POTASH TOP-DRESSING OF AUCKLAND PASTURES.

New Zealand Journal of Agriculture, Volume 53, Issue 6, 21 December 1936, Page 359

POTASH TOP-DRESSING OF AUCKLAND PASTURES.

RESPONSE FROM POTASH AT WAIHI.

J. E. Bell,

Instructor of Agriculture, Pukekohe.

In the last report* on pasture top-dressing in Auckland Province the position was summarized as follows : “ Superphosphate is generally the cheapest and most efficient .phosphate for pasture top-dressing, but on some soils lime is necessary to enable the best results to be obtained from superphosphate. Slag is also quite efficient, but is. not superior, to superphosphate or superphosphate and. lime. Rock phosphates are generally inferior to superphosphate or slag. ■ Potash . responses are not frequent, and, where responses are secured, they are generally slight.” Since this was written the. position as far as potash is concerned has changed somewhat, for in one district and in isolated trials in other districts distinct and payable responses occur. Nevertheless, for most parts of the province the position still obtains that the use of potash gives no response or negligible and unpayable responses as a top-dressing on grassland. Where the good potash responses, are evident, the further, improvement of the sward is slow unless potash is included in the topdressing campaign,' and the .effectiveness of the phosphates and lime applied is very much limited. It follows that much money is being wasted in applying phosphates and lime to soils. markedly deficient in potash. In the Auckland Province soils are almost everywhere deficient in phosphates, and phosphatic top-dressing is most commonly practised. Lime is also deficient in about half the;province, and in some districts to a marked degree. ■ The statement has been made that potash is a silent worker, meaning that it improves production from pastures and yet visible effects from its application to pasture are not apparent, and that it differs from phosphates and lime, from which beneficial effects can be seen to a marked degree when they are applied to phosphatic-deficient or lime-deficient soils. Agricultural works contain, little information on the effect of potash on pastureswhether it has.. any visible effect and what that effect is. -If a fertilizer could merely .increase growth-of the existing sward and . not change its constituents ■ or affect the grazing, the *P. W. Smallfield, Pasture Top-dressing in Auckland Province, this Journal, April, 1935. '

difference would be hard to detect in a grazed pasture, and a fertilizer which did this and made no other change could well be called a silent worker. However, it is impossible for a fertilizer to increase growth and not affect the composition of the sward unless that sward was at the height of perfection or contained only one plant species. Almost all swards contain many species, and if a treatment increases growth it is always to the advantage of the more vigorous and to the disadvantage of the less vigorous constituents. Potash cannot be called a silent worker, because, if it is applied to potash-deficient soils, its effects are visible. The first noticeable effect of potash is in increased clover-growth. If no clovers are present in the sward then potash can effect but little change ; but if clovers are present—they may be stunted and difficult to see—then improvement of the sward is possible. This increased clover-growth is likely to be apparent within a few weeks of application. Definite" signs of improvement are not often lacking one year after application on potash-deficient soils, because there are very few swards that contain no clover. However, danthonia swards subject to much burning frequently contain no clover, and improvement of these has therefore little possibilities. The pasture sward is a battlefield in which continual war is being fought by the different species present for existence. One of the factors which affects the fortunes of the combatants is the kind of management by stock. Some species flourish under more severe grazing than others : some dislike grazing altogether. Another factor is fertility. On grasslands in the Auckland Province fertility is naturally poor, and is therefore an important factor. If the fertility of a soil is improved by an application of potash the soil is rendered capable of supporting the clovers present in a more vigorous state and they grow better, and in doing so they may crush out other species in the sward. As time goes on and the potash deficiency is alleviated by additional applications of potash, the clovers fight among themselves for supremacy. Slowly growing clovers are quickly subdued by ones of faster growth, and as the sward thickens annual clovers, even of the more highly productive kind, are repressed. Where conditions are suitable for its vigour a perennial, species will always oust an annual one, for the weakness of the latter lies in the seedling stage. The annual has, season after season .as a young seedling, to fight for a place in the sward against established vigorous perennial plants. A highly productive permanent clover with an all-the-year-round production, such as white clover, quickly .assumes the ascendancy when the potash deficiency is met, providing, •of course, that there are no other major physical or manurial deficiencies. White clover well established and growing vigorously improves the nitrogen-supply in the soil, and by its more continuous growth throughout the year maintains this supply better than any other clover. Nitrogen is one of. the important plant-foods for the grasses of the pasture .sward. Pasture-plants, for optimum growth, require a continuous large .supply of nitrogen, and this is supplied more effectively by white ■clover than by any other clover-plant. Potash, by inducing vigorous white - clover growth, indirectly improves the nitrogen-supply, and this improvement is reflected in .increased vigour of the non-legumes in the sward. All the nonlegumes in the sward are encouraged to grow at a faster rate, and goes on among them. The faster-growing ones suited to

