SOUR OR ACID SOILS.

Otago Witness, Issue 3250, 28 June 1916, Page 10

SOUR OR ACID SOILS.

As every farmer knows, the presence of acidity in a soil is injurious to plant life. It gives rise to some well-known plant diseases, such as " finger-and-toe " in turnips; it prevents the growth of sweet herbage; and there are some plants—for instance, lucerne —that refuse to grow in acid toils. The Mark Lane Express in a recent issue asks, What are the principal causes of soil acidity? and sets them out, thus: "The decomposition of organic matter accompanied by the formation of various organic compounds, including the production of organic acids. The action of soil bacteria acting upon certain portions of the vegetable matter in the soil. The continued application of acid mineral fertilisers. Thus, when sulphate of ammonia is decomposed in the soil there is a formation of free acid in the soil solution, which is injurious unless counteracted by the presence of a sufficient supply of lime in the soil. It is possible that to the acidity so produced in the absence of adequate lime may be attributed the unsatisfactory results which have sometimes been noticed from the use of sulphate of ammonia in candy soils. The fermentation of green materials: When a heavy crop of green material is ploughed under, fermentation will set in if the conditions of temperature and moisture are favourable, and as a result the toil may become sour unless it is well supplied with bases such as lime, magnesia, etc." Experiments have shown that acidity exercises a toxic effect on plant life, which is injurious to. the growth of nearly all the cultivated crops. Acid soils are infertile because soil bacteria, which are eleborators of plant food, cannot grow in them. A soil may be rich in nitrogen and contain sufficient minerals, but if it is water-legged it is sour and acid, and Mill not produce good crops. If, however, this condition is corrected by drainage and aeration, it becomes a fit habitation for soil bacteria and becomes productive. It is specially important that the soil conditions should be made as favourable as possible to the development of the nitrifying bacteria. The acids in the soil may also liave the effect of bringing into solution minerals that have a bad effect on plants, as for example compounds of alumina and iron. Drainage is essential if the land is waterlogged, and the application of lime to neutralise tha acids. Lime in one form or another is the remedy. It neutralises sourness and prevents the formation if poisonous compounds in the soils. It prevents fungoid diseases, and in pasture lands promotes the growth of the more nutritive herbage. Basic slag owes much of its value to the lime in it, which produces a wholesome and sweet condition of the soil.

It would appear from the result of experiments that for practical farm purposes the neutralising effect of applied lime is not exerted below the depth to which it is incorporated with the soil during the various processes of preparation and cultivation : consequently the more thorough and deeper these operations are the better the distribution and the more effective the action of tlie lime. The incorporation of lime with three or four inches of surface soil is sufficient to produce marked effects on add soils, and, generally, moderate dressings at frequent intervals are to be preferred to heavy dressings at longish periods.