52 THE CHEMISTRY OF THE FARM. 



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. 



Let us suppose that land is laid down with seeds, which 

 after two or three years are ploughed up, and a cereal 

 crop taken. While the land is continuously covered by 

 vegetation the loss of nitric acid 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 been collected from the sub- 

 soil by the roots of the crop, and returned to the surface 

 as animal manure. The latter includes the accumulated 

 receipts from the atmosphere during the three years, 

 minus the quantity lost by drainage and that assimilated 

 by the animals. The accumulated nitrogen will be 

 chiefly in the form of grass roots, stems, and humus. 

 When such land is ploughed up, the vegetable matter and 

 humus are oxidised, and gradually yield their nitrogen as 

 nitric acid. 



Such a mode of cropping has an advantage over a bare 

 fallow in several ways: — 1. The land is turned to profit- 

 able use, food being produced for the farm stock. 2. Both 

 ash constituents and nitrates are collected from the sub- 

 soil, and brought to the surface. 3. The nitrogen is kept 

 in an insoluble form, as vegetable matter, and conse- 

 quently cannot be washed away, but accumulates to a 

 greater extent than in a bare fallow. 4. Humus is pro- 

 duced, the beneficial actions of which have already been 

 noticed. We have laid no stress on the enrichment of the 



