Choice of Time and Type of Topdressing

New Zealand Journal of Agriculture, Volume 74, Issue 2, 15 February 1947, Page 131

Choice of Time and Type of Topdressing

INCREASED production on most farms is closely associated with the efficient use of topdressing. Some of the considerations influencing the choice of fertiliser and the time of application are discussed in this article by P. S. Syme, Instructor in Agriculture, Warkworth.

TV7ITH the gradual return to more ** normal conditions, many farmers are looking forward to the time when something like the pre-war choice of artificial fertilisers will again be available. This wider choice, though it will undoubtedly be welcomed, will pose a problem which may sometimes not be easy to solve. Many farmers have proved to their satisfaction that certain varieties of fertiliser appear to suit the conditions on their farms better than others, but the problem of which to order may be complicated by wide differences in price and uncertainties about deliveries.

Final Decision with Farmer

As it is impossible to give general advice which will apply to any farm, the final decision must lie with the farmer. However, while admitting the excellent results frequently obtained in the past from such fertilisers as basic slag and North African phosphate on certain soil types, it is probably safe to say that farmers who have been reasonably satisfied with superphosphate or serpentine superphosphate would be wise to continue their use should the price range of imported phosphate appear too wide.

On certain farms where slag, and to a less degree North African phosphate, have proved highly efficient, higher prices might well be justified if steep or inaccessible country makes the transport of large quantities of lime too difficult and costly. Though the response to slag might be improved by liming, slag without lime might still prove a better proposition than relatively cheaper superphosphate if that necessitates heavy dressings of lime to produce a response comparable to that obtained from slag alone.

Importance of Lime Observant farmers on limedeficient soils have frequently remarked on the comparatively poor response sometimes obtained from phosphates without sufficient lime, and there can be no doubt that in the past much fertiliser has been wastefully applied. It is probably true also that lime has been used wastefully on soils where the lime deficiency is low.

Admittedly, large tracts of New Zealand show a high lime deficiency, and on such country liming is essential for high production. There are, however, soils on which lime responses are only slight or insignificant, and it is only prudent to try to ascertain what dressing is likely to be profitable before embarking on an extensive liming programme.

Time of Application

Since the first tentative efforts to improve pastures by the use of artificial fertilisers the practice of applying the bulk of the topdressing in the autumn has gradually developed. Though carefully-conducted trials have demonstrated that about the same increase in production is obtained over the year from an application of fertiliser irrespective of the time at which it is applied, the time of application does materially affect the time at which much of this increase is produced. As an autumn application tends to produce much of its increase during the off season when feed is scarcest and most valuable, there is good reason for this practice, quite apart from greater convenience. But if the best results are to be obtained, the fertiliser should be applied early while the ground is still warm and conditions promise a reasonable period of vigorous growth.

If topdressed early, the pasture derives full benefit from the fertiliser and has a good start before cold weather chills the ground. If the grazing management is good, pasture plants which are making vigorous growth at the beginning of the cold weather will continue to make appreciable growth right through the winter. On the other hand, if the fertiliser is applied too late in the autumn, little immediate benefit is obtained; and the response is likely to be delayed until the ground begins to warm up in the spring.

To endeavour to have some selected fields topdressed early and closed up to provide greenfeed when even a little is of special value is therefore good policy. The fact that an increased rate of pasture growth in winter can mean an accelerated growth of pasture in early spring— a critical periodis also a factor of some importance. Winter growth can best be fostered on a rich, wellsheltered, well-drained soil carrying a high proportion of ryegrass in the sward.

Spring Topdressing

Though the bulk of the fertiliser is probably best applied in the autumn, it is often profitable to topdress some of the pastures in the spring. Such an application often proves extremely beneficial on a young autumn-sown pasture and gives the clover that extra encouragement which leads to successful establishment. The hay crop may also benefit considerably from a spring application of fertiliser.

Where topdressing is applied during the summer results depend largely on the rainfall, which at that period is apt to be very uncertain.

Though lime can be applied advantageously at any time of the year, where superphosphate and lime are being applied separately it is desirable that the lime should go on before the superphosphate rather than after it. In that way danger of loss of phosphate through fixation may be minimised. If the fertiliser is available, few farmers now ask whether they can afford to topdress. The question more often is: Can I afford not to topdress? Topdressing is expensive, and every farmer should try to ascertain what manures are most profitable on his land and to use them to the best advantage.