32 THE FORAGE AND FIBER CROPS IN AMERICA 



practise are somewhat masked by the fact that American soils 

 are on an average relatively more virgin and hence presumably 

 better supplied with soluble nitrates, and over a wide area in 

 America the soils are relatively low in phosphates. In America, 

 phosphoric manures frequently have a marked influence upon 

 vegetative growth, especially when used in connection with 

 nitrogenous manures for grasses and potash manures for 

 leguminous crops. 



31. Essential Conditions for the Successful Use of Fertilizers 

 upon Grasses. There are three conditions necessary for a suc- 

 cessful increase of a grass crop through the use of fertilizers 

 of any sort: 



1. The increase will depend on the ability of the land to 

 grow a crop without fertilizers. If the land will now grow 

 only 1,000 pounds of hay to the acre and this small growth 

 is due primarily to the need of fertilizers, then a certain ap- 

 plication of fertilizer may increase the yield to 4,000 pounds 

 per acre. If the same application is made to land already 

 yielding 4,000 pounds of hay per acre, the increase may or 

 may not be 3,000 pounds per acre, depending on whether 7,000 

 pounds are a normal yield with the climatic conditions of the 

 place and the stand of grass. 



2. The increase due to fertilizers depends on the climatic 

 conditions. If the climatic conditions are such as to produce 

 only 1,000 pounds of hay per acre, the addition of fertilizers 

 will not materially increase the yield. If the climatic conditions 

 are such as to produce 7,000 pounds of hay per acre, it may 

 take less fertilizer to increase the yield from 4,000 to 7,000 

 pounds per acre than from 1,000 to 4,000 pounds per acre. 



3. Where the climatic conditions are favorable, grasses 

 respond well to the use of fertilizers; doubtless due, in part 

 at least, to the large number of plants influenced by the fer- 

 tilizers and to large root surface which prevents the loss of the 

 fertilizers applied. An essential condition, therefore, for a 



