POTASH TECHNIQUE

Ellesmere Guardian, Volume LIII, Issue 13, 16 February 1932, Page 8

POTASH TECHNIQUE

NEW CONCEPTION.

MASSIVE DRESSINGS,

BENEFIT TO PLANTS

Potash is definitely the unknown quantity in the fertilising scheme. The text books avoid with care any definite statements regarding the action and peculiarities of potassic fertilisers. It is my belief, writes a contributor, that in a decade or two an entirely new potassic technique may be evolved.

At present, for no clearly discernible reason, it is customary to advise a top-dressing application in New Zealand of 2cwt. per acre of 30 per cent, potash salts. But there really is no valid reason for that recommendation. No one at all, privately or officially, in this country, has attempted exhaustively to determine what is the maximum potassic value.

In the experience of the writer, fruit trees, given massive—apparenty ridiculous —potash dressings, have responded for nine years to that augmentation. Very recently in the Waikato, it has been observed that a 5 cwt. per acre dressing of 30 per cent, salts, applied in 1927, is still effective in palatability determination. Way, in 1850, showed conclusively by his drainage-arresting experiments, that there is no danger whatever of leeching of potash dressings. There is a .doubt at present as to whether or not phosphoric acid, in whatever form applied, leeches. As to potash, there is none; consequently there seems to be no reason to apprehend loss from massive periodical potash dressings. Absorbing Power of Soil.

There is a factor not generally appreciated in this connexion, and that is, the absorbing power of the soil. Perhaps no better illustration of that power can be conveyed in a . few words than the suggestion of a seed of radish or of mustard, placed on a piece of blotting paper. Directly on that seed be it supposed that water is dripped. It would not be until the blotting paper in the vicinity of that little seed was saturated, had absorbed all the water it could hold, that the seed could take up water and so germinate. It is so with potash. ' All soils have, in greater or lesser degree, the power of absorbing and holding applied potash more or less tenaciously. Unquestionably, this power is particularly in evidence in the lighter types. These types are the very ones most likely to require potash dressings by reason of their low potassium content. Thus, meagre potash applications are quite unlikely to reach the plant designed to benefit, being placed beyond its disposal by the high absorbing power of the soil. In a word, the soil, but not the crop, would be enriched. An Improbable Practice. No doubt continuous slight potash dressings would eventually "saturate" the soil, and become of value to the crop. In practice, however, it is highly improbable that a farmer would continue to dress, say, a peat soil, with potash after having experi-

need no advantage from its initial, -hough inadequate, application. It is to be remembered that the absorbing power of soils in relation to [potash is never constant. It must vary according to supply and demand—as potash is made available either by weathering of the natural unavailable supply, or by application of the salts, it falls in intensity, rising again on withdrawal of potassium compounds in crop growth and removal. Potash salts, though water soluble, are not comparable in rapidity of action, «ay, with superphosphate. 'Ihis is due to the slow permeation of the soil particles by the potassium combinations (in solution) which follow the dissociation of the salts as applied to the surface of the land. Itfollows that in the presence of even a low absorbing power, a light dressing of potash will only slowly permeate or spread amid the myriad particles of soil forming the hunting-ground of the root system. A heavy dressing lof potash must obviously achieve this diffusion much more rapidly.. Here, again, is a cogent argument in favour of an initial massive dressing of potash. It is the writer's belief that many an observational test of potash has been nullified by this slow action of [light dressings, the beneficial action

only having commenced after interest jin the trial had lapsed. It is significant that all the recently-recorded successes with potash have been associated with dressings distinctly in advance of the standard or presently accepted ones. Heavy Initial Dressings. Thus, perhaps, in the future, as these facts are recognised, it may [become the accepted practice to ap- | ply an initial massive or heavy potash dressing to land known or suspected to be deficient in available potash either by reason of long continued fertilising with other elements of growth only, or because of diminishing fertility. The accepted massive dressing is unlikely to be less [than scwt. per acre, and may cori- [ ceivably be greater. Such a dressing would be expected to afford full potassic support to the necessarily frequent phosphatic and nitrogenous applications for a term |of years, longer or shorter according to the nature of production per acre of the farm. No additional expense would be incurred by the farmer; indeed, it is probable that the massive dressing plan would, spread over three to five year periods, save money. To summarise the reasons why

massive dressings may enter into the potassic fertilising- methods of the future, it need only be said:—(l) There is no risk of loss of potash by drainage leeching; (2) there is an. ever-present risk that light dressings will merely increase soil content of potassium without benefiting the plant, this factor probably explaining apparent non-response^ to potash where most it is actually required; and (3) by giving reasonably rapid, yet lasting effect, a massive potash dressing would assist the other fertilisers (nitrogen and phosphoric acid) continually to exert their full influence on yield.