POTASH TOP-DRESSING OF AUCKLAND PASTURES.

New Zealand Journal of Agriculture, Volume 54, Issue 1, 20 January 1937, Page 8

POTASH TOP-DRESSING OF AUCKLAND PASTURES.

RESPONSE FROM POTASH AT WAIHI.

J. E. Bell,

Instructor in Agriculture, Pukekohe.

Responses in other Districts. In other districts responses to potash are not so consistent, and cannot be confined to one soil type or to one locality. Nevertheless, isolated striking responses have been obtained on all soils —on peat, on sand, loams, clays, and, silts. There is little doubt that as experimental work progresses soil types in some localities will be recognized to .be potashdeficient to some degree. In different localities and soils the pastures vary somewhat, but the method of improvement by potash is the same in principle. . . : On the gum-land soils of the northern parts of the province a common poor sward is brown-top dominant. Common clovers in such a sward are Lotus species and white clover. One ■ observational trial at Waimauku, Waitemata County, on such a soil was laid down on a dominant-brown-top sward with much Chewings fescue and rib-grass and a scarcity of clovers. A casual inspection did not reveal the presence of better grass species in the sward which was improved in the following sequence by the use of superphosphate plus lime plus potash. First there was an increased growth of Lotus hispidus, Lotus major, subterranean clover, and white clover. The ascendancy of the subterranean clover was marked first, and later the white clover overtopped the subterranean clover and subdued it. Improvement in the better grasses did not occur until the white-clover dominant stage was reached, when many plants of rye-grass, paspalum, cocksfoot, and crested dogstail appeared prominently in the sward. The Chewings fescue has almost entirely disappeared from view, but the more virile brown-top is still there, although not prominent, and has changed in appearance from a dull hue to a healthier deeper green colour, after only two years. The difference between the superphosphate plus lime plus potash plot with its thick carpet. of white clover and vigorous rye-grass and crested dogstail and paspalum, and the superphosphate plus lime plot with its less vigorous sward of clovers and inferior grasses is quite striking. Other plots included one treated with, lime and potash, and at one of the early inspections it was noticed that this plot had arrived at a stage when subterranean clover was the dominant clover, while the superphosphate plus potash plus lime plot had arrived at the stage where white clover was in the ascendant. The lime plus potash plot did not get much beyond the subterranean-clover-dominant stage and white clover did not flourish through phosphate deficiency. Consequently there was not much further improvement in the lime plus potash plot beyond the brown-top - subterranean - clover stage. The vigorous white-clover - dominant stage could only be reached by the use of superphosphate plus potash plus lime. Without a thick vigorous sole of white clover the mat of brown-top remained unchallenged by better grasses. Superphosphate and lime alone or combined could not bring

about this much-desired white-clover growth. The effect of lime in addition to superphosphate, or superphosphate in addition to lime, was as nothing compared with their effect where potash was also used. Thus lime in addition to superphosphate gave only a slight benefit, whereas lime in addition to superphosphate plus potash made quite an appreciable difference. In the same way superphosphate in addition to lime showed minor differences, while superphosphate in addition to lime plus potash gave an almost magical improvement. Potash used alone was useless or perhaps detrimental to a very slight degree. Used with lime its effect was slight and with superphosphate quite good, but not to be compared to where used with superphosphate plus lime. This trial was the first one in which the effect of potash was noted on a sward deficient to a large degree in potash, and most of the principles of potash response which were demonstrated there have since been found to apply equally to other swards on other soils, including the sandy loams of Waihi., < On a loam soil, apparently the result of a volcanic ash shower, at Runciman, Franklin County, the potash has increased by.ioo per cent, the extent of the rye-grass, white and ■ subterranean clover cover of the ground and has decreased the rib-grass, where it was applied in addition to superphosphate and lime. Here the effect of potash to the eye was very small compared with the effect at Waimauku, for the superphosphate plus lime plot contained quite a fair sole of rye-grass and clover. Potash here, though very useful, could not be claimed to be definitely payable as a top-dressing. There are many trials where potash effects small increases and where its use may not be payable. At ciman as at Waimauku, potash was most effective where the lime and phosphate deficiences had been met, and it also added to the effectiveness of lime and superphosphate. On peat land at Kaipaki, Waipa County, potash has greatly improved the pasture sward : applied to a poor paspalum sward it has greatly increased the white-clover,' suckling-clover, and Lotus major growth : white-clover growth was most improved on the superphosphate plus potash plots. At Orewa, Waitemata County, on a sandy soil overlying an ironstone pan, potash showed early improvement in the’ growth of Lotus major and white clover. Here the speed and the extent of further improvement may be limited by lack of soil moisture in summer due to the iron pan. On one trial at Mauku, Franklin County, on basic volcanic soil, a trial has shown responses in white-clover growth on the potashtreated plots. The plot was placed on a field subjected to much cutting for ensilage. Another trial at Ramarama, Franklin County, on a similar soil, has shown also a very strong potash response in increased clover vigour on a field subjected to much cutting for hay. Fields subjected to much cutting for hay or silage appear liable to suffer from potash deficiency. A trial at Waiau Pa, Franklin County, on a gum-land silt, shows the inefficiency of potash where a large lime deficiency is not first corrected. With —and phosphates —potash has given increased growth of white clover; without lime potash proved detrimental. This brings out the important point that on lime-deficient soils potash may prove detrimental if the lime deficiency is not first corrected ; this sometimes occurs both on soils that do respond to potash and those that do not.

