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Influence of paper mulch on a clay soil Reid, Edgar Cameron 1940

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INFLUENCE OF PAPER MULCH ON A CLAY SOIL by EDGAR CAMERON REID  A Thesis submitted f o r the Degree of MASTER  0 -F. S C I E N C E in AGRICULTURE  IN 'THE DEPARTMENT OF AGRONOMY FACULTY OF AGRICULTURE  The U n i v e r s i t y of B r i t i s h Columbia 1940  ACKNOWLEDGMENTS-.  The w r i t e r wishes t o thank Mr. 1. M. S t r a i g h t , Superintendent, Experimental S t a t i o n , Saanichton, B. C., f o r e n t h u s i a s t i c co-operation at a l l times while t h i s i n v e s t i g a t i o n was i n progress; Dr. D. G. L a i r d , P r o f e s s o r of Agronomy f o r many h e l p f u l suggestions i n planning the experiments and i n the preparation and arrangement of t h i s t h e s i s ; Dr. A. G. Loohhead, ' Dominion A g r i c u l t u r a l B a c t e r i o l o g i s t , Ottawa, and also the Imperial Bureau of S o i l Science f o r the transl a t i o n of c e r t a i n German, I t a l i a n and Russian a r t i c l e s , and the w r i t e r p a r t i c u l a r l y wishes t o thank a l l h i s friends f o r t h e i r f a i t h and encouragement, without which t h i s t h e s i s might never have been completed.  TABLE OF CONTENTS  INTRODUCTION REVIEW OF LITERATURE EXPERIMENTAL CHARACTER OF CANTALOUPE •: PROCEDURE S o i l and C l i m a t i c Conditions S o i l Sampling and P l a t i n g BIOLOGICAL STUDIES T o t a l P l a t e Counts Azotobacter Tests D i r e c t Influence of Mulch Paper on Bacterial Activity Carbon Dioxide Production CHEMICAL STUDIES PHYSICAL STUDIES S o i l Temperature Temperature as Influenced by Colour of Paper S o i l Moisture INFLUENCE OF PAPER MULCH ON PLANT GROWTH 1  DISCUSSION CONCLUSIONS BIBLIOGRAPHY  INFLUENCE OF PAPER MULCH ON A CLAY SOIL INTRODUCTION The f i r s t extensive use of paper as a s o i l covering was made i n 1914 by 0 . F. Eokart, of the Olaa Sugar Company i n Hawaii who not only observed that paper mulch helped to control weeds, but also that the crop plants grew more v i g o r o u s l y on the mulched than on the unmulched area. The Hawaiian Pineapple Company made t r i a l p l a n t ings with mulch paper i l l 191? and so e f f e c t i v e d i d the paper prove i n c o n t r o l l i n g weeds and s t i m u l a t i n g crop growth, that by 1931 i t was used on approximately 80 per cent of the pineapple plantings i n Hawaii. From Hawaii the use of mulch paper spread to many countries and i s now being employed on a v a r i e t y of crops under varying c l i m a t i c conditions. With few exceptions, the r e s u l t s from numerous world sources i n d i c a t e increased crop y i e l d s of higher c u a l i t y and e a r l i e r maturity f o l l o w ing the use of mulch paper. Since 1926 paper mulch has been used i n a l i m i t e d way on the more important vegetable crops at the Dominion Experimental S t a t i o n at Saanichton, B r i t i s h Columbia, (24) , and while most crops, p a r t i c u l a r l y the heat l o v i n g ones,have given increased y i e l d s of higher q u a l i t y , the use of mulch paper i s as a rule only j u s t i f i a b l e w i t h s p e c i a l i z e d crops such f o r instance as the cantaloupe. Many research workers have concerned themselves with the e f f e c t s of paper mulch and while not i n e n t i r e agreement, t h e i r general conclusions appear to be that the paper conserves moisture, r a i s e s s o i l temperature and increases the r e t e n t i o n or e l a b o r a t i o n of a v a i l a b l e nitrogen. In view of the importance of paper mulch i n the production of cantaloupes at Saanichton, a study of the b a c t e r i o l o g i c a l , chemical and p h y s i o a l changes o c c u r r i n g i n a mulched s o i l was undertaken i n an e f f o r t to determine the s p e c i f i c f a c t o r or f a c t o r s or combination of same responsible f o r the b e n e f i c i a l e f f e c t s noted. REVIEW OF LITERATURE The e f f e c t of muloh paper on s o i l temperature has been i n v e s t i g a t e d by many workers, the m a j o r i t y of whom  report an increase f o l l o w i n g i t s use. F e r r e t t i , ( 3 ) , i n I t a l y j found, that a paper covering insured higher s o i l temperatures during the e a r l y part of the season, but exerted l i t t l e or no e f f e c t during the summer months. Hartung, (9) , conducting extensive t e s t s f o r the Hawaiian Pineapple Company, found that mulch paper increased the s o i l temperature from 3 to 4 . 3 ° F. over that of the non-papered s o i l . This increase i n temperature was noted i n the top 3 inches of s o i l and the differences were more apparent when the paper was black i n colour. Macoun, ( 1 3 ) , of Ottawa, concluded that paper mulch tended to r a i s e s o i l temperatures, and t h i s he offered as an explanation f o r the observed i n crease i n s i z e of vegetable plants when grown on mulched areas. Magistad, Farden and Baldwin (14) i n Hawaii found that mulch paper stimulated growth by reducing s o i l temperature f l u c t u a t i o n s . Hagruder (15) i n Ohio, a f t e r conducting mulch paper tests with vegetables, concluded that s o i l temperature might be the most Important s i n g l e f a c t o r i n increasing the y i e l d of e a r l y maturing crops. Smith (19) i n C a l i f o r n i a , found that the greater the proportion of the surface covered by paper, the more p o s i t i v e was the e f f e o t on s o i l moisture, s o i l temperature and crop y i e l d . He also found that black papers r a i s e d the s o i l temperatures, whereas grey papers reduced them. I n Hawaii, Stewart, Thomas and Horner (23) recorded temperature d i f f e r e n c e s at a 4-inch depth as great.as 12 to 1 3 ° F. i n the afternoon and 3 degrees during the night i n favour of the mulched areas. Musso ( 1 7 ) , working i n the v i c i n i t y of Leningrad, used d i f f e r e n t coloured papers to b r i n g about what he termed d e s i r a b l e t e m p e r a t u r e changes f o r s p e c i f i c crops. Contrary to the f i n d i n g s of most workers, he found that f o r best growth, plants should be subjected to varying temperature changes and concluded that i t would be advantageous to have a mulch paper that would r e t a r d the warming of the s o i l to midday, but which would encourage warmth from t h i s time on. Musso contended that a paper mulch acts as a medium of i s o l a t i o n between s o i l and a i r temperatures, thus bringing about a marked temperature d i f f e r e n c e , which he concluded to be b e n e f i c i a l to plant growth. A f t e r f o u r seasons' work at Rosslyn, V i r g i n i a , w i t h paper mulch, F l i n t (7) found that the paper served to conserve s o i l moisture, p a r t i c u l a r l y to the 4-inch l e v e l . F l i n t suggested that one of the benefits of the paper l a y i n the more e f f i c i e n t d i s t r i b u t i o n of moisture, thereby p e r m i t t i n g a wider feeding range f o r the plants and enabling them p a r t i c u l a r l y to u t i l i z e the top inch of s o i l which i s r i c h i n a v a i l a b l e plant foods. Smith (19) i n C a l i f o r n i a found that the non-perforated black paper was the most e f f e c t i v e  i n conserving moisture. This e f f e c t s as already noted, was confined to the surface 4 inches of s o i l and Smith concluded that i t was due to the condensation of water underneath the paper. F e r r e t t i (3) observed that a paper covering conserved moisture by reducing evaporation, while Bronsart • (2) found no s i g n i f i c a n t d i f f e r e n c e i n moisture content, between mulched and unmulched s o i l s . Hartung (9) concluded that mulch paper served to maintain a s o i l moisture content, under dry conditions nearer to the optimum f o r plant growth, than had p r e v i o u s l y been achieved i n general p r a c t i c e i n Hawaii. Magistad, Farden and Baldwin (14) noted that mulch paper conserved moisture by reducing evaporation and Stewart, Thomas and Horner (23) found that the s o i l moisture was c o n s i s t e n t l y higher under paper than that found i n the unmulched s o i l area. S h i l o v a (18), i n Russia, t r i e d out d i f ferent types of mulches and found that a black paper mulch was the most e f f i c i e n t f o r maintaining an optimum moisture content i n the s o i l . F l i n t (7) was unable to detect a greater quantity of n i t r a t e s i n s o i l which had been subjected to mulch paper treatment. A f t e r one season's work with vegetables, Magruder (15) concluded that the d i f f e r e n c e s i n n i t r a t e nitrogen content of the s o i l during t h i s period were hardly consistent or l a r g e enough to be responsible f o r the increase i n y i e l d from the paper mulch. Bronsart^ (2) , working with s o i l s that had received no nitrogen f e r t i l i z e r s i n 3 years, took n i t r i f i c a t i o n as an index of the a c t i v i t y of the microorganisms i n the s o i l . His determinations were made at depths of 5 > 15 and 35 cm. and the d i f f e r e n c e s i n n i t r a t e nitrogen i n mgs. per 100 gms, dry s o i l sample, i n favour of the mulched s o i l , were r e s p e c t i v e l y 1.70, .10 and .35 mgs. He concluded that the increase i n n i t r a t e s was due to increased a c t i v i t y of the s o i l micro-organisms under the paper and not due to l e a c h i n g i n the unmulched area. Using samples of l a b o r a t o r y - c u l t u r e d s o i l , F e r r e t t i (5) reported d e f i n i t e gains i n ammoniflcation and n i t r i f i c a t i o n due to paper, with l i t t l e i n f l u e n c e on n i t r o g e n - f i x a t i o n . Magistad, Farden and Baldwin (14) conoluded that because of higher s o i l temperatures and greater s o i l moisture, b i o l o g i c a l processes i n the s o i l were considerably accelerated, r e s u l t ing i n a more r a p i d l i b e r a t i o n of plant food, e s p e c i a l l y n i t r a t e s . Stewart, Thomas and Horner (23) reported that a greater q u a n t i t y of n i t r a t e s was c o n s i s t e n t l y found under muloh paper, which, to these workers, seemed to i n d i c a t e a more r a p i d e l a b o r a t i o n of the p r i n c i p a l plant n u t r i e n t s . Hartung (9) found that mulch paper stimulated n i t r i f i c a t i o n , thereby enhancing the a v a i l a b l e nitrogen content of the s o i l . Yakovleva (29) basing h i s conclusions on the greater amount of nitrogen f i x e d and carbon dioxide evolved from the  oovered s o i l , concluded that paper mulching increased the bio-chemical a c t i v i t i e s of the s o i l . S h i l o v a (18) found that mulch paper increased the accumulation of n i t r a t e nitrogen, as w e l l as bringing about the more complete u t i l i z a t i o n of the n i t r a t e nitrogen by the p l a n t . He also observed that the accumulation of ammonia nitrogen was favoured by mulching, though the amount was i n s i g n i f i c a n t compared with that of n i t r a t e n i t r o g e n . EXPERIMENTAL CHARACTER OF THE CANTALOUPE The plant s e l e c t e d f o r the mulch paper study was the cantaloupe, Cucumis melo, the v a r i e t y chosen being Hale's Best, a netted melon of medium s i z e and e x c e l l e n t q u a l i t y . Being native to A s i a and A f r i c a , the cantaloupe i s more o r l e s s s p e c i f i c i n i t s heat requirements and g e n e r a l l y takes unkindly to the cool nights and the moderate summer day temperatures oommonly experienced a t Saanichton. I t i s d e f i n i t e l y a heat l o v i n g plant and can not be s a i d to be n a t u r a l l y adapted to conditions on Vancouver I s l a n d . Tests at Saanichton i n d i c a t e that success with the crop i s only attained when due oare i s given to date of p l a n t i n g , judicious choice of s o i l and exposure f a c t o r s and the creation of s u i t a b l e environmental conditions through the use of mulch paper, with o r without hot caps. A study of the root system of the cantaloupe (28) gives some i n d i c a t i o n of i t s food requirements and i t s h a b i t of growth. I t has a root system c o n s i s t i n g of a very extensive shallow p o r t i o n and a poorly developed deeper p a r t . The l a t e r a l root system of a cantaloupe plant may have a spread of 10 to 12 f e e t , most of t h i s being found i n the top foot of s o i l . Being a r a p i d l y growing crop under optimum conditions, i t requires an abundance of n u t r i e n t s and u s u a l l y makes i t s maximum growth i n a deep f r i a b l e loam, r i c h i n humus. Analyses of melon plants i n d i c a t e a r e l a t i v e l y high percentage of calcium, which may p o s s i b l y e x p l a i n why cantaloupes appear to do best i n a s o i l with an hydrogen-ion concentration around the n e u t r a l p o i n t . PROCEDURE This study respecting the influence of paper mulch on production of cantaloupes at Saanichton was conducted under f i e l d conditions. The cantaloupes were grown i n a 3-year r o t a t i o n f o l l o w i n g b r o c c o l i and preceding t u l i p s . The area devoted to each crop was approximately . 2 0 acres.  Immediately upon s e t t i n g out the young cantaloupe plants the s o i l was hand-raked and the mulch paper was then l a i d down. Raking was f o r the purpose of preventing lumps from subsequently breaking the paper i f t r o d upon. The edges of the paper were held down with the lumps of earth removed i n " raking. . The paper used was a good grade of b u i l d i n g paper impregnated w i t h asphalt. Each r o l l contained 400 square f e e t , was 30 inches wide and weighed 25 pounds. The experiments reported at t h i s time oovered f o u r years' work, 1935 to 1938 i n c l u s i v e , with some a d d i t i o n a l observations being made i n 1939' S o i l and C l i m a t i c Conditions. S o i l selected f o r the. experiments was a clay loam as determined by the hydrometer method ( 1 ) . Clam s h e l l t o t a l i n g about 15 tons per acre had been applied over a period of years immediately pWced'Jmg^ 1.933 and as a r e s u l t the s o i l had a pH of 7.0. Barnyard and green manures are r e g u l a r l y applied f o r the other crops i n the r o t a t i o n , the p r a c t i c e u s u a l l y followed being to apply the manure immediately p r i o r to p l a n t i n g the b r o c c o l i . Upon h a r v e s t i n g t h i s crop the land i s seeded to a green manure crop which i s turned under p r i o r to the p l a n t i n g of the cantaloupes about the l a t t e r part of May. Records over a 26-year period at Saanichton show that the ma an d a i l y a i r temperatures f o r June, J u l y and August (the main growing months) are r e s p e c t i v e l y 39$ 63 and 62° F. The hours of sunshine f o r the 3 months are r e s p e c t i v e l y 269, 324 and 293 hours, or approximately 900 hours of sunshine between the time of p l a n t i n g the cantaloupes, (May 24) and the time of harvesting at the end of August or e a r l y i n September. As temperature records are not a v a i l a b l e covering a 24-hour period, the t o t a l e f f e c t i v e temperature required to carry the cantaloupe plants through the vegetative and reproductive phases, under Saanichton c o n d i t i o n s , cannot be computed at t h i s time. The mean r a i n f a l l f o r the months of June, J u l y and August over a 26-year period, has been computed r e s p e c t i v e l y at 1.11, .6b and .73 inches per month; the mean y e a r l y r a i n f a l l recorded over a s i m i l a r period i s 30.01 inches per annum. S o i l Sampling and P l a t i n g . A standard system of s o i l sampling was adopted f o r both the mulched and the unmulched areas at the outset i n 1933  and t h i s was only s l i g h t l y modified through out the f o l l o w i n g years. The procedure was as follows: Three representative stands were chosen on each area and three borings were made at each stand, at a distance of nine inches from a p l a n t . In 1935? 1 9 3 ^ and i n 1937* s t e r i l i z e d brass tubes were used - f o r taking the samples, the core of s o i l i n each instance being placed i n a s t e r i l i z e d glass j a r . I n the 1938 t e s t s , s t e r i l i z e d aluminum spoons were used to obtain s o i l samples at the exact depth required. I n order to make conditions as comparable as p o s s i b l e on both the mulched and the unmulched s o i l areas, a l l samples were taken at moisture l e v e l . This e l i m i n a t e d the inch of a i r dry s o i l commonly found on the surface of the unmulched s o i l area during the growing season, which from the standpoint of b i o l o g i c a l l i f e , i s generally considered to be r e l a t i v e l y barren. The glass jars used f o r holding the s o i l samples were provided with approximately 300 gms. of s o i l , sealed with screw tops and taken to the l a b o r a t o r y , where the contents of each j a r was c a r e f u l l y emptied on to a sheet of s t e r i l i z e d paper, q u i c k l y mixed and again placed i n the o r i g i n a l container. From t h i s j a r samples of s o i l were taken f o r b a c t e r i o l o g i c a l counts and moisture t e s t s . These determinations were made without undue delay a f t e r b r i n g i n g the samples i n from the f i e l d . The s o i l s used f o r the a v a i l a b l e n u t r i e n t and hydrogen-ion determinations were immediately a i r - d r i e d . B a c t e r i o l o g i c a l work was pursued at a l l times with pers i s t e n t a t t e n t i o n to a l l the d e t a i l s whereby contamination might be eliminated from the time of sampling t o the pouring of the p l a t e s . Control p l a t e s were always poured to guard against contamination which' might i n t e r f e r e w i t h the f i n a l r e s u l t s . D i l u t i o n s f o r plate counts were made by emploj'-ing the standard technique, beginning with 10 gms. of s o i l , shaking t h i s f o r 13 minutes i n 1000 ml. of s t e r i l i z e d tap water and d i l u t i n g to the desired degree. The d i l u t i o n s used f o r p l a t i n g v a r i e d as f o l l o w s : Actinomyces and b a c t e r i a , 1 : 1 0 0 Thousand o r 1:1 M i l l i o n ; and for f u n g i , d i l u t i o n s v a r i e d from 1:10 Thousand to 1 : 1 0 0 Thousand, depending on seasonal v a r i a t i o n . The media used throughout was that as o u t l i n e d by Fred and Waksman (8) and was as f o l l o w s : Actinomyces — Sodium Asparaginate G l y c e r o l Agar (M33) Bacteria — Sodium Caseinate o r Nutrose Agar (M4) Fungi — Peptons-Gluoose A c i d Medium (Ml8) In 1935 p l a t e counts were made f o r r a d i o b a c t e r i n the  64 <lH  OS  fit  ••H  P*-P  +3 » O OS  -P O  •H  M  O  -P  © Q  o  H  •p  o  0  +»  e •-o +» K\ o o O N cj as H H f £ | vO I  •O • -P o "4  O: CVJ-  o H  o  o ON  O O  o o  OS CO  o  o o o  -JO LT\  CO  o  oo o o  o  CO\Q  o o  H  o o  o  H  CM  O o ONC~O CO H  ©  >»  o o  °  o  o o  o  o o  ©  o  ©  CM O J  O O  O O  K \ CM  o o  CO ON »\  o o  H  o  ON  o r-i  ©  .3  S  o  o o  O O  <tf  ©  CO  -C3 o  H  HA  o o  o o  NNC—  o o CVJ -J3  o  l£\CM  o ur\0  O O  -J3  OJ OJ at  ix\co  H  O O  o  H  ON-*  O o  CO ON  o o  ©  H  f»  H  o o o o o ©•.  O NN.  *.  