Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/532

Rh 508 MANURE TABLE II. Manuring quantities per Acre per Annum. Wheat. Barley. 20 Years 1802-71. 20 Years 18.52-71. Re covered in In crease. Not re covered in In crease. Re covered. Xot re covered. Complex mineral manure and 41 tb of I 32-4 J f - I 32-9 j. 31T, j. 28-5 I 4,3 } - 1 14-G C7-G 67-1 68-5 71-5 54-7 85-4 48 I 49-8 3G-3 10-7 51-9 50-2 G3-7 89-3 Complex mineral manure and 53-3 tt&amp;gt; of Complex mineral manure and 82 lb of Complex mineral manure and 123 lb of Complex mineral manure and 164 It) of Complex mineral manure and 82 lb of Complex mineral and rape cake (61-75 lb Farmyard manure (about 200 lb of The question will naturally be raised, What becomes of the one-half or two-thirds of the nitrogen which is not recovered in the increase of the crops ? The examination of some seventy samples by Dr Voelcker, and a number of independent determinations by Dr Frankland, of the drainage-water from the experimental wheat plots which yielded the above results throw much light on this loss. The following table (III.) contains a summary of some of the more important results obtained. TABLE III. Nitrogen as Nitrates and Nitrites, per 100,000 parts of Drainage Water from Plots differently Manured, in the Experi mental Wheat-field at Rothamstcd, Wheat every year, commencing 1844. Mean of Dr Voclcker s and Dr Frankland s Kesults. Experi ments. Nitrogen.

1-2G4 11 0-353 Complex mineral manure n 0-428 Do. and 41 lb nitrogen as ammonia 11 0-823 Do. and 82 lb nitrogen as ammonia j i 1-439 Do. and 123 tb nitrogen as ammonia n 1-815 Do. and 82 lb nitrogen as nitrate ... 10 1-4J7 These experiments show how great may be the loss of nitrogen by drainage when ammonia salts or nitrates are liberally applied to the land in autumn, should there be much wet weather in winter, or even when applied in spring if there be much heavy rain ; also, that the quantity of nitrogen in drainage water as nitrates is increased in proportion to the amounts of ammonia or nitrate employed on the land. Assuming that from one-quarter to nearly one-half the annual rainfall descends more than 40 inches below the surface, every inch of rain passing through the drains and carrying with it one part of nitrogen m.100,000 of water, there will be a loss of 2| ft&amp;gt; of nitrogen per acre from the manure. Dr Voelcker s analysis of the drainage water of a wheat field manured in autumn by ammonia salts supplying 82 ft) of nitrogen per acre shows that for every inch of rain passing through the drains in January a loss took place of about 8 lb of nitrogen, costing about 1 s. per lb as manure. The loss of nitrogen thus is very large, and shows that by far the largest proportion of the nitrogen of manure which is not recovered in the crop is lost in drainage. In addition to the nitrogen removed in the crop and to that lost in drainage, some small proportion is found by analysis to be retained in the soil itself. The nitrogen may be of advantage to crops grown subsequently, according to the source from which it was derived ; for while ammonia salts and nitrates yield but very small residues, and exert little or no effect beyond the first year, from bones, cake, and other such materials we get large residues of nitrogen in the soil, which tell markedly on future crops. The experiments on drainage water have further shown the absorbent power of soils, and that manuring matters when in contact with soils undergo remarkable changes, being taken up by plants, not in the simple state in which they are applied, but in quite different kinds of combination. Professor Way has the merit of having first proved that all soils possess, in different degrees, the power of absorbing ammonia from its solution in water, and that in passing solutions of salts of ammonia through soils the ammonia alone is absorbed, and the acids of the ammonia salts pass through in combination, generally with lime, or, if lime be deficient, with magnesia or other mineral bases of the soil. In the drainage investigations at Rothamsted, it was found that, although large quantities of ammonia salts were applied to some of the plots, the drainage water from them contained mere traces of ammonia, but at all times of the year nitrates were present in quantity ; from this it would appear that it is chiefly, if not solely, from nitrates that crops build up their nitrogenous organic constituents. Before leaving the subject of drainage water it is worthy of note here that phosphoric acid and potash, the most valuable mineral fertilizing constituents of the manures, passed but little into the drainage water, but were retained almost entirely in the land, while the more abundant and less important mineral matters, such as lime, magnesia, soda, chlorine, sulphuric acid, and soluble silica, passed in large quantities into the drainage water. It follows from these investigations, first, that much more nitrogenous material must be applied to the land than would be needed to produce a given increase in the crop, supposing all the nitrogen to be recoverable ; and secondly, that nitrogenous organic matters when applied to the land undergo decom position, and are gradually resolved into ammonia com pounds, which, after being retained a short time by the soil, are finally oxidized into nitrates, in which form they are most available and beneficial to plants, but are not absorbed by the soil, and are readily washed out by rain. Nitrogen has great forcing properties, and is most beneficial when applied to crops in their early stages. Grass land on which nitrate of soda has been put as a top dressing shows very rapidly and markedly the effects of the manure. Nitrate of soda, unless applied just at the time the crop is ready to take it up, will be largely wasted in drainage ; hence it is usual to apply nitrate of soda as a top dressing in spring. Arnmoniacal manures, such as Peruvian guano, soot, sulphate of ammonia, ifcc., when used for winter wheat, are best applied in autumn, either before the wheat is sown or when it is fairly above ground. On light land they are often used as top dressings for wheat early in spring. The gradual decomposition of farmyard manures gives a more constant supply of nitrogen than the manures already noticed, and as the fermentation of dung proceeds but slowly it is best to apply it, when quite fresh, in autumn or winter, allowing it to decompose in the land and to yield nitrogen as nitrates when required in spring by the fresh growth of vegetation. In the case of nitrogenous organic materials, such as wool or hair refuse, which take even longer than farmyard manure to decompose, it is necessary to apply them some three or four months before the seed is sown. 2. Phosphoric Acid. Next in value to nitrogen as a constituent of manures comes phosphoric acid. Of all the mineral or ash constituents of plants, this is the most im portant, for the simple reason that it occurs in most soils in comparatively small proportions, and is required alike by corn and forage crops in larger quantities than lime, magnesia, and other mineral matters, which occur in most soils in almost inexhaustible quantities, or which, if defi cient, can be easily and cheaply incorporated with the land. Phosphoric acid occurs in soils principally in combination with lime as phosphate of lime, a constituent which enters