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(cotton), a genus of perennial trees, shrubs, and herbs of the family Malvaceae. There are 35 species, distributed in tropical and subtropical regions of Asia, the Americas, Africa, and Australia.
The following four species are most commonly cultivated as textile plants: G. herbaceum, which is grown in Asian countries (now replaced or being replaced by more valuable varieties of other species); G. arboreum, which is raised in India, Pakistan, Bangladesh, Burma, China, and other countries; G. hirsutum, which is grown in the USSR, the USA, Brazil, Mexico, and other major cotton-producing countries; and G. barbadense, which is cultivated in the Arab Republic of Egypt (varieties of Egyptian-type cotton), Sudan, the USSR (varieties of Soviet fine-staple cotton), the USA (varieties of sea island cotton), and other countries. Wild species include G. anomalum and G. capitis-viridis, which grow in the savannas of Africa; G. stocksii and G. areyasianum, which occur in the Arabian Peninsula; G. davidsonii and G. trilobum, which are native to North America; and G. sturtii and G. robinsonii, which are from Australia.
Botanical description. The root systems of cultivated varieties of cotton consist of large taproots that extend as much as 2.4–2.6 m into the ground. The principal mass of active roots, however, is situated at the soil surface and at depths above 50 cm. The stem, which is erect and branching, measures 70 to 200 cm in height. Erect and elongate vegetative (monopodial) branches develop from the axils of the lower leaves. Bent fruiting (sympodial) branches emerge from the axils of the upper leaves, usually from the third to the sixth node. The fruiting branches have one or several internodes of different lengths (short, medium, long, and very long), from which eight to ten or more flower buds are formed. The vegetative branches have lateral branches that produce fruit. In some varieties the flower buds are located directly on the main stem. The alternate leaves are thin or leathery, three-to seven-lobed, and stipulate. The coloration is usually green, although yellow-green or reddish leaves occur in some varieties. The lower leaves are oval-cordate and unstipulate. The large, bisexual flowers have five cream, yellow, or white (in some species, with a red spot) petals. The coloration of the petals changes as the flowers withers, turning orange, red, or lilac. The stamens are concresced with the style. The pistil is three-to five-lobed, and the ovary has three to five chambers.
The fruit, known as a boll, measures 1.5–4.5 cm in diameter and contains 25 to 35 seeds. The boll opens into three to five valves. The ovate or pear-shaped seeds are 0.6–1.5 cm long and measure 0.5–0.8 cm in diameter at the widest part. They are covered with long, predominantly white hairs, which are used as fiber, and often with a short fuzz, known as linters. There are some forms with colored fibers (brown, greenish). One thousand seeds weigh 80–160 g.
Biological features. The vegetative period of cotton is 110 to 145 days. Sprouting occurs between the seventh and tenth day after sowing. The first fruiting branch appears 35 to 40 days after sprouting. After another 25 to 30 days the first flower opens (it flowers for one day), and in 50 to 60 days the first boll opens.
Cotton is a thermophile plant, requiring an average degree day of 2,000°–3,000°C during the vegetative period. Germination occurs at temperatures of 14°–16°C; seedlings perish at 1°–2°C. The optimum temperature for growth and development is 25°–30°C. Temperatures below 17°C and above 40°C are detrimental, causing buds, flowers, and bolls to fall off the plant. Cotton is demanding in regard to conditions of moisture, nutrition, and light. Its transpiration coefficient under Middle Asian conditions averages 600 to 800. During its vegetative period cotton assimilates 6,000 to 8,000 cu m of water per hectare (ha). The average daily assimilation of water by a cotton field is 32.5–62.5 cu m/ha before flowering, 80 cu m/ha at the onset of flowering, 97.5–105 cu m/ha during the period of mass flowering and boll formation, and 47.5 cu m/ha at the beginning of boll maturation. The average nutrient carryover per ton of raw cotton (fibers that have not been ginned) is about 45 kg of N, 16 kg of P2O5, and 48 kg of K2O. The largest amounts of nitrogen, phosphorus, and potassium are assimilated during budding and boll formation. The best soils are light, loamy sierozems; salinated soils are not suitable unless they are reclaimed prior to sowing.
Wild and semiwild forms of cultivated species include relatively drought-resistant shrubs or small trees, which range in height from 1 to 12 m. They have slender fruiting branches and small leaves, flowers, bolls, and seeds. The fiber is sparse, short, and almost always brown or gray in color.
