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The cotton plant is a source for many important products other than fabric. Among the most important is cottonseed, which is pressed for cottonseed oil that is used in commercial products such as salad oils and snack foods, cosmetics, soap, candles, detergents, and paint. The hulls and meal are used for animal feed. Cotton is also a source for cellulose products, fertilizer, fuel, automobile tire cord, pressed paper, and cardboard.
India has emerged as the second largest producer of cotton in the World and occupies the first position in terms of total area under crop production at over 9.44 million hectares. However, the productivity level is still below the world average. Efforts are in place to increase the current productivity to bring it closer to the world average. In addition to meeting the cotton consumption demands by domestic textile industry, India has surplus cotton available for exports. The productivity level of cotton in India varies from zone to zone.
In India, there are nine major cotton growing states which fall under three zones viz. the North Zone (Punjab, Haryana, and Rajasthan), the Central Zone (Maharashtra, Madhya Pradesh, and Gujarat), and the Southern Zone (Andhra Pradesh, Karnataka, and Tamil Nadu). Nearly 65 percent of the cotton crop is cultivated under rainfed conditions in the country.
The crop is generally grown in medium to the deep black clayey soil but is also grown in sandy and sandy loam soil through supplemental irrigation by farmers. Cotton is best grown in soils with an excellent water holding capacity. Aeration and good drainage are equally important as the crop cannot withstand excessive moisture and waterlog. The major soil types suitable for cotton cultivation are alluvial, clayey and red sandy loam. Cotton is grown both under irrigated and rainfed conditions. Being a cash crop, cotton is known for its intensive cultivation. Some production practices like wide plant to plant and row to row spacing and crop traits such as indeterminate growth habit, long duration, render the crop susceptible to a multitude of pests and diseases at all stages of growth. These factors are also responsible for high input use in terms of nutrients and crop protection chemicals. Aggressive production practices by farmers often lead to a very high input use, with little regard to matching returns. The excessive use of inputs, not only escalates the cost of cultivation but also decreases the profitability. It also results in pest resurgence, health, and environmental hazards. Needless to say, excessive use of inputs is laying enormous pressure on land and water. In order to address these issues, WWF-India has developed the concept of operationalizing Better Management Practices (BMPs) for cotton cultivation. BMPs help balance inputs with increased farm yields. This manual has been developed in order to guide the extension worker at the field level to execute Better Management Practices in cotton growing areas. The manual has emerged from the field experiences and results obtained by WWF-India, Thirsty Crop team. The manual outlines the importance of environmentally sustainable cotton production systems and provides information on the methodology and technology pertaining to cleaner and more profitable cotton cultivation. Better Management Practices (BMPs) are agricultural practices which optimize the three pillars of sustainability: social responsibility, environmental integrity, and economic viability by binding together, the financial requirements for agriculture, such as high yield with environmental and social concerns, such as water and pesticide use. These practices allow diverse actors such as farmers, companies, government agencies, NGOs to optimize resource use efficiency, create marketable products, reduce waste, assure market access and reduce the risk of adverse relations with local stakeholders. Better Management Practices, technically speaking, are more environmentally friendly, and promote the use of local resources, and improve the input use efficiency. The practices, apart from improved agronomic practices, can be broadly categorized into five broad areas, namely:
Soil Fertility Management
Pest and Disease Management
Proper Harvesting and Storage
Crop Residue Management
STAGES OF GROWTH
The developmental phases for cotton can be divided into five main growth stages:
- Germination and emergence
- Seedling establishment
- Leaf area and canopy development
- Flowering and boll development
The transitions between these stages are not always sharp and clear. Each stage may also have different physiological processes operating within specific requirements. If producers are aware of these stage-dependent differences in cotton growth and requirements, then many problems in crop management can be avoided, which will result in higher yields and profits.
In spring, the acreage is cleared for planting. Mechanical cultivators rip out weeds and grass that may compete with the cotton for soil nutrients, sunlight, and water, and may attract pests that harm cotton. The land is plowed under and soil is broken up and formed into rows.
