Cotton is a fibre crop, which is highly valuable to the textile industry, and for livestock feeds. It is highly grown in dry areas such as Katsina, Kaduna, Sokoto, Kano, Plateau, Bauchi, Borno and Taraba States. The United States is the largest producer of cotton in the world.
It is only four out of the 35 species from the germs of gossypium that are widely cultivated. These are G. Herbarium, G. Arboretum, G. Hirsute and G. Barbadense.
Distribution: The crop is grown in the United States, India/Pakistan, Africa-Persian, China, Japan.
(i) Ecological requirements: Cotton is a drought resistant plant. It has a good water absorption capacity from the subsoil layers due to its possession of well-developed tap root system characteristic of dicotyledonous plants, and can withstand short-term droughts.
It grows very well with adequate water supply by irrigation system. Before flower budding, when the assimilation surface is relatively small, the cotton does not take in much water. During blossoming, it requires high amount of water supply and less during ripening. The minimum, optimum and maximum temperatures for the germination and early growth of cotton are about 60degrees F, 93degrees F respectively. The most rapid growth and flowering of the plants takes place at temperature range of 91degrees – 97degrees F in the United States, the highest cotton yields comes from areas where the mean July temperatures, range from 81degrees -83degrees F.
Cotton grows well in areas with abundant sunlight hence does not tolerate shading. Optimum conditions for growth are found in areas where cloudiness and sunny days during vegetation, make up 60-70%. Cotton is a short day plant. It requires moderately fertile soil for growth. The soils range from sands to heavy clays with ranges in acidity from a pH of 5.2 to pH greater than 8, (i.e. pH 5.2 to pH 8=). The best cotton lands are mixtures of clay and sandy-loam that contain a moderate amount of organic matter and a moderate amount of available N, P and K. The heavier soils promote later maturity, larger vegetative growth, and greater boll-weevil damage. This is the major reason why cotton is not grown in heavy soils.
(ii) Seed-bed preparation: The first step in seed preparation for cotton is stalk disposal, when cotton follows corn, sorghum or cotton. A rotary stalk cutter often is used. Deep tillage may be done using chisel or subsoiler to increase the yields of cotton on soil with hard pan. The land then may be formed into beds with a listen or middle buster.
Cotton is planted on ridges or beds in most of the humid cotton belt, while level or furrow plantings are more common in the western half of the cotton belt, except under irrigation. Low beds are preferable to ridges owing to the advantages of effective weed control and good moisture conservation. Higher beds may be desirable in wet areas. In the humid tropics, it is very important to properly choose the best time for main soil tillage. The best time is at the end of the wet season.
(iii) Cultural practices: Seeds for sowing must have a high germination capacity (at least 85%). Seeds for sowing are usually prepared at gin mills where the raw cotton (seeds with fibres) are first ginned (the fibre is separated from the seeds) and then delinted (seed fuzz is removed). Chemical methods may also be used for seed preparation. The seeds are treated with concentrated sulphuric acid, H2SO4, or with vapours of mixed acids. The seeds are disinfected by treating with copper trichlor ophenolate (7-8kg/tonne of seeds). Sowing time depends on soil and air temperatures as well as on rainfall. Planting in Nigeria should be done in mid-June on 90cm ridges or 92cm between ridges with intra row spacing of 45cm. Four to six seeds should be planted per hole and later thinned to two plants per stand. Although most of the cotton is planted after mid-July, the best yields are attainable with mid-June planting. Manual broadcasting of cotton seeds followed by preparing beds using harrows or other implements is the most primitive and least effective technique. Drilling machine is the best for sowing because it allows the desired number of seeds to be planted. With hand drilling, furrows are first prepared and seeds sown into these prepared furrows or holes. Holes are prepared on ridges and the seeds are sown into these earlier prepared holes. Various types of sowing include cluster sowing and wide row sowing, but cluster sowing is more widespread.
(iv) Plant care: Thinning of extra seedlings in the field should begin from the period when there is mass emergence of shoot (stem and leaves) and then terminated after appearance of the 1st -2nd leaves. First inter-row cultivation (planting of seedling between two ridges in a furrow) begins when the shoots appear at the depth of 8cm.
As a rule, the second and third cultivations are deeper than the first one. Thinning is the practice that involves the removal of extra seedlings that grow in a field. Supplying is the reverse of thinning, it is the cultural practice where extra seedlings are planted in the spaces that sown seeds do not germinate in a field.
(v) Weeding: Weeding in cotton is done manually or chemically. Weeds within the row spacing or in the row spacings are controlled by cultivation. Weeds within the rows are controlled either manually or chemically. Under large scale production, herbicides may be applied to yield greater outputs. A mixture of Diuron with either Norflurazon or Fluridone or Alachlor or Pendimethalin is effective at the recommended mixing ratios applied at pre-emergence stage.
Alternatively, a mixture of Diuron plus Fluridone at 0.8+ 0.8kg. respectively per hectare is recommended for pre-emergence. For sites with heavy soil (high clay and organic matter) application of a mixture of Duiron and Alachlor at 0.8 + 3,0 kg a.i, respectively per hectare is recommended. Sites with high itch grass infestation and heavy soil will require a mixture of Duiron and Pendimethalin at 0.8 + 3.0kg a. i., respectively per hectare at pre-emergence stage.
