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Industrial Applications of Natural Fibres: Structure, Properties and Technical Applications
CHAPTER
II.7 Cotton Production and Processing
Cotton Production and Processing
Muhammad Rafiq Chaudhry
Head Technical Information Section; International Cotton Advisory Committee; 1629 - K Street,
Suite 702; Washington DC 20006; USA; Tel +1-202-292-1687 (Direct); 1-202-463-6660 x122
(Main) ; Fax +1-202-463-6950; Email: [email protected]
Introduction
Cotton is the most important of all natural fibre crops. In 1960, cotton represented 68 % of all the
fibre consumed in the world and, although non-cotton fibres have benefited from recent
technological developments and managed to erode cotton’s share of the market, as of 2009 cotton
continued to account for no less than 38 % of all the fibre consumed at the end use level.
Manmade industrial fibres can now be manufactured and sold at prices considerably below the price
of cotton. That, plus improvements in their quality characteristics, has made manmade fibres more
attractive than they once were. However, there are a number of features that are highly prized by
consumers and are found exclusively in cotton. Cotton is unique in features such as its
biodegradability, water absorbency, comfort and thermostatic capacity. The manmade fibre industry
is coming up with new quality characteristics and producing renewable resource polyesters like
PLA but so far manmade fibres have not been able to match cotton features and, in all probability,
will hardly be capable of surpassing cotton in those areas.
More than fifty countries plant cotton on at least 10,000 hectares every year. Only about 13 % of the
cotton area is located in developed countries, so cotton is truly a developing country crop. The
International Cotton Advisory Committee (ICAC), an intergovernmental organization established in
1939, maintains world cotton statistics on area, production, yields, trade and prices. The data on the
area planted to cotton, available since 1920/21, indicate that cotton has never been planted on more
than 37 million hectares. In fact, world cotton area has surpassed 36 million hectares on only two
occasions since the ICAC started compiling cotton statistics. On the other hand, after the 1950/51
season, cotton was planted on less than 30 million hectares only once, in 1986/87. So, in the
intervening years, between the 1950/51 season and the present, the world cotton area has remained
between 30 and 36 million hectares (ICAC, 2008a).
In the same period, cotton production increased from 6.5 million tons in 1950/51 to 26.3 million
tons in 2007/08. Since the cotton area remained constant, all increases in production – 400 % over
57 years – may be attributed to increases in yields. Thanks to a more thorough understanding of the
way the cotton plant develops and of how best to meet its needs, cotton yields have increased in all
regions and countries. Research continues to improve the technology for better harvests, but the
toughest challenges still await cotton in the future, for even the highest yielding countries in the
world have attained no more than 50% of the genetic potential of current varieties. New
technologies are continuously narrowing the gap between genetic and recoverable potential in all
fibre crops and thus so in cotton. Biotech cotton as an important component of integrated pest
management has contributed to increasing yields, lowering cost of production and producing cotton
with minimum use of toxic insecticides. Cotton still uses more insecticides (by value) compared to
other field crops but according to Cropnosis Ltd. (2009) recent trend shows that the share of plant
protection chemicals particularly insecticides (by sale value) used on cotton is on decline since
2000.
The world cotton industry is conscious of the fact that the industry needs to continue improving the
sustainability of cotton production. Not only the production practices have to be sustainable but
processing of cotton starting from ginning through to finished products should also be environment
friendly. Efforts are underway to improve economic, environmental and social sustainability of
cotton production and consumption. Organic cotton production is seen as one way of improving
sustainability along with no tillage and minimum tillage techniques.
Cotton consumption has increased at the same pace as production. Back in the 1950’s, only about
three million tons of all cotton production was sold in the international markets. International trade
of raw cotton increased to 9.8 million tons in 2005/06. Shrinking mill use in the European
Community and the United States combined with rising mill use in others has increased the amount
of cotton traded on the international market. Mill use of cotton has increased significantly in China
(Mainland), India, Pakistan and Turkey in the last two decades. Apart from traditional uses of
cotton, cotton use can be increased through composites. Müssig (2008) has presented a review of
cotton mixing with other natural fibres for various composite used.
Origin and History
The origin of the word cotton is still a mystery. However, there is a consensus in the specialized
literature that cotton was derived from the Arabic word al qatan. The oldest written record of the
use of cotton is found in a sacred Hindu text known as the Rig-Veda. Excavations at Mohenjo-daro,
in Pakistan, show that human beings were using cotton fabric as far back as 3,000 B. C. (Gulati and
Turner, 1928). Other discoveries in Peru show that people there were using cotton over 4,500 years
ago. It seems evident that the drive to adopt cotton as a fibre crop stems from peoples’ search for a
material from which to make clothing.
It is reasonable to believe that diploid cottons were used in the Indian sub-continent, whereas
tetraploid cottons prevailed in South America (in Peru and Mexico) before they spread to other parts
of the world. Flax, silk and wool were used long before cotton, and the literature shows that, in the
earliest times, the word cotton was used for many different kinds of fibres. There is no one
unanimous opinion on how cotton was domesticated by man and brought into widespread use, but
most of the work on the origin of cotton concurs in that man has transformed cultivated cotton
species. Fryxell (1979), however, considers it probable that lint production and species
differentiation came about before man took any real interest in the commercial production of cotton.
He also believes that the species were defined independently of each other.
