The cereals (wheat, oats, barley, maize) and peas, potatoes, and linseed are the main cash crops grown in New Zealand. These crops are usually grown in a rotation, which includes fodder crops and a period in pasture, to make use of the fertility of the soil which is built up by growing of pasture and fodder crops to be eaten in the field. It is not the practice, as in some overseas countries, to grow cash crops exclusively without an intervening period in pasture. Unless soil is very fertile it is unusual to grow two cash crops (at least of the same kind) in succession; they are usually interspersed with a fodder crop. The number and kind of crops grown before the land is returned to pasture almost entails a separate decision for each paddock, based mainly on the fertility of the soil and the need for supplementary fodder crops.

Wheat: The area in wheat declined steadily for many years until 1958, which was the lowest recorded for 75 years. But the area has since more than doubled to about 200,000 acres, all of which is harvested for grain. Nearly 10 million bushels of wheat are used in New Zealand each year for flour, and similar uses, and 4 million bushels for feeding to stock and to poultry. The crop at present is about 8 million bushels and the balance is imported from Australia. Improved varieties recently introduced and the build up of soil fertility in recent years are now enabling wheat to yield an average of over 50 bushels per acre. Farmers generally aim to grow wheat after the breaking up of a pasture, or after a fed-off fodder crop or a crop of peas; they seldom grow wheat immediately after a previous grain crop. About three-quarters of the wheat crop is grown in Canterbury and North Otago. The crop there is sown in the autumn (April to June) and the summers are usually dry enough for easy harvesting. In South Otago, Southland, and the North Island it is usual to sow wheat in August or September. In these districts it is often difficult to harvest the grain in good condition. The usual method of harvesting is to head the crop directly with header harvester and bag the grain. In the drier districts handling of the grain in bulk, both at harvest and for storage, is becoming more popular. In bulk handling more care must be taken to see that the grain is dry enough to prevent heating in storage. In districts where weather is less favourable for harvesting much grain may be spoilt because it can not be harvested in dry condition, and thus grain driers are being increasingly used to dry the wheat after harvest and before storage.

Rapid changes are taking place in the preferences being shown for different wheat varieties. Aotea, which was released in 1958, was being grown on 80 per cent of the wheat area by 1961 and had almost entirely replaced Cross 7, the standard variety for many years. Aotea is heavier yielding than Cross 7, but, like it, resists lodging and produces flour satisfactory for baking. Other South Island varieties in 1961 included Arawa, a wheat of poorer baking quality but very suitable for the heavier wheat lands of South Canterbury and North Otago, and Hilgendorf, of high baking quality but generally poor yield. Gabo and Tainui were the main North Island varieties.

Since 1961 Aotea has waned in popularity in favour of two mildew-resistant selections of Cross 7 (1961) and Hilgendorf (1961) – which were made from the earlier susceptible selections – now known as Cross 7 (1935) and Hilgendorf (1947). The new releases yet retain the good qualities of those varieties. Rust-resistant selections of Gabo, known as Mengave and Gamenya, are replacing the former variety in the North Island. These three varieties were tried in Australia, but all the others have been produced for local conditions by the Crop Research Division of the Department of Scientific and Indusrial Research.

Oats: The growing of oats for chaff and grain is much less common now that tractors have almost entirely replaced horses. The chaff acreage has dropped in 20 years from 200,000 to under 20,000, and the grain acreage from 70,000 to 35,000. About 500,000 bushels of threshed grain are processed each year for breakfast foods and a little more than half that quantity is used for seed. The balance, of some 750,000 bushels, depending on the size of the harvest, is used for stock feed. Oats do not demand the same soil fertility as wheat. They may be grown on soils of lower fertility or after wheat in the rotation. Spring sowing of the crop is common in Otago and Southland, where nearly half the oats, both for chaff and for grain, are grown. Most of the grain from this area is used for processing, and the varieties are mainly Onward and Abundance. Canterbury grows almost half the grain and one-third the chaff. In this district autumn sowing is usual and the crops may be grazed in winter. The Algerian and Dun varieties are better suited to autumn sowing and winter grazing than Onward and Abundance. They have a finer straw and a coloured grain and are preferred for horse feeding as either grain or chaff. Algerian is preferred for sowing for green feed. The crop for grain may be harvested with the header either direct or out of the windrow, whereas the crop for chaff must be cut with the reaper and binder, stocked, and stacked for later chaffing. Some farmers stook and stack the crop in case it is needed for chaff in the winter, but if it is not required for that purpose they thresh it for grain in the spring. In a mild winter when feed is not scarce many crops sown for green feed may not be heavily grazed; they may then be kept for either chaff or grain. This practice can have a serious effect on the grain market in the following year.

