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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 M A S T E R 0 -F. S C I E N C E in AGRICULTURE IN 'THE DEPARTMENT OF AGRONOMY FACULTY OF AGRICULTURE The University of B r i t i s h Columbia 1940 ACKNOWLEDGMENTS-. The writer wishes to thank Mr. 1. M. Straight, Superintendent, Experimental Station, Saanichton, B. C., f o r enthusiastic co-operation at a l l times while t h i s investigation was i n progress; Dr. D. G. La i r d , Professor of Agronomy f o r many help f u l suggestions i n planning the experiments and i n the preparation and arrangement of this thesis; 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 trans-l a t i o n of certain German, I t a l i a n and Russian a r t i c l e s , and the writer p a r t i c u l a r l y wishes to thank a l l his friends for t h e i r f a i t h and encouragement, without which this thesis might never have been completed. TABLE OF CONTENTS INTRODUCTION REVIEW OF LITERATURE EXPERIMENTAL CHARACTER OF CANTALOUPE •: PROCEDURE S o i l and Climatic Conditions S o i l Sampling and P l a t i n g BIOLOGICAL STUDIES Total Plate Counts Azotobacter Tests Direct Influence of Mulch Paper on 1 B a c t e r i a l A c t i v i t y 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 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 cover-ing was made in 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 vigorously on the mulched than on the unmulched area. The Hawaiian Pineapple Company made t r i a l plant-ings with mulch paper i l l 191? and so effective did the paper prove i n con t r o l l i n g weeds and stimulating 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 variety of crops under varying climatic conditions. With few exceptions, the results from numerous world sources indicate increased crop yields of higher c u a l i t y and e a r l i e r maturity follow-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 Station 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 lo v i n g ones,have given increased yields 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 with specialized crops such f o r instance as the cantaloupe. Many research workers have concerned themselves with the effects of paper mulch and while not i n entire agreement, t h e i r general conclusions appear to be that the paper conserves moisture, raises s o i l temperature and increases the retention or elaboration of available 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 physioal changes occurring in 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 actor or factors or combination of same responsible f o r the b e n e f i c i a l effects noted. REVIEW OF LITERATURE The effect of muloh paper on s o i l temperature has been investigated by many workers, the majority of whom report an increase following 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 early part of the season, but exerted l i t t l e or no effect during the summer months. Hartung, (9) , conducting extensive tests 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 raise s o i l temperatures, and this he offered as an explanation f o r the observed i n -crease i n size 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 temper-ature fluctuations. 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 single f a c t o r i n increasing the y i e l d of early 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 positive was the effeot on s o i l moisture, s o i l temperature and crop y i e l d . He also found that black papers raised the s o i l temperatures, where-as grey papers reduced them. In Hawaii, Stewart, Thomas and Horner (23) recorded temperature differences 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 different coloured papers to bring about what he termed desirabletemperature changes f o r s p e c i f i c crops. Contrary to the findings 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 retard the warming of the s o i l to midday, but which would encourage warmth from this 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 difference, which he concluded to be b e n e f i c i a l to plant growth. After four seasons' work at Rosslyn, V i r g i n i a , with 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 lay 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 permitting 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 available 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 effects 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 difference 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 previously been achieved i n general practice 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 consistently higher under paper than that found i n the un-mulched s o i l area. Shilova (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 nitrates 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 differences 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 large 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 micro-organisms i n the s o i l . His determinations were made at depths of 5 > 15 and 35 cm. and the differences 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 respectively 1.70, .10 and .35 mgs. He concluded that the increase i n nitrates 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 leaching i n the unmulched area. Using samples of laboratory-cultured 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 influence on nitrogen-fixation. 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, result-ing i n a more rapid l i b e r a t i o n of plant food, especially n i t r a t e s . Stewart, Thomas and Horner (23) reported that a greater quantity of n i t r a t e s was consistently found under muloh paper, which, to these workers, seemed to indicate a more rapid elaboration of the p r i n c i p a l plant nutrients. Hartung (9) found that mulch paper stimulated n i t r i f i c a t i o n , thereby enhancing the available nitrogen content of the s o i l . Yakovleva (29) basing his 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 . Shilova (18) found that mulch paper increased the accumulation of n i t r a t e nitrogen, as well as bringing about the more complete u t i l i z -ation of the n i t r a t e nitrogen by the plant. 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 nitrogen. EXPERIMENTAL CHARACTER OF THE CANTALOUPE The plant selected f o r the mulch paper study was the cantaloupe, Cucumis melo, the variety chosen being Hale's Best, a netted melon of medium size and excellent q u a l i t y . Being native to Asia and A f r i c a , the cantaloupe i s more or less s p e c i f i c i n i t s heat requirements and generally takes unkindly to the cool nights and the moderate summer day temperatures oommonly experienced at Saanichton. I t i s de f i n i t e l y a heat loving plant and can not be said to be naturally adapted to conditions on Vancouver Island. Tests at Saanichton indicate that success with the crop i s only attained when due oare i s given to date of planting, judicious choice of s o i l and exposure factors and the creation of suitable environmental conditions through the use of mulch paper, with or without hot caps. A study of the root system of the cantaloupe (28) gives some indication of i t s food requirements and i t s habit of growth. I t has a root system consisting of a very extensive shallow portion and a poorly developed deeper part. The l a t e r a l root system of a cantaloupe plant may have a spread of 10 to 12 feet, most of t h i s being found i n the top foot of s o i l . Being a rapidly growing crop under optimum conditions, i t requires an abundance of nutrients and usually 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 indicate a r e l a t i v e l y high percentage of calcium, which may possibly explain why canta-loupes appear to do best i n a s o i l with an hydrogen-ion concentration around the neutral point. 