e s e a r c h e r s , such as Welch e t al_ (1971) i n I l l i n o i s and F r y e (1977) i n Tennessee. The use o f c o a t i n g s on N f e r t i l i z e r p e l l e t s to d e c r e a s e t h e i r s o l u -b i l i t y and t h e r e b y r e d u c e l e a c h i n g l o s s e s i s a n o t h e r approach t o improv-i n g N f e r t i l i z e r e f f i c i e n c y . A c o m m e r c i a l l y a v a i l a b l e example o f t h i s i s s u l f u r - c o a t e d u r e a (SCU), which has c o a t i n g s o f s u l f u r , wax, and a m i c r o b i o c i d e t o d e l a y the o x i d a t i o n o f S. The urea i s not s u s c e p t i b l e t o h y d r o l y s i s and subsequent o x i d a t i o n t o n i t r a t e u n t i l the s u l f u r i s o x i d i z e d , which may r e q u i r e s e v e r a l weeks depending on the s o i l tempera-... t u r e and o t h e r f a c t o r s . Use o f SCU has been shown t o d e c r e a s e the l o s s o f NHg v i a v o l a t i l i z a t i o n which o f t e n o c c u r s f o l l o w i n g s u r f a c e a p p l i c a t i o n s o f u r e a (Matocha, 1976) and t o d e c r e a s e l e a c h i n g o f N from a sandy s o i l ( E l Wali e t al_, 1980). However, s t u d i e s by some r e s e a r c h e r s (Terman and A l l e n , 1974) have shown a d e c r e a s e i n N r e c o v e r y by c o r n when SCU was compared w i t h c o n v e n t i o n a l N s o u r c e s . 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 e s e f i n d i n g s i s t h a t t h e r e l e a s e o f N from t h e SCU i s n o t r a p i d enough t o a d e q u a t e l y s u p p l y a r a p i d l y growing p l a n t such as c o r n . A n o t h e r major drawback o f SCU i s i t s c o s t . The 1980 p r i c e p e r kg o f N as SCU i s $2.50 compared w i t h $0.60 f o r u r e a (Green V a l l e y F e r t i l i z e r , 1980). - .6. -D u r i n g the l a s t few y e a r s , s e v e r a l s l o w l y a v a i l a b l e forms o f N have been d e v e l o p e d , such as u r e a - f o r m a l d e h y d e compounds, metal ammonium phos-p h a t e s , oxamide, c r o t o n y l i d e n e d i u r e a , i s o b u t y l i d e n e d i u r e a , t h i o u r e a , urea p y r o l y z a t e , d i c y a n d i a m i d e , and c a l c i u m cyanamide. With the e x c e p t i o n o f u r e a - f o r m a l d e h y d e , most o f t h e s e a r e s t i l l i n the e x p e r i m e n t a l s t a g e . I t i s not l i k e l y t h a t any o f them w i l l e v e r be low enough i n c o s t f o r agronomic a p p l i c a t i o n s . N i t r i f i c a t i o n I n h i b i t o r s The use o f c h e m i c a l n i t r i f i c a t i o n i n h i b i t o r s (NI) which can be c o a t e d onto o r mixed w i t h ammoniacal f e r t i l i z e r s i s a p r o m i s i n g approach t o i m p r o v i n g the e f f i c i e n c y o f N f e r t i l i z e r a p p l i c a t i o n s . The f u n c t i o n o f NI i s t o d e l a y the o x i d a t i o n o f ammonium-based f e r t i l i z e r s i n o r d e r t o m i n i m i z e l e a c h i n g and d e n i t r i f i c a t i o n l o s s e s o f N p r i o r t o the p e r i o d o f maximum c r o p uptake. I d e a l l y , a NI s h o u l d meet s e v e r a l c r i t e r i a : ( i ) i t s h o u l d p e r s i s t i n the s o i l l o n g enough t o p r e v e n t N l o s s e s , but i t s h o u l d be b i o d e g r a d a b l e so t h a t i t does not p e r s i s t i n the s o i l ; ( i i ) i t s h o u l d be s p e c i f i c f o r Nitrosomonas, but not have any d e l e t e r i o u s e f f e c t on o t h e r s o i l m i c r o o r g a n i s m s ; ( i i i ) i t s h o u l d be n o n - t o x i c t o p l a n t s , a n i m a l s , o r humans; ( i v ) i t s c o s t s h o u l d be low enough t o make i t e c o n o m i c a l to use. N-Serve o r n i t r a p y r i n [ 2 - c h l o r o - 6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e ] was the f i r s t p a t e n t e d c h e m i c a l NI (Dow Chemical Co., M i d l a n d , M i c h i g a n ) . A c c o r d i n g t o G o r i n g (1962) N-Serve i s a h i g h l y s p e c i f i c Nitrosomonas i n h i b i t o r which has a low o r d e r o f t o x i c i t y t o the g e n e r a l fungus and - 7 -b a c t e r i a l p o p u l a t i o n s as w e l l as the s e e d l i n g s o f many p l a n t s . I t s main d i s a d v a n t a g e i s t h a t i t i s somewhat v o l a t i l e , and f o r maximum e f f e c t i v e -n e s s , i t needs t o be c o v e r e d w i t h s o i l ( B r i g g s , 1975). More r e c e n t l y , Bundy and Bremner (1973) t e s t e d 24 p o t e n t i a l NI i n a l a b o r a t o r y s t u d y . With the s o i l s used, the average e f f e c t i v e n e s s o f the most p o t e n t i n h i b i t o r s d e c r e a s e d i n the o r d e r : 2 - c h l o r o - 6 - ( t r i c h l o -r o m e t h y l ) - p y r i d i n e ( N - S e r v e ) > 4 - a m i n o - l , 2 , 4 - t r i a z o l e (ATC)>sodium o r potas s i u m a z i d e > 2 , 4 - d i a m i n o - 6 - t r i c h l o r o m e t h y l - j s - t r i a z i n e (CL-1580)>dicy-a n d i a m i d e > 3 - c h l o r o a c e t a n i 1 i d e > l - a m i d i n o - 2 - t h i o u r e a 2 , 5 - d i c h l o r o a n i l i n e > p h e n y l m e r c u r i c a c e t a t e > 3 - m e r c a p t o - l , 2 , 4 - t r i a z o l e or 2-amino-4-chloro-6 - m e t h y l - p y r i m i d i n e ( A M ) > s u l f a t h i a z o l e (ST)>sodium d i e t h y l d i t h i o c a r b a m a t e . F i e l d S t u d i e s w i t h N i t r i f i c a t i o n I n h i b i t o r s Most o f the p u b l i s h e d f i e l d e x p e r i m e n t s w i t h N-Serve have been done u s i n g anhydrous NHg as the N s o u r c e . T h i s i n h i b i t o r may be mixed i n the tank w i t h the NH^ o r i t can be a p p l i e d s e p a r a t e l y , but s i m u l t a n e o u s l y , i n t h e f e r t i l i z e r band u s i n g s e p a r a t e m e t e r i n g equipment. S i n c e t he • i n j e c t i o n equipment n o r m a l l y a p p l i e s the NHg a t a depth o f 12 t o 15 cm, v o l a t i l i z a t i o n o f N-Serve i s g r e a t l y m i n i m i z e d . A few f i e l d e x p eriments have shown i n c r e a s e d c r o p y i e l d s f o l l o w i n g f a l l a p p l i c a t i o n s (Warren e_t a^, 1975) o r s p r i n g a p p l i c a t i o n s (Swezey and T u r n e r , 1962) o f N-Serve w i t h anhydrous NH^. However, many o t h e r s t u d i e s , such as thos e by Cochran e t a]_ (1973), H e n d r i c k s o n e t al_ (1978a), and Touchton e t al_.(1979a) have f a i l e d t o demonstrate any - 8 -s i g n i f i c a n t y i e l d i n c r e a s e s r e s u l t i n g from f a l l o r s p r i n g a p p l i c a t i o n s o f N-Serve w i t h anhydrous NH^. I n c r e a s e d y i e l d s r e s u l t i n g from NI a p p l i -c a t i o n s can u s u a l l y be a t t r i b u t e d t o e f f e c t i v e i n h i b i t i o n o f n i t r i f i c a t i o n w i t h a subsequent r e d u c t i o n i n N l o s s e s . The l a c k o f a p o s i t i v e y i e l d r e s p onse t o NI may be due t o e i t h e r i n e f f e c t i v e c o n t r o l o f n i t r i f i c a t i o n o r t o no l o s s o f N because o f p r e v a i l i n g s o i l and c l i m a t i c c o n d i t i o n s . Only a few f i e l d e x p e r i m e n t s have been conducted where N-Serve has been a p p l i e d i n the f a l l w i t h a s o l i d N f e r t i l i z e r . Huber et a]_ (1969) r e p o r t e d a 15% i n c r e a s e i n w i n t e r wheat y i e l d s a veraged o v e r t h r e e y e a r s when N-Serve (0.67 kg/ha) was b a n d - a p p l i e d w i t h ammonium s u l f a t e (67.5 kg N/ha) i n the f a l l on an Idaho s i l t loam. S o i l samples taken i n March from the N-Serve p l o t s had t h r e e times h i g h e r NH 4 l e v e l s i n the s u r f a c e 15 cm than the p l o t s w i t h no i n h i b i t o r . Touchton e t a j ^ (1979b) found t h a t N-Serve (2.24 kg/ha) i n c r e a s e d c o r n g r a i n y i e l d s by 27% when broad-c a s t and i n c o r p o r a t e d i n the f a l l w i t h 67 kg/ha urea-N a p p l i e d t o an . I l l i n o i s s i l t loam when compared t o a s i m i l a r a p p l i c a t i o n w i t h o u t N-Serve. In c o n t r a s t , Boswell e_t _al_ (1976) found no improvement i n w i n t e r wheat y i e l d s i n G e o r g i a d u r i n g a t h r e e - y e a r s t u d y when f a l l - a p p l i e d N-Serve (1.11 kg/ha) and ammonium s u l f a t e (84 kg N/ha) were b r o a d c a s t and . i n c o r p o r a t e d onto a loamy sand and a sandy loam. S o i l samples taken i n January r e v e a l e d somewhat h i g h e r NH 4 l e v e l s i n the N-Serve p l o t s , but by March t h e r e was no d i f f e r e n c e . The poor e f f e c t i v e n e s s o f N-Serve i n the G e o r g i a s o i l s was l i k e l y due t o the warmer s o i l t e m p e r a t u r e s , c o a r s e r s o i l , and h i g h e r r a i n f a l l , which t o g e t h e r would promote more r a p i d n i t r i -f i c a t i o n and p e r c o l a t i o n l o s s e s o f N. " ? " S t u d i e s where s o l i d N f e r t i l i z e r s have been a p p l i e d i n the s p r i n g w i t h N-Serve have g e n e r a l l y shown d i s a p p o i n t i n g r e s u l t s . H e n d r i c k s o n e t aj_ (1978b) found t h a t the e f f e c t i v e n e s s o f N-Serve was v e r y s h o r t -l i v e d when i t was a p p l i e d w i t h ammonium s u l f a t e t o an i r r i g a t e d loamy sand, p r o b a b l y due t o i t s low o r g a n i c m a t t e r c o n t e n t (1%) which l i m i t e d a d s o r p t i o n o f N-Serve as w e l l as i t s c o a r s e t e x t u r e which a l l o w e d g r e a t e r v o l a t i l i z a t i o n o f the i n h i b i t o r . A l s o , the low c a t i o n exchange c a p a c i t y and the low water h o l d i n g c a p a c i t y o f t h i s s o i l p e r m i t t e d a p p r e c i a b l e movement o f NH^ below the N-Serve t r e a t e d zone. O t h e r f i e l d e x p e r i m e n t s , such as t h o s e by S p r a t t and G a s s e r (1970), Touchton e t a l (1979b), and Boswell e t al^ (1976) have f a i l e d t o show any improvement i n c r o p y i e l d f o l l o w i n g the s p r i n g a p p l i c a t i o n o f N-Serve w i t h s o l i d urea o r ammonium s u l f a t e . ATC N i t r i f i c a t i o n I n h i b i t o r ATC ( 4 - a m i n o - l , 2 , 4 - t r i a z o l e ) i s a more r e c e n t l y p a t e n t e d ( I s h i h a r a Sangyo K a i s h a L t d . , Tokyo, Japan) NI which i s a l s o s p e c i f i c f o r N i t r o - somonas. A c c o r d i n g t o the m a n u f a c t u r e r , ATC i s not p h y t o t o x i c t o s e e d l i n g s , and i t has no e f f e c t on the growth o f s o i l f u n g i o r o t h e r s o i l . b a c t e r i a . L a b o r a t o r y s t u d i e s (Bundy and Bremner, 1973)l ihave shown i t t o be almost as e f f e c t i v e as N-Serve when c o a t e d onto urea or ammonium s u l f a t e and i n c u b a t e d w i t h 10 g s o i l samples i n small c o v e r e d f l a s k s . The l i m i t e d a i r c i r c u l a t i o n i n t h e s e c o n t a i n e r s would have the e f f e c t o f a r t i f i c i a l l y p r o l o n g i n g t he e f f e c t i v e n e s s o f the N-Serve s i n c e v o l a t i l i z a t i o n l o s s e s - 10 -ATC ( 4 - a m i n o - l , 2 , 4 - t r i a z o l e ) HC \ C H N M o l e c u l a r f o r m u l a : M o l e c u l a r w e i g h t : Water s o l u b i l i t y : M e l t i n g p o i n t : C 2 H 4 N 4 84.1 420 g/100 ml a t 20°C 81 °C N-SERVE [ 2 - c h 1 o r o - 6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e ] M o l e c u l a r f o r m u l a : C g H 3 N C l 4 M o l e c u l a r w e i g h t : Water s o l u b i l i t y : M e l t i n g p o i n t : 230.9 0.004 g/100 ml a t 20°C 62°C FIGURE 1:1 Chemical s t r u c t u r e and p r o p e r t i e s o f ATC and N-Serve would be minimized. Thus, under f i e l d conditions, i t i s possible that ATC might be more persistent than N-Serve and thereby control n i t r i f i c a t i o n for a longer period. The chemical structures of ATC and N-Serve are shown in Figure 1. Purpose of t h i s Study As of this date, there have been no results published from f i e l d studies where ATC has been used as a NI. Due to i t s non-volatile nature, this i n h i b i t o r should be more suitable than N-Serve for applications with s o l i d N f e r t i l i z e r s , such as urea or ammonium sulfate. With this in mind, a series of experiments was designed to test the effectiveness of ATC and N-Serve. In the f i r s t experiment (Chapter Two), ATC was applied with urea as a f a l l application to deter-mine i f use of t h i s i n h i b i t o r could minimize losses of N during the winter and spring. In the second experiment (Chapter Three) a laboratory incuba-tion study was conducted to determine i f ATC or N-Serve affected the rate of urea hydrolysis at low s o i l temperatures. In Chapter Four.,, a series of f i e l d experiments with silage corn are discussed. The purpose of these experiments..was to compare the effectiveness of ATC and N-Serve when applied in the spring with urea. Urea was chosen as the N source for these experiments since i t i s rapidly becoming the most popular s o l i d N f e r t i l i z e r in B r i t i s h Columbia, primarily since i t has the lowest cost per kg of N. Anhydrous NH^ was not considered, since very l i t t l e of t h i s form of N i s used in B r i t i s h Columbia. The use of anhydrous NH^ i s generally only practical on large acreages, since costly, pressurized - 12 -o r r e f r i g e r a t e d equipment i s n e c e s s a r y f o r the s t o r a g e and a p p l i c a t i o n o f t h i s f e r t i l i z e r . The chapters p r e s e n t e d i n t h i s t h e s i s were each w r i t t e n i n a s t y l e s u i t a b l e f o r p u b l i c a t i o n i n the S o i l S c i e n c e S o c i e t y o f American J o u r n a l (American S o c i e t y o f Agronomy, 1976). - .13 " LITERATURE CITED American S o c i e t y o f Agronomy. 1976. Handbook and S t y l e Manual Amer. Soc. o f Agron., Madison, Wis. A l l i s o n , F.E. 1955. The enigma o f s o i l n i t r o g e n b a l a n c e s h e e t s . Advan. Agron. 7: 213-250. 3. A l l i s o n , F.E. 1963. L o s s e s o f gaseous n i t r o g e n from s o i l s by c h e m i c a l mechanisms i n v o l v i n g n i t r o u s a c i d and n i t r i t e s . S o i l S c i e n c e 96: 404-409. 4. B o s w e l l , F.C., L.R. N e l s o n , and M.J. B i t z e r . 1976. N i t r i f i c a t i o n i n h i b i t o r w i t h f a l l - a p p l i e d v s . s p l i t N a p p l i c a t i o n s f o r w i n t e r wheat. Agron. J . 68: 737-740. 5. B r i g g s , G.C. 1975. The b e h a v i o u r o f the n i t r i f i c a t i o n i n h i b i t o r "N-Serve" i n b r o a d c a s t and i n c o r p o r a t e d a p p l i c a t i o n s t o s o i l J . S c i . Fd. A g r i c . 26: 1083-1092. Bundy, L.G. and J.M. Bremner. 1973. I n h i b i t i o n o f n i t r i f i c a t i o n i n s o i l s . S o i l S c i . Soc. Am. P r o c . 37: 396-398. 7. Cochran, V.L., R.I. Papendick., and W.M. Woody.: 1973. E f f e c t i v e n e s s o f two n i t r i f i c a t i o n i n h i b i t o r s f o r anhydrous ammonia under i r r i g a t e d and d r y l a n d c o n d i t i o n s . Agron. J . 65: 649-653. 8. El W a l i , A.M.O. F. Le Grand and G.J. Gascho. 1980. N i t r o g e n l e a c h i n g from s o i l and uptake by sugarcane from v a r i o u s u r e a -based f e r t i l i z e r s . S o i l S c i . Soc. Am. J . 44: 119-122. 9. F r y e , W.W. 1977. F a l l - . v s . s p r i n g - a p p l i e d s u l f u r - c o a t e d u r e a , ;. uncoated u r e a , and sodium n i t r a t e f o r c o r n . Agron. J . 69: 278-282. 10. G o r i n g , C.A.I. 1962. C o n t r o l o f n i t r i f i c a t i o n by 2 - c h l o r o - 6 - ( t r i -c h l o r o m e t h y l ) p y r i d i n e . S o i l S c i e n c e 93: 211-218. - 14 -11. Green V a l l e y F e r t i l i z e r and Chemical Co. L t d . 1980. S u r r e y , B.C. 12. Harmesen, R.H., F.W. S o l l o , and T.E. L a r s o n . 1971. The n i t r a t e s i t u a t i o n i n 1 1 1 i n o i s . J . Amer. Water Works A s s o c . 63: 303-310. 13. H e n d r i c k s o n , L.L., L.M. Walsh, and D.R. Keeney. 1978. E f f e c t i v e -ness o f n i t r a p y r i n i n c o n t r o l l i n g n i t r i f i c a t i o n o f f a l l and s p r i n g - a p p l i e d anhydrous ammonia. Agronomy J . 70: 704-708. 14. H e n d r i c k s o n , L.L., D.R. Keeney, L.M. Walsh, and E.A. L i e g e l . 1978. E v a l u a t i o n o f n i t r a p y r i n as a means o f i m p r o v i n g n i t r o g e n e f f i c i e n c y i n i r r i g a t e d sands. Agron. J . 70: 699-704. 15. Huber, D.M., G.A. Murray, and J.M. Crane. 1969. I n h i b i t i o n o f n i t r i f i c a t i o n as a d e t e r r e n t t o n i t r o g e n l o s s . S o i l S c i . Soc. Am. P r o c . 33: 975-976. 16. J o n e s , U l y s s e s S. 1979. F e r t i l i z e r s and S o i l F e r t i l i t y . Reston P u b l i s h i n g Co., Reston Va. 368 p. 17. M a r t i n , J.H., W.H. Leonard, and D.L. Stamp. 1976. P r i n c i p l e s o f F i e l d Crop P r o d u c t i o n . 3rd ed. M a c m i l l a n P u b l i s h i n g Co. New York, NY. 1118 p. 18. Matocha, J . E . 1976. Ammonia v o l a t i l i z a t i o n and n i t r o g e n u t i l i z a t i o n from s u l f u r - c o a t e d ureas and c o n v e n t i o n a l n i t r o g e n f e r t i l i z e r s . S o i l S c i . Soc. Am. J . 40: 597-601. 19. M c E l r o y , M.B., S.C. Wofsy, and Y.L. Yung. 1977. The N c y c l e : p e r t u r b a t i o n s due t o man and t h e i r impact on a t m o s p h e r i c . . n i t r o u s o x i d e and ozone. P h i l o s o p h i c a l T r a n s a c t i o n s o f the Royal S o c i e t y o f London, B. 277: 159-181. 20. P i m e n t e l , D a v i d , L.E. Hurd, A.C. B e l l o t t i , M.J. F o r s t e r , I.N. Oka, . O.D. S h o l e s , and R.J. Whitman. 