FERTILISERS AND SOIL DEPLETION

Hawke's Bay Tribune, Volume XVII, 19 November 1927, Page 12

FERTILISERS AND SOIL DEPLETION

SAFETY OF PHOSPHATES.

The question often arises and the statement is often seen that fertilisers "burn up the soil.” Just what is meant by this statement is very difficult to say. The idea appears to be, however, that fertilisers have some residual effect on the soil that is detrimental to soil fertility, and subsequently lowers crop yields. This idea is partly correct. At the same time long-continued fertiliser treatment has shown that the yield of wheat can be kept up over a lorn period of years by the use of miner-’, fertilisers alone. This has been demonstrated at Rothamstead. The evidence up to date does not, however, warrant a farmer depending on fertilisers alone, but rather to use fertilisers as a supplement to farmyard manure. Other investigations have shown that certain fertiliser materials do have a well-defined action on the soil when used over a long period ot years. Thie action may be beneficial or detrimental according to tho ( feet desired. For example, the long-con-tinued use of sulphate of ammonia on soils which are neutral or acid brings about a strongly acid condition which is very harmful to many crops, but which is highly desirable on golf greens or lawns. Nitrate oi soda, on the other hand, , brings about an alkaline reaction in the soil. Acid phosphate, although in many cases acid itself, actually exerts an alkaline effect on the soil —at least it assists in overcoming the effects of soil acidity. Potash bearing materials have little effect either way, although they are regarded generally as slightly increasing acidity. It has been claimed by some that one constituent alone tends to deplete the Soil of fertility. This idea originated in the fact that when one element alone is added the increased grows draws more heasily on the other plant food constituents of the soil, thereby causing a deficiency for the succeeding crop. This is of very little interest, and does not apply to ordinary farm conditions. Supposing nitrogen alone is added to u soil. This, of course, stimulates growth, and therefore there is a greater draft on the other plant foou in the soil. But if this material is fed on the farm the amount of manure returned is greater; hence the greater removal is more or less balanced. In market garden work the whole product is sold, so there undoubtedly is a loss of plant food. Ac the same time the product is on the market earlier, a higher cash return is received and the plant food can be purchased as fertiliser and still leave the producer ahead of the game. The use of acid phosphate alone is altogether different. Phosphoric acid does not stimulate growth as nitrogen does, and consequently there is not such an increased draft on the soil supply. All our soils are becoming deficient in phosphoric acid, and by the application of phosphates we simply supply an element which is defiicient. There can be little or no harmful effects arise from the use of acid phosphate alone.