Cotton: World’s Leading Agricultural Crop (Thoroughly Explained)

Cotton, one of the world’s leading agricultural crops, is plentiful and economically produced, making cotton products relatively inexpensive. The fibres can be made into a wide variety of fabrics ranging from lightweight voiles and laces to heavy sailcloths and thick-piled velveteens, suitable for a great variety of wearing apparel, home furnishings, and industrial uses.

What Is Cotton?

Cotton is a staple fiber, which means it is composed of different, varying lengths of fibers. It is made from the natural fibers of cotton plants, which are from the genus Gossypium.

It is primarily composed of cellulose, an insoluble organic compound crucial to plant structure, and is a soft and fluffy material. The cotton plant needs lots of sun, a long period without frost, and a good amount of rain.

The term “cotton” refers to the part of the cotton plant that grows in the boll—the encasing for the fluffy cotton fibers. It is spun into yarn that is then woven to create a soft, durable fabric.

Scientific Classification

  • Kingdom: Plantae
  • Division: Magnoliophyta
  • Class: Magnoliopsida
  • Order: Malvales
  • Family: Malvaceae
  • Genus: Gossypium

Etymology

The word “cotton” has Arabic origins, derived from the Arabic word قطن (qutn or qutun). This was the usual word for cotton in medieval Arabic. The word entered the Romance languages in the mid-12th century, and English a century later. Its fabric was known to the ancient Romans as an import but cotton was rare in the Romance-speaking lands until imports from the Arabic-speaking lands in the later medieval era at transformatively lower prices.]

Genome

There is a public effort to sequence the genome of cotton. It was started in 2007 by a consortium of public researchers. Their aim is to sequence the genome of cultivated, tetraploid cotton. “Tetraploid” means that its nucleus has two separate genomes, called A and D. The consortium agreed to first sequence the D-genome wild relative of cultivated cotton (G. raimondii, a Central American species) because it is small and has few repetitive elements.

It has nearly one-third of the bases of tetraploid cotton, and each chromosome occurs only once.[clarification needed] Then, the A genome of G. arboreum would be sequenced. Its genome is roughly twice that of G. raimondii. Part of the difference in size is due to the amplification of retrotransposons (GORGE). After both diploid genomes are assembled, they would be used as models for sequencing the genomes of tetraploid cultivated species.

Without knowing the diploid genomes, the euchromatic DNA sequences of AD genomes would co-assemble, and their repetitive elements would assemble independently into A and D sequences respectively. There would be no way to untangle the mess of AD sequences without comparing them to their diploid counterparts.

The public sector effort continues with the goal to create a high-quality, draft genome sequence from reads generated by all sources. The effort has generated Sanger reads of BACs, fosmids, and plasmids, as well as 454 reads. These later types of reads will be instrumental in assembling an initial draft of the D genome. In 2010, the companies Monsanto and Illumina completed enough Illumina sequencing to cover the D genome of G. raimondii about 50x.

They announced that they would donate their raw reads to the public. This public relations effort gave them some recognition for sequencing the cotton genome. Once the D genome is assembled from all of this raw material, it will undoubtedly assist in the assembly of the AD genomes of cultivated varieties of cotton, but much work remains.

As of 2014, at least one assembled cotton genome had been reported.

Where Did Cotton Originate?

The word cotton comes from the Arabic word “quton.” The earliest production of cotton was in India, where the material dates back to the fifth millennium B.C.

The first cotton gin, which is a tool that separates the cotton fluff from the plant seeds, was invented in India in the thirteenth century. The cotton gin made the production of cotton much easier and faster, helping the fiber spread as a widely-used textile.

During the Industrial Revolution, with the invention of new technologies like the spinning jenny, spinning frame, and spinning mule, Britain became one of the leading cotton producers. All of these spinning machines allowed manufacturers to spin cotton at increased rates.

