The following are the crop details for sweet potato.
Scientific Name: Ipomoea batatas
Species: I. batatas
Local Names: Viazi vitamu (Swahili); Makwasi (Kikamba, Kenya); Mapwoni (Luhya, Kenya)
Sweet potato, a herbaceous perennial vine belonging to the Convolvulaceae family, is cherished for its versatile, edible storage roots or tubers. Native to Central America, this plant has now established itself across the globe. These robust vines, known for their heart-shaped lobed leaves and charming white or lavender flowers, can stretch up to 4m (13 ft) in a single growing season. Tubers come in a fascinating array of shapes and colors, from red, yellow, brown, and white to even purple.
Cultivated mainly in small-scale subsistence farming in East Africa, sweet potatoes are gradually gaining recognition among other indigenous foods. Its tubers are usually white, red, or purple, and increasingly, yellow-fleshed types are garnering popularity due to their high sugar, vitamin A, and lower dry matter content. Consumed either boiled or roasted, often accompanying milk, porridge, soups, or meat, they contribute significantly to diet diversity. Moreover, their young leaves, high in protein and essential vitamins like B1, B2, and folic acid, serve as a nutritious green vegetable. The vines also double as a fodder crop, providing a nutritious feed, especially during the dry season. This remarkable plant, thus, goes beyond being a mere staple, offering considerable nutritional and agronomic advantages.
Sweet potato tubers are consumed raw as a vegetable or processed into flour or starch. The leaves can be eaten raw or cooked.
Sweet potato varieties offer diverse benefits, ranging from yield and performance to culinary value and pest tolerance, with each possessing unique characteristics that reduce the risk of agricultural failure. The different varieties cater to various regional needs and are primarily grown in East Africa for subsistence farming, contributing not only to food diversity but also as a vital fodder crop during dry seasons.
Red-skinned varieties with cream flesh are popular across most regions of Kenya for their high yield. Additionally, the wide range of cultivars extends from the standard white, red, and purple types to the increasingly popular yellow-fleshed ones. The latter are particularly celebrated for their high sugar and vitamin A content, and lower dry matter composition, making them a powerful tool in fighting vitamin A deficiency in children.
Beyond their tubers, sweet potato plants provide young leafy shoots high in protein, approximately 20% of dry weight, and rich in b-carotene, thiamine (vitamin B1), riboflavin (B2), folic acid, and ascorbic acid. These nutrient-rich leaves are often consumed as vegetables, thereby enhancing the plant's versatility and nutritional contribution. With each variety catering to different needs, sweet potatoes continue to gain popularity and form a critical part of the food and agricultural landscape
Sweet potato thrives in sunny conditions but can manage with 30-50% less sunlight. For optimal growth, it prefers an annual rainfall of 600-1600 mm, evenly distributed throughout the growing season. However, dry periods can encourage the growth of storage roots. Despite its drought tolerance, extended dry spells, particularly during planting or root development, can significantly reduce yields.
Soil management, especially maintaining organic matter, is crucial for water retention in rain-fed crops. Organic matter and plant mulches help soil retain moisture, reduce surface evaporation, and prevent soil crusting. They also enhance rainwater absorption. Weeds, competing for water, should be regularly removed and can be used as additional mulch.
Where irrigation is feasible, the aim should be to maintain consistent soil moisture. Watering should sufficiently wet the root zone without causing deep drainage or runoff. Overwatering can lead to nutrient leaching and contamination of water sources. Light-textured soils require more frequent, lesser amounts of irrigation to avoid runoff losses.
Post cultivation, the land is usually fashioned into ridges, or mounds for those working manually. However, in well-drained soils, flat fields are also possible. Ridges on sloping land should align with contours to reduce erosion and increase rainwater absorption. They should be higher in wet areas for better soil drainage.
Sweet potatoes can be planted at any time if there is no critical dry season. Planting early in the rainy season is best in regions with a critical dry season. If the rainy season is long and wet, it is usually planted near the end.
Sweet potato planting material is obtained from either vine cuttings, which is the most common source, or storage roots.
Plant cuttings should be planted at approximately 15 x 20 cm spacing if planting material is to be kept in a multiplication plot before planting the next crop. After 45 days, new growth may be ready for cutting.
After forming ridges or mounds, sweet potato cuttings are planted by burying the lower portion in the top of the ridge or mound. A hole can be dug with a stick or by hand, and soil should be gently pressed around the inserted cutting. The stem is typically positioned at an angle.
According to some workers, cuttings oriented across the ridge yield more than those oriented along the ridge. Ridge spacing in ridge planting systems is typically 90-120 cm, while row spacing is 20-30 cm (3-5 plants per meter). Higher plant density generally results in a lower yield per plant but a higher yield per hectare. With short growing seasons, close spacing is used, and wider spacing may be preferred where the market prefers larger storage roots.
The size and spacing of mounds are determined by soil conditions. They can be planted 75-200 cm apart and with several cuttings per mound. Although some farmers plant two cuttings at each mound, there is little evidence that this is beneficial. Single cuttings are said to produce a higher proportion of large storage roots.
Weed infestation is a problem in the first two months of growth and requires adequate control to ensure high yield. Following that, the vines' vigorous growth effectively covers the ground and smothers weeds. Manual weeding is commonly used in the tropics. Sweet potato responds well to fertilization, especially if the land has been cropped continuously. However, fertilizer is rarely used in the tropics.
To improve soil fertility, manure or good compost should be added. This is a common practice among smallholders and traditional farmers. Around the world, sweet potato is used in a wide range of cropping systems. Rotating sweet potato with other crops such as rice, legumes, and maize is beneficial for disease, pest, and weed control.
The harvesting season for sweet potato storage roots is not well defined; it varies depending on the cultivar, cultural practices, and climate. In tropical countries where sweet potatoes are grown for domestic consumption, 'progressive harvesting' (piece-meal harvesting) is common practice. To avoid weevil damage, it is generally recommended to harvest within 4 months. Manual harvesting with implements such as a stick, spade, or hoe is common in the tropics.