1973. Food p r o d u c t i o n and the energy c r i s i s . S c i e n c e 182: 443-449. - 1 5 -21. P r a s a d , R., G.B. R a j a l e , and B.A. L a k h d i v e . 1971. N i t r i f i c a t i o n r e t a r d e r s and s l o w - r e l e a s e n i t r o g e n f e r t i l i z e r s . Adv. Agron. 23: 337-383. 22. S p r a t t , E.D. and J.K.R. G a s s e r . 1970. The e f f e c t o f ammonium s u l -phate t r e a t e d w i t h a n i t r i f i c a t i o n i n h i b i t o r , and c a l c i u m n i t r a t e , on growth and N uptake o f s p r i n g wheat, r y e g r a s s and k a l e . J . A g r i c . S c i . , Cambridge 74: 111-117. 23. S t e v e n s o n , C.K. and C.S.. B a l d w i n . 1969. E f f e c t o f time and method o f N a p p l i c a t i o n and s o u r c e o f N on the y i e l d and N c o n t e n t o f c o r n (Zea mays L . ) . Agron. J . 61: 381-384. 24. Swezey, A.W. and G.O. T u r n e r . 1962. Crop experiments on the e f f e c t o f 2 - c h l o r o - 6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e f o r the c o n t r o l o f n i t r i f i c a t i o n o f ammonium and urea f e r t i l i z e r s . Agron. J . 54: 532-535. 25. Terman, G.L. and S.E. A l l e n . 1974. L o s s e s o f n i t r o g e n and m i n e r a l n u t r i e n t s from c o r n grown i n greenhouse p o t e x p e r i m e n t s . S o i l S c i . Soc. Am. P r o c . 38: 322-326. 26. T o u c h t o n , J.T., R.G. H o e f t , L.F. Welch, D.L. Mulvaney, M.G. Oldham, and F.E. Z a j i c e k . 1979. N i t r o g e n uptake and c o r n y i e l d as a f f e c t e d by a p p l i c a t i o n < o f n i t r a p y r i n w i t h anhydrous ammonia. Agron . J . 71: 238-242. 27. T o u c h t o n , J.T., R.G. H o e f t , and L.F. Welch. 1979. E f f e c t o f n i t r a -p y r i n on, n i t r i f i c a t i o n o f b r o a d c a s t - a p p l i e d u r e a , p l a n t n u t r i e n t c o n c e n t r a t i o n s , and c o r n y i e l d . Agron. J . 71: 787-791. 28. Ward, P.C. 1970. E x i s t i n g l e v e l s o f n i t r a t e s i n w a t e r s - - t h e C a l i f o r n i a s i t u a t i o n , p. 14-26. J_n N i t r a t e and water s u p p l y : s o u r c e and c o n t r o l . 12th S a n i t a r y Eng. Conf. P r o c , C o l l e g e o f Eng., Univ. o f I l l i n o i s a t Urbana-Champaign. 29. Warren, H.L., D.M. Huber, D.W. N e l s o n , and O.W. Mann. ' 1975. S t a l k r o t i n c i d e n c e and y i e l d o f c o r n as a f f e c t e d by i n h i b i t i n g n i t r i f i c a t i o n o f f a l l - a p p l i e d ammonium. Agron. J . 67: 655-660. - 16 -30. Welch, L.F., D.L. Mulvaney, M.G. Oldham, L.V. Boone, and J.W. P e n d l e t o n . 1971. Corn y i e l d s w i t h f a l l , s p r i n g , and s i d e -d r e s s n i t r o g e n . Agron. J . 63: 119-123. - 17 -C h a p t e r Two EFFECTS OF 4-AMIN0-1,2,4-TRIAZOLE ON TRANSFORMATIONS OF FALL-APPLIED UREA-N ABSTRACT The o b j e c t i v e s o f t h i s s t u d y were: (1) t o d e t e r m i n e i f the n i t r i f i c a -t i o n i n h i b i t o r ATC (4-amino-l , 2 , 4 - t r i a z o l e ) c o u l d m i n i m i z e o v e r w i n t e r N l o s s e s from f a l l - a p p l i e d u r e a ; and (2) t o m o n i t o r the t r a n s f o r m a t i o n s o f f a l l -a p p l i e d urea-N. Urea (200 kg N/ha) w i t h o r w i t h o u t a 1% (by weight o f N) c o a t i n g , o f ATC was a p p l i e d as band and b r o a d c a s t a p p l i c a t i o n s t o a s i l t s o i l i n November, 1977, when the s o i l t emperature a t 10 cm was 1.9°C. The s o i l was sampled t o a depth o f 90 cm a t a p p r o x i m a t e l y one month i n t e r v a l s u n t i l A p r i l and a n a l y z e d f o r NH^- and N0g-N. With the banded a p p l i c a t i o n s , some n i t r i f i c a t i o n o c c u r r e d p r i o r t o J a n u a r y , but from t h i s date u n t i l March t h e r e was l i t t l e change i n s o i l NH^ l e v e l s . As the s o i l warmed from March t o A p r i l (4.7 t o 8.5°C) t h e r e were 50 and 35% d e c r e a s e s i n the 0-15 cm NH^ l e v e l s i n the non-ATC and ATC t r e a t m e n t s , r e s p e c t i v e l y . O v e r a l l , from December t o A p r i l t h e r e were 70 and 48% d e c r e a s e s i n the 0-15 cm s o i l NH^ l e v e l s o f t h e non-ATC and ATC p l o t s , r e s p e c t i v e l y . With the b r o a d c a s t a p p l i c a t i o n s , r e g a r d l e s s o f ATC t r e a t m e n t , n i t r i -f i c a t i o n proceeded s t e a d i l y t h r o u g h o u t the sampling p e r i o d , w i t h 93 and 85% d e c r e a s e s from the December 0-15 cm NH/, l e v e l s i n the non-ATC and ATC - 18 -p l o t s , r e s p e c t i v e l y . I t i s c o n c l u d e d t h a t ATC i s p a r t i a l l y e f f e c t i v e i n m i n i m i z i n g N l o s s e s when a p p l i e d i n the f a l l as a band w i t h u r e a , b ut when b r o a d c a s t t h e r e i s no e f f e c t on n i t r i f i c a t i o n . L e a c h i n g o f the water-s o l u b l e ATC i s the l i k e l y cause o f i t s poor e f f e c t i v e n e s s . S i g n i f i c a n t l e a c h i n g o f urea from the s o i l s u r f a c e was found t o o c c u r d u r i n g the f i r s t month f o l l o w i n g i t s a p p l i c a t i o n . - 19 -INTRODUCTION F a l l a p p l i c a t i o n s o f n i t r o g e n o u s f e r t i l i z e r s a r e not g e n e r a l l y recom-mended, p a r t i c u l a r l y i n a r e a s such as c o a s t a l B r i t i s h Columbia where t h e s o i l seldom f r e e z e s f o r extended p e r i o d s , s o i l t e m p e r a t u r e s a r e o f t e n h i g h enough d u r i n g the w i n t e r f o r slow n i t r i f i c a t i o n to o c c u r , and t h e i n t e n s e w i n t e r r a i n f a l l can l e a d t o c o n s i d e r a b l e l o s s o f N by l e a c h i n g . The h i g h s o i l m o i s t u r e l e v e l s and r e l a t i v e l y warm s o i l t e m p e r a t u r e s which o c c u r i n the s p r i n g a r e a l s o c o n d u c i v e to d e n i t r i f i c a t i o n l o s s e s o f NO^-N. However, s e v e r a l p o t e n t i a l advantages e x i s t f o r f a l l f e r t i l i z e r a p p l i c a t i o n s . M a n u f a c t u r e r s and d e a l e r s p r e f e r t o have t h e i r s a l e s d i s t r i b -uted t h r o u g h o u t the y e a r ; f a r m e r s would l i k e t o s p r e a d t h e i r l a b o r r e q u i r e -ments more e v e n l y through the y e a r ; the s o i l i s o f t e n i n a b e t t e r p h y s i c a l c o n d i t i o n i n the f a l l f o r f i e l d o p e r a t i o n s . Chemical i n h i b i t i o n o f n i t r i f i c a t i o n o f f a l l - a p p l i e d ammoniacal f e r t i l i z e r s o f f e r s a p o t e n t i a l means o f d e c r e a s i n g N l o s s e s from the s o i l by p r e v e n t i n g f o r m a t i o n o f the h i g h l y l a b i l e n i t r a t e i o n . Ammonium i s n o t s u b j e c t t o d e n i t r i f i c a t i o n l o s s , and l e a c h i n g o f NH^ u s u a l l y o c c u r s o n l y i n c o a r s e - t e x t u r e d s o i l s h a v i n g low c a t i o n exchange c a p a c i t i e s . S e v e r a l r e s e a r c h e r s have i n v e s t i g a t e d t he use o f N-Serve [ 2 - c h l o r o -6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e ] as a n i t r i f i c a t i o n i n h i b i t o r which can be a p p l i e d i n the f a l l w i t h ammoniacal f e r t i l i z e r s . Most o f the p u b l i s h e d s t u d i e s have been done u s i n g anhydrous ammonia as the N s o u r c e , s i n c e N-Serve cannot be e a s i l y a p p l i e d w i t h s o l i d f e r t i l i z e r s due t o i t s v o l a t i l i t y (Bremner e t al_, 1978; B r i g g s , 1975). - 20 -R e s u l t s from many r e s e a r c h e r s ( H e n d r i c k s o n e t a l _ . , 1978; Touchton e t a l _ . , 1978, 1979; Warren e t a l _ . , 1975) have shown t h a t N-Serve a p p l i e d i n the f a l l w i t h anhydrous NH^ can s i g n i f i c a n t l y d e c r e a s e t h e r a t e o f n i t r i f i -c a t i o n and thus i n c r e a s e the p r o p o r t i o n ; , o f f a l l - a p p l i e d N which i s a v a i l a b l e i n the s o i l f o r p l a n t uptake d u r i n g the summer. However, f a l l N-Serve a p p l i c a t i o n s have no t always r e s u l t e d i n improved c r o p y i e l d s the f o l l o w i n g s e a s o n . Some p o s s i b l e e x p l a n a t i o n s f o r t h e l a c k o f c r o p r e s p o n s e to f a l l -a p p l i e d N-Serve a r e : (1) c l i m a t i c c o n d i t i o n s which were no t c o n d u c i v e t o N l o s s e s by l e a c h i n g o r d e n i t r i f i c a t i o n ; (2) lower than average y i e l d s due to d r o u g h t o r d i s e a s e ; (3) h i g h r a t e s o f s o i l o r g a n i c N m i n e r a l i z a t i o n d u r i n g the summer. ATC ( 4 - a m i n o - l , 2 , 4 - t r i a z o l e ) i s a more r e c e n t l y d e v e l o p e d n i t r i f i -c a t i o n i n h i b i t o r which i s a l s o s p e c i f i c f o r Nitrosomonas sp. I t has t h e advantage o f b e i n g n o n - v o l a t i l e , and t h u s i s more a p p r o p r i a t e t o use w i t h s o l i d f e r t i l i z e r s . I t s c o s t i s e x p e c t e d t o be l e s s than t h a t o f N-Serve. L a b o r a t o r y i n c u b a t i o n s (Bundy and Bremner, 1973) and f i e l d s t u d i e s ( G u t h r i e and Bomke, 1980) have demonstrated t h a t ATC i s a t l e a s t as e f f e c t i v e as N-S e r v e when c o a t e d onto u r e a . The o b j e c t i v e s o f t h e p r e s e n t s t u d y were: (1) t o m o n i t o r the t r a n s -f o r m a t i o n s and movement o f urea-N d u r i n g t h e w i n t e r and s p r i n g ; (2)) to determine the e f f e c t i v e n e s s o f ATC i n m i n i m i z i n g l o s s e s o f N f o l l o w i n g f a l l a p p l i c a t i o n o f urea as a band o r b r o a d c a s t onto a s i l t s o i l i n the humid c o a s t a l r e g i o n o f the P a c i f i c Northwest. - 21 -METHODS AND MATERIALS The e x p e r i m e n t a l s i t e was l o c a t e d 50 km s o u t h o f Vancouver, B.C. on a p o o r l y d r a i n e d a l l u v i a l s i l t s o i l c l a s s i f i e d as a T y p i c F l u v a q u e n t (Rego Humic G l e y s o l , Can.). The f i e l d had been under c o n t i n u o u s s i l a g e c o r n p r o d u c t i o n f o r t h r e e y e a r s and had r e c e i v e d heavy annual manure a p p l i c a t i o n s f r o m the a s s o c i a t e d d a i r y o p e r a t i o n . Some o f t h e i m p o r t a n t p h y s i c a l and c h e m i c a l p r o p e r t i e s o f the s o i l used i n t h i s s t u d y a r e l i s t e d i n T a b l e 2.1. Bulk d e n s i t i e s were determined u s i n g t h e c o r e method, and p a r t i c l e s i z e a n a l y s i s was done u s i n g the hydrometer t e c h n i q u e ( B l a c k , 1965a). S o i l pH was d e t e r m i n e d i n 0.01 M C a C ^ ( s o i l : s o l u t i o n r a t i o 1:2), t o t a l C by combustion i n a Leco i n d u c t i o n f u r n a c e , t o t a l N by a s e m i m i c r o - K j e l d a h l d i g e s t i o n , and CEC by a n e u t r a l 1 N_ ammonium a c e t a t e e x t r a c t i o n ( B l a c k , 1965b). The average annual p r e c i p i t a t i o n a t t h i s s i t e i s 1270 mm, w i t h 870 mm o c c u r r i n g between November 1 and A p r i l 30, a l m o s t a l l i n the form o f r a i n . The mean annual a i r temperature i s 10 °C, w i t h an average temp-e r a t u r e o f 5 °C from November through A p r i l . The N s o u r c e f o r t h e e x p e r i m e n t was f e r t i l i z e r grade (46% N) p r i l l e d urea (1.4 to 3.0 mm) which was a p p l i e d on 8th November 1977 a t r a t e s o f 0 o r 200 kg N/ha (360 g N/18 m 2 p l o t ) . T h i s was a p p l i e d e i t h e r as a b r o a d c a s t t r e a t m e n t which was r a k e d i n t o the s o i l o r as a narrow (5 cm) band (two 6 m bands per p l o t ) which was c o v e r e d w i t h 8 cm o f s o i l . H a l f o f the f e r t i l i z e d p l o t s r e c e i v e d urea which had been c o a t e d w i t h ATC (one kg ATC per 100 kg urea-N) u s i n g the f o l l o w i n g p r o c e d u r e . The r e q u i r e d Table 2.1. Selected physical and chemical properties at different depths of soil used in winter nitrification study Bulk Water content pH Depth Density at -33 kPa+ Silt Clay Total C Total N CEC CaCl2 cm kg/m3 • % meq/100 g 0-15 840 53.1 85 5 , 6.78 0.60 39.1 4.6 15-30 960 54.3 88 5 5.84 0.48 36.1 4.3 30-60 1100 N.D.* N.D. N.D. 2.94 0.20 23.4 3.6 60-90 1200 N.D. N.D. N.D. 2.03 0.15 15.4 3.4 * N.D. indicates that value was not determined. + 100 kPa = 1 Bar - 23 -q u a n t i t y o f ATC (36% w/v aqueous s o l u t i o n ) was s p r a y e d w i t h a chromatography s p r a y gun onto a t r a y o f urea p r i l l s (one kg) which were shaken by a mechanical s h a k e r . F o l l o w i n g thorough m i x i n g , the c o a t e d urea was d r i e d o v e r n i g h t u s i n g a fan a t room t e m p e r a t u r e , then s e a l e d i n t o p l a s t i c bags. The t r e a t m e n t s were arranged^, i n a c o m p l e t e l y random d e s i g n w i t h t h r e e r e p l i c a t i o n s . A t a p p r o x i m a t e l y one month i n t e r v a l s , s o i l samples were take n from each p l o t to a depth o f 90 cm i n 15 cm i n c r e m e n t s . S i x 2.5 cm c o r e s were randomly o b t a i n e d u s i n g a hand sampler from each b r o a d c a s t p l o t , w h i l e the banded p l o t s were sampled d i r e c t l y i n the c e n t e r o f the f e r t i l i z e r bands, which had been marked w i t h n y l o n s t r i n g s t i g h t l y s t r e t c h e d between p a i r s o f wooden s t a k e s . The samples from each p l o t were mixed and e i t h e r e x t r a c t e d on the sa m p l i n g day o r r e f r i g e r a t e d (2 °C) no more than one day p r i o r t o e x t r a c t i o n . F r e s h s o i l (10 g) was subsampled and e x t r a c t e d w i t h 2 N_ KCl (100 m l ) , and t h e f i l t r a t e was c o l l e c t e d f o r N0 3~, N0 2~ and N H 4 + a n a l y s i s by T e c h n i c o n A u t o a n a l y z e r . The same f i l t r a t e s were a l s o used f o r pH d e t e r m i n a t i o n s . S e p a r a t e 10 g subsamples were o v e n - d r i e d (105 °C) f o r g r a v i m e t r i c m o i s t u r e d e t e r m i n a t i o n s to c o r r e c t t h e N d a t a t o a d r y weight b a s i s . P r e c i p i t a t i o n d a t a were o b t a i n e d from a r a i n g a u g e i n s t a l l e d a t the e x p e r i m e n t a l s i t e . S o i l t e m p e r a t u r e s a t 10, 20, 40 and 75 cm depths were measured weekly u s i n g s i l i c o n e d i o d e s (Hinshaw and F r i t s c h e n , 1970) i n s e r t e d a l o n g two s i d e s o f the e x p e r i m e n t a l a r e a . In a d d i t i o n , a s o i l degree-day i n t e g r a t o r was i n s t a l l e d a t a depth o f 10 cm. These d a t a a r e summarized i n T a b l e 2.2. An a n a l y s i s o f v a r i a n c e was performed on t h e d a t a from each sampling - 24 -d e p t h , and t r e a t m e n t means were t e s t e d f o r s i g n i f i c a n t d i f f e r e n c e s by Duncan's m u l t i p l e range t e s t . Table 2.2 Soi l moisture, prec ip i ta t ion, and average s o i l temperatures between sampling dates, 1977-1978 Depth of Measurement  Sampling Elapsed P r e c i p i - 0-15 15-30 30-60 60-90 date time tat ion 10 cm 20 cm 40 cm 75 cm cm cm cm cm# -days mm : average °C % moisturet 8 Nov. 0 - 1.9 3.0 5.6 8.0 62.0 60.7 72.6 78.4 5 Dec. 27 194§ 1.3 2.1 4.5 6.6 70 .7 + 63.8 73.0 -16 Jan. 69 199§ 0.9 0.4 1.9 3.9 92 .4 + 65.5 79.2 84.5 13 Feb. 97 s 89 1.2 0.5 1.0 2.8 69.0 65.0 75.4 79.7 14 Mar. 126 62 4.7 3.1 3.7 4.3 67.0 62.5 72.7 76.2 4 Apr. 147 64 8.5 5.1 5.3 5.0 68.6 64.5 71.9 78.6 Surface (3-4 cm) frozen on sampling date. A small portion (< 20%) of th is prec ip i ta t ion was snow, which melted pr ior to sampling. t Water retention of 0-15 cm horizon is 62.5% of dry weight at -10 kPa (0.1 bar) tension. The water table was between 75 and 80 cm depth during most of the sampling per iod. - 26 -RESULTS AMD DISCUSSION Banded f e r t i l i z e r a p p l i c a t i o n ( T a b l e 2,3 and F i g u r e 2.1) One month f o l l o w i n g urea a p p l i c a t i o n (December 5) the NH^ concen-t r a t i o n s were v e r y s i m i l a r i n the ATC and non-ATC p l o t s . I t i s l i k e l y t h a t the low average 0-15 cm s o i l temperature (1.3 °C) and h i g h NH^ c o n c e n t r a t i o n s i n t he bands (> 600 ppm) combined t o e f f e c t i v e l y p r e v e n t any n i t r i f i c a t i o n . P r e v i o u s r e s e a r c h e r s (Anderson and B o s w e l l , 1964; W e t s e l a a r ejt a l _ . , 1972) have demonstrated t h a t h i g h l o c a l NH^ c o n c e n t r a t i o n s can i n h i b i t n i t r i f i -c a t i o n , p r o b a b l y due t o t h e low o s m o t i c p o t e n t i a l o f s o l u t i o n i n t h e imme-d i a t e v i c i n i t y o f N f e r t i l i z e r band. I n h i b i t i o n caused by h i g h pH o r n i t r i t e f o r m a t i o n r e s u l t i n g from t h e h i g h c o n c e n t r a t i o n s o f u r e a was n o t a f a c t o r , s i n c e t h e pH o f the s o i l e x t r a c t s n e v e r exceeded 5, and s o i l N0 2-N l e v e l s n e ver exceeded 1 ppm ( d a t a n o t shown). On t h e December sam p l i n g d a t e t h e average NH^ c o n c e n t r a t i o n s o f the 15-30 cm and 30-60 cm l a y e r s were 60 and 18%, r e s p e c t i v e l y , o f the average NH^ c o n c e n t r a t i o n i n t h e 0-15 cm l a y e r s o f the f e r t i l i z e d p l o t s . I t i s n o t l i k e l y t h a t t h e r e was any s i g n i f i c a n t movement o f NH^ i n t h i s s i l t s o i l due t o the h i g h c a t i o n exchange c a p a c i t y (39 meq/100 g ) . A more p l a u s i b l e e x p l a n a t i o n f o r the h i g h NH^ l e v e l s below the s u r f a c e 15 cm i s t h a t unhydro-l y z e d urea was l e a c h e d down t h e p r o f i l e by the 194 mm o f r a i n f a l l which o c