Agriculture. FALLOW LAND.

Waikato Times, Volume XIX, Issue 1571, 29 July 1882, Page 6

Agriculture. FALLOW LAND.

By R. W. Emj:uson Mamvob, IM.C, •—.-*.. F.C.S., Ac. Author qf " The Chemistry of Ayrmdturc."

*The great bulk of an average soil consists t>f clay and other substances, which do ■floii in themselves furnish anything to •growing vegetation, and whose functions Qfre »imply — (1). To hold the roots and keep the plants in their place. (2). To Maintain the conditions of warmth and moisttfte essential to plant life, and— (3). To' absorb and retain assimilable plantiood, so as to prevant its being washed Jottf'of' the land by rains. Associated Hvith the mechanical constituents, as they "may be termed, are the substances which Stater into the composition of plants. Of these a small proportion exists in forms of combination suitable for absorption by the roots of plants, and is preserved by the retentive power of the soil ; -while a fritlch.larger quantity occurs in insoluble and unassimilable conditions, in the form 'of undecoinposed fragments of rock, "mica, &c., and only becomes useful as nutriment for plants when natural 'agencies at work m the soil have rendered '■them soluble, and therefore available, •The amount of available food present in ••even a rich soil rarely exceeds a few tenths per cent., and the constant removal of crops, without restoration be ing made in the form of manure, sooner or later, leads to the exhaustion of this quantity, when, of course, the land becomes infertile. By the process of naked fallowing land which has thus been impoverished becomes again capable of carrying remunerative crops. Pining the period of rest, a portion of "the insoluble or inactive plant-food constituents under the influence of changes of temperature, moisture, the roots of plants, and the action of carbonic acid, produced by the decay of vegetable substances, such as moulds, or hums, become converted from n. locked-up state into available or soluble forms, and hence the renewal of fertility. This is the chenustry of the naked fallow. It may be added that the distinguished English agricultual chemist, Dr J. H. Gilbert, P.R.S., has recently shown that the much despised worms act very beneficially in the soil by enriching the surface with nitrogenous (or ammonia— producing) matters. In fallow land this contribution is much more important than has hitherto been believed to be. Some highly interesting and useful information to the agricultural world by the German chemist — Woollny — on the influence of fallowing on— (1), The temperature. (2). The humidity, and —(3). The decomposition of the soil. It is found that a soil in fallow is warmer in summer, but colder in winter, whilst the variations in the teinpeiature arc much greater than i& the case in a .soil which is covered with a plant surface. Plants interfere with the direct action of the sun on the surface of the .soil, and consume a quantity of heat, which is thus lost to the soil in the evaporation of water from plants, and by nocturnal ladiation. Further, as tht upper organs of perennial plants decay they form a superficial cover to the land, and the cooling effect of the air and radiation is thereby diminished — for fallow land the reverse action takes place ; there js uninterrupted radiation, and the tompeiatiure of the surrounding air h communicated to the stirface of the soil, and thence transmitted to a lower stratum. The amount of moisture in a cultivated soil under vegetation is invariably less than is in the same land under fallow. This holds good for all kinds of soil in fallow, even after harrowing, &c. Experiments on grass and clover land, and on quartz, sand, turf, and clay soils, prove that with the same rainfall a considerably larger quantity of water passes through a soil iv fallow than through a soil which is covered with growing plants. It is evident that fallowing plays a very important part in determining and regulating the humidity of the soil, and in maintaining the crops during the season of drought. It also enables us to comprehend the good results obtained by growing rape after a crop of olose-gi owing and desiccating plants, such as clover especially if the land has been harrowed and kept in fallow some time previous to sowing it, and of wheat after rape. In the latter cuso the soil has had time in the interval to reabsorb a quantity of moisture equal to that withdrawn from it by the preceding crop. The generally moist state of fullow land, together with a higer temperature, promotes the decomposition of vegetable matter, and enriches the air in the soil in carbonic acid. It was found by analysis that the amount of this gas in the air in the soil at a depth of about 18 inches on land in fallow, was on an average, during the summer and autumn months, four times as muoh. as that in grass-land. This carbonic acid, as we have seen, is favorable to the decomposition of insoluble minerals ia tho soil, and the liberation therefrom of available plant-food. Whilst as a rule, it may be Btated that fallowing is advantageous to land, yet under some circumstances, it is actually injurious. It injures sandy soil, when the object ia or should be to keep the soil as much as possible under a plant surface, in order to prevent a washing - out of its soluble constituents ; also, on clayey soils in damp localities, or with muoh rainfall, as the surplus water being unable to escape by percolation, lies stagnant on the surface of the land.