76 THE CHEMISTEY OF THE FARM 



later period of growth than the cereals already men- 

 tioned, and will thus have command of the nitrates 

 produced during the whole summer. Owing probably 

 to this fact it is a crop much less dependent on nitro- 

 genous manure than wheat. 



As cereal crops derive their nitrogen almost exclu- 

 sively from nitrates, and are dependent (save in the 

 case of maize) on the quantity of these salts occurring 

 in the soil before the middle of summer, they rank, 

 notwithstanding the small quantity of nitrogen which 

 they contain, among the crops most benefited by nitro- 

 genous manures. Phosphates, though generally of 

 little use by themselves, are also beneficial (especially 

 in the case of spring-sown crops) when applied with 

 nitrogenous manure. For wheat, superphosphate or 

 slag may be ploughed in before drilling the seed, and 

 nitrate of sodium applied as a top dressing in spring. 

 For barley and oats, sulphate of ammonium and 

 superphosphate may be harrowed in immediately be- 

 fore sowing the seed. "When malting barley of high 

 quality is to be produced the supply of nitrogenous 

 manure must be carefully limited. Nitrate of sodium 

 always gives a larger return in straw than sulphate of 

 ammonium. 



Meadow Hay.— The grasses which form the main 

 bulk of hay belong to the same family of plants as the 

 cereal crops ; the seed, however, in grass bears such a 

 small proportion to the stem and leaf that meadow hay 

 may be regarded as a straw crop. In accordance with 

 this character hay is found to contain a much larger 

 proportion of potash and lime than cereal crops, and 

 a much smaller amount of phosphoric acid. 



The roots of grass being far shorter than those of 