Economic significance. Cotton is one of the principal industrial crops, accounting for more than 50 percent of the world production of textile fiber. The fiber, which makes up 25–40 percent of the raw cotton, is processed into yarn used to manufacture various fabrics (including industrial fabrics), cord for automobile tires, nets and straps, and sheaths for wires. The seeds contain 22–29 percent cottonseed oil, which is used as a cooking oil and in the production of margarine, glycerine, soap, stearin, and lubricants. By-products from cotton ginning and from oil production are used to make cellulose, alcohol, lacquers, linoleum, motion-picture film, cardboard, and insulation materials. The oil cake and meal are used as feed for livestock. The flour, after removal of the toxic alkaloid gossypol, can be used to extract food protein. Acetic, malic, citric, and other organic acids are obtained from cotton leaves. The stems are suitable for the manufacture of heat-insulating tiles. Cotton yields a good amount of nectar, producing up to 300 kg of honey per ha.
History of cotton culture. Cotton is an ancient textile plant. The birthplace of its cultivation is India, where the crop was grown for yarn in the Indus Valley during the Harappan civilization of the third millennium B.C. Cotton is known to have been cultivated in Egypt as early as the first century B.C. There is evidence that fiber from wild cotton was used in China in the second century A.D.; the Chinese first cultivated cotton in the seventh to ninth centuries. In the tenth century cotton was imported from Africa to
|Table 1. Cotton fiber production1|
|Planted area (thousand ha)||Gross fiber production (thousand tons)||Fiber yield (quintals per ha)|
|1Data are from the UN Food and Agriculture Organization (1975)|
|2The yield of raw cotton in the USSR was 25.1 quintals/ha in 1970 and 28.1 quintals/ha in 1976|
|World total ...............||33,012||32,967||34,258||10,798||11,523||12,333||3.3||3.5||3.6|
Spain, where textile manufacture soon arose in Barcelona. The American colonists first planted cotton in the early 17th century, although the native population of America cultivated the plant as early as the third or second millennium B.C. Cotton has been cultivated in Middle Asia since the sixth or fifth century B.C. and in Transcaucasia since the seventh to fourth century B.C.
Table 1 shows the land area under cotton cultivation, the cotton yield, and the gross fiber yield in the world and in individual cotton-producing countries.
Cotton-growing regions in the USSR are Middle Asia (greatest areas in Uzbekistan), Azerbaijan, and southern Kazakhstan. The varieties cultivated are medium-staple G. hirsutum and fine-staple G. barbadense. Twenty-two varieties were regionalized in 1975. The best medium-staple varieties are 108-F, Tashkent–1 (wilt-resistant), 149-F, and 133; the best fine-staple varieties are 9647–1, 8763–1, S–6030, and 5595-V. The principal trends in cotton breeding are directed toward the creation of varieties whose seeds do not contain gossypol, that have pure white fiber, that are adapted to mechanized harvesting, and that are resistant to wilt and, especially, to a complex of other diseases and pests.
Cultivation. Cotton is sown in a rotation system in which two or three fields are planted with alfalfa, six to eight with cotton, and one with corn or sorghum (with cover crops, for example, Persian clover or peas). Preparation of the soil involves gathering the stuhles of the previous planting, washout irrigation and pre-plowing watering, deep autumn plowing, and presowing treatment (harrowing, disking, replowing or cultivation with harrowing, levelling of the area). Fertilizers are applied at the rate of 200–250 kg/ha of N, 100–185 kg/ha of P2Os, and 200–250 kg/ha of K2O; of these, 25–30 percent of the nitrogen, 60–70 percent of the phosphorus, and 50 percent of the potassium fertilizers are used as complete fertilizers during deep autumn plowing; the remainder is applied before sowing, during sowing, and as dressings.
Cotton is sown when the soil temperature is 14°–16°C. The methods of sowing include wide-row (spaced at 60–90 cm), square-nest (60 × 60 cm with six to eight seeds per cluster), single-seed drilling and thick-cluster drilling (with rows spaced at 60–90 cm, with a seed or cluster interval of 15–30 cm). The sowing rate for pubescent seeds is 80–120 kg/ha, and for naked seeds in single-seed drillings 20–30 kg/ha. Seeds are buried to a depth of 4–5 cm. Cotton-field management involves watering (two to 11 waterings at a rate of 2,000–9,000 cu m/ha) during the growing period, thinning (leaving two or three plants per cluster—that is, three to six plants per meter of row), cultivating spacings, weeding by herbicides, dressing, detopping and defoliating before picking. Cotton is harvested with machines or manually when the bolls open. The bollies (unopened or only partly opened bolls) are harvested by cotton strippers; the fiber is separated from the bollies by cotton gins.
Pests of cotton are the turnip moth, the bollworm, cotton aphids, the beet armyworm, and Tetranychidae. Diseases are wilt, root rot, and gummosis.
REFERENCESKhlopkovodstvo. Moscow, 1963.
Khlopkovodstvo i primenenie mineral’nykh udobrenii v SSSR. Dushanbe, 1968.
Zhukovskii, P. M. Kul’lurnye rasteniia i ikh sorodichi, 3rd ed. Leningrad, 1971.
Ter-Avanesian, D. V. Khlopchatnik. Leningrad, 1973.
V. P. KARAMYSHEV