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 in a 3-year rotation following broccoli and preceding t u l i p s . The area devoted to each crop was approximately . 2 0 acres. Immediately upon setting 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 trod 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 building paper impregnated with asphalt. Each r o l l contained 400 square feet, was 30 inches wide and weighed 25 pounds. The experiments reported at t h i s time oovered four years' work, 1935 to 1938 i n c l u s i v e , with some additional observations being made i n 1939' S o i l and Climatic 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 result the s o i l had a pH of 7.0. Barnyard and green manures are regularly applied f o r the other crops i n the rotation, the practice usually followed being to apply the manure immediately p r i o r to planting the bro c c o l i . Upon harvesting t h i s crop the land i s seeded to a green manure crop which i s turned under pr i o r to the planting 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, July and August (the main growing months) are respectively 39$ 63 and 62° F. The hours of sunshine f o r the 3 months are respectively 269, 324 and 293 hours, or approximately 900 hours of sunshine between the time of planting the cantaloupes, (May 24) and the time of harvesting at the end of August or early i n September. As temperature records are not available cover-ing a 24-hour period, the t o t a l effective temperature required to carry the cantaloupe plants through the vegetative and reproductive phases, under Saanichton conditions, 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, July and August over a 26-year period, has been computed respectively at 1 .11, .6b and .73 inches per month; the mean yearly 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 Pl 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 following 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 plant. In 1935? 193^ 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 . In 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. In order to make conditions -as comparable as possible on both the mulched and the un-mulched s o i l areas, a l l samples were taken at moisture l e v e l . This eliminated 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 laboratory, where the contents of each j a r was carefully emptied on to a sheet of s t e r i l i z e d paper, quickly mixed and again placed i n the o r i g i n a l container. From this j a r samples of s o i l were taken f o r bacteriological counts and moisture tests. These determinations were made without undue delay a f t e r bringing the samples i n from the f i e l d . The s o i l s used f o r the available nutrient 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 per-sistent attention to a l l the details whereby contamination might be eliminated from the time of sampling to the pouring of the plates. Control plates were always poured to guard against contamination which' might interfere with the f i n a l results. Dilutions 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 dilutions used f o r plating varied as follows: Actinomyces and bacteria, 1 :100 Thousand or 1:1 M i l l i o n ; and for fungi, dil u t i o n s varied from 1:10 Thousand to 1 :100 Thousand, depending on seasonal v a r i a t i o n . The media used throughout was that as outlined by Fred and Waksman (8) and was as follows: Actinomyces — Sodium Asparaginate Glycerol Agar (M33) Bacteria — Sodium Caseinate or Nutrose Agar (M4) Fungi — Peptons-Gluoose Acid Medium (Ml8) In 1935 plate counts were made fo r radiobacter i n the ••H fit +3 » P*-P © O Q OS o H -P O OS •p o -P O O O -JO LT\ oo o o OO ir\ ix\co O O O O o © o H o o ON o o o o o OS CO o o o o CO o -J3 <tf o o o o CM OJ LCNCM o o CO\Q o o o o NNC— o o o o CVJ -J3 l£\CM o o ur\0 H O O O O OJ OJ at o H H O O O O H H o o o o o o CO ON »\ o o o o K\ CM ° o O o O o o O o O o CM OJ •H M +» 0 e •-o +» K\ o o ON cj as HHf£| vO I • O • -P o "4 o o o o CO NN. r—I OJ o o o o C—O ITs ON H O O o o O H OJ LT\ O O o o CO ON o o o ©•. GNH C—ON o o o o *. H HI O O o o ON-* o o o o O NN. CM O O o o ONC~-O CO H 64 <lH O: CVJ-© © o o 3 n a Ha © © o S3 -C3 © ON © •i o OJ © o CO © o HA H .3 r-i HA © o f» >» a •3 5 H H S >» 0 3 © © o o o cooo o o o o ON O o o o o s0 o C-NQ o o C—urv o o o o CO *£> o o o o OO K\ o o .000 o o o o cvi ur\ CM K\ O O o o OJ -Q ON +» » © o Q 03 •P: o 5 s. .O o. o o "O o o o O OJ o o o o O O O O CM X> S3 00 CO H CM OO o o OJ Os H ft © -O & 4 N\ O 1 as a 1 Hi H C ! O O *4 o o o § O O o o c—c-CVJ H H o o o o C-OJ rf\sO H H O O 00 o o o o OJ CM o o o o •I as •P 3 s o i l , the medium used i n this instance "being Glyoerol-nitrate Agar (21) . The two dilutions 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 Total Plate Counts• Total numbers of actinomyces, bacteria, radiobaoter and fungi were determined i n mulched and unmulched s o i l s at approximately two-week intervals throughout the summer months over a three-year period. Marked variation i n plate counts, even greater than had been anticipated,was observed, hence even the s i x to twelve replications 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 July 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 differences between numbers of actinomyces, bacteria, radiobaoter and fungi 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 table 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 micro-organisms 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 , add-i t i o n a l information as to the general conditions for 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 sprinkle 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 particles and were i d e n t i f i e d as Azotobacter. The profusion of growth on the plates made accurate counting impossible, hence the s o i l inoculum was reduced from one gram to 0 . 5 gms. following the i n i t i a l tests. These plates 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 differences i n Azotobacter numbers under the paper mulch as compared with the unmulched s o i l . Table. 2. Azotobacter counts (ia^frofusaiKte/per gram of drv 1938. Mulched Area Unmulched Area Cropped Uncropped Cropped Uncropped A p r i l 16 3 3 May 23 38 44 . June 23 12 8 4 lb J u l y 12 10 8 . 