THIS week NAREI in Focus begins a series on growing sweet potatoes in Guyana. The sweet potato (Ipomoea batatas [L.] Lam) seemed to have originated in Tropical America, but, the exact location is not known. This crop is now grown throughout the tropics for its edible tubers, which are an important food source in many countries. Guyana is one of the tropical countries in which sweet potato is cultivated. The regions of highest production in Guyana are Regions Three, Four, and Nine. Other regions that grow the crop are Regions Two, Five and Six.

Sweet potato is primarily used as food. Generally, it is consumed directly- the main type of preparation being boiling, baking or frying. In processed form, the tubers can be prepared in many ways for human consumption (canned, frozen, dehydrated or made into flour or starch). For industrial uses, the tuber is a source of starch, glucose, syrup, vinegar and alcohol. The tuber and plant tops are also a source of animal feed. The tuber is fed directly or in processed form and the leaves are fed to livestock as fresh fodder or in the form of silage.

VARIETIES There are several sweet potato cultivars in production in Guyana. Some of these are Black Rock, Strongman and Viola.

ENVIRONMENTAL REQUIREMENTS Sweet potato is adapted to rainfall ranging from 800 – 1000 millimetres per year but it requires good drainage. This crop cannot stand waterlogging and it will not persist in long periods of drought without irrigation. This crop can be grown from sea level to elevations of 2000m. It can also be grown on a wide range of soils. In Guyana, sweet potato is mainly grown on soils rich in organic matter, on loamy soils and sandy soils.

CULTIVATION
Land Preparation should be deep enough to accommodate the sweet potato tubers. Since this crop cannot withstand waterlogged conditions, there must be adequate drainage. The soil should be ploughed and harrowed and adequate drains made. For lighter soils, flat planting can be done but heavier soils should be ridged to facilitate drainage.

PLANTING
Planting material for sweet potato is the slip (stem) of mature plants. The apical portion of the stem should be used. These apical stem cuttings should be about 25 cm long. In order to control pests during the initial stages of growth, planting material should be treated by soaking in an insecticidal solution for approximately ten minutes. The insecticides recommended are Admire at a rate of 1ml /
L of water or Vydate at a rate of 2ml/l of water. Ridges should be 0.75 m apart and cuttings should be planted 0.3m apart.

MAINTENANCE OF CULTIVATION General Maintenance Drains must be properly maintained during rainy periods since sweet potato cannot withstand waterlogging. Fertiliser Application As a general rule, before applying fertilisers, the soil should be analysed to determine the types and amounts to be used.

If a soil analysis is not done the following fertiliser elements may be applied:
Fertiliser Rate of Application
Urea 168 kg/ha
TSP 150 kg/ha
MOP 140 kg/ha
Apply the TSP and MOP to the ridges one or two days before planting. Apply all the Urea six weeks after planting, when the vines are turned to prevent the formation of small tubes at the nodes (joints) of the stems. Weed Control Weed control is important during the early stage of this crop before the vines begin to spread. For a good crop, the weeds need to be controlled during the first six to eight week after planting. Turning of Vines It is customary to turn back the vines from time to time to prevent rooting at the nodes of the plant. This is to ensure a more even crop and fewer smaller tubers.