TOPDRESSING PRACTICES

New Zealand Journal of Agriculture, Volume 74, Issue 3, 15 March 1947, Page 235

TOPDRESSING PRACTICES

VALUABLE pointers on how to make the best use of the limited supplies of fertiliser available are given by P. R. Barrer, Instructor in Agriculture, Christchurch, in the following article, in which he deals with topdressing practices, with special emphasis on the important factor in these times of meeting the difficulty of supply in the wisest manner.

MOST farmers now recognise the value of fertilisers and lime in building up soil fertility and farm production. Experience, together with the results of topdressing and liming trials, has shown the results to be expected in different districts and on different soils. In few districts, there is no noticeable response to the application of phosphates, but in some districts a response to lime or phosphate is obtained only when they are applied together.

As the necessity for the rationing of phosphates still exists, the farmer naturally has to see that the best use is made of the quantities of lime and phosphates available. Consideration may best be given to .this matter now. Best Season for Application The best time for applying fertilisers depends on when. results are desired. Topdressing is generally carried out not only with the object of increasing the total production of grass but also in the hope of making the seasonal production more even. Therefore, the intention is to obtain greater pasture growth during the late autumn, winter, and early spring. To do this topdressing in the autumn before grass growth ceases is most satisfactory. Topdressing in the spring will increase grass production when it is least required. There are cases where spring topdressing may be advisable, an instance being on naddocks from which it is intended to take a hay crop. Also a special-purpose application of sulphate of ammonia or ammoniated superphosphate may be made in the spring on paddocks which are to be shut up-for grass seed production, or where the grass is not thriving. Inability ,to obtain fertiliser at the time of peak demand in the autumn is of course a difficulty and will mean that some farmers will be topdressing later than they would otherwise do.

In topdressing lucerne stands it should be remembered that lucerne is dormant during the winter, and phosphate application should not be made in the autumn when the weeds will benefit at the expense of the lucerne. Topdressing of lucerne should be carried out in the early spring, preferably after the first cut.

Pasture Establishment

In the sowing down - of new pastures lime may be applied before the last harrowing in the preparation of

the seed-bed. Phosphate should be applied at the time of sowing. Where responses are obtained to lime and phosphate their application is as essential for good pasture establishment as the preparation of the seed-bed, the sowing of good-quality Certified seeds, and sowing at the right time. If one or other of these factors is omitted, failure of the pasture may result. As the establishment of a pasture may determine its usefulness over a period of years, attention should be given to the sowing of fertiliser and lime at the correct time rather than when it is too late to do more than help to patch up a poor “strike.”

What Pastures to Topdress

When fertilisers were plentiful the same consideration to the type of pasture topdressed was not given as is given now; many inferior pastures were brought up to a good standard by topdressing alone over a period of years, or in conjunction with the surface sowing of grasses and clovers. At present, however, the best results, though not the most spectacular, are obtained by using available fertiliser on the best pastures, where a choice has to be made between good and poor swards. Young pastures will generally merit topdressing in preference to older pastures, though this would not apply everywhere. On some soil types where deterioration of the sward without fertiliser can be rapid it may pay to prevent an older pasture from running out instead of topdressing a younger pasture which has had relatively generous applications.

Swards with good clover content will be better after topdressing than those which are mainly grass, because the clovers respond particularly to lime and phosphate, and also vigorous clover will provide supplies of nitrogen to ryegrass and other grasses so that they in turn become more vigorous.

Type and Quantity of Fertiliser

The choice of phosphatic fertilisers lies mainly between serpentine superphosphate and straight superphosphate. In the many districts where trials have shown serpentine superphosphate to be equal to or superior to superphosphate, serpentine should be chosen, as 27cwt. of serpentine superphosphate is allocated in place of 1 ton of super-

phosphate. This increases the area topdressed in the ratio of 27 to 20.

It is not possible to make a general recommendation of the quantity of fertiliser to apply an acre, as there is such variation both in soil type and rainfall throughout New Zealand and farmers are restricted at present by the amount allowed under rationing. However, it should be .remembered that an annual application of one bag of fertiliser an acre is usually preferable to applying two bags every two years.

The use of potash in certain localities has been shown to be necessary for the best results. Nitrogenous manures may also be of value for encouraging unthrifty pastures or for seed production.

Special problems arise on othersoils. The use of cobaltised superphosphate should - now be a regularpractice on areas which have shown cobalt deficiency. On the copperdeficient peat soils which occur to a limited extent in New Zealand an annual dressing of 51b.. of crushed bluestone an acre is suitable. The bluestone may be applied alone or mixed with lime, superphosphate, serpentine superphosphate, or other commonlyused manures. Deficient areas on such farms should be topdressed with bluestone for satisfactory results. Copperised superphosphate may be used as an alternative.

Utilisation of Growth

The farmer has not made the most use of phosphate merely by applying it at the right time and to the most suitable paddocks. Fertilisers are applied to improve growth for the best use by stock, and it is in feeding off these pastures that the ultimate value of topdressing is realised. The . grazing of topdressed areas in particular should be controlled. This controlled grazing means that the pastures should neither be continuously nor closely grazed, and should not be allowed to go to rough growth in the spring and summer. Topdressing has its greatest use when it gives more growth in periods of feed scarcity, but to produce most growth at this time the topdressed pastures must be wisely spelled at other times.