CHAPTER X 



CROP REQUIREMENTS FOR NITROGEN, PHOSPHORUS, AND 



POTASSIUM 



A STUDY of Table 23 is sufficient to make one familiar with the 

 requirements of the more important crops of the United States for 

 the three plant-food elements that are now recognized as having 

 money values in commercial fertilizers. Information is also given 

 regarding the amounts of these three elements in different parts of 

 the crop, as in grain, straw, corn stover, and cotton stalks and lint, 

 in order that it may be known with some degree of accuracy how 

 much of each element is removed from the soil in crops and how 

 much is sold from the farm in different kinds of farm produce. 

 The ideal practice is to return to the soil, either directly or in 

 farm manure, all plant food not sold from the farm. 



The data given in Table 23 are on the basis of pounds per acre 

 for crop yields which are large, but which, when the best condi- 

 tions are provided, have been and may be produced with very great 

 profit, yields that may well stand as ideals, desirable and pos- 

 sible to be attained. Approximately proportionate amounts of 

 plant food would be required for any other yields. Thus, if it is 

 preferred to plan to make possible yields only one half as large, 

 then the amounts given in Table 23 may be divided by two. (In 

 Section 3 of the Appendix, data are reported showing the more com- 

 plete composition of a much larger number of crops, but the re- 

 sults there given are derived from a smaller number of analyses 

 than are represented for the crops reported in Table 23; and, 

 consequently, some differences are to be expected.) 



The value of the elements is computed on the basis of the present 

 market prices for plant food from the most abundant natural 

 deposits, delivered in car-load lots to central Illinois, and in suit- 

 able condition for direct application to the land. 



Nitrogen in sodium nitrate 15 cents a pound. 



Phosphorus in ground raw phosphate ... 3 cents a pound. 

 Potassium in kainit 6 cents a pound. 



