Sweet potato
Description
Crop Details
The following are the crop details for sweet potato.
Scientific Name: Ipomoea batatas
Kingdom: Plantae
Order: Solanales
Family: Convolvulaceae
Species: I. batatas
Local Names: Viazi vitamu (Swahili); Makwasi (Kikamba, Kenya); Mapwoni (Luhya, Kenya)
General information.
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.
Uses
Sweet potato tubers are consumed raw as a vegetable or processed into flour or starch. The leaves can be eaten raw or cooked.
Varieties
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
Climate conditions, soil, and water management
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.
Propagation and planting
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.
Planting
Use of stem cuttings:
Farmers obtain mature crop cuttings before or shortly after harvesting storage roots. The cuttings are either used to establish a maintenance field or planted directly into the next sweet potato crop.
The following factors influence yield when using stem cuttings: Choosing 'clean' planting material is critical. This includes removing any insects, soil, or signs of virus or fungal disease from the cuttings.
In general, the apical (tip) portion of the vine is superior to the middle or basal portions. This portion has been shown to establish faster than other portions and is less likely to be infested with sweet potato weevils and fungal pathogens.
For cultivars with long vines, the second or third cut is sufficient. If vine growth has been so rapid that the stem has not matured in the apical portion, the second cutting may be superior to the tip portion.
The number of nodes is more important than the length of the cut. The average size is 20-40 cm, with 5-8 nodes. Field conditions may influence the relationship between cutting length and crop development.
Farmers should experiment to see what length works best for their specific situation. Usually, one-third to two-thirds of the cutting is buried.
A minimum of 2-3 nodes, but up to approximately 8 nodes, are placed beneath the soil. The time between cutting and planting may affect yield depending on the storage conditions for the cuttings.
Storing cuttings in humid conditions for one to two days may encourage node rooting. Longer storage may be detrimental to the establishment due to the depletion of the cuttings' energy reserves.
To reduce losses, remove the leaves from the lower portion of the cutting and store bundles of cuttings in a cool, shady, wind-free location wrapped in a wet cloth or sack. If roots form during storage, they must be carefully planted to avoid root damage.
Use of storage roots: Storage roots are used while there are inadequate stem cuttings available or when pest and disease infestation is so severe that only a few healthy vines remain.
Since the sprouts can be harvested mechanically from the seedbed, they can also be used in highly mechanized production. Healthy storage roots should be selected from high-yielding plants.
The roots are densely planted in a seedbed far from different candy potato crops. To help retain moisture, the roots are covered with about 3 cm of soil, and the bed is covered with straw. When the sprouts have grown effectively, they are cut near their base and planted in the field.
To increase the number of cuttings, remove the sprout tips when they are about 20 cm long to promote branching.
Rapid seed multiplication: Rapid multiplication can be used when a large number of cuttings are required. Although sweet potato growers have not fully acknowledged the value of this practice, it may be the simplest way to produce a large number of planting materials.
The following steps are involved in this method: 30 cm cuttings are taken from established plants or sprouted storage roots. These are then cut into single-node cuttings with the attached leaf. The vine's tip is discarded.
A seedbed is produced by mixing loose, humus-rich soil with ash. Plant the single-node cuttings densely, with the stem section buried and the leaf upright. The seedbed is watered on a regular basis and kept moist, especially during the first week of the establishment. When the seedlings have developed enough roots, they should be transplanted into the field after about 2 weeks.
To avoid damaging the roots, they should be carefully removed from the seedbed. To avoid excessive evaporation and wilting, transplanting should be done in the late afternoon. Degeneration of planting material When the sweet potato is vegetatively propagated for several generations, yield decline is common.
This is usually due to a virus buildup, many of which have no obvious symptoms. This frequently gives the impression that a new variety (carrying few viruses) yields significantly higher than traditional varieties, when in fact it may not be any better after a year or two of virus accumulation. Heat treatment and meristem culture (from research institutions) can be used to remove viruses.
Depending on the severity of the original virus infestation, this process typically results in a yield increase of 20 to 200% for both vines and roots. The higher yield may be maintained in the field for several years before the virus load has built up.
References
Planting method
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.
Husbandry
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.
Harvesting
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.
