FERTILITY OF THE SOIL 27 



Barnyard manure is added to give nitrogen and other 

 elements to the soil. Before the nitrogen in the organic 

 matter can be used by the crops, it must be changed 

 into nitrates by the bacteria in the soil. Thus the soil 

 bacteria are the direct producers of nitrogen plant food. 



THE PLANT ON THE LEFT WAS GROWN IN POOR SOIL, THE OTHER IN GOOD SOIL 



The legumes, such as the clovers, peas, beans, and 

 alfalfa, in addition to furnishing valuable crops for man, 

 are of great value in increasing the nitrogen supply. 

 On the roots of the legumes may be found small swell- 

 ings or nodules, in which are colonies of bacteria which 

 have the power of taking the nitrogen from the air 



