Everything you need to learn about sweet potato cultivation, harvest and growth.
Introduction to Sweet Potato:
Sweet potato is believed to be a native of tropical America. It is now widely grown throughout the tropics and some parts of the temperate zone. Large-scale cultivation of the crop is common in Mexico, Central America, South America, and Mediterranean region of Europe, Africa, India, China, Japan and the Pacific Islands.
Sweet potato is a very important crop of India, perhaps the most important root crop and its tubers are considered to be a poor man’s food. The area under it is roughly about 2, 30,000 hectares and the total production is about 16,00,000 tonnes. The average yield is 7000 kg per hectare. Of the different states, Bihar, Orissa, Tamil Nadu, UP, West Bengal, Maharashtra and Punjab are regarded important in respect of sweet potato cultivation.
Sweet potato (Ipomoea batatas (L.) Poir.) belongs to the family, Convolvulaceae. The plant is a twining and trailing perennial herb, which may vary from 0.6 to 6 m in length. It bears adventitious roots that end in swollen tubers (tuberous roots), which may be white or red skinned. Leaves petioled, simple and alternate and they vary in form, shape, size and lobation.
Flowers, if present, have different shades of red, violet or bluish colour. Sepals 5 are ovate or linear. Petals 5, connate; corolla campanulate or may be funnel shaped. Stamens 5 are Carpels connate; ovary 1-3 or 4 – celled. Style is undivided; stigma capitate. Fruit a 4 – to 6 – valved capsule with 1 to 4 small black flattened seeds.
Climate and Soil Required for Sweet Potato:
The plant thrives in moderately warm climate and requires at least four months of warm weather for proper growth. It cannot stand frost, which damages the foliage badly. If high yields of tubers are required, the temperature should not be below 26.6°C.
Sweet potato does best on sandy loam soils. Light soil is very suitable for proper root growth. A moderate proportion of sand in the top soil with fairly retentive subsoil is considered ideal. For the kharif crop, drainage is essential and hence uplands are preferable. Sweet potato requires soil with slightly acidic reaction (pH 5.2 to 6.7).
Cultivation of Sweet Potato:
The plant is propagated vegetatively by vine-cuttings or from sprouts produced on its tuber-like roots. The selected roots are planted in well prepared nursery beds, on ridges, at a distance of 60 cm from one another; the distance between two adjacent tubers being 25 cm. and planting is usually done in the second fortnight of February.
The sprouts are cut and planted again in a second nursery. Finally, the cuttings from this nursery are planted at a distance of 20 cm within a row, the distance between the adjacent rows being about 60 cm. The number of cuttings required to plant one hectare of land is about 80,000. Planting is done either in flat beds or on ridges.
The planting of cuttings in northern India is done in June-July and in central and southern India in October-November. The crop is grown in both kharif and rabi in some parts of the country. Farmyard manure or compost may be applied at 10 tonnes per hectare at the time of land preparation. In order to obtain good yields of the crop, application of 60 kg each of nitrogen and phosphorus and 120 kg of potash per hectare is recommended.
Since sufficient soil moisture is necessary for crop, irrigation is resorted to after the cuttings have been planted, Besides increasing the yield, irrigation, which is given 2-4 times during dry weather, improves the grade and quality of marketable tubers.
Harvesting and Yield:
The crop takes about 4-5 months to mature. The leaves turn brown, indicating that the crop is ready for harvesting. The vines are cut and removed 4-5 days earlier than the harvesting date. The tubers are then dug up with the help of spades.
The average yield of tuber varies from 10-15 tonnes per hectare.
Uses of Sweet Potato:
The tubers of sweet potato are very rich in starch (16%). They contain some sugar (4%), protein and fat also. The tubers are used as food and may be eaten raw, boiled or roasted. Besides, they are consumed as a common vegetable and are also used for canning, dehydrating and flour manufacture.
Sweet potatoes are a good source of starch, glucose syrup and alcohol. The tubers are sometimes used in the preparation of sweetmeats. In certain countries, tubers are fed to horses, cattle and pig. Different parts of the green plants, like vine tops and leaves, can also be used as fodder.
Varieties of Sweet Potato:
Some of the important varieties are:
Pusa Suffaid, Pusa Lai, Pusa Sunheri, SP-3, SP-9, Ranger, Bhadrakali, Hosur Red, Gold Rush, Centennial, H 42, C 71, Op 5, Co 2, C 43. S 30, H 33, R 55, H 268, V 35, Kalmegh, Panama Suthna etc.
Diseases of Sweet Potato:
The common diseases of sweet potato are:
(i) Leaf spot caused by Cercospora batatae and C. bataticola, which can be controlled by spraying the crop with 1% Bordeaux mixture.
(ii) Charcoal rot caused by Macrophomina phaseoli, which can be controlled by raising vines from roots, in an un-infected locality.
(iii) Soft rot caused by Rhizopus nigricons, which can be controlled by disinfecting walls and floors of storage rooms.
(iv) Black rot caused by Ceratostomella fimbriata, which can be controlled by treating the seed tubers with mercuric chloride solution (1 in 1000) or 2.5 Borax solution.
Insect Pests of Sweet Potato:
The common insect pests of the crop are:
(i) Sweet potato weevil (Cylas formicarius), which can be controlled by using tolerant varieties like H 41, H 42, H 268 and RS 5 or by removing infested plants and tubers regularly, by planting deep-rooting varieties and also by applying 5% Aldrin or Chlordane dust to the soil at the base of the plants when infestation is observed and, in severe cases, by spraying 0.5% Fenthion or Fenitrothion solution at biweekly intervals (3-4 times, starting from 1 month after planting).
(ii) Sphinx hawk moth (Agrius convolvuli), which can be controlled by dusting 10% BHC.
(iii) Bihar hairy caterpillar (Diacrisia obliqua), which can be controlled by 10% BHC or spraying 0.05% Dichlorvos.
(iv) Leaf beetles (Aspidomorpha miliaris), which can be controlled by dusting 5% BHC.
(v) Assassin bug (Oncocephala tuberculoid), which can be controlled by dusting 5% BHC.