14 PROFITABLE MANURING, 



in the form of plant food. Nitrogen is the most expensive 

 of the three elements of plant food and costs from two to 

 three times as much per pound as either potash or phos- 

 phoric acid ; the latter two cost about the same per pound. 

 A rough example will illustrate the broad general principles 

 of profitable manuring at its best. Assuming that potash 

 and phosphoric acid cost each 5 cents per pound, and nitrogen 



15 cents per pound, and that to grow a fair crop of clover 

 requires per acre 90 pounds of potash and 20 pounds of 

 phosphoric acid, there would be a total cost for plant food 

 of $5.50 per acre. The crop will contain 82 pounds of 

 nitrogen, 90 pounds of potash and 20 pounds of phosphoric 

 acid with a value as follows : 



Nitrogen 82 Ibs. at 15 cts $12.30 



Potash 90 " " 5 " , 4.50 



Phosphoric acid 20 " " 5 " i.oo 



Total $17 80 



Cost 5.50 



Gain $i 2.30 



While these results are theoretical, pure and simple, 

 still they represent the problem of using legumes profitably. 

 In many crops the margin of profit is narrow, and it is only 

 by making use of legume nitrogen that the results may 

 show a balance on the right side. It is not enough that a 

 farmer in these days must know the nature of manures 

 generally, but he must also know how to make the most of 

 and all of them. 