However, it was the American Eli Whitney’s invention of the mechanical cotton gin which led to increased production of the material in the United States and Europe. This new tool, which separated the seeds from the cotton quickly and efficiently using machine power, cut down the hours of manual labor needed to produce a bale of cotton from 600 hours to just 12. Around the same time, America, particularly the Southern states, began producing more high-quality cotton, as the fibers were slightly longer and stronger.

With a few occasional falls in production, such as during the Civil War, the United States is still one of the leading producers of cotton in the world, falling just behind China and India.

Where Does Cotton Grow?

Cotton grows in nearly all tropical and subtropical regions around the world, including the U.S., China, India, Uzbekistan, Pakistan, Brazil, and Turkey.

In the United States, Texas is the largest cotton producer, and the South Plains region in the northern part of the state is the largest contiguous cotton-growing area in the world.

Different Types of Cotton

There are four commercially grown species of cotton, all domesticated in antiquity:

  1. Gossypium hirsutum: Upland cotton, native to Central America, Mexico, the Caribbean, and southern Florida (90% of world production).
  2. Gossypium barbadense: Known as extra-long-staple cotton, native to tropical South America (8% of world production).
  3. Gossypium arboreum: Tree cotton, native to India and Pakistan (less than 2%).
  4. Gossypium herbaceum: Levant cotton, native to southern Africa and the Arabian Peninsula (less than 2%).

Types of cotton based on fibre characteristics.

Pima cotton: Considered the finest type of cotton in the world, Pima cotton’s fibers are extra soft and extra long. The cotton is native to South America and the American Southwest. Pima cotton fabric is very highly sought after, as it is resistant to fading, tearing, and wrinkling.

Egyptian cotton: Egyptian cotton is very similar to Pima cotton. The two are even in the same scientific class: Gossypium barbadense. It has the same resistant qualities, but it is grown in the Nile River Valley in Egypt.

Upland cotton: Upland cotton has very short fibers and makes up about 90% of the world’s total cotton production. The crop is native to and grown in Central America, Mexico, the Caribbean, and southern Florida.

Organic cotton: Organic cotton is any type of cotton that is grown without chemicals and from plants that are not genetically engineered.

Hybrid varieties are also cultivated. The two New World cotton species account for the vast majority of modern cotton production, but the two Old World species were widely used before the 1900s. While cotton fibers occur naturally in colors of white, brown, pink, and green, fears of contaminating the genetics of white cotton have led many cotton-growing locations to ban the growing of colored cotton varieties.

Cultivation of the Cotton Plant

The various species of cotton grown as agricultural crops are native to most subtropical parts of the world and were domesticated independently multiple times. Cotton can be found as perennial treelike plants in tropical climates but is normally cultivated as a shrubby annual in temperate climates.

Whereas it grows up to 6 meters (20 feet) high in the tropics, it characteristically ranges from 1 to 2 meters (3 to 6.5 feet) in height under cultivation. Within 80–100 days after planting, the plant develops white blossoms, which change to a reddish color.

The fertilized blossoms fall off after a few days and are replaced by small green triangular pods, called bolls, that mature after a period of 55–80 days. During this period the seeds and their attached hairs develop within the boll, which increases considerably in size. The seed hair, or cotton fibre, reaching a maximum length of about 6 cm (2.5 inches) in long-fibre varieties, is known as lint.

Linters, fibres considerably shorter than the seed hair and more closely connected to the seed, come from a second growth beginning about 10 days after the first seed hairs begin to develop. When ripe, the boll bursts into a white, fluffy ball containing three to five cells, each having 7 to 10 seeds embedded in a mass of seed fibres.

Two-thirds of the weight of the seed cotton (i.e., the seed with the adhering seed hair) consists of the seeds. The fibres are composed of about 87 to 90 percent cellulose (a carbohydrate plant substance), 5 to 8 percent water, and 4 to 6 percent natural impurities.

Although cotton can be grown between latitudes 30° N and 30° S, yield and fibre quality are considerably influenced by climatic conditions, and best qualities are obtained with high moisture levels resulting from rainfall or irrigation during the growing season and a dry, warm season during the picking period.

