Peanut (groundnut)

The following are the crop details for Groundnuts

• Scientific name: Arachis hypogaea
• Local names: Njugu (Swahili)
• Order: Fabales
• Family: Fabaceae
• Genus: Arachis

Harvesting peanut

Peanut kernels

Peanut with flower

Peanut flower and bee

Harvesting peanut

Peanut field

Peanut seedlings

Peanut foliage

Peanut foliage

Groundnuts are small erect or trailing herbaceous legumes, about 15 to 60 cm high. The fruit is a pod with one to five seeds that develop underground within a needle-like structure called a peg.

The leaves are arranged in alternate pairs and have leaf-like attachments near the stalk. The groundnut plant produces yellow, orange, cream, or white flowers which produce 'pegs', characteristic floral structures which sink into the ground to grow the pod. The pods can reach up to 10 cm (4 in) in length and can contain between 1 and 5 seeds. The plant can reach 0.6 m (2 ft) in height depending on the variety and as an annual plant, survives only one growing season. 

The seeds are rich in oil (38-50%), protein, calcium, potassium, phosphorus, magnesium, and vitamins.

Groundnuts also have considerable medicinal value. They are reported to be useful in the treatment of diseases such as hemophilia, stomatitis, and diarrhea. 

In sub-Saharan Africa, groundnuts are a basic staple crop, cultivated mainly by small-scale farmers both as subsistence and as a cash crop. It is an important source of protein and other nutrients for poor rural communities. In Africa, groundnut yields are traditionally low, due to unreliable rains, little technology available to small-scale farmers, pest and disease occurrence, poor seed variety, and increased cultivation on marginal land (ICRISAT).

Groundnuts may also be referred to as peanut, monkeynut, or earth nut. Groundnuts originated in South America from southern Bolivia to north-western Argentina. The Portuguese took them from Brazil to West Africa and then to southwestern India in the 16th century. Africa is now regarded as a secondary center of diversity.

Peanut Processing

Roasted, salted peanuts

There are two main varieties of groundnuts in Kenya:

• Runner type
• Bunch type

The runner is a large variety and it's highly preferred because of high yields, it matures in 90-100 days. Bunch varieties are small, tastier, and highly marketable, it matures in 60- 75 days.

Other varieties include Red Valencia, Red Oriata, Manipinta, Makulu Red, Bukene, Homa Bay, Texas Peanut, and Atika.

Red Valencia: This variety is easy to grow and produces two to five kernels per long pod. It’s slightly smaller in size and has a sweeter taste with papery red seed covers.

Groundnuts are grown in most tropical, subtropical, and temperate countries between 40°N and 40°S latitude, especially in Africa, Asia, North, and South America.  They are grown in the warm tropics and subtropics below 1500 m above sea level, and in temperate humid regions with sufficiently long warm summers. The optimum mean daily temperature to grow is 30°C and growth ceases at 15°C. Cool temperatures delay flowering. Groundnuts cannot stand frost. Between 500 and 600 mm of water reasonably well distributed through the growing season allows good production.

Groundnuts are drought-tolerant species and can withstand severe lack of water, but the yield is generally reduced. If harvesting conditions are wet, aflatoxins (severe poison produced by some fungi such as Aspergillus spp) may develop on the nuts. Aflatoxin contamination is a major hazard to human and animal health. When groundnuts are poorly dried and stored, they pick mold and dirt, which attracts fungi, that release aflatoxin chemicals that are dangerous to human health, especially the liver.

Pods develop underground and must be recovered at harvest, therefore crumbly, well-drained soils are preferred, but plants grow and develop adequately on heavier clay soils. For optimum growth, soil pH should be in the range of 5.5 to 6.5, though Bunch types tolerate more acidic conditions (pH 4.5) and some cultivars grow well in alkaline soils up to pH 8.5.

Most commercially grown peanuts are used for the extraction of their oil which is used in cooking. The by-product of oil extraction is a pressed cake which is used as animal feed and also in the production of peanut flour. Raw kernels are also commonly roasted and eaten as a snack food.

The vegetative residues from the crop are excellent forage.

Peanut is usually propagated from seed. Seeds should be planted in a well-prepared seedbed in soil that is loose and crumbly with no large clumps. The seedbed should be free from weeds which will compete with the peanut seedlings. Weeds may be removed by hand cultivating or through the use of an appropriate herbicide. Peanut seeds should be planted by hand to a depth of 3–5 cm (1–2 in). It is best to ridge the soil or use flat beds as this will make harvesting the peanuts easier.

After ploughing and harrowing to a fairly good tilth, ridges that are 80 cm apart with flattish tops, should be made so that two rows of nuts can be planted on each ridge. Seeds for planting should be well selected: they should be clean, well-filled, and without any blemishes. Seeds should be kept in their pods and shelled a few days before planting. Planting depth is like maize about 5 to 8 cm. Seed rate is 40 to 50 kg/ha depending on the size of the seeds.

They can be grown as a sole crop and also intercropped with maize, soybean, and cassava. It is also a good intercrop for upland rice, sorghum, okra, sugarcane, and sunflower.

In some areas, they are grown under perennial tree crops such as coconut, oil palm, or rubber. Groundnuts when used as intercrop for upland maize and planted along the contour reduce soil runoff. The plant also reduces the population of African bollworms because it serves as a hiding place for beneficial insects. There is an increase in the yield of groundnuts when intercropped with early-maturing pigeon peas.

To achieve maximum economic yields, weeds must be eliminated. Groundnuts are poor competitors with weeds during the early stages of growth. Weeding should be done early while at the same time earthing up the ridges to encourage "pegging" i.e. young nuts penetration through the soil. Once pegging has started, only hand weeding should be undertaken to avoid disturbing the young nuts or damaging the flowers. Clean weeding should be done in up to 6 weeks after which hand weeding should take over.

The only peculiar nutrient requirement is for calcium (Ca) in the podding zone. Calcium is absorbed directly by the pods if soil moisture is adequate. A shortage of Ca in that zone will result in empty pods (especially in Runner cultivars). The crop's needs for nitrogen should be satisfied with symbiotic fixation by strains of Rhizobium of the cowpea group, so nitrogen fertilizers are not generally required. 

In some areas of acid soils, lime is applied to raise the pH and supply Ca. Moisture stress during flowering or pod filling reduces yield therefore irrigation is important during those periods to minimize or eliminate the stress, and increase production and seed quality. Where yields are unsatisfactory (heavily eroded soils) an application of 200 kg/ha of rock phosphate is recommended.  

Bunch cultivars are harvested 85-100 days after sowing and Runner cultivars 110-130 days after sowing in the warm tropics. Dig a few plants up to see if the nuts are ready. The nuts should be brown on the outside, firm, and dry. Usually, at maturity the inside of the pods is grey and some rattling occurs when pods are shaken. Severe disease of foliage sometimes results in harvesting before seeds are fully mature.

Plants should be carefully dug out to avoid nuts breaking off and remaining in the ground. Dry for 2-3 days, then rip the pods from the bushes and place them on mats to dry for another 7-10 days to about 10% moisture. 

Shelling should be done by hand. Broken, dirty, or damaged nuts should be discarded as these will lower the quality and hence the selling price. When the groundnuts are poorly dried and stored, they pick mold and dirt, which attracts fungi, that release aflatoxin chemicals that are dangerous to human health, especially the liver. Nuts to be used as seeds the following year should not be shelled.