Yam Farming
After harvesting, yams have a resting period for about three to four months throughout the dry season before they make suitable seeds. Disease-free plants produce suitable cuttings for growing yams and need planting before they sprout, usually in August. Gardeners cut tubers crosswise into three pieces. The cuttings lie out for one week to callous over after being washed with Bordeaux mixture, a solution of copper sulfate and lime in water, to protect them from diseases such as tuber rot.
Yams favor loose clay soil with good drainage. Gardeners test soils and adjust pH levels to about 5.5. They plow the planting area and dig trench rows with 3 1/2 feet between them. Gardeners then add compost into the trenches and check the soil for proper drainage. Tuber crops do not grow well in overly wet soils and require loose soil to allow room for drainage and growth.
Harvesting
In terms of area harvested, 4.6 million hectares were planted worldwide in 2007, with about 4.3 million in Central and West Africa.
Consumption
Yam tubers consist of about 21% dietary fiber and are rich in carbohydrates, vitamin C and essential minerals. Worldwide annual consumption of yams is 18 million tons, with 15 million in West Africa. Annual consumption in West Africa is 61 kilograms per capita. Yams are boiled, roasted, baked or fried. In Africa they are also mashed into a sticky paste or dough after boiling the yam.
Cultivation practices
Y am is grown on free draining, sandy and fertile soil, after clearing the first fallow. Land is prepared in the form of mound or ridge or heap of 1 metre (3 ft 3 in) height.
The ya ms recommended for such soil conditions in Nigeria are white y am or white guinea ya m (Discorea rotundata) and water ya m or yellow y am (Discorea alata).
Planting is done by seed ya m or cut setts from ware tubers. One day before planting, the tubers have to be subjected to treatment with wood ash or a fungicide (thiabendazole) to prevent damage to the soils.
The setts are planted at an interval of 15–20 centimetres (5.9–7.9 in) with the cut face facing up. Mulching is essential during October–November with dry grass or plant debris weighed down with balls of mud.
Dosage of fertilizer application, as essential, is decided after chemical analysis of the soil samples. Manual weeding by hoeing is done three or four times depending on the rate of weed growth.
Two Stakes, each of 2 metres (6 ft 7 in) height are used for staking the plants to vine over it; one for two plants with the other used for bracing with the adjacent stakes. Sorghum stovers are also used for this purpose in the savannah land.
Pest and disease control is addressed by cultural control and chemical methods; the pests which affect the plant are nematodes such as root knot Meloidogyne spp. and ya m nematode (Scutellonema bradys), and insects such as y am shoot beetle, y am tuber beetle and crickets.
Weeding of the field is essential and maintaining a 2–3 metres (6 ft 7 in–9 ft 10 in) weed free border around the field is to be ensured. Disease resistant [cultivars] are normally recommended for use. Harvesting is done before the vines become dry and soil becomes dry and hard.
Generally, a yield of 10–15 tonnes per ha for white y am and 16–25 tonnes for water y am are obtained by following prescribed management practices. The harvested ya ms are stored by tying them with ropes.
They have a shelf life of about 5 months. Warehouses where they are stored should be made rodent proof with a metal base and wire netting. Rotten buds and sprouted buds should be removed.
Harvesting
In terms of area harvested, 4.6 million hectares were planted worldwide in 2007, with about 4.3 million in Central and West Africa.
In West and Central Africa tubers are planted between February and April, depending on whether in humid forest or on the savanna, and are harvested 180 to 270 days later.
Care is needed during harvesting to minimize damage to tubers that lead to rot and a decrease in market value. Harvested tubers normally stay dormant (do not develop sprouts) for 30 to 120 days depending on environmental conditions, the date of harvest, and the species. This means that only one crop cycle is possible per year, possibly restricting supply.
Consumption
Yam tubers consist of about 21% dietary fiber and are rich in carbohydrates, vitamin C and essential minerals. Worldwide annual consumption of yams is 18 million tons, with 15 million in West Africa. Annual consumption in West Africa is 61 kilograms per capita. Yams are boiled, roasted, baked or fried. In Africa they are also mashed into a sticky paste or dough after boiling the yam.
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