GREEN MANURING.

Globe, Volume XXIII, Issue 2214, 31 March 1881, Page 4

GREEN MANURING.

fOOMPILBD 808 THH " WHHKLV BEHSB."] The question as to how lands devoted to the cultivation of grain can he manured is one that, ignore it as ho pleases, tho mm who devotes himself to agriculture muat, if he wishes to obtain grain from his land in payable quantities, give it a practical solution. Alroady, in Virions parts of this provincial diatriot, farm after farm can be seen, in the early spring of the year, especially if that be a dry season, culling out in tones made eloniitnt by parched- up crops, that tho boil is exhausted, or nearly so, and wants help before it oan again yield such crops of cereals as wore produoed the first or second year after tho land was broken up. Thorn are several methods by whioh the land can bo rncuporated. Wo need hardly say we are not going to advise that tho system whioh obtiiins in England—viz., of carting manure on to tho land—should be had recourse to in Canterbury, because tho cost of labor and the scarcity of manure would be two fatal obstacles to such a course. There certainly is tho plan wbioh obtains largely with well-to-do farmers of laying such lands down to giviss ; and there is also the alternative of sowing green crops to bo eaton off by sheep. As to the first, but few farmers oould afford to do this—" whilst the grass grew they would starve" 5 and as to the feeding off prooesß, some would bo ucablo to purohase the stock, and in many caaes the condition of their subdividing fonces would ?revent thorn letting tho green crop for feed, t is in this onse that green manuring is tho only alternative. Tho process of green manuring ia based upon principles which are sufficiently intolligible. Plants derive their nourishment partly from the soil through thoir roots, a::d partly by tho atmosphere through their leaves ; from the soil they extract a portion of thoir organio and the whole of their mineral constituents. If, as was at one time believed, they were wholly dependent upon the soil, wo should have some difficulty to account for the beneficial action of the process now under consideration. The beautiful experiments of Priestly, Saussure, Daubony, and others, have, [however, taught us that by means of their leaves plants decompose carbonio acid, whioh is always present in the air, liberating the oxygen, and appropriating tho carbon to their own purposes; and, further, that from the volatile carbonate and nitrate of ammonia they derive supplies of nitrogon for the formation of their albuminous constituents. Professor Liebig, in proof of tho materials of vegetation being derived in great part from tho air, points to the case of ancient forests, suoh as those of North America, whiohafteruouriahingunchacked for ages, and producing enormous quantities of timber, yet eventually leave the soil in a state of riohness and fertility, that a century of the wasteful cropping of the firßt settlers will hardly suffice to impoverish it. This is a oase of natural green manuring on a largo scale. Carbon and nitrogen are extracted from the air in sufficient quantity not only to build up the structures of the gigantio trees of the forest, but by the periodical falling of the loaves and smaller branohes, to form a thick bed of vegetable mould. But the benefits derivable from green manuring are, in part, referriblo to the action of the roots of plants. If, instead of leaving the land exposed only to tho action of the tho atmosphere, we crop it with a plant whose roots run in every direction for food—and, it whon this plant has arrived at considerable growth, we turn it into the surfaoe soil, wo ave not only enriched tho latter by elements derived from tho air, but also by matters both mineral and vegetable, fetched up from the Bubßoil. The plant thus aots the part of collecting tho nourishment for a future crop in a way that no mechanical subsoiling or trenching oould effeot.

The putrefactive fermentation of animal and vogetablo aubstanoes ie much accelerated by moisture. Dry wheat, or bean straw, as ovevy farmer knows, takes a long time to decay in the aoil, but a green and succulent vegetablo rapidly fermonto, giving rise to the aame products in the soil aa it would out of it, and these beoome immediately available mi manure, inaimuch as the ammonia of the air is absorbed and retained by the soil itself, independently of any kind of vegetation. The advantage of groen manuring over an ordinary fallow must bo reforred to the increase by the leaves of the carbonaceous matter only, and by the roots of the carbonaceous, aeotized, and mineral matters, which are, in this manner, oonoentrated in the surface aoil. Theoretically, that plant will bo most adaptad for the purposes of green manure which presents the largest surface of leaves for the collection of atmospheric food, and sends down the deepost roots for the mineral wealth of the subsoil, and the crop which will be the most benefitted by the supply of manure thus afforded, will be that ono which, besides throwing out its roots laterally, or being a shallow feeder, is, at the same time, most dependent on the soil for nourishment. Vegetable aubstanoes in their green and auooulent state are powerful fertilizers when thoroughly incorporated with the soil. Tho moat pertinent explanation of this faot is fui-nished by the consideration that they supply the identical elements that future crops require ; in the same manner that out of the materials of one house, another may be elaborated. And it ia true that many of these materials exist in such anion and affinity aa to render them especially adapted for the nutrition of the future crops, for it is a recognised troth in physiology that both animala and plants take up and assimilate from their food a portion of their bulk in the preciae form in which it exists in that food.

The praotico of growing orops for the apooiul purpose of ploughing in as a manure for ouocoeding crops, ia not justified by this consideration merely. It would seem to be a waato of time and material to convert the elements of vegetable growth into living forma twioe before they ore made profitable. "Why grow a lupin or olovei plant one season to be buried in order that from its remains a cabbage or a turnip maybe produced ? Why, if you build your house, do you not fetch your materials direct from the quarry ? These questions would be unanswerable did plants obtain all their food from the soil. But such is not the case, a great portion of the bulk of green orops is obtained from atmosphoric sources ; and after a green crop is ploughed in, the soil necessarily contains more of the organic element essential to vegetable nutrition than it did before the orop was grown; it is rioher, in fact, by the carbon, oxygen, hydrogen and nitrogen, which the green orop lias obtained from aouroes independent of the soil. In like manner the crop grown after a green crop has been ploughed in has the advantage of a ready supply of mineral elements, wLioh have been worked up by the roots of the fertilising orop for the soil and subsoil, and which in many instances, owing to their sparing solubility, are with difficulty obtained under ordinary circumstances. The practice of restoring fertility to exhausted soils by laying down to pasture for several years, aud tho advantage to succeeding green crops from the introduction into the rotation of depastured seeds, or even clover mown and carried off tho field, illustrate the manner in which green crops aro beneficial as manuros. It ia ovident that. i£ such crops did not return to tho soil some other elttments than those which they found thore, «o length of timo under green crop would restore fertility bo an impoverished soil; but that, on tho contrary, under the constant abstraction of phosphates in tho bones, and of valuable organic elements in tho flesh, fat, and blood of animals depastured upon it, deterioration would take place. But the practice of green manuring is one that ia sanctioned by the authority of oxporience, as well as of tboory. In the remains and stems of clovor crops, of depastured ooeds, we receive the advantage of a groon manure, tho value of whioh, in promoting the growth of oata and wheat, is well understood by overy fariruir. Q-reon manures grown for the special purpose of being incorporated with the soil in their Fresh st;ito are usually those of quick growth, and capable of being grown upon poor soils. Those that have beon recommended for this purpose are Italian rye grass, olover, buak wheat, lupine, rye, rape, mustard, tares, &o. Mustard and rape may be sown on light soils offer an early crop of graiD, whilst for stronger lands a green orop of rye or tares may bo ploughed in, and will furnish the succeeding wheat crop with useful food. Tho best time to plough in in when the crop shows for flower ; it has then acquired its greatest manuring power.

Closely connected with this subject comes Che rotation of crops, whioh wo shall aonsider in a future article.