Soil Bacteria and the Nitrogen Cycle 



401 



Bureau of Agriculture, P. I. 

 Fig. 247. Cowpeas, which, like other legumes, accumulate nitrogen from the air and 

 build it into organic compounds. The advantage of growing a legume in any system of 

 crop rotation is that these compounds may be added to the soil by plowmg the plants under. 



So the ever changing nitrogen compounds pass from the soil to 

 higher plants, to animals, to a succession of bacteria, and by the 

 changes that they undergo they increase or decrease the fertility 

 of the soil. If we understand each of these stages in the cycle 

 and the conditions that favor the changes from one stage to 

 another, and the injection of atmospheric nitrogen into the 

 cycle, we can improve the nitrate content of soils and greatly 

 increase crop yields. 



REFERENCE 



Marshall, C. E, Microbiology (3d edition), 

 delphia; 192 1. 



P. Blakiston's Son & Co., Phila- 