2 ' 9 August 3 2 2 2 • ^ 5 August 13 10 .3 - <i J? 6 August 30 ' 2 .1 .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 possibly to the consistent use of only 0 . 3 gms. of s o i l sprinkled over the mannite medium. The colonies were s u f f i c i e n t l y well differentiated to permit of closer observation and study. The summary of a l l counts made from A p r i l to August (1938) 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 plates. Here again no s i g n i f i c a n t difference i n numbers of Azotobacter was apparent between the mulched and the unmulched s o i l areas. The highest mean Azotobacter count for the season was found on the unmulched, uncropped plots which were l e f t uncultivated, except that given f o r weed control, with the mulched, cropped area being s l i g h t l y higher than the unmulched, cropped plot s . Direct Influence of Mulch Paper on Bacterial A c t i v i t y . As coal t a r products are sometimes used i n the making of the building paper commonly used f o r mulching purposes, i t was suggested that t h i s paper might oontain certain growth promoting substances. On giving consideration to the p o s s i b i l i t y of these being effective under f i e l d conditions, i t was assumed that they must be water soluble. Mulch paper was aooordingly macerated with warm water and incorporated into sodium caseinate agar i n varying concentrations. Plates prepared with this medium were seeded with giant colonies of two different protein s p l i t t i n g actinomyoes. The influence of the paper mulch was determined by measuring the digested casein ring appearing as clear areas around each individual oolony i n the muloh paper plates as compared with controls. Measurements were made over a 6-day period at approximately the same time each morning. Plates replicated b and 12 times f o r mulch paper and oontrols respectively were prepared and incubated at 28° C. The averages of these replications and results with the varying concentrations of paper used are presented i n Table 3 . A study of t h i s table wi11 indicate that the mulch paper, at the concentrations specified, had varying effects 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 this point digestion of the casein decreased with increasing concentration. On the other hand, wi th Ul-G, stimulation i s noted at a l l concentrations up to b per cent with the maximum occurring at 3 per cent. Slides were pre-pared from each of the muloh paper concent rations and from the checks. Microscopic examination did not indicate any variation i n c e l l structure or, staining properties from the various plates, i n either the Ml-1 or Ul-C series. The (G.otft.aclfe effect of mulch paper on s o i l organisms was also observed i n the following manner: Washed sand was dried 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 this sand medium and ster-i l i z e d i n the autoclave. Each plate was then seeded with 30 co of a water suspension of the 2 organisms, Ml - 1 and Ul-C, which had been grown on sodium caseinate agar and brought to optimum moisture oontent through addition of water. S t e r i l i z e d mulch paper discs, the same diameter as the plates, 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 for 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 con-cerned. On l i f t i n g up the mulch paper discs, 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, indicating the entire absence of toxic material i n the paper, at least i n respect to the two organisms studied. Table 3°. Direct influence of mulch paper on bacterial a c t i v i t y as measured by casein digestion. Organisms Studied Ml-1 » tt ii ii Ul-G tr w it ti Concentration Days When Observations Made, of Medium Measurements i n Millimeters. 1 2 3 4 3 6 check . 8 10 13 ,15 ' 20 2 4 • 75 % 6 9 1 0 1 4 21 2 4 1 .50 % 7 1 0 1 4 .. 1 7 23 2 6 3 V 6 7 8 12 1-6- 17 6 % # # 6 9 1 4 i 1 7 check 6 10 13 16 2 0 23 . 7 5 % • 7 16. 1 8 2 i 22 23 1 . 5 0 % 6 1 0 12 15 1 8 2 4 3 % 6 22 26 29 32 3 3 6 % ' 7 1 3 17 2 1 2 4 - 26. # : No indication of protein s p l i t t i n g evidenced; co growth only„ Carbon Dioxide Production. The evolution of carbon dioxide i s often used as a. measure of biological a c t i v i t y i n a s o i l (20) and f o r com-parative purposes at le 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 , respiration 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 tins 6 .3 inches high with an inside diameter of 4 .3 inches. The inside 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 joints 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 inside the chamber. The procedure adopted f o r the respiration chamber studies was as follows: 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. Aliquots of barium hydroxide (.IN) were drawn off 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 controls. 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 accord-ingly 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 this 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. In selecting 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 tissue which might interfere 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 did not indicate any si g n i f i c a n t difference i n bac 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 1933"38 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 for available nutrients ( 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 . Available nutrient tests and hydrogen-ion determin-ations. 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 25 .5 5 175 5 Unmulched 25 .5 5 175 5 -June 22 Mulched 25 • 5 5 175 & 7.5 Unmulched 8 .25 5 175 6 7-5 J u l y 22 Mulched 25 . 5 0 5 175 6 7c2 Unmulched 25 • 25 5 175 ; 2 7.2 September 3 Mulched 25 . 50 5 175 6 Unmul ohed 5 , 2 5 5 175 3 -1931 • May 20 Mulched 1" 15 .50 8 125 7.2 Unmulched 1" 15 . 50 8 125 - •7e2 June 4 Mulched 1" 50 .50 8 150 7 .1 ti 4« 25 .50 8 150 — . 7.1 Unmulched 1" 10 .50 8 150 - 7.0 July 8 Mulched 1" 25 . 75 5 175 7 .0 25 . 7 5 5 175 - 7 .4 Unmulched 1" 3 .75 5 175 7 .1 » 4 « 8 .75 5 175 - 7e2 July 30 Mulched 1" 25 . 5 0 5 175 7*1 ii 411 8 .50 5 175 - 7.2 Unmulched 1" 8 . 50 4 175 7.1 3 . 2 5 4 175 - 7.1 August 9 Mulched 1" 25 .50 8 175 7.1 n 411 w- . 5 0 8 175 - -7*1 Unmulched 1" 20 „50 8 175 7.1 it 4»i 10 .75 8 175 - 7.1 August 31 Mulched 1" 40 .50 5 175 7.2 11 41J 8 .50 5 175 — b .8 Unmulched 1" 3 .50 5 175 7-2 «» 411 8 . 5 0 5 175 b .8 September 13 Mulched 1" rt 411 Unmulched 1" it 4» • 1 9 3 8 Mulched 2 " , Unmulched 3" A p r i l 1 6 Mulched Unmulched May 23 Mulched Unmulched June 23 Mulched-cropped tr uncropped Unmulch ed-c ropp e d " uncropped J u l y 1 2 Mulched-cropped " uncropped Unmul ch e d-c ro p p e d " uncropped Aug. 3 Mulched-cropped n uncropped Unmulched-cropped • " uncropped Aug. 13 Mulched-cropped " uncropped Unmulche d-c roppe d M uncropped Aug. 30 Mulched™cropped n uncropped Unmul c h e d-c ro p pe d " uncropped Nitrate J L Ca Mg pH 30 .30 3 173 - 7.2 13 .50 3 173 7-1 10: .30 5 173 7.4 10 .30 3 173 - 7.4 2 .50 3 173 7 7.2 2 .30 5 173 7 7.2 3 .30 3 173 7 7«2 2 . 