CHAPTER XXIV 

 BUYING PLANT FOOD FOR THE SOIL 



The three fertilizer constituents are nitrogen, phospho- 

 rus, and potassium, for the reason that in lands long 

 cultivated they have been diminished more nearly in the 

 soil. \Yhile there is just now a great deal of controversy 

 as to the real office of a fertilizer, still, there is no question 



COW PEAS AND FERTILIZERS AND A POOR SOIL 



1. Phosphorus and potassium, but no nitrogen 



2. Nitrogen, but no phosphorus and potassium 



3. No fertilizers of any kind applied 



about their value on many lands. It may be that a fer- 

 tilizer has some other office besides that of supplying plant 

 food . nevertheless, plant food is a factor in soil fertility. 

 The office of nitrogen. We have learned that many 

 elements are essential to the perfect development of the 

 plant and that each has a special work to do. which work 

 cannot in any case be done by any other clement. Xitro- 