According to Stewart (1994, updated in 2009) fifty species have been discovered so far, of which
nineteen have not yet been fully defined. Some of them are quite difficult to propagate and many
species do not even have the outgrowth (fibre) on the seed coat at all (Table 1). Despite the many
known species, there are only four recognized cultivar species of cotton: two diploid, Gossypium
arboreum and Gossypium herbaceum, and two tetraploid, Gossypium hirsutum and Gossypium
barbadense. The 2n = 26 diploid cottons are also called short staple cottons. G. hirsutum is usually
referred to as Upland cotton and all extra long staple/extra fine cottons (also known as Pima or Giza
types in Egypt) belong to G. barbadense. (The species known as Sea Island cotton also belongs to
G. barbadense).
Almost 97 % of all cotton produced around the world is accounted for by Upland cotton, with the
remainder – only 3 % of world production – made up by all other species.
Interspecific and
intraspecific commercial cotton hybrids are grown on over four million hectares in India. Hybrids
are also grown on a significant scale in China, Vietnam and some other countries, but their share in
world production is hard to establish. Diploid species are grown in Bangladesh, India, Iran,
Myanmar, Pakistan and Thailand, but India is the only country where all four cultivated species are
grown on a commercial scale. World cotton statistics indicate that about 90 % of all cotton is grown
in the Northern Hemisphere and about 10 % in the Southern Hemisphere.
Table 1: Recognized Gossypium Species, Organized by Germplasm Pools (Source: Compiled by
Dr. James McD. Stewart, University Professor, University of Arkansas, AR, USA (2009).)
Species
Genome1 Notes
Primary (1°) Germplasm Pool
G. hirsutum
AD1
Current & obsolete cultivars, breeding stocks, primitive and wild
accessions
G. barbadense
AD2
Current & obsolete cultivars, breeding stocks, primitive and wild
accessions
G. tomentosum
AD3
Wild, Hawaiian Islands
G. mustelinum
AD4
Wild, Northeast Brazil
G. darwinii
AD5
Wild, Galapagos Islands
Secondary (2o) Germplasm Pool
G. herbaceum
A1
Cultivars and land races of Africa and Asia Minor; one wild from
Southern Africa
G. arboreum
A2
Cultivars and land races from Asia Minor to Southeast Asia & China;
some African
G. anomalum
B1
Wild, two subspecies from Sahel and Southwest Africa
G. triphyllum
B2
Wild, Southwest Africa
G. capitis-viridis
B3
Wild, Cape Verde Islands
G. trifurcatum
(B)
Wild, Somalia
G. longicalyx
F1
Wild, trailing shrub, East Central Africa
G. thurberi
D1
Wild, Sonora Desert, USA
G. armourianum
D2-1
Wild, Baja California (San Marcos Island), USA
G. harknessii
D2-2
Wild, Baja California, USA
G. davidsonii
D3-d
Wild, Baja California Sur, USA
G. klotschianum
D3-k
Wild, Galapagos Islands
G. aridum
D4
Wild, arborescent, Pacific slopes of Mexico
G. raimondii
D5
Wild, Pacific slopes of Peru
G. gossypioides
D6
Wild, South central Oaxaca, Mexico
G. lobatum
D7
Wild, arborescent, Central to Eastern Michoacán
G. trilobum
D8
Wild, West central Mexico
G. laxum
D9
Wild, arborescent, Central Guerrero, Mexico
G. turneri
D10
Wild, North west Mexico
G. schwendimanii
D11
Wild, arborescent, South central Michoacán & East Guerrero, Mexico
G. sp. nov.
(D)
Eastern Guerrero, Mexico
Tertiary (3o) Germplasm Pool
G. sturtianum
C1
Wild, ornamental, Central Australia
G. robinsonii
C2
Wild, Western Australia
G. bickii
G1
Wild, Central Australia
G. australe
(G)
Wild, North Transaustralia
G. nelsonii
(G)
Wild, Central Australia
G. anapoides (new)
(K)
Wild, erect, North Kimberleys, Australia
G. costulatum
(K)
Wild, ascending, west coast N Kimberleys, Australia
G. cunninghamii
(K)
Wild, ascending, northern tip of NT, Australia
G. enthyle
(K)
Wild, erect, N Kimberleys, Australia
G. exgiuum
(K)
Wild, prostrate, N Kimberleys, Australia
G. londonerriense
(K)
Wild, ascending, N Kimberleys, Australia
G. marchantii
(K)
Wild decumbent, Australia
G. nobile
(K)
Wild, erect, N Kimberleys, Australia
G. pilosum
(K)
Wild, ascending, N Kimberleys, Australia
G. populifolium
(K)
Wild, ascending, N Kimberleys, Australia
G. pulchellum
(K)
Wild, erect, N Kimberleys, Australia
G. rotundifolium
(K)
Wild, prostrate, N Kimberleys, Australia
G. stocksii
E1
Wild, Arabian Peninsula and Horn of Africa
G. somalense
E2
Horn of Africa and Sudan
G. areysianum
E3
Arabian Peninsula
G. incanum
E4
Arabian Peninsula
G. bricchettii
(E)
Somalia
G. benadirense
(E)
Somalia, Ethiopia, Kenya
G. vollensenii
(E)
Somalia
1
The genomic grouping of the Australian species is under study. Where used.
( ) indicate provisional genomic placement for the species in question.
Phenology
The cotton plant is a perennial tree, but domesticated varieties were bred to grow as annuals. It has a
tap root system, and its fibrous roots may penetrate into the soil as deep as 1.5 – 1.8 meters in
search of nutrients and water (Chaudhry and Guitchounts, 2003). Thanks to its abundant root
system, cotton can manage to survive in water-deficit conditions, and that is why it is generally
considered to be a dryland crop.
