More than 35,000 farmers in Nyanza and Western Kenya are harvesting double yields per acre after adopting the high-producing orange-fleshed sweet potato varieties from a research organization, International Potato Center (CIP).
Demand for the Orange-Fleshed Sweetpotato (OFSP) is turning the food into a cash crop for the farmers in at least five counties as big retailers like Tuskys supermarket salivate for the produce for bread and cake baking.
CIP, which is targeting 35,000 farmers by 2018, is supplying planting materials to growers in Homa Bay, Siaya, Kisumu, Migori, and Nyamira counties in its Scaling Up Sweetpotato Through Agriculture and Nutrition (SUSTAIN) programme.
In places like Kisii-a neighbor of Nyamira County, Food and Agriculture Organisation says one-acre yields four tonnes or 10 tonnes per hectare of ordinary sweet potato.
CIP agronomist Sammy Agili says the five OFSP- Kabonde, Vita, SPK 004, and Ejumla- give an output of up to 7.2 tonnes per acre or 18 tonnes per hectare.
One requires 16,000 vine cuttings per acre.
“One bag contains 1,000 vines between 2cm and 3cm. CIP identified some farmers who are raising the planting materials in Western and Nyanza. The nurseries are regularly inspected by the Kenya Plant Health Inspectorate Service for quality,” he says.
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With fine soil tilt, the vines are planted on ridges at the onset of rains. Water in the first two months is critical for root and new leaf development.
“Well-drained fertile soils will give high yields. Rain of 500mm per year is sufficient for good growth, with water being critical at planting and bulging bulking times,” he says.
OFSP varieties mature between three and six months.
The varieties are increasingly becoming popular in Kenya and many other African countries such as Malawi, Mozambique, and Ethiopia, among others because of their high nutritional value.
Agili says the intense orange colour in the flesh means high vitamin content. OFSP are rich in vitamin A, with up to 14mg per 100g.
There are three main challenges facing the production of sweet potato. They include weevil attack, Sweetpotato Virus Disease Virus Disease SPVD, and alternaria fungal infection.
SPVD is highly destructive and can wipe out the entire farm.
The agronomist says the key element in controlling the challenges is knowing the source of the planting material and removing or roughing out affected vines.
For the weevils, which attack the storage roots as they mature, sealing soil cracks will help. The weevils enter the soil through the cracks to attack the storage roots.
Harvesting must be done when the leaves have started turning yellow, which is an indication of maturity.
Early harvesting will lead to premature produce that will shrink and be of poor quality. Late harvesting encourages the development of fibrous roots and attack from weevils, he says.
The use of oxen to plough out the roots from the ridges is preferred during harvesting. Hoes and other sharp implements inflict cuttings and bruises on the skin, which will be entry points for destructive micro-organisms.
OFSP can be cured to increase their shelf-life for up to seven months.
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Dr Agili is the project agronomist for SUSTAIN, which is one of CIP’s Orange-Fleshed Sweet Potato projects in Western and Nyanza regions in Kenya.