In many countries cotton (Gossypium spp.) is one of the most important fibre producing plants. Cotton crop not only provides fibre for the textile industry, but also plays a role in the feed and oil industries with its seed, rich in oil (18 – 24%) and protein (20 – 40%). An estimated 350 million people are engaged in cotton production either on-farm or in transportation, ginning, baling and storage. China consumes 40% of the world’s raw cotton. Australia and Egypt produce the best quality cotton in the world. Cotton is a major export revenue source for Burkina Faso, Benin, Uzbekistan, Mali, Tajikistan, Ivory Coast, Kazakhstan, Egypt and Syria. The world’s lowest cost cotton producers are Australia, China, Brazil and Pakistan.
The USA and Israel are two of the highest cost cotton producers in the world. World’s main cotton exporters are the USA, Uzbekistan, Brazil and Australia. World cotton demand has increased steadily since the 1950s at an average annual rate of growth of 2%.
In terms of global production, cotton is the foremost fibre crop. Present world production is some 25.5 million tons of seed cotton from 34.8 million ha. China, USA and India are the world's major cotton producing countries, accounting for nearly 60% of the world production. Nearly 53% of cotton produced in the world is subsidized. Cotton producing countries that subsidize their domestic industry include the USA, China, Greece, Spain, Turkey, Brazil, Mexico, Egypt and India.
Cotton is grown in more than 100 countries accounting for 40% of the world fibre market. The cotton is raised in diverse climates such as tropical, sub-tropical and temperate climates.
The development of the crop is sensitive to temperature. Cool nights and low daytime temperatures result in vegetative growth with few fruiting branches. The crop is very sensitive to frost and a minimum of 200 frost-free days is required. The length of the total growing period is about 150 to 180 days. Depending on temperature and variety, 50 to 85 days are required from planting to first bud formation, 25 to 30 days for flower formation and 50 to 60 days from flower opening to mature boll. Cotton is a short-day plant but day-neutral varieties exist. However, the effect of day length on flowering is influenced by temperature. Germination is optimum at temperatures of 18 to 30 °C, with minimum of 14 °C and maximum of 40 °C.
Delayed germination exposes seeds to fungus infections in the soil. For early vegetative growth, temperature must exceed 20 °C with 30 °C as desirable. For proper bud formation and flowering, daytime temperature should be higher than 20 °C and night temperature higher than 12 °C, but should not exceed 40 and 27 °C respectively. Temperatures between 27 and 32 °C are optimum for boll development and maturation but above 38 °C yields are reduced. Strong and/ or cold winds seriously affect the delicate young seedlings and at maturity will blow away fiber from opened bolls and cause soiling of the fiber with dust. Continuous rain during flowering and boll opening will impair pollination and reduce fiber quality. Heavy rainfall during flowering causes flower buds and young bolls to fall.
Cotton is grown on a wide range of soils but medium and heavy textured, deep, well drained, fertile clayey, alluvial, chernozom and laterite soils with good water holding characteristics are preferred. Acid or dense sub soils limit root penetration. The pH range is 5.5 to 8 with 7 to 8 regarded as optimum. The crop is tolerant to soil salinity. The plant propagation is by seed. The plant density varies between 100,000 to 160,000 plants/ ha under high density and between 14,000 to 37,000 plants/ ha under low density population.
Adoption of drip irrigation and fertigation in cotton proved to be technically feasible and economically viable and beneficial in many ways in many countries. Drip irrigation in many diverse agro-ecological situations registered higher yield (15 to 30 %) besides saving in water (30 to 45 %) and improving lint quality in comparison to conventional furrow, overhead sprinkler and centre pivot sprinkler irrigation methods. Under Adana, Turkey agro-climatic conditions subsurface drip irrigated cotton raised on 11 ha registered seed cotton yield of 5.5 to 5.8 tons/ha (33% increase over furrow irrigated cotton) besides saving 30% water, 20% energy, 15% labor and 5% plant protection chemicals.
For high yields, the seasonal crop water requirements for cotton were estimated to be 350 to 900 mm/ ha under range of climatic conditions and varying length of growing season (150 – 210 days) with an average daily evapotranspiration rate of 4 to 8 mm/ day. Irrigation scheduling using either daily growing rate or leaf water potential measurements by pressure chamber enabled efficient use of water, fertilizer and energy inputs. Cotton is a heavy feeder of nutrients. The aim of the fertigation program is to cover the difference between crop demand and supply. The ability of drip system to apply nutrients by fertigation frequently according to crop developmental stages gives the grower the ability to react to the plant needs in the most efficient way.
Other best management practices include irrigation scheduling, protection of crop from pests & diseases, need based weed management, defoliation, harvesting and post harvesting operations to minimize yield losses.