Farming Sweet Potatoes The Right Way

An acre of land under sweet potatoes has a yielding potential of eight to 14 tonnes in four to six months.

Once shunned as a food crop for the poor, the sweet potato with its myriad of health benefits and its ability to be grown with little or no pesticide application has gained a pride of place at the breakfast tables of many households.

Sweet potato production costs stand at less than half their selling price. However, to get such a bumper harvest and return, farmers have to practice the right crop establishment practices.

Planting material

This begins with the selection of certified high yielding, disease and pest resistant propagation materials. Sweet potato planting material is not available in agrovets this makes sourcing for the right seeds/ vines difficult for most farmers.

Vegetative material can be got from farmers accredited with localised propagation of sweet potato planting material. Vine cuttings are preferred to roots as they are free from soil-borne diseases. They are also higher-yielding and offer bigger and better-formed tubers. Vines used for planting should be no more than three generations removed from the original certified seedlings to get the best results.

An average of 10 to 20 tonnes/ha can be got from improved sweet potato varieties.

Factors 
Target Market- The orange-fleshed sweet potato has little fibre content making it favoured for chips, crisps and purees. Processors prefer even shaped potatoes while regular consumers go for bigger sized ones.

Red skinned and yellow-fleshed sweet potato variety is the most grown in the country because of its equally high consumer demand.

Nutritional variance- Orange fleshed sweet potatoes are rich in beta carotene, a precursor for vitamin A. This is similar to nutrients you can get from carrots that helps build eyesight

Purple fleshed sweet potatoes contain anthocyanin, an antioxidant helpful in preventing cancers.

Growing conditions

Different sweet potato varieties are suited to regions with varied rainfall patterns but on average they thrive in areas with 600-1600 mm per year of rain, some do well in more dry conditions. Irrigation should be done on a frequent basis to keep moisture levels consistent.

Ideal growing altitudes are 2100m above sea level with warm temperatures not below 10C and averaging 24C. Soil PH should be 5.6-6.6 Ph.

Sweet potatoes require well-drained soils with plenty of sunshine. Most soils do not need fertilizers while requiring little manure for their growth. Manuring is recommended to get healthier vines and tubers.
In soils that are very poor, a basal compound 17:17:17 fertilizer can be applied at a rate of 100 kilograms per hectare.

Planting

Being fairly hardy crops, sweet potatoes can be planted at any time in regions with no critical dry season. Planting should be done during the onset of short rains, and at the tail end of long rains.

An acre will need 16,000 seedlings.

All soils other than clay-soils which have a high bulk density and poor aeration which retard tuber formation are suitable for the growing of sweet potatoes. Planting vines can be stored for a day or two in humid conditions to promote rooting at the nodes which enables for easy establishment once moved to the field. The roots however should be managed carefully whilst planting to avoid potential damage.

The cultivar should be healthy as well as being free from pests and diseases. The tip of the sweet potato vine is better than the middle portion for propagation as it is less of a pest and disease carrier.

Using vines also leaves the entire tuber for consumption or selling compared to the use of roots for propagation requiring some roots be left for the next season’s planting. Planting vines should ideally be 25-30cm long this avoids wastage while shorter vines take longer to establish and are poor yielders.

Irrigation 

More important, the vine should have at least five to eight nodes. At a depth of four to six centimetres a minimum of two to three nodes or one third to two thirds. Up to eight nodes can be buried in the soil.

Watering should be done regularly at the first 1½ months when the cultivar is young and weak; once vines germinate it’s easy for them to store food. Irrigation can be done twice a week thereafter; you ought to wet the root zone without causing run-off; overwatering causes leeching (loss of nutrients). Sandy soils require more watering than clay-based soils or soils with high organic matter. Excessive watering causes exponential growth of vegetative material but reduced tuber sizes. Sweet potatoes act as a cover crop suppressing the growth of weeds as well as enabling the soil to retain moisture and prevent erosion.

A farmer need only practice weeding on the first two months before the crawling vines smother the weeds. Within two weeks of planting the first weeding is done after the second weeding two weeks after that when earthing up.

Once mature, sweet potatoes are harvestable for up to 12-18 months at four-week harvesting intervals. A prolonged stay in the field means roots have to mobilise assimilates for vines to continue growing, affecting the quality of tubers harvested. Diseases and pests such as moles and weevils also build-up if your crop is not rotated.

Ridging

Early thorough tillage is necessary to create a deep loose bed. Sweet potatoes should ideally be grown on ridges, with 30cm spacing between each vine, and one metre of spacing between furrow and ridge to allow for easy root multiplication and development as well as offer space for field management. Ridges offer enough space and loose soil for the rooting system to develop enabling tubers to extend and become bigger.

Harvest 

Once mature, sweet potatoes are harvestable for up to 12-18 months at four-week harvesting intervals. A prolonged stay in the field means roots have to mobilise assimilates for vines to continue growing, affecting the quality of tubers harvested.