o o  C—ON  o o  OJ  H HI  ©  o  O o  GNH  O o  O O  O o  o  o CM OJ  o o  LCNCM  o o CO NN.  o o  r—I OJ  o o C—O  O o H  ITs ON  H  O o O  OJ LT\  © o  ©  o  ©  S3  •3 5  3  a  0  3  ©  o  O o  •i  O O O O o ©  o o o  OO i r \  Ha  o  na  ON  +»  »  o  •P:  © o Q 03  ft © -O & 4 N\ O 1 as a 1 Hi H C ! O O  *4  •I  as  o  o  O  o o  o o cooo  o o  ON  o o C-NQ  s0 o  o  o.  5 s.  o  .O  o o  o §  o  OJ  o  O  "O o O  O  o o c—cH o o  H  CVJ  o o  C - O J  rf\sO H H  O 0  o o  0  O  o  o  o o  OJ CM  o o  •P  3  o  o  C—urv  o  .000  o  O  o  O  0  o  Os  o  O O  CO H CM  0  S3  OJ -Q  o  cvi ur\  o o  o o  o o  o o CM K \  o o  K \  o o  C O *£>  o o  OO  o o  O O O O CM X>  OJ  H  s o i l , the medium used i n t h i s instance "being G l y o e r o l - n i t r a t e Agar (21) . The two d i l u t i o n s used were 1:100 Thousand and 1:1 M i l l i o n . In 1 9 3 7 and i n 1 9 3 8 Azotobacter counts were made using the mannite agar medium as modified by Curie ( 3 ) . BIOLOGICAL STUDIES T o t a l P l a t e Counts• T o t a l numbers of actinomyces, b a c t e r i a , radiobaoter and f u n g i were determined i n mulched and unmulched s o i l s at approximately two-week i n t e r v a l s throughout the summer months over a three-year period. Marked v a r i a t i o n i n p l a t e counts, even greater than had been anticipated,was observed, hence even the s i x to twelve r e p l i c a t i o n s were not s u f f i c i e n t to smooth out the i r r e g u l a r i t i e s . In 1935 a s l i g h t increase i n t o t a l numbers during June and J u l y were apparent under the paper mulch, but these observations were not v e r i f i e d during the subsequent two years. Hence no s i g n i f i c a n t d i f f e r e n c e s between numbers of actinomyces, b a c t e r i a , radiobaoter and f u n g i i n mulched and unmulched s o i l s were demonstrated. Due to inconclusiveness of data only that f o r 193b and 1 9 3 7 i s presented i n t a b l e 1 . Note i r r e g u l a r i t y i n data. Azotobacter Tests. Azotobacter represent an important group of s o i l microorganisms and t h e i r physiology i s such that should there be a v a r i a t i o n i n numbers i n mulched and unmulched s o i l s , addi t i o n a l information as to the general conditions f o r growth would be forthcoming. Tests were therefore undertaken i n 1 9 3 7 to determine t h e i r numbers i n the s o i l , with and without paper muloh. The procedure adopted was to s p r i n k l e a 1-gram sample of s o i l on plates of Curie's mannite agar (3) and incubate at 28° C. A f t e r 4 - 7 days white gelatinous colonies ( l a t e r turning yellow-brown) appeared around the s o i l p a r t i c l e s and were i d e n t i f i e d as Azotobacter. The profusion of growth on the p l a t e s made accurate counting impossible, hence the s o i l inoculum was reduced from one gram to 0 . 5 gms. f o l l o w i n g the i n i t i a l t e s t s . These p l a t e s were prepared p e r i o d i c a l l y throughout the summer of 1 9 3 7 and an examination of the data reveals no s i g n i f i c a n t d i f f e r e n c e s i n Azotobacter numbers under the paper mulch as compared w i t h the unmulched s o i l .  Table. 2.  Azotobacter counts (ia^frofusaiKte/per gram of drv 1938.  Mulched Area Cropped A p r i l 16  Uncropped  3 38  June 23  12  8  J u l y 12  10  8  2  2  August 13  10  August 30  ' 2  Cropped  Uncropped  3  May 23  August 3  Unmulched Area  44 .  .3  .1  4 .2  lb '  9 • ^ 5  2 - <i J?  6  .20  9  # : Composite samples taken from those areas l a t e r designated as mulched and unmulched. A greater degree of success accompanied the i s o l a t i o n of Azotobacter i n 1 9 3 8 , due p o s s i b l y to the consistent use of only 0 . 3 gms. of s o i l s p r i n k l e d over the mannite medium. The colonies were s u f f i c i e n t l y w e l l d i f f e r e n t i a t e d to permit of c l o s e r observation and study. The summary of a l l counts made from A p r i l to August i s shown i n Table 2 and reported i n each instance as number of colonies per gram of dry s o i l , computed from a mean of 6 p l a t e s . Here again no s i g n i f i c a n t d i f f e r e n c e i n numbers of Azotobacter was apparent between the mulched and the unmulched s o i l areas. The highest mean Azotobacter count f o r the season was found on the unmulched, uncropped p l o t s which were l e f t u n c u l t i v a t e d , except that given f o r weed c o n t r o l , with the mulched, cropped area being s l i g h t l y higher than the unmulched, cropped p l o t s . (1938)  D i r e c t Influence of Mulch Paper on B a c t e r i a l A c t i v i t y . As coal t a r products are sometimes used i n the making of the b u i l d i n g paper commonly used f o r mulching purposes, i t was suggested that t h i s paper might oontain c e r t a i n growth promoting substances. On g i v i n g consideration to the p o s s i b i l i t y of these being e f f e c t i v e under f i e l d conditions,  i t was assumed that they must be water s o l u b l e . Mulch paper was aooordingly macerated w i t h warm water and incorporated i n t o sodium caseinate agar i n varying concentrations. Plates prepared with t h i s medium were seeded with giant colonies of two d i f f e r e n t p r o t e i n s p l i t t i n g actinomyoes. The influence of the paper mulch was determined by measuring the digested casein r i n g appearing as c l e a r areas around each i n d i v i d u a l oolony i n the muloh paper plates as compared with c o n t r o l s . Measurements were made over a 6-day period at approximately the same time each morning. Plates r e p l i c a t e d b and 12 times f o r mulch paper and oontrols r e s p e c t i v e l y were prepared and incubated at 28° C. The averages of these r e p l i c a t i o n s and r e s u l t s with the varying concentrations of paper used are presented i n Table 3. A study of t h i s table wi11 i n d i c a t e that the mulch paper, at the concentrations s p e c i f i e d , had varying e f f e c t s on the two organisms i n question. In the case of the Ml-1 organism, concentration of 1.3 per cent s l i g h t l y stimulated a c t i v i t y while beyond t h i s point d i g e s t i o n of the casein decreased with increasing concentration. On the other hand, wi th Ul-G, s t i m u l a t i o n i s noted at a l l concentrations up to b per cent with the maximum occurring at 3 per cent. S l i d e s were prepared from each of the muloh paper concent rations and from the checks. Microscopic examination d i d not i n d i c a t e any v a r i a t i o n i n c e l l structure or, s t a i n i n g properties from the various p l a t e s , i n e i t h e r the Ml-1 or Ul-C s e r i e s . The (G.otft.aclfe e f f e c t of mulch paper on s o i l organisms was also observed i n the f o l l o w i n g manner: Washed sand was d r i e d and sodium caseinate f l u i d medium added; eight-inch p e t r i plates were then f i l l e d with t h i s sand medium and s t e r i l i z e d i n the autoclave. Each p l a t e was then seeded w i t h 30 co of a water suspension of the 2 organisms, M l - 1 and Ul-C, which had been grown on sodium caseinate agar and brought to optimum moisture oontent through a d d i t i o n of water. S t e r i l i z e d mulch paper d i s c s , the same diameter as the p l a t e s , were then placed d i r e c t l y over the sand, covered with a p e t r i plate and incubated at room temperature f o r 8 days. Unmulched sand plates were s i m i l a r l y made up and incubated. At the end of the 8-day period, the unmulched plates showed a dense white growth, t y p i c a l of the organisms concerned. On l i f t i n g up the mulch paper d i s c s , a s i m i l a r heavy growth was found to be growing d i r e c t l y on the paper, i n d i c a t i n g the e n t i r e absence of t o x i c m a t e r i a l i n the paper, at l e a s t i n respect to the two organisms studied.  Table 3°. Direct influence of mulch paper on b a c t e r i a l a c t i v i t y as measured by casein digestion. Organisms Studied  Ml-1  Concentration of Medium  check  »  1.50  ii  3  ii  6  Ul-G  % V %  8  .75%  2  10  9  6  7  10  3  7  8  #  #  6  • 7  24  14  21  24  17  23  26  12  1-6-  17  10 ..  '  6  20  ,15  14  3  4  13  6  6  check  tr  1  .  • 75 %  tt  Days When Observations Made, Measurements i n M i l l i m e t e r s .  9  14  i  1 7  10  13  16  20  23  16.  18  2i  22  23  w  1.50  %  6  10  12  15  18  24  it  3  %  6  22  26  29  32  33  6  % '  7  13  17  21  24  ti  # : No i n d i c a t i o n of protein s p l i t t i n g evidenced; co growth only„  -  26.  Carbon Dioxide Production. The evolution of carbon dioxide i s often used as a. measure of b i o l o g i c a l a c t i v i t y i n a s o i l (20) and f o r comparative purposes at l e a s t , i s generally considered to be of • value. For the purpose of measuring the production of carbon dioxide from mulched and unmulched s o i l s , r e s p i r a t i o n chambers s i m i l a r to those described by Smith, Brown and M i l l a r ( 2 0 ) , were made and set up. The chambers were made out of grain storage t i n s 6 . 3 inches high with an i n s i d e diameter of 4 . 3 inches. The i n s i d e was thoroughly l i n e d with l i q u i d p a r a f f i n , a l l j o i n t s being made a i r t i g h t . Aeration was provided through a guard tube of soda lime. A metal rack, also covered with p a r a f f i n , served to suspend the beaker of earth i n s i d e the chamber. The procedure adopted f o r the r e s p i r a t i o n chamber studies was as f o l l o w s : 100 ml. portions of barium hydroxide were added to each chamber, 200 gms. of s o i l i n a wide mouth beaker were placed on the metal rack and each chamber closed, sealed and l e f t to incubate at room temperatures. A l i q u o t s of barium hydroxide (.IN) were drawn o f f p e r i o d i c a l l y by means of a stop cock placed i n the bottom of the chamber and t i t r a t e d with .IN hydrochloric .acid. Duplicate chambers were used f o r comparing the production of carbon dioxide from the mulched and unmulched s o i l s and c o n t r o l s . From the difference between the check and the s o i l t i t r a t i o n s , the number of m i l l i grams of carbon dioxide evolved per 200 gms.. s o i l was accordingly calculated. The s o i l s used were obtained from the mulched and the unmulched s o i l s at a depth of 1 inch and were incubated as soon as the moisture content was determined. When t h i s had been done, s u f f i c i e n t s t e r i l e water was added to each sample to bring i t up to an optimum of 23 per cent moisture. I n s e l e c t i n g the 200-gram sample, due care was taken to eliminate any p a r t i c l e s of l i v i n g root t i s s u e which might i n t e r f e r e with the readings. S o i l samples were taken p e r i o d i c a l l y throughout the summer of 1937 and determinations made but the data d i d not i n d i c a t e any s i g n i f i c a n t d i f f e r e n c e i n b a c t e r i a l a c t i v i t y between mulched and unmulched s o i l s . CHEMICAL STUDIES 1 9 3 3 " 3 8 Mulched and unmulched s o i l s were subjected p e r i o d i c a l l y throughout the growing season to semi-quantitative tests f o r a v a i l a b l e n u t r i e n t s ( 2 2 ) . While i t must be admitted that the procedure used lacks preciseness, i t does, bearing i n mind i t s l i m i t a t i o n s , permit of comparison between two s o i l  Table. 