772 PRINCIPLES OF SOIL MICROBIOLOGY 



4. Reaction and buffer content of the soil. The decomposition of available 

 nitrogenous substances (in the liquid part of the urine) leading to the forma- 

 tion of ammonia and nitric acid, on the one hand, and the decomposition of the 

 carbohydrates which may lead to formation of some organic acids, on the other, 

 are important in this connection. The buffering properties of the residual 

 "humus" are considerable. 



5. The introduction of large quantities of readily available energy, as well 

 as of nitrogen and minerals, will in itself greatly stimulate bacterial activities. 



6. Finally the introduction of large quantities of living bacteria in the manure 

 may result in a change of the qualitative composition of the soil flora and fauna. 



A number of observations have been made concerning the increase 

 in the numbers of bacteria in the soil as a result of addition of manure. 

 The number of bacteria present in the soil was found 13 to depend not 

 only upon the manure added but also upon the cultural methods and 

 crop grown. Fallowing of a soil leads to a decrease in numbers of 

 bacteria as compared with the untreated soil, while manuring and 

 fallowing lead to a decided increase. 14 Chester 15 stated in 1898 that 

 "the greater the organic matter or humus in the soil the greater, pari 

 passu, is the number of bacteria." 



The increase in bacterial numbers in the soil as a result of the addi- 

 tion of stable manure has been explained as due to the introduction of 

 large numbers of bacteria with the manure; or due to the introduction 

 of readily decomposable organic matter which stimulates bacterial 

 activities. The fertilizing effect of the manure, aside from the quanti- 

 ties of fertilizer constituents contained within them, was believed to 

 be due merely to the bacterial content of the manure. 16 ' 17 Frequent 

 small applications of manure rather than large applications made at 

 longer intervals were, therefore, recommended. The bacteria intro- 

 duced into the soil, with small quantities of manure, were believed 18 

 to be valuable in bringing about a more rapid decomposition of a green 

 manure crop. 



13 Caron, A. Landwirtschaftlich-Bakteriologische Probleme. Landw. Vers. 

 Sta., 45: 401-418. 1895. 



14 Hiltner and Stunner, 1903 (p. 12). 



16 Chester, F. D. Soil bacteria and their relation to agriculture. Del. Agr. 

 Exp. Sta. Bui. 40. 1898; The microbiological analysis of soils. Ibid. Bui. 65, 

 1904. 



16 Hellstrom, P. On the effect of animal manures on marsh soils. (Exp. 

 Sta. Rec, 11: 627. 1900.) 



17 Stoklasa, J. Uber die Wirkung des Stallmistes. Chem. Centrbl. Jahrg., 

 78: (N. F. 11): 1702. 1907; also Stoklasa and Ernest, 1905 (p. 34). 



18 Lipman, J. G., McLean, H. C, et al. The influence of mechanical composi- 

 tion of the soil on the availability of nitrate of soda and dried blood. N. J. 

 Agr. Exp. Sta. Bui. 268. 1914. 



