PASTURE TOPDRESSING

Wairarapa Times-Age, 26 February 1940, Page 9

PASTURE TOPDRESSING

ENSURING EFFICIENT USE OF FERTILISERS

EFFECT ON SUPPLEMENTARY

NEEDS OF WAIRARAPA LANDS.

(By N. Lamont, Instructor in Agriculture, Masterton, and chairman of the District Primary Production Council.)

Since writing a short article on pasture topdressing for these columns, I have received a few enquiries on what might be termed finer points of the subject from farmers who are anxious

to utilise fertiliser as efficiently as possible in order to increase the productivity of their grasslands. In addition, a recent issue of a widely read periodical published an article which severely criticised the Department of Agriculture’s general recommendations in a style which certainly could not be described as encouraging to farmers who are sincerely anxious to adopt the most effective practices. For these reasons, it is felt that the following remarks may interest farmers generally and. it is hoped, clear up some of the doubts that have been raised.

The statement has been questioned that topdressing accentuated the need for supplementary feeding. It must be obvious that if a certain farm carries say 60 cows without topdressing and 100 with topdressing, then considerably more winter feed will be necessary to supply this increased number. It is, of course, true that early autumn topdressing increases Winter production from pasture —indeed it may well double it—-but this does not alter the fact. What actually happens is something like this—without topdressing a farm carrying 60 head all the year round would grow enough grass in the flush to feed say 95 cows but only enough in the winter to feed say 25. On the other hand, the same area topdressed, although it might produce enough grass to feed 50 cows through the winter, would grow enough in the flush period to feed 150. That is to say, by topdressing, the winter carrying capacity is increased but the margin between the flush and low production periods is also increased, with the result that more provision must be,made for winter feeding.

Over the past two or three years particularly, a large number of ill-con-sidered opinions have been circulated with reference to the injurious influence on stock of heavy dressings of artificial fertilisers in general and superphosphate in particular. It seems possible that some of these statements have resulted from the persons responsible reading overseas literature which concerns farming conditions very different from our own. It is common knowledge that artificial fertilisers are no substitute for organic manures on country that is continuously cropped. Indeed we find in England, and for that matter in this country, that it is a standard practice to work on a definite rotational system whereby arable crops are planted only on areas that have been in pasture for a period of years. The expression is common in English publications—‘'To cash in on the accumulated fertility of grassland” —and it arises from the fact that under reasonable management a soil accumulates fertility when carrying a good sole of grass grazed by stock. The Eng-, lish farmer as we know goes to considerable trouble and expense to collect the manure voided by his stall fed animals but in this country, except for that collected in milking shed yards, ets, all the animal manure produced by a pasture is returned to enrich the soil with those vital organic elements Which are known to be of such very great importance. While the value of green manuring cannot be denied, it is in some quarters given an exaggerated importance. The growing of a legume such as red clover, lupins, etc, undoubtedly enriches the soil by its very presence and it is questionable whether very much net benefit is obtained by ploughing in, over that derived from the stock manure returned by grazing animals which eat the same quantity of herbage. It must be borne in mind that a standing green crop contains,, after all, probably over 80 per cent of' water.

Related to the above is the question Of artificial nitrogenous manures and the Department has been criticised because; it does not advocate these widely. Briefly the position is this: Artificial nitrogenous manures are represented principally by sulphate of ammonia which is th£ cheapest of this type. As a result of practical experiments it has been found that this manure can be very dangerous. There is no doubt that its use in early spring increases growth noticeably but definite harm to soil and pasture has been found to occur on many soil types, particularly if it has been applied a number of times on the same paddock. Farmers who find themselves seriously short of feed in early spring would be justified in using sulphate of ammonia as an emergency measure but it should not be relied upon as a regular practice, unless careful experiment under the individual conditions have shown that the common slumping after-effects do not occur.

As a general rule, it is considered that New Zealand farmers have a much safer and cheaper source of nitrogen in the clovers of the pasture. Feed the clovers with superphosphate and the cloVels Will feed the soil with nitrogen both directly and through grazing stock. Feilds officers of the Department are frequently asked whether lime dressings are necessary on a particular property and usually an answer can be given from experience and experiments on similar soil types. For instance it is known that the shingle plains in the Waifarapa respond well to lime and its use can therefore be generally advocated. There is, however, no substitute for actual field experiment and all farmers should do their own experimenting, ft is Very simple to flin out a strip across a paddock and watch results —and this should be repeated where there is any variation either in soil type or in previous history of the paddock. It has been said that lime should only be advocated for soils rich in humus or for clays. This is pure armchair guesswork. In this district at least, we know that our ' lightest shingle country responds well[ to lime and we do not consider these i

soils to be overburdened with humus or clay. As pointed out in the previous article —the manure for this district is superphosphate—with two strong allies-* one is lime, and the other is subterranean clover.