The Value of Lime For Soil Acidity Correction

Poverty Bay Herald, Volume LXI, Issue 18587, 22 December 1934, Page 13

The Value of Lime For Soil Acidity Correction

TN view of the conflict of opinion as * to whether, at a high co,st, it is profitable to use lime in the Gisborne district, a bulletin issued by the Cawthron institute on the subject should be of interest.

The bulletin states that the advance of science during the last 300 years has shown the nature of the factors which operate in the amelioration of many soils by lime treatment, and lias amply confirmed the wisdom of early English agriculturalists in making periodical applications ot chalk to their soils.

The art of liming as practised in certain parts of England is one ,of the oldest soil treatments of which there is historical record. When the Romans came to England in 55 B.C. they found that chalking and marling were established practices. The inhabitants of those early times must, therefore, have noticed that soils receiving such dressings gave better crops. This tradition of liming periodically was .observed in England until comparatively recently, when increased cost of labor made it. uneconomic to employ such large dressings of lime. Leaching Effect.

Experimental work carried out over many years has shown that localities with moderate to high rainfall are invariably characterised bv the occurrence of acid s.oils from which lime and other bases have been leached by the long-continued percolation of rain-water. On such soils lime treatment has resulted for many crops in striking improvements, both in yield and quality. For many years the exact role of lime in the amelioration of soil was a matter of much speculation among agriculturists, but it is now known that lime affects the soil in a number of ways, among which may be mentioned (a) the neutralisation of soil acidity, (b) the improvement of the physical texture of soil, (c) the stimulation to bacterial activity, (d) the conservation of plant, food, (e) t tic liberation of plant food, (f) action oil fungus diseases. Acid soils are commonly characterised by a special association of weeds such as spurry, sorrel, gorso and moss, and these plants frequently serve as indicators pointing to the desirability of lime treatment.

In addition acid soils of the loam texture group are easily recognised by the experienced' farmer on account of their bad textural qualities. Drainage on such soils is poor. A good tilth is difficult to obtain and if. caught by a hot ,suu and drying wind after ploughing they dry into hard intractable lumps. Lime treatment, is such soils profoundly affects their textural qualities, improves drainage, aeration and the ability of the farmer to secure at satisfactory seed-bed. These beneficial effects result from the action of dissolved calcium carbonate on the very small “clay” particles. Lime is absorbed by the clay particles, thereby changing their properties. They now flocculate into “crumbs,” and the soil loses those very adhesive and sticky qualities which are detrimental to drainage, aeration, and the formation of good tilth. Effect on Bacterial Activity.

Bacterial activity on acid soils is less vigorous than on limed soils. An acid soil may contain less than 3,000,000 bacteria a gram of soil, while neutral soils may contain as many as .100,000,000 bacteria in the same weight ,of soil. The rate of decomposition of organic matter and the production of soluble nitrates from it., therefore, goes on much more rapidly in neutral or Ijmed soils than in acid soils. Not only are soluble nitrates produced as a result of bacterial activity, but other plant foods are released from the decomposition of organic matter, thereby materially assisting plant growth.

Not only are ammonia and nitrateproducing bacteria stimulated by the lime treatment of acid soils, but the way is paved for the free development of other classes of bacteria which may be present in only small numbers in acid soils. Azotobaeter belongs to this category, and possesses the remarkable property of fixing atmospheric nitrogen and forming soluble nitrates which are available for plants. On soils possessing a satisfatcory lime-status, considerable gains in the nitrogen level may result from the activity ot! this bacterium.

Other groups of bacteria live in association with the roots of leguminous plants, and, as is the case with azotobaeter, are capable, of fixing atmospheric nitrogen and converting it into more complex nitrogenous compounds available for plant nutrition. Clover, peas, beans, and lucerne arc all instances of plants which, under favorable circumstances, are associated with symbiotic bacteria, resulting in fhc formation of root nodules.