GR2EN CROPS 91 



produced will be more or less washed out, and the 

 benefit of the fallow greatly diminished. A mass of soil 

 at Eothamsted, five feet deep, left for thirty years un- 

 cultivated, unmanured, and kept free from weeds, has 

 lost by drainage in the last twenty-three years from 

 15 — 60 lbs. of nitrogen in the form of nitrates per acre 

 per annum, the loss being least in dry seasons and most 

 in wet ones. Bare fallow can be used with advantage 

 only on clay soils, and in a tolerably dry climate ; with 

 a large rainfall the practice must result in a serious 

 loss of soil nitrogen. 



Crreen Crops.— The most usual plan for bringing land 

 into condition for the growth of cereals is the cultiva- 

 tion of green crops. These may be ploughed in, form- 

 ing what is termed green manuring ; or consumed on 

 the land by the farm stock ; or the crop may be 

 removed, consumed in cattle-sheds or in the farmyard, 

 and the resulting manure brought on to the land. 

 The principle in every case is that the constituents of 

 the crop shall be returned to the soil. The consump- 

 tion of the crop off the land, and the bringing back 

 of farmyard manure, is the most imperfect of these 

 modes of restoration, owing to the losses which occur 

 during the making of farmyard manure. 



Let us suppose that land is laid down with grass and 

 clover seeds, and after two or three years is pbughed 

 up and a cereal crop taken. Whilst the land is con- 

 tinuously covered by vegetation the loss of nitrates 

 by drainage will be reduced to a minimum. If the 

 grass is fed off on the land the surface soil will at the 

 end of the three years be considerably enriched both 

 with ash constituents and nitrogen. The former have 