3 0 3 173 7 7.2 23 .30 5 200 7 7.2 23 • 30 3 200 7 7.0 20 .30 3 200 7 7.1 .20 .30 5 200 7 6 . 8 25 .30 3 200 7 7.2 23 .30 7 200- 7 7.2 23 ••• .30 3 200 7 7.2 23 .30 3 200 7 7.2 23 ' .30 3 200 7 7.2 23 .30 3 200 7- 7.2 13 1 . 7 200 7 7»2 13 1 . 7 200 7 7.1 33 .30 3 200 7 7.1 30 ; .30 3 200 7 •7.0 30 • 1 . 3 200 7 6.9 30 '.I*- ' 3 200 7 6.9 30 .30 3 200 7 7 .0 40 .50 3 200 7 6 . 9 33 .30 3 200 7 6.9 33 . 3 0 3 200 7 7.0 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 dried, then l i g h t l y pulverized i n a mortar before measuring out the sample f o r analysis. Nutrient tests over a 4-month period i n 1 9 3 3 indicated a s l i g h t increase i n the concentration of available nitrates 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, indicated more nitrates at a l l depths, from the unmulched s o i l areas. In 1 9 3 7 the nitrat 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 difference between the two areas. One possible explanation for this variation i n n i t r a t e content i n the mulched and unmulched s o i l s from year to year might be that the melon plants varied 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 Island. Comparatively cold, 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 plots, which did not have the benefit of the extra heat units supplied by the paper as did those on the mulched plots. 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 es 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 better melon year, the plants on the unmulched plots were able to make good growth, thereby u t i l i z i n g more. of the s o i l n i t r a t e s . Due to the better 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 bacteria, thus ultimately giving 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 -ation i n the available nutrients, other than n i t r a t e s , i n the mulched and the unmulched s o i l s either 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 early spring, as were also the n i t r a t e s . Under Saanichton conditions at lea s t , the available nitrates were leached away by the winter rains, and generally 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 bi 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 colorimetrie method. The accuracy of this procedure was -12-Available nutrient tests on mulched and unmulched melon plant tissues ^ 1937* Nitrates Phosphorus Potassium August 3 Mulched Unmulched August 13 Mulched Unmulched High Very high High High High Deficient to medium High Low High Medium to high Low High September 4 Mulched Unmulched Medium to high Very high Very high High . Very high Very high September 20 Mulched Unmul ch ed Low Very high Very high High Very high Very high checked against a standard potentiometer apparatus and found to be satisfactory. Barium sulphate (10) was found very useful i n clearing the s o i l solution and tests indicated that i t s use did not materially effect the accuracy of the readings. As Table 4 w i l l indicate, 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 fluctuating s l i g h t l y from month to month. Available nutrient tests were run on mulched and unmulched plant tissues i n 1937> employing the Thornton pro-cedure ( 2 3 ) . Terminable growth material was used f o r this purpose, as i t was considered to be the most suitable. The outstanding finding i n these tests was the extra supply of nitrates i n the unmulched plants and the higher phosphorus content i n the case of mulched melon plants. PHYSICAL STUDIES. S o i l Temperature. S o i l temperatures were recorded throughout the growing season of 1937 and 1 9 3 8 . Readings were taken three times daily on both mulched and unmulched s o i l s . During 1937 thes<= readings were taken at 1 M and An depths, while at only a 2" depth i n 1 9 3 8 . 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 in each instance. In order to f a c i l i t a t e comparisons between the mulched and the unmulched conditions, the da 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 for recording the a i r temperatures were wall thermometers mounted on a stout stake. A l l instruments, before being set i n pos 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 difference i n s o i l temperatures between the mulched and the unmulched s o i l areas either i n 1 9 3 7 or i n 1 9 3 8 . The data does suggest, however, that s l i g h t l y higher temperatures do prevai l under the paper during the early 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. Consistently 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 . Mulched Area 1" 4" A i r May 17 -23 May 24-31 June 1-10 June 14-21 June 22-30 July 2-9 July 10-17 July 19-24 Ju l y 26-31 Aug. 2-9 Aug. 10-17 Time 8 A.M. 37.7 1 P.M. 68.1 3 P.M. 69.4 8 A.M. 60.4 1 P.M. 71.1 3 P.M. 74.6 8 A.M. 66.4 1 P.M. 81.1 3 P.M. 82.8 8 A.M. 6 2 . 6 1 P.M. 6 8 . 3 P.M. ' 6 8 . 6 8 A.M. 6 3 . 3 1 P.M. 7 7 . 3 3 P.M. 7 7 . 3 8 A.M. 6 9 . 6 1 P.M. 83.9 3 P.M. 8 3 . 8 8 A.M. 71.4 1 P.M. 84. 3 P.M. 8 3 . 7 8 A.M. 69.7 1 P.M. 82 .8 3 P.M. 8 3 . 8 A.M. 68.7 1 P.M. 79.6 3 P.M. 80 .6 8 A.M« bb.7 1 P.M. 78. 3 P.M. 77 .6 8 A.M. 64.2 1 P.M. 74.2 3 P.M. 74. 3 b . 3 6 3 . 4 b3.4 61. 67 .6 6 8 . 1 6 b . 3 7 4 . 9 7 3 . 7 6 2 . 4 37 .4 66.1 b 2 . 7 67-7 3 9 . 6 63-3 6 4 . 9 7 2 . 2 71 .7 7 4 . 4 71.7 6 8 . ' 6 6 , 4 77 .9 7 3 . 4 8 2 . 2 7 3 . 0 7 0 . 4 71 .3 7 9 . 4 7 6 . 6 8 2 . 77.2 6 9 . 2 b9.3 80.3 79 .7 8 4 . 6 82* 6 9 . 6 6 . 8 77 .6 7 3 . 79- 7 3 . 8 6b. 0 6 . 7 7 b . 4 7 3 . 7 8 . 7 3 . 6 63.4 64 .3 7 2 . 7 2 . 8 74. 7 3 . 2 Unmulched Area 1" 4" A i r 3 b . 3 b . 4 6 8 . 1 6 3 . 69.6 6 1 . 4 60 b 0 . 3 71 .3 6 6 . 4 7 4 . 1 67 . 67.4 6 3 . 7 7 9 . 1 73.2 8 1 . 3 7 4 . 3 62. 61.6 3 7 . 6 8 . 4 66.9 6 1 . 3 6 8 . b 8 . 3 3 8 . 8 b 4 . 7 - b 3 . 63*4 7 8 . 1 7 4 . 6 7 0 . 6 77.2 7 6 . 1 70.6 6 8 . 1 6 7 . 7 6 3 . 8 3 . 9 8 0 . 6 7 4 . 1 8 7 . 8 5 . 2 7 3 . 7 7 4 . " 7 1 . 4 7 0 . 3 8 7 - 7 8 2 . 7 7 3 . 6 8 6 . 8 8 3 . 2 77 .2 7 2 . 3 7 0 . 7 6 8 . 9 0 . 2 8 4 . 8 7 8 . 8 87-8 8 8 . 2 80.6 7 1 . 3 7 0 . 8 6 3 . 8 3 . 0 8 2 . 0 7 2 . 8 3 . 4 8 2 . 6 7 2 . 68 .4 6 8 . 2 6 3 . 1 8 2 . 1 80. 7 3 . 3 8 1 . 3 8 2 . 3 7 3 . 4 6 5 . 8 6 b . 61.3 7 8 . 7 7 7 . 7 7 0 . 7 7 8 . 7 8 . 7 71.2 Time Mulched Area 1" 41* A i r Unmulched Area 1" 4" A i r Aug, 18-24 8 A.M. 64. 64.5 65.8 1 P.M. 7 3 . 70.2 71.8 5 P . M . 71 .7 7 1 . 8 71.2 Aug. 25-31 8 A . M . 0 O . 3 61. 59.2 1 P.M. 6 8 . 3 6 7 . 68.2 5 P.M. 6 8 . 3 6?.5 6 7 . Sept. 1-8 8 A . M . 61.2 62. 62 .7 1 P.M. 72.2 70.2 74.5 5 P.M. 7 1 . 72.7 71-7 Sept. 10.-25 8 63- • 63.4 o4.6 1 P.M. 73.2 71 .8 7 8 . 5 P.M. 72.6 74.8 76.4 66.2 6 5 . 8 62. 75-7 75 .3 68.5 7 5 . 2 76 . 6 8 . 8 60.8 60.8 5 6 . 3 71 .3 7 0 . 5 6 5 . 8 71 .7 7 2 . 3 64. 62. 62. 59*3 75 .2 75-7 7 2 . 7 4 . 7 7 5 . 7 69-7 6 3 . 6 6 3 . 6 77-8 7 7 . 6 7 8 . 4 62. 75. 7 9 . 2 7 4 . Table 6. Summary of thermometer readings on mulched and unmulched cropped areas at Saanichton i n 1 9 3 8 . Mulched Area Unmulched Area May 28 -- June 3 Time 7.30 A.M. 1 P.M. 5 P.M. S o i l 2" 65.4 8 1 . 6 8 2 . 6 June 4 -• 13 7 .30 1 5 A.M. P.M. P.M. 69.1 8 4 . 8 4 . 