Sweet Potato
Sweet Potato
The Sweet Potato is a staple food crop especiallyin the South, and should not be confused withthe Yam (Dioscorea sp.) which is somethingelse, but unfortunately the common name hasbeen used incorrectly for the true Sweet Potato.The Sweet Potato can be grown from southernN.J. and southern Ill. southward on a commer-cial scale, but the areas with long hot summers(Zones 8, 9, to) are usually the best growingareas. However, the home gardener in thenorthern part of the country can sometimesgrow a few hills just for the fun of it, if theplants are set out after the middle of June andthe roots are not subjected to frost of any kind.These are vines, grooving luxuriantly on thesurface of the soil, with alternate, triangular toheart-shaped leaves, often deeply lobed accord-ing to variety. They seldom bear flowers exceptin the area about Key West and the mosttropical parts of Tex. The tubers are browncolored, often with yellow or orange mixed in,are oval in shape and a hill of 6-8 well filled-outtubers is considered normal.
They grow best on warm sandy soils withplenty of available moisture, but not wet. Theydo not grow well on dry or muck soils. The Sweet Potato is a staple food crop especiallyin the South, and should not be confused withthe Yam (Dioscorea sp.) which is somethingelse, but unfortunately the common name hasbeen used incorrectly for the true Sweet Potato.The Sweet Potato can be grown from southernN.J. and southern Ill. southward on a commer-cial scale, but the areas with long hot summers(Zones 8, 9, to) are usually the best growingareas. However, the home gardener in thenorthern part of the country can sometimesgrow a few hills just for the fun of it, if theplants are set out after the middle of June andthe roots are not subjected to frost of any kind.These are vines, grooving luxuriantly on thesurface of the soil, with alternate, triangular toheart-shaped leaves, often deeply lobed accord-ing to variety. They seldom bear flowers exceptin the area about Key West and the mosttropical parts of Tex. The tubers are browncolored, often with yellow or orange mixed in,are oval in shape and a hill of 6-8 well filled-outtubers is considered normal.
They grow best on warm sandy soils withplenty of available moisture, but not wet. Theydo not grow well on dry or muck soils
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Sweet Potato
Synonyms: B. napus L. var. chinensis O.K. Schult, B. pekinensis (Lour.) Rupr., B. petsai Bailey, B. campestris L.
Some authorities now consider that Brassica campestris L. is a more valid name and that this species should be divided into two varieties: var. chinensis (Paak-ts’oi) and var. pekinensis (Pe-tsai). Other authorities regard these two varieties as subspecies.
COMMON NAMES
Chinese Cabbage, Spoon Cabbage, White Cabbage, Shantung Cabbage, Chefoo Cabbage, Flowering Cabbage, Celery Cabbage, Pekin cabbage (Eng.); Paak-ts’oi, Pak-choi (Chin.); Chou de Chine (Fr.); Chinakohl (Ger.); Chinese Kool (Neth.); Col China, Repollo (Chino (Sp.); Pe-tsai (Mal. and Indon.); Pechay (Philipp.); Mkaheji (Swah.).
CENTRE OF ORIGIN AND DISTRIBUTION
The species B. chinensis is presumed to have originated in eastern Asia; the variety pekinensis appears to have a more definite centre of diversity in China. Both forms (Paak-ts’oi and Pe-tsai) are important crops in most areas of the Far East and South-east Asia.
Diploid chromosome number: 2n = 20.
AREAS OF CULTIVATION
Widely grown in Malaysia, Indonesia, the Philippines, China, Taiwan, East and West Africa, South America and the Caribbean. The variety pekinensis (Rupr.) is commonly referred to as Pe-tsai and is becoming more widely grown than the variety chinensis (Paak-ts’oi)
BOTANICAL DESCRIPTION
A biennial herb, grown as an annual.
Basal leaves: broad, shining, 20-50 cm in length, petioles thickened and white. Flowers: bright or pale yellow, approximately 1 cm in length.
Fruit: a siliqua, slender, 3-6 cm in length.
Seeds: round, dark brown; weight of 1000 seeds = 3 g.
ENVIRONMENTAL RESPONSE
Tolerant to a wide range of soil conditions, including pH, although excessively well-drained soils are unsuitable for this crop which matures rapidly. Normally grown at elevations up to 1500 m although the leaves are liable to damage by winds in exposed situations. Withstands periods of relatively high rainfall but requires full exposure to sun for optimum development. Flowering is reduced under high temperature conditions but relatively low temperatures of less than 16°C promote precocious flower production. A diurnal variation of 5-6°C appears to increase the vigour of the plant and an optimum temperature range is 15-20°C. High yielding, firm-headed crops of the Pe-tsai type are produced at high elevations during cool weather; at lower elevations heading is less likely to occur.
CULTURAL REQUIREMENTS
Propagation and planting
Seeds are sown in nursery beds and transplanted to rows 4045 cm apart, plants 3040 cm apart in the row. May be sown direct and seedlings thinned to 30-40 cm apart For the Paak-ts’oi non-heading type, 1.5-2 kg seed is required per hectare for transplanted seedlings, to provide a plant population of 200 plants/ha. For the Pe-tsai heading form, 0.6 kg of seed is required to provide a plant population of 60 000 plants/ha.
Irrigation
This is required at regular intervals to maintain a constant rate of growth; mulching assists in conserving soil moisture and reducing weed competition.
Nutrient requirements
Nitrogenous top-dressing is required at regular intervals to obtain full leaf development.
GROWTH PERIOD AND HARVESTING
Headed (Pe-tsai) plants may be harvested 50-80 days from sowing seed and may attain a height of 40-50 cm. Loose-growing, non-heading (Paak-ts’oi) forms may be harvested 40-60 days from sowing.
Yield
Depending on cultivar, environmental conditions and plant density, yields ranging from 5-30 t/ha for Paak-ts’oi may be obtained; an average yield would be 15 t/ha. Yields of 10-50 t/ha, with an average of 20 t/ha, may be obtained from the heading (Pe-tsai) form.
Seed production
Flowering and seed formation of the Pe-tsai type is encouraged by relatively low temperatures and a daylength of more than 12-13 hours; Paak-ts’oi tends to flower and set seed at relatively high temperatures and in long days.
A cross-pollinated crop, yielding approximately 500 kg seed per hectare. B. chinensis should be isolated from B. juncea, with which it is cross-compatible. It is not cross-compatible with the cultivated varieties of B. oleracea. Plants for seeding should be selected for resistance to early bolting. Time of flowering depends on local type and its reaction to climatic conditions.
PREPARATION FOR MARKET AND STORAGE
Heads should be firm and the outer leaves light green to yellow-green, with no discoloration or pest or disease injury. The heads are normally trimmed directly after harvesting, all damaged or unsightly leaves and remains of roots being removed. They should then be kept in the shade before being packed into boxes or crates.
Storage of heads for periods up to 30-40 days, at a temperature of 0°C is Possible.
USE AND NUTRITIONAL COMPOSITION
The leaves are prepared as a cooked vegetable or eaten raw in salads, particularly the Pe-tsai form. The leafy (Paak-ts’oi) cultivars have a nutritive value which is twice that of White Cabbage but the heading (Pe-tsai) forms have a lower food value than the leafy forms.
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