c u r r e d d u r i n g t h i s time i n t e r v a l . The low i n i t i a l s o i l t e mperatures (1.9 and 3.0 °C a t 10 and 20 cm depth) would g r e a t l y d e c r e a s e t h e r a t e o f urea h y d r o l y s i s ( O v e r r e i n and Moe, 1967). Urea i s known t o be o n l y weakly adsorbed by s o i l o r g a n i c m a t t e r (Chin and K r o o n t j e , 1962), and i t moves T a b l e 2.3 Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n banded and c o n t r o l p l o t s on v a r i o u s sampling dates as a f f e c t e d by urea-N and ATC n i t r i f i c a t i o n i n h i b i t o r , 1977-1978 N i t r o g e n ATC kg/ha Sampling depth cm NH 4-N Sampling date (days from N a p p l i c a t i o n ) 8 Nov. (0) 5 Dec. (27) 16 Jan. (69) 3 Feb. (97) 14 Mar. (126) 4 Apr. (147) N0 3-N NH4-N N0 3-N i 4 - N N0 3-N NH4-N N0 3-N yg N/g dry s o i l NH4-N N0 3-N N0 3-r 0 0 0-15 4 40 25 10 8 6 11 6 7 7 8 8 15-30 2 41 12 26 8 10 9 9 5 9 6 10 30-60 6 30 16 32 11 25 9 20 7 17 7 13 60-90 8 23 + 7 32 11 21 14 18 7 20 200 0 0-15 4 30 626 11 316 35 363 42 377 60 189 28 15-30 2 33 351 28 299 42 303 49 219 82 246 75 30-60 7 32 79 27 n o 30 84 32 87 51 105 59 60-90 6 19 - 18 21 28 21 17 24 23 29 200 2.0 0-15 5 33 603 8 476 18 498 23 482 49 313 56 15-30 2 39 387 24 272 30 213 32 260 52 137 96 30-60 6 33 138 27 72 29 84 25 105 30 104 62 60-90 6 20 - - 19 20 18 20 19 25 23 31 Samples n o t o b t a i n e d . Values r e p r e s e n t average o f t h r e e r e p l i c a t e p l o t s . - 2 8 -through the s o i l a l m o s t as e a s i l y as NOg i n r e s p o n s e t o water movement (Wagenet e t a j _ . , 1977). Thus, c o n d i t i o n s were f a v o r a b l e f o r l e a c h i n g o f the a p p l i e d u r e a . L e a c h i n g o f NOg was a l s o e v i d e n t , s i n c e the c o n c e n t r a t i o n o f NOg i n the 0-15 and 15-30 cm l a y e r s was c o n s i d e r a b l y reduced between November 8 and December 5. Samples were no t taken from the 60-90 cm depth on t h e l a t t e r d a t e , but i t i s l i k e l y t h a t a good p o r t i o n o f t h e NOg i n the 0-60 cm zone was l e a c h e d away. D e n i t r i f i c a t i o n was p r o b a b l y not an i m p o r t a n t f a c t o r c a u s i n g l o s s o f NOg from the 0-30 cm zone, s i n c e t h e low temperature (< 2 °C) would r e s u l t i n v e r y slow r a t e s o f d e n i t r i f i c a t i o n ( C r a s w e l l , 1978; S t a n f o r d e t a K > 1975). However, t h e r e was a g r e a t e r p o t e n t i a l f o r d e n i t r i f i c a t i o n i n the 30-90 cm zone, where t h e average temperature was 5-6 °C d u r i n g t h i s p e r i o d , and o r g a n i c m a t t e r (4.3%) was p r o b a b l y n o t a l i m i t i n g f a c t o r . Between December 5 and J a n u a r y 16 t h e r e were 21 and 50% d e c r e a s e s i n the 0-15 cm s o i l NH 4 l e v e l s o f t h e ATC and non-ATC t r e a t e d p l o t s , r e s p e c t i v e l y . Some o f t h i s d e c r e a s e was l i k e l y due t o d i f f u s i o n o f NH^ away from t h e zone o f h i g h c o n c e n t r a t i o n i n the band. T h i s d e c r e a s e i n NH^ c o n c e n t r a t i o n would have made c o n d i t i o n s more f a v o r a b l e f o r n i t r i f i c a t i o n by i m p r o v i n g t h e o s m o t i c p o t e n t i a l as w e l l as i n c r e a s i n g t h e a v a i l a b i l i t y o f the NH 4 s u b s t r a t e t o the n i t r i f y i n g m i c r o b e s . The g r e a t e r d e c r e a s e i n NH^ and i n c r e a s e i n NOg l e v e l s a s s o c i a t e d w i t h the non-ATC p l o t s s u g g e s t s . t h a t the ATC was h a v i n g some e f f e c t as an i n h i b i t o r . The NOg i n c r e a s e s were not s u f f i c i e n t to a c c o u n t f o r the d e c r e a s e i n NH^, but i t i s p r o b a b l e t h a t a l a r g e p o r t i o n o f any NOg formed was l e a c h e d o u t o f the p r o f i l e by the 199 mm o f p r e c i p i t a t i o n . S o i l m o i s t u r e l e v e l s i n c r e a s e d t h r o u g h o u t the - 2 9 -p r o f i l e , and the 60-90 cm l a y e r was s a t u r a t e d ( T a b l e 2.2). i n d i c a t i n g a p o t e n t i a l f o r l e a c h i n g l o s s e s . From J a n u a r y 16 t o March 14 t h e r e was v e r y l i t t l e change i n s o i l NH^ c o n c e n t r a t i o n s i n the 0-15 cm and 15-30 cm l a y e r s under e i t h e r t r e a t -ment. The c o l d s o i l t e mperatures d u r i n g t h i s time s e r v e d as an e f f e c t i v e n i t r i f i c a t i o n i n h i b i t o r . P r e c i p i t a t i o n was l e s s i n t e n s e d u r i n g t h i s p e r i o d , and N0^ l e a c h i n g d i d n o t appear t o o c c u r , s i n c e NO^ l e v e l s i n the 0-15 and 15-30 cm l a y e r s d i d not d e c r e a s e . S o i l m o i s t u r e l e v e l s d e c r e a s e d t h r o u g h o u t the p r o f i l e d u r i n g t h i s time. D u r i n g the 21 days between March 14 and A p r i l 4 t h e r e were 35 and 50% d e c r e a s e s i n s o i l NH^ c o n c e n t r a t i o n s i n t h e 0-15 cm l a y e r s o f the ATC and non-ATC p l o t s , r e s p e c t i v e l y . The average 10 cm s o i l temperature d u r i n g t h i s time was 8.5 °C, which has been shown t o be h i g h enough f o r f a i r l y r a p i d n i t r i f i c a t i o n (Anderson and B o s w e l l , 1964). F u r t h e r m o r e , a l t h o u g h the average temperature was 8.5 °C, t e m p e r a t u r e s d u r i n g t h e daytime would have been h i g h e r . On a sunny day (March 14) the s o i l t emperature a t 10 cm depth i n c r e a s e d from 1.9 t o 8.8 °C between t h e hours o f 1000 and 1400. Campbell e t al_. (1973) have demonstrated i n growth chamber experiments t h a t f l u c t u a t i n g (3 t o 14 °C) t e m p e r a t u r e s can r e s u l t i n h i g h e r n i t r i f i c a t i o n r a t e s than the c o r r e s p o n d i n g mean temperature (8.5 ° C ) . Thus, n i t r i f i c a t i o n may have proceeded a t a f a s t e r r a t e than would be p r e d i c t e d from the mean s o i l temperature a l o n e . The s m a l l e r p e r c e n t a g e d e c r e a s e i n t h e NH^ c o n c e n t r a t i o n o f the ATC p l o t s c o u l d have been due t o some r e s i d u a l e f f e c t o f the ATC i n h i b i t o r , o r i t c o u l d have been caused by the i n h i b i t o r y e f f e c t o f the h i g h e r NH„ - 30 -c o n c e n t r a t i o n . I t i s l i k e l y t h a t much o f the w a t e r - s o l u b l e ATC was l e a c h e d o u t o f the s o i l by the 610 mm o f p r e c i p i t a t i o n r e c o r d e d t h r o u g h A p r i l 4. However, t h e r e i s no p u b l i s h e d l i t e r a t u r e d e a l i n g w i t h t h e mechanisms o f ATC a d s o r p t i o n and t r a n s p o r t i n the s o i l . A number o f s t u d i e s (Anderson and B o s w e l l , 1964; W e t s e l a r ejt aj_., 1972) have demonstrated t h a t n i t r i f i -c a t i o n r a t e s t e n d t o d e c r e a s e as NH 4 s u b s t r a t e l e v e l s i n c r e a s e d beyond the optimum c o n c e n t r a t i o n . N i t r a t e l e v e l s d i d not show the c o n s i s t e n t i n c r e a s e s which s h o u l d have been a s s o c i a t e d w i t h the a c c e l e r a t e d n i t r i f i c a t i o n r a t e s . I t i s p r o b a b l e t h a t much o f t h e NO^ which formed was l o s t by l e a c h i n g o r d e n i t r i f i c a t i o n . Some l e a c h i n g d i d o c c u r , as e v i d e n c e d by the i n c r e a s e d s o i l m o i s t u r e l e v e l s ( T a b l e 2.2). The h i g h s o i l m o i s t u r e and o r g a n i c m a t t e r l e v e l s t h r o u g h o u t t h e p r o f i l e p r o v i d e d i d e a l c o n d i t i o n s f o r d e n i t r i f i c a t i o n t o o c c u r , and the i n c r e a s i n g s o i l t e m p e r a t u r e s d u r i n g t h i s time would have s t i m u l a t e d d e n i t r i f i c a t i o n r a t e s , p a r t i c u l a r l y d u r i n g sunny days when t h e s o i l s u r f a c e was warmed c o n s i d e r a b l y . B r o a d c a s t F e r t i l i z e r A p p l i c a t i o n ( T a b l e 2.4 and F i g u r e 2.1) On t h e f i r s t s a m p l i n g d a t e f o l l o w i n g u r e a a p p l i c a t i o n (December 5), NH^ l e v e l s i n the 0-15 cm l a y e r s o f t h e non-ATC p l o t s were much h i g h e r than those i n the ATC p l o t s . T h i s was u nexpected, s i n c e t h e ATC t r e a t m e n t s s h o u l d have r e s u l t e d i n h i g h e r NH^ l e v e l s . I t i s p o s s i b l e t h a t a t t h e low s o i l temperature (< 2 °C) ATC may have i n h i b i t e d urea h y d r o l y s i s f o r a p e r i o d o f time f o l l o w i n g a p p l i c a t i o n . The 194 mm o f r a i n which f e l l d u r i n g November c o u l d have l e a c h e d a l a r g e p o r t i o n o f any u n h y d r o l y z e d urea out o f T a b l e 2.4 Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n b r o a d c a s t and c o n t r o l p l o t s on v a r i o u s sampling dates as a f f e c t e d by urea-N and ATC n i t r i f i c a t i o n i n h i b i t o r , 1977-1978 Sampling date (days from N a p p l i c a t i o n ) N i t r o g e n ATC Sampling 8 N o v" <°> depth 5 Dec. (27) 16 Jan. (69) 3 Feb. (97) 14. Mar. (126) 4 Apr. (147) NH4-N N0 3- NH4-N N0 3-N NH4-N N0 3-N NH4-N N0 3-N NH 4-N N0 3-N NH4-N N0 3-N kg/ha cm kg N/ha" 200 200 2.0 0-15 5 51. 31 12 10 8 14 8 9 9 10 10 15-30 4 59 17 38 12 15 13 13 7 12 9 14 30-60 19 99 53 105 37 82 30 66 22 56 23 44 60-90 28 82 + - 25 115 41 74 51 64 24 70 0-90 56 291 - - 84 219 98 161 89 142 66 137 0-15 4 30 246 12 164 37 62 30 51 41 18 28 15-30 5 62 66 33 36 35 17 35 8 42 10 55 30-60 23 96 51 86 40 83 31 79 20 75 33 109 60-90 20 71 - - 37 66 36 68 35 74 23 89 0-90 52 259 - - 277 220 146 212 113 231 83 280 0-15 4 50 81 15 58 27 36 17 12 31 12 38 15-30 3 62 18 51 14 33 13 35 8 34 9 49 30-60 17 113 36 106 32 123 33 100 23 95 24 109 60-90 31 75 - - 40 96 42 82 37 88 26 114 0-90 56 300 - - 144 279 123 235 80 248 71 310 + + Samples n o t o b t a i n e d . V a l u e s r e p r e s e n t average o f t h r e e r e p l i c a t e p l o t s . 1 , - 32 the top 60 cm. In the non-ATC p l o t s h y d r o l y s i s was a p p a r e n t l y s u f f i c i e n t l y r a p i d t o p r e v e n t much movement o f N. In the banded p l o t s any i n h i b i t o r y e f f e c t o f ATC on u r e o l y s i s was masked by the s t r o n g o s m o t i c i n h i b i t i o n caused by the c o n c e n t r a t e d f e r t i l i z e r bands. D u r i n g the f o u r months from December 5 to A p r i l 4 t h e r e was a s t e a d y d e c r e a s e i n t h e NH 4 c o n t e n t o f the 0-15 cm l a y e r s under both t r e a t m e n t s , w i t h NH^ d e c r e a s i n g from 81 t o 12 and 246 to 18 kg N/ha i n the ATC and non-ATC p l o t s , r e s p e c t i v e l y . S i m i l a r NH 4 d e c r e a s e s were o b s e r v e d i n the 15-30, 30-60 and 60-90 cm l a y e r s , thus i n d i c a t i n g t h a t n i t r i f i c a t i o n was o c c u r r i n g c o n t i n u o u s l y d e s p i t e the low s o i l t e mperatures ( T a b l e 2.2). L e a c h i n g and d e n i t r i f i c a t i o n p r o b a b l y removed a s u b s t a n t i a l p o r t i o n o f the n i t r a t e which was formed, s i n c e n i t r a t e l e v e l s d i d n o t show the c o n s i s t e n t i n c r e a s e s which would be e x p e c t e d f r o m n i t r i f i c a t i o n . On the l a s t s a m p l i n g d a t e ( A p r i l 4) t h e r e were 203, 363, and 381 kg/ha o f (NH 4 + N0g)-N r e m a i n i n g i n t h e upper 90 cm o f t h e c o n t r o l , non-ATC and ATC t r e a t m e n t s , r e s p e c t i v e l y . T h i s r e p r e s e n t e d l o s s e s o f 144 ( 4 1 % ) , 148 ( 2 9 % ) , and 175 (31%) kg/ha o f the N which was p r e s e n t f o l l o w i n g the November 8 urea a p p l i c a t i o n s t o t h e s e p l o t s . Of the t o t a l m i n e r a l N r e m a i n i n g i n the upper 90 cm o f the f e r t i l i z e d p l o t s on A p r i l 4, an average o f 79% was i n the form o f NOg and 71% was below 30 cm. There was no d i f f e r e n c e due t o the pr e s e n c e o f ATC. S i n c e a t l e a s t two more months would e l a p s e b e f o r e any s u b s t a n t i a l c r o p uptake o f N might o c c u r , i t i s u n l i k e l y t h a t much o f t h i s N would be a v a i l a b l e to a c r o p c o n s i d e r i n g the p o t e n t i a l f o r l e a c h i n g and d e n i t r i f i c a t i o n l o s s e s d u r i n g t h i s p e r i o d o f warmer s o i l t emperatures and heavy r a i n f a l l ( average A p r i l and May p r e c i p i t a t i o n = 122 mm). - 33 -The b r o a d c a s t ATC t r e a t m e n t had no e f f e c t on n i t r i f i c a t i o n r a t e s i n the s u r f a c e 15 cm. The h i g h s o l u b i l i t y o f ATC i n water would r e n d e r i t s u s c e p t i b l e t o l e a c h i n g l o s s e s . B e f o r e the urea h y d r o l y z e d , i t i s p o s s i b l e t h a t i t and ATC may have moved t o g e t h e r through t h e s o i l , but once NH 4 formed ATC would have l e a c h e d away. ATC may have had some e f f e c t a t 30-60 cm, s i n c e t he r a t e o f NH^ l o s s was much s l o w e r a t t h i s depth i n the ATC p l o t s than the non-ATC p l o t s , p a r t i c u l a r l y d u r i n g t h e p e r i o d from December 5 to F e b r u a r y 13. T h i s c o u l d have been due to l e a c h i n g o f the u n h y d r o l y z e d urea and ATC t o t h i s d epth. F i g . 2.1. NH4-N i n the 0-15 cm h o r i z o n s on v a r i o u s sampling d a t e s e x p r e s s e d as % of NH4-N p r e s e n t i n Dec. 5 samples, 1977-78. Data p o i n t s f o r each s a m p l i n g date accompanied by the same number are 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 . 0 5 ) . - 35 CONCLUSIONS When urea was a p p l i e d on November 8 as a band, NH^ c o n c e n t r a t i o n s one month f o l l o w i n g t h e N a p p l i c a t i o n were s i m i l a r r e g a r d l e s s o f ATC t r e a t m e n t , but a f t e r two months the NH^ c o n c e n t r a t i o n i n the 0-15 cm l a y e r s w i t h ATC was s i g n i f i c a n t l y h i g h e r . There was no n i t r i f i c a t i o n i n t h i s l a y e r between J a n u a r y 16 and March 14 when t h e s o i l temperature averaged 3 °C. Between March 14 and A p r i l 4 when t h e temperature o f the 0-15 cm l a y e r a v e r a g e d 8.5 °C, n i t r i f i c a t i o n p roceeded a t a r a p i d r a t e , but t h e r e was a g r e a t e r p e r c e n t a g e l o s s o f NH^ from t h e s u r f a c e l a y e r o f t h e non-ATC p l o t s . These r e s u l t s s u g g e s t t h a t f a l l a p p l i c a t i o n o f urea w i t h ATC as a band may be somewhat e f f e c t i v e i n m i n i m i z i n g N l o s s e s , a l t h o u g h s p r i n g a p p l i c a t i o n s would c e r t a i n l y be more e f f i c i e n t . One month a f t e r N a p p l i c a t i o n a s u b s t a n t i a l p o r t i o n o f the NH^ was found below 15 cm i n both banded and b r o a d c a s t p l o t s , i n d i c a t i n g t h a t l e a c h -i n g o f u n h y d r o l y z e d u r e a had taken p l a c e . T h i s s u g g e s t s t h a t urea s h o u l d be a p p l i e d e a r l i e r i n the f a l l when t h e s o i l i s warm enough f o r more r a p i d h y d r o l y s i s , a l t h o u g h t h i s would a l s o i n c r e a s e the r i s k o f n i t r i f i c a t i o n . S a f e r f e r t i l i z e r s t o use would be ammonium s u l f a t e o r anhydrous ammonia, which c o u l d be a p p l i e d l a t e i n the y e a r w i t h l i t t l e p o s s i b i l i t y o f l e a c h i n g . In c o n t r a s t t o the banded urea, n i t r i f i c a t i o n o f b r o a d c a s t urea proceeded c o n t i n u o u s l y t h r o u g h o u t the w i n t e r r e g a r d l e s s o f ATC t r e a t m e n t . I f NH^-N i s e x p r e s s e d as a p e r c e n t a g e o f the amount p r e s e n t i n t h e 0-15 cm l a y e r on December 5, by A p r i l 4 t h e r e were 7, 15, 30 and 52% r e m a i n i n g i n the b r o a d c a s t -ATC, b r o a d c a s t +ATC, banded -ATC, and banded +ATC p l o t s , r e s p e c t i v e l y ( F i g u r e 2.1). - 36 -Thus, broadcasting urea in the f a l l leads to large losses of N, even in the presence of ATC. I t i s possible that a n i t r i f i c a t i o n i n h i b i t o r with a low water s o l u b i l i t y , such as N-Serve, might be more effective under the intense leaching conditions existing during the P a c i f i c Northwest winters. These results also have important implications for spring N applications. Urea should only be applied in the spring when the s o i l has warmed enough for rapid hydrolysis. Otherwise, leaching of unhydrolyzed urea may take place i f r a i n f a l l occurs shortly after N application. - 37 -LITERATURE CITED Anderson, O.E. and F.C. B o s w e l l . 1964. The i n f l u e n c e o f low temperature and v a r i o u s c o n c e n t r a t i o n s o f ammonium n i t r a t e on n i t r i f i c a t i o n i n a c i d s o i l s . S o i l S c i . Soc. Am. P r o c . 28: 525-529. B l a c k , C A . ( e d . ) . 1965. Methods o f s o i l a n a l y s i s , P a r t I. P h y s i c a l and m i n e r a l o g i c a l p r o p e r t i e s , i n c l u d i n g s t a t i s t i c s o f measurement and s a m p l i n g . Agronomy 9: 1-770. Am. Soc. o f Agron., Madison, Wi. B l a c k , C A . ( e d . ) . 1965. Methods o f s o i l a n a l y s i s , P a r t 2. Chemical 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 . Agronomy 9: 771-1525. Am. Soc. o f Agron., Madison, Wi. Bremner, J.M., A.M. Blackmer and L.G. Bundy. 1978. Problems i n use o f n i t r a p y r i n (N-Serve) t o i n h i b i t n i t r i f i c a t i o n i n s o i l s . S o i l B i o l , and Biochem. 10: 441-442. B r i g g s , G.C. 1975. The b e h a v i o u r o f t h e n i t r i f i c a t i o n i n h i b i t o r "N-Ser v e " i n b r o a d c a s t and i n c o r p o r a t e d a p p l i c a t i o n s to s o i l . J . S c i . Fd. A g r i c . 