(vi) Nutrient requirements: Cotton is a fibre crop that has a high requirement for phosphorus P and Boron, B. Fertilisers, which contain these nutrients, are applied to the field where cotton is planted either in simple or compound fertiliser form. Fertilisers containing phosphorus and Boron in form of boronated superphosphate and Murate of potash should be applied during seed preparation, or soon after planting by placing in holes 5cm deep and 8cm away from the seed. Avoid delay in the application of the nutrients. It is preferably good to apply intro-chalk (CAN) in two split doses, one half at 3 weeks oust before thinning) and the second half at 8 weeks after sowing. Fertiliser should be applied into shallow grooves about 8cm away from the plant and cover with soil immediately after application. In case, simple fertiliser such as superphosphate is used, then enough boron-containing materials, preferably borax, (Na2B4O7,*10H2O) should be added to give the appropriate rate of Boron. Borax contains 10.6%B.
(vii) Varieties: There are many varieties of cotton grown in different regions depending on the climatic conditions, soil type, sunlight, soil pH, and nutrients found in these agro- ecological zones or vegetational belts. In Nigeria, cotton belts are divided into the northern, southern and the eastern zones. Samaru 71 variety is recommended for planting in the northern and southern cotton zones. Samaru 77 is recommended for the Eastern cotton zones. Northern zone includes Kano, Sokoto, Kaduna, and Katsina, Plateau States, northern half of Niger State and Borgu area of Kwara State. The Eastern Zone includes Borno, Bauchi and Adamawai Taraba States. Cotton variety “Allen 26” is still very popular in Okpebho, Agbazillo, Etsako and Akoko-Edo Local Government Area of Edo State.
(viii) Harvesting: Harvesting of cotton is done from the time the boils open. Manual harvesting is carried out by hand picking. The first hand picking is done when 30-40% of the boils open, the second when 35-40% and the third picking in two or three weeks after the second one. The last one is done to remove the remaining boils.
Cotton is also harvested using mechanical method. Under this method, mechanical pickers are equipped with rotating steel spindles attached to revolving drums or moving bars. It is widely carried out in developed countries where about 98% of cotton is harvested through this method. Strippers or scrappers are other forms of mechanical harvesting. In the mechanical pickers, the spindles are fluted rods, smooth rods or barbed cones.
The moistened spindles pull the lint and seeds from the opened boils after which they are pushed from the spindle with a doffer, and then conveyed to a basket mounted on the picker. Cotton to be harvested mechanically often is treated with chemical to remove or dry the leaves. These treatments reduce much dampness (owing to the presence of high moisture content), fiber staining and trash from seed cotton, they also prevent clogging of picker spindles with trash or leaf juices. The early removal of leaf of the ripened boll helps to provide better ventilation, thereby preventing boll from rotting on the lower branch of the plants. This also reduces lodging of the plant. Chemicals are used to enhance the falling off of leaves from ripened boils of cotton. These chemicals are called defoliants. The defoliants used include calcium cyanamid, a sodium chlorate sodium metaborate mixture, magnesium chlorate-hexahydrate, and certain organic phosphorus compounds. During harvesting, dessicants may be used to kill the plants promptly without applying defoliants to effect the falling off of leaves, an example of dessicant used is pentachlorophenol. Dessicants should only be applied at a time when 80-90% of the boils are open. This is so because failure to adhere to the directive results in a heavy loss of cotton production.
(ix) Processing cotton ginning: The ginning of cotton seeds after it has been picked is done in the ginnery. Ginning involves separation of the fibres from the seed after removal of dirts, hulls and other trash. Damp or wet cotton is put through a drier before ginning. Dry lint contains 8% moisture or less. Cotton ginned within a day after the harvest have more long fibres of improved spinning quality than those ginned after many days of harvest.
Uses of cotton
(i) Production of textile materials: The bulk of cotton produced in Nigeria is used for clothing and household goods. The textile industry extremely depends on the supply of cotton for their production of the textile materials such as clothes, bags, belts, carpets, pads, hose and twine. Others are rayon baiting, yawnings and other cellulose products.
(ii) Source of feed: A percentage of crushed cotton lint contains oil, the meal has a high protein content used for livestock feeds, but it contains a toxic substance called gossypol. This tends to reduce the amount of cotton seed meal that can safely be added to poultry or livestock rations. Cottons with few glands on the leaves, and in the seeds, are low in gossypol.
(a) Leaf Curl Disease (i)
Causative agent: Fungus.
Species: Fusariun Aspergillus, penicillium and Pythium.
Transmission: Transmitted through contaminated seeds or infected seedlings.
(i) Appearance of waterlogged cells.
(ii) Death of cotton plants.
(b) Leaf Curl Disease (ii)
Causative agent: Virus.
Transmission: It is transmitted by aphids.
(c) Antracnose disease
Causative agent: Fungus.
Species: Collectotrichum gossypium.
(i) Appearance of red spots in the leaves, boils and stem.
(ii) Deforms the stem, leaves and boils to black.
(i) By treating seeds with dilute acid before planting.
Cotton blight and cotton black-arm diseases are caused by bacteria.
Pests of Cotton:
Trips and spidermit, insects, bollworms, boll suckers, cotton stained – Dysdercus SPP.
(i) By spraying with insecticides
(ii) By biological method.