Cottonseed is mechanically planted by machines that plant up to 12 rows at a time. The planter opens a small furrow in each row, drops in seed, covers them, and then packs more dirt on top. Seed may be deposited in either small clumps (referred to as hill-dropped) or singularly (called drilled). The seed is placed 0.75 to 1.25 in (1.9 to 3.2 cm) deep, depending on the climate. The seed must be placed more shallowly in dusty, cool areas of the Cotton Belt, and more deeply in warmer areas.
With good soil moisture and warm temperature at planting, seedlings usually emerge five to seven days after planting, with a full stand of cotton appearing after about 11 days. Occasionally disease sets in, delaying the seedlings’ appearance. Also, a soil crust may prevent seedlings from surfacing. Thus, the crust must be carefully broken by machines or irrigation to permit the plants to emerge.
Approximately six weeks after seedlings appear, “squares,” or flower buds, begin to form. The buds mature for three weeks and then blossom into creamy yellow flowers, which turn pink, then red, and then fall off just three days after blossoming. After the flower falls away, a tiny ovary is left on the cotton plant. This ovary ripens and enlarges into a green pod called a cotton boll.
The boll matures in a period that ranges from 55 to 80 days. During this time, the football-shaped boll grows and moist fibres push the newly formed seeds outward. As the boll ripens, it remains green. Fibres continue to expand under the warm sun, with each fibre growing to its full length—about 2.5 in (6.4 cm)—during three weeks. For nearly six weeks, the fibres get thicker and layers of cellulose build up the cell walls. Ten weeks after flowers first appeared, fibres split the boll apart, and cream-colored cotton pushes forth. The moist fibres dry in the sun and the fibres collapse and twist together, looking like ribbon. Each boll contains three to five “cells,” each having about seven seeds embedded in the fibre.
At this point the cotton plant is defoliated if it is to be machine harvested. Defoliation (removing the leaves) is often accomplished by spraying the plant with a chemical. It is important that leaves not be harvested with the fibre because they are considered “trash” and must be removed at some point. In addition, removing the leaves minimizes staining the fibre and eliminates a source of excess moisture. Some American crops are naturally defoliated by frost, but at least half of the crops must be defoliated with chemicals. Without defoliation, the cotton must be picked by hand, with labourers clearing out the leaves as they work.
GROWTH AND DEVELOPMENT OF A COTTON PLANT
- Cotton Planting Populations / Seeding Rate.
- Row Spacing
- Root Development
- Vegetative Development
- Reproductive Development formation of the floral buds/balls/squares in the terminal of the plant
1.Cotton Planting Populations / Seeding Rate :
- High plant populations should be avoided unless very aggressive management practices are to be used in combination with proper variety selection. When cotton plant populations are too high, the following can occur:
- Later initiation of fruiting (higher node vs. lower populations) with a somewhat shortened boll loading period due to running out of time at the end of the season.
- Decreased drought tolerance.
- Increase in fruit shedding with the typically associated more vegetative and more difficult to control plants during the mid to late season.
- Increased need for more aggressive PGR use during the cropping season.
- Increase in the number of small bolls.
- Too low of plant population can also reduce yield potential. Reduced cotton stands can:
- Encourage vegetative development. Low populations actually help to manage aggressive growth, but the plants develop more nodes and fruiting position per node in thinner stands. This is primarily a response to light penetration into the canopy. The plants get “bigger around” and fill in the available space.
- Increase plant size.
- Delay reproductive development – Low populations typically fruit earlier (low node) but require time to accumulate a fruit load that allows for optimal yield. All of this takes time, which may or may not be beneficial; but adds management challenges in late planting and short-season scenarios.
- Shift more bolls to outer fruiting branches and vegetative branches.
- Increase boll size and micronaire value at some fruiting positions.
TIPS FOR 2:1 SKIP ROW CONFIGURATIONS
- Skip-row planting may allow for better light penetration before canopy closure.