Barley: Barley for grain is almost entirely spring sown and, because most of the grain is needed for malting, the crops tend to be concentrated in those districts known to produce grain of good malting quality. Barley for malting must be capable of high and rapid germination and those types are preferred which are of low nitrogen content, plump, and undamaged by threshing. About 2 million bushels of barley are needed each year for malting. The rest of the crop, apart from seed, is used in stock foods. As barley for grain is spring sown it can follow potatoes or a winter-feed crop in the rotation. Land which is fertile, but not too rich in nitrogen, and moist enough during the season, is preferred for this crop. Almost three-quarters of the barley-grain crop is grown in Canterbury with a relatively heavy concentration in the Ellesmere and Ashley Counties. The Waimea County in Nelson and the Manawatu County in the Wellington Land District are also favoured localities. As barley grown in the North Island is used entirely for stock feeding its malting quality is of no moment. Though the best malting barley is obtained by cutting and stooking the crop to allow it to condition before threshing, the header harvester is now widely used. It is better to thresh the barley out of the windrow rather than to head it directly. A selection from the Australian variety, Research, made by the Crop Research Division, takes up two-thirds of the acreage, the balance being made up mainly of the Danish variety, Kenia. Another Danish variety, Carlsberg, is being grown for feed grain because of its higher yield, but it is not acceptable for malting and brewing. A small area of Cape and Black Skinless varieties is grown, as seed of these varieties is in demand for sowing green-feed crops.

Maize: Maize demands a frost-free growing period. Thus maize for grain is concentrated in the northern parts of the North Island, mainly in the Gisborne and, to a lesser extent, the Bay of Plenty districts. Most of the grain is fed to poultry, though some, mainly home grown, is fed to pigs. The maize crop is a gross feeder and needs a well drained, highly fertile soil. River flats are generally well suited to maize growing. To obtain high yields maize needs to be sheltered from heavy wind, and should not be sown until the soil has warmed up in the spring. Mid-October is quite early enough. Unlike other cereals, which are sown moderately thickly in 7-in. drills, maize is sown thinly spaced in rows usually 36 in. apart, the aim being to have one plant established in each 8–10 in. of row. The crop does not mature until late autumn, when mechanical pickers are used to pull the cobs from the plants and strip the husk. The cobs are then stored over winter in long cribs open to the air to dry out and mature before the grain is shelled from them. With the introduction of grain driers, an increasing proportion of the maize crop is being harvested and shelled in one operation, and the grain then artificially dried until it is of a sufficiently low moisture content for safe storage. Easily pollinated varieties were once widely grown, but today only one of these – Marigold – is grown to any extent. Doublehybrid seed is now widely used, much of it grown by the Department of Agriculture from parent material imported each year from the United States. The present hybrids are W575, W643, W647, and W690.

Peas: Garden varieties account for about three-quarters of the peas grown for threshing as ripe seeds. This seed is resown to produce green peas to be used fresh or preserved by canning or quick freezing. The rest of the crop is made up of field varieties, which are used dry for split peas and soup powders, for boiling, or for pigeon feeding. The inferior peas of both groups may be used in stock foods.

The pea crop is rather risky. As it will not withstand extremes of moisture it is best grown in a mild and dry climate and in a moisture-retentive soil. Garden varieties are affected by adverse conditions more than the field varieties. Nearly two-thirds of the peas for threshing are grown in Canterbury, and the balance in Marlborough and Wellington. Most of the crop is exported, mainly to Britain and Australia where it is used for seed. The garden varieties are usually grown by farmers under contract to merchants, who themselves are under contract to supply overseas buyers. A small portion of the crop is used locally.

Quality is important in all threshed peas. Contracting merchants take particular care to maintain a high standard of purity in their seed stocks, and most farmers rogue out off-type plants from their growing crops. The colour of the threshed peas is also important. This is generally best if the crop is cut when the top pods are just past their best for table use and left to condition in the windrow before threshing. Because of the risk of damage by rain and loss by wind, most growers, however, prefer to wait until the crop is fully ripe before cutting it, and then to pick it up immediately with the header harvester. Any shrivelled, cracked, discoloured, or off-type peas are removed in the subsequent machine dressing. The varieties Greenfeast, Onward, Victory Freezer, and William Massey are most widely grown for the garden-pea-seed trade. For boiling peas, soup powders, and sometimes for splitting, the Blue Prussian variety is used. Partridge is used for splitting and by pigeon fanciers overseas.

