FACTS FOR FARMERS.

Waikato Times, Volume VI, Issue 323, 9 June 1874, Page 2

FACTS FOR FARMERS.

EXHAUSTION OF SOILS. On oomparing tho general composition of our .arable S01I3 with that of other soils, where tho means of abundant manuring aro at hand, a most notable peculiarity presents itself, and one which, doubtless, hai Tery considerable influenctj on the whole problem, both of temporary and permanent exhaustion. Tho peculiarity wo refer to is the general deficiency of organic matter. With a view to getting a clear insight into the influence which organic matter exerts in the soil, we purpose I© briefly consider the nature of what is culled organic matter, and m what way it is so instrumental in the economy of agriculture. All plants and animals — organisms — are composed of two distinct classes of substances — those which are fixed and will not readily decompose by the action of heat or oxydation, as potash, lime, magnesia, iron, sulphuric, phosphoric, and silicic acids. Chemists call these the mineral food of plants. They remain in the soil, do not exhale, and aro not carried off, or brought back by atmospheric agenciesThese, although they form but a very minute proportion by weight of tho plant, are still quite indispensable, so that no plant will thrive unless those minerals are present, which it individually requires. The other class is the organic or volatile portion ; that part which is liable to decomposition by heat, and which is combustible in the presence of the oxygen of the air. By far the greater bulk of all organic bodies, whether animal or vegetable, consist of the four elements — carbon, oxygen, hydrogen, and nitrogen. Thes» are held together in the organism in the most complicated compounds, as long as the mysterious force which we call vitality operates. As soon us this ceases its functions, or r in other words, when death ensues, whether to plant or animal, these four substance* tend to loosen themselves from the more complicated combinations, and to assume lower and leu complex forms. The presence of the oxygen of the atmosphere is an element required in order that this decomposition shall take place. It unites with the carbon, forming carbonic acid, and the hydrogen and nitrogen are liberated in combination as ammonia. The same result is obtained either by rapid combustion or by the slower process of decay, the results in each instance being the same, that is, the production of carbonic u cid gas and ammonia. Whenever any vegetable matter is incorporated with the I porous soil, so that there is an access of air to it, the result is invariably the production of these two most importa nb gases. There has been a controversy for- some years past among scientific men themselves as to whether the gases thus derived enter the plant by the roots, and contribute to the plant the necessary carbon and nitrogen, or whether tho atmosphere alone is competent to supply these bodies in sufficient quantities. Probably the growing plant gathers them from both sources ; but as our desire is to avoid all scientific points upon which any diversity of opinion exists, we pass this question over as not being Eecessary to our subject, and we confine ourselves to the consideration of what all scientific men are agreed upon, and that is the fact that both the? e gases — carbonic acid and ammonia — net with wonderful power on the soil itself, modifying its chemical composition, and acting beneficially, by causing such changes as to render the ingredients of the soil more available to the roots of plants. The meckanical action on the soil caused by the gradual decay of the vegetable substances enclosed is a very important point to be considered. By that decay the soil is rendered more porous, and much more able to exercise those curious functions upon whieh, in a great measure, fertility depends. One of the most important of these, and one of special interest to us, in a country with a deficient rainfall, is the power of absorbing and retaining moisture during longthened periods of drought. This faculty is very largely dependent upon the state of the soil with regard to its organic constituents. No soil having a large deficiency in these will have the power of retaining sufficient moisture for the nourishment of the plants growing upon it during any extra dry period. Now arises the very practical question — how can this deficiency be made good, or at least, what can be done to render the exhaustion of organic matters less rapid ? One of several methods which present themselves to us, and one which we> consider should be introduced into our agricultural system here, is the growth and ploughing in of green crops; and our favorite for this is ' Mustard.' i , This well-known crop has been used as a green manure formanr ages, and although the advantnges which undoubtedly do accrue from the use of it as a fertiliser were not known scientifically to those cultivators of the soil who went beforous, yet we have abundant evidence that even from the most remote times, mustard and other similar Crucifero) were grown and ploughed in as a green manure. The mustard during its rapid growtli sends down rootsinto the subsoil, and brings up thence many of the mineral constituents of wheat in a form in which they are easily avadable bj the wheat plant. It is instrumental in bringing tip from the subsoil to the soil Jood for wheat, which could not possibly have been otherwise available. During its ultimate decomposition in the soil, and in the presence of the succeeding wheat plant it presents to the wheat those sub-< stances which it requires, both vegetable and mineral, in a, foym in which they can. be easily assimilated and appropriated, besides contributing to the soil a larger proportion of organic matter than it previously held. — Sout/Z Au&lrahaa Advertiser.