SOILS AND FERTILIZERS 



in 



productive results, will require at least 10 pounds of 

 nitrogen, 15 pounds of phosphorus, and 20 pounds of 

 potash each year, but the amount of any fertilizer re- 

 quired can never be stated in exact figures, for different 

 soils and different plants need varying amounts, so 

 that any figures are misleading, experience being the 

 only safe guide in determining the quantity to be used. 

 It is also necessary to know what available amount 

 of the needed elements any given fertilizer contains, in 

 order to estimate how much of it to use. 



The following table is useful for reference as it gives 

 the approximate percentage of food elements in the 

 most common commercial fertilizers : 



1 Refuse from extracting oils from castor bean. 



