IO FARM CROPS 



As this air passes through the soil, the bacteria 

 composing the tubercles assimilate the nitrogen and 

 hold it as available plant food for the plant sup- 

 porting their own parasitic bodies, and for crops 

 coming after. 



Great quantities of atmospheric nitrogen can thus 

 be stored in the soil. Since nearly one-half of the 



INCREASING POTATO YIELDS 



When mineral fertilizers were applied, the potato crop 

 was greatly increased. These contrasts are shown here. Acid 

 phosphate and sulphate of potash were the carriers of these 

 elements. 



total cost of commercial fertilizers comes from nitro- 

 gen, it follows that it is rational farming to grow 

 alfalfa, clover, cowpeas or other leguminous 

 crops so as to diminish or entirely do away with 

 the buying of costly nitrogen. 



Potassium and phosphorus, the other two ele- 

 ments often deficient in the soils, must be supplied 

 artificially, since they are minerals and cannot be 

 drawn from the air. As yet the widest chemical 

 or plant speculator has never dared to hope to find 



