110 



WHEAT 



The values of the fertilizing constituents are 

 calculated at the market price of car lots as 

 follows: 



Nitrogen in sodium nitrate 15c per pound 



Phosphorus in ground rock phosphate 3c per pound 



Potassium in kainit 6c per pound 



TABLE VII 



Amounts of plant food constituents in fertile 

 soils: ("Fertilizers and Crops" by VanSlyke) 



The average weight of an acre of soil to the 

 depth of nine inches is taken as 2,500,000 pounds. 

 The great bulk of the soil consists of inert ma- 

 terials, as clay and sand, composed largely of 

 aluminum and silica. The plant food constituents 

 are present only in relatively small proportions. 

 The combined amounts of nitrogen, phosphorus 

 and potassium in fertile soils are usually less 

 than 1% and only a very small proportion of these 

 small amounts are in forms immediately available 

 for the use of plants. Considering the small 

 amounts required by crops, the supply of plant 

 foods in the soil will theoretically last a very long 

 time. For instance comparing Tables V and VI 

 it will be seen that the average fertile soil con- 

 tains enough phosphorus in nine acre-inches to 

 produce more than 200 twenty-five bushel wheat 



