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TUBER INFORMATION
SWEET
POTATO (Ipomoea batatas)
Tuberous-rooted
perennial, belonging to the family Convolvulaceae, usually
grown as an annual; top herbaceous, drying back to ground
each year; stems forming a running vine up to 4 m long,
usually prostrate and slender, with milky juice, lateral
stem-branches arising from the short stem and usually
not branched; leaves ovate-cordate, borne on long petioles,
palmately veined, angular or lobed, depending on variety,
green or purplish; flowers white or pale violet, axillary,
funnel-shaped, borne singly or in cymes on short peduncles;
pods round; seeds 1-4 per pod, flattened, hard-coated,
angular. The crop is native to the American Tropics. Introduced
and cultivated in many tropical and subtropical countries,
there becoming important food crop, especially in India,
China, Philippine Islands, and the South Seas Islands
(Reed, 1976).
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)
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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
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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.
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.
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.
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.
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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.
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.
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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 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).
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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.
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