40 THE CHEMISTRY OF THE FARM. 



Cereal Crops. — These contain much less nitrogen than 

 either the leguminous or root crops ; about three-quarters 

 of the nitrogen is in the corn, and only one quarter in the 

 straw. The amount of phosphoric acid is not very different 

 from that found in other crops ; this ingredient is, in fact, 

 the most constant of all the constituents of crops ; it is 

 chiefly concentrated in the corn. Potash and lime are 

 present in much smaller quantity than in other crops ; 

 they are chiefly concentrated in the straw. 



The presence of a large amount of silica is characteristic 

 of the cereal crops ; they possess apparently a capacity for 

 feeding on silicates not enjoyed by other crops. The base 

 of the silicate is made use of by the plant, while the silica 

 itself is excreted upon the surface of the leaves and straw. 

 It has been shown that silica is by no means essential 

 for the growth of cereals ; they take it up freely, but 

 can also do without it. * 



The autumn sown cereals (wheat and rye) have both 

 deeper roots, and a longer period of growth, than the 

 spring sown cereals, and are better able than the latter 

 to supply themselves with the necessary ash constituents 

 from the soil. Barley possesses a considerable development 

 of root near the surface, and is apparently more capable 

 of obtaining nitrogen from the soil than wheat. 



Cereal crops derive their nitrogen almost exclusively 

 from nitrates ; the form in which the great bulk of the 

 nitrogen is present in the soil is unsuitable for them. 

 Notwithstanding, therefore, the small amount of nitrogen 

 contained in cereal crops, they rank among those most 

 benefited by nitrogenous manures. Phosphates, though 

 of little use by themselves, are also beneficial (especially 

 in the case of spring crops) when applied with nitrogenous 



