Harvested cotton in Tennessee (2006)
Successful cultivation of cotton requires a long Frost -free period, plenty of sunshine, and a moderate rainfall, usually from 600 to 1200mm (24 to 48 Inch). Soil usually need to be fairly heavy, although the level of Nutrient does not need to be exceptional. In general, these conditions are met within the seasonally dry tropics and subtropics in the Northern and Southern hemispheres, but a large proportion of the cotton grown today is cultivated in areas with less rainfall that obtain the water from irrigation. Production of the crop for a given year usually starts soon after harvesting the preceding autumn. Planting time in spring in the Northern hemisphere varies from the beginning of February to the beginning of June. The area of the United States known as the South Plains is the largest contiguous cotton-growing region in the world. It is heavily dependent on Irrigation water drawn from the Ogallala Aquifer. Cotton is a thirsty crop, and as Water resources get tighter around the world, economies that rely on it face difficulties and conflict, as well as potential environmental problems. For example, cotton has led to Desertification in areas of Uzbekistan, where it is a major export. In the days of the Soviet Union, the Aral Sea was tapped for agricultural irrigation, largely of cotton, and now Salination is widespread.