Replacement of Winter Fodder Crops Susceptible to Cauliflower Mosaic

New Zealand Journal of Agriculture, Volume 95, Issue 6, 16 December 1957, Page 535

Replacement of Winter Fodder Crops Susceptible to Cauliflower Mosaic

By

M. L. CAMERON,

Instructor in Agriculture, Department of Agriculture, Timaru OVER the past two seasons the incidence of cauliflower mosaic virus in Canterbury has greatly reduced the reliability of white-fleshed turnips and a number of swede varieties. In many districts farmers are faced with the problem of reducing their dependence on these formerly reliable crops, which carried large numbers of stock over winter.

SWEDES and turnips have, in the past, proved to be a most economical winter supplement and usually serve as a convenient step in pasture renewal. Consequently their total or partial replacement is a problem which cannot be solved simply, since the management of the whole farm can become involved. Several alternative brassica crops are available, but these cannot be grown satisfactorily on all soils and it is convenient to consider the problem in relation to the following two soil groups. Soils Suited to White-fleshed Turnips On the lighter and drier soils of Canterbury, white-fleshed turnips, by virtue of their quick growth and low fertility and moisture requirements, have been found to be the only winter brassica crop which can be grown satisfactorily. It is on these soils that the effects of cauliflower mosaic have been severe. Since no direct replacement crop can be grown, the solution lies in the adoption of one or several farm-management practices aimed at reducing dependence on the turnip crop. Though, in this article, these practices are dealt with separately, it is likely that several such practices

would need to be adopted on any one farm to replace the turnip crop fully or partially. Though at present the likely effects of cauliflower mosaic in future turnip crops cannot be predicted, the continued use of the crop may be a justifiable risk in many districts. Late Sowings and Turnip-grass Mixtures Two practices can be employed to lessen the risk of crop failure. Field observations have indicated that when sowings are delayed until late February or early March the likelihood of crop failure is less. Quick-maturing turnips must be used for late sowings. An early winter can seriously affect the growth of such late-sown crops, and it may be advisable to sow only a portion of the crop at this time. The risk associated with the turnip crop may be further reduced by sowing a mixture of white-fleshed turnips and Italian or short-rotation ryegrass. This method requires little extra preparation of the land, but early sowing of the mixture is advisable. If the turnip crop fails, early sowing allows time for the grass to make increased growth before the onset of winter.

Greenfeeds Cereal greenfeeds can also be valuable, particularly where early sowings of turnips have failed. Though from the point of view of nutrition, Italian or short-rotation ryegrass is to be preferred to the cereal greenfeeds, the latter can be sown later and require less land preparation. Thus when an apparently good turnip crop fails late in autumn, cereal greenfeeds may well be the only means of improving the winter feed position. Lupins can be grown as an alternative crop, though generally their popularity is declining. When sown with turnips, greenfeed, or grass, they provide a useful insurance against turnip failure. Autumn-saved Grass Perhaps one of the most satisfactory ways of guarding against shortages of winter feed is in the saving, of autumn pasture growth for use during winter and particularly just before lambing. By exploiting seasonal pasture growth in this manner it is possible to reduce greatly dependence on special fodder crops. Though under Canterbury conditions a high standard of management is required if sheep are to be wintered entirely on grass, it should be possible on many farms to shut up a considerable area of pasture for this purpose. Strict rationing of the grass crop is necessary, particularly if autumn growth has been less than expected, and ample supplies of good hay must be available.

Grass can be saved to the greatest extent in areas where lambs are quitted earliest, since a large part of the farm can be shut up early for flushing and saved grass. Some light land farms over the past two winters have been able to carry 1000 ewes for a month on 30 to 40 acres of saved grass, this ration, of course, being supplemented with hay. In these years autumn growth has been good and winters mild, but the practice has great possibilities. Seasonal variations in grass yield can be compensated for by varying the hay ration and stricter or laxer rationing of the available grass. It must be emphasised that saved grass can be produced only from highquality, well-balanced pastures. Hay and Silage Supplements The basis of all management techniques aimed at reducing dependence on winter brassica crops lies in the provision of adequate high-quality hay. Today in much of Canterbury such a requirement usually means lucerne hay, and except in the higherrainfall foothills or on the poorly drained coastal soils, there are few areas there where good lucerne or lucerne-grass mixtures cannot be grown. Techniques of establishing and maintaining lucerne have been improved considerably in recent years, and when reduction of the area of winter brassica crop is planned serious consideration should be given to the establishment of a lucerne or lucernegrass stand. The latter can also pro-

vide valuable winter grazing. Deficiencies in winter feed crops can be levelled out by the adjustment of the hay ration to maintain the desirable rising plane of nutrition. In these functions silage has a . similar place. Though this supplement is generally more. expensive to conserve than hay, particularly if the area to be handled is large and baling is necessary, there are many farms where silage has a valuable place, even if not made every year. In contrast to hay it can be stored cheaply for long periods and can contribute much to the stability of winter and summer feed programmes in years of shortages. Soils Suited to Swedes and Chou Moellier In the moister and in the cooler regions swedes and chou moellier are grown or can be grown for winter feed. Though many of the most popular swede varieties have shown little resistance to cauliflower mosaic, varieties such as Calder, Sensation, and Wilhelmsburger have given quite satisfactory results under very unfavourable conditions. Chou moellier has proved very resistant. It would be prudent in areas suited to the growing of swedes to sow only those varieties which will crop well in the presence of cauliflower mosaic. Where fertility is high mangels and fodder beet can greatly reduce dependence on swedes and turnips. Both mangels and fodder beet require intensive cultivation, but on the other hand give high yields and are ex-

tremely reliable. However, their use as a substitute for swedes or turnips is likely to be restricted to soils where high yields can be obtained. Concentrates Over the past few years concentrates have been used to a limited extent in commercial flocks. Generally they have been used in small quantities to supplement low- or poor-quality feed reserves. Though concentrates as a total ration are unlikely to compete with fodder produced on the farm, there is every possibility that they may form a valuable part of the ration for young stock on farms near their maximum carrying capacity. Concentrates cannot be classed strictly as an alternative to winter brassica crops, but they can materially assist in balancing lowquality fodder in years of shortage. Other Alternatives to Swedes As in the regions where whitefleshed turnips are the only satisfactory brassica crop, greenfeeds, saved grass, hay, and silage can- all be used on the soils suited to the growing of swedes and chou moellier. Most of these alternatives fit into the management of the developed farm more easily than they do on the property under development. On the latter there are few crops which can be used to replace the swede crop as an economical and necessary step in pasture renewal, and while resistant varieties are available this crop should be persevered with wherever possible. Pasture Renewal a Governing Factor The alternative crops and management practices mentioned in this article are suggested as ways in which dependence on winter brassica crops can be reduced. Obviously all would riot be used on any one farm, but it is likely that adjustment of the farm programme to include those which suit the management could help considerably in reducing feed shortages should the turnip or swede crop fail. In reality they are not so much alternatives as practices which have evolved on highly developed farms in an effort to make most use of the grass produced, and as such can be confidently recommended. However, it should always be borne in mind that a reduction in the area of winter brassica crop or its elimination from the farm programme usually results in a slowing of the rate of pasture renewal, which, over a period of years, could result in a deterioration in pasture quality. Where fertility has been built to a high level and experience has demonstrated the lasting qualities of the pastures, this may not be a serious consideration, but .where these factors are doubtful, the question of regular pasture renewal must be considered as a vital policy question.