26O SOILS AND FERTILIZERS 



to power of assimilating nitrogen. Next to nitrogen they 

 stand most in need of phosphoric acid. There exists in 

 many soils a greater deficiency of available phosphoric 

 acid and potash than of nitrogen, although, in general, 

 cereal crops are better able to procure these elements 

 than they are nitrogen. The humic phosphates are 

 utilized by nearly all the cereals. 



310. Wheat. This crop is more exacting in its food 

 requirements than barley, oats, or rye. It is compara- 

 tively a weak feeding crop, and the soil should be in a 

 higher state" of fertility than for other grains. The ex- 

 tensive experiments of Lawes and Gilbert give valuable 

 information regarding the effects of manures on wheat. 

 Their results are given in the following table : 75 



AVERAGE YIELD OF WHEAT PER ACRE 



BUSHELS 



No manure for 40 years .... 

 Minerals alone for 32 years . 

 Nitrogen alone for 32 years . . . 

 Farmyard manure for 32 years . . 

 Minerals and nitrogen for 32 years 1 

 Minerals and nitrogen for 32 years 2 



14 



231 



1 86 pounds of nitrogen as sodium nitrate. 

 2 86 pounds of nitrogen as ammonium salts. 



The food requirements of wheat are such that it should 

 be given a favored position in the rotation. It may follow 

 clover, provided the clover sod is light and is fall plowed. 



