Sweet Potato

The cultivation of sweet potato has traditionally been confined to varying growing systems such as open land highland, rice fallow system, under shade, owita and homestead conditions. Sweet potato has remarkable ability to convert solar and soil energies into carbohydrates giving impressive yields under marginal and stress situations having low input requirements and little attention, wide adaptability, flexibility in crop management and non-seasonality make sweet potato a viable crop in all agro ecological zones excluding high elevations.

Recommended Varieties

CARI-9

CARI-273

CARI-426

Wariyapola-red

Wariyapola-white

Ranabima

BW-8 (Shanthi)

BW-21 (Chitra)

Gannoruwa-Sudu

Variety

Age (month)

Flesh colour

CARI-9

3 1/2 - 4

Light yellow

CARI-273

3 1/2 - 4

Light yellow

CARI-426

3 1/2

Orange

Wariyapola-red

3 1/2

White

Wariyapola-white

3 1/2

White

Ranabima

3 1/2 - 4

Light yellow

BW-8 (Shanthi)

3 1/2

White

BW-21 (Chitra)

3 1/2

White

Gannoruwa - Sudu

3 1/2 - 4

Light yellow


Variety Discription

CARI-9

Semi-vine plant type with entire to very slightly lobbed leaves. Root tubers have dark pinkish skin with highly variable tuber shapes which are fusiform.


CARI-273

Semi-vine plant type with entire leaves. The mature leaves are green in colour and the tender leaves are light green with purple at margin. Petioles are light green with purple at leaf end and petiole base. Root tubers are fusiform shape with purple coloured skin.


CARI-426

It is a polycross hybrid and maternal parent is a native variety Beli-batala. It has a bushy plant type with deeply cut leaf laminas. Vines and leaves are green in colour with purplish green tender leaves. Root tubers are highly uniform and fusiform in shape having pinkish orange skin.


Wariyapola red


It is a selection from the local sweet potato collection and planting material is available in all sweet potato growing areas. Semi-vine plant type with entire to very slightly lobbed leaves. Root tubers are highly uniform and fusiform in shape having purple skin.

Wariyapola white

Wariyapola white is a mutant, originated from the variety Wariyapola red. Semi-vine plant type with entire to very slightly lobbed leaves. Root tubers are highly uniform and fusiform in shape having white skin.


Ranabima

Semi-vine plant type, the leaves are entire to slightly lobbed, vines are yellowish green except tender vine apices are slightly pigmented. The root tubers are round elliptical shape with pink skin.


BW - 8 (Shanthi)

It is a natural selection from Kalutara district. BW - 8 is a semi-vine type plant with light green stems. Leaf type is moderately lobbed with purple colouration at the base of the leaf on the lower side. Tuber shape is egg shaped with tapering ends and skin colour is white.


BW - 21 (Chitra)

It is a natural selection from Galle district. Viny plant type with moderately lobbed leaves. Mature leaves are green while the young leaves are reddish brown in colour. It has conical shape root tubers with white skin.

Gannoruwa Sudu

It is a polycrose hybrid and material parent is recommended variety CARI-426. Semi-vine plant type with numerous major branches. Entire vines are green in colour except the very tender vine apices which are slightly pigmented with moderately lobbed leaves. The root tubers are round to elliptical shape, highly uniformed with white skin.

Field Establishment

Climate

Sweet potato is grown in the tropical, sub tropical and warm temperate regions of the world. Sweet potato is a sun loving crop. It requires considerable amount of rain during the growth period and a dry period during root formation. Warm sunny days and cool nights are very much favourable for storage root formation in sweet potato. Tuber yields are reduced considerably if drought occurs within first six weeks after planting.


Soil

Sweet potato can be successfully grown in a variety of soils, however well drained sandy loam soils are best suited. On heavy clay soils shoots grow well, but yield of tubers will be poor with deformed tubers.


