POTASH MANURES.

King Country Chronicle, Volume VI, Issue 446, 9 March 1912, Page 6

POTASH MANURES.

When potash ig excluded from the soil and vegetation is cultivated thereon.the plants are weak and sickly with a tendency to a creeping habit. It is found that soda cannot replace the absence of potash. Marshall's hypothesis, which is the generally accepted one, is to the effect that the growth is weak and sickly owing to the inability of the plant to form starch in the absence of potash. When all the other constituents of the soil are in excess, but the potash becomes deficient, the plant, remains stagnant in its growth. If the famine a" potash has not lasted too long, and chloride of potash solution be added, the plant recovers and forms starch. The amount of potash in soils runs from 0.1 and 0.2 up to O.S and 1.0 percent. It therefore follows that we can have about 21 tons per acre of potash to the land. As a crop of wheat removes only a few pounds, it would take from 50 to 100 years, to remove one ten.

Potash in most countries shows no appreciable effect on many crops, as, for example, on wheat. It must be remembered that potash is returned to the land, from the crop that is cut, in most farming, from farmyard manure, and so on. Potash is the one of the three indispensable constituents of the soil of which there is least drain. The best guide as to whether potash should be used or not is by means of a series of Sots in the field. A farmer can readily test this for himself by buying a few cwts. of potash salts, and marking the lots on which he applies it. This is a much more satisfactory method than analysis. The latter is complicated by the complexity of combination of the potash present, and it is also difficult to get representative samples. One can often tell from the character of the vegetation if there ia any likelihood of a deficiency of potash in the soil. If the percentage of potash is low, the legumes disappear and the grasses become taller. There is little likelihood of our needing potash manures in New Zealand. There are, however, special conditions and contingencies on all farms, when it is desirable to use potash manure. The forms in which it comes on the market are the sulphate, the chloride, and as kainit. On the farm there is normally a gain in potash from wood ashes. The potash in the soil exists in a number of different forms, but chiefly as a double silicate of potash and alumina. Only

the merest fraction is soluble at any one time in the soil. The absence of lime makes the potash more inert. Quicklime applied to the soil is indirectly a means of supplying potash. The soils most benefited by the application of potash are thin soils and limestones, and occasionally peaty soils.