Nearly 750,000 acres of brassicas and some 50,000 acres of cereals are grown for supplementary feed crops each year. There is also some winter and early spring grazing from much of the area of autumn-sown wheat and oats (perhaps 125,000 acres), which is grown primarily as a grain crop.
Turnips and Swedes: These two crops, similarly managed and used, are fairly widely grown throughout New Zealand. Swedes and yellow-fleshed turnips do best under cool, moist conditions, as they make most of their growth in the later part of the season. They are used almost entirely for winter feeding.
These crops are more commonly grown in the southern districts, particularly Southland, and to some extent in the cooler and moister districts in the North Island. White-fleshed turnips can be grown more successfully during the warmer seasons of the year, as they are more tolerant of dry and sunny weather. They are used not only for winter feeding (for which they are widely grown in Canterbury) but also for late-summer feeding, particularly in dairying districts where pasture growth suffers in dry summers. Turnips and swedes yield heavy crops on well drained soils containing ample organic matter and having an even supply of moisture. But they are so valuable for supplementary feeding that they are often grown under less suitable conditions where yields may be only a quarter of those grown under ideal conditions.
Some crops may be used by pulling roots and carrying them out to stock. The more common method is to turn the cattle or sheep on to the area to feed off the growing crop in “breaks”. These are made by fencing off a large enough part of the crop to maintain the stock for 10 days to a fortnight. This method entails less labour than feeding out and is far less wasteful than allowing the stock to wander through the whole crop. In some districts the swede tops are used for fattening late lambs, after which the bulbous roots are eaten by adult sheep.
At one time all turnip and swede seed was imported from England, but during the Second World War seed was harvested locally and sufficient seed to meet local requirements has since been produced in New Zealand. Most of the varieties grown are similar to the main English ones, but two have been developed in New Zealand to meet local conditions. One, named “Calder”, resists attack by the mosaic virus; the other, “Wye”, resists attack by clubroot diseases. These diseases, with dry rot, are the main diseases of turnips and swedes. Work is being done to develop resistance to dry rot also.
Rape: This crop was once regarded as the best feed for fattening lambs, but the acreage is declining for two reasons: improved pastures have now made it possible to fatten many more lambs without any special fattening crop; and rape is so easily attacked by pests and disease that other crops are being grown instead. Rape is required primarily in lamb-fattening districts where summer grass production is low. Half the total acreage is in Canterbury and a quarter in Otago. In Hawke's Bay, once a big rape-growing area, it has been largely replaced by chou moellier. It is usual to feed rape in breaks to avoid waste. Grazed portions of the crop are closed to stock to conserve second growth for winter feeding. It was once common practice to provide a grass run-off to lambs grazing on rape, but now it is usual to confine them on rape entirely. White butterfly, diamond-backed moth, and cabbage aphid seriously infest rape, which is also subject to club-root disease. New Zealand produces enough rape seed for its needs. Two new varieties have been developed, one is resistant to clubroot, and the other to aphid infestation.
Chou Moellier and Kale: The green crops grown under these names are both members of the kale family; chou moellier is known in England as marrow-stemmed kale. The crop grown as kale in New Zealand is known in England as thousand-headed kale. Stock relish the stems of chou moellier, but this plant tends to drop its leaves during winter. Kale, while having a fibrous, unpalatable stem, is more hardy and carries its leaves well throughout the winter. Two-thirds of the total chou moellier crop is grown in the North Island. Kale (about only a tenth of the total chou moellier crop), is grown mostly in Southland and Otago. These crops are grown mainly for winter feeding, though chou moellier has come into favour recently as an alternative to rape for lamb fattening and as a cattle feed in late summer. Kale may be used similarly. Crops of chou moellier and kale which are not needed for late-autumn feeding can be reserved for use in winter. Crops lightly grazed in early summer will recover to provide winter feed. Kale and chou moellier crops are more resistant than other brassica crops to clubroot and dry rot and are not so subject to insect attack. Heavy crops of chou moellier are best cut and fed out as required, though less labour is needed if the cut crop is left to be eaten where it falls and the standing portion protected by an electric fence. If it is intended to feed the crop in breaks, fencing is made easier if swedes are drilled in the lines where the fences will later be placed.
Cereals: The area of cereals grown specifically for green feed is small compared with the area sown for a grain crop which is grazed at some stage as part of its management for grain. Oats are the main cereal grown specifically for green feed; some maize and barley are also grown, but very little wheat or rye. Maize, being frost tender, is grown almost entirely in the North Island, mainly in South Auckland. It is used as a supplementary feed in late summer, chiefly for dairy cows. The other cereals are used as additional feed during late autumn, winter, or early spring. They are sown in early autumn, frequently after the harvest of a grain crop. Half the acreage of green-feed cereals is grown in Canterbury and a quarter in Otago and Southland. If winter feed is plentiful, green-feed cereal crops (other than barley) which have been lightly grazed may be allowed to grow on for a chaff or grain crop in the following harvest. Autumn-sown cereal-grain crops are commonly grazed in early spring either to control rank growth and prevent later lodging, or because there is little other late-winter feed to keep stock in reasonable condition. Wheat and oats are the cereals most commonly managed in this way. Overgrazing of the crops at this stage may prejudice a satisfactory grain harvest later. A small acreage of cereals is grown for grain for feeding on the farm and about 20,000 acres of oats are grown for chaff, some of which will be home fed and some sold.