26: 1083-1092. Bundy, L.G. and J.M. Bremner. 1973. I n h i b i t i o n o f n i t r i f i c a t i o n i n s o i l s . S o i l S c i . Soc. Am. P r o c . 37: 396-398. Campbell, C.A., V.O. Biederbeck, and F.G. Warder. 1973. I n f l u e n c e o f s i m u l a t e d f a l l and s p r i n g c o n d i t i o n s on the s o i l system: I I I . E f f e c t o f method o f s i m u l a t i n g s p r i n g temperatures on 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 , and m i c r o b i a l p o p u l a t i o n s . S o i l S c i . Soc. Am. P r o c . 37: 382-386. C h i n , Wei-tsung and Wybe K r o o n t j e . 1962. Mechanisms o f urea a d s o r p t i o n by s o i l s . S o i l S c i . Soc. Am. P r o c . 26: 479-481. C r a s w e l l , E.T. 1978. Some f a c t o r s i n f l u e n c i n g d e n i t r i f i c a t i o n and n i t r o g e n i m m o b i l i z a t i o n i n a c l a y s o i l . S o i l B i o l . Biochem. 10: 241-245. G u t h r i e , T.F. and A.A. Bomke. 1980. N i t r i f i c a t i o n i n h i b i t i o n by N-Serve and ATC i n s o i l s o f v a r y i n g t e x t u r e . S o i l S c i . Soc. Am. J . - 4 4 : 314-320. H e n d r i c k s o n , L.L., L.M. Walsh, and D.R: Keeney.. 1978. E f f e c t i v e n e s s o f n i t r a p y r i n i n c o n t r o l l i n g n i t r i f i c a t i o n o f f a l l and s p r i n g -a p p l i e d anhydrous ammonia. Agron. J . 70: 704-708. - 38 -12. Hinshaw, R. and L . J . F r i t s c h e n . 1970. Diodes f o r temperature measure-ment. J . A p p l . M e t e o r o l o g y 9: 530-532. 13. O v e r r e i n , L.N. and P.G. Moe. 1967. F a c t o r s a f f e c t i n g urea h y d r o l y s i s and ammonia v o l a t i l i z a t i o n i n s o i l . S o i l S c i . Soc. Am. Proc. 31:. 57-61. 14. S t a n f o r d , G., S. D z i e n i a , and R.A. V a n d e r P o l . 1975. E f f e c t o f temperature on d e n i t r i f i c a t i o n r a t e i n s o i l s . S o i l S c i . Soc. Am. P r o c . 39: 867-870. 15. Touchton, J.T., R.G. H o e f t , and L.F. Welch. 1978. E f f e c t o f n i t r a p y r i n on n i t r i f i c a t i o n o f f a l l and s p r i n g - a p p l i e d anhydrous ammonia. Agron. J . 70: 805-810. 16. Touchton, J.T., R.G. H o e f t , L.F. Welch, D.L. Mulvaney, M.G. Oldham, and F.E. Z a j i c e k . 1979. N i t r o g e n uptake and c o r n y i e l d s as a f f e c t e d by a p p l i c a t i o n s o f n i t r a p y r i n w i t h anhydrous ammonia. Agron. J . 71: 238-242. 17. Warren, H.L., D.M. Huber, D.W. N e l s o n , and O.W. Mann. 1975. S t a l k r o t i n c i d e n c e and y i e l d o f c o r n as a f f e c t e d by i n h i b i t i n g n i t r i f i c a t i o n o f f a l l - a p p l i e d ammonium. Agron. J . 67: 655-660. 18. Wagenet, R.J., J.W. B i g g a r , and D.R. N i e l s e n . 1977. T r a c i n g t h e t r a n s f o r m a t i o n s o f urea f e r t i l i z e r d u r i n g l e a c h i n g . S o i l S c i . Soc. Am. J . 41: 896-902. 19. W e t s e l a a r , R., J.B. P a s s i o u r a , and B.R. S i n g h . 1972. Consequences o f banding N f e r t i l i z e r s i n s o i l . P l a n t and S o i l 36: 159-175. - 39 -C h a p t e r Three EFFECTS OF LOW TEMPERATURES AND NITRIFICATION INHIBITORS ON UREA HYDROLYSIS ABSTRACT The r e s u l t s o f a urea h y d r o l y s i s s t u d y conducted a t 2 and 12°C u s i n g a s i l t s o i l i n d i c a t e d t h a t t h e r e was no e f f e c t o f the n i t r i f i c a t i o n i n h i b i -t o r s ATC ( 4 - a m i n o - l , 2 , 4 - t r i a z o l e ) and N-Serve [ 2 - c h l o r o - 6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e ] on u r e a h y d r o l y s i s a t two o r twenty times the recommended a p p l i c a -t i o n r a t e . The r a t e o f h y d r o l y s i s a t 2°C was about h a l f t h a t a t 12°C, s u g g e s t i n g t h a t l e a c h i n g o f urea might o c c u r f o l l o w i n g i t s a p p l i c a t i o n t o a c o l d s o i l . However, use o f n i t r i f i c a t i o n i n h i b i t o r s s h o u l d n o t i n c r e a s e l e a c h i n g l o s s e s o f u r e a . - 40 -INTRODUCTION Urea i s v e r y s o l u b l e i n water (78 g/100 ml a t 5 °C) and i s o n l y weakly adsorbed by s o i l o r g a n i c m a t t e r ( C h i n and K r o o n t j e , 1962). Thus, i t moves t h r o u g h t h e s o i l a l m o s t as r e a d i l y as NO^ i n r e s p o n s e ' t o water movement (Wagenet e t al_, 1977). I t i s t h e r e f o r e i m p o r t a n t t h a t urea h y d r o l y z e s r a p i d l y f o l l o w i n g i t s a p p l i c a t i o n , s i n c e u n h y d r o l y z e d urea may move t h r o u g h t h e s o i l - p r o f i l e . . w i t h p e r c o l a t i n g w a t e r . The use o f n i t r i f i c a t i o n i n h i b i t o r s (NI) such as N-Serve [ 2 - c h l o r o - 6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e ] and ATC (4-amino-1 , 2 , 4 - t r i a z o l e ) has been suggested as a means o f i n c r e a s i n g t he e f f i c i e n c y o f f a l l - a p p l i e d o r s p r i n g - a p p l i e d ammoniacal N by d e l a y i n g t h e f o r m a t i o n o f n i t r a t e . Due t o the p o t e n t i a l f o r l e a c h i n g o f u r e a , i t i s i m p o r t a n t t o det e r m i n e i f t h e s e i n h i b i t o r s have any d e l a y i n g e f f e c t on urea h y d r o l y s i s , p a r t i c u l a r l y a t t h e low s o i l t e m p e r a t u r e s found i n the l a t e f a l l o r e a r l y s p r i n g . An e a r l i e r s t u d y (Bundy and Bremner, 1974) d e a l t w i t h the e f f e c t s o f NI on urea h y d r o l y s i s a t 30 °C. A t t h i s t e m perature complete h y d r o l y s i s o c c u r r e d w i t h i n t h r e e days r e g a r d l e s s o f t h e p r e s e n c e o f ATC o r N-Serve. The purpose o f the p r e s e n t s t u d y was to de t e r m i n e i f ATC o r N-Serve have any d e l a y i n g e f f e c t on urea h y d r o l y s i s a t 2 o r 12 °C, t e m p e r a t u r e s which a r e commonly found i n the s o i l d u r i n g t h e l a t e f a l l o r e a r l y s p r i n g . - 41 -METHODS AND MATERIALS The s o i l used i n t h i s s t u d y was c o l l e c t e d from t h e s u r f a c e 15 cm o f a s i l t c l a s s i f i e d as a Rego Humic G l e y s o l ( T y p i c F l u v a q u e n t , U.S.). Some o f t h e i m p o r t a n t p r o p e r t i e s o f t h i s s o i l a r e as f o l l o w s : s o i l pH i n 0.01 M C a C l 2 ( s o i l s o l u t i o n r a t i o 1:2), 4.8; t o t a l C, 4.9%; t o t a l N, 0.47%; CEC, 32.6 meq/100 g; sand, 8%; s i l t , 87%; m o i s t u r e c o n t e n t a t -10 kPa (0.1 b a r ) , 3 59.9%; bulk d e n s i t y , 840 kg/m . P a r t i c l e s i z e a n a l y s i s was d e t e r m i n e d by t h e hydrometer method, and m o i s t u r e r e t e n t i o n a t -10 kPa by the p r e s s u r e membrane method ( B l a c k , 1965a). T o t a l C was d e t e r m i n e d u s i n g a Leco i n d u c t i o n f u r n a c e , t o t a l N by s e m i - m i c r o - K j e l d a h l d i g e s t i o n , and CEC by n e u t r a l 1N^  ammonium a c e t a t e e x t r a c t i o n ( B l a c k , 1965b). The i n c u b a t i o n p r o c e d u r e was a - i s l i g h t m o d i f i c a t i o n from t h a t o f Mulvaney and Bremner (1977). F i v e gram p o r t i o n s o f a i r - d r i e d and s i e v e d (1 mm) s o i l were weighed i n t o 60 ml screw-cap p l a s t i c b o t t l e s . D i s t i l l e d water (1 ml) was added t o a l l t h e b o t t l e s , which were then capped, shaken, and p r e i n c u b a t e d 3 days a t e i t h e r 2 o r 12 °C (70 b o t t l e s per t e m p e r a t u r e ) . F o l l o w i n g the p r e i n c u b a t i o n , 1 ml o f an aqueous s o l u t i o n c o n t a i n i n g 2000 yg u r e a ( r e a g e n t grade) w i t h e i t h e r no NI, 10 yg ATC, 10 yg N-Serve, 100 yg ATC, o r 100 yg N-s e r v e was added, wti'th each t r e a t m e n t b e i n g a p p l i e d t o 28 samples. The f i n a l water c o n t e n t was 40% by w e i g h t , which was 2/3 o f - f i e l d c a p a c i t y . These NI a d d i t i o n s were e q u i v a l e n t t o 2.5 and 25 kg/ha o f a c t i v e i n g r e d i e n t , which i s two and twenty times the recommended a p p l i c a t i o n r a t e f o r s o i l s w i t h h i g h o r g a n i c m a t t e r c o n t e n t . H a l f o f the b o t t l e s were i n c u b a t e d a t 2 °C and h a l f a t 12 °C, u s i n g - 42 -thermographs to continuously record the temperatures, which did not vary more than 1 °C from the desired set t ings . Each day the bot t le tops were removed for a few seconds to al low gaseous exchange in order to prevent anaerobiosis. Loss of water from the samples, which was determined g rav imet r i ca l l y , was not s i gn i f i can t . On each sampling date (0, 2, 3, 4 , 7, 11, 21 days) , 10 bot t les (5 treatments x 2 rep l ica tes) were removed from each incubator. F i f t y ml of 2 N KC1 (containing 5 ug/ml phenylmercuric acetate as a urease inh ib i to r ) was added to the bo t t l es , which were mechanically shaken for 1 hour. The extracts were f i l t e r e d and analyzed by the d iacety l monoxime co lor imetr ic procedure (Douglas and Bremner, 1970). Percent hydrolysis {% H) was calculated using the formula % H = (mg urea los t /2 .00 mg) x 100. The zero d a y extract ion was immediately a f te r the addi t ion of urea. The purpose of th is ext ract ion was to determine the actual urea content in the s o i l s at t h i s t ime, which was found to range from 1.94 to 2.04 mg/5 g of s o i l , with a mean of 1.98 mg. RESULTS AND DISCUSSION As shown in Table 3.1 a f te r two days of incubat ion, there was no s i gn i f i can t e f fect from e i ther ATC or N-Serve on the hydrolysis of urea. Af ter 1 day, there were some di f ferences in the % hydrolysis between t rea t -ments. At 2 °C the NI treatments a l l had about hal f the % hydrolysis of the no NI con t ro l , whereas there was no such trend at 12 °C. By the second day there was very l i t t l e di f ference in hydrolysis rates due to NI T a b l e 3.1. E f f e c t s o f temperature, N-Serve and ATC on u r e a h y d r o l y s i s i n a s i l t s o i l . E l a p s e d time f o l l o w i n g urea a d d i t i o n , days Chemical 11 21 Temperature added Cone. 1 2 4 7 0 C ug/g % urea h y d r o l y s i s ( s t a n d a r d d e v i a t i o n ) * 2 None 0 15.4 (2.1) 19.8 (2.1) 37.9 (1.2) 55.3 (0.4) 77.3 (1.1) 99.1 (0.2) ATC 2 7.9 (4.2) 14.5 (1.3) 37.9 (1.2) 55.5 (2.1) 76.4 (2.5) 98.5 (0.2) N-Serve 2 5.4 (0.7) 19.2 (2.8) 37.9 (1.2) 51.7 (0) 75.1 (0.7) 98.5 (0.1) ATC 20 7.8 (1.4) 18.3 (6.8) 37.0 (0) 54.3 (1.7) 78.4 (0.7) 98.2 (0.4) N-Serve 20 6.9 (0) 15.4 (5.4) 39.2 (1.6) 54.6 (1.2) 77.9 (1.1) 98.5 (0) Average 8.7 17.4 38.0 54.3 77.0 98.6 12 None 0 17.3 (0) 36.6 (0) 72.5 (3.9) 97.7 (1.1) 100 (0) - -ATC 2 11.1 (0.7) 38.5 (2.7) 66.5 (5.1) 96.2 (3.3) 100 (0) - -N-Serve 2 18.0 (6.7) 38.5 (0) 71.4 (1.8) 96.8 (0.3) 100 (0) - -ATC 20 21.1 (1.3) 36.5 (5.4) 70.0 (0) 96.4 (0.9) . 100 (0) -N-Serve 20 15.9 (2.0) 39.5 0.3) 63.7 (2.8) 93.0 (1.3) 100 (0) - -Average 16.7 37.9 68.3 96.0 100 CO + S o i l samples (5 g a i r - d r y ) were i n c u b a t e d (2 o r 12 °C, 2 ml o f water) a f t e r t r e a t m e n t w i t h 2 mg o f urea and 0, 10 o r 100 yg o f compound s p e c i f i e d . urea h y d r o l y s i s = (mg urea lost/2.OOmg) x 100, v a l u e s r e p r e s e n t average o f d u p l i c a t e samples. - 44 -t r e a t m e n t . Thus, any i n h i b i t i o n o f h y d r o l y s i s caused by ATC o r N-Serve was o f v e r y s h o r t d u r a t i o n . These r e s u l t s i n d i c a t e t h a t use o f ATC o r N-Serve a t t he r a t e s used i n t h i s study s h o u l d not promote l e a c h i n g l o s s e s o f N by d e l a y i n g the h y d r o l y s i s o f u r e a . The lower r a t e o f NI i n t h i s s tudy (2 jjg/g s o i l ) a pproximates concen-t r a t i o n s i n t h e s o i l f o l l o w i n g b r o a d c a s t a p p l i c a t i o n s . The h i g h e r r a t e (20 jug/g s o i l ) would be more comparable t o t h a t found i n the s o i l i n the zone o f banded a p p l i c a t i o n s . As an example, d u r i n g a s t u d y o f NI d e g r a d a t i o n r a t e s i n a s i l t y c l a y loam, Touchton ^ t &]_.• (1978)'found a p p r o x i m a t e l y 10 yg N-Serve /g s o i l 15 days a f t e r a banded a p p l i c a t i o n o f N-Serve (0.56 kg/ha). D u r i n g the f i r s t few days a f t e r the a p p l i c a t i o n the c o n c e n t r a t i o n o f N-Serve c o u l d have been much g r e a t e r . Thus, i f N-Serve o r ATC were t o cause any d e l a y i n urea h y d r o l y s i s , the e f f e c t would be g r e a t l y a c c e n t u a t e d i n banded a p p l i c a t i o n s due t o the much h i g h e r l o c a l c o n c e n t r a t i o n s o f t h e s e c h e m i c a l s i n the band. Urea h y d r o l y s i s was s t r o n g l y t e m p e r a t u r e dependent, which c o n f i r m s the r e s u l t s o f p r e v i o u s r e s e a r c h e r s ( O v e r r e i n and Moe, 1967). On each sampling date the average % h y d r o l y s i s o f the 12 °C samples was a p p r o x i m a t e l y t w i c e t h a t o f the 2 °C samples, which agrees w e l l w i t h t h e o r e t i c a l c a l c u -l a t i o n s f o r e n z y m a t i c r e a c t i o n s . The added u r e a was a l m o s t c o m p l e t e l y h y d r o l y z e d w i t h i n 7 days a t 12 °C, whereas a t 2 °C, 21 days were r e q u i r e d f o r complete h y d r o l y s i s . S o i l s h a v i n g l e s s o r g a n i c m a t t e r s h o u l d h y d r o l y z e urea more s l o w l y due t o lower u r e a s e a c t i v i t y (Bundy and Bremner, 1974; Conrad, 1940). These r e s u l t s s u g g e s t t h a t when the s o i l t emperature i s below 12 ®C, - 4 5 -urea s h o u l d not be a p p l i e d i n a r e a s where heavy r a i n f a l l o c c u r s . A t 12 °C 7 days may be r e q u i r e d f o r complete h y d r o l y s i s , d u r i n g which time any un-h y d r o l y z e d urea would be s u s c e p t i b l e to l e a c h i n g l o s s e s . A f i e l d experiment (T. F . G u t h r i e , u n p u b l i s h e d data) demonstrated t h a t urea-N which was a p p l i e d t o a s i l t i n the f a l l i n c o a s t a l B r i t i s h Columbia (2 °C s o i l t emperature a t 10 cm depth) was l e a c h e d more than 30 cm f o l l o w i n g 194 mm o f r a i n f a l l . L oss o f urea-N by NH3 v o l a t i l i z a t i o n i s r e c o g n i z e d as a s e r i o u s problem, p a r t i c u l a r l y f o l l o w i n g s u r f a c e a p p l i c a t i o n s when the s o i l i s r e l a t i v e l y d ry and warm ( V o l k , 1959). F o r t h i s r e a s o n , i t has been recommended t h a t urea be a p p l i e d t o a c o o l s o i l f o l l o w e d by r a i n f a l l o r i r r i g a t i o n , but t h i s would tend t o promote l e a c h i n g o f the u r e a . I f i r r i g a t i o n i s a p p l i e d f o l l o w i n g urea a p p l i c a t i o n , t he amount o f water used s h o u l d be m i n i m i z e d t o p r e v e n t e x c e s s i v e l e a c h i n g o f u r e a . Urea a p p l i c a t i o n s i d e a l l y s h o u l d be made when the s o i l i s warm enough (> 12 °C) f o r r a p i d h y d r o l y s i s i n o r d e r to min i m i z e urea l e a c h i n g . However, t h i s t emperature would a l s o f a v o r n i t r i f i c a t i o n , and the r e s u l t i n g NO3 would be e a s i l y l e a c h e d . Thus, f a l l a p p l i c a t i o n s o f urea where heavy w i n t e r r a i n f a l l o c c u r s would p r o b a b l y r e s u l t i n l a r g e N l e a c h i n g l o s s e s r e g a r d l e s s o f the s o i l t emperature a t the time o f urea a p p l i c a t i o n . The b e s t approach f o r s p r i n g a p p l i c a t i o n s would be t o a p p l y urea to a warm (> 12 °C) m o i s t s o i l t o encourage r a p i d h y d r o l y s i s and, i f NH3 v o l a t i l i z a t -i o n i s a problem, t o c o v e r the urea w i t h 2 t o 4 cm o f s o i l as s u g g e s t e d by the r e s u l t s o f E r n s t and Massey (1960). - 46 -LITERATURE CITED B l a c k , C A . ( e d . ) . 1965. Methods' o f s o i l a n a l y s i s , P a r t 1. P h y s i c a l and m i n e r a l o g i c a l p r o p e r t i e s , i n c l u d i n g s t a t i s t i c s o f measurement and s a m p l i n g . Agronomy 9: 1-770. Am. Soc. o f Agron., Madison, WI. B l a c k , C A . ( e d . ) . 1965. Methods o f s o i l a n a l y s i s , P a r t 2. Chemical 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 . Agronomy 9: 771-1572. Am. Soc. o f Agron., Madison, WI. Bundy, L.G. and J.M. Bremner. 1974. E f f e c t s o f n i t r i f i c a t i o n i n h i b i t o r s on t r a n s f o r m a t i o n s o f urea n i t r o g e n i n s o i l s . S o i l . B i o l . Biochem. 6: 369-376. C h i n , Wei-tsung and Wybe K r o o n t j e . 1962. Mechanisms o f urea a d s o r p t i o n by s o i l s . S o i l S c i . Soc. Am. P r o c . 26: 479-481. Conrad, J.P. 1940. H y d r o l y s i s o f urea i n s o i l s by t h e r m o l a b i l e c a t a -l y s i s . S o i l S c i . 49: 253-263. Douglas, L.A. and J.M. Bremner. 1970. E x t r a c t i o n and c o l o r i m e t r i c d e t e r m i n a t i o n o f urea i n s o i l s . S o i l S c i . Soc. Am. P r o c . 34: 859-862. E r n s t , J.W. and H.F. Massey. 1960. The e f f e c t s o f s e v e r a l f a c t o r s on v o l a t i l i z a t i o n o f ammonia formed from urea i n the s o i l . S o i l S c i . Soc. Am. Proc. 24: 87-90. Mulvaney, R.L. and J.M. Bremner. 1977. E v a l u a t i o n o f a n t i m e t a b o l i t e s f o r r e t a r d a t i o n o f urea h y d r o l y s i s i n s o i l s . S o i l S c i . Soc. Am. J . 41: 1024-1027. O v e r r e i n , L.N. and P.G. Moe. 1967. F a c t o r s a f f e c t i n g urea h y d r o l y s i s and ammonia v o l a t i l i z a t i o n i n s o i l . S o i l S c i . Soc. Am. P r o c . 