Cotton harvesting
Cotton harvesting
Cultivation
Successful cultivation of cotton requires a long frost-free period, plenty of sunshine, and a moderate rainfall, usually from 600 to 1200 mm (24 to 48 inches). Soils need to be fairly heavy, although the level of nutrients does not need to be exceptional.
In general, these conditions are met within the seasonally dry tropics and subtropics 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 beginning of February to the beginning of June. The area of the United States the South Plains is the largest contiguous cotton-growing region in the world. While dryland (non-irrigated) cotton is successfully grown in this region, consistent yields only produced with heavy reliance on irrigation water drawn from the Ogallala Since cotton is somewhat salt and drought tolerant, this makes it an attractive arid and semiarid regions. As water resources get tighter around the world, economies that rely on it face difficulties and conflict, as well as potential environmental.
For example, improper cropping and irrigation practices have desertification in areas of Uzbekistan, where cotton is a major export. In the days Soviet Union, the Aral Sea was tapped for agricultural irrigation, largely of cotton, now salination is widespread.
Genetic modification
Genetically modified (GM) cotton was developed to reduce the heavy reliance on pesticides. The bacterium Bacillus thuringiensis (Bt) naturally produces a chemical harmful only to a small fraction of insects, most notably the larvae of moths and butterflies, beetles, and flies, and harmless to other forms of life. The gene coding for Bt toxin has been inserted into cotton, causing cotton to produce this natural insecticide in its tissues. In many regions, the main pests in commercial cotton are lepidopteran larvae, which are killed by the Bt protein in the transgenic cotton they eat. This eliminates the need to use large amounts of broad-spectrum insecticides to kill lepidopteran pests (some of which have developed pyrethroid resistance). This spares natural insect predators in the farm ecology and further contributes to noninsecticide pest management.
Bt cotton is ineffective against many cotton pests, however, such as plant bugs, stink bugs, and aphids; depending on circumstances it may still be desirable to use insecticides against these. A 2006 study done by Cornell researchers, the Center for Chinese Agricultural Policy and the Chinese Academy of Science on Bt cotton farming in China found that after seven years these secondary pests that were normally controlled by pesticide had increased, necessitating the use of pesticides at similar levels to non-Bt cotton and causing less profit for farmers because of the extra expense of GM seeds.
However a more recent 2009 study by the Chinese Academy of Sciences, Stanford University and Rutgers University refutes this.
They concluded that the GM cotton effectively controlled bollworm. The secondary pests were mostly miridae (plant bugs) whose increase was related to local temperature and rainfall and only continued to increase in half the villages studied. Moreover, the increase in insecticide use for the control of these secondary insects was far smaller than the reduction in total insecticide use due to Bt cotton adoption.
The International Service for the Acquisition of Agri-biotech Applications (ISAAA) said that, worldwide, GM cotton was planted on an area of 16 million hectares in 2009.
This was 49% of the worldwide total area planted in cotton. The U.S. cotton crop was 93% GM in 2010 and the Chinese cotton crop was 68% GM in 2009.
The initial introduction of GM cotton proved to be a huge success in Australia - the yields were equivalent to the no transgenic varieties and the crop used much less pesticide to produce (85% reduction).
The subsequent introduction of a second variety of GM cotton led to increases in GM cotton production until 95% of the Australian cotton crop was GM in 2009.
Cotton has also been genetically modified for resistance to glyphosate (marketed as Roundup in North America), an inexpensive and highly effective, but broad-spectrum herbicide. Originally, it was only possible to achieve glyphosate resistance when the plant was young, but with the development of Roundup Ready Flex, it is possible to achieve glyphosate resistance much later in the growing season.
GM cotton acreage in India continues to grow at a rapid rate, increasing from 50,000 hectares in 2002 to 8.4 million hectares in 2009. The total cotton area in India was 9.6 million hectares (the largest in the world or, about 35% of world cotton area), so GM cotton was grown on 87% of the cotton area in 2009.
This makes India the country with the largest area of GM cotton in the world, surpassing China (3.7 million hectares in 2009). The major reasons for this increase is a combination of increased farm income ($225/ha) and a reduction in pesticide use to control the cotton bollworm.
Cotton has gossypol, a toxin that makes it inedible. However, scientists have silenced the gene that produces the toxin, making it a potential food crop.
Organic production
Organic cotton is generally understood as cotton, from plants not genetically modified, that is certified to be grown without the use of any synthetic agricultural chemicals, such as fertilizers or pesticides.
Its production also promotes and enhances biodiversity and biological cycles.
United States cotton plantations are required to enforce the National Organic Program (NOP). This institution determines the allowed practices for pest control, growing, fertilizing, and handling of organic crops.
As of 2007, 265,517 bales of organic cotton were produced in 24 countries, and worldwide production was growing at a rate of more than 50% per year.
Pests and weeds
The cotton industry relies heavily on chemicals, such as fertilizers and insecticides, although a very small number of farmers are moving toward an organic model of production, and organic cotton products are now available for purchase at limited locations. These are popular for baby clothes and diapers. Under most definitions, organic products do not use genetic engineering.
Historically, in North America, one of the most economically destructive pests in cotton production has been the boll weevil. Due to the US Department of Agriculture’s highly successful Boll Weevil Eradication Program (BWEP), this pest has been eliminated from cotton in most of the United States. This program, along with the introduction of genetically engineered Bt cotton (which contains a bacterial gene that codes for a plantproduced protein that is toxic to a number of pests such as cotton bollworm and pink bollworm), has allowed a reduction in the use of synthetic insecticides.
Other significant global pests of cotton include the pink bollworm, Pectinophora gossypiella; the chili thrips, Scirtothrips dorsalis; and the cotton seed bug, Oxycarenus hyalinipennis.
Harvesting
Most cotton in the United States, Europe, and Australia is harvested mechanically, either by a cotton picker, a machine that removes the cotton from the boll without damaging the cotton plant, or by a cotton stripper, which strips the entire boll off the plant. Cotton strippers are used in regions where it is too windy to grow picker varieties of cotton, and usually after application of a chemical defoliant or the natural defoliation that occurs after a freeze. Cotton is a perennial crop in the tropics, and without defoliation or freezing, the plant will continue to grow.
Cotton continues to be picked by hand in developing countries.
