PROPAGATION
Sweet potatoes are propagated from sprouts, vine cuttings and storage roots); sprouts are the most preferred.
Propagation by sprouting; Sprouts are shoots or young vines that grow from the sweet potato tuber (the storage root) when it is placed in a favorable environment, such as warm and moist conditions. A farmer can use these sprouts for planting by cutting them and transplanting them into the field. This method is commonly referred to as vegetative propagation from sprouts. They are grown from plant stock selected for its attributes, disease and pests tolerance and off-types. Approximately 75 kg of planting stock sweet potatoes are needed to produce enough sprouts to plant one hectare.
Propagation by vine cutting: Tip cuttings of about 30 to 40 cm long with approximately eight nodes are collected from the nursery bed, or the last established planting. Tip cuttings should be taken from crops that are old enough to provide material without excessive damage. Avoid “back cuts” as these will have variable maturity and result in significant yield reduction. The lower leaves should be cut away as tearing these off may damage the nodes that will produce the roots. This method of propagation is also recommendable.
Cuttings can be left under a moist cloth in the shade for a couple of days to promote nodal rooting before planting in the field.
At the recommended plant spacing, 330 cuttings are required for a 100 m row.
Propagation by storage roots; This refers to planting the whole or part of the sweetpotato tuber (storage root) directly into the soil to allow it to produce sprouts, which will later develop into vines and grow into mature plants. The storage root provides the nutrients needed for the sprouts to form. The storage root itself does not grow into a new plant but serves as a source of shoots. This method of propagation is not recommendable as it results in very low yields and is not suitable for commercial production.
Planting vine cutting tips:
Always plant the vine cuttings at about 45° into heaps as this promotes good even root development.
Make sure that half of the cutting or three to four nodes are buried at a spacing of 30 cm between plants.
Cuttings need to be watered at or immediately after planting. The vines require adequate water at this stage for development.
You can consider planting sweet potatoes in different sections of your land at different times. This allows for a continuous supply of sweet potatoes over the harvest period.
Mechanical planters are recommended for large scale farmers.
Sprout production
Sprouts are produced from the conditioned roots in cold frames, heated beds, or field beds of clean sand or fumigated sandy soil. Conditioned roots are covered by more soil sand, though not too much. Four to five weeks are needed to develop strong plants if the soil in the plant beds has been kept at 23 to 26°C. Six to eight weeks may be needed if roots have not been “pre-conditioned”. Adequate moisture is especially critical to germination of the sprouts and proper root formation on the sprouts.
Planting the sprouts
Sprouts should be taken from the plant beds when 6 to10 leaves and a strong root system have developed on each one. They are set out into the field as early as possible when the soil has warmed and the risk of frost or a cold weather period has passed. Plants should be spaced 30 to 38 cm apart in rows that are 1 m apart. This requires approximately 14, 520 plants per hectare. Management of water is very critical to avoid transplant shock.
SOIL PREPARATION
Bed formation
Sweet potatoes are grown on raised beds or ridges.
Ridges are recommended because of the following advantages:
1. Ridges allow adequate drainage.
2. Ridges provide easy harvesting with a mechanical digger.
3. They give high quantity and quality yields as they give room for easy development of roots.
4. They conserve moisture
5. They are easy to make.
6. Soil erosion exposing root tubers is very minimal.
If using a mechanical digger at harvest time it is important to match the width of the ridges with the width of the digger mouth. Spacing the mounds at 1,5 to 2,0 m apart (depending on the tractor width) with a roadway every six rows allows access for boom spray.
Spacing: Optimum plant density depends on cultivar, but is usually around 40 000 plants per hectare. Rows may vary from 1 to 1,25 m apart; in-row spacing is usually 25 to 30 cm.
Seeding rate: The number of cuttings required to plant 1ha varies between 30 000 and 60 000, depending the specific spacing used.