Cotton is usually planted in late spring, allowed to remain in the field during the harsh summer
months, and harvested in early fall. After harvesting, the cotton seed has a dormancy period of
about one month. The seed germinates well in soils at a temperature of over 15 ºC and sufficient
moisture in the soil for the seed to absorb and bust allowing the root and shoot to be formed. Under
normal conditions, the seed germinates at 5 – 6 days after planting and, if by the tenth day the
germination rate is inadequate, the decision to replant can be made. Radicular growth is the first to
start, forming the root even before the plumule breaks through the surface to emerge from the soil
and form two cotyledonary leaves. At least 50 – 60 heat units are required for a seedling to break
the surface of the soil (Kerby and Hake, 1996).
In cotton, the cotyledonary leaves have a maximum life of 40 days and are different in shape from
true leaves. The first true branch usually emerges on the 5th to 6th node. The first branches on the
cotton plant are monopodial branches, sometimes also called vegetative branches. Monopodial
branches are few in number, no more than 5 – 6, and sometimes they may be merely rudimentary
with only sympodial branches visible on the plant. Monopodial branches do not bear fruit directly
and give the plant a more voluminous look as compared to a sympodial type of plant (Fryxell,
1984). The formation of monopodial branches ceases as soon as the first sympodial branch appears
on the plant. As a result of the fruiting function of the secondary and tertiary branches, monopodial
plants are usually characterized by late maturity.
The cotton plant has a palmate leaf with well developed mid rib and lobes. Deeper cuts in lobes may
turn the leaf shape into okra and super okra types, which are genetic characters (compare Figure 1).
The okra leaf shape, controlled by a single, partially dominant gene, was once thought to have a
negative correlation with yield, but this linkage has been broken or disproved and okra leaf varieties
are successfully grown on a commercial scale, although in a limited number of countries. The leaf
mid rib may have a nectary that secretes a sugary juice (food for insects) or the leaf may have no
nectary at all.
Figure 1: Different Leaf Shapes in Cotton
The cotton plant has a complete flower with well-defined calyx, corolla, androcium and gynaecium.
The five sepals are fused, and the bud/flower is covered by three heart shaped brackets/bracteoles
with deep cuts. The base of each bracket also has a nectary. Sepals, fused to form the calyx, do not
grow in size along with the petals (corolla) and style, but do anchor a large number of anther
filaments. The five petals are tightly folded and become visible through the bracteoles only a day
before the flower opens. The bud usually blooms into an open white flower 3 – 4 hours before noon,
and by then the anther dehiscence has already taken place, assuring self-pollination. Although the
stigma is still receptive at the time of petal opening, cross-pollination can take place only in the
presence of anthers. Pollen grains have spikes and are too heavy to be carried by the wind and,
therefore, have to be transported either by insects or manually. Technically, cotton is a crosspollinated crop, but under most conditions it behaves like a self-pollinated crop (Afzal and Ali,
1983; Munro, 1987).
A 2 % rate of natural outcrossing is common under most conditions whenever two varieties are
planted in close proximity (Chaudhry and Guitchounts, 2003; Afzal and Ali, 1983). A separation of
about fifty meters between varieties is usually considered enough to avoid any outcrossing.
Outcrossing may be higher – up to 50 % or even greater – but it depends on the time of anther
dehiscence, petal opening and insect activity in the field. Pollination takes place immediately as
pollen grains are shed but fertilization may take 12 – 20 hours. The ovary is superior with 4 – 5
carpels that ultimately become locks/lobes in an open boll. The ovules are linearly placed in two
rows in each lobe and each ovule must be fertilized to form a seed. Some diploid species may have
only three carpels or lobes and exceptionally some genotypes may have up to six lobes, but no
Upland varieties with such characters are in commercial cultivation anywhere in the world.
On the day following anthesis, the petals turn pink. The next day, they turn dark purple, start
withering and ultimately shed, leaving the young green bolls exposed to the vagaries of the weather.
Unfertilized flowers inevitably drop off. At about 35 days after planting, the first flowers can be
seen in the field, and it takes another 25 days for the buds to bloom into open flowers (see Figure 2).
Technically, flowers may be referred to as bolls as soon as they have been fertilized, but the actual
boll becomes visible only after the petals have been shed.
Figure 2: Open Cotton Flower
A freshly fertilized flower takes another 45 – 50 days to become an open boll ready to be picked.
All these time spans will ultimately be determined by the number of degree-days and other abiotic
growing conditions. There are, of course, differences among varieties, but they do not play decisive
roles. Early bud formation, together with the rate of horizontal and vertical flower/boll formation,
will determine crop maturity or earliness.
Plant Nutrition
Soil is composed of five components: air, water, organic matter, inorganic matter, or nutrients, and
microorganisms. The relative quality of soil depends on the proportions of these constituents. The
addition of organic matter increases the air- and water- retention capacity of soil and provides more
favourable conditions for microorganisms to survive and flourish. Cotton can best be grown on
sandy loam soils with a pH ranging from 6 to 8. The five elements that are applied to cotton are
nitrogen (N), phosphorous (P), potassium (K), boron (B) and sulphur (S). Zinc (Zn) and other
micronutrients are applied to cotton in fewer than five countries in the world (Chaudhry, 2008). In
others, like Ethiopia and Tanzania, farmers may not apply nitrogen to cotton because they cannot
afford it, but nitrogen is applied to cotton almost everywhere else. In countries, such as Argentina,
where it is still not applied commonly, research has established a positive effect on yield (Chaudhry,
2008).
