84 SOILS 



6,984 pounds ; phosphorus, 2,824 pounds ; and potassium, 

 12,460 pounds. 



When these amounts are considered in connection with 

 the requirements of the four crops corn, wheat, clover 

 and timothy for the fifty-year period, we get the supply 

 value of each ingredient. 



By simple calculation : 



Nitrogen will last 2.30 fifty-year periods, or 115 years. 



Phosphorus will last 3.28 fifty-year periods, or 164 

 years. 



Potassium will last 5.12 fifty-year periods, or 256 years. 



A SURE WAY TO IMPROVE THE SOIL 



Four important factors to take into account. But 

 there are four other factors that enter into this furnishing- 

 supply consideration besides the supposedly-available 

 stores. These factors are : 



1. The constant contribution to the available store 

 from previously unavailable material. 



2. The return to the land of straw, stover and other 

 manurial refuse. 



3. The increase of the nitrogen supply through the 

 legumes. 



4. The help that comes from the subsoil. 



