l68 SOILS AND FERTILIZERS 



phosphoric acid, and 30 pounds of potash. When the 

 nitrogen is worth 16 cents per pound, the phosphoric 

 acid 6 cents, and the potash 5 cents, the clover hay has 

 a manurial value of $7.94 per ton. Lawes and Gilbert 

 estimate that 80 per cent of the fertility in fodders is, 

 as a rule, returned in the manure. 



In the preceding table are given the pounds of nitro- 

 gen, phosphoric acid, and potash per ton of some farm 

 products. 58 



186. Commercial Value of Manures. - - When the value 

 of farm manure is calculated on the same basis as com- 

 mercial fertilizers, it will be found that stable manure 

 is worth from $2 to $3.50 per ton. The value of the 

 increased crops resulting from its use varies with con- 

 ditions. Farm manures favorably influence the yield of 

 crops for a number of years. As for example, a dress- 

 ing of 8 tons of manure will make average prairie land 

 yield upwards of 20 bushels per acre more corn the 

 first year, 5 bushels more wheat the second year, and 8 

 bushels or so more of other grains the third year, with 

 slightly increased yields in subsequent years, all due 

 to the original application of the manure. It is often 

 necessary to apply farm manure in order to secure a 

 stand of clover, which enriches the soil with nitrogen. It 

 sometimes takes from two to three years for the manure 

 entirely to repay the cost of its application. Its influence 

 is felt, however, for a much longer time. In calculating 

 the value of farm manure, the returns from its use for a 



