Cotton (Revised)

Introduction

Gossypium hirsutum commonly known as upland cotton, belongs to the Malvaceae family and the Gossypium genus. The genus Gossypium is quite diverse, encompassing approximately 50 species, which makes it one of the largest genera within the Malvaceae family. Alongside Gossypium hirsutum, there are three other cultivated Gossypium species: Gossypium arboreum (Tree Cotton), Gossypium barbadense (Sea Island Cotton) and Gossypium herbaceum (Levant cotton). Cotton as a tropical crop originates from several locations (southern Africa, south-east Asia and Peru). There are annual and biennal species, as well as perennial varieties. It produces a yellow, white and purple-red blossom, and is a hermaphrodite.

Gossypium hirsutum is thought to have been domesticated around 5,000 to 6,000 years ago in present-day Mexico and Central America. From there, it spread to other regions through trade and exploration. Today, it is widely cultivated across various continents for its valuable fibers and seeds. Gossypium hirsutum is the most important and widely cultivated species in the cotton industry, accounting for over 90% of global cotton production. It is a tetraploid species with an AD-genome and is believed to have been independently domesticated in different regions. Gossypium hirsutum prefers well-drained, sandy, loamy, or clayey soils with good water retention. It is often cultivated in irrigated or rain-fed agricultural systems. Additionally, the plant requires a sufficient amount of sunlight for optimal growth and fiber development. 
Utilization of Gossypium hirsutum revolves around its valuable fibers and seeds. Cotton fibers known as "lint," are extensively used in the textile industry to produce a wide range of products such as clothing, beddings, sewing thread and industrial materials. Short fibres or "linters" are processed into papers, twine, automobile upholstery, explosives, plastics, and photographic film. Cottonseed oil, obtained from its seeds, is edible and finds use in a range of products, such as margarine, cooking oils, soap, cosmetics, lubricants, and protective coatings. The remaining seed cake is used as livestock feed, and cotton stalks find applications in paper, paperboard, and cement-bonded particle board production.
Gossypium hirsutum plays a pivotal role in the global cotton market. The key cotton species marketed extensively are Gossypium hirsutum itself, along with Gossypium barbadense (known as extra-long staple or Pima cotton). Gossypium hirsutum dominates the market due to its high yield, adaptability to various growing conditions, and efficient lint production. On the other hand, Gossypium barbadense is known for producing longer, finer, and more expensive fibers, making it highly sought after for high-quality textiles.
Key cotton producers in the world include China, the United States, India, Pakistan, Brazil, and Uzbekistan. Benin, Mali, Burkina Faso, and Ivory Coast are the highest cotton-producing countries in Africa and account for about 50% of the region's produce. These countries contribute significantly to global cotton production, meeting the demands of the textile industry and other cotton-based products.
(Ikitoo, E.C., 2011, Todou, G. & Konsala, S., 2011).

Species account

Gossypium hirsutum is the most extensively grown cotton species globally, covering a significant portion of cotton farming worldwide. Its adaptability to diverse climates and relatively high productivity have contributed to its widespread cultivation. 
G. hirsutum is an annual or perennial shrub that typically grows to a height 1 to 3 metres. It has a robust and bushy growth habit, with the stems and leaves covered in fine hairs, which gives it the name "hirsutum," meaning hairy). Leaves: heart-shaped and have a slightly rough texture due to the fine hairs. They are a vibrant green color and contribute to the plant's lush appearance. Flowers: large and typically white or creamy-yellow in color, with a bell-shaped appearance. One of the most notable characteristics of Gossypium hirsutum is its fruit, known as a cotton boll. These bolls contain numerous seeds surrounded by fluffy white fibers, which are the valuable cotton fibers used in various industries.
The length of the cotton fibers produced by G. hirsutum falls between those of Gossypium arboreum (tree cotton) and Gossypium barbadense (Sea Island cotton). While not as long as the premium-quality Sea Island cotton, upland cotton's fibers are still versatile and suitable for for a wide range of products, including clothing, home textiles, and industrial materials (Ikitoo, E.C., 2011).
 

