Sweet potato is a perennial crop which is cultivated in tropical and subtropical lowland agro- ecologies, although it is well adapted to other climatic zones and can be grown over widely different environments. Sweet potato gives high yields under the right growing conditions.
Sweet potato has the potential to yield more under unfavourable conditions than many other crops, which is why it is so important for household food security in many places of the world.
This article will give in detail on all you should do to grow your Sweet potatoes.
Climatic Requirements
Temperature
Sweet potatoes adapt well to tropical warm climates and grow best during summer. Sweet potatoes are cold sensitive and should not be planted until all danger of frost is past.
The optimum temperature for the best growth and optimal yields is between 21 and 29 °C, although Sweet potatoes can tolerate temperatures as low as 18 °C and as high as 35 °C.
Storage Sweet potato roots are sensitive to changes in soil temperature, depending on the stage of root development. Sweet potato should be grown in full sunlight for maximum yields
Altitude
Most Sweet potato varieties grow well from sea level up to 1,700 m above sea level (m.a.s.l.). Some Sweet potato varieties even grow up to 2,500 m.a.s.l. but have poorer taste and lower dry matter.
Soil Requirements
Site selection and soil
Sweet potatoes grow well on a well-drained sandy loam. Heavy clay soils should be avoided as they can retard Sweet potato root development, resulting in growth cracks and poor root shape.
Lighter soils are more easily washed from the roots at harvest time. The optimal soil pH for growing your Sweet potato ranges from 5.6 to 6.5.
Site preparation
The selected site to grow your Sweet potatoes should be cleared to remove all vegetation and this should be achieved through ploughing.
You should apply lime to your soil to match optimal soil pH requirements and this should be done after soil test.
Rotavate your Sweet potato field and make ridges (banks) 30 - 60 cm (1 - 2 ft) high and 60-90 cm (2 - 3 ft) apart.
You should also apply a pre-emergent weedicide to soil according to the manufacturer’s recommendation before planting the crop.
Cultivation Practices
Propagation
Sweet potatoes are propagated from slips (stem cuttings) which can be obtained from the previous Sweet potatoes crop.
Small Sweet potato tubers can be used to produce nursery plants from which Sweet potato slips are cut.
Select slips from plants 2-3 months old. Use the Sweet potato plant tips since they are healthy, vigorously growing and free from pest and disease.
Cutting collection
Sweet potato tip cuttings of about 30 to 40 cm long with approximately eight nodes should be collected from your nursery bed, or the last established planting.
Tip cuttings should be taken from Sweet potatoes that are old enough to provide material without excessive damage.
At the recommended plant spacing, 330 Sweet potato cuttings are required for a 100 m row. Select the best Sweet potato plants with a high yield and no string (rat-tail) roots.
Planting cuttings
Sweet potato cuttings should be planted at about a 450 angle into heaps as this promotes good, even root development for optimal yields. Half of the cutting or three to four nodes should be buried at a spacing of 30 cm between plants.
Mechanical Sweet potato planters are available and used on large-scale plantings but manual Sweet potato planting is widely practised. Planting time is mainly determined by the climate of your location.
Sweet potato plants are damaged by light frost and the plants require high temperatures for a period of 4 to 5 months to yield well.
Cold spells during winter can be a risk to your Sweet potatoes, depending on the climate of the specific area.
Spacing
Optimum plant density depends on cultivar, but is usually around 40 000 Sweet potato plants per hectare is recommended. Rows may vary from 1 to 1,25 m apart; in-row spacing is usually 25 to 30 cm.
Seeding rate
The number of Sweet potato cuttings required to plant 1 ha varies between 30 000 and 60 000, depending on the specific spacing used on your field.
Fertilisation
The recommended fertiliser rate for sweet potato production is based on crop removal figures. The estimated crop removal in kg per ha is given below:
- 100 kg Nitrogen (N)
- 90 kg Phosphorus (P)
- 200 kg Potassium (K)
- 200 kg Calcium (Ca)
Crop Rotation and Plot Separation
You should rotate your Sweet potato with other crops, or 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.
Sweet potato perform 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.
Irrigation
Sweet potato responds well to increasing moisture in your field, but is considered a drought-tolerant crop because it is deep rooted and capable of developing storage roots under very dry conditions.
Water your field 18 to 20 mm per week early in the season, 40 to 45 mm per week during the middle part of the season when Sweet potato storage roots are enlarging rapidly and a reduction to about 20 mm late in the season.
Excessive moisture early in the season delays Sweet potato storage root development and enlargement; late in the season, it induces cracking and/or rotting of roots.
Weed Control
Weeds may be a problem early in crop growth of your Sweet potato plants before vigorous vine growth covers the beds as plants become established.
A number of control strategies may be used such as application of herbicides.
Pest Control
A fallow period should followed in your Sweet potato field to prevent build-up of soil-borne pests and diseases.
Planting a green manure crop after harvest helps to suppress any regrowth and weeds as well as improving soil structure in your field, and is essential for the long-term health of the soil for growing your Sweet potatoes.
Harvesting
Sweet potatoes are harvested by hand with a help of a hoe.
You dig and remove mature Sweet potato tubers. Root maturity can vary between varieties.
Harvesting sweet potato requires suitable equipment for commercial production.