4 . A v a i l a b l e nutrient tests and hydrogen-ion determinations. A l l nutrients reported i n parts per m i l l i o n . Nitrate  P  Ca  /Mg  PH  1935  0-b" Depth  May 29  Mulched Unmulched  June 22  Mulched Unmulched  J u l y 22 September 3  25 25  .5 .5  5 5  175 175  5 5  25  8  •5 .25  5 5  175 175  &  6  7.5 7-5  Mulched Unmulched  25 25  .50 • 25  5 5  175 175  6 2  7c2 7.2  Mulched Unmul ohed  25 5  .50 ,25  5 5  175 175  6 3  -  Mulched 1" 15 Unmulched 1" 15  .50 .50  8 8  125 125  -  •7e2  Mulched 1" 50 ti 4« 25 Unmulched 1" 10  .50 .50 .50  8 8 8  150 150 150  —.  -  7.1 7.1 7.0  3  .75 .75 .75 .75  5 5 5 5  175 175 175 175  -  7.0 7.4 7.1 7e2  25 8 Unmulched 1" 8  .50 .50 .50 .25  5 5 4 4  175 175 175 175  -  7*1 7.2 7.1 7.1  .50 .50 „50 .75  8 8 8 8  175 175 175 175  -  7.1 -7*1 7.1 7.1  .50 .50 .50 .50  5 5 5 5  175 175 175 175  1931 May 20 June 4  July 8  •  Mulched 1" Unmulched 1" »  J u l y 30  4«  25 25  8  Mulched 1" ii  411  3  August 9  Mulched 1" n  411  25  w-  Unmulched 1" 20 it  August 31  ;  -  4»i  10  Mulched 1"  40  41J  8  11  Unmulched 1" «»  411  3  8  7.2  7.2 —  b.8 7-2  b.8  Nitrate September 13  Mulched 1" rt  411  Unmulched 1" it 4» •  J L  Ca  Mg  pH  30 13 10: 10  .30 .50 .30 .30  3 3 5 3  173 173 173 173  -  7.4 7.4  7.2 7-1  1938  Mulched 2 " , Unmulched 3 " April 16  Mulched Unmulched  2 2  .50 .30  3 5  173 173  7 7  7.2 7.2  May 23  Mulched Unmulched  3 2  .30 .30  3 3  173 173  7 7  7«2 7.2  June 23 Mulched-cropped uncropped Unmulch ed-c ropp e d " uncropped  23 23 20 .20  .30 • 30 .30 .30  5 3 3 5  200 200 200 200  7 7 7 7  7.2 7.0 7.1 6.8  July 12  25 23 23 ••• 23  .30 .30 .30 .30  3 7 3 3  200 200200 200  7 7 7 7  7.2 7.2 7.2 7.2  Mulched-cropped uncropped Unmulched-cropped • " uncropped  23 ' 23 13 13  .30 .30  3 3 7 7  200 200 200 200  7 77 7  7.2 7.2 7»2 7.1  Mulched-cropped " uncropped Unmulche d-c roppe d uncropped  33 30 ; 30 30  .30 .30 • 1.  '.I*- '  3 3 3 3  200 200 200 200  7 7 7 7  7.1 •7.0 6.9 6.9  Mulched™cropped uncropped Unmul c h e d-c ro p pe d " uncropped  30  .30 .50 .30 .30  3 3 3 3  200 200 200 200  7 7 7 7  7.0 6.9 6.9 7.0  tr  Aug. 3  Mulched-cropped " uncropped Unmul ch e d-c ro p p e d " uncropped n  Aug. 13  M  Aug. 3 0  n  40  33 33  1. 1.  conditions. In a l l cases the s o i l used represented a composite sample. I t was f i r s t a i r d r i e d , then l i g h t l y p u l v e r i z e d i n a mortar before measuring out the sample f o r a n a l y s i s . Nutrient t e s t s over a 4-month period i n 1 9 3 3 i n d i c a t e d a s l i g h t increase i n the concentration of a v a i l a b l e n i t r a t e s i n the mulched s o i l . Tests on August 2 0 i n 1 9 3 6 on s o i l samples at depths of from 0 to 6 inches, i n d i c a t e d more n i t r a t e s at a l l depths, from the unmulched s o i l areas. In 1 9 3 7 the n i t r a t e content was d e f i n i t e l y higher i n the mulched s o i l , while i n 1 9 3 8 there was no appreciable d i f f e r e n c e between the two areas. One p o s s i b l e explanation f o r t h i s v a r i a t i o n i n n i t r a t e content i n the mulched and unmulched s o i l s from year t o year might be that the melon plants v a r i e d i n t h e i r n i t r a t e requirements according to the season. That of 1 9 3 6 , f o r instance, was not p a r t i c u l a r l y favourable f o r melons on Vancouver I s l a n d . Comparatively c o l d , wet weather i n the c r i t i c a l month of June p a r t i c u l a r l y delayed growth i n the unmulched p l o t s , which did not have the benefit of the e x t r a heat u n i t s supplied by the paper as d i d those on the mulched p l o t s . Consequently, the melon plants on the unmulched plot made poor growth, u t i l i z i n g l i t t l e of the s o i l n i t r a t e s and henoe the comparatively high n i t r a t e test as compared with the mulched s o i l . Conversely, the season of 1 9 3 7 was a b e t t e r melon year, the plants on the unmulched p l o t s were able to make good growth, thereby u t i l i z i n g more. of the s o i l nitrates. Due to the b e t t e r heat conditions afforded by the paper, i t i s also assumed that a more favourable environment i s set up f o r the n i t r i f y i n g b a c t e r i a , thus u l t i m a t e l y g i v i n g a higher n i t r a t e content to the mulched s o i l . As a study of Table 4 w i l l show, there was l i t t l e v a r i a t i o n i n the a v a i l a b l e n u t r i e n t s , other than n i t r a t e s , i n the mulched and the unmulched s o i l s e i t h e r from month to month or from year to year. The concentration of phosphorus and potassium both remained r e l a t i v e l y constant, with the amounts of calcium being s l i g h t l y lower i n the e a r l y s p r i n g , as were a l s o the n i t r a t e s . Under Saanichton conditions at l e a s t , the a v a i l a b l e n i t r a t e s were leached away by the winter r a i n s , and g e n e r a l l y i t i s not u n t i l the advent of higher temperatures i n May and June, that more are elaborated by b i o l o g i c a l a c t i v i t y i n the s o i l . Hydrogen-ion determinations were determined by the c o l o r i m e t r i e method. The accuracy of t h i s procedure was  -12A v a i l a b l e nutrient t e s t s on mulched and unmulched melon plant tissues ^ 1937*  Nitrates  Phosphorus  Potassium  High Very high  High Deficient to medium  High Medium to high  High High  High Low  Low High  Medium to high Very high  Very high  Very high  High .  Very high  Low Very high  Very high High  Very high Very high  August 3 Mulched Unmulched August 13 Mulched Unmulched September 4 Mulched Unmulched September 20 Mulched Unmul ch ed  checked against a standard potentiometer apparatus and found to be s a t i s f a c t o r y . Barium sulphate (10) was found very useful i n c l e a r i n g the s o i l s o l u t i o n and tests indicated that i t s use d i d not m a t e r i a l l y e f f e c t the accuracy of the readings. As Table 4 w i l l i n d i c a t e , no s i g n i f i c a n t difference was noted i n the pH values between the mulched and the unmulched s o i l s , both f l u c t u a t i n g s l i g h t l y from month to month. A v a i l a b l e nutrient tests were run on mulched and unmulched plant tissues i n 1937> employing the Thornton procedure ( 2 3 ) . Terminable growth m a t e r i a l was used f o r t h i s purpose, as i t was considered to be the most s u i t a b l e . The outstanding f i n d i n g i n these t e s t s was the extra supply of n i t r a t e s i n the unmulched plants and the higher phosphorus content i n the case of mulched melon plants. PHYSICAL STUDIES. Soil  Temperature.  S o i l temperatures were recorded throughout the growing season of 1937 and 1 9 3 8 . Readings were taken three times d a i l y on both mulched and unmulched s o i l s . During 1937 thes<= readings were taken at 1 and A depths, while at only a 2" depth i n 1 9 3 8 . M  n  A i r temperatures at 9 inches above ground l e v e l were also taken at the same times as were the s o i l temperatures. A l l readings were taken from duplicate thermometers, the mean of the two readings being reported i n each instance. In order to f a c i l i t a t e comparisons between the mulched and the unmulched conditions, the d a i l y readings f o r 7-day periods were averaged. The s o i l thermometers used were of the hot-bed type, while those used f o r recording the a i r temperatures were w a l l thermometers mounted on a stout stake. A l l instruments, before being set i n p o s i t i o n , were c a r e f u l l y checked against a thermometer of known accuracy. An examination of the data as presented i n Tables 5 and 6 reveals no s i g n i f i c a n t d i f f e r e n c e i n s o i l temperatures between the mulched and the unmulched s o i l areas e i t h e r i n 1 9 3 7 o r i n 1 9 3 8 . The data does suggest, however, that s l i g h t l y higher temperatures do p r e v a i l under the paper during the e a r l y part of the season, with a tendency toward lower temperatures during the l a t t e r part of the season. Mulched s o i l shows a narrower temperature range throughout the season than the unmulched. C o n s i s t e n t l y higher a i r temperatures were recorded over the mulch paper both i n 1 9 3 7  Table 3 . Summary of thermometer readings on mulched and unmulched s o i l areas at Saanichton i n 1 9 3 7 .  Time  Mulched Area 1" 4" Air  Unmulched Area 1" 4" Air  May  17-23  8 A.M. 1 P.M. 3 P.M.  37.7 68.1 69.4  3b.3 63.4 b3.4  May  24-31  8 A.M. 1 P.M. 3 P.M.  60.4 71.1  61.  60  67.6 68.1  71.3 74.1  1 P.M.  8 A.M.  66.4 81.1  67.4  3 P.M.  82.8  6b.3 74.9 73.7  62.  June 1-10  74.6  3b. 68.1 69.6  3b. 4 63. 61.4 b0.3 66.4 67. 63.7 73.2 74.3  79.1 81.3  8 A.M. 62.6 1 P.M. 68. 3 P.M. ' 6 8 . 6  66.1  67-7  37.4 b2.7 39.6  68.4 68.  66.9 b8.3  37. 61.3 38.8  June 22-30  8 A.M. 1 P.M. 3 P.M.  63.3 77.3 77.3  63-3 72.2 74.4  64.9 71.7 71.7  b4.778.1 77.2  b3. 74.6 76.1  63*4 70.6 70.6  J u l y 2-9  8 A.M. 1 P.M.  69.6  68.  83.9  3 P.M.  83.8  77.9 82.2  ' 66,4 73.4 73.0  68.1 83.9 87.  67.7 80.6 85.2  63. 74.1 73.7  8 A.M. 1 P.M. 3 P.M.  71.4 84.  70.4 79.4 82.  71.3 76.6 77.2  74." 87-7 86.8  71.4 82.7 83.2  70.3 73.6 77.2  8 A.M. 1 P.M.  69.7 82.8 83.  69.2  b9.3 79.7 82*  72.3 90.2 87-8  70.7 84.8 88.2  68. 78.8 80.6  66.8 73. 73.8  71.3 83.0 83.4  70.8 82.0 82.6  63. 72. 72.  06.7 73. 73.6  68.4 82.1 81.3  68.2  80.  63.1 73.3 73.4  64.3 72.8 73.2  65.8 78.7 78.  6b. 77.7 78.7  June 14-21  J u l y 10-17  J u l y 19-24  3 P.M. J u l y 26-31  Aug. 2-9  Aug.  10-17  83.7  62.4  80.3 84.6  1 P.M.  8 A.M.  68.7 6 9 . 79.6 77.6  3 P.M.  80.6  8 A.M« 1 P.M. 3 P.M.  bb.7 78. 77.6  7b.4 78.  8 A.M. 1 P.M. 3 P.M.  64.2 74.2 74.  63.4 72. 74.  79-  6b.  61.6  82.3  61.3 70.7 71.2  Time Aug, 18-24 8 A.M. 1 P.M.  Mulched Area 1" 4* A i r 1  64.  64.5  5 P.M.  73. 71.7  70.2 71.8  Aug. 25-31 8 A . M . 1 P.M. 5 P.M.  0O.3 68.3 68.3  67.  8 A.M. 1 P.M. 5 P.M.  72.2 71.  Sept. 1-8  Sept. 10.-25 8 1 P.M. 5 P.M.  61.2  63- •  73.2 72.6  61. 6?.5 62.  70.2  72.7 63.4  71.8 74.8  Unmulched Area 1" 4" Air  71.2  75-7 75.2  65.8 75.3 76.  59.2 68.2 67.  60.8 71.3 71.7  60.8 70.5 72.3  64.  62.7 74.5 71-7  62. 75.2 74.7  62. 75-7 75.7  59*3 72. 69-7  o4.6 78. 76.4  63.6 77-8 78.4  63.6 77.6 79.2  62.  65.8 71.8  66.2  62.  56.3 65.8  68.5 68.8  75. 74.  Table 6. Summary of thermometer readings on mulched and unmulched cropped areas at Saanichton i n 1 9 3 8 . Mulched Area  Unmulched Area  Time S o i l 2" 7.30 A.M. 65.4 1 P.M. 81.6 5 P.M. 82.6  59. 69.6 69-7  June 4 -• 13  7.30 A.M. P.M. 1 P.M. 5  69.1 84. 84.3  63-1 70.3 70.  