140 SOILS AND FERTILIZERS 



varies with conditions. Farm manures favorably in- 

 fluence the yield of crops for a number of years. 

 After a dressing of 8 tons of farm manure, average 

 prairie land will yield 20 bushels per acre more corn 

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

 and 8 bushels more of other grains the third year, 

 with slightly increased yields in subsequent years. 

 It takes about three years for the manure to entirely 

 repay the cost of its application. Its influence is felt 

 however for a much longer time. It is sometimes 

 stated that the phosphoric acid and potash in stable 

 manure is not as soluble as that in commercial 

 fertilizers, and consequently is worth less. While 

 not so soluble in the form of manure, it frequently 

 happens that the phosphoric acid and potash in 

 the commercial fertilizers become, through fixation 

 processes, less soluble when mixed with the soil than 

 the same elements in stable manure. 



Stable manure is valuable not only for the fertility 

 contained but also because it makes the inert plant 

 food of the soil more available and exercises such a 

 favorable influence on the water supply of crops ; 

 hence it is justifiable to assign the same value to the 

 elements in well-prepared farm manures as to those in 

 commercial fertilizers. 



If well-prepared stable manure is not worth $2.50 

 per ton, then too much, accordingly, is paid for com- 

 mercial forms of plant food. 



INFLUENCE OF AGE AND KIND OF ANIMAL 



174. Manure from Young and Mature Animals. 