3 June 14 - 20 7 .30 1 5 A.M. P.M. P.M. 67.1 7 8 . 3 7 9 . 4 June 21 - 27 7 . 3 0 1 5 A.M. P.M. P.M. 8 8 . 1 June 28 - July 4 7.30 1 5 A.M. P.M. P.M. 6 7 . 7 8 0 . 1 8 0 . 7 July 5 - 12 7.30 1 5 A.M. P.M. P.M. 6 6 . 3 8 2 . 8 4 . A i r S o i l 2" 5 9 . 64. 6 9 . 6 8 1 . 3 69-7 82.5 63-1 67.1 7 0 . 3 81 .5 70. 8 2 . 5 59,7 66-. 4 6 8 . 4 7 8 . 4 69. 79-5 65 7 0 . 9 7 3 . 7 8 6 . 9 7 5 . b 8 9 . 3 5 9 . 3 6 7 . 4 b7.4 8 1 . 67.4 81 .4 6 3 . 3 6 7 . 7 0 . 5 8 4 . 3 7 0 . 1 8 4 . 1 A i r 5 8 . 7 69.5 69.1 6 2 . 1 7 0 . 3 70.4 5 9 . 6 8 . 67.7 64 7 2 . 7 75.2 5 8 . 1 6 0 . 6 7 . 3 61.4 7 0 . 6 9 . 3 Time July 13 - 19 7 .30 A.M. 1 P.M. 3 P.M. July 20 - 27 7*50 A.M. 1 P.M. 5 P.M. July 28 - August 4 7*30 A.M. 1 P.M. 5 P.M. August 5 - 1 2 7 .30 A.M. 1 P.M. 5; : P.M. August 13 - 20 7 .30 A.M. 1 P.M. •' 5 P.M. August 22 - 29 7.3O A.M. 1 P.M. 5 P.M. Aug. 30 - Sept. 7 7 .30 A.M. 1 P.M. 5 P.M. September 8 - 15 7.30 A.M. 1 P.M. 5 P.M. Mulched Area Unmul ched Area S o i l 2" Ills 9 1 . 1 A i r b 8 . 1 7 9 . 82 .7 S o i l 2" .72.7 8 9 . 6 91,9 "• A i r 68.1 78 .3 79.1 7 0 . 6 84.1 8 6 . 6 6 5 . I 76 .9 76 .6 71 .7 84 .1 84 .1 62 .7 74.4 75 .6 6 6 . 3 80.4 83.5 • '6i-.lV-6 8 . 3 71 .3 67 .7 80 .1 8 1 . 3 58.4 •66.5' 6 9 . 3 6 3 . I 77 .1 77 .5 58..9 6 6 . 4 6 8 . 3 b3.6 77.3 ^ 76 .8 5 6 . 4 64.9 65.8 64 .3 74.1 76.6 57.4 67 .1 67. 62.8 73.8 73 .8 5 5 . 3 63.5 64.4 63. 74.4 7b.9 5 6 . 9 : 68 .1 69 .5 62.4 74.3 75 .3 56.4 67 .7 6 7 . 9 6 1 . 3 6 8 . 9 7 0 . 5 53 .9 64. 63 .6 6 1 . 3 6 9 . 4 70 .5 51 .3 61.9 60 .6 60.7 "71.1 7 2 . 3 5 5 . 4 57.3 6 6 . 3 60.1 71 .5 71-. 3 .-54 .3 65.5 64 .6 Table ,7> Summary of thermometer readings on mulched and unmulched,uncropped areas at Saanichton i n 1 9 3 8 . May 2 8 - June 3 June 4 - 1 3 June 14 - 2 0 June 2 1 - 2 7 June 2 8 - July 4 July 3 - 1 2 J u l y 1 3 - 1 9 July 2 0 - 2 7 July 2 8 - August 4 August 3 - 1 2 August 13 - 20 August 2 2 - 2 9 Time 7• 30 A.M. 1 P.M. 5 P.M. 7.30 A.M. 1 P.M. 5 P.M. 7.30 A.M. 1 P.M. 3 P.M. 7 .30 A.M. 1 P.M. 5 P.M. 7.30 A.M. 1 P.M. 3 P.M. 7»30 A.M. 1 - P.M. 5 P.M. 7.30 A.M. 1 P.M. 5 P.M. 7 .30 A.M. 1 P.M. 5 P.M. 7 . 3 0 A.M. 1 P.M. 3 P.M. 7 . 3 0 A.M. 1 P.M. 5 P.M. 7 .30 A.M. 1 P.M. 5 P.M. 7.30 A.M. 1 P.M. 5 P.M. Mulched S o i l 2" 65. 9.1 1. ~TTr 5 9 . 7 0 . 7 7 0 . 7 6 8 . 7 6 3 . 5 82.4 72 .3 8 2 . 5 71 .1 66*9 60.4 77 .9 6 9 . 3 7 8 . 3 6 9 . 3 8 1.1 5 . 8 6 . 6 3 . 6 7 5 . 4 77-3 6 8 . 3 60.7 79.4 6 8 . 9 7 8 . 9 6 8 . 9 6 6 . 7 6 3 . 5 8 1 . 7 7 3 . 81.4 72 .5 2 . 1 7 . 4 8 7 . 1 1 . 2 . 1 8 4 . 0 . 9 6 7 . 2 .9 7 9 . 8 3 . 9 7 9 . 6 7 . 7 6 3 . 9 8 0 . 1 71 .9 8 1 . 5 7 4 . 3 6 6 . 7 7 . 3 7 6 8 . 7 8 . 5 9 . 8 62. 8. 64.4 60. 76.4 7 0 . 3 77 .8 7 0 . 62.9 60.1 7b.4 67 .9 77-4 7 2 . 4 Unmulched b o i l 2" 64.9 80.6 8 1 . 1 . 7 7 . 5 8 9 . 6 6 8 . 3 8 1 . 4 8 I . 9 6 8 . 1 85.7 8 6 . 3 7 3 * 3 9 0 . 2 9 3 . 1 7 3 . 6 . 1 8 . 4 6 9 . 1 8 2 . 4 8 5 . 2 6 7 . 7 8 O . 3 8 1 . 64.4 9 . 3 1. 64.1 8 0 . 3 8 3 * 9 A i r 5 8 . 6 9 , 1 6 9 . 6 7 . 7 61.9 8 1 . 7 69.4 8 2 . 3 69.I 67.4 39.4 7 8 . 3 6 8 . 7 9 . 9 6 8 . 1 6 3 . 1 7 4 . 1 7 6 . 3 58o9 6 7 . 7 6 8 . 3 6 3 . 5 72 . 71 .4 6 8 . 3 8 2 . 3 8 4 . 3 64.7 78.9 7 9 . 7 60 .9 7 2 . 7 7 4 . 3 5 8 . 7 6 8 . 6 6 9 . 5 6 8 . 7 6 9 . 2 57.6 7 0 . 7 72.9 Mulched Time S o i l 2 " Aug. 3 0 - Sept. 7 7 . 3 0 A.M. 61.1 1 P.M. 7 1 . 1 5 P.M. 7 1 . 8 September 8 - 1 5 7 . 3 0 A.M. 61.4 1 P.M. 7 4 . 1 5 P.M. 7 2 . 1 A i r 5 7 - 9 6 8 . 5 6 8 . 5 61 .8 72. 6 9 . Unmulched S o i l 2 " A i r 6 2 . 3 5 3 . 6 7 2 . 9 66. 7 4 . 5 6 5 . 6 6 2 . 5 6 . 4 7 7 - 7 0 . 7 7 8 . 1 6 8 . 1 Table 8 . Summary of thermometer readings on blackened untreated, mulched and unmulched areas. Mulched Areas Unmulched Blackened Normal June 20 - 2 8 7 . 3 0 A.M. 1 P.M=. 5 P.M. 66.2 8 0 . 8 3 . 3 6 4 . 6 7 6 . 7 7 8 . 5 6 2 . 6 7 3 . 7 7 6 . 7 June 29 - July 7 7 . 3 O A.M. 1 KM-'. 5 P.M. 6 6 . 5 7 6 . 9 81.0 6 4 . 1 7 2 . 6 7 5 - 3 6 3 . 1 72.2 7 5 . July 1 1 - 1 9 7.30 A.M. 1 P.M. 5 P.M. 6 7 . 8 8 2 . 1 • 8 2 . 6 6 5 . - 7 6 . 5 7 5 . 9 64. 7 6 . 8 7 7 . 1 July 2 0 - 2 8 7 . 3 0 A.M. 1 P.M. 5 P.M. 7 2 . 3 • 9U1 95.2 6 9 . 5 8 4 . 1 86.2 6 9 . 3 84.2 8 8 . 4 July 3 1 - August 8 7 . 3 0 A.M. 1 P.M. 5 P.M. 7 0 . 7 8 4 . 5 8 7 . 7 6 8 . 5 8 3 . 8 5 . 2 llf 8 7 . 3 Daily Mean: June 2 0 - August 8 79.2 7 5 . 7 4 . 9 7 July 7 August8 Figure 3,Showing the effect 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. -14-and 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 indicate a s l i g h t increase i n s o i l temperatures i n early 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 this was not c l e a r l y understood u n t i l 1939, when 2 areas 13 by 30 feet were blackened with lamp black and linseed o i l and temperature readings taken, these being compared with 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 proportional to the temp-erature ; the maximum difference occurring i n July 27 at 5 P.M. when the normal mulch registered 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 explain the lower s o i l temperatures recorded on the mulched areas aft e r the l a t t e r part of June, as indicated i n Tables 5 and 6 . As the mulch pap er bleaches, the heat i s reflected rather than absorbed, with a consequent loss 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 bact e r i o l o g i c a l tests 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 centi-grade , u n t i l a constant weight was reached. In 1937 and i n 1938, periodic moisture tests were made from May to September f o r c a p i l l a r y moisture; i n 1937 these tests 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 indicated 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. Capillary 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 feet, this being deemed large enough to provide uniform conditions of humidity; i t was kept at a l l times i n a shaded portion of the laboratory, away from any direct sunlight. 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 plots , 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 plots f o r the same year, i n fact the unmulched cropped plots show an average of 0 . 5 % higher moisture content. This i s undoubt-edly due to the higher moisture requirements of the larger plants and higher y i e l d occurring under mulched conditions. A study of the data on the cropped areas for 1 9 3 7 reveals no difference i n moisture content i n s o i l s of the mulched and unmulched plots f o r the reasons given above. Upon referring to the r a i n f a l l data i n Table 1 0 one finds an explanation f o r the higher moisture content i n the unmulched s o i l as observed i n the data for 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 (H 2 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 CO K\ ON H © ft ft O m o CO K\ ON H ON H © o ~) CM © .a = O CM I © O E i—I CM 3 © & s O CM © O © O H .3 © s •H En ON ON ON CM CO c-ON o H ON « CO ON o ON NO o ON CO o. ON OJ K\ o NO' CM NO C— » } » © e-ITS o C— <* ON ITS NO NO H o • 0 1 © 0 UN CO H X\ -o O H CO CO ON NO o ON CM © O H ON H ON NO -O K\ H © NO o OJ CO NO NO CM » e 8 » • e-8 OJ NO CO H, H ON KY u\ 1 O NO » ® o ® « K\ r4 r-NO NO ON • H H ON ON e © I © © ® c— ND H CO -r4 NO NO O CM 1 CO N© • © '» . © Lf\ NO o 1—f Lf\ * « o (X\ o H © ON » cd ' e •P w ft © © CO S ^ i S'zn* 0 1 1 1? 