Potash Deficiency in Land in Rotorua District

New Zealand Journal of Agriculture, Volume 81, Issue 1, 15 July 1950, Page 21

Potash Deficiency in Land in Rotorua District

THOUGH the pumice soils of the North Island were once rich in potash, tests made in the Rotorua district have shown that generally land in the district is now deficient in potash. This article by C. R. Taylor, Fields Instructor, Department of Agriculture, Rotorua, points out the need for this deficiency to be remedied by the application of potash dressings.

AS far back as 1912, B. C. Aston, a former Chief Chemist of the Department of Agriculture, in discussing in “The New Zealand Journal of Agriculture” the pumice soils and their treatments with phosphates also emphasised the great need for building up the humus content as a pre-requi-site to successful agricultural development. In referring to the importance of legumes in this respect he stated: “The dominant plant food required by legumes is potash, and this is present in abundance in the pumice.” Some 4 years later, during the First World War, the same writer in' an article dealing with the problem of shortage of potash caused by Allied countries being cut off from the world’s main source of supply, Stassfurt, Germany, commented on a statement by Professor Berry, of the West of Scotland Agricultural College, concerning the potash richness of bracken fern ash: “In New Zealand, where fern may grow to a height of 10ft. to 12ft., it seems possible that the yield of ash per acre may be considerably larger

[than the amount given by Professor Berry], and on a rich potash soil, such as the pumice lands of the North Island, this fern might prove a more feasible source of potash than seaweed. ...” From the above quotations it is clear that by whatever standards were employed 30 and more years ago to measure availability of plant nutrients in a soil, potash was considered to be in ample supply in the pumice soils of the Central Plateau, of which Rotorua forms part. As legumes like red clover grew most luxuriantly on virgin pumice country after the burning off of the bracken fern (rich in potash) and scrub and an application of phosphatic fertiliser only, it can be safely

accepted that potash is not, as rightly stated by Aston, deficient under these conditions. Results of Topdressing Trials But how long will the pumice country go on producing at a high level without the aid of added potash? Until 2 years ago there was no satisfactory answer to this question, as little thought had been . given to it. Pastures under good management that were in poorer condition than would be expected were generally considered to have suffered through wartime economy in topdressing and it was thought that as soon as adequate supplies of phosphates were again available pastures could be restored to their

former condition. However, in manycases this did not happen, and topdressing trials which included a potash treatment and an excellent method of quick testing of soils and plant tissues were used to investigate the trouble. So far nearly 50 soil samples from different parts of the pumice country of the Rotorua district have been examined for potash and other plant nutrients, and the results from these and those of topdressing experiments and plant-tissue tests have frequently indicated very clearly that potash is no longer in plentiful supply generally, but it is very deficient in many localities. It is not proposed in this article to deal with the whole of the investigation up to the present time, but rather, to acquaint farmers concerned with the problem that lies ahead of them so that steps may be taken to deal with it. As far as it is known at present the districts of Oturoa and Kaharoa and parts of Ngongotaha, Mamaku, Reporoa, and ' Broadlands are chiefly affected by potash deficiency. Those farms longest under cultivation, some for more than 40 years, are the most deficient and those of more recent development, if at all deficient, are the least so. Ample Potash in Night Paddocks Night paddocks on dairy farms, regardless, of the age of property, are almost invariably in good condition and contain ample potash, but fields cut more or less regularly for hay, although frequently receiving more phosphates, have often been found to be in great need of potash treatment. Ordinary day paddocks are usually between these two extremes. Urine contains most of the potash from the food consumed by an "animal, which is one reason for the good condition of night paddocks. Hay, on the other hand, can rob a field of more than lcwt. of potash annually, and if the field is cut frequently for hay for some years and the potash is not fed back on to the paddock, the result can be serious. A symptom of potash deficiency in pastures which have had good general management and have received regular and adequate dressings of phosphates is a lack of good clover growth and a decided tendency for browntop, sweet vernal, flat weeds, and moss to replace ryegrass and cocksfoot. Lucerne also has been found to suffer severely under conditions similar to those responsible for pasture deterioration. Wherever potash has been applied in such cases at lcwt. per acre (early spring or early autumn seem the best periods for pasture and spring for lucerne) excellent responses have been obtained in a few weeks. If the extra expense of the potash' is a financial difficulty, it would seem perfectly safe either to reduce the amount of normal phosphatic topdressing or withhold it for a year, provided such topdressing has not been neglected in the past. Investigation is being made to determine the most suitable amount of potash to apply after the initial application, and information on this will be published as soon as it becomes available.

THOUGH present all the year round, the danger of short hitching implements to tractors is more acute in August and September, when South Island farmers are harrowing wheat to aid its tillering and North Island farmers are harrowing pasture to spread sheep and cow dung and fed-out hay that has not been eaten by . stock. When sharp turns are made with short-hitched sets of harrows, the bar engages on the tyre and rides up the wheel, as in the illustration, so that the driver is in danger of severe injury. To avoid this danger there should be fitted between the harrows and. the tractor a length of chain or wire rope long enough not to foul- the rear wheel when sharp turns are made. Short-hitched-implements are more likely to ride up the wheel of a steel-wheeled tractor, especially one fitted with A grips instead of spade lugs. This danger is also present to a less degree with trailer-drawn implements with a short drawbar, though contact between the rear wheel or crawler tracks and the drawbar more usually results in damage to the implement or the tractor tyre than in a human injury. Exercise care when sharp turns must be made with a tractor and fit longer hitches where necessary.

—C. J. CROSBIE,

Farm Machinery Instructor,

Department of Agriculture, Christchurch.