Land preparation

Till to a depth of 25cm. Soils must be well drained and well aerated for a successful tuber growth. Ridge and furrow method, mound method, narrow bed and broad bed method are practiced in sweet potato cultivation in different areas. Ridge and furrow method and narrow bed method are better than other methods.


Planting material requirement

Vine cuttings are suitable for planting. The vine tip cuttings are found to be best to get higher tuber yield from sweet potato. In some varieties recurrent use of vines as planting material for more than 5,6 seasons showed marked decrease in yield. For these varieties root tubers can be sprouted and get cuttings. About 55,000 - 60,000 cuttings are required to plant one hectare.


Time of planting

Under rainfed conditions, plant with the Yala and Maha rains. In the wet zone in both Yala and Maha and in the dry zone in Maha season only.

Under irrigated conditions, planting can be done at any time of the year.


Nursery preparation
To produce enough planting material a nursery can be prepared.

Planting and spacing

No of cuttings and method of planting depend on the method of bed preparation. Spacing between 2 plants is 20cm. In ridge and furrow method cuttings are planted at a spacing of 90cm x 20cm. Vines of 20-25cm length with at least 5 leaves are found to be ideal as planting material.

Crop Management

Fertilizer use

Application of fertilizer should be done before 45 days to get a maximum vegetative growth of the crop. After 45 days vegetative growth should be minimise and root production must be increased. Basal fertilizer should apply after 15 days and top dressing at 45 days after planting.

For fertile soils, fertilization should be discouraged because sweet potato when over fertilized grows vines and leaves at the expense of fleshy roots.


Recommended fertilizer

.

Basal Kg/ha


Top dressing

Urea

60

60

Conc. Super phosphate

120

-

Muriate of potash

120

60


Weeding and earthing-up

Sweet potato is a quick growing crop and it covers the soil quickly and suppresses most of the weeds. However, weeding may become necessary particularly in the early stages of growth. To protect the crop from weeds at least 2 weedings and earthing up has to be given within 45 days after planting along with fertilizer application.


Insect control

Sweet Potato Weevil: Cylas formicarius


Damage

* Adults feed on epidermis of vines & leaves scraping oval patches and make round feeding punctures on external surface of tubers.

* Lavae feed inside the vines caused malformation, thickening & cracking of affected vines.

* Lavae tunnel tubers, deposit frass & it causes decay

Management

1. Dip cuttings of sweet potato in a solution of systemic insecticide for 25-30 minutes before planting.

  1. To avoid cracking soil at the base of the vine, earthining up of soil and regular watering is necessary
    3. To retain moisture & cracking mulching is also necessary

    Disease control

Diseases are not serious in sweet potato. However root rot caused by Fusarium has been identified in sweet potato. The symptoms are yellowing of leaves and later drying of vines and rotting of roots.

Control-measures are improved drainage, ensure field sanitation and use resistant varieties.

Harvesting & Post-harvest Technology

Yield

Recommended varieties gives a average yield of 18-22 t/ha under good management.

Variety

Yield t/ha

Texture of cooked tuber

CARI-9

16 - 18

Dry starchy

CARI-273

18 - 20

Wet starchy

CARI-426

22 - 24

Wet

Wariyapola - white

22 - 25

Wet starchy

Wariyapola - red

14 - 15

Wet starchy

Ranabima

22 - 25

Wet starchy

Shanthi

12 - 14

Wet starchy

Chitra

12 - 14

Wet starchy

Gannoruwa Sudu

22 - 25

Wet starchy


Harvesting

The crop attains maturity in 3 1/2 to 4 months after planting depending upon the variety and environmental conditions. The maturity of tubers can be determined by cutting fresh tubers. The cut surface of the immature tubers gives a dark greenish colour while in mature tubers, the cut ends dry clearly. After removing the vines tubers are dug out without causing injury.


Post-harvest handling

The harvested roots can be transported to the market or can be stored. The tubers are normally cured by keeping in a open place for 4 to 7 days. After curing sweet potato roots can be stored for 3 months.