The continuous use of nitrogen for over five decades has reduced the cost-benefit ratio compared to
the early days of the introduction of nitrogen. Nitrogen is applied to cotton in various forms, but all
of it is taken up from the soil by the plant in nitrate form (NO3). Nitrogen is usually split into 2 – 3
doses and applied prior to planting, the bud formation stage and at mid-boll formation stage (ICAC,
2008b). Nitrification must take into account losses into the air in the form of nitrogen gas, leaching
into the soil or utilization by diverse microorganisms before the plant manages to absorb it.
Nitrogen is a must for healthy plant growth, but too much nitrogen may result in an imbalance
between reproductive and vegetative growth.
Phosphorous is used by the plant as a growth regulator and, consequently, its impact on fibre quality
is minimal. Phosphorous does not move in the soil and the standard recommendation is always to
apply phosphorous before or during planting and work it well into the soil. Phosphorous deficiency
is more likely to occur in soils with a pH over 7.5, and phosphorous-deficient crops take on a dark
green colour and show stunted growth. A severe shortage may result in reddish-purple leaves,
reduced flowering and delayed maturity of set bolls. Older cotton leaves quickly translocate
phosphorous to younger bolls, so older leaves are more likely to show phosphorous deficiency
symptoms (Oosterhuis and Howard, 2008).
Potassium may or may not have an effect on yield. Potassium deficiency symptoms usually appear
in the form of yellowish-white mottling in the area between leaf veins or on the leaf margins. In
cases of severe deficiency, the leaves may be bronzed and curled downward, but symptoms always
proceed from the bottom to the top of the plant. The symptoms will depend on the availability of
potassium in the soil, so if potassium had been added to the preceding wheat crop, it is usually
recommended to skip any application of potassium on cotton. Potassium is most needed by the plant
at the boll maturing stage. Leaves and stem continue accumulating potassium during the vegetative
growth period, and leaves quickly give up their potassium to the maturing bolls. Of all the parts of
the cotton plant, bolls have the highest concentration of potassium (Awan, 1988).
Table 1: Chemical composition of the cotton plant parts (Source: Awan, 1988)
Plant Part
Nitrogen
Phosphorous
Potassium
Calcium
Magnesium
Sulfur
in %
in %
in %
in %
in %
in %
Root
0.82
0.12
1.06
0.45
0.25
0.06
Stem and branches
1.06
0.08
1.60
0.69
0.25
0.05
Leaves
2.30
0.15
2.49
3.15
0.52
0.42
Burr
1.08
0.18
3.50
1.28
0.26
0.17
Seed
3.13
0.43
2.10
0.18
0.33
0.33
Fibre
0.18
0.28
2.28
0.08
0.05
0.05
The addition of boron improves boll retention and boll opening by moving carbohydrates from the
leaves to the bolls. Boron also affects root tip growth, synthesis of DNA and RNA and plays an
important role in the elongation of the pollen tube thus enhancing seed setting. Soils with less that
1.5 % organic matter (sandy soils) are usually deficient in boron. All the boron is taken up by the
plant in the form of boric acid. Some soils may be naturally rich in boron and never require boron
application.
Sulfur is another micronutrient used on cotton in some countries. Organic matter is the primary
storehouse of sulfur in the soil; thus, soils low in organic matter may possibly require sulfur
applications (Chaudhry, 1999). Symptoms of calcium (Ca), magnesium (Mg), molybdenum (Mo),
copper (Cu), manganese (Mn) and zinc (Zn) deficiency are complicated and hard to differentiate
from nitrogen and other nutrient deficiencies. They are used only in very rare situations.
Physiology
The cotton plant, like all other plants, absorbs carbon, hydrogen and oxygen from the air. So, there
is no dearth of these elements for the cotton plant to carry on photosynthesis and grow.
Carbohydrates are formed during photosynthesis, and some plant species have the potential to
utilize almost all the carbohydrates formed during photosynthesis: these are known as C4 plants.
Thanks to their ready access to an abundant supply of carbohydrates, C4 plants have high growth
rates. The cotton plant is unable to utilize all available carbohydrates and tends to burn or release
some part into the air by photorespiration. Cotton photorespires about 30 % of the photosynthetic
rate and thus belongs to the category of C3 plants (Cothren, 1999). Photorespiration in cotton is
known to be catalyzed by the same enzyme that catalyzes the fixation of carbohydrates in the first
position. Thus, elimination of photorespiration to convert cotton to the C4 category does not seem to
be possible.
Of all the approaches used to try to minimize the photorespiration rate in cotton, only two are worth
mentioning: application of methanol and CO2 enrichment (Mauney et al., 1992). Both methods
showed promise in the early experimental stages, but neither could be successfully commercialized
in any country.
The cotton plant produces many times more leaves than it does bolls. Genetically, each and every
axil of a leaf, on the main stem or on the branches, is supposed to bear either a branch or a fruiting
bud. This is, in fact, the case but most fruiting buds are shed even before they become visible to the
naked eye. Thus, the real number of bolls that will remain on the plant to maturity is only a small
percentage of the actual boll spots occurring on the plant.
