PLANT FOOD 41 



sium, and when this is the case, this element. can be 

 suppHed with marked profit, either in the form of 

 potassium chlorid or potassium sulphate. 



The other necessary elements of plant food are 

 usually present in the soil in sufficient quantities to 

 meet all of the requirements of the plant. 



The corn plant requires an abundant supply of all 

 of these elements of plant food for maximum growth 

 and production. The only elements enumerated above 

 usually deficient in soils are nitrogen, phosphorus and 

 potassium. Therefore the corn grower is chiefly con- 

 cerned with the problem of keeping his soil well sup- 

 plied with these three all-important elements of plant 

 food in order that the productive capacity of his fields 

 may be maintained undiminished. 



No other question merits more thoughtful atten- 

 tion on the part of the corn grower than this one of the 

 maintenance of the fertility of the soil. There is only 

 one way in which this can be done, namely, by keep- 

 ing good physical conditions and returning to the land 

 all of the fertility which is taken off by cropping, and 

 also that which is removed by the blowing, washing 

 or leaching of the soil. There is no other way. 



When phosphorus or potassium is lacking in the 

 soil, if sufficient manure is not available to supply these 

 elements in ample amounts they may be secured in 

 the form of commercial fertilizers and applied directly 

 to the land. 



METHODS OF OBTAINING NITROGEN 



It has been demonstrated, on the other hand, that 

 the atmosphere is the most economical source of nitro- 

 gen for all general farming. 



The leguminous crops, such as clover, cowpeas, soy 

 beans and alfalfa, are most generally used in the various 



