4-i Report of the Department of Agronomy of the 



The following table shows the approximate amounts of nitrogen, 

 phosphorus, potassium, calcium and magnesium removed per acre 

 annually by good yields of some common farm crops. 



Table I. — Approximate Amounts of Chemical Elements Removed from 



Soil by Crops. 



While these crops are larger than are commonly grown they are 

 not larger than a farmer would wish to raise, nor are they larger 

 than it is possible and profitable to produce under good systems of 

 soil management. And so it is for such crops we must provide in 

 the future if we are to solve satisfactorily the problem of soil fertility. 



Note. - The term phosphoric acid as used in fertilizer parlance refers to an oxide 

 of phosphorus (P2O5) and not phosphoric acid (H3PO4). But it is more rational 

 and explicit and will avoid confusion of terms if when dealing with the subject of 

 phosphorus we speak in terms of the element phosphorus (P) instead of its numerous 

 compounds. This is in accord with the practice of speaking of the element nitrogen 

 (N) instead of ammonia (NH 3 ) as was formerly the case. One pound of P-Os contains 

 .4366 pound of phosphorus, P, and so to convert weights or percentages of P2O6 

 into P multiply by .4366, or for practical purposes .44 is sufficient. Thus 15 per ct. 

 P2O5 is equivalent to 6.6 per ct. P (15 x .44 = 6.6). 



Similarly instead of potash (K 2 0) we should say potassium (K). One pound K2O 

 contains .83 pound of potassium (K). To convert weights or percentages of KaO 

 in K multiply by .83. 



