Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/73

 AGRICULTURE. PART

47

II.

Of the various Operations upon the Soil, in order to prepare it for the Recsp-' tion and Nourijhment of Plants. hills ought to be covered, to prevent the exhalation of S e c t. I. Of Manures. vegetable food. But the difficulty is, how to execute it. TG'Very fubftance which promotes the growth of plants -Some propofe a thin layer of earth for this purpofe; ■*"'* is denominated a manure. others, that a pit fhould be dug, built with flags at the As to the operation of manures, fome maintain, that fide, and covered with a roof. The former would anthey give to the earth an additional quantity of the vege- fwer very well, -were it not for the additions that are table food; others, that they are of no other ufe than conftantly making to dunghills; and the latter is fo to divide the foil, and therefore that tillage may be fub- expenfive, that few people will chufe to make trial of ftituted’in their place. This lafl opinion was embraced it. When dung comes from the liable or byre, it is mixed by Mr Tull, and is the fundamental principle in his with ftraw; which abforbs the moifture, and prevents it horfe-hoeing hulbandry. A minute divilion of the foil from exhaling till the ftraw itfelf putrefies. When in will da. a great deal; but the experience of all ages this fituation, if it be laid thick upon the top of the fhows that it will do much more by the addition of ma- dunghill, there being but a fmall furface expofed to the nure. air, the juices will be tolerably well preferved. In Scotland, it is the univerfal practice to dung lands, As dung thus lofes its beft qualities by being expofed that are in conftant tillage, at leal! once' in five years ; to the fun and weather, it ought to be plowed in as foon and it eonfifts with obfervation, that the ground is con- as poflibk, after being laid upon land. If fufficiently fiderably enriched the firft year, but that the crops gra- putrefied, it ffiould be plowed in with a fhallow furrow, dually decline till the virtues of the dung are entirely ex- as its juices are waffied down by the rain : It fhould likehaufted. wife be fpread very equally; for when large pieces lie Some manures lofe their virtue by being long expofed fcattered up and down, they become a nidus to infedts to the air. If dung be kept after it is fufficiently rotted, ■ and vermin. the moft valuable part of it will evaporate. Others, as lime and marks, are of an oppofite nature: the longer Of Lime. they are expofed to the air, their utility to the land is improved, fftom this circumftance it is probable, that Lime being of an alkaline nature, attra&s acids: marks and lime attraA fomething from the air which ren- Hence it is fuppofed to communicate to the foil a power . ders them more favourable to vegetation. the vegetable food from the air. Lime There is a great variety of fubftances which, when of attradHng heavy fubftance, and penetrates deep into the foil; laid upon land, adl as manures. But the moft ufual ma- itis afometimes even below the reach of the plow. nures in this country are dung, lime, marks, afhes, foot, By fermenting with'finks acids, it breaks down and divides fea-weed, fhells, tic. the foil into fmall particles, and makes it foft, mellow^ and evidently in a ftate of fermentation. It likewife diffolves oils, and all animal and vegetable fubftances, and Of Dung. converts them into vegetable food. This quality ren*. Dung is properly the excrement of animals ; but what ders it peculiarly ufeful in deftroyirg root-weeds. commonly goes by that name, is a mixture of excre- Thefe being the general properties of lime, it is fup■ ments, putrefied vegetable and animal fubftances. If pofed to have a twofold operation upon land. When a dunghills be kept after they are fufficiently rotted, the large quantity is ufed, efpecially after being long expooily and more volatile parts, which are the beft ingre- fed to the air, it promotes vegetation by giving a kind of dients, fly off. They fhould likewife be placed in a ftimulus foil, and making it exert itfelf. This, dry fituation, and raifed high at the fides, to prevent operation toof the lime is not merely hypothetical; for expethefe r parts from being carried off by water ; for much rience fhews, that land thoroughly limed may be reduced u ater prevents the uniform putrefasftion of dunghills of to a poorer condition by cropping, than if it had nor this mixed kind. at all. It is even poffibk to reduce limed To promote a proper putrefadlion, the dung fhould been tolimed a caput mortuum; and the more frequently and not be laid in fmall heaps, but fpread thick upon the dung- land the better the hill ; for by this means the fermentation commences foon- to this ftate. land is plowed, it is the fooner reduced er, the natural fap is preferved, and the dung is prevent- Lime alfo enriches land, by augmenting the vegetable ed from being burnt, or f.re-fanged, as it is termed by aliment. When intended for this purpcfe, only a fmail farmers. Dung, when burnt in this manner, is dry, quantity fhonld be employed; as a fmall quantity of white, and ufekfs as a manure. It is agreed, that dung- hme is fuftkient to impregnate a large quantity of earth,and