To avoid damage to the cotton by wind or rain, it is picked as soon as the bolls open, but since the bolls do not all reach maturity simultaneously, an optimum time is chosen for harvesting by mechanical means. Handpicking, carried out over a period of several days, allows selection of the mature and opened bolls, so that a higher yield is possible.

Handpicking also produces considerably cleaner cotton; mechanical harvesters pick the bolls by suction, accumulating loose material, dust, and dirt, and cannot distinguish between good and discolored cotton. A chemical defoliant is usually applied before mechanical picking to cause the plants to shed their leaves, thus encouraging more uniform ripening of the bolls.

Morphology

Cotton has a more complex structure than the other crops. A matured cotton fiber is a single, elongated complete dried multilayer cell that develops in the surface layer of cottonseed. It has the following parts.

The cuticle is the outermost layer. It is a waxy layer that contains pectins and proteinaceous materials.
The primary wall is the original thin cell wall. Primary wall is mainly cellulose, it is made up of a network of fine fibrils (small strands of cellulose).

The winding layer is the first layer of secondary thickening it is also called the S1 layer. It is different in structure from both the primary wall and the remainder of the secondary wall. It consists of fibrils aligned at 40 to 70-degree angles to the fiber axis in an open netting type of pattern.

The secondary wall consists of concentric layers of cellulose it is also called the S2 layer, that constitute the main portion of the cotton fiber. After the fiber has attained its maximum diameter, new layers of cellulose are added to form the secondary wall. The fibrils are deposited at 70 to 80-degree angles to the fiber axis, reversing angle at points along the length of the fiber.

The lumen is the hollow canal that runs the length of the fiber. It is filled with living protoplast during the growth period. After the fiber matures and the boll opens, the protoplast dries up, and the lumen naturally collapses, leaving a central void, or pore space, in each fiber. It separates the secondary wall from the lumen and appears to be more resistant to certain reagents than the secondary wall layers. The lumen wall is also called the S3 layer.

Pests and Diseases

Cotton is attacked by several hundred species of insects, including such harmful species as the boll weevil, pink bollworm, cotton leafworm, cotton flea hopper, cotton aphid, rapid plant bug, conchuela, southern green stinkbug, spider mites (red spiders), grasshoppers, thrips, and tarnished plant bugs. Limited control of damage by insect pests can be achieved by proper timing of planting and other cultural practices or by selective breeding of varieties having some resistance to insect damage.

Chemical insecticides, which were first introduced in the early 1900s, require careful and selective use because of ecological considerations but appear to be the most effective and efficient means of control. Conventional cotton production requires more insecticides than any other major crop, and the production of organic cotton, which relies on nonsynthetic insecticides, has been increasing in many places worldwide.

Additionally, genetically modified “Bt cotton” was developed to produce bacterial proteins that are toxic to herbivorous insects, ostensibly reducing the number of pesticides needed (). Glyphosate-resistant cotton, which can tolerate the herbicide glyphosate, was also developed through genetic engineering.

The boll weevil (Anthonomus grandis), the most serious cotton pest in the United States in the early 1900s, was finally controlled by appropriate cultivation methods and by the application of such insecticides as chlorinated hydrocarbons and organophosphates.

A species of boll weevil resistant to chlorinated hydrocarbons was recorded in the late 1950s; this species is combatted effectively with a mixture of toxaphene and DDT (dichlorodiphenyltrichloroethane), which has been outlawed in the United States and some other countries, however.

The pink bollworm (Pectinophora gossypiella), originally reported in India in 1842, has spread throughout the cotton-producing countries, causing average annual crop losses of up to 25 percent in, for example, India, Egypt, China, and Brazil.

Controls and quarantines of affected areas have helped limit the spread of the insect, and eradication has been possible in a few relatively small areas with sufficiently strict controls. The bollworm (Heliothis zea, also known as the corn earworm) feeds on cotton and many other wild and cultivated plants. Properly timed insecticide application provides fairly effective control.

