770 PRINCIPLES OF SOIL MICROBIOLOGY 



may take place as a result of addition of celluloses to the soil. However, 

 the true cellulose-decomposing bacteria are usually not determined, 

 since they do not develop (as Spirochaeta cytophaga) on the ordinary 

 plate. The actual increase in bacterial numbers resulting from addition 

 of celluloses, as shown by the ordinary plate, may be a result of develop- 

 ment of bacteria feeding upon synthesized or intermediary products, 

 which result from the activities of fungi and aerobic cellulose decom- 

 posing bacteria. Under anaerobic conditions, however, it is the bacteria 

 which are greatly stimulated by the addition of celluloses. Pure cellu- 

 lose may even depress the development of bacteria which develop on the 

 ordinary plate. 5 Straw, however, stimulates the development of bac- 

 teria due to the presence of soluble carbohydrates and proteins. 



The stimulative effect of proteins upon the development of spore- 

 forming and non-spore forming bacteria has been recorded by a number 

 of observers. Urea stimulates the development of various bacteria, 

 especially certain non-spore forming rods. 



Natural organic matter, like straw, plant stubble and green manures, 

 as well as stable manures or organic fertilizers, consist of a number of 

 various substances. The addition of this organic matter to the soil 

 will stimulate the development of various groups of organisms. 6 The 

 greater the protein content of the organic materials added to the soil, 

 the greater is the development of bacteria in preference to the fungi, 

 as shown in table 86. 



It has been shown elsewhere (p. 517) that the addition of organic 

 matter of a wide carbon-nitrogen ratio to the soil leads to a considerable 

 reduction of the nitrate nitrogen, which results in a harmful effect 

 upon plant growth. However, the following year a beneficial effect 

 may be noted, 7 due to the subsequent decomposition of the synthesized 

 protoplasm. In some cases it has been claimed 8 that the depressing 

 effect of a straw mulch upon nitrate formation in the soil is due to 

 the checked evaporation of the soil moisture which lowers the tempera- 



5 Hill, H. H. The effect of green manuring on soil nitrates under greenhouse 

 conditions. Va. Polyt. Inst. Agr. Exp. Sta. Tech. Bui. 6, 121-153. 1915. 



6 Waksman, S. A., and Starkey, R. L. Influence of organic matter upon the 

 development of fungi, actinomycetes and bacteria in the soil. Soil Sci., 17: 

 373-378. 1924. 



7 Bredemann, G. Untersuchungen liber das Bakterien-Impfpraparat "Heyls 

 concentrated nitrogen producer" (Composite Farmogerm). Landw. Jahrb., 

 43: 669-G94. 1913. 



8 Albrecht, W. A., and Uhland, R. E. Nitrate accumulation under the straw 

 mulch. Soil Sci., 20: 253-268. 1925. 



