|Better Farming Series 16 - Roots and Tubers (FAO - INADES, 1977, 58 p.)|
|How to grow sweet potatoes|
As a rule, sweet potatoes are grown on ridges or mounds after deep tilling.
This way is better than growing them on the flat.
The mounds and ridges protect them from too much moisture. The ridges are made about 75 centimetres apart.
But it is still better to plant sweet potatoes on round mounds 30 to 40 centimetres high and 1 metre apart. The mounds should be made as narrow as possible.
This forces the plant to bend its roots downward quickly. In bending, the roots build up food reserves and develop tubers.
The farmer must know his varieties well. He must know how long they take to form tubers, and see to it that the harvest will be in the dry season.
It is better to plant several times, at intervals, so that the whole plantation does not become ready for harvest at the same time. By doing this, you can lift the sweet potatoes as and when you need them.
Sweet potatoes are propagated from cuttings or from tubers.
- Propagation from cuttings
Propagation from cuttings is possible only when the sweet potatoes remain in the field all through the year. The cuttings should be 20 to 40 centimetres long, with three to five growth buds. It is best to take them from the tips of young stems. Take the cuttings only when you are ready to plant them, and keep them in the shade until they are inserted in the soil. Propagation from cuttings is the most economic way of increasing your plants.
Plant cuttings at a slant, leaving 3 or 4 centimetres above ground, and press the soil down firmly. If you plant them on mounds, you can put four or five cuttings in a circle on each mound. This will give you a planting density of between 15 000 and 30 000 plants to the hectare.
- Propagation from tubers
If you do not have any plants of sweet potatoes with enough leafy growth to provide cuttings, you can propagate from tubers.
In this case, the tubers must be made to sprout in a cool nursery bed. If the tubers are large, cut them into several pieces. After about a month, remove from the tubers the young shoots that are 15 to 20 centimetres long and plant them.
This method of propagation from tubers is usually done only on a part, say one third, of the area on which sweet potatoes are to be grown. Later, cuttings from the plants thus obtained can be used to enlarge the plantation.
CONTROL OF WEEDS
One or two cultivations in the early stages of growth are enough. In 4 to 6 weeks after planting, the plant's own leafy growth will closely cover the soil.
When cultivating, remake the mounds at the same time.
CONTROL OF DISEASES AND PESTS
Sweet potatoes attacked by diseases and insects yield only a small harvest of poor quality.
You must wait 3 to 5 years before growing sweet potatoes again on the same field.
- Rot and fungi
Diseases that kill the growing plants are caused chiefly by various fungi. Some fungi make the leaves turn yellow and wither. Other fungi make the stems or tubers rot. Signs of the disease are yellow leaves and black marks inside the stems and tubers.
Other fungi cause the young plant to rot. It stops growing. The roots and the tubers already formed turn black. It is not long before the whole plant withers and dies.
To control most forms of rot, you must choose resistant varieties. Do not use for propagation cuttings or tubers taken from plantations attacked by rot.
Do not grow sweet potatoes on the same soil 2 years in succession.
- Insect pests
Sweet potatoes may be attacked by certain insects, especially by weevils.
The adult insects eat the leaves, stems and tubers. The female insects lay their eggs in the stems or roots; the larvae tunnel into the tubers. Serious damage is caused by weevils.
To control the weevils, use insecticides. Before planting tubers and cuttings, dip them in a solution of Dieldrin.
In places where harvested sweet potatoes are stored, they can be fumigated with phostoxin in tablets.
Depending on the varieties of sweet potato and on the way they are grown, yields vary from 4 to 7 tons per hectare on average. On a modern and well- cared- for plantation, yields may be much higher, and may even be more than 20 tons per hectare.
The length of time for which sweet potatoes can be kept differs with the varieties and the harvesting season. If they are harvested in dry weather, the tubers may be stored for 2 or 3 months.
But part of the harvest may be destroyed by rot during storage. Damaged tubers are most quickly attacked. Damp conditions encourage rot.
To prevent rot, dry the tubers in the sun for a time after harvesting.
For good keeping, the tubers of sweet potatoes should be harvested when they are quite ripe, when the stems and leaves have turned yellow. Take care not to damage the tubers. Remove all diseased and damaged tubers. Dry the tubers in the sun. Store them under cover in a dark, dry, cool, well- aired place. Put them on dry ground or on boards supported on posts, and do not heap them up too much.