the grazing conditions outstrip the other plants, and in some cases eliminate them entirely. In a reasonably well-grazed sward"’rye-grass if present, assumes control, but rye-grass, . not having the ability of white clover to cover the ground, does not eliminate the other grasses,as white clover through its stoloniferous growth suppresses other clovers. Thus dressings of potash finally improve a sward through distinct phases. First, increase in growth of all the clovers present, the elimination of slower-growing and of annual species, and the establishment of a thick, vigorous sole of white clover,, then improvement of the pasture-grasses of higher production and the suppression,of the more poorly productive ones. '■ At the same time the weeds are greatly suppressed or eliminated by white-clover growth. Some weeds more fitted to the better growth conditions survive to. a limited-extent. i The aim of every farmer should be to obtain on all his pastures a vigorous Sole Of white clover. In potash-deficient soils this is not possible with the use of. lime and phosphate, even with heavy applications. The addition of potash enables the white clover to thrive, bringing about increased grass-growth and increased production of farm-products, and will put .the 1 phosphate and lime top-dressing of the sward on a more economic footing. Even the effect of the stockdroppings are limited by the lack of potash in the soil. Stock-droppings on potash-treated plots provided a richer verdue than the droppings on plots not so treated in potash-responsive soils. . . . Waihi Responses. The Waihi Plains, Ohinemuri County, do not consist of level country but comprise gently rolling downs, in area about six miles long by four miles wide. They are surrounded almost entirely by high scrub-covered or bush-clad hills. The soils are derived from volcanic-ash showers. The "country is well watered by streams. The soils on the rolling downs are sandy loams. ’ Alongside the streams are small level stretches of land comprising alluvial soils of a heavier nature than the sandy loams. Small patches of the alluvial soils are covered by a small amount of peat. On . the alluvial soils the pastures are quite good and are composed mainly of rye-grass and white clover, with much sweet vernal, crested’ dogstail, timothy, cocksfoot, • and rib-grass. On the peat areas the pasture is also, quite highly productive, but contains much Yorkshire fog and some Lotus major. The much more prevalent sandy-loam soils have been grassed with some difficulty.' The soil being light, consolidation for a grass-seed bed has been hard to accomplish, and the pastures after a few years have deteriorated to a poor type of pasture. The -soils are deficient to a very large degree in phosphate, and these poor pastures have been improved to a great extent by phosphatic top-dressing.' Fields on the sandy-loam soils are in various stages of development from sweet vernal,. Chewings fescue, Poa pratensis, hair-grass, catsear’ lamb’s tongue; suckling clover, Lotus major swards to rye-grass, white-clover, cocksfoot, timothy, rib-grass swards. The pastures - are generally rather poor and contain a short supply of white clover and rye-grass, and there is much Poa pratensis, sweet vernal, catsear, lamb’s tongue, rib-grass, Lotus major, and suckling clover. Some fields on the three different soil types on the plains contain a fair proportion of paspalum, which grows quite well. . .

The climate is a wet one, the average rainfall for Waihi being ■B7 in. per annum, and this rainfall is evenly distributed. The winters .are rather cold, with a fair amount of cold winds, but the summers are not unduly hot. The pastures are in a normal season kept well supplied with moisture and grow well throughout the summer. Supplementary ■crops are rarely grown, and farmers rely on hay and silage made from permanent pasture for winter feed. Successful farming, therefore, depends almost entirely on the establishment and maintenance of highly productive swards of grass. . Trials to test the value of potash and lime in the Waihi district were laid down in September, 1934. On the alluvial soils alongside streams there was no response to potash, and its use there is unwarranted. On' the peat the results are not definite. On the undulating lighter country potash made the first improvement in clover-growth in the spring a few weeks after the plots were laid down. The clovers present in the sward, ■ suckling clover, Lotus major, and white clover, showed improvement in growth and vigour, and the effect was so outstanding that'the potash portions stood out at a distance in some trials because of the deeper green colour caused by the increased cover of the clovers of the surface of the sward. In the summer following, 1934-35, the climatic conditions were dry, and the effect from potash largely disappeared. In. this, potash differs from lime, the effect from which .appears more marked on clover-growth in dry summers and is not so .apparent in the flush spring months. Throughout the winter following, the response from potash improved until the spring, when the responses were again marked. The following summer, 1935-36, was a wet one, .and responses from potash continued to be strong. A feature of the responses in the past summer was the much better grazing of the potash-treated plots in January. The white clover is fairly quickly replacing the Lotus major and suckling clover, and in some of the plots these poorer-producing species have been eliminated. . Where the pasture is fairly , good, comprising better grasses such as rye-grass, cocksfoot, timothy, and white clover, there is not much change in the cover of the different grasses, nor is it possible, because there is little room for improvement in that direction ; but with the increase in whiteclover vigour there has been a growth improvement of the grasses and a great improvement. in the production of the sward. On the poorer pastures the transformation is more startling because there is .more room for improvement. As the white clover assumes charge, the previously stunted and inconspicuous rye-grass grows vigorously, and poorer grasses and weeds such as hair-grass, catsear, and lamb's tongue disappear. A few of the ’ rib-grass and weed plants more fitted to endure higher-fertility conditions under the management survive, or may increase to a limited extent. The better grasses appear more prominently in the sward because they grow taller, and in tillering occupy wider territory. ■ ' Of the six trials on the undulating sandy loam of the Waihi Plains, .all have shown definite response to potash, and it appears that potash top-dressing on those, soils in the locality will give payable returns.

Analyses of soil-samples have been made of the soils where the trials are being carried out at Waihi. The following table shows the results of the analyses, type of soil, and the potash response obtained for each experiment :

That there is no correlation between response to potash in the field to the potash content of the soil is quite apparent from a study of the above table. Soils from experiments 16/1/301 and 16/1/307 are extraordinarily high in available potash and yet show a response to potash. Analyses were taken from the top three inches of the soil. The only conclusion that can be assumed is that soil analysis is as yet a very poor guide to the need for potash applications to the soil. - . .

(To be continued.)

Experiment. Percentage present of Available Potash. Potash Response. Soil Type. . : 16/1/299 0-018 Good Sandy loam. 300 0 • 025 >> • • • ; > 301 0-098 ) 5 . 302 . 0-037 Very good >> 304 0-029 Good .. ' f > 306 0-018 303 . 0-053 Nil ... Alluvial loam. 305 • 047 307 0-140 Slight Peat over alluvial loam.