- Skip-row planting may provide some level of moisture conservation advantage over solid row cotton.
- By adopting 2:1 skip row spacing, seed and technology costs will not be saved as most or all of the seed that would have been planted in the skipped row should be evenly distributed in the planted rows.
- Carefully read planter manuals to determine settings to achieve the desired population per acre of land, not per planted acre.
- Since cotton plants will eventually fill the skipped row, all over-the-top applications from mid-to-late-season, should be calculated as if the cotton were planted in solid rows.
- Particular care should be taken to keep the skipped row weed free until canopy closure.
The roots may be 3 feet deep in some soils when the above ground portion of the plant is only about 14 inches. The taproot may penetrate the soil from less than 1.5 feet to as much as 9 feet while the lateral roots remain fairly shallow, less than 3 feet. On deep alluvial and irrigated soils in California, roots reach a depth of 3 to 4 feet when the young plants are only 8 to 10 inches high, with a final depth at maturity of 9 feet. The bulk of the root system is located in the upper 3 feet, but this is dependent upon the soil moisture, soil physical structure and vigour of the individual plant. The total root length continues to increase as the plant develops until the maximum plant height is achieved and fruit begins to form. Total root length begins to decline as older roots die. Furthermore, root activity begins to decline as the boll load develops and carbohydrates are increasingly directed toward developing the fruit.
The developmental rate of a new node is significantly slower when the plant is water stressed. Typically this produces shorter stature plants. Nodes give rise to main stem leaves and branches. Main stem leaves and branches are spirally arranged on the stem in a three-eighths phyllotaxy above the cotyledonary node. Two types of branches are produced: monopodial are the vegetative branches and sympodial are the fruiting branches. Monopodial branches are structurally similar to the main stem. Growth is from a single terminal bud and tends to grow in an upright position. Sympodial branches are produced by the main stem and monopodial branches and grow at an acute angle to the main stem. Every sympodial branch has a main stem leaf associated with the branch. As the branch extends from the main stem, each new fruiting node has an extending leaf and a fruiting structure or square at each node. Elongation of the internode behind the flower bud and leaf causes them to extend away from the main stem. The development of this branch terminates in a square, but a second leaf and square develop in the axil of the first leaf and similarly extend away from the first leaf and square by internode elongation. Repetition of this process produces several squares and leaves resulting in the typical zigzag appearance of the fruiting branch. The flowers are opposite the leaves on the sympodial branches and develop more rapidly than monopodial branches.
Final plant height is also a function of the extension of main stem nodes. Within cotton varieties, the seasonal total numbers of main stem nodes is strongly influenced by determinacy and growing environment. Cotton breeding and selection for earliness has favoured shorter statured, more determinant cotton varieties. However, management factors such as excessive nitrogen fertilizer and excessive square loss from insect feeding can cause even moderate stature plants to grow excessively tall and rank
5.Reproducti ve Development
The boll develops rapidly after fertilization and reaches its full size within three weeks (Fig. 6). An additional four to five weeks are required for boll maturation. Seeds attain their full size about three weeks after fertilization, but do not reach maturity until shortly before the boll opens. Fibres attain their full length in about 25 days after fertilization with the maximum growth rate occurring during the first 10 to 15 days of this period. Thickening of the fibre begins at about 16 days after fertilization and continues until the boll is mature.
Fibre thickening occurs by the daily deposition of consecutive layers of cellulose on the inner wall of the fibre in a spiral fashion. The degree of thickening and the angle of the spirals affect fibre strength and maturity. Fibre elongation and maturity can be impacted by numerous factors from fertilization to maturity until the boll opens, the fibre is a living cell, but upon opening the fibre is exposed to the air and soon dries out and becomes twisted. In addition to the long fibres, most commercial cultivars (excluding GossypiumBarba dense) have very short white or coloured fibres on the seed called linters or fuzz fibres.
