Groundnuts are the second most widely grown legume in Uganda, after beans. There has been a substantial increase in the growing of groundnuts as both a food and cash crop because of increased awareness of their value as a source of proteins (23–25% content) and oil (45–52% content). They also have the advantage of generating residual nitrogen in the soil, which benefits subsequent crops, especially when groundnut residues are incorporated into the soil during ploughing.
Despite the high demand for groundnuts, farmers’ yields continue to be low, averaging 560kg/ha of dry seed. Well-managed plots, using the right varieties, can yield 2500–3,000kg or more. At the moment, a kilogramme goes for sh3,500 to sh5,000. Groundnut paste goes for sh6,000.
Groundnuts do not yield well in dry areas or at altitudes above 15,00m (around 5,000ft). Optimum temperatures are 27–30 °C for vegetative growth and 24–27 °C for reproductive growth. Between 450mm and 1250mm of evenly distributed rainfall is required annually for good growth and yield.
All soils, other than heavy ones, are suitable for growing groundnuts. However, the best are deep, well-drained sandy, sandy loam or loamy sand soils.
Groundnuts require adequate levels of phosphorus, potassium, magnesium and particularly calcium, which are required for maximising yield and good quality seed.
To avoid the spread of pests and diseases, groundnuts should not be grown continuously on the same land.
A rotation of three years or longer can usually reduce diseases, pests and weed problems. Because of the incidence of pests and soil-borne diseases, groundnuts should not be grown after cotton, although cotton can be used in rotation after groundnuts.
Good land preparation provides suitable soil conditions for rapid and uniform germination, good root penetration and growth as well as steady pod development. Land should be prepared early, before the rains start, so that sowing can take place early in the rains. All previous crop residues and weeds should be removed or buried.
Seedbeds should be smooth to provide good soil-to-seed contact after sowing.
For farmers who use tractors, deep turn the soil to bury the residue and weeds, using a disc plough, three to four weeks before planting.
In wet, low-lying areas, it may be worth considering planting the groundnuts on ridges can prevent waterlogging and improve weed control and harvesting. Ridges should be made at, or just before sowing and should be flat-topped.
Pods should be shelled one to two weeks before sowing and only good quality seed selected for sowing. Damaged, small or shrivelled seeds should be discarded. It is good practice to purchase certified seed at regular intervals, preferably every two to three years.
To control seedling blights caused by soil bacteria and fungi, and also other fungal diseases, a fungicide treatment is recommended. Thiram gives good protection and can be applied as a dust at 120g of thiram/100kg of seed. The dust must be uniformly mixed with the seed.
It is important to be aware that some varieties of groundnut seed require a period of dormancy between harvesting and sowing.
Farmers should plant as soon as there is adequate moisture in the ground to ensure good germination. In general, groundnuts are planted between February 15 and April 15 during the first season and in early August for the second season.
Planting early in the season helps to improve yields and seed quality as well as reduce the incidence of rosette disease.
Long duration varieties should only be planted with the first rains in the first season. Short duration varieties can be planted in either season.
Seeds should be sown at a depth of 5–6cm. To ensure uniform sowing depth, germination and crop stand, it is suggested that a groove of 5–6cm in depth is made along the rows for planting.
Once the seed has been planted at the right depth and spacing, the soil is pressed down to ensure good contact with the seeds, enabling them to extract moisture more effectively.
It is important to sow groundnut seeds in rows and at the right spacing as this helps reduce the incidence of rosette disease, ensures a more uniform pod maturity, better quality seed and maximises yield.
The recommended spacing ensures that there is good plant population. The recommended space between rows is 45cm. Row spacing can be reduced from 45cm to 30cm, if desired and this will allow earlier ground cover and help prevent serious weed problems.
- Groundnuts cannot compete effectively with weeds, particularly 3–6 weeks after sowing. Therefore, early removal of weeds is important.
- Two to three times of weeding are recommended. The first should be done before flowering and at least one other during pegging.
- If early weeding is done well and crop spacing recommendations followed, then the weeds that come up later are smothered with the vigorous growth of the crop.
- When weeding, it is important to avoid covering the bottom of the plants with earth (including earthing up) as this can increase diseases such as white mould, reduce flowering and pod development and, therefore, reduce pod yield.
- Once flowering and pegging begins, it is advisable to weed by hand pulling, rather than by using a hoe, as this is less likely to disturb any developing pods.
Pre and post-emergence herbicides may be used to eradicate weeds. Herbicides such as alachlor (Lasso®) can be used before crop and weed emergence, and bentazone (Basagran®) and fluazifop-p-butyl (Fusilade Super®) following emergence. Follow the manufacturers’ instructions with regard to dosage.
Groundnut rosette disease is caused by a complex of viruses that are transmitted by aphids. It can occur at high levels and can often produce 100% loss in yield.
There are two forms of symptoms seen in the crops: ‘chlorotic’ (yellow and stunted) and ‘green’ (green and stunted). Late planted crops and wide spacing can increase the incidence of rosette disease, so these should be avoided. Rosette-resistant varieties of groundnuts are available (for example Serenut 2, Igola 1, and these eliminate the need for spraying insecticides to control the aphids.
Systemic insecticides such as dimethoate (Rogor EC40®) can be sprayed at a dosage of 50ml in 20 litres of water for 14 days after crop emergence and then at 10-day intervals for a total of four sprays.
Late leaf spot occurs later in the season and has nearly circular lesions which are darker than those of early leaf spot. Late leaf spot does not normally affect yield production as severely as early leaf spot.
On the lower leaf surface where most of the sporulation occurs, the lesions are black. Since the leaf spot pathogens survive mainly in crop debris, practices such as crop rotation, burying crop debris during land preparation and early sowing can significantly reduce the incidence of diseases.
Groundnut leaf miner is a comparatively new pest. It is the larva of a small moth which burrows and mines into the leaflets of the plant. When the larvae have grown, they come out of their mines and pull the leaves together with threads.
Severe cases of leaf miner damage make the crop look as if it has been burnt and severe crop losses can occur. It is suggested that systemic insecticides are used as soon as quantities of mines are observed.