Contrary to the name, sweet potatoes are not related to irish potatoes as the latter are members of the Solanaceae family, which also includes,tree tomatoes eggplant, tomatoes, capsicum, red pepper while sweet potatoes belong to the morning-glory family or Convolvulaceae. China is the world’s largest grower of sweet potatoes, providing about 80% of global supply. There are over 100 traditional and improved varieties of sweet potatoes and their flesh colors range from white, red and purple. However Orange Fleshed Sweet Potatoes whose popularity is increasing in in Kenya substantially higher than traditional varieties translating into higher income for the farmers. Likewise O F S P is rich in Beta-carotene a pre-cursor to vitamin A and it’s a great source if vitamin E, in addition to providing essential vitamins and minerals. Malnutrition due to deficiency of micro-nutrients in the diet, affects the health of over half the world's population. Vitamin A deficiency which is common leaves people susceptible to blindness and poor body immune system. Research has shown that Consumption of Orange Fleshed Sweet Potatoes effectively controls vitamin A deficiency. This is a practical long-term food-based approach particularly suitable in children who are most vulnerable to vitamin A deficiency. The roots are commonly eaten boiled or mashed. O F S P is developed by researchers through bio-fortification, a process of breeding staple food crops that are rich in bio-available nutrients. Sweet potatoes are relatively drought resistant and are therefore suitable for climate change adaptation in the current times Global warming.
This crop requires friable well drained soils, optimum, and temperatures of 12 ยบ- 25°C and annual rainfall of 600-1600 mm during the growing season. Relatively dry weather favors formation of storage roots and development sweet potatoes.
Land should be prepared with an aim of loosening the compacted soil below, for achievement of a good tilth .This facilitates making of planting hills or ridges, to avoid obstruction during root development.
Farm yard manure has been found to give a good response in sweet potatoes and it should be spread over the bed just before ridging or mounding is done. However in very poor soils a farmer can apply compound fertilizer like 17:17:17 at a 100 Kg per Ha in two splits, one at planting and the other after 2 weeks during first weeding.
Sowing should be done at the beginning of the rains for a rain fed crop. Disease free vines of about 30cm in length are planted on hills or ridges, at a spacing of 1metre from row to row and 30cm from one vine to the other. Bury 2/3 of the vine at a planting depth of 4-6cm.
The 1st weeding must be done within 2 weeks after planting. The second weeding should come up two weeks after the first during earthing up.
Pests:
Sweet potato weevil is the most significant pest in sweet potatoes production, and its attacks are characterized by thickening and cracking of the vines due to feeding by the adult weevil while larvae bores into the tuber leaving holes. This leads to a bitter taste.
Control: Integrated pest management is recommended, as the follows:-
· Crop rotation
· Use of clean planting material, deep planting and regular earthing up to fill soil cracks around plants
· Early planting and prompt harvesting
· Practice good field sanitation i.e. weeding, burn infested material
· Plant away from last year crop
· If seriously infested spray with a recommended pesticide.
· Organically incorporate a good amount of lantana camara before planting to repel the weevils
Sweet potato moth
Symptoms: Caterpillar bore into the main stem leading to the roots. Vines with severe tunneling show weak growth and poor foliage development and later yellows, wilts and dies. Infested plants show poor storage root formation.
Control: Handpick caterpillars or attacked vines and destroy them. If seriously infested spray with dimethoate
Diseases: Sweet potato virus is the most significant disease in this crop. It is characterized by dwarfing of plant, yellowing of vines and young leaves, excessive branching, dark brown to blackish corky spots in the roots.
Control
- Use resistant or tolerant varieties where available
- Use disease-free planting material
- Practice proper field sanitation
- Control the white flies and aphids which spread it.
- Crop rotation
Maturity period: Maturity period for sweet potatoes is 4-6 months.
The output ranges from four to eight tons per acre.