8! 1 d a t a r e l a t i v e *° moisture determinations f o r 1 9 3 7 - 3 0 period. May 2 7 June 9 13 . i f 1 5 16 :•: 1 ': 1 1 9 20 22 23 2 9 July 2 3 7 10 ... 13-18 Aug. 5 9 10 - 11 12 13 16 17 21 22 24 2 5 29 3 0 Sept. 4 1 5 Total f o r June 19.3*7 . 0 2 inches .04 .41 . 0 2 . O b . 0 2 . 9 1 " . 2 8 ' : .. . 0 7 .45 . 4 5 m . .14 . 0 1 1938 2 . 8 7 Trace Trace Trace . 3 4 ' ' .01 .04 • .39 .04 .01 .02 . 7 8 Total f o r August I . 9 6 . 0 2 inches .61 . 0 3 . 1 7 . 0 3 . 1 0 . 4 5 . 0 1 . 0 3 . 5 9 . 0 2 1.10 . 0 2 .02 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 plots. 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 lacking i n the unmulched. Not only do the mulched plants establish themselves more readily, but t h e i r extra vigour throughout the season i s readily apparent to the most casual observer. In 1937 preliminary observations were recorded concern-ing the effect of mulch paper on the root development of malm plants. Representative plants from the mulched and the unmulched areas, which i n the green condition weighed 1360.8 and 283.5 gms. respectively, were selected f o r study. The roots were exposed by digging a trench 2 feet deep at a radius of 18 inches from each plant. Then by means of a small, 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 prevailing 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 within 1 inch of the surface of the s o i l , while those of the unmulched were 2 inches from the surface. Apart from position and size l i t t l e difference 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 typical plants were selected i n each area i n 1937 and the l a t e r a l s measured at defi n i t e periods. The mean d a i l y growth rate, as determined over the 12-day period from July 12 to July 24, was 1.82 inches for the mulched plants, compared with .97 inches i n the case of the melon plants on the unmulched area. When the melon plants had attained 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 leaf 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 lea f f o r the mulched and the unmulched plants were 4.05 and 3*15 inches respectively, while the maximum diameters at right angles to the mid-rib were 5»32 and 4.30 inches. In 1939 yields were taken from those melon plants grow-ing 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 results 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. In 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 11 . Summary of yields on mulched and unmulched areas,. 1939» • ' Mulched Area Blackened Normal Number of Plants on Test Marketable F r u i t s Y i e l d Per Plant 39 Number per plant 5*5 Weight (lbs.) average 8.1 Unmarketable F r u i t s Number per plant 4.2 Weight (lbs.) average 3°3 Total Number per plant 9-1 ~ F i u " 1 ' 7 * 1 Weight (lbs.) average 11.6 Yiel d Per Plant 70 3.8 5.6 3.5 3.1 7.3 8.7 Unmulched Y i e l d Per Plant 29 1 . 6 2.0 1.1 .8 2.7 2.8 Green Weight of Tops (lbs.) 2.9 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 fruits per plant. DISCUSSION Af t e r a 5-year study of mulch paper on a clay loam at Saanichton, results indicate that the paper does d e f i n i t e l y stimulate growth, but the various factors contributing to t h i s increased growth have not been s p e c i f i c a l l y determined. The findings to date would indicate that temperature and moisture may be the major factors. With respect to bacteriological studies i t was f e l t that t o t a l counts would possibly give a more comprehensive picture relative to the a c t i v i t i e s of the s o i l organisms i n the break-ing down and the elaboration of plant food i n the s o i l , than might be attained by the detailed study of the functions of any s p e c i f i c group. Total counts were therefore made f o r actinomyces, bacteria and fungi 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 quantitative study of the micro-organisms under mulch paper, reported an increase i n bact-e r i o l o g i c a l numbers due to paper. Unfortunately, however, his observations were based on only one month's findings and consequently do not show any seasonal trends. While plate counts are generally considered to present only a part of the b i o l o g i c a l picture 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 indicating b a c t e r i a l a c t i v i t y . Taking the evolution 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 , respiration chambers studies were conducted i n 19371 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 . 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. Physiological and microscopic examinations indicated that Azotobacter chroococcum was active under both s o i l conditions. Considering the increase i n available nitrates found generally i n mulch paper s o i l s and the consistently more vigorous, verdant growth of the plants, i t was rather to be expected that the nitrogen-fixing Azotobacter might be present i n greater quantities under the paper, but actual colony counts f a i l e d to substantiate this theory. To determine further the influence of mulch paper on ba c t e r i a l a c t i v i t y , mulch paper was incorporated into sodium caseinate agar i n varying concentrations and then seeded with two aotinomyces cultures. The effect 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 indicated that the paper had l i t t l e s i g n i f i c a n t effect on the a c t i v i t y of the two organisms in question. The suggestion having been made that the paper might contain certain growth promoting substances, barley seedlings i n culture solutions were used to test the influence of a mulch paper extract on plant growth. Measurements, of tops and roots were made, which indicated that the mulch paper extract had no sign i f i c a n t effect on plant growth. Periodic semi-quantitative determinations f o r available plant nutrients (22) were made over a four-year period. In 1935 end again i n 1937 the tests indicated a de f i n i t e increase i n nitrates i n the mulched s o i l s . In 193&, however, the tests indicated more nitrates under the unmulched conditions, and i n 1938 there was no marked difference between the mulched and unmulched s o i l s . This vari a t i o n i n n i t r a t e content from year to year i s not quite clear, 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 consistently good growth under Saanichton conditions, while the unmulched plants varied with season, and usually, the poorer the growth, the more nitrates were found i n the s o i l . Possibly, as Magruder (15) found under Ohio conditions, the differences in plant growth were due to other factors than those of n i t r a t e s . Equipment did not permit of more exacting quantitative 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 realized that these tests gave only approximate values, serving, i n the writer's opinion, t h e i r greatest usefulness i n demonstrating the presence of available nutrients at t h e i r extreme concentrations. From