Its plants are subject to diseases caused by various pathogenic fungi, bacteria, and viruses and to damage by nematodes (parasitic worms) and physiological disturbances also classified as diseases. Losses have been estimated as high as 50 percent in some African countries and in Brazil.

Because young seedlings are especially sensitive to attack by a complex of disease organisms, treatment of seeds before planting is common. Some varieties have been bred that are resistant to a bacterial disease called angular leaf spot.

Soil fumigation moderately succeeded in combatting such fungus diseases as fusarium wilt, verticillium wilt, and Texas root rot, which are restricted to certain conditions of soil, rainfall, and the general climate. The breeding of resistant varieties, however, has been more effective.

Pests

  • Boll weevil, Anthonomus grandis
  • Cotton aphid, Aphis gossypii
  • Cotton stainer, Dysdercus koenigii
  • Cotton bollworm, Helicoverpa zea, and native budworm, Helicoverpa punctigera, are caterpillars that damage cotton crops.
  • Some other Lepidoptera (butterfly and moth) larvae also feed on cotton – see list of Lepidoptera that feed on cotton plants.
  • Green mirid (Creontiades dilutus), a sucking insect
  • Spider mites, Tetranychus urticae, T. ludeni and T. lambi
  • Thrips, Thrips tabaci and Frankliniella schultzei

Diseases

  • Alternaria leaf spot, caused by Alternaria macrospora and Alternaria alternata
  • Anthracnose boll rot, caused by Colletotrichum gossypii
  • Black root rot, caused by the fungus Thielaviopsis basicola
  • Blight caused by Xanthomonas campestris pv. malvacearum
  • Fusarium boll rot caused by Fusarium spp.
  • Phytophthora boll rot, caused by Phytophthora nicotianae var. parasitica
  • Sclerotinia boll rot, caused by the fungus Sclerotinia sclerotiorum
  • Stigmatomycosis, caused by the fungi Ashbya gossypii, Eremothecium coryli, (Nematospora coryli) and Aureobasidium pullulans

Growing and Harvesting

The cotton plant is a warm-season woody perennial shrub, which is grown as an annual field crop. Because the plants are grown in various environments, cotton farmers can choose from many varieties of cotton that are bred to be productive in various environmental and cultural conditions. After the seeds are planted and the plants begin to grow and develop, they must be protected from insects, diseases, and weeds.

After the plant flowers, the cotton fibers (lint) develop on the seed in the boll in three stages. In the “elongation” stage (0 to 27 days), the fiber cell develops a thin, expandable primary wall surrounding a large vacuole, and the cell elongates dramatically. During the “thickening” stage (15 to 55 days), the living protoplast shrinks, while a secondary wall composed almost entirely of cellulose is deposited inside the primary wall.

By the “maturation” stage, the secondary wall fills most of the fiber cell volume, leaving a small central cavity (the lumen) containing the cytoplasm and the vacuole. As the boll opens, the fiber cells rapidly desiccate, collapse, and die. As the tubular cells collapse, they assume a flat, ribbon-like form with twists, called “convolutions.”

Before harvesting, the plants are defoliated to prevent foliage from interfering with mechanical harvesting. Approximately 85% of the total U.S. crop is machine picked and the remaining 15%, primarily from Texas and Oklahoma, is machine stripped. Machine pickers harvest cotton from open bolls, leaving unopened and empty bolls on the plant.

This is accomplished with revolving spindles that pluck the fiber out of the boll. Machine strippers strip the entire plant of opened and unopened bolls. The fiber removed from the plant also contains cottonseeds and is referred to as “seed cotton.” The harvested seed cotton is transported to the gin.

How Is Cotton Processed?

Cotton production is a very involved process, from planting cotton seeds to picking the cotton crop to process it in a cotton gin.