The shedding of fruit forms is inevitable in cotton because of many factors. There are two
physiological theories of fruit shedding in cotton. (1) The balance between auxin and growthretarding hormones is disturbed and the result is shedding. The anti-auxin hormones increase in
quantity and become more active, signaling the plant to form bolls at a slower rate or even
inhibiting the formation of any more bolls on the plant. Guin (1986) has discussed in detail the role
of hormones in abscission during reproduction. (2) The number of bolls increases beyond a certain
limit determined by the vegetative mass of the plant, thus reducing the availability of carbohydrates
and inhibiting the formation of bolls. Extremely high temperatures can hamper fertilization and that
too results in shedding. Insect pressure and various other types of stress also cause shedding, but
those factors affect buds more than anything else. Fertilized flowers are rarely shed. When bolls are
shed, more often than not, it will be due to abiotic stresses, such as water shortages, nutrient
deficiencies and insect damage.
The leaf is the most important part of the cotton plant. The leaves are the food factory for the plant,
and, in cotton, only healthy leaves can bear fruiting buds, flowers and bolls. Physiologists have
determined that leaves on the 5th node from the top are the most active on the plant (See details in
Chaudhry, 2002). Leaf condition is a good indicator of plant health, nutrient status, water deficiency
and insect pest damage, particularly sucking insects, as well as of most diseases. Leaves that are
affected by insect pests become incapable of retaining buds and shed them at a very early stage.
Leaves must be healthy to have a good harvest.
As in all deciduous trees, cotton leaves mature and reach their natural shedding stage. As the leaves
age, an abscission layer, which is carbohydrate in nature, is formed between the leaf petiole and the
stem or branch. The process of abscission layer formation is enhanced in cotton by the application
of desiccants and defoliants. Defoliation is a pre-requisite for machine picking of cotton, but when
harvest aids are applied too early in the cycle of the plant, i.e., when less than 60 to 70 % of the
bolls have opened, it reduces the yield and also affects fibre quality. Leaves may be hairy or nonhairy and they come in various shades of green or red. Average growth and fruiting period is given
below.
Growth and Fruiting of Cotton
Stage
Period
Plant Age
Planting to emergence
4 to 10 days
4 –10 days
Emergence to first true leaf
8 days
12 – 18 days
Emergence to second true leaf
9 days
21 – 27 days
Second true leaf to pinhead square (seventh node)
18 to 21 days
39 – 48 days
Pinhead square to matchhead square
9 to 10 days
48 – 58 days
Matchhead square to first one-third grown square
3 to 6 days
51 – 64 days
First one-third grown square to first white bloom
12 to 16 days
63 – 80 days
First white bloom to first open bolls
40 to 60 days
103 – 140 days
Harvest bolls set in first four weeks of blooming
96 %
91
Insect Pests and Their Control
– 128 days
The cotton plant is naturally vulnerable to damage by a number of insect pests. About 17 % (by
value) of all insecticides used worldwide are sprayed on cotton, making it the top insecticide
consumer among all field crops. On the other hand, cotton’s share of pesticide use (by value) is less
than 8%, and it has been declining steadily over the last 10 years (various reports from Cropnosis
Ltd., Edinburgh, UK). The Mexican boll weevil, Anthonomus grandis, which is limited to the
Americas, is the most destructive pest in the Western Hemisphere. Elsewhere in the world, the
American bollworm, Helicoverpa armigera, is the most widespread and most commonly occurring
pest on cotton. The pink bollworm, Pectinophora gossypiella, was once a more serious pest,
particularly in China, India and Pakistan, but now the American bollworm has taken the lead.
Among sucking insects, the whitefly, Bemisia tabaci, is the most widely occurring and serious pest
on cotton. The whitefly has spread to many countries in the last two decades.
The American bollworm and the whitefly are notorious for developing resistance to insecticides.
Repeated use of a particular chemical product on multiple generations year after year stimulates the
insect’s ability to tolerate higher doses of insecticide. The basic resistance development mechanisms
reported in cotton insects are: reduced penetration through the cuticle, ability to metabolize and
excrete toxic chemicals, insensitivity of the target site (nervous system), development by the insect
of resistant genes that are passed on to subsequent generations (Russell, 2005; Kranthi, 2004) .
Australia, China, India, Pakistan and many West African countries have had to deal with this
situation because of the indiscriminate use of insecticides. The problem has been resolved through
the application of a wise rule of thumb: use insecticides only as a last resort. Other useful
recommendations are: avoid using a single class of chemical over a long period of time; program
insecticide applications to hit the most susceptible stage in the life cycle of the insect; do not
underdose or overdose insecticides; spray properly at the recommended thresholds and, when
choices are available, use different classes of chemicals every year.
Insecticide use is on the decline in most countries, and the future of pest control in cotton lies in
integrated pest management, wherein biotech cotton (compare chapter IV.5 DNA-analytical method
for the identification of animal and plant fibres) would be an important component. External control
through chemicals will ultimately be replaced by a combination of control measures, including:
biological control (natural and specially introduced), host plant resistance, cultural control,
legislative control, special control (e.g., male sterility) and above all, biotech control.
Among the pests affecting cotton are: arthropods, mites, pathogens and weeds. Research in various
countries has shown that it is extremely important to control weeds in order to get the maximum
benefit from fertilizers and insect and disease control. Cultural control of weeds is the most
widespread method, but it is slowly being replaced by herbicides. Biological control was tried for
decades against various weeds but never attained commercial scale. Biological weed control is the
intentional release of pathogens to attack specific weeds, but, when there are a wide variety of
weeds (broad leaf and grasses) occurring at the same time, it becomes impossible to control all of
them with a single pathogen. Furthermore, the high cost of pathogen augmentation, environmental
impact on pathogen activity (including low weed population), negative effects on the cotton plant
and poor effectiveness in getting rid of weeds at early stages are some of the other difficulties that
worked against the use of biological methods to control weeds. The only non-chemical control
method that is gaining ground is conservation tillage, but it is impractical when the amount of land
is limited, as is the case in small-scale farming systems. Herbicides have their own consequences
but, because of their ability to control weeds more effectively, herbicide use will continue to spread
to more countries.