Common related species
•    Gossypium arboretum L.- Tree Cotton (English); Coton, Cotonnier, Coton arborescent, Cotonnier rouge (French).
•    Gossypium barbadense L.- Egyptian Cotton, Pima Cotton, Sea Island Cotton (English); Coton, Cotonnier, Cotonnier d’Egypte, Coton des Indes occidentales (French).
•    Gossypium herbaceum L.- Cotton, Arabian cotton, Levant cotton (English); Coton, cotonnier, cotonnier herbacé, cotonnier d’Asie, cotonnier africain (French); Algodoeiro, algodoeiro asiático (Portugease).
1.    Gossypium barbadense commonly known as extra-long staple cotton or Sea Island cotton, is primarily found in subtropical and tropical regions, thriving in warm climates with abundant sunlight and moderate rainfall. It is native to South America, particularly along the coastal areas of Peru, Ecuador, and northern Chile. Over time, the cultivation of this cotton species has spread to other regions around the world, including parts of the Caribbean, certain African countries, and even some areas in the southeastern United States. Sea Island cotton, is a woody, perennial shrub that typically grows to a height of 1.2 to 2 meters), though some varieties may reach greater heights. Leaves: broad, dark green, and possess a lobed or palmate shape, providing an aesthetically pleasing appearance to the plant. Flowers: large, funnel-shaped, and come in various colors, including creamy white, yellow, and pink. These blooms emit a pleasant fragrance, attracting pollinators like bees and butterflies. The most significant feature of G. barbadense lies in its cotton fibers, which are highly valued for their length, fineness, and strength. The fibers can grow up to 1.5 to 2.5 inches (3.8 to 6.4 centimeters) long, making them significantly longer than those of other cotton species. This characteristic contributes to the exceptional quality and softness of the textiles produced from Sea Island cotton. While Gossypium barbadense offers premium-quality, extra-long staple fibers, it is cultivated on a smaller scale due to its specific climate requirements (Todou, G. & Konsala, S., 2011)

2.    Gossypium arboretum- commonly known as tree cotton or Asian cotton, is native to the Indian subcontinent and is widely distributed in countries such as India, Pakistan, Bangladesh, and parts of China. It has been cultivated for centuries in these regions for its cotton fibers and other uses. Gossypium arboreum is a small, woody shrub with a distinct tree-like appearance, growing up to 6 to 10 feet (1.8 to 3 meters) in height. Stems: sturdy and covered with a grayish or brownish bark, lending it the appearance of a miniature tree. Leaves: broad and deep green, usually divided into three to five lobes. The foliage creates a lush canopy that provides shade and protection for the developing cotton bolls. Flowers: bell-shaped and come in various colors, including white, yellow, and pink. These blooms often have a crimson or maroon spot at their base, adding a touch of elegance to the plant's overall appearance. One of the primary characteristics that distinguish G. arboreum from its counterparts is the length of its cotton fibers. The fibers produced by tree cotton are shorter compared to those of Gossypium barbadense and some other cultivated species. This makes it less desirable for high-quality textiles, but it is still used for various other purposes. The plant also has a compact and bushy form, giving it a distinctive appearance reminiscent of a small tree unlike other related species. (Brink, M., 2011)

3.    Gossypium herbaceum commonly known as Levant cotton or the Arabian cotton is believed to be one of the oldest cultivated cotton species, with its origins dating back to ancient times. It is native to the semi-arid regions of sub-Saharan Africa and Arabia. Over the centuries, its cultivation has spread to other parts of the world with suitable climates, including parts of Africa, the Middle East, and Southern Europe. Gossypium herbaceum is an annual herbaceous plant that typically reaches a height of 3 to 6 feet (0.9 to 1.8 meters). Stems: unlike some other cotton species with woody stems, Levant cotton has a soft, herbaceous stem that becomes woody as the plant matures. Leaves: are broad and lobed, varying in color from light to medium green. The foliage provides a lush appearance, and the leaves have a soft texture. Flowers: creamy white to yellow in color, with a funnel-shaped structure. They possess a delicate fragrance that attracts pollinators, such as bees and butterflies 
(pza.sanbi.org, Jimu, L., 2011.).

