194 Agricultural Bacteriology. 



The material that is turned under in the cover crop 

 furnishes food for innumerable bacteria, and by-prod- 

 ucts of their growth act on the mineral part of the soil, 

 rendering the lime, potassium, and phosphorus available 

 to the green plant. It also furnishes food for a class of 

 bacteria to be described in a subsequent chapter that aid 

 in maintaining the nitrogen content of the soil. A part 

 of the organic matter of the crop plowed under accumu- 

 lates in the soil as- humus which has a most favorable 

 effect on the physical condition of the soil. In the con- 

 servation of the nitrogen of the soil it is apparent that 

 the best practice is not to allow the land to lie idle, but 

 to keep it covered with a crop. 