67.1 81.5 82.5  62.1 70.3 70.4  June 14 - 20  7 . 3 0 A.M. P.M. 1 P.M. 5  67.1 78.3 79.4  59,7  66-. 4  59.  May 28 -- June 3  June 21 - 27 June 28 - J u l y 4 J u l y 5 - 12  Air  68.4  S o i l 2" 64. 81.3 82.5  69.  78.4 79-5  65 73.7 75. b  70.9 86.9 89.3  7 . 3 0 A.M. P.M. 1 P.M. 5  88.1  7.30 A.M. P.M. 1 P.M. 5  67.7 80.1 80.7  59.3  b7.4 67.4  67.4 81. 81.4  7.30 A.M. P.M. 1 P.M. 5  66.3 82. 84.  63.3 70.5 70.1  67. 84.3 84.1  Air 58.7 69.5  69.1  68.  67.7  64 72.7 75.2 58.1 60.  67.3  61.4  70. 69.3  Time 7.30 A.M. 1 P.M. 3 P.M. 7*50 A.M. 1 P.M. 5 P.M.  J u l y 13 - 19 J u l y 20 - 27  J u l y 28 - August 4  7*30 1  5  August 5 - 1 2  7.30 1 5;:  August 13 - 20  7.30 •'  August 22 - 29  1 5  7.3O 1 5  Aug. 30 - Sept. 7  7.30 1  September 8 - 15  5 7.30 1 5  Mulched Area  Unmul ched Area  S o i l 2"  S o i l 2"  91.1  70.6 84.1 86.6  65.I 76.9 76.6  Ills  A.M. P.M. P.M.  66.3  A.M. P.M. P.M. A.M. P.M. P.M.  74.1 76.6  A.M. P.M. P.M.  Air b8.1 79. 82.7  • '6i-.lV-  Air 68.1  .72.7 89.6  78.3  91,9  "• 79.1  71.7 84.1 84.1  74.4  62.7  75.6  58.4  68.3 71.3  67.7 80.1 81.3  63.I 77.1 77.5  58..9  b3.6  56.4  77.3 76.8  ^ 64.9 65.8  64.3  57.4 67.1  62.8 73.8  67.  73.8  55.3 63.5  80.4 83.5  63. 74.4 7b.9  A.M. 6 1 . 3 P.M. 6 8 . 9 P.M. 7 0 . 5 A.M. 60.7 P.M. "71.1 P.M. 7 2 . 3  66.4 68.3  56.9 68.1 69.5  :  62.4 74.3 75.3  •66.5' 69.3  64.4  56.4 67.7 67.9  51.3  63.6  61.3 69.4 70.5  55.4  60.1  57.3  54.3  71.5  65.5  53.9  64.  66.3  71-. 3 .-  61.9 60.6  64.6  Table ,7> Summary of thermometer readings on mulched and unmulched,uncropped areas at Saanichton i n 1 9 3 8 . Mulched Time S o i l 2" ~TTr 7• 30 A.M. 65. 59. 1 P.M. 9.1 7 0 . 7 5 P.M. 1. 70.7  May 2 8 - June 3 June 4 - 1 3  7 . 3 0 A.M.  1  P.M. P.M.  5  June 14 - 2 0  7.30 A.M.  7.30 1  A.M. P.M. P.M.  1.1  85 .  63.6 75.4 77-3  7.30 3  7»30 1 5  5  7 . 3 0 A.M.  P.M. P.M.  7.30  A.M. P.M. P.M.  1 5  7 . 3 0 A.M.  1 5  August 2 2 - 2 9  P.M. P.M.  1 3  August 13 - 20  P.M. P.M.  7 . 3 0 A.M.  1  August 3 - 1 2  A.M.  7 . 3 0 A.M.  5  J u l y 2 8 - August 4  A.M. P.M. P.M.  - P.M. P.M.  1 2 0 - 2 7  71.1 60.4 69.3 69.3  1  July  82.5 66*9 77.9 78.3  June 2 8 - J u l y 4  July 1 3 - 1 9  72.3  P.M. P.M.  5  July 3 - 1 2  63.5  82.4  1  3  June 2 1 - 2 7  68.7  P.M. P.M.  7 . 3 0 A.M.  1 5  P.M. P.M.  86.  Unmulched 2" Air 64.9 58.  boil  80.6  81.  69,1  69.  67.7 81.7 82.3  61.9 69.4 69.I  67.4  39.4  78.3 79.9  68. 68.1  1.7 7.5  63.1  89.6  74.1 76.3  68.3  60.7  79.4  68.3  78.9  68.9 68.9  81.4 8I.9  58o9 67.7 68.3  66.7 81.7  63.5 73.  68.1  63.5 72. 71.4  81.4  72.5  2.1 7.4 87.1  1. 2.1 84.  0.9 2.9 83.9  85.7 86.3  93.1  68.3 82.3 84.3  67. 79. 79.  73.  64.7  6.1 8.4  78.9 79.7  67.7 80.1 81.5  63.9 71.9 74.3  69.1 82.4 85.2  60 .9 72.7 74.3  66.  62. 68. 68.7  8O.3  67.7  58.7 68.6 69.5  77.3 78.  59.8  64.4 60. 76.4 7 0 . 3  73*3  90.2  81.  64.4  77.8  70.  1.  9.3  68.7 69.2  62.9  60.1  64.1  57.6  80.3 83*9  70.7 72.9  7b.4  77-4  67.9 72.4  Time Aug.  30  -  Sept. 7  7.30  1 5 September  8 -  15  7.30  1 5  Mulched Soil 2" Air  A.M. P.M. P.M.  71.1 71.8  A.M. P.M. P.M.  74.1 72.1  61.1  61.4  Unmulched Soil 2 " A i r  57-9 68.5 68.5  62.3 72.9 74.5  61.8 72. 69.  53.6  66. 65.6  62.  56.4  7778.1  70.7 68.1  Table 8 . Summary of thermometer readings on blackened untreated, mulched and unmulched areas. Mulched Areas Blackened June 20 - 2 8  June 29 - J u l y 7 July 1 1 - 1 9  July 2 0 - 2 8  J u l y 3 1 - August 8  D a i l y Mean:  Normal  7.30 1 5  A.M. P.M=. P.M.  66.2  64.6  80. 83.3  76.7 78.5  7.3O 1 5  A.M. KM-'. P.M.  66.5 76.9  64.1 72.6 75-3  7.30 A.M.  81.0 67.8 82.1 • 82.6  Unmulched  65. 76.5 75.9  62.6 73.7 76.7 63.1  72.2  75.  64.  1 5  P.M. P.M.  7.30 1 5  A.M. P.M. P.M.  • 9U1  7.30 1 5  A.M. P.M. P.M.  70.7 84.5 87.7  68.5 83. 85.2  llf  79.2  75.  74.97  June 2 0 - August 8  72.3  95.2  -  69.5 84.1  86.2  76.8 77.1 69.3  84.2 88.4  87.3  July 7 Figure 3,Showing the e f f e c t on s o i l temperatures of a r t i f i c i a l l y blackening the mulch paper i n 1939.  August8  -14and i n 1938 In comparing the temperature readings on the mulched and the unmulched, uncropped areas shown f o r 1958 i n Table 7, i t i s to be noted that the range of a i r temperatures i n the uncropped areas are higher than on the corresponding cropped areas. This also holds to a more l i m i t e d degree with the s o i l temperatures. Temperature as Influenced by Colour of Mulch Paper. Tables 5 and 6 i n d i c a t e a s l i g h t increase i n s o i l temperatures i n e a r l y season due to the use of mulch paper, but t h i s advantage i s only noticeable f o r a r e l a t i v e l y short time, the unmulched s o i l temperatures being higher than the mulched from mid-season on. The explanation of t h i s was not c l e a r l y understood u n t i l 1939, when 2 areas 13 by 30 f e e t were blackened with lamp black and l i n s e e d o i l and temperature readings taken, these being compared w i t h the unpainted paper and with the unmulched areas. Readings were not taken u n t i l June 20, when the untreated paper had been bleached by exposure to the sun during May and June. I t w i l l be apparent from Table 8 that there i s an appreciable increase i n s o i l temperatures due to the blackening of the mulch paper. The difference i n 1939 apparently was p r o p o r t i o n a l to the temperature ; the maximum d i f f e r e n c e occurring i n J u l y 27 at 5 P.M. when the normal mulch r e g i s t e r e d 89 degrees Fahrenheit and the blackened 99*5 degrees. The unmulched reading at the same time was 92.3 degrees Fahrenheit. In the l i g h t of t h i s data i t i s now possible to e x p l a i n the lower s o i l temperatures recorded on the mulched areas a f t e r the l a t t e r part of June, as i n d i c a t e d i n Tables 5 and 6 . As the mulch pap er bleaches, the heat i s r e f l e c t e d rather than absorbed, w i t h a consequent l o s s of heat units retained by the s o i l under the mulch paper. S o i l Moisture. P r i o r to 1937> moisture determinations on the mulched and the unmulched s o i l areas were made only on those occasions when b a c t e r i o l o g i c a l t e s t s were oonducted and were made f o r t o t a l moisture only. This was done by drying a 10-gram sample of s o i l i n an e l e c t r i c oven maintained at 105 degrees c e n t i grade , u n t i l a constant weight was reached. In 1937 and i n 1938, p e r i o d i c moisture t e s t s were made from May to September f o r c a p i l l a r y moisture; i n 1937 these t e s t s included determinations at depths of 1 and 4 inches from the cropped areas only and i n 1938 samples were taken  -15-  at a 2-inch depth, from both cropped and uncropped areas as i n d i c a t e d i n Table 10. • Glean c u l t i v a t i o n was maintained throughout the season on the unmulched areas with no attempt being made to maintain a dust mulch. Determinations at a l l times were made i n duplicate and as f a r as possible were conducted the same day as the samples were tfeken, the s o i l being stored i n a i r - t i g h t glass jars from time of sampling u n t i l the determinations were made. C a p i l l a r y moisture was determined by a i r drying 10 gms. of s o i l at room temperatures i n standard aluminum drying pans, these being placed i n a glass covered cage to prevent dust contamination. The cage measured 2 by 2 by 1 f e e t , t h i s being deemed l a r g e enough to provide uniform conditions of humidity; i t was kept at a l l times i n a shaded portion of the l a b o r a t o r y , away from any d i r e c t s u n l i g h t . The s o i l samples were kept under these conditions u n t i l a constant weight was attained. An examination of the data, r e l a t i v e to the uncropped p l o t s , as presented i n Table 9 shows c l e a r l y the influence of paper mulch on the conservation of moisture. Here i t i s to be observed that the average moisture l e v e l under the mulch was 3 » 2 % higher than i n the unmulched s o i l . This difference i s not observed i n the s o i l s of the cropped p l o t s f o r the same year, i n f a c t the unmulched cropped plots show an average of 0 . 5 % higher moisture content. This i s undoubtedly due to the higher moisture requirements of the l a r g e r plants and higher y i e l d o c c u r r i n g under mulched conditions. A study of the data on the cropped areas f o r 1 9 3 7 reveals no d i f f e r e n c e i n moisture content i n s o i l s of the mulched and unmulched p l o t s f o r the reasons given above. Upon r e f e r r i n g to the r a i n f a l l data i n Table 1 0 one f i n d s an explanation f o r the higher moisture content i n the unmulched s o i l as observed i n the data f o r August 3 0 . One i s safe i n concluding from the foregoing data that paper mulch does conserve appreciable amounts of moisture.  -p  © o  © ft  a •H © CO  © ft W © CO CO © 03  ©  o  2  (H  a © a  0 O ©  •P CQ •H O  0 >>. !4 cd  H H •H ft CO  O ON  © H &  CO EH  ©  ft ft  o PH  o  B  ©  ft ft O  m  o  K\  CO ON  H  CO K\ ON  H  ON  H  © o ~) CM  © CM  .a = O  I © 3  O E i—I CM  © O CM  &s  © O  © O  .3  H  ©  s  En  •H  ON ON ON  ©  CO  cON  ON  CM  o ON  o  ON  NO  CO  ©  o  NO  OJ N O  NO  »  ©  ©  K\  ©  H NO  CM  CO CO  «  NO  ®  H CO  N ©  *«  © cd  H  © CO  ©  •P  » ft  Lf\  O  ON  ®  u\  OJ  H, KY O  o K\ r4 N O  ON ©  H -r4  NO '» .  CO  o  1—f  o  H  ON  ON  8  1  I  1  (X\  o.  H ON  o  ON « CO  NO -O  » ITS  <* NO ©  e  e-  ON ®  ON  K \ C—  »  o  H  » r-  NO ON ©  ND  ©  NO  ON  H 0  NO  »  C— NO  0  CO  H X \  -o  O H  CO CO  ON  e  H  c—  N O  CM  Lf\  NO  ON  o  •  O H  o  1  OJ CM  }  •  •  NO'  o e-  o ITS  •  UN  CM  'e  w  * ? ! fSo^r i 1S9'3 7z- n 3 0 period. 0 1 1 1  8  1  d a t a  r e l a t i v  e *° moisture determinations 19.3*7  May  . 0 2 inches .04  27  June 9 13  .41 .02  .Ob  . i f  . 0 2 inches .61  .02 .91 " . 2 8 ' : .. .07  15  16 :•: 1 ': 1 19  .45  20 22 23  .45  m  .  .14  29  .01  Total f o r June July 2 3 7 10 ... 