92 Keport of the Acting Director and Chemist of the 



upon untreated portions of soil witli the same crops on other por- 

 tions of the same soil treated with different quantities of fertilizing 

 materials. 



The Kind of Crop Grown. — It is a well-known fact that differ- 

 ent crops need different quantities of nitrogen, potash and phos- 

 phoric acid compounds. If we know with a fair degree of accuracy 

 how many- pounds of nitrogen, potash and phosphoric acid a crop of 

 any kind will remove from the soil, then we have fairly definite 

 knowledge of the amounts of different forms of plant-food to apply 

 to the soil to insure a crop. If we could not depend upon the soil 

 to furnish any plant-food, then we should use, at least, the amounts 

 of fertilizing materials removed by one crop. 



In the following table, we give the number of pounds of nitrogen, 

 phosphoric acid and potash used by different kinds of crops grown 

 on one acre of land. The yields have been made variable within 

 fairly wide limits so as to cover most cases found in actual experi- 

 ence. The calculations are based upon the most reliable analyses 

 available. 



In studying this table, we must keep in mind that the figures do 

 not in every case represent the amount of plant-food removed from 

 the soil. Thus, with clovers, beans, peas and other leguminous 

 crops, a, portion of the nitrogen is obtained from the air and hence 

 we need to apply less nitrogen in the form of fertilizer than appears 

 to be called for by the table. In the case of fruits, like apples, 

 pears, plums, etc., it will be found safe often to apply larger quanti- 

 ties than the table calls for, because the figures in the table do not 

 indicate the demands made by the tree in increasing its growth : 



