32 ELEMENTS OP 



ble humus in a soil may be increased to a certain de- 

 gree by cultivation and alternate cropping', still there 

 cannot be the smallest doubt, that a soil must (without 

 help) ultimately lose those of its constituents, which are 

 removed in the seeds, roots, and leaves of the plants 

 raised upon it. 



To prevent this loss, and, as a further object, to ena- 

 ble us to raise increased quantities of productions, de- 

 manding more sustenance than the land will naturally 

 yield, is the object of the application of the various sub- 

 stances used as manures. They will prove useless, in- 

 jurious, or valuable, precisely as they are accurately or 

 inaccurately adapted to meet the deficiency. 



Land, when not employed in raising food for animals 

 or man, should, at least, be applied to the purpose of 

 raising manure for itself; and this, to a certain extent, 

 may be effected by means of green crops, which, by 

 their decomposition, not only add to the amount of veg- 

 etable mould contained in the soil, but supply the alka- 

 lies that would be found in their ashes. That the soil 

 should become richer by this burial of a crop, than it 

 was before the seed of the crop was sown, will be under- 

 stood by recollecting that three-fourths of the whole or- 

 ganic matter buried has been derived from the air : 

 that by this process of plougjiing in, the vegetable mat- 

 ter is more equally diffused through the whole soil, and 

 therefore more easily and rapidly decomposed ; and that 

 by its gradual decomposition, ammonia and nitric acid 

 are certainly degenerated, though not so largely as 

 when animal matters are employed. He who neglects 

 the green sods, and crops of weeds that flourish by his 

 hedgerows and ditches, overlooks an important natural 

 means of wealth. Left to themselves, they ripen their 

 seeds, exhausting the soil, and sowing them annually 

 in his fields : collected in compost heaps, they add ma- 

 terially to his yearly crops of grain. 



