CHAPTER VII 



LEGUMES 



Restoring Nitrogen to the Soil. From a study of 

 the table on fertilizing substances in different soils, 

 and a comparison of this table with the one on fer- 

 tilizing substances in farm crops, it will be seen that 

 nitrogen is the element which, from ordinary soils 

 and under ordinary conditions of farming, is likely 

 to be the soonest exhausted. Ordinarily, then, the 

 farmer's attention should be turned to methods of 

 restoring nitrogen. If a sufficient quantity of manure 

 were produced on the farm, of course the best method 

 of fertilizing would be to apply barnyard manure to 

 the soil, as it not only contains nitrogen, but also phos- 

 phoric acid and potash, the other needed elements. 

 But it is not always possible to do this. There is a 

 class of plants, however, called legumes, that have the 

 power to add nitrogen to the soil. Peas, beans, clover, 

 alfalfa, cowpeas, and soja beans belong to this class. 

 It is^the purpose of this chapter to explain the manner 

 in which these plants add nitrogen to the soil. 



Composition of Air. The air that we breathe is 

 composed largely of two gases oxygen and nitrogen. 



