Lime’s Important Role In Soil Fertility

Press, Volume CVII, Issue 31409, 30 June 1967, Page 6

Lime’s Important Role In Soil Fertility

It is common knowledge that to grow well, plants must have access to readily available supplies of nutrients.

These may already be in a fertile soil, but most frequently, especially under intensive cropping it becomes necessary to add them in the form of fertilisers, a need which is accentuated in areas of high rainfall where leaching occurs, a process which also increases soil acidity. Intensely acid ground causes weak growth and sometimes complete failure, in particular with leguminous Slants such as peas and beans, fence the need for lime.

Liming plays a considerable role In soil fertility quite apart from supplying the vital element, calcium, and assists in reducing the soil acidity level.

It can reduce the susceptibility of some plants to disease sueh as club root of brassicas. Certain bacteria are stimulated into activity such as those which break down organic matter with the result that the availability of nutrients such as nitrogen increases. Liming can also promote better use by plants of phosphatlc and potassic fertilisers. The earthworm population increases, thus increasing such matters as soil aeration.

It also helps to improve drainage through clay particle floculatlon, and can be used to bind some sandy soils, making them more water retentive. Over-liming, however, can cause potato scab, and decreases the availability of such trace elements as boron, iron, manganese and zinc, apart from causing insolubility of phosphates in the soil.

A deficiency of iron is the most important and likely complaint where soil alkalinity Is high. Its lack in plants Induces a chlorotic or yellowing effect on the young leaves

and in severe cases can result in die-back of the terminal shoot. Plant Sensitivity Some examples of plant sensitivity to lime deficiency are:— Very tolerant: Azaleas, rhododendrons, ericas, conifers. Fairly tolerant: Potatoes, strawberries. Fairly sensitive: Cabbage, maize, turnips, kale. Sensitive: Carrots, onion, lettuce, celery. Very sensitive: Peas, beans. The presence of preponderance of certain weeds has always been regarded as an indication of soil acidity. Although one should not jump to immediate conclusions if these are noticed in proportionately greater numbers than usual, they do offer some indication. These include sheep sorrel, spurrey mass, and wiry grasses such as bent and red fescue. Long, undecomposed organic matter in the soil, and club root in cauliflower, cabbage and turnips, are other passible signs of soil acidity. The problem which usually worries many gardeners is when to lime, how often, and how much. Certain factors have been presented so far and from this can be realised that an excess can generally cause more damage than too little; that greater quantities are needed in higher rainfall areas; and that lime in itself can prove beneficial to the soil alone. It should also be borne in mind that the optimum soil growing condition for most plants is slightly acid, with a P.H. rating between 6 and 6.5. The pH of a soil indicates, in simplest terms, the degree of acidity on a scale ranging from 0 (very acid) through to 4.2 (about the most acid soil encountered in New Zealand) 7 (neutral) to 14 (exceptional alkalinity).

Most New Zealand toils vary between 4.5 to 6.5.

The rating is obtained by subjecting to tests soil samples taken at random from from various parts of a plot to a depth of about 12 inches. This can de done through professional concerns offering such services, or by approximate methods, using a kit set made up for this purpose and available from retail stores and agricultural produce merchants.

Average Application For those who are less meticulous, or less interested in their garden soils, the average vegetable plot could be given up to Boz a square yard every two to four years. It does not really matter when it is applied but it is preferable to allow several weeks to elapse before sowing. Early autumn is regarded as most suitable as there is then a greater abundance of moisture present, more vacant space and more materials decomposing in the soil. Evenness of distribution should be observed as there is little lateral movement of the material in the soil. For this reason finely ground lime is best

Lime can be bought in various forms under the same name. They are: (1) Hydrated lime, which is very fine and used in making up Bordeaux mixture and is extremely soluble. It may also be sold as agricultural lime. (2) Quick lime or builders’ lime (calcium oxide) which can cause temporary injury to vegetation if applied to growing plants and is very quickly available to plants under suitable conditions. (3) Carbonate of lime is a ground limestone which varies in its appearance and purities depending from where it comes. It is relatively slowly available and not injurious to plants. If used, about double the quantity would be needed in preference to quick lime and lj times as much instead of hydrated lime. »