Successful cultivation of cotton requires a long
frost-free period, plenty of sunshine, and a moderate rainfall, usually from 60 to 120 cm (24 to 47 in).
Soils usually 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 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. Cotton is naturally a perennial
but is grown as an annual to help control pests.
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. While
dryland (non-irrigated) cotton is successfully grown in this region,
consistent yields are only produced with heavy reliance on
irrigation water drawn from the
Ogallala Aquifer.
Since cotton is somewhat salt and drought tolerant, this makes it an attractive crop for 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 problems.
[45][46][47][48][49] For example, improper cropping and irrigation practices have led to
desertification in areas of
Uzbekistan, where cotton 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.
Cotton can also be cultivated to have colors other than the yellowish off-white typical of modern commercial cotton fibers.
Naturally colored cotton can come in red, green, and several shades of brown.
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, called
Bt 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.
But 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 2009 study by the Chinese Academy of Sciences, Stanford University and Rutgers University refuted 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. A 2012
Chinese study concluded that Bt cotton halved the use of pesticides and
doubled the level of ladybirds, lacewings and spiders.
The
International Service for the Acquisition of Agri-biotech Applications (ISAAA) said that, worldwide, GM cotton was planted on an area of 25 million hectares in 2011. This was 69% of the worldwide total area planted in cotton.
GM cotton acreage in India grew at a rapid rate, increasing from
50,000 hectares in 2002 to 10.6 million hectares in 2011. The total
cotton area in India was 12.1 million hectares in 2011, so GM cotton was
grown on 88% of the cotton area. This made India the country with the
largest area of GM cotton in the world. A long-term study on the economic impacts of Bt cotton in India, published in the Journal
PNAS in 2012, showed that Bt cotton has increased yields, profits, and living standards of smallholder farmers.
The U.S. GM cotton crop was 4.0 million hectares in 2011 the second
largest area in the world, the Chinese GM cotton crop was third largest
by area with 3.9 million hectares and Pakistan had the fourth largest GM
cotton crop area of 2.6 million hectares in 2011.
The initial introduction of GM cotton proved to be a success in
Australia – the yields were equivalent to the non-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 making Australia the country with the fifth largest GM cotton crop in the world.
Other GM cotton growing countries in 2011 were Argentina, Myanmar,
Burkina Faso, Brazil, Mexico, Colombia, South Africa and Costa Rica.
Cotton has been genetically modified for resistance to
glyphosate
a broad-spectrum herbicide discovered by Monsanto which also sells some
of the Bt cotton seeds to farmers. There are also a number of other
cotton seed companies selling GM cotton around the world. About 62% of
the GM cotton grown from 1996 to 2011 was insect resistant, 24%
stacked product and 14% herbicide resistant.
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 and 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. In the United States, organic 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
.
