LEGUMINOUS CROPS AND FERTILITY 297 



peas, beans, vetch, clover, and lucern, are able to 

 secure large quantities of nitrogen from the air 

 through the activity of bacteria that live and grow 

 on the roots of such plants. The leguminous crop 

 should be sown in the usual way, and when it is well 

 past the flowering stage should be plowed into the 

 ground. Naturally, annual legumes, such as peas 

 and beans, should be used for this purpose. The 

 crop thus plowed under contains much nitrogen, 

 which is gradually changed into a form suitable for 

 plant assimilation. In addition, the acid substances 

 produced in the decay of the plants tend to liberate 

 the insoluble plant-foods and the organic matter is 

 finally changed into humus. In order to maintain a 

 proper supply of nitrogen in the soil the dry-farmer 

 will probably soon find himself obliged to grow, every 

 five years or oftener, a crop of legumes to be plowed 

 under. 



Non-leguminous crops may also be plowed under 

 for the purpose of adding organic matter and humus 

 to the soil, though this has little advantage over the 

 present method of heading the grain and plowing 

 under the high stubble. The header system should 

 be generally adopted on wheat dry-farms. On 

 farms where corn is the chief crop, perhaps more 

 importance needs to be given to the supply of organic 

 matter and humus than on wheat farms. The 

 occasional plowing under of leguminous cro])s would 

 be the most satisfactory method. 