Cotton quality is defined by the length, maturity, strength and micronaire of the fibre. These qualities are determined by the genetic makeup of specific plant varieties, the climatic conditions experienced by the crop, and the management of the crop through production and harvest. For example, bolls maturing late in the season, when temperatures are lower, require a longer period for fibre growth and development and usually produce less lint often of lower quality.
Understanding cotton growth and development is critical in order to implement sound management strategies for maximum yields and profits. Cotton is a perennial plant with an indeterminate growth habit and has a very dynamic growth response to environment and management. Site-specific management strategies need to be taken into consideration to optimize yields. Furthermore, management strategies should be flexible to allow for changing environmental conditions.
6.Harvesting / Picking :
Cotton Fibre Structure
Cotton fibres have a fibrillary structure. The whole cotton fibre contains 88 to 96.5% of cellulose, the rest are non-cellulosic polysaccharides constituting up to 10% of the total fibre weight. The primary wall in mature fibres is only 0.5-1 µm thick and contains about 50% of cellulose. Non-cellulosic constituents consist of pectins, fats and waxes, proteins and natural colorants. The secondary wall, containing about 92- 95% cellulose, is built of concentric layers with alternatic shaped twists. The layers consist of densely packed elementary fibrils, organized into micro fibrils and macro fibrils. They are held together by strong hydrogen bonds. The lumen forms the centre of the fibres. Cotton is composed almost entirely of the polysaccharide cellulose. Cotton cellulose consists of crystalline fibrils varying in complexity and length and connected by less organized amorphous regions with an average ratio of about two-thirds crystalline and one-third non-crystalline material, depending on the method of determination.
The primary wall is about 1 µm thick and comprises only about 1 % of the total thickness of cotton fibre. The major portion of the non-cellulosic constituents of cotton fibre is present in or near the primary wall. Non cellulosic impurities, such as fats, waxes, proteins, pectins, natural colorants, minerals and water-soluble compounds found to a large extent in the cellulose matrix of the primary wall and to a lesser extent in the secondary wall strongly limit the water absorbency and whiteness of the cotton fibre. Pectin is located mostly in the primary wall of the fibre.
Macro structure of cotton
Polymer system of cotton
Physical properties of cotton
Tenacity – The strength of cotton fibres is attributed to the good alignment of its long polymers (that is its polymer system is about 70 per cent crystalline), the countless, regular, hydrogen bond formations between adjacent polymers, and the spiralling fibrils in the primary and secondary cell walls. It is one of the few fibres which gains strength when wet. It is thought this occurs because of a temporary improvement in polymer alignment in the amorphous regions of the polymer system. The improved alignment when wet results in an increase in the number of hydrogen bonds, with an approximate 5 per cent increase in fibre tenacity.
Elastic plastic nature – The cotton fibre is relatively inelastic because of its crystalline polymer system, and for this reason cotton textiles wrinkle and crease readily. Only under considerable strain will cotton polymers give and slide past one another.
Hygroscopic nature – The general crispness of dry cotton textile materials may be attributed to the rapidity with which the fibres can absorb moisture from the skin of the fingers. This rapid absorption imparts a sensation of dryness which, in association with the fibres inelasticity or stiffness, creates the sensation of crispness. The hygroscopic nature ordinarily prevents cotton textile materials from developing static electricity.
Thermal properties – Cotton is not thermoplastic and hence excessive application of heat energy reasons the cotton fibre to char and bum, without prior melting.
Luster – Lintreated cotton has no pronounced luster. Therefore in order to make it lustrous they need to be mercerized.
Effect of Acids – Cotton fibres are weakened and destroyed by acids. Acids hydrolyze the cotton polymer at the glycosidic oxygen atom which connects the two glucose units to form the cellobiose unit. Mineral acids being stronger than organic acids will hydrolyse the cotton polymer more quickly.
Effect of Bleaches – The most common bleaches used on cotton textile materials are sodium hypochlorite and sodium perborate. They are: oxidizing bleaches and bleach because of the oxygen liberated from them.
