THE GERM LIFE OF THE SOIL 



131 



166. Decomposition of nitrogenous organic matter. — 

 The main difference between the decomposition of non- 

 nitrogenous and nitrogenous organic matter is that in the 

 latter nitrogen and usually sulfur play a part. The sulfur 

 is not of so much importance, but it is very necessary that 

 we should follow the various processes through which nitro- 

 gen is transformed from organic substances into the final 

 forms in which it is again used by plants or returned to the 

 air. These processes will be treated under the following 





A 5 C D 



Fig. 24. — Appearance of some soil germs under the microscope. (A) free 

 living nitrogen-fixing bacteria (Azotobacter) , (B) bacteria that cause one 

 step in the production of nitrates from ammonia (Nitrosomonas), (C) nitro- 

 gen-fixing bacteria from the nodules of leguminous plants (Radicicola), 

 (D) ammonia-forming bacteria (Proteus vulgaris). 



heads : (1) ammonification ; (2) nitrification ; (3) denitri- 

 fication. 



Organic nitrogenous matter when it first enters the soil 

 as plant or animal remains or as solid farm manure or green- 

 manure is largely in the form of what are known as proteids. 

 As soon as such material is incorporated in any normal 

 soil, decomposition begins and the rate at which it proceeds 

 depends on the character of the soil in which the process 

 is going on. There are several different forms of bac- 

 teria that are capable of decomposing proteins and there 

 are always enough of these in any arable soil to do the work 

 if the soil has the proper moisture, ventilation and heat and 

 is not acid. 