1318 Aug.  1938  2.87  .03  Trace Trace Trace  5  .34  9  .17 .03 .10  '  ' .01 .04 •  10 - 11 12 13 16 17 21 22 24  .45 .01 .03 .59 .02  25  .39 .04 .01 .02  29  .78  30  Total f o r August Sept.  4 15  I.96 .02  .02  1.10  INFLUENCE OF PAPER MULCH ON PLANT GROWTH Every year with the advent of warm weather, one observes the almost phenomenal growth of the melon plants on the mulched paper p l o t s . With the s o i l temperature holding above 70 F., the melon plants on the mulch paper spring to l i f e as though the mulched s o i l contains a stimulant which i s l a c k i n g i n the unmulched. Not only do the mulched plants e s t a b l i s h themselves more r e a d i l y , but t h e i r e x t r a vigour throughout the season i s r e a d i l y apparent to the most casual observer. In 1937 preliminary observations were recorded concerning the e f f e c t of mulch paper on the root development of malm p l a n t s . Representative plants from the mulched and the unmulched areas, which i n the green c o n d i t i o n weighed 1360.8 and 283.5 gms. r e s p e c t i v e l y , were s e l e c t e d f o r study. The roots were exposed by digging a trench 2 f e e t deep at a radius of 18 inches from each p l a n t . Then by means of a s m a l l , slow stream of water, the roots were l a i d bare, gently separated from the s o i l and weighed, the mulched being 42 gms. and the unmulched 26.5 gms. Under the conditions p r e v a i l i n g at Saaniohton i n 1937 (and i n other years when observations were made), the main feeding roots of the mulched plant were found to be w i t h i n 1 inch of the surface of the s o i l , while those of the unmulched were 2 inches from the surface. Apart from p o s i t i o n and s i z e l i t t l e d i f f e r e n c e i n the character of the respective root systems was noted. In order to determine the approximate growth rate of the melons on the mulched and the unmulched areas, 5 t y p i c a l plants were selected i n each area i n 1937 and the l a t e r a l s measured at d e f i n i t e periods. The mean d a i l y growth r a t e , as determined over the 12-day period from J u l y 12 to J u l y 24, was 1.82 inches f o r the mulched p l a n t s , compared with .97 inches i n the case of the melon plants on the unmulched area. When the melon plants had a t t a i n e d t h e i r maximum growth which i n 1937 was on September 3 , representative leaves were taken from 5 t y p i c a l plants on each area, weighed and measured. The mean weight of each l e a f from the plants on the mulched area was 5•57 gms. compared with 4.08 gms. on the unmulched. The mean lengths of mid-rib per l e a f f o r the mulched and the unmulched plants were 4.05 and 3*15 inches r e s p e c t i v e l y , while the maximum diameters at r i g h t angles to the mid-rib were 5»32 and 4.30 inches.  In 1939 y i e l d s were taken from those melon plants growing on the mulched and the unmulched areas and from areas where the paper had been a r t i f i c i a l l y blackened. These r e s u l t s are presented i n table 11 and indicate that the blackened mulch gave an increase of approximately 33 per cent i n t o t a l number and also i n t o t a l weight of f r u i t s over the untreated paper, with 2.39 per cent increase i n number and 300 per cent increase i n weight over the unmulched. I n respect of green weight of tops, the blackened mulch gave an increase of 61 per cent over the untreated paper and a 400 per cent increase over the plants on the unmulched s o i l area.  Table 1 1 .  Summary of y i e l d s on mulched and unmulched areas,. 1939»  Number of Plants on Test  •  '  Mulched Area Blackened Normal  Unmulched  Yield Per Plant  Yiel d Per Plant  39  Yield Per Plant  70  29  5*5 8.1  3.8 5.6  1.6  4.2 3°3  3.5 3.1  1.1 .8  7.3 8.7  2.7 2.8  Marketable F r u i t s Number per plant Weight (lbs.) average  2.0  Unmarketable F r u i t s Number p e r plant Weight (lbs.) average Total Number per Fplant ~ " ' Weight (lbs.) average  7*1 9-1 11.6  Green Weight of Tops (lbs.)  2.9  i  u  1  1.8  (j Figure 6. Showing the effect of a r t i f i c i a l l y blackening the mulch paper ° on the green weight of tops and the number of cantaloupe f r u i t s per plant.  DISCUSSION A f t e r a 5-year study of mulch paper on a clay loam at Saanichton, r e s u l t s i n d i c a t e that the paper does d e f i n i t e l y stimulate growth, but the various f a c t o r s c o n t r i b u t i n g to t h i s increased growth have not been s p e c i f i c a l l y determined. The f i n d i n g s to date would i n d i c a t e that temperature and moisture may be the major f a c t o r s . With respect to b a c t e r i o l o g i c a l studies i t was f e l t that t o t a l counts would p o s s i b l y give a more comprehensive p i c t u r e r e l a t i v e to the a c t i v i t i e s of the s o i l organisms i n the breaking down and the e l a b o r a t i o n of plant food i n the s o i l , than might be a t t a i n e d by the d e t a i l e d study of the functions of any s p e c i f i c group. Total counts were therefore made f o r actinomyces, b a c t e r i a and f u n g i from mulched and unmulched s o i l s , but no consistent differences were recorded throughout the 5-year period of study. F e r r e t t i (5)> one of the few workers, who have attempted a q u a n t i t a t i v e study of the microorganisms under mulch paper, reported an increase i n bacte r i o l o g i c a l numbers due to paper. Unfortunately, however, h i s observations were based on only one month's findings and consequently do not show any seasonal trends. While plate counts are g e n e r a l l y considered to present only a part of the b i o l o g i c a l p i c t u r e e x i s t i n g i n any s o i l at a given time, yet as pointed out by Thornton (26,27) they have some value i n i n d i c a t i n g b a c t e r i a l a c t i v i t y . Taking the e v o l u t i o n of carbon dioxide as an index of b i o l o g i c a l a c t i v i t y , r e s p i r a t i o n chambers studies were conducted i n 1937 but here again no s i g n i f i c a n t difference i n a c t i v i t y was observed under laboratory conditions between the mulched and the unmulched s o i l s . 1  Tests for-Azotobacter, the aerobic nitrogen f i x i n g organism, were conducted on mulched and unmulched s o i l s i n 1957 and 1938» using Curie's mannite agar (3) but s i g n i f i c a n t differences were not observed. P h y s i o l o g i c a l and microscopic examinations i n d i c a t e d that Azotobacter chroococcum was a c t i v e under both s o i l conditions. Considering the increase i n a v a i l a b l e n i t r a t e s found g e n e r a l l y i n mulch paper s o i l s and the c o n s i s t e n t l y more vigorous, verdant growth of the p l a n t s , i t was rather to be expected that the n i t r o g e n - f i x i n g Azotobacter might be present i n greater q u a n t i t i e s under the paper, but a c t u a l colony counts f a i l e d to substantiate t h i s theory. To determine f u r t h e r the i n f l u e n c e of mulch paper on b a c t e r i a l a c t i v i t y , mulch paper was incorporated i n t o sodium caseinate agar i n varying concentrations and then seeded with  two aotinomyces c u l t u r e s . The e f f e c t of the paper on the metabolism of the s o i l organisms was measured by t h e i r a b i l i t y to break down the casein i n the media. Measurements over a 6-day period i n d i c a t e d that the paper had l i t t l e s i g n i f i c a n t e f f e c t on the a c t i v i t y of the two organisms i n question. The suggestion having been made that the paper might contain c e r t a i n growth promoting substances, barley seedlings i n c u l t u r e s o l u t i o n s were used to t e s t the influence of a mulch paper extract on plant growth. Measurements, of tops and roots were made, which i n d i c a t e d that the mulch paper extract had no s i g n i f i c a n t e f f e c t on plant growth. P e r i o d i c semi-quantitative determinations f o r a v a i l a b l e plant n u t r i e n t s (22) were made over a four-year period. I n 1935 end again i n 1937 the t e s t s i n d i c a t e d a d e f i n i t e increase i n n i t r a t e s i n the mulched s o i l s . I n 193&, however, the t e s t s i n d i c a t e d more n i t r a t e s under the unmulched conditions, and i n 1938 there was no marked difference between the mulched and unmulched s o i l s . This v a r i a t i o n i n n i t r a t e content from year to year i s not quite c l e a r , but may be due to the varying n i t r a t e requirements of the melon plants and t h e i r a b i l i t y to u t i l i z e the supply i n the s o i l . The melon plants ,!©n'." thVmuloke&\-plots made c o n s i s t e n t l y good growth under Saanichton c o n d i t i o n s , while the unmulched plants v a r i e d with season, and u s u a l l y , the poorer the growth, the more n i t r a t e s were found i n the s o i l . P o s s i b l y , as Magruder (15) found under Ohio conditions, the differences i n plant growth were due to other f a c t o r s than those of n i t r a t e s . Equipment d i d not permit o f more exacting q u a n t i t a t i v e tests being made on the n i t r a t e content of mulched and unmulched s o i l s . I t i s r e a l i z e d that these t e s t s gave only approximate values, s e r v i n g , i n the w r i t e r ' s opinion, t h e i r greatest usefulness i n demonstrating the presence of a v a i l a b l e nutrients at t h e i r extreme concentrations. From t h i s standpoint they are considered to be of some value f o r comparing two s o i l s with the same p h y s i c a l c h a r a c t e r i s t i c s , as they e x i s t e d under the conditions o u t l i n e d f o r t h i s experiment. No s i g n i f i c a n t differences were observed i n the r e l a t i v e amounts of phosphorus, potassium and calsium under mulched and unmulched conditions. A v a i l a b l e n u t r i e n t t e s t s were run on plant tissues ( 2 5 ) , care being taken to secure comparable portions of the melon plants from both the mulched and the unmulched areas. The unmulched plants gave a higher a v a i l a b l e n i t r a t e t e s t than d i d the plants from the mulched area, where the s o i l had been found  to contain more n i t r a t e s . The mulched plants definitelycontained more phosphorus than d i d the unmulched, which f a c t might e x p l a i n the e a r l i e r maturity that i s found generally with the mulched plants from year to year. Colorimetric determinations f o r hydrogen-ion concentrations were made p e r i o d i c a l l y on mulched and unmulched s o i l s , with l i t t l e difference being noted from year to year on these two areas. Both s o i l s h e l d c o n s i s t e n t l y around n e u t r a l i t y , ranging from b.8 to 7»4, with a mean pH reading of approxima t e l y 1 ml. The accuracy of these determinations, as w e l l as the method employed f o r c l e a r i n g cloudy s o i l solutions by the a d d i t i o n of barium sulphate (10) , was assured by p e r i o d i c checking with proven electrometric hydrogen-ion equipment. S o i l temperature studies at a 2-inch depth would indicate l i t t l e s i g n i f i c a n t d i f f e r e n c e between the mulched and the unmulched s o i l s , except i n May and June, at 8 A.M., 1 P.M. and 5 P.M., when the paper has been l e f t untreated and consequently subject to bleaching. When the paper, however, was treated to preserve the black colour, preliminary tests i n d i c a t e d that the mulch paper s o i l temperatures were approxima t e l y 2, 4 and 6° F. higher than the unmulched s o i l throughout the day. 1  A i r temperatures over the mulched paper (untreated) were c o n s i s t e n t l y higher than over the unmulched, both i n 1937 and i n 1938. Readings were taken 9 inches above ground l e v e l and showed an increase of approximately 2°F. This obviously was due to the use of mulch paper. Temperature and growth r e l a t i o n s are d i f f i c u l t to separate from other f a c t o r s , hence the heat requirement i s d i f f i c u l t to evaluate ( l b ) . One method of evaluating the temperature factor i s to e s t a b l i s h a plant zero base ( 4 ) , or that temperature below which development i s comparatively quiescent. E f f e c t i v e temperatures are computed from t h i s plant zero up, the assumpt i o n being that the effectiveness of temperature i n promoting growth i n p l a n t s , i s d i r e c t l y proportional to the number of degrees of e f f e c t i v e heat units above t h i s plant zero base. Erwin, Shepherd and Morgan i n Iowa (4) set the zero f o r muskmelons at 55° E. and used the summation method f o r evaluating the t o t a l e f f e c t i v e temperatures, with due conside r a t i o n being given to the sunshine f a c t o r . They found that the crops were matured under e f f e c t i v e temperatures ranging approximately between 2100 and 2400*° F. T h e i r f i n d i n g s indioated that the temperatures i n June had the greatest e f f e c t on time of maturity of any s i n g l e month and that temperatures i n J u l y had the l e a s t . The temperature records at Saanichton do not cover a 24-hour period, hence the t o t a l e f f e c t i v e  -21temperatures f o r the mulched and the unmulched areas cannot he compared with conditions holding i n Iowa. I t i s suggested at t h i s time, however, that herein may l i e one of the secrets of mulch paper s t i m u l a t i o n . In a d d i t i o n to i t s a b i l i t y to absorb more heat on the mulched area (when the paper i s b l a c k ) , the mulch paper also acts as a r e s e r v o i r f o r heat units over a 24-hour period, thus tending to create more optimum growth conditions f o r the plant throughout the season. P a r t i c u l a r l y would t h i s be e f f e c t i v e i n the c r i t i c a l month of June, when every degree of heat i s needed to give the newly set plant an early stimulus. Preliminary tests at Saanichton would i n d i c a t e that the colour of the paper plays an important part i n the heat units absorbed by the paper. F u r t h e r work now i n progress may i n d i c a t e that c e r t a i n coloured papers may m a t e r i a l l y e f f e c t the amount of heat absorbed by the s o i l under the paper ( 1 7 ) . Moisture determinations at Saanichton would i n d i c a t e that there i s a s i g n i f i c a n t difference i n moisture content between the mulched and the unmulched s o i l s . Moisture t e s t s from cropped and uncropped s o i l s showed that the paper d i d serve to conserve more moisture than d i d the uncovered s o i l . This surplus apparently was u t i l i z e d by the greater plant growth commonly found under the mulched conditions which sometimes gave a lower percentage than d i d the unmulched. I t i s suggested that mulch paper may have some e f f e c t on the s o i l moisture index, since L i n f o r d (12) has shown that more moisture i s absorbed by a s o i l stored under darkened conditions than one kept i n the l i g h t . Kalinovsky and Ivanova (11) found that i f peat, manure or straw were used f o r mulching purposes, a change was brought about i n the "climate" of the atmospheric l a y e r s adjacent to the s o i l , causing water to condense. At Saanichton, water of condensation c o l l e c t e d on the under side of the blackened paper, with a l e s s e r amount on the untreated paper. Preliminary root measurements of mulched and unmulched melon plants i n d i c a t e d l i t t l e difference i n the respective root systems. Leaf measurements i n d i c a t e d that the mean diameter of the leaves from the mulched plants was 1.02 inches greater than from the unmulched. F i s h e r (6) working with apple t r e e s , found that the s i z e of the f r u i t was increased by a l a r g e r l e a f area and found a p o s i t i v e c o r r e l a t i o n between s i z e of f r u i t and l e a f extent. This c o r r e l a t i o n has s t i l l to be proved f o r melons, but r e s u l t s at Saanichton would point i n t h i s d i r e c t i o n , as the f r u i t s from the mulched plants are i n v a r i a b l y l a r g e r than those from the unmulched.  Measurements were made at the height of the growing season, when the mean d a i l y growth rate f o r the mulched plants was found to be 1.82 inches, compared with .97 inches i n the case of the melon plants on the unmulched area. One-year t e s t s i n d i c a t e d that blackening the mulch paper with lamp black and l i n s e e d o i l m a t e r i a l l y increased the y i e l d of cantaloupes. The y i e l d s of f r u i t per plant from the blackened mulch, untreated mulch and unmulched areas were r e s p e c t i v e l y 1 1 . 6 , 8.7 and 2.9 pounds, i n d i c a t i n g that f o r the season of 1939, blackening the paper gave increased returns.  CONCLUSIONS Results with a black b u i l d i n g mulch paper on a clay loam s o i l at Saanichton were as f o l l o w s : (1) T o t a l p l a t e counts f o r actinomyces, b a c t e r i a and fungi i n d i c a t e that there i s l i t t l e s i g n i f i c a n t difference i n the mulched and the unmulched areas at depths varying from 2 to 6 inches. (2) B i o l o g i c a l a c t i v i t y , as measured by the e v o l u t i o n of carbon dioxide i n r e s p i r a t i o n chambers, showed no appreciable difference between the mulched and the unmulched s o i l s . (3) Nitrogen f i x a t i o n , as i n d i c a t e d by p l a t e counts on mannite agar f o r Azotobacter, the aerobic n i t r o g e n - f i x i n g organism, showed no s i g n i f i c a n t d i f f e r e n c e between the two areas i n question. (4) Laboratory tests i n d i c a t e d that macerated mulch paper i n concentrations of .75? 1.50 > 3»0 and 6 per cent r e s p e c t i v e l y , while s l i g h t l y i n f l u e n c i n g c e r t a i n microorganisms, had no apparent e f f e c t on barley seedlings when grown i n media containing t h i s m a t e r i a l . (5) A water soluble muloh paper extract i n concentrations of 1, 3 and 5 per cent r e s p e c t i v e l y , had no apparent e f f e c t on barley seedlings when grown i n a n u t r i e n t s o l u t i o n to which the e x t r a c t had been added. (b)  In some seasons mulch paper increased the quantity of  for^ll  (7)  s e a s o n s ^  t h Q  S o i 1  '  b  u  t  t h i s  E n d i n g d i d not hold  Mulch paper increased the s o i l temperatures s l i g h t l y i n  -23-  the month of June,but presumably due to subsequent bleaching, t h i s advantage was hot maintained over the unmulched area ^ unless the paper was a r t i f i c i a l l y blackened. (8) A i r temperatures were approximately 2 degrees Fahrenheit higher over the mulched area throughout the greater part of the growing season. (9) Blackening the paper i n the 1939 t e s t s increased s o i l temperatures to a maximum of 10 degrees Fahrenheit over the untreated paper and increased the y i e l d per plant by 33 per cent. (10) When the two uncropped areas were compared,it was found that the mulched p l o t s conserved 3•2% more moisture than d i d the unmulched p l o t s . (11) I t i s concluded that the b e t t e r growth and higher y i e l d s obtained with cantaloupes under mulch paper i s due to the cumulative e f f e c t of the paper i n conserving moisture and i n s t o r i n g heat with a r e s u l t a n t increase i n e f f e c t i v e heat u n i t s during the period of growth. BIBLIOGRAPHY (1) Bouyoucous,G.J.,1927»The hydrometer as a new and rapid method f o r determining the c o l l o i d a l oontent of s o i l s . S o i l S c i . 23:319-32. (2) Bronsart,H.von,1931. N i t r i f i c a t i o n i n s o i l s under paper mulch. Gartenbauwiss 4:233* (3) Curie,I.H.,1931* A method f o r the study of Azotobacter and i t s a p p l i c a t i o n to f e r t i l i t y p l o t s o i l s . S o i l S c i . 32:9-24. (4) Erwin,A.T.,Shepherd,G. and Morgan,N.D.,1938. Marketing Iowa cantaloupes. Bul.373»Agric.Exper.Sta.,Ames,Iowa. (5) F e r r e t t i , C . , 1 9 3 1 . S o i l covering and b a c t e r i a l a c t i v i t y . Mem.Lab.Pat.C.Batt.R.lst. Agrar.Pisa 3,no.51:26. (6) Fisher,D.V., 1934. Leaf area i n r e l a t i o n to f r u i t s i z e and t r e e growth. Sci.Agric.14:512-518. (7) F l i n t , L . H . , 1 9 2 8 . Crop plant s t i m u l a t i o n with paper mulch. Tech. B u i . 75. U.S.D.A. (8) Fred,E.B. and Waksman,S.A. ,1928.-  Laboratory Manual  of General Microbiology. New York.  McGraw-Hill Book Company, Inc.,  (9) Hartung, W. J . , 1926. The functions of paper mulch i n pineapple c u l t u r e . Hawaiian Pineapple Company, L t d . , Honolulu, Hawaii. (10) Hester, J . B., Blume, J . M. and Shelton, Florence A., 1937» Rapid chemical t e s t s f o r coastal p l a i n s o i l s . B u i . 95. V i r g i n i a Truck Exper. S t a . (11) Kalinovsky, P. and Ivanova, N. 1938. Mulching, one of the methods of Stakhanov a g r i c u l t u r a l p r a c t i c e s . Khim. S o t s t a l . Zemled. No. 1 2 : 6 3 - 9 . (12) L i n f o r d , L. B., 1926. R e l a t i o n of l i g h t to s o i l moisture phenomena. S o i l S c i . 