Effect of Sunlight and weather – The ultra-violet rays of sunlight provide photo chemical energy whilst the infra-red rays provide heat energy essential to degrade the cotton polymers in the pressure of atmospheric oxygen, moisture and air pollutants. The breakdown of polymers takes place through diverse hydrolysis reactions. The beginning degradation is noticed as a slight fibre discoloration. Fading of colored cotton textile is partially because the breakdown of the dye molecules in the fibre’s polymer system.
Color Fastness – Cotton is easy to dye and print. The classes of dye which may be used to color cotton are azoic, direct, reactive, sulphur and vat dyes. The polar polymer system easily attracts any polar dye molecules into the polar system. Therefore, dye molecules which can be dispersed in water will be absorbed by the polymer system of cotton.
However– the dye molecules can enter solely the amorphous regions of the polymer system of cotton. The small inter polymer spaces in the crystalline regions of the polymer system prohibit the entry of the crystalline molecules.
Mildew – Cotton is damaged by fungi. Heat and dampness support the growth of mildew. The fungi produce a chemical compound which has the power of changing cellulose to glucose. The fungi feed on the molecules of sugar: Cotton treated with acrylo nitrite is resistant to mildew.
Insects – Moths and beetles do not change cotton. Silver fish will eat cotton cellulose especially if heavily starched.
The cotton module is cleaned, compressed, tagged, and stored at the gin. The cotton is cleaned to separate dirt, seeds, and short lint from the cotton. At the gin, the cotton enters module feeders that fluff up the cotton before cleaning. Some gins use vacuum pipes to send fibres to cleaning equipment where trash is removed. After cleaning, cotton is sent to gin stands where revolving circular saws pull the fibre through wire ribs, thus separating seeds from the fibre. High-capacity gins can process 60, 500-lb (227-kg) bales of cotton per hour. Cleaned and de-seeded cotton is then I 0 compressed into bales, which permits economical storage and transportation of cotton. The compressed bales are banded and wrapped. The wrapping may be either cotton or polypropylene, which maintains the proper moisture content of the cotton and keeps bales clean during storage and transportation.
Every bale of cotton produced in the United States must be given a gin ticket and a warehouse ticket. The gin ticket identifies the bale until it is woven. The ticket is a bar-coded tag that is torn off during inspection. A sample of each bale is sent to the spinning unit for evaluation, where it is assessed for
- Leaf content
- Fibre length
- Trash content.
The results of the evaluation determine the bale’s value. Inspection results are available to potential buyers. After inspection, bales are stored in a carefully controlled warehouse. The bales remain there until they are sold to a mill for further processing.
Today, nearly all cotton is stored in modules, which look like giant loaves of bread. Modules allow the cotton to be stored without losing yield or quality prior to ginning. Specially designed trucks pick up modules of seed cotton from the field and move them to the gin. Modern gins place modules in front of machines called module feeders. Some module feeders have stationary heads, in which case, giant conveyors move the modules into the module feeder. Other module feeders are self-propelled and move down a track that alongside the modules. The module feeders literally break the modules apart and “feed” the seed cotton into the gin. Other gins use powerful pipes to suck the cotton into the gin building. Once in the cotton gin, the seed cotton moves through dryers and through cleaning machines that remove the gin waste such as burs, dirt, stems and leaf material from the cotton. Then it goes to the gin stand where circular saws with small, sharp teeth pluck the fibre from the seed.
From the gin, fibre and seed go different ways. The ginned fibre, now called lint, is pressed together
Types of Ginning
Previous to the introduction of Modern Machinery, ginning was performed by hand or by machines of a primitive character such as the “Foot Roller” and its improvement the “Churka”.