31: 57-61. To u c h t o n , J.T., R.G. H o e f t , and L.F. Welch. 1978. N i t r a p y r i n degrada-t i o n and movement i n s o i l . Agronomy J . 70: 811-816. V o l k , G.M. 1959. V o l a t i l e l o s s e s o f ammonia f o l l o w i n g s u r f a c e a p p l i c a -t i o n o f urea t o t u r f o r bare s o i l s . Agron. J . 51: 746-749. Wagenet, R.J., J.W. B i g g a r and D.R. N i e l s e n . 1977. T r a c i n g the t r a n s -f o r m a t i o n s o f urea f e r t i l i z e r d u r i n g l e a c h i n g . S o i l S c i . Soc. Am. J . 41: 896-902. - 47 -Cha p t e r Four NITRIFICATION INHIBITION BY N-SERVE AND ATC IN SOILS OF VARYING TEXTURE ABSTRACT A l t h o u g h numerous l a b o r a t o r y s t u d i e s have demonstrated the e f f e c t i v e -ness o f c e r t a i n n i t r i f i c a t i o n i n h i b i t o r s , many f i e l d s t u d i e s have f a i l e d t o show any s i g n i f i c a n t c r o p r e s p o n s e t o i n h i b i t o r t r e a t m e n t s . Most f i e l d s t u d i e s t o da t e have o n l y e v a l u a t e d N-Serve [ 2 - c h l o r o - 6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e ] , which cannot be c o n v e n i e n t l y a p p l i e d w i t h s o l i d f e r t i l i z e r s due to i t s v o l a t i l i t y . ATC ( 4 - a m i n o - l , 2 , 4 - t r i a z o l e ) i s a n o n - v o l a t i l e , water-s o l u b l e n i t r i f i c a t i o n i n h i b i t o r which can be e a s i l y c o a t e d onto s o l i d f e r t i l i z e r s w i t h o u t v o l a t i l i z a t i o n l o s s . The o b j e c t i v e o f t h i s r e s e a r c h was t o compare the e f f e c t o f N-Serve and ATC on s i l a g e c o r n (Zea mays L.) p r o d u c 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 two s o i l s ( s i l t and loamy s a n d ) . Urea was co a t e d w i t h t h e i n h i b i t o r s a t a r a t e o f 1% o f a c t i v e i n g r e d i e n t per w e i g h t o f N and a p p l i e d as a band o r b r o a d c a s t i n the s p r i n g o f 1977 and 1978. The NH^-N/NO^-N r a t i o i n the s o i l was c a l c u l a t e d f o r each sampling date as an i n d i c a t o r o f i n h i b i t o r e f f e c t i v e n e s s . N e i t h e r i n h i b i t o r s i g n i -f i c a n t l y a f f e c t e d n i t r i f i c a t i o n when a p p l i e d as a b r o a d c a s t t r e a t m e n t t o e i t h e r s o i l . In the s i l t , both i n h i b i t o r s were e q u a l l y e f f e c t i v e i n d e l a y i n g n i t r i f i c a t i o n when banded, but i n the loamy sand ATC had a f i v e times h i g h e r NH^/NOg r a t i o than N-Serve t h r e e weeks f o l l o w i n g a p p l i c a t i o n . The e f f e c t i v e -ness o f N-Serve p e r s i s t e d much l o n g e r i n the s i l t (86 days) than i n t h e loamy - 48 -sand (23 d a y s ) . T h i s suggested t h a t v o l a t i l i z a t i o n o f N-Serve s e v e r e l y l i m i t e d i t s e f f e c t i v e n e s s i n the loamy sand. There was no s i g n i f i c a n t improvement i n c r o p y i e l d s o r N c o n t e n t due t o i n h i b i t o r t r e a t m e n t i n e i t h e r s o i l . ATC i s recommended f o r f u r t h e r f i e l d e v a l u a t i o n i n c o n j u n c t i o n w i t h b a n d - a p p l i e d s o l i d f e r t i l i z e r s , p a r t i c u l a r l y i n c o a r s e - t e x t u r e d s o i l s . - 49 -INTRODUCTION There a r e a number o f p o t e n t i a l advantages a s s o c i a t e d w i t h d e l a y i n g n i t r i f i c a t i o n o f ammonium-based f e r t i l i z e r s through the use o f chemical n i t r i f i c a t i o n i n h i b i t o r s ( N I ) . By p r e v e n t i n g r a p i d f o r m a t i o n o f n i t r a t e i n the s o i l , l e a c h i n g and d e n i t r i f i c a t i o n l o s s e s o f N s h o u l d be l i m i t e d , thus i n c r e a s i n g the e f f i c i e n c y o f N f e r t i l i z e r s . Lower c o n c e n t r a t i o n s o f n i t r a t e i n the s o i l s h o u l d r e s u l t i n l e s s c o n t a m i n a t i o n o f the ground water w i t h t h i s c hemical as w e l l as reduced e m i s s i o n s o f n i t r o u s o x i d e (N 20) from d e n i t r i f i c a t i o n . I n h i b i t i o n o f n i t r i f i c a t i o n would a l s o d e c r e a s e the e m i s s i o n o f N^O which has been found t o o c c u r d u r i n g the b i o l o g i c a l o x i d a t i o n o f ammonium (Bremner and Blackmer, 1978). R e d u c t i o n o f N£0 e m i s s i o n s c o u l d be i m p o r t a n t due t o t h e c u r r e n t h y p o t h e s i s t h a t N^O r e l e a s e d t o t h e atmosphere may u l t i m a t e l y l e a d t o p a r t i a l d e s t r u c t i o n o f the ozone l a y e r ( H u t c h i n s o n and M o s i e r , 1979; M c E l r o y e t a]_., 1977). Use o f NI to i n c r e a s e p l a n t uptake o f NH^ r e l a t i v e t o NOg has been shown t o reduce the r i s k o f t o x i c a c c u m u l a t i o n o f NOg i n p l a n t t i s s u e ( M i l l s e t a l _ . , 1976; T u r n e r and Macgregor, 1978). I n c r e a s i n g p l a n t uptake o f NH^ has a l s o been shown to d e c r e a s e the i n c i d e n c e o f s t a l k r o t i n c o r n Warren e t a]_., 1975), but h i g h NH^/NOg r a t i o s have r e s u l t e d i n d e c r e a s e d y i e l d s o f p o t a t o e s ( H e n d r i c k s o n e t a l _ . , 1978). S i n c e G o r i n g (1962) f i r s t r e p o r t e d t h e r e s u l t s o f h i s s t u d i e s w i t h N-Serve [ 2 - c h l o r o - 6 - ( t r i c h l o r o m e t h y l ) p y r i d i n e ] , the f i r s t p a t e n t e d chemical i n h i b i t o r s p e c i f i c f o r Nitrosomonas sp., a number o f o t h e r i n h i b i t o r s have been d e v e l o p e d . Bundy and Bremner (1973) e v a l u a t e d 24 p o s s i b l e NI u s i n g - 50 -l a b o r a t o r y s o i l i n c u b a t i o n s and c o n c l u d e d t h a t N-Serve and ATC (4-amino-1 , 2 , 4 - t r i a z o l e) were t h e most e f f e c t i v e under t h e i r e x p e r i m e n t a l c o n d i t i o n s . The NI which has been t e s t e d i n almo s t a l l f i e l d s t u d i e s to date has been N-Serve; t h e r e have been no p u b l i s h e d f i e l d e xperiments i n v o l v i n g the use o f ATC. ATC i s much e a s i e r t o work w i t h s i n c e i t can be c o a t e d onto s o l i d f e r t i l i z e r s and a p p l i e d t o the s o i l w i t h o u t r i s k o f v o l a t i l i z a t i o n l o s s e s . In a d d i t i o n , i t s h i g h water s o l u b i l i t y (420 g/100 ml H 20 a t 20°C) would e n a b l e t h i s i n h i b i t o r t o d i f f u s e through the s o i l as r a p i d l y as the N f e r t i l i z e r . T h i s chemical i s not c o m m e r c i a l l y a v a i l a b l e , but i t s c o s t i s ex p e c t e d to be lower than t h a t o f N-Serve. Thus, ATC would appear to be a good c a n d i d a t e f o r f i e l d e v a l u a t i o n . The purpose o f t h i s s t u d y was to compare t h e e f f e c t i v e n e s s o f ATC and N-Serve when a p p l i e d t o two d i f f e r e n t s o i l s i n the humid environment o f c o a s t a l B r i t i s h Columbia. - 51 -METHODS AND MATERIALS The experiments were conducted f o r two y e a r s (1977-78) a t two s i t e s w i t h i n 50 km o f Vancouver, B r i t i s h Columbia. S i t e 1 was a t i l e . d r a i n e d l o w l a n d s i l t formed from a l l u v i a l d e p o s i t s ; U.S. c l a s s i f i c a t i o n was a T y p i c F l u v a q u e n t (Rego Humic G l e y s o l , Can.). T h i s s o i l had been under c o n t i n u o u s c o r n f o r t h r e e y e a r s as p a r t o f a commercial d a i r y o p e r a t i o n and had r e c e i v e d heavy annual manure a p p l i c a t i o n s . R o o t i n g depth was e s t i m a t e d t o be about 70 cm, s i n c e below t h i s depth e x c e s s i v e m o i s t u r e r e s t r i c t e d r o o t r e s p i r a t i o n . S i t e 2 was a w e l l - d r a i n e d upland loamy sand formed from g l a c i a l t i l l ; U.S. c l a s s i f i c a t i o n was a T y p i c Haplohumod (Humic P o d z o l , Can.). R o o t i n g depth was r e s t r i c t e d to t h e upper 45 cm due t o the high b u l k d e n s i t y (1400 kg-m ) o f th e Ae h o r i z o n . P e r t i n e n t s u r f a c e (0-15 cm) s o i l p r o p e r t i e s f o r the s i l t and loamy sand, r e s p e c t i v e l y , were: s o i l pH i n 0.01M C a C ^ ( s o i l : s o l u t i o n r a t i o 1:2), 4.5 and 5.4; t o t a l C, 4.9% and 4.5%; t o t a l N, 0.47% and 0.27%; CEC, 32.6 and 23.9 meq/100 g; bulk d e n s i t y , . 842 and 1160 kg-m" 3; sand, 8% and 76%; s i l t , 87% and 18%. T o t a l C was d e t e r m i n e d u s i n g a Leco i n d u c t i o n f u r n a c e , t o t a l N by a s e m i m i c r o - K j e l d a h l d i g e s t i o n , and CEC by a n e u t r a l IN;ammonium a c e t a t e e x t r a c t i o n ( B l a c k , 1965). The N s o u r c e f o r a l l experiments was f e r t i l i z e r grade p r i l l e d urea (1.4 t o 3.0 mm), a p p l i e d i n the s p r i n g a t r a t e s o f 0 , 50, o r 100 kg N/ha. The h i g h e s t r a t e i s somewhat lower than t h a t commonly used f o r s i l a g e c o r n i n t h i s a r e a (130 kg N/ha), but t h e purpose o f t h i s s tudy was t o compare the y i e l d s o f c o r n w i t h and w i t h o u t t h e i n h i b i t o r s a t lower than optimum N a p p l i c a t i o n r a t e s . N i t r o g e n was a p p l i e d e i t h e r as a b r o a d c a s t t r e a t m e n t - 52 -which was r a k e d i n t o the s o i l o r as a narrow (5 cm) band which was c o v e r e d w i t h 7.5 cm o f s o i l 30 cm from the seed row. The l o c a t i o n o f each band was marked by s t r e t c h i n g a n y l o n s t r i n g between two wooden s t a k e s . N i t r i f i c a t i o n i n h i b i t o r t r e a t m e n t s c o n s i s t e d o f 1% o f a c t i v e i n g r e d i e n t per w e i g h t o f N o f e i t h e r N-Serve o r ATC. The r e q u i r e d q u a n t i t y o f ATC (36% w/v aqueous s o l u t i o n ) was s p r a y e d w i t h a chromatography s p r a y gun (S.S. M a l h i , p e r s o n a l communication) onto a t r a y o f urea p r i l l s which were shaken by a mechanical s h a k e r . F o l l o w i n g thorough m i x i n g , the c o a t e d urea was d r i e d o v e r n i g h t a t 23°C, then s e a l e d i n p l a s t i c bags. Due t o the v o l a t i l i t y o f N-Serve a d i f f e r e n t method (L.D. B a i l e y , p e r s o n a l communication) was n e c e s s a r y f o r c o a t i n g t h i s c hemical onto the u r e a . One kg batches o f urea were weighed i n t o c l e a n 3.78 l i t e r p a i n t t i n s , the c a l c u l a t e d q u a n t i t y o f N-Serve (22.2% w/v i n x y l e n e ) was added, and the cans were t i g h t l y s e a l e d and shaken f o r 10 minutes. The batches were a l l mixed t o g e t h e r i n a l a r g e g l a s s d e s s i c a t o r where they were s t o r e d . W i t h i n 24 hours o f f i e l d a p p l i c a t i o n , the N-Serve p l u s urea t r e a t m e n t s were weighed out i n t o t r i p l e t h i c k n e s s p l a s t i c bags. The d e t a i l s o f each experiment a r e g i v e n i n T a b l e 4.1. In 1977 a c o m p l e t e l y random d e s i g n was used, whereas randomized, complete b l o c k s were used i n 1978, w i t h t h r e e r e p l i c a t i o n s i n a l l e x p e r i m e n t s . I n d i v i d u a l p l o t s c o n s i s t e d o f f o u r rows o f s i l a g e c o r n (Zea mays L., DeKalb 22) p l a n t e d 84 or 75 cm a p a r t , w i t h an average s e e d i n g r a t e o f 69,000 o r 55,000 p l a n t s / h a i n S i t e s 1 and 2, r e s p e c t i v e l y . In 1977 (Exp. 1) urea w i t h and w i t h o u t 1% ATC was e i t h e r b r o a d c a s t or banded when a p p l i e d t o the s i l t s o i l i n a s i n g l e June a p p l i c a t i o n when the p l a n t s were 30 cm h i g h . In 1978 1% N-Serve was added as a n o t h e r i n h i b i t o r t r e a t m e n t i n the s i l t , but a l l t r e a t m e n t s were banded T a b l e 4;1. Experimental c o n d i t i o n s p r e v a i l i n g d u r i n g s t u d i e s o f the e f f e c t s o f ATC and N-Serve on n i t r i f i c a t i o n and c o r n p r o d u c t i o n . Experiment V a r i a b l e 1 2% 3 4 S o i l t e x t u r e s i l t s i l t loamy sand loamy sand P l o t s i z e , m 7.6 x 3.35 7 x 3.35 6 x 3 3 x 2 B a n d s / p l o t x l e n g t h , m 4 x 7.6 4 x 7.0 4 x 6.0 2 x 3.0 N f e r t i l i z e r r a t e , kg/ha 0, 50, 100# 0, 50, 100# 0, 50, 100# 0, 100 N i t r i f i c a t i o n i n h i b i t o r ATC, none ATC, N - S § v none ATC, N-S, none ATC, N-S, none N placement band, b r o a d c a s t band o n l y band o n l y band, b r o a d c a s t N a p p l i c a t i o n date 14 June 1977 12 June 1978 9 May 1978 9 May 1978 P l a n t i n g d a t e 26 May 1977 24 May 1978 10 May 1978 f a l l o w +Manure a p p l i c a t i o n to s i l t i n 1977, but not i n 1978. # In a d d i t i o n , 12 kg N/ha a p p l i e d as s t a r t e r band .5 cm t o the s i d e and 5 cm below the seed. § N-Serve i s a b b r e v i a t e d as N-S. - 54 -(Exp. 2 ) . The r e s u l t s o f o t h e r r e s e a r c h e r s ( B r i g g s , 1975; Boswell e t a l . , 1976) have shown t h a t N-Serve i s r e l a t i v e l y i n e f f e c t i v e when b r o a d c a s t , and our 1977 r e s u l t s i n d i c a t e d t h a t the same i s t r u e f o r ATC. In 1978 N-Serve and ATC were a l s o compared when a p p l i e d t o the loamy sand a t S i t e 2 (Exp. 3 ) . A t t h i s s i t e the c o r n was hand p l a n t e d , and the N t r e a t m e n t s were a p p l i e d on the day f o l l o w i n g s e e d i n g . A l l c o r n p l o t s r e c e i v e d a s t a r t e r band a p p l i c a t i o n o f N and P (12 and 26 kg/ha, r e s p e c t i v e l y ) a t s e e d i n g . P o t a s s i u m (80 kg K/ha) was b r o a d c a s t a t t h i s time a l s o . The c o r n p l o t s a t S i t e 1 r e c e i v e d a p o s t -emergence t r e a t m e n t o f 2 kg/ha a t r a z i n e f o r weed c o n t r o l . A d j a c e n t t o the c o r n f i e l d a t S i t e 2 a f a l l o w f i e l d (Exp. 4) was a l s o t r e a t e d w i t h N-Serve o r ATC-coated urea which was e i t h e r banded o r b r o a d c a s t . The purpose o f t h i s f a l l o w e x p eriment was to e l i m i n a t e the e f f e c t o f c r o p uptake o f N i n o r d e r t o more a c c u r a t e l y a s s e s s s o i l N t r a n s f o r m a t i o n s . The p l o t s were sampled ( s i x 2.5 cm d i a m e t e r c o r e s / p l o t ) a t two o r t h r e e week i n t e r v a l s t o a depth o f 30 cm (Exp. 1, 3, 4) o r 60 cm (Exp. 2 ) . Banded p l o t s were sampled d i r e c t l y i n the c e n t e r o f the marked bands, whereas b r o a d c a s t p l o t s were randomly sampled. The samples were s e p a r a t e d i n t o 15 cm i n c r e m e n t s which were r e f r i g e r a t e d (2°C) and e x t r a c t e d w i t h i n 48 hours u s i n g 2_N_ KC1 (10 g m o i s t s o i l : ! 0 0 ml KC1). The s o i l e x t r a c t s were a n a l y z e d f o r N H 4 +, N0 2~ and N0 3~ u s i n g a T e c h n i c o n A u t o a n a l y z e r I I . A s e p a r a t e 10 g sample o f each s o i l was o v e n - d r i e d (105°C) t o determine the m o i s t u r e c o n t e n t i n o r d e r to c a l c u l a t e t h e N c o n c e n t r a t i o n s on a d r y weight b a s i s as w e l l as to determine s o i l m o i s t u r e t e n s i o n s u s i n g s o i l water r e t e n t i o n c u r v e s . The pH o f t h e e x t r a c t s was a l s o determined but the d a t a i s n o t r e p o r t e d s i n c e t h e r e was v e r y l i t t l e v a r i a t i o n , w i t h v a l u e s r a n g i n g between 4 and 5. - 55 -The l e a f o p p o s i t e and below the e a r was sampled a t s i l k i n g time ( A u g u s t ) , and e a r s p l u s s t o v e r were h a r v e s t e d from the two c e n t e r rows o f each p l o t i n mid-September. F r e s h weights o f the e a r s p l u s s t o v e r were taken i n the f i e l d , and subsamples were o b t a i n e d f o r N a n a l y s i s and water c o n t e n t . T o t a l K j e l d a h l N ( i n c l u d i n g NOg) (Bremner, 1965) was d e t e r m i n e d on the e a r l e a f and e a r p l u s s t o v e r samples f o l l o w i n g d r y i n g (70°C) and g r i n d i n g i n a s t a i n l e s s s t e e l W i l e y m i l l . N i t r a t e i n the e a r l e a f was d e t e r m i n e d by s h a k i n g 0.5 g samples o f the ground l e a v e s w i t h 100 ml d i s t i l l e d w a t e r , f o l l o w e d by f i l t r a t i o n and a n a l y s i s on t h e A u t o a n a l y z e r I I . A i r t e m perature and p r e c i p i t a t i o n r e c o r d s were o b t a i n e d from moni-t o r i n g s t a t i o n s l o c a t e d 5 km and 0.1 km, r e s p e c t i v e l y , from S i t e s 1 and 2. S o i l t e mperatures a t 10, 20 and 40 cm were m o n i t o r e d u s i n g s i l i c o n e d i o d e s (Hinshaw and F r i t s c h e n , 1970) i n s t a l l e d i n the e x p e r i m e n t a l a r e a . In a d d i t i o n , a s o i l degree-day i n t e g r a t o r was i n s t a l l e d a t the 10 cm depth o f S i t e 2 i n 1978 ( T a b l e 4.2). An a n a l y s i s o f v a r i a n c e was performed on the data from each e x p e r i m e n t , and t r e a t m e n t means were t e s t e d f o r s i g n i f i c a n t d i f f e r e n c e s by Duncan's m u l t i p l e range t e s t . Table 4.2. Soil moisture .tension, average soiL temperature (TO cm depth) arid cumulative precipitation between sampling dates at Sites .1 and 2:, 1977 and 1978. 1977 Site 1 1978 Site 1 1978 Site 2 Sample date Soil temp.# Moisture tension Pptn.