Elements of agricultural chemistry and geology

by Jas. F. W. Johnston

Sea-weeds decompose with great ease when collected in heaps or spread upon the land. During their decay, they yield not only organic food to the plant but saline matters also, to which much of their efficacy both on the grass and the corn crops is no doubt to be ascribed.

2. Manuring with dry Vegetable Matter.—Almost every one knows that the saw-dust of most common woods decays very slowly—so slowly, that it is rare to meet with a practical farmer who considers it worth the trouble of mixing with his composts. This property of slow decay is possessed in a certain degree by all dry vegetable matter. Heaps of dry straw alone, or even mixed with earth, will ferment with comparative difficulty and with great slowness. It is necessary, therefore, to mix it, as is usually done, with some substance that ferments more readily, and which will impart its own condition to the straw. Animal matters of any kind, such as the urine and droppings of cattle, are of this character; and it is by admixture with these that the straw which is trodden down in the farm-yard is made to undergo a more or less rapid fermentation.

The object of this fermentation is twofold—first, to reduce the particles of the straw to such a minute state of division, that they may admit of being diffused through the soil; and, second, that the dry vegetable matter may be so changed by exposure to the air, and other agencies, as to be fitted to yield both organic and inorganic food to the roots of the plants it is intended to nourish.

We have seen that this decomposition takes place very speedily, and of its own accord, when the vegetable matter is green, but that it can be induced or brought on in the case of dry straw by the agency of animal matter. The same means will cause the fermentation of any other vegetable substance which is in a minute state of division. Even saw-dust made into a compost heap with soil or sods, and watered regularly and copiously with the liquid manure of the farm-yards, may be thus converted into a fertilizing vegetable mould.

Differences of opinion have prevailed, and discussions have taken place, as to the relative efficacy of long and short—or of half fermented and of fully rotten dung. But if it be added solely for the purpose of yielding food to the plant, or of preparing food for it, the case is very simple. The more complete the state of fermentation—if not carried too far—the more immediate will be the agency of the manure; hence the propriety of the application of short dung to turnips and other plants it is desirable to bring rapidly forward; but if the manure be only half decayed, it will require time in the soil to complete the decomposition, so that its action will be more gradual and prolonged.

Though in the latter case the immediate action is not so perceptible, yet the ultimate benefit to the soil, and to the crops, may be even greater, supposing them to be such as require no special forcing at one period of the year. With a view to this slow amelioration, vegetable matter of any kind may be added with benefit, if in a sufficient state of division, to the soil. Even saw-dust applied largely to the land, has been found to improve it, though little at first, yet more during the second year after it was applied, still more during the third, and most of all in the fourth season after it was mixed with the soil. That any dry vegetable matter, therefore, does not produce an immediate effect, ought not to induce the practical farmer to despise the application to his land—either alone, or in the form of a compost—of every thing of the kind he can readily obtain. If his fields are not already very rich in vegetable matter, both he and they are likely to be ultimately benefitted by such additions to the soil.

Rape Dust.—It is from the straw of the corn-bearing plants, or from the stems and leaves of the grasses, that the largest portion of the strictly vegetable manures applied to the soil is generally obtained or prepared. But the seeds of all plants are much more enriching than the substance of their leaves and stems. These seeds, however, are in general too valuable for food to admit of their application as a manure. Still the refuse of some, as that of different kinds of rape-seed after the oil is expressed, and which is unpalatable to cattle, is applied with great benefit to the land. Drilled in with spring wheat, or scattered as a top-dressing in spring at the rate of 5 cwt. to an acre, it gives a largely increased and remunerating return. It is applied with equal success to the cultivation of potatoes, and generally it may be substituted for farm-yard manure at the rate of about 1 cwt. of rape dust for each ton of manure.

Malt Dust consists of the dried sprouts of barley, which, when the sprouted seed is dried in the process of malting, break off and form a coarse powder. This is found to be almost equal to rape dust in fertilizing power.

Charcoal Powder possesses the remarkable property of absorbing noxious vapours from the air and soil, and unpleasant impurities from water. It also sucks into its pores much oxygen from the air. Owing to these and other properties, it is a valuable substance for mixing with liquid manure, night-soil, farm-yard manure, ammoniacal liquor, or other rich applications to the soil. It is even capable by itself of yielding slow supplies of nourishment to living plants, and is said, in many cases, without any admixture, to have been used with advantage in practical agriculture. In moist charcoal the seeds of the gardener are found to sprout with remarkable quickness and certainty.

Soot, whether from the burning of wood or of coal, is of vegetable origin, and consists chiefly of a finely-divided charcoal, possessing the properties above mentioned. It contains, however, ammonia and certain other substances in small quantity, to which its well known, and especially its immediate, effects upon vegetation are in part to be ascribed.