Varieties and countries of origin
Worldwide there are about 33 million hectares of cotton crops. Economically, the most important varieties are Gossypium hirsutum and Gossypium barbadense.
G. hirsutum: 
•     Upland cotton
•     80-90% of world market
•    short to medium fibres (2-3 cm; middle stapled variety)

G. barbadense: 
•     Sea Island cotton
•    10-20% of global market
•     high-quality, long to very long fibres (3-4 cm; long stapled variety)
In addition, the annual G. herbaceum or the hardy cotton bush G. arboreum produces fibres with a length of 1.8-2.2 cm. Long stapled varieties are cultivated mostly in Egypt and Peru. The middle-stapled varieties from the USA, short stapled varieties in AsiaG. barbadense is more susceptible to pests due to its long vegetation period G. hirsutum, ripens far quicker (some varieties after only 150 days).
All of the cotton varieties with coloured fibres, formed from crossings between wild varieties (from Peru) and crops, have provoked a certain interest in the natural textile processing industry. Until now, mostly brown, green and beige varieties had been cultivated.
Organic cotton production is most widely spread in the USA (about 4000 ha). Yet ecological cotton projects also exist in Egypt, Argentina, Brazil, Greece, India, Mali, Nicaragua, Paraguay, Peru, Tanzania, Turkey and Uganda.
 
Uses and contents
Cotton can be seen as a classic dual-purpose plant (fibres and oil). A harvest yielding 1000 kg of cotton/ha can be broken down thus:
•    about 320 - 420 kg fibres (raw cotton)
•    about 200 - 250 kg seed cakes or flourabout 100 - 150 kg oil
•    about 200 kg shells
•    about 20 kg retained seeds
•    about 40 kg dirt

 
Ecological conditions

Cotton performs best in desert climates, under irrigation. It grows on lowland below 1000 m. The optimum temperature for germination is 34degC, for the growth of seedlings 24-29degC, and for later continuous growth 34degC. Low temperature increases the production of vegetative branches and extends the cropping period. Cotton is susceptible to frost. High temperature increases the number of fruiting branches and reduces the cropping period. Cotton is a sun-loving plant and cannot tolerate shade, particularly in the seedling stage. Reduced light intensity, caused by long-lasting overcast weather, shading from inter planted crops or too dense a stand, retards flowering and fruiting and increases boll shedding. Shedding of over 50% of squares, flowers or young bolls, due to early bollworm attack, drought or water logging, is normal. Upland cottons are day-neutral.
The crop will not tolerate very heavy rainfall and, where grown as a rain-fed crop, the average rainfall is usually 800-1200 mm. Adequate, but not excessive, moisture is required for early vegetative growth. The first flowering period requires relative dryness to speed up formation of fruiting branches. An increase in moisture is required for boll setting and renewed growth, followed by dry weather for ripening and harvest. Sufficient soil moisture is essential during the flowering period.
In the tropics most cotton is grown by smallholders who sell their seed cotton to the ginneries. Ginneries may be privately, cooperatively or state owned. 
Cotton can be grown on a variety of soils from light sandy soils to heavy alluvium and calcareous clays. Soils must be permeable to water and to roots to a depth of at least 100 cm, preferably over 150 cm, with pH 5.5-8.5. Cotton is one of the salt-tolerant crops.