Linseed and Linen Flax: These two crops, used for widely different purposes, are of the same botanical species. By selection varieties of linseed are now grown which return heavy yields, rich in good quality oil, used mainly in the paint industry. The residue left from the extraction of oil makes a valuable concentrate for stock feeding. Linen-flax varieties have been selected on the basis of the yield and quality of the linen fibre contained in the straw, though the seed of these varieties can also be used for oil and stock feed. Linseed does not require special soils, though it succeeds best with a well distributed rainfall during growth, followed by dry conditions at ripening. For linen flax, uniformity, both of soil and of growing conditions, is essential to produce even, high-grade fibre. High soil fertility, though not harmful to linseed, produces in linen flax a coarse, harsh fibre. At present from 15,000 to 20,000 acres of linseed are grown each year, most of it under contract to an oil factory. The crop is grown mainly in Canterbury with a little also in Southland and Otago. Better soil fertility and higher yielding varieties have doubled the yields of linseed over those of 20 years ago. It is usual to direct-head linseed, but weedy or uneven crops are better windrowed and allowed to condition before threshing.

Linen flax was not grown in New Zealand until the early years of the Second World War when, within two seasons, the acreage increased to 20,000 and 17 processing factories were built. Since then the acreage has steadily declined, until now only about 700 acres are grown each year near the only remaining factory, at Geraldine, in South Canterbury. The crop is harvested at a rather earlier stage of growth than linseed, a special machine pulling the plants from the ground to obtain greater straw and fibre length. After the seed is removed the straw is retted and scutched to extract the fibre.

Potatoes: The growing of potatoes is more widely distributed than that of other cash crops because the product is perishable, and also there is the advantage of the considerable differences in harvesting periods in various districts. These differences in time are determined largely by the most risk in a district, as potatoes will not withstand frosting. Many householders grow some potatoes for their own needs. A little over 20,000 acres produce each year for marketing an average of 100,000 tons of table potatoes and 20,000 tons of seed potatoes. Many commercial growers produce their own seed. The average yield of potato crops varies considerably from season to season, so that, even with a constant planting, surpluses and shortages are likely from time to time. About two-fifths of the commercial crop is grown in Canterbury, about one-fifth in each – Auckland and Wellington, and smaller amounts in Hawke's Bay, Nelson, Otago, and Southland. Potatoes are grown in many types of soil, but they prefer a well drained, fertile silt loam which does not dry out unduly. The soil and its yield potential influence the choice of variety. Main-crop potatoes are usually planted in a rotation with other cash crops. They can follow almost any other crop, but are often planted after grass and before wheat. Crops for early marketing are often planted in rotation with vegetable crops, rather than with the recognised field crops.

In frost-free areas, like the Pukekohe district south of Auckland, the earliest plantings are made in April or May and harvesting of new potatoes for immediate sale begins in August. In the South Island, however, main crop potatoes are usually planted in October and harvested about May to provide potatoes until new ones are plentiful again. Other districts observe intermediate planting and harvesting dates. Many of these crops are dug at an immature stage for sale without storing. Spraying or dusting to prevent potato blight is a feature of the Pukekohe district where potato growing would otherwise be uneconomic. Commercial potato crops are almost all planted by mechanical planters. Mechanical diggers are used, but the tubers are usually picked up and bagged by hand. Crops for immediate sale may be dug immature, the state of the market often influencing the time of digging. Main-crop potatoes which are to be stored are left in the ground until the skins have hardened. They are stored in sacks in darkened sheds or in the open under a protective cover of straw, or loose in long clamps with a good straw cover. If potatoes are to be delivered for sale direct from the paddock they are sorted to size and grade as they are picked up. But if they are to be stored sorting may be left until the potatoes are being prepared for sale. Seed potatoes may be stored in more light than eating potatoes as greening of the tubers spoils table potatoes but benefits seed potatoes and checks excessive sprouting. Only a few of the many varieties of potatoes planted in New Zealand are grown commercially. Arran Banner and Ilam Hardy are the most widely used for early crops; Aucklander Short Top, Katahdin, and King Edward for mid-season harvesting; and Glen Ilam, Dakota, Sebago, and Arran Chief for late harvesting.