412 NATURE AND PROPERTIES OF SOILS 



the circumstances under which the nitrogen is made avail- 

 able to plants, and the conditions that are likely to encourage 

 its loss from the soil. 



228. Ammonification may be considered as the second step 

 in the simplification which nitrogenous compounds undergo 

 in the soil. As the name implies, it is the stage of the decay 

 process in which ammonia is one of the important products. 

 Like other processes of decomposition, there are many species 

 of organisms capable of producing ammonia, the higher fungi 



Fig. 58. — Some soil organisms important in the nitrogen cycle, (a) 

 Azotobacter agilis; (b) nitrate bacteria. Urea bacteria, (c) Uro- 

 bacillus miguelii and (d) Urobacillus leubii. 



and algae as well as bacteria participating in the change in the 

 character of the nitrogen compounds. 



Different soil organisms display diverse abilities in con- 

 verting the nitrogen of the same organic material into am- 

 monia, some acting more rapidly or more thoroughly than 

 others. In tests by certain investigators in which the same 

 bacteria were allowed to act on different substances, the order 

 of their efficiency was reversed with a change of substance. 

 This characteristic preference of a class of organisms for the 

 decomposition of certain substances is made evident by the 

 experiments of Sackett, 1 who found that in some soils dried 



1 Sackett, W. G., The Ammonifying Efficiency of Certain Colorado 

 Soils; Colo. Agr. Exp. Sta., Bui. 184, 1912. 