Agronomic aspects

Site requirements 
In its early stages of growth, cotton requires an arid climate with a plentiful supply of water. Afterwards, the weather needs to be dry, especially after the capsules have opened, for if water can enters the capsules it will have a detrimental effect on the quality. The vegetation period generally lasts around 180-220 days (varieties such as G. hirsutum that mature rapidly can be harvested after only 150 days). Very high yields have been reported from the arid areas of the CIS and in Egypt using irrigation.
Because cotton loves the heat, yet is also highly susceptible to frost, temperatures of around 26-28degC are ideal for its development. Lots of sun has a very positive effect during the blossoming and fruit setting periods, in cases of 50% and more cloud during the vegetation period it makes little sense to plant cotton. Cotton cannot withstand shade. Cotton is also a short-day plant, and such conditions will accelerate its growth. The correct climatic conditions are generally found between the 28deg northern and 47deg southern latitudes.
A strong wind can suck the fibres out of the capsules and blow them away. Today's varieties are tolerant with regard to salinity (up to a salinity of 0.5-0.6%). The soil's pH value should be between 6 and 8. In addition, cotton also requires deep, well-drained and ventilated soil, in order to properly develop its system of tap-roots (resistance to drought). The site's elevation plays a large role when planting coloured varieties of cotton, because the intensity of the sun's rays has a strong effect. At least the green varieties tend to bleaching when the intensity increases too much (Peru).
 
Seeds and shoots 
The fertilization process is generative. Most wild Gossypium varieties are perennial. Annual varieties are most generally used for cultivation, which conclude their development cycle during one single vegetation period. Local and regionally produced seeds should be used, which will have developed a tolerance or resistance against the pests most commonly found in the region. Because the sale of seeds is usually controlled by government authorities, it is important to try to acquire untreated seeds of the desired variety early enough.
During the last few years, hybrid seeds have been developed that provide high yields. Yet this method makes it impossible to use self-produced seeds from the crop, and a new supply of seeds must be bought for the next season.
Because cotton can be affected by various root and damping off diseases, in certain cases, it is worthwhile considering pre-treating the seeds. In contrast to conventional cotton crops, only micro-organisms, which work antagonistically, are used. In Egypt, for example, the seeds are treated with Bacillus subtilis, Gliocladium penicilloides and/or a suspension of trichoderma. In order to improve the nutrient availability for the young plants in India, the seeds are additionally treated with Azotobacter and bacteria strains capable of breaking down phosphorous.
 
