CROP HUSBANDRY-SWEET POTATO CULTIVATION PRACTICES IN KERALA

SWEET POTATO (Ipomoea batatas)

Sweet potato requires a warm humid tropical climate with a mean temperature of about 22 ºC. 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.

Season
Rainfed crop: June-July, September-October
Irrigated crops: October-November (for uplands) and January-February (for low lands)

Varieties
Improved varieties: H-41, H-42, Sree Nandini, Sree Vardhini, Sree Retna, Sree Bhadra, Kanjanghad, Sree Arun, Sree Varun

Local varieties: Badrakali Chuvala, Kottayam Chuvala, Chinavella, Chakaravalli, Anakomban,

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.

Manuring
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.

Irrigation
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.

Aftercultivation
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 sannhemp 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.

Plant protection
a. Dip the vines in 0.05% fenthion or fenitrothion or monocrotophos suspension for 5 to 10 minutes prior to planting. This is to control the sweet potato weevil.

b. Spray the crop, one month after planting and subsequently three more times at tri-weekly intervals with any of the insecticides mentioned above to control field infestation by the sweet potato weevil.

Integrated control of sweet potato weevil
(a) Remove and destroy the crop residues of the previous crop.
(b) Use healthy and weevil-free planting materials.
(c) Apply Eupatorium odoratum leaves as mulch @ 3 t/ha at 30 DAP.
(d) Drench with 0.05% endosulfan, fenthion or fenitrothion at 65 DAP and earthing up at 80 DAP.
(e) 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.
(f) Use pheromone traps (3Z Dodecenyl 2E butenoate).

Harvesting
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.