The important diseases affecting cotton are fusarium wilt, caused by Fusarium oxisporum,
verticilium wilt, caused by Verticillium dahliae, seedling damping-off, caused by Rhizoctonia
solani and bacterial blight, caused by Xanthomonas campestris pv. malvacearum. Leaf curl virus
disease caused by geminiviruses has been wreaking havoc in Pakistan since 1992/93. The whitefly
is the primary vector of cotton leaf curl virus (CLCV) disease, which was already an established
pest in Pakistan. The disease also spread to India and has been detected in China. In the past, the
cotton leaf curl virus disease caused damage in Sudan but has never been as big a threat as it is now.
Most diseases in the world are controlled either through seed treatment or cultural means if the
genetic resistance to the pathogen/disease is not available in the germplasm. Chemical control has
been reported in a number of countries, but cotton rarely receives consecutive chemical sprays
against diseases in any country. A latent threat from diseases will always exist.
Biotech Cotton
Herbicide resistant biotech cotton was planted on a commercial scale for the first time in the United
States in 1995/96. The following year biotech cotton resistant to lepidoptera was planted on a
commercial scale in Australia and the U.S. Herbicide plus insect resistant stacked gene biotech
cotton became commercially available in 1997/98. By 2008/09, eleven countries had approved
biotech cotton. Many genes were identified and inserted into the cotton genome in the first 14 years
after the adoption of biotech cotton in the 1990’s, but cry1Ac (Mon 531) has continued to be the
leading gene for over 15 years in the area of insect control.
Biotechnology is the technology with the fastest rate of adoption in the history of agriculture.
Among its major benefits are: higher yields, lower insecticide requirements, environmental safety,
human safety and lower cost of production. The benefits are not uniform and vary greatly from
country to country, from environmental safety alone to the whole range of the abovementioned
benefits. The technology also came with a number of conditions: producers had to plant refuge
crops, biosafety regulations had to be adopted, along with suspicions especially in the context of
future events.
By the 2008/09 season, Argentina, Australia, Brazil, Burkina Faso, China, Colombia, India,
Indonesia, Mexico, South Africa and the United States had already commercialized biotech cotton.
Burkina Faso commercialized biotech cotton in June 2008, and many other countries are
experimenting with it. Biosafety regulations/protocols and technology fees are the two main hurdles
standing in the way of the adoption of biotech cotton. Biotechnology research, not only in cotton,
but in general, received a big boost from the adoption of biotech crops. Many countries have
invested heavily in biotechnology research because they believe that the future of crop improvement
lies in biotechnology applications.
In spite of the advantages of biotechnology, the field is not free of controversy, particularly with
respect to food crops. A clear distinction must be made between the technology and the product.
The technology is the ability to isolate and insert genes into non-related species, whereas the
product or products developed through biotechnology are the insect and herbicide resistant cottons
currently in use. A given product may or may not be good, but the technology cannot be denied or
discarded. There is no doubt that biotechnology can be misused, as was the case with the
Technology Protection System in cotton, but that threat is not exclusive to biotechnology.
The biotech transgenes currently available in cotton, as well as in many other crops and fields of
endeavor, are just the beginning. They are the vanguard of a great many things yet to come.
Fertilizer efficiency, gene silencing, higher photosynthetic rates (for higher yields), transgene
breeding within Gossypium species, enhanced oil content in the seed and many more aspects are
already being explored. SmartStaxT (Monsanto, St. Louis, USA and Dow AgroSciences LLC,
Indianapolis, USA), the biotechnology industry's first-ever eight-gene stacked combination in corn,
is already close to becoming a reality. Crop breeding is now moving toward “directed breeding” and
the development of custom tailored genotypes.
Biotechnology has the potential to improve water, energy and stress management, as well as fibre
quality. In cotton, the second generation of products will come in the form of drought-tolerant and
fertilizer-efficient plants. The focus is shifting from altered agronomic traits to management of
abiotic stresses. The possibility also exists of using the cotton plant as a biofactory in which to
isolate the genes that encode the required biosynthetic enzymes and then returning them to the
cotton plant to produce the compounds of interest.
The third generation of biotech products may likely address the issue of improved lint quality,
particularly in the form of longer and stronger fibres.
Cotton Harvesting and Ginning
Most of the world’s cotton is hand picked. Cotton is picked entirely by machine only in Australia,
the Brazilian savannas, Greece, Israel, Spain and the US. The decision to employ hand pickers or
mechanized picking is determined exclusively by labour availability and cost. Hand picking is a
gentler way of picking cotton and thus technically preferred over machine picking. Hand picking
preserves fibre quality and also does not require extensive cleaning during ginning.
There are only two kinds of seedcotton harvesters, i.e. pickers and strippers. Pickers, also called
spindle pickers, were introduced in the U.S. in 1942 (Baker and Griffin, 1984). Multiple columns of
rotating spindles are arranged around a rotating drum which projects the spindles toward the open
bolls on the plant. The rotating spindles wrap the seedcotton around them; then the rotary or
stripped doffer brushes the seedcotton away from the spindles. The seedcotton thus removed is
collected in a basket behind the tractor. Pickers are now available that can pick cotton at variable
row distances and the seedcotton can be packed into small bales and heaped in the field.