As the cotton industry developed, greater production than these were capable of was necessary, and machines driven by power were introduced. Numerous forms of gins have been tried, but at the present time only three are used to any large extent. They are
- Knife Roller Gin / Roller Gin
- Saw Gin (Fig. 20)
- Macarthy Gin
- Single Roller Gin – McCarthy Gin
- Double Roller Gin
- Knife Roller Gin
The constructional detail of the machine is clearly shown in fig. The seed cotton is placed in bulk on the table. By means of the reciprocating motion of the table by the crank arrangement, the seed cotton comes into contact with knife roller (formed of a number of knife discs).
Auxiliary roller breaks the large cluster of seed cotton and maintains a constant supply of cotton to knife roller. Knife portion being arranged in such a manner that anything coming into contact with it is given a reciprocal or to and fro motion as well as being subject to a striking action due to its revolution. The seed cotton is carried forward in the direction of knife roller’s motion until it is brought into touch with leather roller. This roller, which has a much roughened surface, due spirally-formed saw cuts. Has pressing against, it by means of spring and steel doctor Knife. The cotton fibres brought into contact with the leather adhere to it, and are carried round past .the knife. It is impossible for the seeds to follow. So, seeds will remain at the point of contact of the doctor knife and leather roller, with the fibres still connected with it. The essential feature of this gin now comes into play. The knife roller is so set as to act upon, these adhering seeds, and it gives to them a gentle to and fro motion, repeated very quickly ‘and at the same time a slight striking action or pressure also repeated quickly. The combined action soon causes the seeds to separate from the fibres and to fall down through the grid to floor. The freed fibro passing forward is stripped from the roller by some arrangement of the stripping board. The seed cotton not taken up by one leather roller is brought round into contact with another 1eather roller where same process as described above is gone through and to which the same parts equally apply.
- Saw Ginning Machine
- Macarthy Ginning Machine
and dragged forward till the seeds reach the edge of a stationary knife. The edge where the fibre is caught is the ginning point. By the downward motion of the moving knife, the seeds are detached from the cotton at the ginning point and are thrown out through the slots of the grid. It is important that the grooves of the rollers should be kept well open and when the leather roller becomes smooth, the rough file should be applied occasionally to the surface to keep the same grip and pull on the fibre. The seeds are then hammered by means of the rapidly moving knife whereby some fibres are separated. In subsequent cycles, the remaining fibres also get separated. This process is continued till all the fibres from the seed get removed. The Single Roller McCarthy Gin technology is most suitable for handpicked, low trash cotton of medium, long and extra long staple length. This technology retains maximum natural fibre parameters of the cotton during the ginning hence treated best.
2. Double Roller Gin – Double Roller is the improved version of McCarthy Single Roller Gins. In a double roller (DR) gin, two spirally grooved leather rollers, pressed against two stationary knives with the help of adjustable dead loads, are made to rotate in opposite directions at a definite speed. The three beater arms (two at the end and one at the centre of beater shaft) are inserted in the beater shaft and two knives (moving knives) are then fixed to the beater arms with proper alignment. This assembly is known as beater assembly, which oscillates by means of a crank or eccentric shaft, close to the leather roller. When the seed cotton is fed to the machine in action, fibres adhere to the rough surface of the roller and are carried in between the fixed knife and the roller such that the the are partially gripped between them. The oscillating knives (moving knives) beat the seeds from the top and separate the, which are gripped from the seed end. This process is repeated a number of times till all spin-able fibres are separated from the seeds, which are carried forward on the roller and doffed out of the machine. The ginned seeds drop down through the slots provided on the seed grid, which is part and parcel of beater assembly, which also oscillates along with the moving knives. This technology also retains the maximum natural , parameters of the cotton similar to McCarthy Single Roller Gin but produces double or more quantity of fibre at same electrical power and processing cost hence most cost effective. Therefore maximum McCarthy Single Roller Gins have been replaced by this technology in case of handpicked cotton. In Double Roller Ginning Technology one can gin all types of cotton of the world by simple setting adjustments, hence this technology has rapidly replaced majority of McCarthy Single Roller Gins and has become most preferred technology for handpicked cotton where trash contents are lower in the seed cotton.