Sowing methods 
If the cotton is to be planted by machines, then the seeds need to be rid of the fluff that surrounds them (otherwise the seeds stick together). This is not necessary when the seeds are sown by hand. The temperature should not fall below 18degC. Temperature of 35degC is optimal. The seeds should be sown at a depth of maximum 5 cm. 
The density depends upon the method utilised (manual or by machine). Bio-dynamic farmers in Egypt sow several seeds by hand every 20 cm into the prepared planting rows (distances between the rows 60-70 cm). Between 3 and 4 weeks later, the plants are inspected and all but the 2 strongest specimens removed. The plant population of rain-fed cotton of small-scale farmers in Tanzania is much lower. The farmers sow cotton by broadcasting the seeds on the flat land or in rows at a spacing of 90 cm between and 30 - 50 cm in the rows. Some farmers sow also on ridges with the same spacing. 
Mechanical methods usually leave 70 cm (50-120 cm) between the rows and 20 cm (20-60 cm) distance between the seeds. When the harvest is done mechanically, varieties such as G. hirsutum that produce few branches are sown every 8-10 cm with a distance between the rows of 15-20 cm. 
Cotton is either planted on flat soil, ridges or in furrows. Furrow drilling is employed mainly as a protection against quicksand. Ridges are used in soils, which are difficult to drain, and in regions with little rainfall, as this eases irrigation and facilitate the seeping in of the water into the soil. Its disadvantages are more difficult sowing and tilling of weeds. The cotton is sown in the lower third of a ridge in high-content soils and the upper third for low content soils. The seeds should be watered as soon as possible after sowing. 
During the first 3 weeks, the shoots can offer little resistance against weeds, but this improves until the thick crop growth has no more problems in the area. For this reason, a suitable position in the crop rotation, suitable soil cultivation method and preparation of the seed beds should be taken care of to prevent an excessive growth of weeds during the early growth phases. On irrigated soils, irrigation is carried out prior to sowing in order that the weed seeds germinate and grow. The resulting growth of weeds can then be easily removed by appropriately cultivating the soil, before the cotton is sowed. The final soil treatment before planting should include the spreading of compost.
For cultivation done using animal-drawn (oxen or water-buffaloes) implements time requirements are: 15 animal days and person-days/ha, or by hand: 50 person-days/ha. By 2 or 4-wheeled tractors (150 kWh/ha).
The land should be prepared early and to a depth of at least 15 cm. To maintain soil organic matter, liberally apply or incorporate plant residues and animal manure during land preparation. Planting should be early, as soon as rainfall is adequate for the germination and growth of the crop. Cotton grown by smallholders is commonly planted with a delay, because the food crops are given priority. In hand planting, cotton is usually sown at a seed rate of 11-14 kg/ha and at a depth of about 25 mm with 3-6 seeds per hole in rows or ridges. Ridges are an advantage as they can be tied to conserve water under dry conditions and aid drainage under wet conditions. Thinning is done when the plants are 6-10 cm high, and two plants per hill are usually left. The optimum spacing depends on the size and fruitfulness of the plant permitted by local conditions. It also depends on the interactions between variety, soil and climate. The optimum spacing ranges from 80-20 to 100-40 cm, with one or two plants per hill. Plant densities may vary between 40,000 and 100,000 plants per ha, but are generally between 50,000 and 60,000 plants per ha. 
 
Husbandry
Cotton seedlings are sensitive to competition from weeds. Weeds should be controlled early to prevent damage to the crop. Control weeds against the first flush of weeds before sowing and plant the seeds closely. Weed early and frequently. Place manure some 6 weeks after sowing. These measures help to reduce hand weeding to some 15 person-days (work of one person done per day) per ha. It also helps to reduce attack by pests harbored by weeds.
 
Irrigation
Intervals between irrigation should be 2-3 weeks on deep permeable sandy loams to heavy clays and less for very light, very heavy and shallow soils. The irrigation period should be 19 weeks. Excessive irrigation besides being a waste of water increases risk of disease incidence. Most irrigation is by gravity using furrows. Water saving is possible by alternate furrow irrigation or by hand watering with a hose pipe. The latter is only applicable in small plots. 
 
Nutrients and organic fertilization strategies
Compost, decomposed animal dung and mulching material are used to supply the soil with sufficient organic material. This supports the cotton's growth. Potassium can be supplied by spreading wood ashes, and phosphorous by adding rock phosphate. Usually, the soil is prepared before the cotton is sown by spreading compost that is mixed with ashes and rock phosphate. In some areas, animal manure that has been composted is used for fertilization. It should be applied inside the furrow close to the plant lines or in each plant hole. The above is only applicable to smallholder farmers. It is not practicable where cotton is a plantation crop as in Egypt, Sudan and Tanzania.
 
Crop rotation and inter cropping
Cotton should not be grown for more than 3 years on the same field. It is important that cotton is grown in rotation with other crops. This helps to improve and maintain soil fertility. Crop rotation and mixed cropping help prevent build-up of pest population, diseases and weeds. Cotton grows well in rotation with cereals, tobacco and legumes. Particularly good yields can be achieved when cotton is grown after pulses (soybean, chickpea, pigeon pea, groundnut etc.), horticultural crops like chilies or vegetables, and after sugarcane and wheat. 
Cotton intercrops such as maize, sorghum, beans, and peanut create a natural balance of pests, natural enemies, and weeds in the cotton field environment. Maize or tobacco planted in every 20 rows of cotton attracts African bollworm. Sunflower or cowpea sown in every 5 rows of cotton attracts moths when planted as trap crops. Castor bean (Ricinus communis) attracts caterpillars. Rice when rotated with mungbean and cotton disrupts the life cycles of pests attacking these crops. However, the timing of planting of inter crops, trap crops, and border crops should be planned to flower at the same time with cotton. 