Mechanized baling of seedcotton as part of the picking process saves time and eliminates the need
to stop the picking operation to allow time to empty the basket. The stripper harvester strips the
entire plant carrying away open bolls, non-open bolls and a great deal of plant material.
Figure 3: Cotton field ready for picking (left); Machine picking of cotton (right)
The big difference between machine picking and hand picking (aside from the greater stress the
fibre suffers) is the quantity of trash in the seedcotton (compare chapter IV.6 - Cotton / Worldwide
Standardisation & Harmonisation). Hand picking has the least trash, followed by picker harvesting.
Picker harvesting may have 6 – 8 % trash, depending on the extent of defoliation, but about 10 to 12
% of the seedcotton is lost in picking. Most of the lost seedcotton falls to the ground, but some
remains on the plant. Stripper-harvested cotton may have up to 25 % trash. Moreover, stripped
cotton may have higher nep content, higher short fibre content, shorter staple length and a lower
uniformity ratio compared to spindle-picked cotton. Stripper picking is less expensive than spindle
picking. Mechanically harvested cotton is usually stored in modules in the field before being taken
to the gin.
Ginning is the process of separating lint from seed. Basically, only two types of gins are available in
the world, roller gins and saw gins. In roller ginning, fibres are held between the rollers and pulled
away from the seed coat. Roller ginning is relatively slow process, but it preserves fibre quality
better than saw ginning. On the other hand, roller ginning allows trash, motes and immature seeds to
be carried through the rollers and in with the lint. The trend in roller ginning today is toward
aggressive cleaning of the seedcotton and gentle cleaning of the lint to limit fibre damage
(Whitelock et al., 2007). Recently, more efficient roller gins have been developed but they are still
not as efficient as saw gins.
The development of the saw gin by Eli Whitney in 1793 (see Figure 4) revolutionized cotton
ginning and paved the way for large-scale production and processing of cotton (see Figure 5).
Figure 4: The saw gin by Eli Whitney; adapted from Eli Whitney's Patent for the Cotton gin, March
14, 1794; Records of the Patent and Trademark Office; Record Group 241, National Archives.
Figure 5: Schematic Drawing of a Ginning Process .- adapted from (Continental Eagle Corporation,
Prattville, U.S.A., 2009).
Now, about 85 % of all the cotton in the world is ginned on saw gins. Most countries have either
saw gins or roller gins, except in Egypt where only roller ginning is done because the country grows
only long staple and extra long staple cotton, i.e., G. barbadense. Countries like India, Sudan, the
U.S. and some Central Asian countries where G. hirsutum and G. barbadense are produced at the
same time have saw gins as well as roller gins. Some African countries, particularly in Eastern
Africa, gin medium staple cotton, i.e. G. hirsutum, on roller gins.
The saw gin process is relatively harsh. It involves pulling as well as beating actions. Modern saw
gins vary greatly in their design but, in practical terms, they all operate on the same basic ginning
principle. Depending upon its trash content, seedcotton may pass through multiple processing stages
to eliminate bolls, sticks and other trash before the seedcotton reaches an actual gin stand. The gin
saws, rotating at a high rate of speed, grasp the seedcotton and draw it through huller ribs spaced
between the saws. Fibres are easily drawn through the closely spaced ginning ribs, but the ribs are
placed in such a way that the seeds cannot pass through the spaces between them. The saws, moving
in a clockwise direction, push the fibres through to the backside of the gin stand while the seeds are
collected at the bottom. The fibres are then carried by an air stream to the lint cleaners for further
processing. The lint comes out fluffy, and part of the trash is automatically eliminated during
ginning.
The ginning process may be harsh, but it is still sensitive to the moisture content of the seedcotton.
Fibre quality can best be preserved when the seedcotton is ginned at an 8 % moisture content. A
seedcotton moisture level below 8 % improves lint grade, but reduces lint colour and increases short
fibre content. Thus, the ginning process comprises cleaning of seedcotton and lint, along with
separation of the lint from the seeds, all in a rigorous sequence of precise actions, including
adjustment of humidity and temperature. Recently, a sensor-based ginning system called
“IntelliGin” has been developed. It automatically adjusts humidity, temperature and cleaning to
achieve the best ginning results (Yankey, 1999).
The thermopneumatic and mechanical processing of cotton does not affect many fibre qualities but
does seriously affect fibre length. Fibre breakage is much higher in saw ginning, resulting in shorter
fibre length and higher short fibre content. Length uniformity, as well as strength, are both slightly
compromised as a consequence of the shorter fibres, but micronaire and colour remain intact
(compare chapter IV.6 - Cotton / Worldwide Standardisation & Harmonisation).
Unginned, hand picked cotton does not have neps, so neps are attributed to machine picking and
ginning processes. Saw ginning produces more neps than roller ginning. Lint samples are drawn for
quality testing before the cotton is pressed and formed into bales. Most experts recommend
wrapping bales in cotton fabric and pressing them at a standard density, but bale density and size
continue to vary greatly among countries (ICAC, 2008b). Bales must be stored at 7.5 % moisture in
order to avoid lint colour degradation.
Torn between the facts that roller ginning is comparatively slow and saw ginning is relatively harsh,
the industry has been exploring a number of new ginning technologies, including differential
ginning, cage ginning and Templeton rotary ginning (Chaudhry, 1997). The objective is to preserve
the quality of the roller gin and attain the speed of the saw gin. Humidity and temperature
adjustments, along with the cleaning process, also require improvement. So, the third goal in
ginning research is minimal processing of cotton without sacrificing cleanliness and quality.