Of course, on soils where there is little or no lime deficiency the use of potash without lime can make full improvement. Thus, on one other trial at Waiau Pa, on a lighter soil not very responsive to lime, potash is equally effective in increasing white, clover on both imed and unlimed areas.'

Besides trials showing strong and payable potash responses, there are many trials where it shows to a very slight and apparently unpayable extent. In these trials phosphates or phosphates plus lime dressings are sufficient for white-clover establishment, and continued growth and high production can be obtained without potash. On a large number of trials potash shows no response whatever.

All the observations in this article are based on the effect of annual dressings of 30 per cent, of potash salts at 2 cwt. per acre. These are heavy applications, made purposely so that soils deficient in potash to the slighest degree can be more easily detected. Yet even so, in some trials the increases due to potash appear so great that these heavy and costly applications appear payable. The first task is to locate soils responsive to potash. The next is to lay down, on potash-responsive soils, trials devised to show the effect of- smaller amounts of potash than 2 cwt. so that fairly definite advice can be given as to the economic quantity to apply. Thanks are due to the numerous farmers who placed fields at the disposal of the Department for the experiments.

Summary of L.P.K. Trials at Waihi and other Localities.

Plots are pegged out in farmers’ pasture fields, and the different plots are top-dressed with different treatments or combinations of treatments. The common type of trial is called the L.P.K. observational trial, which is laid down to locate the responses to carbonate of lime and 30 per cent, potash salts. In the L.P.K.' trial the lime and potash are applied at heavy rates, so that differences can be more readily discovered, the lime being applied at the rate of 1 ton per acre at laying-down and at 5 cwt. per acre thereafter annually, the potash at

2 cwt. per acre annually, the phosphate (superphosphate) being applied at the normal rate of 3 cwt. per acre annually. The L.P.K. trial comprises eight plots as follows : . (1) No manure. . . (5) Lime. (2) Superphosphate. (6) Lime plus superphosphate. (3) Superphosphate plus potash. (7) Lime plus superphosphate plus potash. (4) Potash. ' . (8) Lime plus potash.

. The trials are laid down in duplicate. Comparisons are effected by observations carried out every three months; and the effects of the different treatments are noted thereby every season of the year. Not only is the effect noted,' but the degree of the effect is recorded .by numerals i to 5, indicating the superiority to the untreated plot. Thus, o indicates no improvement or detriment over the untreated plot, 1 slight, 2 fair, 3 good, 4 very good, and 5 excellent responses by the particular treatment. The following table shows the responses on many of the trials in the Auckland Province where good potash responses have been obtained, and of all the trials at Waihi that have been down two years.

In accordance with the provisions of section 7 (2) of the Noxious Weeds Amendment Act, 1934, the Franklin County Council has assumed the administration of the Noxious Weeds Act, 1928, and its Amendments.