22:233. (13) Macoun, I . T., 1930. Ottawa, Canada. '  Report of the Dom.  Horticulturist,  (14) Magistad, 0 . C., Farden, C. A. and Baldwin, W. A., 1935. Bagasse and paper mulches. J . Am. Soc. Agron. Ootober 1935• (15) Magruder, R., 1930. Paper mulch f o r the vegetable garden. Bui. 447« Ohio A g r i c . Exper. Sta. (16) M i l l e r , E. C., 1938. Plant Physiology. McGraw-Hill Book Company, Inc., New York. (17) M U S S Q , J . 0 . , 1932. P f l a n z . Dfing l i b : 3 6 1 - 7 3 -  A study of s o i l mulching.  Ztschr.  (18) S h i l o v a , E. I . , 1935Mulching i n r e l a t i o n to biochemical processes i n s o i l . Leningr. Univ. Uchen. Zap. 1:133"  68.  (19) Smith, A., 1931. E f f e c t of paper mulches on s o i l temperature, s o i l moisture and y i e l d s of o e r t a i n crops. H i l g a r d i a V o l . 6. (20) Smith, F. B., Brown, P. E. and M i l l a r , H. C., 1935. rhythmical nature of m i c r o b i o l o g i c a l a c t i v i t y i n s o i l as i n d i c a t e d by the e v o l u t i o n of C02.  The  (21) Smith, N. R., 1928. The i d e n t i f i c a t i o n of B. radiobaoter and i t s occurrence i n the s o i l . J . Bact. 15:20.  (22) Spurway, C. H., 1933. system of s o i l diagnosis. East Lansing, Michigan.  S o i l testing - a practical Tech. B u i . 132. A g r i c . Exper. Sta.  (23) Stewart, G. R., Thomas, E. G. and Horner, J . , 192b. Some e f f e c t s of mulching paper on Hawaiian s o i l s . S o i l S c i . 22:35-58.  (24) S t r a i g h t , E. M., 1929. Report of the Superintendent, Exper. S t a . Saanichton, Canada. (25) Thornton, S. F., Conner, S. D. and Eraser, R. R., 1934. The use of rapid chemical t e s t s on s o i l s and plants as aids i n determining f e r t i l i z e r needs. C i r . 204, A g r i c . Exper. S t a , Purdue Univ. (2b) Thornton, H. G. and Gray, P. H. H., 1930. The f l u c t u a t i o n of b a c t e r i a l numbers and n i t r a t e content of f i e l d s o i l s . Proc. Royal soc. Series B 106:399-417. (27)  Thornton, H. G., 1935«  Private  communication.  (28) Weaver, J . E. and Bruner, W. E., 1927. Root development of Vegetable Crops. McGraw-Hill Book Company, Inc., New York. (29) Yakovleva, V., 1933* Biochemical s o i l processes i n r e l a t i o n to mulching. Khim. S o t s i a l . Zemled. 6:24-30.  * ' ADDITIONAL REFERENCES TO BE READ WITH THE THESIS (1) Bryan, C. S., 1938. I d e n t i f i c a t i o n of Phtomonas, Azotobacter and Rhizobium o r Acbromobacter upon i n i t i a l i s o l a t i o n . S o i l S c i . 45:185. (2) Gamp, A. F., 1 9 3 0 . Mulch paper p r o j e c t . A g r i c . Exper. S t a . Rept. 1930:88-89.  Univ. F l o r i d a  (3) Clark, L. H., 1931* Farming under paper. Africa 5:557-8.  Farming i n South  (4) Gonn, H. J . , 1 9 1 7 * S o i l f l o r a studies. Tech. B u i . 60. N.Y. A g r i c . Exper. S t a .  V . Actinomyces.  (5) Conn, H. J . , 1918. Microscopic study of b a c t e r i a and f u n g i i n s o i l . Tech. B u i . 64. N.Y. A g r i c . Exper. S t a . (6) Conn, H. J . , 1 9 2 1 . The use of various culture media i n c h a r a c t e r i z i n g actinomyces. Tech. 83• N. Y. A g r i c . Exper. Sta. (7) Conn, H. J . , 1932. A microscopic study of c e r t a i n changes i n the m i c r o f l o r a of the s o i l , Tech. B u i . 204 N.Y, A g r i c . Exper. S t a . (8) Crouch, Mary, 1931. B a o t e r i o l o g y of mulched s o i l s . Sta. Saanichton, B. 0 . (unpublished)  Exper.  (9) C u t l e r , D. W. and B a l . D. ¥., 1926. Influence of protozoa on the process of n i t r o g e n - f i x a t i o n by Azotobacter chroococcum. Ann. Appl. B i o l . 13:516. (10) C u t l e r , D. W. and Crump, L. M., 1935« Problems i n S o i l Microbiology. Rothamstead Monograph on A g r i c u l t u r a l Science. 1935.  (11) F l i n t , L. H., 1929. Suggestions f o r paper mulch G i r . 7 7 . U.S.D.A. (12) F l i n t , L. H., 1935.  trials.  P r i v a t e communication.  (13) Hutchins, A. E., 1935• Mulch paper i n vegetable production. B u i . 2 9 8 . Univ. Minn. A g r i c . Exper. S t a . (14) Jones, L. H., 1931. The e f f e c t of decomposing paper on plant growth. Ann. Rept. 1930. Mass. A g r i c . Exper. Sta. B u i . 271.  (15) Keen, B. A. and R u s s e l l , E. J . , 1921. Factors determining s o i l temperature. J , A g r i c . S c i . 11:211. (16) Lochhead, A. G., 1 9 3 1 - 3 8 .  P r i v a t e communications.  (17) 'Lbchhead, A. G., 1937* Progress report of the Dom. Agric. B a c t e r i o l o g i s t , Ottawa, Canada. (18) Lochhead, A. G., and Taylor, C. B., 1938. Qualitative studies of s o i l micro-organisms. 1. General i n t r o d u c t i o n . 11. A survey of the b a c t e r i a l f l o r a of s o i l s d i f f e r i n g i n fertility. Canadian J . of Res. 16:152-73. 1  (19) Lyon, T. L. and Buckman, H. 0 . , 1937. The Nature and Properties of S o i l s . The MacMillan Company, New York. (20/ Magistad, 0 . C., 1935*  P r i v a t e communication.  (21) Raber, 0 . , 1929- P r i n c i p l e s of Plant Physiology. MacMillan Company, New York.  The  (22) Savage, 0 . G. , 1934. Paper mulches f o r pineapples. Gaz. N. S. Wales 45:335-36. (23) Society of American B a c t e r i o l o g i s t s , 1938. Methods f o r the pure Culture Study of B a c t e r i a .  Agric.  Manual of  (24) Starkey, R. L., 1938. Some influences of the development of higher plants upon the microorganisms i n the s o i l . V I . Microscopic examination of the rhizosphere. S o i l S c i . 45:207-4-9. (25) Thompson, H. C. and P l a t e n i u s , H., 1931. Results of paper mulch experiments with vegetable crops. Proc. Am. Soc. Hort. Sci.  28:305-308.  (26) Thornton, H. G. and Gray, P. H. H., 1934. The numbers of b a c t e r i a l c e l l s i n f i e l d s o i l s as estimated by the r a t i o method. Proc. Royal Soc. Series B 115:522-43. (27) Waksman, S. A., 1932. P r i n c i p l e s of S o i l Microbiology. The Williams and Wilkins Company, Baltimore. (28) Westover, K. C., and McCubbin, E. N., 1933. The influence of s o i l type on r e s u l t s from paper mulch t r i a l s with the pepper and egg plant. Amer. Soc. of Hort. S c i . 30-31-1933-34.  Influence of Paper Mulch on a Clay S o i l .  Photographic  Section.  Acknowledgement.  The writer wishes to aoknowledqethe appreciated assistance of Dr. P.A.Boving,Professor Emeritus, U n i v e r s i t y of B r i t i s h Columbia,for help with c e r t a i n of the black and white photographs and also of H.I.Edwards, Food Products Laboratory.Vancouver, B.C.,for neverf a i l i n g a i d i n the preparation of the natural colour photographs. r  '  - '  '•  '  • '  Figure 7. A n a t u r a l colour photograph of t u l i p s , t h i s crop being grown at Saanichton i n the melon r o t a t i o n .  Figure 9.Ploughing i n a green manure crop p r i o r to the p l a n t i n g of the melons.The 3 year r o t a t i o n followed Included t u l i p s and b r o c c o l i .  r  ^  Figure 10.Showing how the melon transplants were placed i n t o small t r i a n g u l a r openings i n the muloh paper. Two a d d i t i o n a l s t r i p s of paper were l a i d before the next row of melons were planted,which r e s u l t e d i n p l a n t i n g distances of b by 3 f e e t .  Figure 11.The ground was hand-raked before the paper was a p p l i e d , the lumps of earth and stones thus removed were then used to anchor the paper.  Figure 12.Hot caps were used to advantage as a p r o t e c t i o n against unfavourable weather changes i n 1937.Air and s o i l thermometers can also be seen i n the foreground.  Figure 13.A t y p i c a l melon plant growing on mulch paper. This covering apparently supplies the necessary heat stimulus needed by the young plants i n the c r i t i c a l month of June.  Figure 14. A t y p i c a l melon plant growing on the unmulched s o i l area and planted at the same time as the mulched plant shown i n Figure 13*  Figure 15. I l l u s t r a t i n g the comparative growth of the melon plants growing on the mulched and the unmulched s o i l areas i n 1935.  Figure 1 6 . I l l u s t r a t i n g the comparative vigour of the melon plants on the mulched and the unmulched s o i l areas i n 1937.  Figure 1 7 . P a r t i a l roojfc system of a melon plant grown on mulch paper.  Figure 1 8 . P a r t i a l root system of a melon plant grown on the unmulched s o i l area.Apart from the f a c t that the paper tended to bring the roots c l o s e t to the surface, there was l i t t l e s i g n i f i c a n t d i f f e r e n c e between the root systems of the plants grown on the two areas.  Figure 19* Type of r e s p i r a t i o n chamber used to measure the evolution of carbon dioxide from mulched and unmulched s o i l s . L i t t l e s i g n i f i c a n t difference was apparent between these two areas,at l e a s t as measured by the apparatus here i l l u s t r a t e d .  Figure 20. Colonies of actinomyces as they appeared on sodium asparaginate medium,plated from s o i l obtained from the mulch paper area.Plate counts extending over 3 year p e r i o d , would i n d i c a t e l i t t l e s i g n i f i c a n t d i f f e r e n c e i n t o t a l numbers of actinomyces, bacteria o fungi between the mulched and the unmulched s o i l areas  Figure 21.Colonies of actinomyces plated from unmulched soil.  Figure 22. Colonies of b a c t e r i a l and actinomyces) plated from mulched s o i l . Note the c l e a r areas around c e r t a i n c o l o n i e s . i n d i c a t i n g the a b i l i t y of the organism to break down the casein i n the medium.This p r o t e i n - s p l i t t i n g action was used to advantage to measure the d i r e c t e f f e c t of mulch paper on b i o l o g i c a l a c t i v i t y ( s e e Table 3 ) .  Figure 23« Colonies of bacteria plated from the unmulched s o i l area.  F i g u r e 24. Azotobacter c o l o n i e s from mulched appearing on C u r i e ' s mannite agar medium.  soil  F i g u r e 23.Azotobacter c o l o n i e s from unmulched s o i l . P h y s i o l o g i c a l t e s t s i n d i c a t e d these to be s i m i l a r to those i s o l a t e d from the mulched s o i l , b o t h apparently belonging to the s p e c i e s A z o t o b a c t e r chrooooocum.  F i g u r e 26. Showing the contact e f f e c t of mulch paper on a s o i l o r g a n i s m , i n d i c a t i n g that the paper had no i n h i b i t o r y e f f e c t on the growth of the aotinomyces i n q u e s t i o n .  

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