Pasture Notes.

Digger (Invercargill RSA), Issue 17, 9 July 1920, Page 13

Pasture Notes.

SOIL MOISTURE. Every farmer knows that if there were no moisture in the soil there would be no vegetation, hecause plants can only assimilatp food when it is in a state of solution. As droughts come and go, we are more and more impressed with the necessity of man coming to the aid of nature and assisting her to store and conserve the rains tnat fall on the surface of the soil. I say "surface of the soil" hecause all the rain that falls is not immediately absorhed as it falls, - except the soil is brought to a condition in which. it can immediately assimilate it. That the arable farmer can aid in the storing and conserving of soil moisture is without a doubt, but the man who farms pasture land only, is more or less helpless. The relations between soil and water are the same everywhere, but the laws which govern them require modification for soils of different types. The water in the soil acts in three different ways, the types of water heing known as hygroscopic, capillary, and gravitational. The hygroscopic water is that which is absorbed by a dry soil from the atmosphere, and the quantity absorbed depends upon the charactex of the soil. The soil with the finest particles absorbes the greatest quantity of atmospheric moisture, but water of this kind affords little help to the farmer. Capillary water constitutes the main supply to cultivated plants, and it acts in a manner similar to the action of oil in a la-mp wick. As the attraction of the oil is towards the dry part of the wick, so is the capillary water in the soil drawn to the dry parts. The attraction is principally upwards, but it also extends slowly in a horizontal direction. ,, Gravitational water always tends downwards, hut. when not carried too far it may he brought back by the force of capillarity tq be used by growing plants. Under certain goil conditions, capillary and gravitational laws work beneficially for the farmer. It is the farmer's part to see that such soil conditions exists ; and the key to the whole matter is good cultivation. If the natural law of capillarity is allowed to run its eourse unchecked, there will be great waste of soil moisture, hecause the capillary force draws the moisture to the surface of the soil where it is wasted by evaporation. How can the farmer prevent the waste? He can prevent it to a great extent by surface cultivation which interferes with the capillary action, and thus, to- a considerable degree, blocks the passage of the moisture to the surface or, to put it more plainly, the cultivating implement cuts the connection between the. upper and lower layers of soil. The newly cultivated upper layer of soil is called a soil mulch. As to the Ipss of soil moisture by gravitation, the farmer can prevent it to a considerable extent by deep and thorough pr,eparatory, cultivation, hecause the more completely the soil is pulverised, the greater will be the quantity of moisture held by it for the use of plants. Soil brought to such a condition, acts like a sponge, retaining and holding a maximum quantity of moisture. The question natural ly arises, .do 'New Zealand farmers aid nature to minimise the serious effects of drought by acting so as to regulate the laws which govern the action of capillari /, and gravitation? It requires only a curhory glance fo convince us that, in the average case, we do not, although there are many exceptions. As a rule, we sow or plant our crops in such a way as to make surface cultivation impossible, and nature punishes us for our carelessness. We sow our turnips, rape and other forage, or fallow crops broadcast, close the gate of the paddock, and allow nature to work her will. In a suitable seaso'n we get a crop. In a dry one we may get half a crop, or none at all. Nature will work .unaided, but the result is often disastrous to the farmer when his intelligent help is withheld. The pi'inciple of surface cultivation, as a means of conserving the soil moisture, has for many years been recognised by the British farmer, and the drier the weather, •the more does he realise the necessity of persistently stirring the soil among his forage or fallow crops. To that end he sows or plants his crops frrrows, sufficiently far apart to admit of intercultivation, and he never dreams of doing otherwise, under any circumstances. The soil mulch, which is the result of intercultivation, is of the greatest benefit when the soil is thoroughly dry, and such cultivation should never Be attempted when the soii is wet or even

very damp. It is then of little value. When the surface soil is very dry, and beavy rains come, jthe benefit of the soil mulch is cancelled for the time heing, and the cultivation must be repeated as soon as the surface soil is sufficiently dry. When heavy rains fall, they have the effect of connecting the dry surface soil with the sub-soil, and if the cultivation is fiot renewed, the moisture is drawn quickly to the surface and wasted by evaporation. If the laws of nature never vary, and we are quite convinced that they do not, we can but conclude that heavy rolling, after the seed is sown, must also result in a waste of soil moisture, and if we do roll, we should at once form a soil mulch by using the harrows. This remark, of course, refers more to heavy clay soils than to light sandy cnes. All gardeners are well aware of the benefits accruing from a mulch consisting of dry straw, leaves, or dry manure, and such soil coverings are even more effective than a natural soil mulch. A thin layer of soil on top of the straw will make the mulch still more effective. Many farmers. regard a covering of stones as the hest of all mulches, and the contention seems to be proved by the fact that the dry chalk soils . of some of the Southern English counties — have remarkable power of retaining their moisture and the mulch consists of a thick covering of flints which are1, of course, quite natural. It should be perfectly clear that one of the sources of soil moisture waste, namely, evaporation from the surface, may he controlled to a certain extent on arable land by judicious surface cultivation. Another source of waste, and a very serious one, is the growth of weeds among the cultivated crops, and this may also be controlled by intercultivation. Weeds rob the crops, not only of food, but also of a very considerable quantity of moisture. They take up water directly from the soil through their roots, and evaporate a great deal through their leaves. -