PRINCIPLES OF SOIL MICROBIOLOGY 



adding a small amount of a certain organic substance (usually 1 per 

 cent) rich in nitrogen, such as hoof meal, cottonseed meal, dried blood, 

 or a pure protein, such as casein, to 100 grams of fresh soil, placing the 

 mixture in a tumbler in the presence of sufficient water and incubating 

 for 7 to 10 days; the ammonia formed is then determined. Even 

 with this method, the differences obtained between the formation 

 of ammonia in different soils were found 45 to be due to a number of 

 causes other than the microbial flora of the soil. This becomes self- 

 evident when we consider the following factors: (1) a large number of 

 soil organisms are capable of decomposing proteins with the formation 

 of ammonia; (2) the amount of ammonia formed depends also upon the 

 nature of the carbon of the organic matter added to the soil in the form 

 of nitrogenous and non-nitrogenous substance; (3) a part of the ammonia 

 changes into nitrates, depending upon the physico-chemical, chemical 

 and biological condition of the soil; (4) the amount of ammonia that a 

 soil can hold depends upon its initial reaction, nature of absorbed bases 

 and buffer content. 



However, according to some investigators, 46 no necessary fundamental 

 difference exists between bacteriological processes in soil and solution 

 media. Among the important factors in soil and in solution, the nature, 

 quantity, and distribution of substrate, aeration, diffusion, absorption, 

 destruction or evaporation of metabolic products, reaction of the 

 medium, temperature and duration of experiment are all of importance. 

 Ammonia accumulation can be readily used as an index of the activities 

 of pure cultures of microorganisms or of the complex soil flora upon 

 proteins or different organic materials. 



The course of ammonia accumulation and the course of C0 2 produc- 

 tion from the same nitrogenous organic substance added to the soil were 

 found 47 to run parallel, tending to indicate that both can be taken as 

 indices of the rapidity of decomposition of organic matter in the soil. 

 However, when the curves of NH 3 accumulation from dried blood and 

 C0 2 evolution from another organic substance, like soy bean meal, were 

 compared, even in the same soil, no parallelism at all was observed. 48 



46 Temple, J. C. The value of the ammonification test. Ga. Agr. Exp. Sta. 

 Bui. 126. 1919. 



46 Lohnis, F., and Green, H. H. Methods in soil bacteriology. VII. Ammoni- 

 fication and nitrification in soil and solution. Centrbl. Bakt. II, 40: 457-479 

 1914. 



47 Gainey, 1919 (p. 685). 



48 Neller, 1918 (p. 685). 