* Sample date Soil temp. Moisture tension Pptn. Sample, date Soil temp. Moisture tension Pptn. 0-15 15-30 0-15 15-30 0-15 15-30 cm cm cm cm cm cm °C kPaS — cm °C kPa cm °C — kPa - — cm 14 June 13.5 30 15 - 12 June 17.0 60 20 - 9 May 13.0 30 15 -30 June 15.0 30 15 0.6 4 July 17.2 110 40 0 1 June 13.2 35 20 10.8 13 July 14.5 50 25 2.1 25 July 19.5 270 200 0.3 16 June 17.4 40 25 2.6 27 July 15.4 170 110 1.4 15 Aug. 18.9 160 200 4.8 11 July 19.2 25 40 1.4 10 Aug. 19.9 250 190 0 6 Sept. 16.0 30 25 9.6 7 Aug. 20.8 100 50 0.4 6 Sept. 16.7 50 120 13.2 - - - - 29 Aug. 17.4 25 20 12.7 Average soil temperature since previous sampling date, value for f i rs t date is actual temperature when N applied. Supplemental irrigation was not applied to any of the f ie lds. 100 kPa = 1 bar tension RESULTS AND DISCUSSION Thre e p o s s i b l e measures o f n i t r i f i c a t i o n i n h i b i t o r e f f e c t i v e n e s s were c o n s i d e r e d : (1) c o n c e n t r a t i o n o f NH^; (2) sum o f c o n c e n t r a t i o n s o f NH^ and N0 3 ( E N ( 3 ) r a t i o o f Nh^/NOg. The f i r s t two o f t h e s e parameters would o b v i o u s l y have much h i g h e r v a l u e s i n samples from p l o t s where t h e N was a p p l i e d a t the h i g h e r r a t e o r banded, r e g a r d l e s s o f the i n h i b i t o r t r e a t m e n t . The r a t i o o f NH^/NOg s h o u l d be more ind e p e n d e n t o f r a t e o f N o r method o f a p p l i c a t i o n , and thus would be a b e t t e r measure o f i n h i b i t o r e f f e c t i v e n e s s . Use o f t h i s r a t i o c o u l d h e l p t o l e s s e n t h e i n h e r e n t v a r i a b i l i t y a s s o c i a t e d w i t h s a m p l i n g a f e r t i l i z e r band. C o n c e n t r a t i o n o f NOg by i t s e l f was not c o n s i d e r e d a good measure o f n i t r i f i c a t i o n i n h i b i t i o n due t o i t s g r e a t e r p o t e n t i a l f o r l o s s , e i t h e r by l e a c h i n g , d e n i t r i f i c a t i o n o r p l a n t uptake. The d i s c u s s i o n which f o l l o w s w i l l f o c u s on t h e dat a from t h e 0-15 cm s o i l samples and the 100 kg N/ha t r e a t m e n t s . Seldom were s i g n i f i c a n t d i f f e r e n c e s due t o i n h i b i t o r t r e a t m e n t s found below 15 cm. Trend s o b s e r v e d a t t h e lower r a t e o f N a p p l i c a t i o n were s i m i l a r t o tho s e o f the h i g h e r N r a t e , but t h e d i f f e r e n c e s between t r e a t m e n t s were s m a l l e r . V a l u e s g i v e n f o r N0_ 3 i n c l u d e N02> but NO2-N was not found t o exceed one ppm i n any sample. 1977 S i l t ( E x periment 1) S o i l R e s u l t s A s i g n i f i c a n t l y h i g h e r (p < 0.01) NH^/NOg r a t i o due t o t h e p r e s e n c e o f ATC was found i n a l l 0-15 cm samples taken from the banded N p l u s ATC p l o t s d u r i n g t he e n t i r e 84 day sampling p e r i o d ( F i g . . 4 . 1 ) . No s i g n i f i c a n t d i f f e r -ences were o b s e r v e d when the N and ATC were b r o a d c a s t . The e l e v a t e d N H „ / N 0 o ro O Z E CL CL I* X z E CL CL co 40 f 60 27 July (Tasseling) TIME FOLLOWING A P P L I C A T I O N OF NITROGEN ( D A Y S ) F i g u r e 4.1. R a t i o o f ppm Nfty-N/ppm NO3-N i n 0-15 cm depth o f 1977 s i l t as a f f e c t e d by method -of N a p p l i c a t i o n , presence o f n i t r i f i c a t i o n i n h i b i t o r , and time. In t h i s and subsequent f i g u r e s d a t a p o i n t s f o r each sampling date accompanied by the same number are not s i g n i f i c a n t l y d i f f e r e n t (P ^  0.05). - 59 -r a t i o a s s o c i a t e d w i t h the banded ATC t r e a t m e n t i n d i c a t e s t h a t some i n h i b i t i o n o f n i t r i f i c a t i o n p e r s i s t e d t h r o u g h o u t t h e growing season. On t h e f i r s t s a m p l i n g d a t e (16 days f o l l o w i n g N a p p l i c a t i o n ) , urea banded w i t h o u t ATC had a s i g n i f i c a n t l y h i g h e r NH^/NOg r a t i o than the b r o a d -c a s t urea p l o t s , but by t h e second sampling d a t e (29 days) t h i s d i f f e r e n c e was n e g l i g i b l e ( F i g . 4 , 1 ) . T h i s i n h i b i t i o n o f n i t r i f i c a t i o n caused by h i g h l o c a l urea c o n c e n t r a t i o n s has been r e p o r t e d p r e v i o u s l y ( W e t s e l a a r e t a l . , 1972) and i s thought to be caused p r i m a r i l y by t h e low o s m o t i c p o t e n t i a l o f s o l u t i o n i n t h e immediate v i c i n i t y o f t h e N f e r t i l i z e r band. I n h i b i t i o n caused by h i g h pH and N0 2 a c c u m u l a t i o n was not l i k e l y i n t h i s s i t u a t i o n s i n c e the pH o f t h e s o i l e x t r a c t s never exceeded 5, and s o i l NO^-N concen-t r a t i o n s n e ver exceeded 1 ppm. The c o n c e n t r a t i o n o f NH^ i n t h e 0-15 depth showed a s i m i l a r r e s p o n s e to the p r e s e n c e o f ATC ( F i g . 4.2). With the e x c e p t i o n o f the f i r s t s a mpling d a t e , t h r o u g h o u t the growing season t h e r e was a s i g n i f i c a n t l y h i g h e r (P < 0.05)'NH^ c o n c e n t r a t i o n i n the banded p l o t s which r e c e i v e d ATC than i n the banded p l o t s which d i d n o t . A g a i n t h e r e was no s i g n i f i c a n t d i f f e r e n c e i n the b r o a d c a s t p l o t s due to a p p l i c a t i o n o f ATC. S o i l NOg l e v e l s (0-15 cm) 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 lower i n the banded ATC p l o t s than i n t h o s e w i t h -out ATC, but t h e r e were no c o n s i s t e n t d i f f e r e n c e s between the b r o a d c a s t t r e a t -ments ( d a t a not shown). The sum o f NH^ p l u s NOg was a poor i n d i c a t o r o f i n h i b i t o r e f f e c t i v e -n e s s , s i n c e i t d i d not r e v e a l any s i g n i f i c a n t d i f f e r e n c e s due to the p r e s e n c e o f ATC u n t i l 57 days f o l l o w i n g N a d d i t i o n ( F i g . 4.3). T h i s i n d i c a t e s t h a t t h e r e was p r o b a b l y l i t t l e l o s s o f NO- by l e a c h i n g o r d e n i t r i f i c a t i o n p r i o r t o TIME FOLLOWING A P P L I C A T I O N OF NITROGEN ( D A Y S ) F i g u r e 4.2. C o n c e n t r a t i o n o f NH4-N (ppm) i n 0-15 cm depth o f 1977 s i l t as a f f e c t e d by method o f N a p p l i c a t i o n , presence o f n i t r i f i c a t i o n i n h i b i t o r , and time. 2 I I I 1 1 L_ -10 0 20 40 60 80 TIME FOLLOWING APPLICATION OF NITROGEN (days) F i g u r e 4 . 3 . Sum o f exchangeable (ppm NH4+HO3) - fi i n 0-15 cm depth o f 1977 s i l t as a f f e c t e d by method o f N a p p l i c a t i o n , presence o f n i t r i f i c a t i o n i n h i b i t o r , and time. - 62 -t h i s d a t e . L e a c h i n g l o s s e s were not l i k e l y , s i n c e o n l y 4 .1 cm o f r a i n f a l l was r e c o r d e d through J u l y 27 ( T a b l e 4.2) and most o f t h i s would have been used by t h e c r o p . Thus, even though t h e r e was more r a p i d n i t r i f i c a t i o n i n the non-ATC p l o t s , c o n d i t i o n s were no t f a v o r a b l e f o r N 0 3 l o s s , and the EN was not s i g n i f i c a n t l y lower. However, on the August 10 s a m p l i n g date t h e r e was a s i g n i f i c a n t l y h i g h e r ZN i n the banded p l o t s w i t h ATC than i n the p l o t s w i t h -o u t ATC. On the same da t e t h e r e was a l s o a much h i g h e r N H ^ / N O ^ r a t i o i n the banded ATC p l o t s than on the p r e v i o u s sampling d a t e . These d a t a s u g g e s t t h a t i n the banded ATC p l o t s between J u l y 27 and August 10 t h e r e was e i t h e r a de c r e a s e i n the n i t r i f i c a t i o n r a t e compared t o the r a t e o f NH^ f o r m a t i o n o r e l s e t h e r e was an i n c r e a s e i n the p l a n t uptake o f NO^ r e l a t i v e t o N H ^ . I n c r e a s e d s o i l temperatures between J u l y 27 and August 15 ( T a b l e 4 . 2 ) s h o u l d have r e s u l t e d i n more r a p i d m i n e r a l i z a t i o n o f s o i l o r g a n i c N , but h i g h e r s o i l m o i s t u r e t e n s i o n s i n t h i s n o n - i r r i g a t e d f i e l d (170 t o 250 kPa) c o u l d have caused a c c u m u l a t i o n o f NH^ due t o th e g r e a t e r s e n s i t i v i t y o f the n i t r i f y i n g p o p u l a t i o n to m o i s t u r e s t r e s s , as sugg e s t e d by o t h e r r e s e a r c h e r s ( M i l l e r and Johnson, 1964; Reichman e t a l _ . , 1966 ) . However, i f t h i s were t r u e , then a l l o f t h e t r e a t m e n t s s h o u l d have e x h i b i t e d an i n c r e a s e d N H ^ / N O ^ r a t i o , whereas o n l y t h e banded ATC t r e a t m e n t had a s i g n i f i c a n t i n c r e a s e . P l a n t uptake o f r e l a t i v e l y immobile i o n s such as N H 4 i s r e g u l a t e d by the d i f f u s i o n r a t e as w e l l as by th e r a t e o f r o o t i n t e r c e p t i o n o f t h e s e i o n s , whereas m o b i l e i o n s such as N 0 3 a r e f r e e to move to the r o o t s by mass f l o w . Thus, d u r i n g the p e r i o d o f maximum N uptake i t i s p o s s i b l e t h a t the N H ^ / N O ^ r a t i o i n the s o i l c o u l d be i n c r e a s e d by more r a p i d c r o p removal o f NOo than NH.. However, i f the c o n c e n t r a t i o n o f N H . i s a l r e a d y v e r y low, then / - 63 -t h e r e would he l e s s o f an e f f e c t on the NH^/NO^ r a t i o . The banded ATC p l o t s which had a h i g h NH^ c o n c e n t r a t i o n (200 ppm) on J u l y 27 showed a l a r g e i n c r e a s e i n t he NH^/NOg r a t i o , whereas i n the banded p l o t s w i t h o u t ATC and the broad-c a s t p l o t s which had much lower NH^ c o n c e n t r a t i o n s (60 and 10 ppm, r e s p e c t t i v e l y ) t h e r e were much s m a l l e r r a t i o i n c r e a s e s . The p e r i o d from J u l y 27 to August 10 c o r r e s p o n d e d t o the time o f t a s s e l and s i l k f o r m a t i o n , which i s thought to be the time o f maximum N uptake by the c o r n p l a n t (Terman and N i g g l e , 1973; B a r - Y o s e f and K a f k a f i , 1972). A t h i r d h y p o t h e s i s f o r the i n c r e a s e d NH^/NOg r a t i o i n the banded ATC p l o t s i s the p o s s i b i l i t y t h a t high ambient c o n c e n t r a t i o n s o f NH^ may r e s t r i c t N0 3 uptake, as s u g g e s t e d by Jackson (1978). T h i s i n h i b i t i o n o f NOg / uptake might be r e v e r s e d when the NH^ c o n c e n t r a t i o n r e l a t i v e to the NOg c o n c e n t r a t i o n drops below a c e r t a i n l e v e l , t h u s i n c r e a s i n g the NOg uptake and c o n s e q u e n t l y t h e NH^/NOg r a t i o i n the s o i l (W.A. J a c k s o n , p e r s o n a l communication). The remainder o f t h i s d i s c u s s i o n w i l l f o c u s on the NH^/NOg r a t i o i n the s o i l , s i n c e t h i s parameter had h i g h e r F t e s t v a l u e s than the NH^ c o n c e n t r a t i o n a l o n e , and p r o v i d e d a b e t t e r s e p a r a t i o n o f the t r e a t m e n t means. The r a t i o appears t o be a more s e n s i t i v e i n d i c a t o r o f i n h i b i t o r e f f e c t i v e n e s s , p a r t i c u l a r l y d u r i n g the f i r s t h a l f o f the growing season b e f o r e the time o f maximum c r o p uptake o f N. 1978 S i l t ( E x periment 2) S o i l R e s u l t s As shown i n F i g . 4.4 the NH^/NOg r a t i o i n the banded ATC p l o t s was s i g n i f i c a n t l y h i g h e r f o r 86 days than i n the p l o t s w i t h o u t i n h i b i t o r , A Urea + ATC, Ba / \ N Urea + N-Serve, Ba / \ U Urea only, Ba • / \ § 20 4 0 7 ~ 60 80 12"June 2 5 July (Tasseling) F i g u r e 4 . 4 . R a t i o o f ppm NH4-N/ppm NO3-N i n 0-15 cm depth o f 1978 s i l t as a f f e c t e d by method o f N a p p l i c a t i o n , presence o f n i t r i f i c a t i o n i n h i b i t o r , and time. - 65 -i n d i c a t i n g .that ATC was. a g a i n an e f f e c t i v e n i t r i f i c a t i o n i n h i b i t o r f o r the e n t i r e s e a s o n . The banded N-Serve r a t i o s were c o n s i s t e n t l y lower than the ATC r a t i o s , but not s i g n i f i c a n t l y lower u n t i l t h e l a s t s a m p l i n g d a t e . Thus ATC and N-Serve were e q u a l l y e f f e c t i v e n i t r i f i c a t i o n i n h i b i t o r s f o r t h e f i r s t 64 days f o l l o w i n g N a d d i t i o n . Both o f the banded i n h i b i t o r t r e a t m e n t s had l a r g e i n c r e a s e s i n t h e i r NH 4/N0 3 r a t i o s between J u l y 25 and August 15, as seen a t the same p e r i o d i n the 1977 banded ATC p l o t s . A g a i n , t h i s i s p r o b a b l y l a r g e l y a f u n c t i o n o f p r e f e r e n t i a l p l a n t uptake o f NO^ r e l a t i v e t o NH^ d u r i n g t h i s p e r i o d o f r a p i d N and water uptake. There was p r e c i p i t a t i o n d u r i n g t h i s t i m e , and the s o i l water c o n t e n t i n c r e a s e d ( T a b l e 4.2) so n i t r i f i c a t i o n would not have been l i m i t e d by low s o i l m o i s t u r e . L e a c h i n g o f NO^ out o f t h e 0-15 cm zone was p r o b a b l y not a f a c t o r , s i n c e t h e r e was no i n c r e a s e i n s o i l m o i s t u r e ( T a b l e 4.2) or NO^ c o n c e n t r a t i o n ( d a t a not shown) i n the 15-30 cm zone on August 15. D e n i t r i f i c a t i o n c o u l d a l s o be a cause o f NO^ d i s a p p e a r a n c e , but i t i s u n l i k e l y t h a t t h e small i n c r e a s e i n s o i l m o i s t u r e (31.4% to 38.1% o f d r y wei g h t ) would be enough to s t i m u l a t e a l a r g e i n c r e a s e i n the d e n i t r i f i c a t i o n r a t e . 1978 Cropped Loamy Sand (Experiment 3) S o i l R e s u l t s The NH^/NOg r a t i o s i n F i g . 4.5 i n d i c a t e t h a t banded ATC was a much more e f f e c t i v e i n h i b i t o r than banded N-Serve f o r the f i r s t 63 days f o l l o w i n g a p p l i c a t i o n i n the loamy sand. N e i t h e r i n h i b i t o r was e f f e c t i v e a f t e r 63 days, as the NH^/NO^ r a t i o s were not s i g n i f i c a n t l y h i g h e r than t h o s e o f banded urea a l o n e on t h i s d a t e . There was no n i t r i f i c a t i o n i n h i b i t i o n a s s o c i a t e d w i t h the banded urea-no i n h i b i t o r t r e a t m e n t , s i n c e the NH^/NO, r a t i o o f t h i s t r e a t m e n t F i g u r e 4.5. R a t i o o f ppm NH 4-N/ppm MO3N i n 0-15 cm depth o f 1978 cropped loamy sand as a f f e c t e d by method o f N a p p l i c a t i o n , type o f n i t r i f i c a t i o n i n h i b i t o r , and time. - 67 -was no h i g h e r than t h a t o f the b r o a d c a s t urea t r e a t m e n t ( d a t a not shown). I t i s l i k e l y t h a t t h e r a i n f a l l (10.8 cm) between N a p p l i c a t i o n and the f i r s t s a m pling date tended to d i l u t e the f e r t i l i z e r band and d e c r e a s e the os m o t i c p o t e n t i a l o f the s o i l s o l u t i o n . A l s o , t h e r e would be g r e a t e r movement o f both water and s a l t s i n t h i s c o a r s e - t e x t u r e d s o i l than i n the s i l t . More than h a l f o f the 10.8 cm p r e c i p i t a t i o n o c c u r r e d on the f i f t h day f o l l o w i n g urea a p p l i c a t i o n . I t i s not l i k e l y t h a t much n i t r i f i c a t i o n would have o c c u r r e d by t h i s time even i n t h e p l o t s w i t h o u t i n h i b i t o r t r e a t m e n t s , thus l i t t l e NO^ s h o u l d have been l e a c h e d a t t h i s t i m e . L e a c h i n g seemed to have l i t t l e i n f l u e n c e on the e f f e c t i v e n e s s o f the h i g h l y w a t e r - s o l u b l e ATC. The NH^/NO^ r a t i o s o f the banded ATC p l o t s t h r e e weeks f o l l o w i n g a p p l i c a t i o n were a p p r o x i m a t e l y the same i n both t he s i l t and the loamy sand, even though t h e r e was no l e a c h i n g i n the s i l t . The reduced e f f e c t i v e n e s s o f N-Serve i n the loamy sand compared to the s i l t c o u l d be a f a c t o r o f the loamy sand's lower o r g a n i c m a t t e r c o n t e n t , c o a r s e r t e x t u r e , o r b o t h . P r e v i o u s r e s e a r c h e r s ( B r i g g s , 1975; Toughton e t a l . , 1978) have found t h a t N-Serve i s more e f f e c t i v e i n s o i l s h a v i n g h i g h e r o r g a n i c matter due to g r e a t e r s o r p t i o n by the o r g a n i c f r a c t i o n which h e l p s to p r e v e n t v o l a t i l i z a t i o n l o s s . However, t he somewhat h i g h e r carbon c o n t e n t o f the s i l t s o i l i s p r o b a b l y not enough to ac c o u n t f o r the g r e a t d i f f e r e n c e i n N-Serve e f f e c t i v e n e s s . The l a r g e t e x t u r a l d i f f e r e n c e between the two s o i l s o f f e r s a more p l a u s i b l e e x p l a n a t i o n . H e n d r i c k s o n et_ al _ . (1 978) a p p l i e d u r e a c o a t e d w i t h N-Serve as a s i d e d r e s s band t o an i r r i g a t e d loamy sand and found o n l y s m a l l i n c r e a s e s i n s o i l NH^ o r NH^/NO^ r a t i o s due t o the i n h i b i t o r . They c o n c l u d e d t h a t the poor e f f e c t i v e n e s s o f the i n h i b i t o r i n t h i s s o i l was due t o - 6 8 -l e a c h i n g o f the N f e r t i l i z e r o u t o f the N-Serve t r e a t e d zone as w e l l as r a p i d v o l a t i l i z a t i o n o f the N-Serve. Gaseous d i f f u s i o n i n the loamy sand would be enhanced by i t s abundance o f connected a i r - f i l l e d pore space. V o l a t i l i z a t i o n o f N-Serve might r e a d i l y o c c u r i n t h i s s o i l even i f p l a c e d w e l l below the s u r f a c e , s i n c e a d i r e c t pathway may e x i s t between t h e i n c o r p o r a t e d N-Serve and the atmosphere. L e a c h i n g o f the urea away from the N-Serve may a l s o have o c c u r r e d i n the loamy sand. The g r e a t e r p e r s i s t e n c e o f the e f f e c t i v e n e s s o f both N-Serve and ATC i n the s i l t i s e s p e c i a l l y s t r i k i n g s i n c e the i n h i b i t o r s and urea were a p p l i e d to the s i l t one month l a t e r when the s o i l was a p p r e c i a b l y warmer ( T a b l e 4.2). L a b o r a t o r y s t u d i e s (Bundy and Bremner, 1973; G o r i n g , 1962) have shown t h a t the e f f e c t i v e n e s s o f both i n h i b i t o r s d e c r e a s e s w i t h i n c r e a s i n g s o i l t emperature. But the d i f f e r e n c e i n t e x t u r e between t h e s e two s o i l s i s a p p a r e n t l y a more im p o r t a n t f a c t o r than the temperature i n d e t e r m i n i n g the p e r s i s t e n c e o f the i n h i b i t o r a c t i v i t y . L a b o r a t o r y s t u d i e s (Bundy and Bremner, 1973; G o r i n g , 1962) have i n d i c a t e d t h a t N-Serve i s more e f f e c t i v e i n c o a r s e - t e x t u r e d s o i l s , but t h e c o n f i n e d n a t u r e o f t h e s e s t u d i e s p r e v e n t e d gaseous l o s s o f N-Serve from the s o i l . A l s o , u n l i k e the s i t u a t i o n i n the f i e l d , t h e r e would be l i t t l e movement o f N o r i n h i b i t o r through the s o i l by l e a c h i n g . In c o n t r a s t to the r e s u l t s from the s i l t . s o i l t h e r e was o n l y a small i n c r e a s e i n the NH^/NO^ r a t i o s between J u l y and August i n t h e loamy sand p l o t s w i t h i n h i b i t o r s . By the J u l y sampling date (63 d a y s ) , both i n h i b i t o r s had c o m p l e t e l y l o s t t h e i r e f f e c t i v e n e s s , and the l e v e l o f NH^ was l e s s than 10 ppm i n a l l p l o t s ( d a t a n o t shown). Thus, even though c r o p uptake lowered the NO^ c o n c e n t r a t i o n s c o n s i d e r a b l y , t h e NH^/NO^ r a t i o s i n c r e a s e d o n l y s l i g h t l y . - 69 -1978 F a l l o w Loamy Sand ( E x p e r i m e n t 4) S o i l R e s u l t s As i n the cropped loamy sand, the banded ATC t r e a t m e n t i n i t i a l l y had a much h i g h e r NH^/NOg r a t i o than the o t h e r t r e a t m e n t s ( F i g . 