this stand-point they are considered to be of some value f o r comparing two s o i l s with the same physical c h a r a c t e r i s t i c s , as they existed under the conditions outlined for this experiment. No s i g n i f i c a n t differences were observed i n the relative amounts of phosphorus, potassium and calsium under mulched and unmulched conditions. Available nutrient tests were run on plant tissues (25) , 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 available n i t r a t e test than did 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 definitely-contained more phosphorus than did the unmulched, which fact might explain 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 pe 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 held consistently around ne u t r a l i t y , ranging from b .8 to 7»4, with a mean pH reading of approxim-ately 1 ml. The accuracy of these determinations, as well as the method employed f o r clearing cloudy s o i l solutions by the addition of barium sulphate (10) , was assured by periodic 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 difference 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 indicated that the mulch paper s o i l temperatures were approxim-ately 2, 4 and 6° F. higher than the unmulched s o i l throughout the day. A i r temperatures over the1 mulched paper (untreated) were consistently 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 relations are d i f f i c u l t to separate from other factors, 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 establish a plant zero base (4), or that temperature below which development i s comparatively quiescent. Effective temperatures are computed from t h i s plant zero up, the assump-tio n being that the effectiveness of temperature i n promoting growth i n plants, i s d i r e c t l y proportional to the number of degrees of effective heat units above this 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 effective temperatures, with due consid-eration being given to the sunshine factor. They found that the crops were matured under effective temperatures ranging approximately between 2100 and 2400*° F. Their findings indioated that the temperatures i n June had the greatest effect on time of maturity of any single 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 effective -21-temperatures f o r the mulched and the unmulched areas cannot he compared with conditions holding i n Iowa. I t i s suggested at this time, however, that herein may l i e one of the secrets of mulch paper stimulation. In addition to i t s a b i l i t y to absorb more heat on the mulched area (when the paper i s black), the mulch paper also acts as a reservoir f o r heat units over a 24-hour period, thus tending to create more optimum growth conditions for the plant throughout the season. P a r t i c u l a r l y would this be effective 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 indicate that the colour of the paper plays an important part i n the heat units absorbed by the paper. Further work now i n progress may indicate that certain coloured papers may materially effect the amount of heat absorbed by the s o i l under the paper ( 1 7 ) . Moisture determinations at Saanichton would indicate that there i s a sig 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 tests from cropped and uncropped s o i l s showed that the paper did serve to conserve more moisture than did 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 some-times gave a lower percentage than did the unmulched. It i s suggested that mulch paper may have some effect on the s o i l moisture index, since Linford (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 mulch-ing purposes, a change was brought about i n the "climate" of the atmospheric layers adjacent to the s o i l , causing water to condense. At Saanichton, water of condensation collected 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 indicated l i t t l e difference i n the respective root systems. Leaf measurements indicated that the mean diameter of the leaves from the mulched plants was 1.02 inches greater than from the unmulched. Fisher (6) working with apple trees, found that the s i z e of the f r u i t was increased by a larger l e a f area and found a positive correlation between size of f r u i t and le a f extent. This correlation has s t i l l to be proved f o r melons, but results at Saanichton would point in th i s direction, as the f r u i t s from the mulched plants are invariably larger than those from the unmulched. Measurements were made at the height of the growing season, when the mean daily growth rate for 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 tests indicated that blackening the mulch paper with lamp black and linseed o i l materially increased the y i e l d of cantaloupes. The yields of f r u i t per plant from the blackened mulch, untreated mulch and unmulched areas were respectively 11 .6, 8.7 and 2.9 pounds, indicating that f o r the season of 1939, blackening the paper gave increased returns. CONCLUSIONS Results with a black building mulch paper on a clay loam s o i l at Saanichton were as follows: (1) Total plate counts f o r actinomyces, bacteria and fungi indicate 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 evolution of carbon dioxide i n respiration 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 indicated by plate counts on mannite agar f o r Azotobacter, the aerobic nitrogen-fixing organism, showed no si g n i f i c a n t difference between the two areas i n question. (4) Laboratory tests indicated that macerated mulch paper i n concentrations of .75? 1.50 > 3»0 and 6 per cent respectively, while s l i g h t l y influencing certain microorganisms, had no apparent effect on barley seedlings when grown i n media containing this material. (5) A water soluble muloh paper extract i n concentrations of 1, 3 and 5 per cent respectively, had no apparent effect on barley seedlings when grown i n a nutrient solution to which the extract had been added. (b) In some seasons mulch paper increased the quantity of f o r ^ l l s e a s o n s ^ t h Q S o i 1 ' b u t t h i s Ending did not hold (7) Mulch paper increased the s o i l temperatures s l i g h t l y i n - 2 3 -the month of June,but presumably due to subsequent bleaching, this 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 tests 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 plots conserved 3•2% more moisture than did the unmulched plots. (11) I t i s concluded that the better growth and higher yields obtained with cantaloupes under mulch paper i s due to the cumulative effect of the paper i n conserving moisture and i n storing heat with a resultant increase i n effective heat units 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 application to f e r t i l i t y plot 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) Ferretti,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 size and tree growth. Sci.Agric.14:512-518. (7) Flint,L.H. , 1 9 2 8 . Crop plant stimulation with paper mulch. Tech. Bui. 75 . U.S.D.A. (8) Fred,E.B. and Waksman,S.A. ,1928.