Some of the basic factors to be considered when selecting a a site for sweatpotato farming includes:
- Altitude: Sweetpotato grows well from sea level upto 1,700m above sea level (m.a.s.l.). Some varieties even grow up to 2,500m.a.s.l. but have poorer taste and lower dry matter.
- Soils: Sweetpotato can be grown on many types of soil but does best on deep, moderately fertile, sandy loam soils, which produce high quality storage roots with an attractive shape and appearance. Adequate drainage and soil aeration are important, which is one of the reasons the crop is usually grown on mounds, ridges or beds. Sweetpotato does best on slightly acid soils, with optimal pH 5.6-6.6, but can tolerate soils with higher and lower pH.
Sweetpotato, like other crops, obviously benefits from good soil fertility. As a root crop, sweetpotato has a high requirement for potassium. However, a high soil nitrogen content may lead to excess foliage growth and limited root production, particularly in humid environments. Farmers rarely add fertiliser to their sweetpotato crop, but the crop benefits from residual fertility when it follows or is intercropped with a fertilised crop such as maize. During land preparation, the mounds, beds or ridges may be constructed by heaping soil up and over the residues of previous crops or vegetation from fallow periods, to provide fertility for the sweetpotato crop and to loosen any compressed soil that might hinder root formation. Farmyard manure, compost, or green manures can be very beneficial, if available, but may be more likely to be applied in a kitchen/ backyard garden setting than in a large production field. Ash is rich in potassium, and can be incorporated into soils to help boost sweetpotato root formation.
- Crop rotation and plot separation: As with any crop, it is advisable to rotate sweetpotato with other crops, or to have a fallow period between crops, in order to reduce the build up of diseases, such as viruses, and pests such as weevils and nematodes (though there are not many problems with the
latter in SSA). Sweetpotato does well following cereals or legumes, but it is not recommended for it to follow other root and tuber crops, particularly cassava, due to their similar nutrient requirements.
Sweetpotato has been reported to be a good first and last crop in the rotation following fallow. As the first crop, it leaves the soil easy to prepare for the next crop, although very fertile soils may produce lots of vines but few or no storage roots. It is also advisable, though not always possible, to try to separate new sweetpotato fields from recently harvested or existing fields, particularly in environments where weevils and viruses are a problem. A barrier crop between old and new plantings, or a gap of >120m can help prevent weevils from finding the new sweetpotato crop. If there is no choice but to re-use an old sweetpotato field then complete incorporation or removal of the old storage roots and vines (which can be burnt or fed to livestock) may help reduce the spread of pests and diseases to the new crop. If possible sweetpotato should only be grown once every three years on the same soil, in order to limit pest and disease carry over problems. This is particularly important where a new variety is being introduced into an area.
- Access to land: In most parts of SSA, men are considered the owners of land and make all decisions regarding land allocation even when the crop such as sweetpotato is largely grown and controlled by women. It is critical for development workers to be sensitive to male control over land and ensure that men are consulted about project activities even where they are not directly involved.