4.6).. The r a t i o s f o r a l l t r e a t m e n t s were 5-10 times h i g h e r than those i n the a d j a c e n t cropped e x p e r i m e n t . 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 i s the d i f f e r e n t band s p a c i n g i n the two e x p e r i m e n t s . Due t o space l i m i t a t i o n s , s m a l l e r p l o t s were used i n the f a l l o w e x p e r i m e n t , and more c o n c e n t r a t e d bands o f u r e a f e r t i l i z e r were a p p l i e d (22.2 g urea compared t o 16.7 g u r e a per m o f band). The r e s u l t s o f W e t s e l a a r e t al_. (1972) have shown t h a t n i t r i f i c a t i o n r a t e s can be reduced by i n c r e a s i n g t h e d i s t a n c e between bands w h i l e m a i n t a i n i n g equal r a t e s o f N a p p l i c a t i o n per ha ( i . e . , i n c r e a s i n g the l o c a l c o n c e n t r a t i o n o f f e r t i l i z e r N). Both b r o a d c a s t i n h i b i t o r t r e a t m e n t s had h i g h e r Nh^/NOg r a t i o s f o r the f i r s t 63 days than t h e b r o a d c a s t t r e a t m e n t w i t h o u t i n h i b i t o r , but the d i f f e r e n c e s were not s i g n i f i c a n t . Thus, b r o a d c a s t i n g the i n h i b i t o r t r e a t m e n t s was not an e f f e c t i v e means o f s l o w i n g n i t r i f i c a t i o n i n e i t h e r s o i l . T h i s agrees w i t h the f i n d i n g s o f B r i g g s (1975), who showed t h a t b r o a d c a s t N-Serve was r a p i d l y l o s t by v o l a t i l i z a t i o n , w h i l e i n c o r p o r a t i o n at 3 cm depth g r e a t l y r e t a r d e d i t s l o s s . The e x p l a n a t i o n f o r the poor response o f b r o a d c a s t ATC t r e a t m e n t s may be due t o i t s h i g h s o l u b i l i t y i n w a t e r . When the ATC p l u s u r e a i s b r o a d c a s t , each f e r t i l i z e r g r a n u l e i s exposed t o a much l a r g e r volume o f s o i l than when i t i s banded. Thus t h e r e would be a g r e a t e r d i l u t i o n o f the ATC by the s u r r o u n d i n g s o i l m o i s t u r e . In a d d i t i o n , b r o a d c a s t t r e a t m e n t s o f e i t h e r i n h i b i t o r would be more s u s c e p t i b l e t o b i o l o g i c a l d e g r a d a t i o n , s i n c e each g r a n u l e i s exposed t o a g r e a t e r number o f s o i l m i c r o o r g a n i s m s . N-Serve was more p e r s i s t e n t i n the f a l l o w f i e l d than i n t h e cropped z o £ 0. C L X E a. a. o 20 40 60 80 TIME FOLLOWING APPLICATION OF NITROGEN (days) F i g u r e 4.6. R a t i o o f ppm Nty-N/ppm NO3-N i n 0-15 cm depth o f 1978 f a l l o w loamy sand as a f f e c t e d by method o f N a p p l i c a t i o n , type o f n i t r i f i c a t i o n i n h i b i t o r , and time. - 71 -f i e l d . In the cropped f i e l d both N-Serve and ATC l o s t t h e i r e f f e c t i v e n e s s w i t h i n 63 days, whereas i n the f a l l o w f i e l d ATC became i n e f f e c t i v e a f t e r 63 days, but the a c t i v i t y o f N-Serve p e r s i s t e d f o r 90 days. T h i s f i n d i n g has not been p r e v i o u s l y r e p o r t e d i n t h e l i t e r a t u r e . I t i s p o s s i b l e t h a t t h e g r e a t e r m i c r o b i a l a c t i v i t y a s s o c i a t e d w i t h the r h i z o s p h e r e o f the corn r o o t s l e d to more r a p i d d e g r a d a t i o n o f N-Serve but had no e f f e c t on ATC. P r e v i o u s r e s e a r c h (Redemann e_t aj_., 1965) has shown t h a t N-Serve can be taken up by p l a n t r o o t s , but no s t u d i e s have been r e p o r t e d on p l a n t uptake o f ATC. No August i n c r e a s e i n the NH^/NO^ r a t i o s o f the banded ATC o r N-Serve p l o t s o c c u r r e d i n the f a l l o w f i e l d . T h i s s u g g e s t s t h a t p r e f e r e n t i a l c r o p removal o f NO^ was p r o b a b l y t h e p r i m a r y cause o f the i n c r e a s e d NH^/NO^ r a t i o s a t t h i s same time i n the cropped f i e l d s . Crop R e s u l t s In 1977 a t S i t e 1 t h e r e were no s i g n i f i c a n t d i f f e r e n c e s due t o N r a t e o r i n h i b i t o r f o r e i t h e r y i e l d o f dr y m a t t e r o r % t o t a l N i n the h a r v e s t e d c r o p dr the l e a v e s a t s i l k i n g ( T a b l e 4.3). T h i s was p r o b a b l y due t o the heavy a d d i t i o n o f manure d u r i n g the p r e v i o u s w i n t e r and the consequent h i g h r a t e o f o r g a n i c N m i n e r a l i z a t i o n . T o t a l m i n e r a l N i n the c o n t r o l p l o t s (0-15 cm) averaged 97 ppm on J u l y 13 and o n l y d e c r e a s e d to 65 ppm by September 6 (d a t a not shown). Thus, the r a t e o f N m i n e r a l i z a t i o n from the manure and s o i l o r g a n i c m a t t e r was s u f f i c i e n t f o r maximum y i e l d o f s i l a g e c o r n . A l t h o u g h no manure was added t o the s i l t p r i o r t o the 1978 se a s o n , r e s i d u a l N m i n e r a l i z a t i o n r a t e s were s t i l l too hig h to r e v e a l any s i g n i f i c a n t d i f f e r e n c e s due to t r e a t m e n t s f o r y i e l d o f dr y m a t t e r or % t o t a l N i n the crop Table 4.3. Yield of silage dry matter, % total N in harvest and silk leaves in Experiments 1, 2 and 3 as affected by rate of N, type of NI and place-ment of N. Experiment 1 (1977 silt) Experiment 2 (1978 si l t ) Experiment 3 (1978 1. sa.) Treatment Yield+ Total N cropt Total N leaf # Yield Total N crop Total N leaf Yield Total N crop Total 1 leaf t/ha OI t/ha OI t/ha OI lo lo 10 0 N Control 20.9 1.05 '2.82 18.8 1.04 2.82 12.7a # # 0.96 2.28a 50 N Ba + 18.1 1.17 2.76 18.4 1.06 2.71 15.3b 0.92 2.27a 50 N Ba + ATC 18.4 1.10 2.95 19.7 1.06 2.86 16.8b 1.01 2.42a 50 N Ba + N-S - - - 19.8 1.02 2.78 17.0b 1.00 2.41a 50 N Br 20.3 1.19 2.82 - - - - -50 N Br + ATC 18.3 1.18 2.71 - - - - - -100 N Ba 18.9 1.08 2.68 19.6 1.05 2.80 18.5c 1.15 2.88b 100 N Ba + ATC 17.9 1.26 2.92 20.7 1.08 2.88 17.5bc 1.03 2.87b 100 N Ba + N-S - - - 18.7 1.10 2.91 18.4c 1.17 3.01b 100 N Br 19.7 1.23 2.89 - - - - - -100 N Br + ATC 19.1 1.22 2.81 _ _ _ _ PO Data values represent average of 3 replicate plots. 'Ba represents banded plots, Br represents broadcast plots. + +Includes ears plus stover. # Leaves harvested at time of silking. Values in each column accompanied by the same letter or without a letter are not significantly different (P < 0.05). - 73 -o r s i l k l e a v e s . The EN i n the c o n t r o l p l o t s was lower than i n 1977 (maximum o f 36 ppm d u r i n g the season, data not shown), but s t i l l too high to show any y i e l d r e s p o n s e to added N. In the loamy sand t h e r e were s i g n i f i c a n t responses to r a t e o f N f o r y i e l d o f c o r n d r y m a t t e r and t o t a l % N i n the s i l k l e a v e s , but not f o r t o t a l % N i n the c r o p . There was s t i l l no s i g n i f i c a n t r e s p o n s e to i n h i b i t o r t r e a t -ment, but where 50 kg urea-N/ha was a p p l i e d , t h e r e was a 10% i n c r e a s e i n both y i e l d o f d r y m a t t e r and % N i n the c r o p when e i t h e r ATC or N-Serve were added w i t h the u r e a . T h i s s u g g e s t s t h a t the e f f i c i e n c y o f the urea f e r t i l i z e r was i n c r e a s e d s u f f i c i e n t l y to improve the y i e l d a t the lower r a t e o f N. A t t h e h i g h e r r a t e o f N, even though t h e r e were l a r g e s i g n i f i c a n t d i f f e r e n c e s i n the s o i l NH^ and NH^/NOg r a t i o s due to the i n h i b i t o r t r e a t m e n t s , t h e r e were o n l y s m a l l d i f f e r e n c e s i n the EN (0-30 cm) due to i n h i b i t o r t r e a t m e n t s (data not shown). A p p a r e n t l y , t h e r e was i n s u f f i c i e n t l e a c h i n g o r d e n i t r i f i c a t i o n o f NOg to lower the y i e l d s i n the n o n - i n h i b i t o r p l o t s . I f t h e r e had been more p r e c i p i t a t i o n , g r e a t e r l o s s o f NOg might have o c c u r r e d , and the p r e s e n c e o f the i n h i b i t o r s might have r e s u l t e d i n y i e l d i n c r e a s e s . The c o n c e n t r a t i o n o f NOg i n the ear l e a v e s a t s i l k i n g was not s i g n i f i c a n t l y a f f e c t e d by the i n h i b i t o r t r e a t m e n t s i n any o f the experiments (data not shown). C o n d i t i o n s were a p p a r e n t l y s u f f i c i e n t l y f a v o r a b l e f o r n i t r a t e r e d u c t a s e a c t i v i t y t h a t the h i g h e r l e v e l s o f NOg absorbed by the p l a n t s i n the n o n - i n h i b i t o r p l o t s were reduced to l e v e l s s i m i l a r t o those i n the i n h i b i t o r p l o t s . Dry m a t t e r y i e l d s i n a l l experiments were somewhat above those commonly - 74 o b t a i n e d by farmers i n t h i s a r e a (13-16 t / h a ) . The o n l y 0 N c o n t r o l t r e a t m e n t w i t h a lower y i e l d was t h a t i n the loamy sand (.1.2.7 t / h a ) . These y i e l d s r e f l e c t the high r a t e s o f o r g a n i c N m i n e r a l i z a t i o n i n t h e s e s o i l s and h e l p to e x p l a i n the l a c k o f response to the n i t r i f i c a t i o n i n h i b i t o r s . - 75 -CONCLUSIONS The NH^/NOg r a t i o appears to be a b e t t e r i n d i c a t o r o f n i t r i f i c a t i o n i n h i b i t o r e f f e c t i v e n e s s than NH^ c o n c e n t r a t i o n a l o n e o r t h e sum o f NH^ p l u s NOg, p a r t i c u l a r l y i n the e a r l i e r p a r t o f the growing season. T h i s r a t i o tended to i n c r e a s e i n the cropped p l o t s d u r i n g t h e p e r i o d o f maximum N uptake, but showed no i n c r e a s e i n the f a l l o w p l o t s d u r i n g t he same p e r i o d . Both ATC and N-Serve were e q u a l l y e f f e c t i v e n i t r i f i c a t i o n i n h i b i t o r s when banded i n the s i l t , but ATC was more e f f e c t i v e than N-Serve i n the cropped loamy sand, p r o b a b l y due t o more r a p i d v o l a t i l i z a t i o n o f N-Serve i n the c o a r s e - t e x t u r e d s o i l o r l e a c h i n g o f urea out o f the zone o f N-Serve a p p l i c a t i o n . N e i t h e r i n h i b i t o r was e f f e c t i v e when b r o a d c a s t . The e f f e c t i v e -ness o f both i n h i b i t o r s p e r s i s t e d l o n g e r i n the s i l t (86 days) than the loamy sand (63 d a y s ) . S i n c e ATC i s much e a s i e r to c o a t onto s o l i d f e r t i l i z e r s , i t appears t h a t t h i s i n h i b i t o r i s a good c a n d i d a t e f o r f u r t h e r f i e l d e v a l u a t i o n i n c o n j u n c t i o n w i t h b a n d - a p p l i e d s o l i d f e r t i l i z e r s . There was no s i g n i f i c a n t improvement i n crop y i e l d o r N c o n t e n t due to i n h i b i t o r t r e a t m e n t i n e i t h e r s o i l . T h i s was a p p a r e n t l y due t o c o n d i t i o n s which f a v o r e d h i g h m i n e r a l i z a t i o n r a t e s o f s o i l o r g a n i c N as w e l l as l i t t l e l o s s o f NOg from t h e s o i l . Some improvement i n crop y i e l d might have been seen i f t h e s o i l had a lower o r g a n i c N c o n t e n t o r i f c o n d i t i o n s had been more f a v o r a b l e f o r l e a c h i n g and d e n i t r i f i c a t i o n l o s s e s o f NO,,. - 76 -LITERATURE CITED 1. B a r - Y o s e f , B. and V. K a f k a f i . 1972. Rates o f growth and n u t r i e n t uptake o f i r r i g a t e d c o r n as a f f e c t e d by n i t r o g e n and phosphorus f e r t i l i z a t i o n . S o i l S c i . Soc. Am. P r o c . 36 : 9 3 1 - 9 3 6 . 2. B l a c k , C A . (ed.) 1965. Methods o f S o i l A n a l y s i s , P a r t 2 . 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N i e l s o n and J.G. MacDonald ( e d . ) . N i t r o g e n i n the environment. Volume 2 , pp. 4 5 - 8 8 . Academic P r e s s , New York. 12V. M c E l r o y , M.B., S.C. Wofsy and Y.L. Yung. 1977. The n i t r o g e n c y c l e : p e r t u r b a t i o n s due t o man and t h e i r impact on a t m o s p h e r i c n i t r o u s o x i d e and ozone. P h i l o s o p h i c a l T r a n s a c t i o n s o f the Royal S o c i e t y o f London, B. 277: 1 5 9 - 1 8 1 . - 77 -13. M i l l e r , R.D. and D.D. Johnson. 1964. The e f f e c t o f s o i l m o i s t u r e t e n s i o n on CO2 e v o l u t i o n , n i t r i f i c a t i o n and N m i n e r a l i z a t i o n . S o i l S c i . Soc. Am. P r o c . 28: 644-647. 14. M i l l s , H a r r y A., A.V. B a r k e r and D.N. Maynard. 1976. N i t r a t e a c c u -m u l a t i o n i n r a d i s h as a f f e c t e d by n i t r a p y r i n . Agron. J . 68: 13-17. 15. Redemann, C.T., R.T. M a r t i n , J.D. Wien and J.G. Widofsky. 1965. T r a c e r s t u d i e s o f r e s i d u e s from 2 - c h l o r o - 6 - ( t r i c h l o r o m e t h y l ) -p y r i d i n e i n p l a n t s . J . A g r i c . Food Chem. 13: 518-521. 16. Reichman, G.A., D.L. Grunes and F.G. V i e t s , J r . 1966. E f f e c t o f s o i l m o i s t u r e on 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 i n two n o r t h e r n p l a i n s s o i l s . S o i l S c i . Soc. Am. P r o c . 30: 363-366. 17. Terman, G.L. and J.C. Noggle. 1973. N u t r i e n t c o n c e n t r a t i o n changes i n c o r n as a f f e c t e d by d r y matter a c c u m u l a t i o n w i t h age and response t o a p p l i e d n u t r i e n t s . Agron. J . 65: 941-945. 18. Touchton, J.T., R.G. H o e f t and L.F. Welch. 1978. N i t r a p y r i n d e g r a d a t i o n and movement i n s o i l . Agron. J . 70: 811-816. 19. T u r n e r , M.A. and A.N. Macgregor. 1978. An e v a l u a t i o n o f " T e r r a z o l e " as a n i t r i f i c i d e f o r i m p r o v i n g the e f f i c i e n c y o f use o f n i t r o g e n o u s f e r t i l i z e r s on p a s t u r e . N.Z.J. A g r i c . Res. 21: 39-45. 20. Warren, H.L., Huber, D.M., N e l s o n , D.W. and Mann, D.W. 1975. S t a l k r o t i n c i d e n c e and y i e l d o f c o r n as a f f e c t e d by i n h i b i t i n g n i t r i f i c a t i o n o f f a l l - a p p l i e d ammonium. Agron. J . 67: 655-660. 21. W e t s e l a a r , R., J.B. P a s s i o u r a and B.R. S i n g h . 