Organic Cotton
Cotton grown without the use of synthetically compounded chemicals, such as pesticides, growth
regulators, defoliants, fertilizers, etc., is called organic cotton. Organic farming started in England
based on the theories developed by Albert Howard in An Agricultural Testament; biodynamic
agriculture developed from the teachings of Rudolf Steiner, in Germany in the 1920s; and biological
agriculture started in Switzerland by Hans-Peter Rusch (Wakelyn and Chaudhry, 2007). Other terms
used interchangeably to describe organic cotton are: ‘green,’ ‘biological’ ,‘clean,’ ‘natural’ and
‘ecological’ cotton.
The United States National Organic Standards Board defined organic production as follows:
“Organic agriculture is an ecological production management system that promotes and enhances
biodiversity, biological cycles and soil biological activity. It is based on minimal use of off-farm
inputs and on management practices that restore, maintain and enhance ecological harmony (AMS,
2009).” The basic standards of the International Federation of Organic Agriculture Movement
(IFOAM) state that “Organic agriculture [also known as “Biological” or “Ecological” agriculture or
protected equivalent forms of these words (in other languages)] is a whole-system approach based
upon a set of processes resulting in a sustainable ecosystem, safe food, good nutrition, animal
welfare and social justice. Organic production therefore is more than a system of production that
includes or excludes certain inputs (IFOAM, 2008).”
Organic cotton may also be defined in many other ways, but all organic cotton production must
comply with the requirements of “certified organic” cotton. For cotton to be sold as ‘organic
cotton’, it must be certified by an independent organization that verifies that it meets or exceeds
defined organic agricultural production standards. Each certifying company may have its own
standards and list of allowed and prohibited products, but all agree that biotech cotton, in any form,
is not eligible for certification as organic cotton. Extensive use of biotech varieties has affected the
organic cotton area in the USA. Many countries have defined criteria for organic labelling and
despite all deviations between different regulations one clear agreement can be identified – the
absolute ban on genetic engineering (compare chapter IV.5 - DNA-analytical method for the
identification of animal and plant fibres ).
Commercial production of organic cotton started in the early 1990s in Egypt and the United States.
About 12,000 tons of organic cotton was produced in the world in 1995/96, and the U.S. share was
about 65 %. But since the adoption of biotech cotton, organic production in the USA has declined to
only 2 % of world production in 2007/08. Twenty-one countries produced organic cotton in
2007/08, and production reached over 140,000 tons (Figure 1). The three major post-ginning
processes in the conversion of raw cotton fibre into a finished fabric are: spinning, fabric
manufacturing (weaving and knitting), and dyeing and finishing. To produce organic textiles,
certified organically produced cotton must be processed according to processes certified as organic.
All wet processing facilities should have water conservation and resource management in place and
should conform to waste water disposal standards.
Figure 6: Organic cotton production in the world
The term organic is a labelling or marketing tool. Organic producers and promoters assert that
organic production is more sustainable and environmentally friendly than conventional production.
No one can doubt that conventional production uses more toxic chemicals, but either method can be
sustainable. The one is more environmentally friendly while the other may be more economically
friendly. The United Nations Commission on Environment and Development implies sustainability
as “Sustainable development is a development that meets the needs of the present without
compromising the ability of future generations to meet their own needs” (1987). The three
fundamentals of sustainability are environmental, social and economical and organic cotton as well
as conventional cotton can meet these criteria. Organic production is at least as technical as
conventional production, if not more so. People started producing organic cotton without any
extensive research to determine the most suitable varieties for organic production, weed control
methods and so on.
Unfortunately, there is still not enough research in the area of organic cotton for efficient
production. With the increased emphasis on minimal use of agrochemicals, particularly pesticides
for sustained production of conventional cotton, production of organic cotton would appear to have
a future. Organic cotton will continue to hold a small niche in the market, but it must be developed
into a producer-driven initiative rather than a labelling or a marketing tool. Less expensive and
more effective means of pest control, soil enrichment and harvest aids (in the case of mechanical
picking) must be explored and implemented within the organic standards.
Conclusion
Cotton is the most important natural fibre. Many species of cotton are known but only four of them
are grown on commercial scale. Approximately 97 % of all cotton produced belongs to the species
G. hirsutum, 3 % to G. barbadense and less that 1 % are G. arboreum and G. herbaceum. The
cotton plant is naturally vulnerable to a variety of pests, particularly insects. After over two decades
of extensive insecticide use in cotton, integrated pest management applications are reducing the
number of insecticide applications on cotton. Insect resistant biotech cotton has emerged as a
successful alternative for controlling lepidopteron insects. The awareness to produce and process
cotton using sustainable methods is growing. Almost half of the cotton produced in the world gets
assured irrigation while the other half comes from rainfed conditions. Most cotton is still picked by
hand, machine picking is adopted only if labour is not available or expensive. Organic cotton is less
than 1 % of world production and will continue as a niche market. There is a great need to find
alternate uses of cotton for enhancing cotton consumption in the world. High man-made fibre prices
and recent technological development has opened new avenues for cotton to be used in making
‘non-wovens’ and mixing with other natural fibres for producing biodegradable composites. Cotton
can also be mixed with man-made fibres depending upon mechanical and morphological properties
of the mixing materials and resultant products.
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