Vigna subterranea

Origin and cultivation

The origin of the Bambara groundnut is West Africa^[4] and the region of cultivation is Sub-Saharan Africa's warm tropics.^[5] Bambara nut grows well any where groundnut (peanut) grows and so is vastly present from Kwara state and throughout the northern parts of Nigeria.

Importance

Bambara groundnut represents the third^[6] most important grain legume in semi-arid Africa. “It is resistant to high temperature and is suitable for marginal soils where other leguminous crops cannot be grown”.^[7] In addition, it makes very little demand on the soil^[8] and has a high nutritive value with 65% carbohydrate^[9] and 18% protein^[9] content. For these reasons it is not prone to the risk of total harvest failure even in low and uncertain rainfall regions. "Due to its high protein value it is a very important crop for people in Africa^[8] Despite its nutritional value, it is still considered as one of the prioritized neglected and underutilized species in Benin.^[10]

Culinary use

The seeds are used for food and beverage because of their high protein content^[11] and for digestive system applications.^[11] The entire plant is known for soil improvement^[11] because of nitrogen fixation. In West Africa, the nuts are eaten as a snack, roasted and salted, processed into cake, or as a meal, boiled similar to other beans.

In South Eastern Nigeria, particularly in Enugu, the dried bambara beans are ground into a fine powder, then mixed with palm oil, water and pumpkin leaves and then poured into banana leaf wraps or 1 litre cellophane bags before being boiled into a kind of cakey pudding to make "okpa", a common breakfast food in Enugu, Nsukka and Ngwo Nigeria. In Niger State and upper Kwara state the Nupes and Yorubas have a delicacy called Sagidi, a meal sold in every Friday and Saturday market. Just like Groundnut Cake (Kulikuli cake), the Bambara nut is processed to Kangu cake starting from Kwara through northern Nigeria, Chad and Niger. During the rainy season in many parts of central Nigeria like Jos, the fresh bambara beans are cooked with their shells still on them. The beans are then eaten as a snack just like boiled groundnuts.

Soil requirements

Optimal soils for Bambara groundnut production are sandy soils to prevent waterlogging. Optimal soil depth is between 50 and 100 cm,^[11] with a light soil texture.^[11] soil fertility should be low^[11] and soil pH is best suited between 5 and 6.5^[11] and should not be lower than 4.3^[11] or higher than 7.^[11]

Climate requirements

The production is best suited between a latitude of 20° - 30°,^[11] i.e. the tropical wet and dry (Aw)^[11] and the subtropical dry summer (Cs)^[11] climate zones. Optimal temperature is between 19 °C^[11] and 30 °C.^[11] Temperatures below 16 °C^[11] and above 38 °C^[11] are not suited for the production of bambara groundnut. The bambara groundnut is very drought resistant.^[5] The minimal annual rainfall requirement is about 300 mm^[11] and optimal annual rainfall is between 750 mm^[11] and 1400 mm^[11] and should not exceed 3000 mm.^[11]

Cropping system

The cropping system is semi-permanent and the Bambara groundnut can be cultivated as single crop or as intercrop.^[11] Best suited intercrops are sorghum, millet, maize, peanut, yams and cassava.^[11]

Bambara groundnut is mainly cultivated as intercrop, however the planting density varies between 6 and 29 plants per square meter.^[12] For woodland savannas of Côte d'Ivoire the highest yield is attainable with a plant density of 25^[13] plants per square meter.

Fertilization

Since Vigna subterranea is usually intercropped, no fertilizer is applied. A yield of 1000 kg seed and 925 kg leaves remove 55.7 kg N,^[14] 26.2 kg K,^[14] 25.1 kg C,^[14] 7.8 kg P^[14] and 6.6 kg Mg.^[14] Since Bambara groundnut is a legume, phosphor is the most important nutrient. An application rate of 60 kg/ha^[15] of P2O5 is recommended for bambara groundnut in Yola, Adamawa State Nigeria.

Production

World production of Vigna subterranea increased from 29,800 tonnes in 2015.^[16] in 1972 to 79,155 tonnes^[16]

Production Year 2013 (Source FAOSTAT)[16]	Area Harvested (Ha)	Yield (kg/ha)	Production (tonnes)
Mali	120,000	9,498	113,981
Niger	68,000	4,412	30,000
Burkina Faso	55,000	8,909	49,000
Cameroon	43,392	8,444	36,639
Democratic Republic of the Congo	4,828	750	14,000
World	315,392	7,724	243,620

Pest and diseases

Pest and diseases are not considered to be a serious problem for Vigna subterranea.^[14]

Reported diseases:^[14]

• Leaf spot (Cerscospora canescens and Phyllosticta voandzeia)
• Powdery mildew (Erysiphe sp.)
• Wilt (Fusarium sp.)
• Leaf blotch (Phomopsis sp.)
• Stem rot (Scleorotium rolfsii)

Reported pests:^[14]

• Aphids (Aphis sp.)
• Bruchids (Callosobruchus sp.)
• Leaf hoppers (Hilda patruelis)
• Termites
• Root-knot nematodes (Meloidogyne javanica)
• Rodents
• Parasitic plants (Alectra vogelii and Striga gesnerioides)

Growth

The growth cycle is between (min-max) 90–170 days^[11] and under optimal conditions the cycle is about 120–150 days^[5] to pod maturity. Flowers appear 40–60 days^[5] after planting. 30 days^[5] after pollination the pod reaches maturity and during another 55 days^[5] the seeds fully develop. Every 30 days they are produced again.

Generative reproduction

Generative reproduction is for the Bambara groundnut autogamous^[5] (self-fertilization) and cleistogamous^[5] (self-pollinating).