176 



Transformation of Nitrogen 



stances, the greater will be the synthesis of microbial protoplasm, 

 leading to a greater assimilation of the nitrogen and to a smaller 

 accumulation of ammonia. (4) Various soil conditions, as well as 

 differences in the composition of the nitrogenous and the accom- 

 panying non-nitrogenous organic substances, lead to the develop- 

 ment of different microorganisms capable of decomposing the ni- 

 trogenous materials; the carbon-nitrogen metabolism of these micro- 

 organisms is different; this leads, therefore, to differences in the 

 amounts of ammonia liberated in a free state. 



These reactions result in a transformation of a larger or smaller 

 part of the nitrogen of the organic complexes into ammonia, which, 

 either as such or after it has been oxidized to nitrate, is available as 

 a source of nitrogen for the growth of cultivated plants. In view of 

 the great economic importance of the liberation of ammonia, numer- 

 ous contributions have been made to the subject, known as "ammoni- 

 fication." These studies have been chiefly limited to adding about 

 1 gm of the nitrogenous organic material to 100 gm of soil, mixing, 

 placing in timnblers, then bringing the moisture content of the soil 

 to optimum (60 per cent saturation), incubating for 4-14 (usually 

 7) days, then measuring the amount of ammonia present in the soil 

 by distilling with MgO. 



Thus, in the presence of available carbohydrates (Table 37), two 



Table 37. Influence of Carbohydrate upon Ammonia Formation in Soil 



(from Kelley) 



factors are at work: first, less of the protein is decomposed, since 

 the bacteria and fungi prefer the carbohydrate to the protein as a 

 source of energy; second, the ammonia that has been formed from 

 the decomposition of the proteins may be reassimilated by the micro- 



