CEREAL CROPS 229 



ample, wheat grown on prairie soil containing soda in 

 equally abundant and soluble forms as the potash, will 

 contain relatively little soda compared with the potash 

 in the crop. 36 



CEREAL CROPS 



292. General Food Requirements. — Cereal crops con- 

 tain a high per cent, of silica and evidently possess 

 the power of feeding upon some of the simpler silicates 

 of the soil, 73 liberating the base elements which are 

 utilized as food, while the silica is deposited in the 

 outer surface of the straw. As previously stated, cer- 

 eal crops although they do not remove large amounts 

 of total nitrogen from the soil require special help in 

 obtaining this element. There is, however, a great 

 difference among the cereals as to power of assimila- 

 ting nitrogen. Next to nitrogen these crops stand 

 most in need of phosphoric acid. The humic phos- 

 phates are utilized by nearly all of the cereals. 



293. Wheat. — This crop is more exacting in its 

 food requirements than barley, oats, or rye. Wheat 

 is comparatively a weak feeding crop, and the 

 soil should be in a higher state of fertility than for 

 other grains. The extensive experiments of Lawes 

 and Gilbert have given valuable information regard- 

 ing the effects of manures on wheat. The results are 

 given in the following table : 74 



