Arable crops are harvested in New Zealand using combine harvesters, also known as headers.
The time of harvest is determined by the moisture content of the grain, which should usually be below 14%. Most farmers will have a moisture meter to measure small samples of grain from various parts of the paddock.
Most arable crops, particularly cereals, are direct-headed. This means the header first cuts the plants 5–10 centimetres above ground level, and then moves them directly into the machine where they pass through a series of revolving drums and shaking platforms that separate the grain from the straw. The straw is discarded on the ground at the rear of the machine and the grain is held in a hopper in the header until it is transferred to a truck.
The latest combine harvesters can harvest 10 hectares of wheat an hour, or about 100 tonnes. The hopper in the harvester can hold about 8 tonnes of wheat. Usually the grain is fed straight into bulk bins on trucks. Compared to the tough work needing many hands in the late-1800s wheat bonanza, the only workers required for a modern harvest are the harvester operator and a couple of truck drivers.
How the harvested grain is stored depends on its intended market – some is taken directly to the purchasing company, while other crops are held in silos on the farm until they are sold.
If the crop is very weedy it may be necessary to windrow a crop before harvest. This involves cutting it and leaving it to dry on the ground until it can be harvested. If the crop has too much green vegetation it will not separate well inside the header. This generally occurs when the autumn is very wet.
The grain may also need to be dried before storage. Special drying silos blow air through the grain to reduce the moisture content so it can be stored without the seed germinating or micro-organisms growing. Drying facilities on farms are particularly important in Southland, which is wetter than other arable cropping regions.
The straw is a by-product of the harvest. It may be:
- incorporated back into the soil during the next cultivation
- burnt, and the ash mixed into the soil
- baled for sale and uses such as mushroom production, bedding for animals or garden mulch.
Crop yields vary considerably between farms, soil types and seasons, so it is difficult to give average values. Farmers growing wheat for feed expect yields of 10 tonnes of grain per hectare. Milling wheat yields are generally lower, around 6–7 tonnes per hectare, while barley may yield 7–8 tonnes per hectare. Pea yields in New Zealand are around 4–5 tonnes per hectare.
The crops with the highest yield may not necessarily be the most profitable, since the costs of production may affect margins.