THE FARM.

North Otago Times, 15 February 1913, Page 4 (Supplement)

THE FARM.

SOME POINTS WORTH THE ATTENTION OP FARMERS. LAND DRAINAGE. One characteristic of undrained soils is their coldness. As the air passes over a wet surface evaporation takes place with greater or less rapidityi, according to the state of| atmospheric humidity and to the degree of motion of the wind. This is easily exemplified with regard to tho last-mentioned factor by moistening the forefinger and exposing it to the air, when a'sensation of coldness will be oxperienced upon the side exposed to the direction of the wind, which simple experiment is sometimes tried when the motion of the air is too light for one to ho sure from what point tho wind comes. This proceeding is not often necessary in Tasmania, where high winds are commonly prevalent, and the quarter whence they come unmistakable. These winds exert a most powerful evaporating influence, with, a corresponding lowering of temperature, which is liable to exert an injurious effect upon soils as well as upon stock and vegatation, The latter may ho protected to a large extent by shelter belts of trees and other means, though with regard to the soil the sun exerts a powerful evaporative effect, which is, however, to some extent compensated by the heat which it imparts. In the case, however, of the undrained soil, this benefit is largely • nullified by the physical properties of water in relation to heat. Warmed-up water is

lighter than cold, and if the source of heat is applied to the surface the warmer water remains there, and the water beneath it remains for a long, time unafhwtcd. On the other hand, if heat is applied to water from beneath, the water rapidly rises to the surface, layer after layer coming up, until the water acquires one uniform temperature, and eventually boils, i! sufficient heat is applied. This property of water is exemplified in the process of heating a copper Immersed in the liquid, it wall be found warm at the top and colder as the hand is more deeply immersed, In the case of water being cooled ■at the surface by wind evaporation or by a reduction o! the atmospheric temperature, as in the case of frost, ft cold layer is formed upon the surface, which sinks owing to the contraction of its particles, which renders it heavier. This same process goes on in the case of an undrained soil, which approaches the saturated condition near the surface.; but, where a comparatively dry layer of soil of any thickness overlies the saturated'soil beneath it, reduction of temperature by the above-mentioned process need not be seriously considered. The coldness of the surface in the latter case would be owing to evaporation of the water brought up from below by capillary attraction, and this might affect the growth of crops to a serious extent, as well as act in an injurious manner upon the health of stock,, especially in the case of grass land so circumstanced. The effect of evaporation in reducing temperature is well exemplified in the case of the porous earthenware jars used to keep water cool in warm climates, or in that of the porous butter-cool-ers now so much used in ho'ffiholds. The water carried ofi by evaporation, especially in dry windy weather, from exposed reservoirs and water tanks 1b very .great, and where these can be covered in there is naturally much less waste of water from this cause, which, although an invisible one, should be sufficiently manifest in its effects to make It worth while,' in districts where water is scarce, to go to the expense of roofing in (where this is practicable) reservoirs or tanks devoted to water storage. In my previous article the beneficial effect of the conveyance of atmospheric oxygen through the soil by means of water containing it in solution was spoken of from the point of view of its chemical action. This chemical action, moreover, produces heat, which may not, of course, bo very apparent, but must, nevertheless, havo its effect in rendering a soil warmer. Drained soils, both on this account and from other causes alluded to in the foregoing, and because water condensing from its gaseous condition in the atmosphere to that of rain evolves the heat which was previously latent in its particles, much of this finding its way into the soil when there is a free passage for moving water. The warming-up of the atmosphere after a showe'r of rain is often noticed, and is due to the heat being discharged which was previously employed in keeping the water in its vapourised or gaseous condition. On account, therefore, of the warmth of drained soils and the greater freedom with fvhich the roots of crops can pass down into the subsoil in the more favourable circumstances thus afforded them, the harvest is generally earlier upon such soils, and the quality of the grain superior, as well as greater in quantity; Moreover, drained soils are easiest to work, manures arc more effective when employed upon them, and the health of stock tends t 0 he better. It must not he overlooked, too, that tillage operations lan be undertaken mucli earlier in the spring upon drained soils, and (his is another reason why crops tend to mature earlier upon them.-By J. H. Colbourn, Agricultural Chemist, Tasmania.