1972. Consequences o f banding n i t r o g e n f e r t i l i z e r s i n s o i l . P l a n t S o i l 36: 159-175. - 78 -C h a p t e r F i v e SUMMARY AND CONCLUSIONS The aim o f t h i s t h e s i s was t o determine i f the n i t r i f i c a t i o n i n h i -b i t o r s N-Serve and ATC c o u l d i n c r e a s e the e f f i c i e n c y o f urea f e r t i l i z e r so t h a t f a r m e r s might use lower N a p p l i c a t i o n r a t e s , t h e r e b y s a v i n g money, energy, and d e c r e a s i n g the p o t e n t i a l n e g a t i v e impacts o n i t h e a q u a t i c and at m o s p h e r i c e n v i r o n m e n t . In C h a p t e r Two, an ex p e r i m e n t was d e s c r i b e d where urea was a p p l i e d to a s i l t loam near Vancouver, B.C. i n the f a l l as a band o r b r o a d c a s t t r e a t m e n t w i t h o r w i t h o u t ATC n i t r i f i c a t i o n i n h i b i t o r . When the urea was b r o a d c a s t , e i t h e r w i t h o r w i t h o u t ATC, n i t r i f i c a t i o n p roceeded s t e a d i l y from November u n t i l A p r i l d e s p i t e n e a r - f r e e z i n g s o i l t e m p e r a t u r e s . T h i s f i n d i n g s u g g e s t s t h a t o t h e r forms o f N, i n c l u d i n g manure-N, may a l s o n i t r i f y i f b r o a d c a s t i n the f a l l under s i m i l a r c l i m a t i c c o n d i t i o n s . Any n i t r a t e which forms would be h i g h l y s u s c e p t i b l e t o l o s s i n the s p r i n g v i a l e a c h i n g o r d e n i t r i f i c a t i o n due t o the heavy p r e c i p i t a t i o n which nor-m a l l y o c c u r s . The banded a p p l i c a t i o n s o f urea r e s u l t e d i n v e r y l i t t l e n i t r i f i c a -t i o n u n t i l March, p r o b a b l y due t o NH^ + t o x i c i t y as w e l l as o s m o t i c i n -h i b i t i o n o f t h e n i t r i f i e r s caused by the h i g h s a l t c o n c e n t r a t i o n i n the band. T h i s s u g g e s t s t h a t banding ammoniacal f e r t i l i z e r s may be one way o f d e c r e a s i n g N l o s s e s from f a l l a p p l i c a t i o n s . ATC had no e f f e c t on n i t r i f i c a t i o n When b r o a d c a s t w i t h u r e a , b u t t h e r e was some i n h i b i t i o n when i t was banded, as i n d i c a t e d by h i g h e r - 79 -N H 4 + ' l e v e l s i n the s p r i n g . L e a c h i n g o f the w a t e r - s o l u b l e ATC was the p r o b a b l e cause o f i t s poor e f f e c t i v e n e s s . L e a c h i n g o f urea was a l s o found t o o c c u r , as e v i d e n c e d by i n c r e a s e d NH^ + l e v e l s a t the 30-60 cm d e p t h , p a r t i c u l a r l y w i t h the banded t r e a t m e n t s . In C h a p t e r T h r e e , a l a b o r a t o r y study was d e s c r i b e d where ATC and N-Serve were a p p l i e d a t two d i f f e r e n t r a t e s w i t h u r e a t o a s i l t and i n c u b a t e d a t 2 and 12°C. The purpose o f t h i s e x p e r iment was t o determine i f e i t h e r o f t h e s e NI have any e f f e c t on the h y d r o l y s i s r a t e o f u r e a , as w e l l as t o examine the e f f e c t o f s o i l temperature on the r a t e o f urea h y d r o l y s i s . The r e s u l t s i n d i c a t e d t h a t n e i t h e r NI had any e f f e c t on h y d r o l y s i s , but low temperatures g r e a t l y d e l a y e d the r a t e . T h i s s u g g e s t s t h a t i f urea i s a p p l i e d t o a c o l d s o i l (<12°C) a p o t e n t i a l f o r l e a c h i n g l o s s o f N e x i s t s s h o u l d a heavy r a i n f a l l o c c u r , as was o b s e r v e d i n the w i n t e r n i t r i f i c a t i o n s tudy ( C h a p t e r Two). In C h a p t e r Four, a s e r i e s o f summer exp e r i m e n t s w i t h s i l a g e c o r n (Zea mays L.) were d e s c r i b e d where urea was a p p l i e d w i t h o r w i t h o u t ATC o r N-Serve as a band o r b r o a d c a s t t r e a t m e n t on two s o i l s , a s i l t and a loamy sand. The i n h i b i t o r s were much more e f f e c t i v e when banded than when b r o a d c a s t . 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 i s t h a t when the i n h i b i t o r s were banded they were exposed t o a s m a l l e r number o f s o i l m i c r o o r g a n i s m s , and thus b i o l o g i c a l d e g r a d a t i o n , would have taken p l a c e more s l o w l y . C o n t r a r y t o e x p e c t a t i o n s , both i n h i b i t o r s were more e f f e c t i v e i n the s i l t than the loamy sand. The c o a r s e r t e x t u r e o f the loamy sand :. - 80 -a p p a r e n t l y r e s u l t e d i n g r e a t e r v o l a t i l i z a t i o n o f the N-Serve and a l l o w e d more e x t e n s i v e l e a c h i n g and d i f f u s i o n o f the ATC. The h i g h e r o r g a n i c m a t t e r c o n t e n t o f the s i l t may have r e s u l t e d i n s t r o n g e r a d s o r p t i o n o f the o r g a n i c i n h i b i t o r s , which would have p r o l o n g e d t h e i r e f f e c t i v e n e s s . In comparing the two i n h i b i t o r s , ATC was s l i g h t l y more e f f e c t i v e than N-Serve i n the s i l t s o i l , but i n the loamy sand ATC was much more e f f e c t i v e . The e f f e c t i v e n e s s o f N-Serve was o f much s h o r t e r d u r a t i o n than ATC i n the loamy sand, undoubtedly due t o i t s v o l a t i l i z a t i o n from the c o a r s e - t e x t u r e d s o i l . A l t h o u g h the s o i l a n a l y s e s i n d i c a t e d t h a t the i n h i b i t o r s were e f f e c -t i v e i n d e l a y i n g n i t r i f i c a t i o n , p a r t i c u l a r l y i n the s i l t , the c r o p data 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 due t o e i t h e r NI. Manure a p p l i c a t i o n s which o c c u r r e d p r i o r t o i n i t i a t i o n o f t h e e x p e r i m e n t s on the s i l t r e s u l t e d i n h i g h r a t e s o f o r g a n i c N m i n e r a l i z a t i o n . Because o f t h i s t h e r e was no p o s s i b i l i t y o f o b t a i n i n g growth response from N f e r t i l i z e r o r NI, s i n c e even the u n f e r t i l i z e d p l o t s had h i g h y i e l d s . In the loamy sand t h e r e was a s i g n i f i c a n t r e sponse t o N, but s t i l l no r esponse t o NI. T h i s was p a r t l y because the NI were l e s s e f f e c t i v e i n t h i s s o i l . A more im p o r t a n t f a c t o r which was p r o b a b l y p a r t l y r e s p o n s i b l e f o r l a c k o f c r o p r e s p o n s e to NI i n both s o i l s was the r e l a t i v e l y dry weather which p r e v a i l e d d u r i n g both summers o f the s t u d y . H i g h e r r a i n f a l l would have caused g r e a t e r l o s s o f NOg" by l e a c h i n g and d e n i t r i f i c a t i o n which would have i n c r e a s e d the p o s s i b i l i t y o f a y i e l d r e sponse t o NI. - 81 -A l t h o u g h c r o p y i e l d s were not a f f e c t e d , ATC and N-Serve d i d d e l a y n i t r i f i c a t i o n f o r more than 60 days i n the loamy sand and more than 80 days i n the s i l t . Thus, ,use o f NI does have the p o t e n t i a l f o r i n c r e a s -i n g t he e f f i c i e n c y o f N f e r t i l i z e r . As the c o s t o f N f e r t i l i z e r con-t i n u e s t o r i s e , the use o f NI w i l l become more e c o n o m i c a l l y v i a b l e . I f the c o s t o f urea-N i s assumed t o be 60<£/kg, then 100 kg N/ha would c o s t $60/ha. The c u r r e n t p r i c e o f N-Serve i s $21/kg o f a c t i v e i n g r e d i e n t . By u s i n g N-Serve i t may be p o s s i b l e t o o b t a i n an optimum c r o p y i e l d by u s i n g o n l y 50 kg. N/ha ($30) and 0.5 kg/ha N-Serve ($10.50) f o r a t o t a l N f e r t i l i z e r c o s t o f $40.50 per ha, o r a s a v i n g s o f almost $20/ha. The c o s t o f ATC i s not a v a i l a b l e a t t h i s t i m e , but i t i s e x p e c t e d t o be some-what lower than N-Serve a c c o r d i n g t o the m a n u f a c t u r e r . F u r t h e r s t u d i e s i n v o l v i n g ATC and N-Serve remain t o be done. O p t i m i z a t i o n o f the r a t e o f NI a p p l i c a t i o n s f o r d i f f e r e n t s o i l s would r e q u i r e d e t e r m i n i n g the e f f e c t o f a d d i n g v a r i o u s r a t e s o f N-Serve and ATC t o s o i l s . A l s o , o t h e r reduced forms o f N f e r t i l i z e r such as anhydrous ammonia and ammonium s u l p h a t e c o u l d be combined w i t h ATC o r N-Serve. I t would a l s o be o f c o n s i d e r a b l e i n t e r e s t t o compare the e f f i c i e n c y o f s u l f u r - c o a t e d urea w i t h t h a t o f urea c o a t e d w i t h i n h i b i t o r s . F i n a l l y , the e f f e c t o f v a r y i n g the w i d t h o f band s p a c i n g o f ammoniacal f e r t i l i z e r s on n i t r i f i c a t i o n r a t e s s h o u l d be examined as an a l t e r n a t e means o f i m p r o v i n g N f e r t i l i z e r e f f i c i e n c y . - 82 -Appendix 1.1 F i e l d d e s c r i p t i o n o f s i l t s o i l used i n s t u d y S o i l C l a s s i f i c a t i o n : Rego Humic G l e y s o l , Can. ( T y p i c F l u v a q u e n t , U.S.) L o c a t i o n : 600 m W o f King George Highway, 300'm N o f Nicomekl R i v e r i n S u r r e y , B.C. K i t z e l farm a t 13975 40th Avenue. HORIZON r a n DEPTH (U.S.) U n - (cm) DESCRIPTION (Ap) Ap (Ah) Ah ( C l g ) 0-20 20-35 Cgl 35-70 (C2g) Cg2 70+ Dark brown (10 YR 4/2.5, m); s i l t ; weak, medium g r a n u l a r ; v e r y f r i a b l e ; many f i n e and medium r o o t s ; d i f f u s e , wavy boundary t o : Brown (10 YR 4/3, m); s i l t ; weak, medium s u b a n g u l a r b l o c k y ; f r i a b l e ; many f i n e r o o t s ; a b r u p t , wavy boundary t o : G rayish-brown (2.5 Y 5/2, m); s i l t loam; common, c o a r s e , d i s t i n c t pale, y e l l o w m o t t l e s (5 Y 7/4, m) i n the form o f s l i g h t l y hard tubes around o l d r o o t c h a n n e l s ; moderate, c o a r s e , s u b a n g u l a r b l o c k y ; f i r m ; many r o o t s i n upper p a r t t h i n n i n g t o few i n lower p a r t ; d i f f u s e wavy boundary t o : Dark gray (10 YR 4/1, m); s i l t loam; many c o a r s e , prominent p a l e y e l l o w m o t t l e s (5 Y 7/4, m) i n the form o f s l i g h t l y hard tubes around o l d r o o t c h a n n e l s ; moderate, c o a r s e , s u b a n g u l a r blocky; f i r m ; o c c a s i o n a l f i n e r o o t s i n upper p a r t ; lower boundary undetermined. - 83 -Appendix 1.2 F i e l d d e s c r i p t i o n o f loamy sand s o i l used i n study S o i l C l a s s i f i c a t i o n : Humic P o d z o l , Can. ( T y p i c Haplohumod, U.S.) L o c a t i o n : U n i v e r s i t y o f B r i t i s h Columbia, 110 m N o f M e t e o r o l o g i c a l S t a t i o n , 30 m W from road HORIZON r. DEPTH n r c r D T D T T m , (U.S.) C a n ' (cm) • DESCRIPTION (Ap) A p 0-40 (E) 40-48 ( B h ) B H • 48-60 ( B h l > ) B f 60-80 (II- C l g ) II C g l 80-100 Very dark g r a y i s h brown (10 YR 3/2, m); loamy sand; s i n g l e g r a i n ; l o o s e ; v e r y f r i a b l e ; abundant f i n e r o o t s ; some t h i n l e n s e s o f decayed wood and bark a t the a b r u p t wavy boundary t o : Dark g r a y i s h brown (10 YR 3.5/2, m); loamy sand; g r a n u l a r ; f r i a b l e ; few f i n e r o o t s ; a b r u p t wavy boundary t o : Dark brown (7.5 YR 3/1, m); loamy sand; weak medium s u b a n g u l a r b l o c k y b r e a k i n g t o f i n e t o medium g r a n u l a r ; f i r m t o f r i a b l e ; r o o t s a b s e n t ; some l e n s e s o f s t r o n g brown (7.5 YR 5/6 m); g r a d u a l wavy boundary t o : Dark y e l l o w i s h brown (10 YR 4/6, m); sand; a n g u l a r b l o c k y b r e a k i n g t o s i n g l e g r a i n ; f i r m ; r o o t s a b s e n t ; a b r u p t wavy boundary t o : G r a y i s h brown m a t r i x (2.5 Y 5/3, m); loam; w i t h many d i s t i n c t medium y e l l o w i s h r e d (5 YR 5/8, m); m o t t l e s ; s t r o n g c o a r s e p l a t y b r e a k i n g t o medium a n g u l a r b l o c k y ; f i r m ; r o o t s a b s e n t ; d i f f u s e boundary t o : - 84 -HORIZON r DEPTH (U.S.) C a n- (cm) DESCRIPTION ( I I C 2 g ) I I * C 2 100-110 + ' G r a y i s h brown m a t r i x (2.5 Y 5/1, m); s i l t loam, w i t h many d i s t i n c t c o a r s e y e l l o w i s h r e d m o t t l e s (5 YR 5/8, m); s t r o n g c o a r s e p l a t y b r e a k i n g t o medium a n g u l a r b l o c k y f i r m ; r o o t s a b s e n t ; lower boundary undetermined. Appendix 2.1. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1977 s i l t (Experiment 1) on v a r i o u s sampling dates as a f f e c t e d by r a t e o f urea-N, pr e s e n c e o f ATC n i t r i f i c a t i o n i n h i b i t o r ( N I ) , and method o f a p p l i c a t i o n . Sampling date (days from N appli c a t i o n ) Rate Appl. of NI Method 27 May (-18) 30 June (16) 13 J u l y (29) 27 J u l y (43) 10 Aug. (57) 6 Sept. (84) N NH4-N N03-N NH4-N N03-N NH4-N N03-N NH4-N N03-N NH4-N N03-N NH4-N Kg/na P9 N/g dry soi1 0 to 15 cm 0 None - 8 76 16 76 10 87 3 45 5 26 5 60 50 None BA 10 46 213 123 71 185 24 120 41 75 9 84 50 ATC BA 7 70 • 225 73 175 109 39 58 34 31 41 57 100 None BA 8 55 506 23 154 255 59 172 54 107 16 160 100 ATC BA 8 40 536 63 370 88 201 51 275 31 167 54 50 None BR 8 57 18 73 19 108 5 57 6 24 5 71 50 ATC BR 7 65 35 69 17 106 83 42 13 24 15 45 100 None BR 7 73 17 95 14 124 10 88 16 33 16 104 100 ATC BR 7 103 61 90 33 138 10 75 13 42 16 71 15 to 30 cm 0 None - 4 36 4 31 11 27 5 23 5 13 6 15 50 None BA 4 39 19 37 14 26 24 52 5 8 7 19 50 ATC BA 3 35 8 28 16 24 39 40 6 10 10 24 100 None BA 10 26 14 19 15 18 87 117 31 21 11 31 100 ATC BA 3 39 14 26 16 16 124 58 82 24 42 24 50 None BR 3 44 6 37 13 23 7 28 6 13 6 21 50 ATC BR 4 . 37 7 26 15 20 9 20 4 9 7 15 100 None BR 4 54 6 34 11 28 11 29 5 8 11 21 100 ATC BR 5 79 5 36 16 47 15 23 5 6 13 22 * N i t r i f i c a t i o n i n h i b i t o r r a t e s were 1% o f N a p p l i e d as a c t i v e c h e m i c a l i n g r e d i e n t . ** B r o a d c a s t treatments i n d i c a t e d by BR, banded treatments by BA. Bands were spaced 85 cm a p a r t . V a l u e s r e p r e s e n t averages o f t h r e e r e p l i c a t e p l o t s , rounded to n e a r e s t i n t e g e r . Appendix 2.2. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1978 s i l t ( E x periment 2) on v a r i o u s sampling d a t e s , as a f f e c t e d by r a t e o f urea-N, p r e s e n c e and type o f n i t r i f i c a t i o n i n h i b i t o r ( N I ) . Rate Sampling date (days from N appli c a t i o n ) of NI* 12 June (0) 4 July (22) 25 July (43) 15 Aug. (64) 6 Sept. (86) N 0 None 7 26 4 21 100 None 5 26 6 34 100 ATC 8 21 9 36 100 N-Serve 6 24 7 33 50 None 7 26 4 28 50 ATC 7 27 7 22 50 N-Serve 6 22 7 24 30 to 60 cm 0 None 6 21 4 31 100 None 5 24 51 76 100 ATC 8 26 76 42 100 N-Serve 5 29 32 29 50 None 6 19 30 67 50 ATC 4 21 61 47 50 N-Serve 2 23 40 40 NH4-N N03-N NH4-N NOj-N NH4~N N03-N NH4-N NOj-N NH4-N N03-N kg/ha ug N/g dry s o i l * 0 to 15 cm 0 None 4 44 5 23 3 28 4 32 4 29 100 None 3 44 92 163 22 105 38 109 28 83 100 ATC 3 46 163 135 71 64 98 55 69 53 100 N-Serve 7 49 107 104 35 56 65 45 24 61 50 None 4 35 72 140 15 56 28 75 5 66 50 ATC 3 42 151 178 5 21 29 54 13 43 50 N-Serve 3 42 140 111 33 37 34 42 24 30 15 to 30 cm 2 9 2 7 4 8 2 15 8 31 4 25 4 15 7 11 6 13 3 17 6 14 5 21 5 17 6 7 5 12 2 5 6 8 4 17 6 11 6 9 4 12 4 31 6 15 2 13 5 52 33 38 5 18 42 39 25 21 5 12 21 38 31 24 5 15 36 67 16 24 3 12 16 39 19 22 3 16 24 39 17 28 8 14 * N i t r i f i c a t i o n i n h i b i t o r r a t e s were 1% o f N a p p l i e d as a c t i v e c h e m i c a l i n g r e d i e n t . A l l N and NI a p p l i c a t i o n s were banded w i t h 85 cm s p a c i n g . V a l u e s r e p r e s e n t averages o f t h r e e r e p l i c a t e p l o t s , rounded to n e a r e s t i n t e g e r . Appendix 2.3. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1978 cropped loamy sand (Experiment 3) on v a r i o u s sampling dates as a f f e c t e d by r a t e o f urea-N, p r e s e n c e and type o f n i t r i f i c a t i o n i n h i b i t o r ( N I ) , and method o f a p p l i c a t i o n . Sampling date (days from N appli c a t i o n ) Rate of N NI Appl.** Method 9 May (0) NH4-N NO3-N 1 June (23) 16 June (38) 11 Ju l y (63) 7 Aug. (90) 29 Aug. (112) NH4-N NO3-N NH4-N NO3-N NH4-N NO3-N NH4-N NO3-N NH4~N NO3-N kg/ha 0 to 15 cm . yg N/g dry s o i l + 0 None - 4 12 5 13 2 14 50 None BA 4 9 5 80 2 45 50 ATC BA 4 13 11 72 3 104 50 N-Serve BA 5 10 10 61 4 76 100 None BA 4 13 5 158 3 68 100 ATC BA 4 14 139 101 106 179 100 N-Serve BA 4 12 29 98 26 143 100 N-Serve BR 5 13 9 40 3 49 100 None BR 4 11 5 64 2 81 15 to 30 cm 0 None - 6 6 3 10 7 11 50 None BA 7 6 3 19 9 12 50 ATC BA 8 6 3 24 8 24 50 N-Serve BA 6 7 4 22 11 18 100 None BA 6 7 3 54 11 42 100 ATC BA 5 6 3 34 6 40 100 N-Serve BA 7 7 27 69 7 71 100 N-Serve BR 7 6 2 9 9 8 100 None BR 6 9 3 19 6 20 11 55 36 38 62 50 89 44 46 6 6 8 5 13 12 30 6 13 1 2 5 12 2 2 1 2 2 4 8 4 4 11 25 27 13 11 3 3 3 3 3 3 3 3 3 3 3 4 3 4 11 9 4 7 * N i t r i f i c a t i o n i n h i b i t o r r a t e s were 1% o f N a p p l i e d as a c t i v e c h e m i c a l i n g r e d i e n t . ** B r o a d c a s t treatments i n d i c a t e d by BR, banded tre a t m e n t s by BA. Bands were spaced 75 cm a p a r t . + V a l u e s r e p r e s e n t averages o f t h r e e r e p l i c a t e p l o t s , rounded to n e a r e s t i n t e g e r . Appendix 2.4. Ammonium-N and n i t r a t e - N c o n c e n t r a t i o n s i n 1978 f a l l o w loamy sand (Experiment 4) on v a r i o u s sampling dates as a f f e c t e d by prese n c e and type o f n i t r i f i c a t i o n i n h i b i t o r (NI) and method o f a p p l i c a t i o n . / Rate of N kg/ha NI' Appl. Method Sampling date (days from N ap p l i c a t i o n ) 9 May (0) 0 to 15 cm 1 J u " e (23) 16 June (38) 11 J u l y (63) 7 Aug. (90) 29 Aug. (112) NH4-N N0 3-N NH4-N NO3-N NH4-N NO3-N NH4-N NO3-N NH4~N NO3-N NH4~N NO3-N 0 None _ 6 12 3 8 100 None BA 5 15 40 125 100 ATC BA 6 18 385 57 100 N-Serve BA 6 14 137 106 100 None BR 6 15 3 47 100 ATC BR 6 14 39 52 100 N-Serve 15 to 30 cm BR 8, 15 21 45 0 None _ 6 5 2 12 100 None BA 6 8 2 34 100 ATC BA 5 6 7 39 100 N-Serve BA 5 6 6 39 100 None BR 5 5 2 18 100 ATC BR 6 4 2 14 100 N-Serve BR 5 6 2 16 yg N/g dry s o i l + 2 41 166 183 2 8 9 11 246 169 161 40 56 48 9 93 29 53 9 9 7 4 8 55 130 3 11 10 24 154 206 134 48 83 60 9 41 36 42 11 12 11 2 2 6 15 2 2 2 27 98 135 97 43 37 43 16 37 43 37 9 21 15 3 4 9 18 4 4 3 18 36 99 38 20 33 23 20 48 54 38 34 42 29 * N i t r i f i c a t i o n i n h i b i t o r r a t e s were 1% o f N a p p l i e d as a c t i v e c h e m i c a l i n g r e d i e n t . ** B r o a d c a s t treatments i n d i c a t e d by BR, banded tre a t m e n t s by BA. Bands were spaced 100 cm a p a r t . + V a l u e s r e p r e s e n t averages o f t h r e e r e p l i c a t e p l o t s , rounded to n e a r e s t i n t e g e r . Appendix 3. Selected physical and chemical properties of soils used in thesis research, 1977-1978. Depth cm 0-15 15-30 30-60 60-90 0-15 15-30 Sand I S i l t % 85 N.D. N.D. 76 N.D. 88 N.D. N.D. 18 N.D. Bulk Dens. kg/m Par t . Dens. 3 840 960 1100 1200 1160 N.D. 2390 2450 2650 N.D. 2450 2630 -10 kPa 59.9 60.8 N.D. N.D. 42.0 33.5 -33 kPa % H 20 53.1 54.3 N.D. N.D. 31.2 24.3 -1500 kPa 24.1 26.3 N.D. N.D. 13.1 10.9 Exch. Na Exch. K 0.22 0.28 0.42 0.64 0.08 0.09 Exch. Ca me/100 g Exch. Mg CEC, pH7 0.97 0.80 0.33 0.28 0.68 0.56 10.3 8.3 2.5 1.2 8.5 6.7 1.83 1.61 1.23 0.98 0.78 0.66 39.1 36.-1 23.4 15.4 23.9 22.9 Total C 6.8 5.8 2.9 2.0 4.5 4.3 Total N 0.60 0.48 0.20 0.15 0.27 0.26 

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