  • While cotton was picked and separated by hand in the early days, today, most cotton production starts with a cotton picker (which picks the entire plant) or a cotton stripper, with strips the boll off the plant.
  • After the cotton is picked, it is baled and stored in the fields before it is sent to the gins.
  • At the gins, the cotton bales are cleaned and fluffed to separate the material from dirt, seeds, and lint.
  • After the cotton has gone through the gins and is completely separated from the seeds, the raw cotton is compressed and stored, ready to ship off to textile mills for further production.
  • The cleaned and fluffed cotton is put through a carding machine, which further cleans the material and forms the short fibers into a long untwisted rope that is then ready for spinning and weaving.

Cotton Fiber and Cottonseed

The fruit of the cotton plant is called a “cotton boll.” In it are the seeds, which are surrounded by cellulose fibers. When the boll ripens, it splits open and the fibers are exposed. The fiber’s cellulose is arranged in a way that gives them a high degree of strength, durability, and absorbency.

Each fiber is made up of twenty to thirty layers of cellulose coiled in a neat series of natural springs. When the boll is opened, the fibers dry into flat, twisted, ribbon-like shapes and become kinked together and interlocked. This interlocked form is ideal for spinning into a fine yarn or thread.

Its fibers are used to make a number of textile products. These include terrycloth, used to make highly absorbent bath towels and robes; denim, used to make blue jeans; chambray, popularly used in the manufacture of blue work shirts (from which we get the term “blue-collar”); along with corduroy; seersucker and cotton twill.

Socks, underwear, and most T-shirts are made from cotton. Bed sheets are also often made from cotton. Cotton is also used to make yarn used in crochet and knitting. While many fabrics are made completely of cotton, some materials blend cotton with synthetic fibers such as polyester or rayon.

In addition to the textile industry, cotton is used in fishnets, coffee filters, tents, and bookbinding. The first Chinese paper was made of cotton fiber, as is the modern United States dollar bill and federal stationery.

The cottonseed, which remains after the cotton is ginned (the fibers and seeds separated), is used to produce cottonseed oil. After refining, cottonseed oil can be consumed by humans like any other vegetable oil. The cottonseed meal that is left is generally fed to livestock.

Ginning

Ginning, in its strictest sense, is the process of separating cotton fibers from the seeds –– the process revolutionized by Eli Whitney’s invention of the cotton gin in 1794. Today’s cotton gin is required to do much more. To convert the harvested cotton into marketable products (fiber and seed), gins have to dry and clean the seed cotton (removing plant parts and field trash), separate the fiber from the seed, further clean the fiber, then place the fiber into an acceptable package while preserving its quality.

American upland cotton is “saw ginned.” Saw gins use cylinders with saw teeth to pull seed cotton between ribs, thus separating the fiber from the seeds. Saw gin stands can operate at capacities as high as 12 (480-lb) bales per hour. Approximately 835 saw gins are located throughout the cotton-producing regions in the United States. Pima cotton is “roller ginned.” Roller ginning, a slower, gentler process than saw ginning, is limited to the areas that produce Pima cotton (West Texas, New Mexico, Arizona, and California).

The ginning process yields two products with cash value –– cotton fiber and cottonseed. After ginning, the fiber is compressed into bales. At this stage, the fiber is referred to as “raw cotton.” Samples are taken from both sides of each bale and sent to the U.S. Department of Agriculture for classing. The cottonseeds removed during ginning are shipped to cotton oil mills.

Short fibers (“linters”) that were not removed by ginning remain on the seeds. At the oil mill, the linters are removed from the seeds by delinting machines, employing the same principles as saw gins. If seeds are run through a delinting machine once, the linters produced are known as “mill-run linters.”

Most mills run the seed through twice, producing “first-cut” and “second-cut” linters. First-cut linters consist of longer, more resilient fibers and are used in many nonwoven products. Second-cut linters consist of shorter fibers and are used to produce high-grade bond paper and as a source of cellulose in the chemical industry. After the linters are removed, the cottonseed is converted into food for people, feed for livestock, fertilizer, and mulch for plants.

Another by-product of the ginning process is “motes.” Motes are small, immature seeds with fiber attached. They are removed at a different stage of the ginning process. The fiber can be removed from the motes by a delinting machine. This fiber, called “gin mote fiber,” is also used in nonwoven products.

