Groundnuts are a versatile, high-value crop with strong demand for raw kernels, peanut butter, peanut oil and other products. For South African farmers, they offer an opportunity to diversify production and generate income, but success depends on choosing suitable soil and following the right planting, nutrition and crop-management practices.
By Dr Wikus Snijman, Project Manager: Groundnut Breeder Seed, ARC Grain Crops Division
Locally, groundnuts are grown in the summer rainfall region under irrigation and dryland conditions. Initially, smallholder farmers, mainly from the northern and eastern parts of South Africa, produced groundnuts for their own consumption, and these remain an important source of nutrition in the northern parts of KwaZulu-Natal and Mpumalanga.
Recently, some of these farmers have entered the commercial market through incentives offered by processors to boost South Africa’s production and to keep the groundnut industry viable. This has opened new business opportunities for developing and commercial farmers.
Groundnuts are important to the South African market, both as a local crop and as an export commodity that can generate foreign exchange earnings.
Background
Groundnuts (Arachis hypogaea L.) are divided into two groups, namely the Virginia and Spanish–Valencia groups. It is generally accepted that groundnuts were introduced to South Africa by Portuguese seafarers and slave traders in the form of the Spanish-type cultivar Natal Common.
The early Natal settlers conducted the first groundnut trials in 1853, testing the locally available cultivar alongside the Virginia type favoured by the settlers.
The Spanish type is highly suitable for South African conditions because it is adapted to adverse environmental conditions, is more disease-resistant, has a shorter growing cycle and appears to have little fresh-seed dormancy.
In the 1960s, the Agricultural Research Council’s Grain Crops Division started a groundnut breeding programme in Potchefstroom, where the Spanish bunch groundnut variety is still being produced.
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Starting your own groundnut operation
Soil
Sandy soil is best for groundnut production. Groundnuts have a well-developed taproot system, which, depending on the soil type, can reach a depth of 1,8 metres. Soils with high potential for groundnut production are therefore typically deep (1,5–2 metres deep), well drained red and/or yellow with a high fine-sand fraction, such as sandy loam. The pH (measured using potassium chloride, or KCl) should range between 5,5 and 7.
Seedbed preparation is very important. The seedbed must be moist, even and firm to ensure good contact between the soil particles and the seed, which will promote good germination and root development.
The most suitable soils for groundnut cultivation are Avalon, Bainsvlei, Clovelly, Hutton and Glencoe. Physical limitations such as shallow soil or compacted layers must be avoided because they restrict taproot development.
Seed germination is rapid when soil moisture and temperature are optimal. Seeds planted at a depth of less than 50 mm are exposed to relatively warmer soil, which can promote rapid germination. However, seeds planted too shallowly may dry out quickly, resulting in poor germination and uneven plant stands.
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Water
The areas where groundnuts can be grown successfully under rainfed conditions are limited because the crop requires adequate moisture. The Spanish type is recommended in these areas, as it is more water-use efficient because of its upright growth habit and short growing season. Annual rainfall of 500 mm to 700 mm provides optimum conditions for groundnut production.
Planting should not be done until at least 50 mm of rainfall has been measured over a short period. Seed germination can be accelerated by planting in moist, warm soil.
Temperature
Groundnuts originate from the tropical areas of South America and therefore require a growing period of at least 160 frost-free days and high temperatures. Avoid planting in dry soil or cold, wet soil. Planting in soil of at least 15°C, measured at a depth of 5 cm, ensures fast germination and produces healthy seedlings.
A germination rate of 95% can be achieved at temperatures between 18°C and 30°C.
Suitable vegetative growth occurs best at temperatures between 20°C and 35°C, and a daytime temperature of 27°C is most suitable for flower development. A daytime temperature of 29°C and a nighttime temperature of 23°C are optimal for pod formation.
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Fertiliser
The type of fertiliser is determined by the soil analysis.
Groundnuts are not highly dependent on nitrogen fertilisation because, as legumes, they can fix atmospheric nitrogen with the aid of root-nodule bacteria. These bacteria convert atmospheric nitrogen into forms of nitrogen that the plant can use. Active nitrogen-fixing nodules have a pinkish appearance, whereas inactive nodules are green when dissected.
In rural fields, phosphorus levels are usually low and additional phosphorus may be required.
Like other crops, groundnuts require adequate levels of potassium for normal growth and development. Where potassium levels are low, it can be supplemented at a rate of up to 10 kg per hectare.
On the other hand, an excess of potassium in the soil can induce calcium deficiency – and calcium is crucial for seed development. In calcium-deficient soils, groundnuts may produce lower yields and kernels of poorer quality.
Production practices
Planting should begin when soil moisture is adequate and the seedbed has been properly prepared. To establish a good planting density, about 50 kg of seed should be planted per hectare.
On smaller pieces of land, seeds can be spaced 8 cm apart within the row, with 90 cm between rows. In high-rainfall areas, the spacing between rows can be reduced to 75 cm.
The seed should be planted at a depth of 5 cm, and slight pressure should be applied to the planting row to maximise contact between the soil and the seed. When planting implements are used, the seed and fertiliser are deposited simultaneously. If planting is done by hand, the fertiliser can be spread evenly over the area after planting.
It is important to apply a pre-emergence herbicide.
Pest control are usually not a major concern. However, when an infestation reaches 10%, action should be taken. Aphids, rust and leaf spot tend to be more common than other pests and diseases.
An appropriate insecticide should be applied to control aphids, and fungicides to control rust and leaf spot when necessary, following current recommendations and label instructions. Maintaining the groundnut fields throughout the season is important.
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Harvesting takes place about 150 days after planting. The whole plant is lifted from the ground and can be placed in heaps or windrows to dry. After two weeks, the leaves and stems can be removed and shelling can begin.
Care must be taken during shelling to prevent damage to the kernels. Split and damaged kernels result in lower returns than whole, choice-grade kernels. Groundnut yields range from 1,5 tonnes per hectare to 4 tonnes per hectare.
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