Harvest, post-harvest practices and markets 

Harvesting
In Africa generally, cotton is hand-picked. This creates work for farmers' families or village laborer, usually women. It also produces clean seed cotton that can be ginned easily and cheaply in low-cost ginneries. One picker can harvest 25-40 kg of seed cotton per day depending on the availability of open bolls. Picking is very laborious. It should be done every 3-4 weeks, so that open cotton is not left in the field for too long which may result in a change of the color and reduced the quality of the lint. It is then sorted into clean and stained cotton before marketing. Harvesting begins about 4 months after sowing, lasts for 2 months and 2-3 pickings are usually done. Optimal dryness of cotton is critical during the harvesting process. In forested regions or following late rains, extra drying on racks may be necessary. 
Mechanical harvesting is employed in areas with vast land due to the expensive nature of hand-picking. To facilitate mechanical harvesting in these areas, they plant low-growing, weakly-branching cultivars close together and use defoliants on the plants before harvesting. However, this method necessitates heating and shaking to remove impurities, leading to increased brittleness of the cotton fiber (Ikitoo, E.C., 2011).

Post-harvest practices
After picking, the seed cotton is cleaned and transported in bags or sheets to the ginnery for checking, weighing, sorting. To ensure the best possible seed quality, the seed from the first portion of the crop picked is separated and stored separately in clearly marked bags. This high-quality seed can be used for future planting, helping farmers maintain productivity in the long run.
The lint from the early-picked cotton is considered the most mature and strong. This premium lint can fetch better prices in the market due to its superior characteristics.
After the cotton harvest, it's crucial to uproot and burn the cotton stems. This practice prevents the buildup of pests and diseases, safeguarding the health of future crops (Ikitoo, E.C., 2011). 

Markets 
Cotton is a vital commodity in the global market, serving as a primary raw material for the textile industry. Key producers of cotton worldwide include China, India, the United States, Pakistan, and Brazil. 
Together, they constitute roughly 75% of the world's cotton production, and China stands as the largest global producer, contributing to more than 23% of the total output. 
In these key cotton-producing regions, cotton industry relies on a mix of traditional and modern marketing practices. Local farmers often sell their produce to intermediaries or local cooperatives, who aggregate the cotton and then sell it to larger cotton merchants or ginners.
These ginners further process the cotton by removing seeds and impurities, turning it into bales, and then selling it to textile mills or exporters. In some cases, the cotton may be traded on commodity exchanges to facilitate international trade. In recent years, there has been an increasing trend towards digital marketing platforms and direct trade between cotton producers and textile companies, facilitated by online marketplaces and e-commerce platforms. This shift has streamlined the marketing process and reduced intermediaries, enabling faster transactions and better prices for cotton farmers.
Cotton in Africa is mainly grown by smallholder farmers, often alongside subsistence crops with very few major plantations. Benin, Mali, Burkina Faso, and Ivory Coast are the leading cotton producers in Africa, collectively responsible for approximately 50% of the region's output. Significant importers of African cotton include Bangladesh, Vietnam, China, and Malaysia. 
African cotton markets often suffer from limited infrastructure, inadequate access to credit, and fluctuating international prices, affecting the income and livelihoods of smallholder farmers. The marketing of cotton in African regions typically involves government-led initiatives, cooperatives, and partnerships with international organizations. These entities work to connect farmers to global markets and negotiate fair prices. However, there is a growing movement towards improving local processing capabilities and promoting value addition to increase revenue for African cotton-producing countries (Africa Cotton Market Insights. (n.d.), Ikitoo, E.C., 2011).