- Laboratory Manual of General Microbiology. McGraw-Hill Book Company, Inc., New York. (9) Hartung, W. J . , 1926. The functions of paper mulch i n pineapple culture. Hawaiian Pineapple Company, Ltd., Honolulu, Hawaii. (10) Hester, J . B., Blume, J . M. and Shelton, Florence A., 1937» Rapid chemical tests f or coastal p l a i n s o i l s . Bui. 95. V i r g i n i a Truck Exper. Sta. (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 practices. Khim. So t s t a l . Zemled. No. 12 : 6 3 - 9 . (12) Linford, L. B., 1926. Relation 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. Report of the Dom. H o r t i c u l t u r i s t , Ottawa, Canada. ' (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 Agric. 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. A study of s o i l mulching. Ztschr. Pflanz. Dfing lib:361-7 3 -(18) Shilova, E. I . , 1935- Mulching i n r e l a t i o n to bio-chemical processes i n s o i l . Leningr. Univ. Uchen. Zap. 1:133" 68. (19) Smith, A., 1931. Effect of paper mulches on s o i l temperature, s o i l moisture and yields of oertain crops. Hilgardia Vol. 6. (20) Smith, F. B., Brown, P. E. and M i l l a r , H. C., 1935. The rhythmical nature of microbiological a c t i v i t y i n s o i l as indicated by the evolution of C02. (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. S o i l testing - a p r a c t i c a l system of s o i l diagnosis. Tech. Bui. 132. Agric. Exper. Sta. East Lansing, Michigan. (23) Stewart, G. R., Thomas, E. G. and Horner, J . , 192b. Some effects of mulching paper on Hawaiian s o i l s . S o i l S c i . 22:35-58. (24) Straight, E. M., 1929. Report of the Superintendent, Exper. Sta. Saanichton, Canada. (25) Thornton, S. F., Conner, S. D. and Eraser, R. R., 1934. The use of rapid chemical tests 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, Agric. Exper. Sta, Purdue Univ. (2b) Thornton, H. G. and Gray, P. H. H., 1930. The fluctuation of bacterial 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 re 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 or 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., 1930. Mulch paper project. Univ. Florida Agric. Exper. Sta. Rept. 1930:88-89. (3) Clark, L. H., 1931* Farming under paper. Farming i n South A f r i c a 5 : 5 5 7 -8 . (4) Gonn, H. J . , 1 9 1 7 * S o i l f l o r a studies. V . Actinomyces. Tech. Bui. 60. N.Y. Agric. Exper. Sta. (5) Conn, H. J . , 1918. Microscopic study of bacteria and fungi i n s o i l . Tech. Bui. 64. N.Y. Agric. Exper. Sta. (6) Conn, H. J . , 1921. The use of various culture media i n characterizing actinomyces. Tech. 83• N. Y. Agric. Exper. Sta. (7) Conn, H. J . , 1932. A microscopic study of certain changes i n the microflora of the s o i l , Tech. Bui. 204 N.Y, Agric. Exper. Sta. (8) Crouch, Mary, 1931. Baoteriology of mulched soils. Exper. Sta. Saanichton, B. 0 . (unpublished) (9) Cutler, D. W. and Bal. D. ¥., 1926. Influence of protozoa on the process of nitrogen-fixation by Azotobacter chroococcum. Ann. Appl. B i o l . 13:516. (10) Cutler, 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. 1 9 3 5 . (11) F l i n t , L. H., 1929. Suggestions f o r paper mulch t r i a l s . G i r . 77. U.S.D.A. (12) F l i n t , L. H., 1935. Private communication. (13) Hutchins, A. E., 1935• Mulch paper i n vegetable production. Bui. 298. Univ. Minn. Agric. Exper. Sta. (14) Jones, L. H., 1931. The effect of decomposing paper on plant growth. Ann. Rept. 1930. Mass. Agric. Exper. Sta. Bui. 271. (15) Keen, B. A. and Russell, E. J . , 1921. Factors determining s o i l temperature. J , Agric. S c i . 11:211. (16) Lochhead, A. G., 1 9 3 1 - 3 8 . Private 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 introduction. 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 f e r t i l i t y . 1 Canadian J . of Res. 16:152-73. (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* Private communication. (21) Raber, 0 . , 1929- Principles of Plant Physiology. The MacMillan Company, New York. (22) Savage, 0 . G. , 1934. Paper mulches f o r pineapples. Agric. Gaz. N. S. Wales 45:335-36. (23) Society of American Bacte r i o l o g i s t s , 1938. Manual of Methods f o r the pure Culture Study of Bacteria. (24) Starkey, R. L., 1938. Some influences of the development of higher plants upon the microorganisms i n the s o i l . VI. Micro-scopic examination of the rhizosphere. S o i l S c i . 45:207-4-9. (25) Thompson, H. C. and Platenius, H., 1931. Results of paper mulch experiments with vegetable crops. Proc. Am. Soc. Hort. S c i . 28:305-308. (26) Thornton, H. G. and Gray, P. H. H., 1934. The numbers of bacterial 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 results 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, University of B r i t i s h Columbia,for help with certain of the black and white photographs and also of H.I.Edwards, Food Products Laboratory.Vancouver, B.C.,for never-f a i l i n g aid in the preparation of the natural colour photographs. r ' - ' ' • ' • ' Figure 7. A natural colour photograph of t u l i p s , t h i s crop being grown at Saanichton i n the melon rotation. Figure 9.Ploughing i n a green manure crop p r i o r to the planting of the melons.The 3 year rotation 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 into small triangular openings i n the muloh paper. Two additional s t r i p s of paper were l a i d before the next row of melons were planted,which resulted i n planting distances of b by 3 feet. Figure 11.The ground was hand-raked before the paper was applied, 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 protection 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 17.Partial 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 fact that the paper tended to bring the roots closet to the surface, there was l i t t l e s i g n i f i c a n t difference between the root systems of the plants grown on the two areas. Figure 19* Type of respiration 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 least 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 period, would indicate l i t t l e s i g n i f i c a n t difference 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 s o i l . Figure 22. Colonies of bacterial and actinomyces) plated from mulched s o i l . Note the clear areas around certain colonies.indicating 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 direct effect of mulch paper on b i o l o g i c a l activity(see Table 3). Figure 23« Colonies of bacteria plated from the unmulched s o i l area. Figure 24. Azotobacter colonies from mulched s o i l appearing on Curie's mannite agar medium. Figure 23.Azotobacter colonies from unmulched s o i l . Physiological tests indicated these to be similar to those isolated from the mulched soil,both apparently belonging to the species Azotobacter chrooooocum. Figure 26. Showing the contact effect of mulch paper on a s o i l organism,indicating that the paper had no inhibitory effect on the growth of the aotinomyces in question. 

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