Sweet potato or sakaravalli kizhangu (Ipomoea batatas) is a crop grown for its sweet tasting starchy, tuberous roots rich in beta-carotene and anti oxidants. The crop is an herbaceous perennial vine, bearing heart-shaped or lobed leaves and medium-sized flowers. The edible tuberous root is long and tapered, with a smooth skin whose color ranges between red, purple, brown and white, and flesh colour ranges between white, yellow, orange, and purple.
It is native to the tropical parts of America and is now cultivated throughout tropical and warm temperate regions. China is the leading producer accounting for more than 80 % of the world production. About two lakh hectares of land are under sweet potato cultivation in India. The crop is cultivated mostly in Orissa, West Bengal, Bihar and Uttar Pradesh.
Climate & Soil
Sweet potato requires a warm humid tropical climate with a mean temperature of about 22ºC. Though sensitive to frost, it can also be grown in the hills up to an altitude of 1500-1800 m as a summer crop. Under rainfed conditions the crop requires a fairly well distributed annual rainfall of 75-150 cm. Being a photosensitive crop, sunny days and cool nights are favourable for better tuber development.
The crop can be grown on a variety of soils having good drainage, but grows best in fertile sandy loam soils. Heavy clayey and very light sandy soils are not suitable for proper tuber development.
Improved varieties: H-41, H-42, Sree Nandini, Sree Vardhini, Sree Rethna, Sree Bhadra, Kanjanghad, Sree Arun, Sree Varun & Sree Kanaka
Sree Arun: A high yielding, early maturing sweet potato with pink skin and cream flesh developed at the Central Tuber Crops Research Institute (CTCRI), Sreekariyam. It is suited to the upland and lowland conditions and it can be grown all through Kerala. Average yield is 20-28 t/ha.
Sree Kanaka: Short duration sweet potato with cream coloured skin and dark orange coloured flesh developed at the CTCRI. Average yield is 10-15 t/ha.
Sree Varun: A high yielding, early maturing variety with cream skin released from CTCRI. Average yield is 20-28 t/ha in 90-100 days.
Local varieties: Badrakali Chuvala, Kottayam Chuvala, Chinavella, Chakaravalli, Anakomban
Propagation & Planting
Rainfed crop: June-July, September-October
Irrigated crops: October-November (for uplands) and January-February (for low lands)
Preparation of land
Work the soil to a fine tilth by ploughing or digging to a depth of 15-25 cm. Make ridges 25-35 cm high, 60 cm apart for planting vines.
Seeds and sowing
Sweet potato is propagated by means of vine cuttings. To obtain vine cutting, raise nurseries from selected tubers using the following method. Eighty kg of medium sized weevil free tubers (each of 125-150 g) are required for planting in the primary nursery area (100 m2 to plant one hectare).
Plant the tubers at a spacing of 30-45 cm on ridges formed at 60 cm apart and replant in secondary nursery of about 500 m2 area at a spacing of 25 cm. Apply urea 15 days after planting at 1.5 kg / 100 m2 in the primary nursery. To ensure better plant growth in the secondary nursery, 5 kg of urea has to be applied in two split doses on 15th and 30th day after planting. Vines obtained from the freshly harvested crop are also planted in similar nursery area to obtain sufficient planting material. Cuttings obtained from the apical and near apical portions of the vines are preferable for planting in the main field. Storing of cut sweet potato vines with intact leaves, in bundles covered with banana leaves (dipped in water) and kept under shade for two days prior to planting is recommended. Irrigate the nursery every alternate day during the first 10 days and once in 10 days, thereafter. Vines will be ready for planting on the 45th day.
In the main field, plant vine cutting of 20-25 cm length on ridges 60 cm apart and at a spacing of 15-20 cm between the vines. The cuttings can also be planted on mounds taken at a spacing of 75 x 75 cm. On the top of each mound, 3-6 cuttings can be planted. Plant the vine cuttings with the middle portion buried deep in the soil and the two cut ends exposed to the surface. Ensure sufficient moisture in the soil for early establishment of the cutting. Provide adequate drainage and prevent water logging.
Apply cattle manure or compost at 10 t/ha at the time of preparation of ridges. The recommended N:P2O5:K2O dosage for sweet potato is 75:50:75 kg/ha. For the reclaimed alluvial soils of Kuttanad, the recommendation is 50:25:50 kg/ha. Apply N in two equal split doses, the first at the time of planting and the second 4-5 weeks after planting. Apply full dose of P2O5 and K2O at the planting time.
When grown as irrigated crop, provide irrigation once in 2 days for a period of 10 days after planting and thereafter once in 7-10 days. Stop irrigation 3 weeks before harvest. But one more irrigation may be given 2 days before harvest. IW / CPE for higher tuber yield in non-rainy periods is 1:2 (approximate interval of 11 days). The application of N and K2O at the rate of 50 kg/ha is recommended for the crop grown under irrigation.
Conduct two weeding and earthing up operations about 2 weeks and 5 weeks after planting. The top dressing of fertilizers may be done along with the second aftercultivation. Prevent development of small slender tubers at the nodes by turning the vines occasionally during active growth phase.
Rotation and mixed cropping
Under irrigated conditions, sweet potato can be rotated with rice and planted during December-January after harvest of the second crop of rice. As a mixed crop, it can be grown along with colocasia, amorphophallus etc. Under rainfed conditions, green manure crops such as kozhinjil and sunnhemp can be grown after harvest of the sweet potato and later incorporated into the soil at the time of land preparation for the succeeding crop.
Sweet potato weevil (Cylas formicarius)
A serious pest of sweet potato that infest the crop in the field, in storage sheds, and in propagation beds.The adults and larvae of the weevil damage the tuber by feeding and making tunnels just under the skin.
1) Remove and destroy the crop residues of the previous crop.
2) Use healthy and weevil-free planting materials.
3) Apply Eupatorium odoratum leaves as mulch @ 3 t/ha at 30 DAP.
4) Trap adult weevils using sweet potato pieces (of about 6 cm diameter) of 100 g size, kept at 5 m apart during 50 to 80 DAP at 10 days interval. Tubers may be cut and kept inside wire cages to avoid rat damage.
5) Use pheromone traps (3Z Dodecenyl 2E butenoate).
The duration of the crop depends on the variety; but in general, the crop can be harvested in about 3.5-4 months after planting. Harvest the crop when leaves begin to turn yellow and the tubers mature. The maturity of tuber can be ascertained by cutting fresh tubers. The cut surface will dry clear if the tuber is mature and becomes dark green if immature. Harvest the crop by digging out the tubers without causing injury. The average yield is 20-25 t/ha.