What Are the Characteristics of Cotton?

Cotton has a number of distinguishing characteristics that make it such a popular fiber in the textile industry.

  • Softness: The cotton plant is soft and fluffy and results in a fabric that often retains that soft feel.
  • Durability: The cotton plant’s cellular structure is strong, creating a tough and wear-and-tear resistant fabric.
  • Absorbency: Cotton fabric is a very absorbent fabric because there is a lot of space between the cotton fibers.
  • Holds dye well: Due to its absorbent nature, cotton takes dye very easily and can be made into a wide variety of colors.
  • Breathability: The fiber structure of cotton makes it more breathable than synthetic fibers.
  • No static cling: Cotton does not conduct electricity, therefore static is not an issue with cotton.

Physical Properties of Cotton

The three cotton fiber properties most often considered in nonwoven applications are micronaire, length, and strength. Neps may also be considered for applications where visual appearance is important.

Micronaire

Micronaire is an airflow measurement of fiber fineness. It is performed on a weighed test specimen, which is compressed to a specific volume in a chamber. Air is forced through the specimen and the resistance to the airflow is measured. This resistance is proportional to the linear density of the fibers (expressed in micrograms per inch), adjusted for the maturity of the fiber (because micronaire and maturity are highly correlated within each cotton variety). If the exact linear density of the fibers needs to be determined, the maturity of the fibers must be determined by another measurement. In a typical year, the micronaire range for upland cotton is 3.0 to 5.5. Because denier is approximately equal to micronaire divided by 2.82, upland cotton ordinarily ranges from about 0.7 to 2.3 denier.

Fiber Length

Cotton fiber length varies genetically and any sample of cotton fiber shows an array, or distribution, of fiber length. The HVI reports fiber length as the mean length of the longer half of the fibers in the sample (the upper-half-mean length) in hundredths of an inch. Figure 1 shows a typical fiber length array. Fiber lengths normally are between 1.0 and 1.25 inches for U.S. upland raw cotton, as long as 1.6 inches for Pima cotton, and less than 0.5 inches for linters and comber noils (the portion of shorter fibers removed by the combing operation).

Fiber Strength

The HVI system measures fiber strength by clamping a bundle of fibers, with 1/8 inch between the two sets of jaws, and measuring the force required to break the fibers. Results are reported as grams per tex or grams per denier. A “tex” is a unit equal to the weight in grams of 1,000 meters of fiber. Therefore, the strength reported is the force in grams required to break a bundle of fibers one tex unit in size.

Neps

A “nep” is a small knot of tangled fibers, often caused biologically or by mechanical processing. Neps can detract from the visual appearance of fabrics by causing white specks. Neps can be measured with the Zellweger Uster Advanced Fiber Information System (AFIS) nep tester and are reported as total neps per gram of cotton and mean nep diameter in millimeters. Nep formation during processing can be minimized through the use of appropriate equipment and settings.

6 Common Uses for Cotton

Cotton has many uses, across a number of different industries.

  • Woven fabrics: Cotton is used to make a variety of woven fabrics, including canvas, denim, damask, flannel, and more.
  • Clothing: It is a fixture of the textile industry as a result of its mass production, soft feel, durability, and absorbency. It is frequently used for T-shirts, blue jeans, dresses, sweats, and so much more.
  • Bedsheets and towels: Since cotton is extremely soft and absorbent, it is an ideal fabric for bedroom linens and towels needed to sop up the moisture.
  • Underwear: For the same reasons, cotton makes comfortable and durable undergarments.
  • Home decor: It is also used throughout the home for upholstery, curtains, rugs, pillows.
  • Cottonseed oil: Cottonseed is a byproduct of the cotton production process, and the seeds are used to manufacture cottonseed oil, which is used for salad dressing and margarine. It can also be used in makeup, soap, candles, and more.

Source: Masterclass, Britannica, Cottoninc, Wikipedia, New World Encyclopedia

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