Chemistry, inorganic and organic : with experiments / by Charles Loudon Bloxam.
- Bloxam, Charles Loudon, 1831-1887.
- Date:
- 1875
Licence: Public Domain Mark
Credit: Chemistry, inorganic and organic : with experiments / by Charles Loudon Bloxam. Source: Wellcome Collection.
649/708 (page 621)
![(11.) Solid excrements of various animals, containing the insoluble salts (especially phosphates) of the animal's food, as well as easily putres- cible organic matters yielding much ammonia and sulphuretted hydrogen. (12.) Guano, the dung of carnivorous sea-birds, which owes its very high value, partly to the large propo]-tion of urate of ammonia and other nitrogenised organic substances which it contains, and partly to the pre- sence of phosphates and salts of the alkahes. (13.) Soot, which appears to act chiefly by virtue of the salts of ammonia derived from the destructive distillation of the coal. The chief substance employed for acting chemically upon the consti- tuents of the soil, so as to render them more servicable to the plant, is lime, ■wliich modifies in a very important manner both the organic and mineral portions of the soil. Its action upon the former consists in j)romoting its decay, and the conversion of its elements into those forms, viz., carbonic acid, water, ammonia, and nitric acid, in which they may be of service to the plant. Upon the inorganic constituents of the soil, lime acts by assisting the decomposition of minerals, particularly of those which con- tain the alkalies (such as feldspar), and thus converting them into soluble forms. In some cases fertility is restored to an apparently exhausted soil, with- out the addition of manure, by allowing it to lie fallow for a time, so that under the influence of the air and moisture, such chemical changes may take place in it as will again replenish it with food available for the crops. It is not even necessary in all cases that the soil should be altogether re- leased from cultivation: for even though it may refuse to feed any longer one particular crop, it may furnish an excellent crop of a difierent description, and, which is more remarkable, it may, after growing two or three diff'erent crops, be found to have regained its power of nourishing the very crop for which it was before exhausted. Experience of this has led to the adoption of the system of rotation of crops, by which a soil is made to yield, for example, a crop of barley, and then successive crops of grass, beans, turnips, and barley again. The possibility of this rotation is partly accounted for by the difference in the mineral food removed from the soil by different crops; thus turnips require much of the alkalies and lime; wheat, much alkali and silica; barley, much hme, and silica; and clover, much lime, so that the soil which had been exhausted for wheat, because it no' longer contained enough soluble silica, might still yield sufficient alkali and hme to a crop of turnips, and when the alkali was exhausted, might furnish enough lime to a crop of clover, after which, in consequence of the chemical changes allowed by lapse of time in the soil, more of the original minerals com- posing it might have been decomposed and rendered available for a fresh wheat crop. Another explanation of the benefit of systems of rotation may be given in those cases in which the d6bris of the preceding crop are allowed to remain on the land. Some plants extending tlieir roots more deeply into the soil, avail themselves of mineral food Avhich is beyond the reach of plants furnished with shorter roots, and when the refuse of the former plants is ploughed into the land, the surface is enriched with the food collected from the sub-soil. Our knowledge of the chemical operations taking place in the plant and resulting in the elaboration of tlio groat variety of vegetable products' is very slight indeed. We appear to have sufficient evidence that suar](https://iiif.wellcomecollection.org/image/b21497382_0649.jp2/full/800%2C/0/default.jpg)
