APPLICATION OF LIME

Te Awamutu Courier, Volume 60, Issue 4234, 22 January 1940, Page 2

APPLICATION OF LIME

AN EXPERT’S OPINION. WHEN AN EXCESS IS REACHED. Before Canterbury farmers took up liming seriously there were few critics who issued occasional warnings of the danger of excess liming, comments the Press. The New Zealand user has not reached that stage yet—not by a long way. according to an opinion of lime effects in an article in the British Farmer and Stockbreeder. Though the quantities that can bo usefully and safely applied vary according to the type of soil, the climate and the cropping policy, It can be said, acording to the writer quoted, that spreads of more than 2J tons of quicklime to the acre, or equivalent quantities of slaked lime and carbonate are excessive and wasteful, although not necessary harmful in all cases. The equivalent of 21 tons of burnt lime is approximately 5 tons of carbonate, and nobody in New Zealand ever heard of more than 5 tons an acre of carbonate being applied in general farm practice. One to two tons are the maximum in initial dressings in Canterbury, although somewhat larger quantities have been applied in wetter climates. When we commence to treble the quantities at present applied, then some of the possible results pointed out by the writer as follows are worth observing. THE DANGER POINT. When used in excess, lime, instead of enriching the soil, actually reduces the fertility. In the first place, the organic matter of humus is destroyed, the loss of which not only affects the workability of the soil, but also removes the valuable nitrogen compounds it contains. This fact is particularly marked upon light, open soils and when dealing with these it is preferable to apply lime in the form of carbonate. One beneficial effect of liming in moderation is that certain plant foods, particularly potash and phosphate, are set free and become available for crops. If too much lime is applied, however, more phosphate and potash are set free than can be taken up by plants, so that these foods are washed out by rain and are lost. Certain plant diseases also become prevalent when soil conditions are rendered too alkaline by excessive applications of lime. A well known example is common scab in potatoes. Hence, when potatoes are included in the rotation, lime should be applied only in sufficient quantity to make the soil neutral, and as long as possible before the planting of the next potato crop. “Take-all,” the fungoid disease of wheat, is also favoured by the alkaline soil condition caused by too heavy liming. Burnt lime is more concentrated, i.e., while the cost a ton may be double, it is cheaper a unit of calcium oxide than ground limestone. Weight tor weight, burnt, lime contains about twice as much of the essential "element” (calcium oxide) as ground limestone. To produce the same effect it is, therefore, essential to apply twice as much ground limestone. The burning of lime is a difficult operation, and the quality of the product, moreover, is variable. On the other hand, ground limestone consists solely of the crushed natural rock, and is not subjected to any burning process, and is therefore of constant composition from the chemical point of view. Owing to its caustic action, burnt lime cannot be stored on the form or applied to land during the growing season.

It should be remembered that the final effect on the land of both burnt lime and the ground natural rocks is the same, except that burnt lime is perhaps for heavy clays, since it has a stronger “lightening” effect. Tests of soils taken in Canterbury some years ago showed that only about 1 per cent showed neytral content. Although some allowance has to be made for the lighter rainfall in this province than in England, it would appear that we are a long way off the danger point in the quantities of lime used.