Published on November 15, 2016
1. COURSE :PRINCIPLES AND PRACTICES OF WATER MANAGEMENT COURSE NO : AGRON 504 CREDITS : 3 (2+1) TOPIC : WATER MANAGENT IN COTTON
2. Cotton (Gossypium hirsutum) is grown for fibre and seed. Present world production is about 21 million tons lint and 59.7 million tons seed cotton from about 33.98 million ha. (FAOSTAT, 2001). The origin of cotton is still uncertain. The development of the crop is sensitive to temperature. Cool nights and low daytime temperatures result in vegetative growth with few fruiting branches. The crop is very sensitive to frost and a minimum of 200 frost- free days is required. The length of the total growing period is about 150 to 180 days. Depending on temperature and variety, 50 to 85 days are required from planting to first bud formation, 25 to 30 days for flower formation and 50 to 60 days from flower opening to mature boll. No clear distinction can be made in crop growth periods since vegetative growth is continued during flowering and boll formation and flowering is continued during boll formation.
3. Cotton is a short-day plant but day-neutral varieties exist. However, the effect of day length on flowering is influenced by temperature. Germination is optimum at temperatures of 18 to 30°C, with minimum of 14°C and maximum of 40°C. Delayed germination exposes seeds to fungus infections in the soil. For early vegetative growth, temperature must exceed 20°C with 30°C as desirable. For proper bud formation and flowering, daytime temperature should be higher than 20°C and night temperature higher than 12°C, but should not exceed 40 and 27°C respectively. Temperatures between 27 and 32°C are optimum for boll development and maturation but above 38°C yields are reduced.
4. Cotton is extensively grown under rainfed conditions. Although the crop is relatively resistant to short periods of waterlogging, heavy rainfall, however, can cause lodging. Continuous rain during flowering and boll opening will impair pollination and reduce fibre quality. Heavy rainfall during flowering causes flower buds and young bolls to fall.
5. Cotton is grown on a wide range of soils but medium and heavy textured, deep soils with good water holding characteristics are preferred. Acid or dense subsoils limit root penetration. The pH range is 5.5 to 8 with 7 to 8 regarded as optimum. The fertilizer requirements of cotton under irrigation are 100 to 180 kg/ha N, 20 to 60 kg/ha P and 50 to 80 kg/ha K. Two-thirds of the nutrients are taken up during the first 60 days of the growing period. Nitrogen should be readily available at the start of -the growing season; normally two applications are given with one after sowing and the other prior to flowering. Phosphate is applied before sowing. Plant spacing normally varies between 50/100 x 30/50 cm.
6. The crop is tolerant to soil salinity. Yield decreases at different ECe values are: 0% at ECe 7.7 mmhos/cm; 10% at 9.6, 25% at 13, 50% at 17 and 100°/ at ece 27 mmhos / cm.
7. Depending on climate and length of the total growing period, cotton needs some 700 to 1300 mm to meet its water requirements (ETm). In the early vegetative period, crop water requirements are low, or some 10 percent of total. They are high during the flowering period when leaf area is at its maximum, or some 50 to 60 percent of total. Later in the growing period the requirements decline. In relation to reference evapotranspiration (ETo) the crop coefficient (kc) for the different development stages is: for the initial stage 0.4-0.5 (20 to 30 days), the development stage 0.7-0.8 (40 to 50 days), the mid-season stage 1.05-1.25 (50 to 60 days), the late-season stage 0.8-0.9 (40 to 55 days), and at harvest 0.65-0. 7.
8. Following figure shows growth periods of cotton (after P.T. Walker)
9. To enhance root development, adequate water should be available in the soil at the time of sowing and pre-irrigation is required when stored soil water from pre-season rainfall is not available. In the vegetative period (1) irrigation may be scheduled when some 60 percent of the available soil water over the first 0.75 m has been taken up by the crop. During flowering (2) depletion of some 70 percent of available soil water will in general check vegetative growth without impairing yields; delayed irrigation during this period may cause considerable flower and bud shedding. During yield formation (boll filling) (3) and ripening (4), the soil water depletion may increase from 60 percent to higher values as the season progresses and depending on climate and depth of stored soil water, irrigation can be terminated 4 to 5 weeks before final picking. When grown under conditions of high groundwater tables, even for short duration, and when soils are wet for long periods, the yield decrease may be up to 50 percent, not withstanding unrestricted water use. This may be due to inadequate soil aeration. The same phenomenon has been noticed under very frequent irrigation application.
10. Cotton is grown under a great variety of irrigation systems of which furrow irrigation is the most common surface system. In regions where the demand for water is great and water resources are small, sprinkler and drip irrigation methods become more and more accepted to economize on water applied and restrict return flow of low quality. In the Near East region, cotton is also grown under controlled flood or spate irrigation, where with little or no rain a one-time pre-sowing irrigation of 0. 5 to 1 m depth stores sufficient water in the root zone to allow the crop to reach maturity. Under such treatments soils must be deep and have a high water holding capacity. With growing season from August to March with ETm = 700 to 750 mm and ETa = about 450 mm, farmers' yields are about 800 kg/ha, with a maximum of about 1 700 kg/ha seed cotton.
11. Convenient check basin of square (2 m x 2 m to 4m x 4m) or rectangular size is used for irrigation. The water is kept within the basin and not allowed to run off. The size of ridges or bunds depends upon the depth of water to be impounded in the basin. The water is turned on to the upper side and is turned off following application of the required quantity of water. This method is more efficient in fine textured soil. Yet, the drawback of this is the requirements for high degree of leveling for uniform distribution of water. However, for small streams, this method can be suitably adopted.
12. This is most common in South Zone since wastage of water is minimized in this method. On sloppy lands, furrow slopes may be limited to 0.3 % and the length of the furrow may be reduced to control erosion and provide the needed drainage. Loam and clay loam soils are best adopted to furrow irrigation because the water holding capacity and intake rate are generally within the range that will permit uniform distribution of water. Furrow irrigation is not suitable for very sandy soil due to high intake rate.
13. Here, the distance between the two rows of cotton is 60 cm for supplying irrigation and the gap adjacent to the row is 90 cm (Normal row spacing is 75 cm). The space available in skip furrow can be intercropped with pulses if two rows of cotton is spaced at 60 cm and the gap adjacent to the row is 120 cm for intercropping (conventional row spacing is 90 cm). In 2:1 skip row planting, recommended for very scarce water available areas where one out of 3 furrows is skipped i.e., not planted. The population in unit area is maintained as in solid planting by reducing the plant to plant spacing in the planted rows by one third (i.e. 22.5 cm instead of 30 cm). Sprout irrigation is given for the planted rows and the other irrigations are given only in the furrows between the planted rows. Here, 60 to 67% saving of irrigation water can be achieved without sacrificing cotton yield.
14. Here, the crop is planted just like in the conventional method as there is no variation in spacing but variation in water application (areas). Water is applied in alternate rather than in all furrows (Irrigating odd & even furrows alternatively). Thus, 1st irrigation is applied in furrows which do not receive the 2nd irrigation and so on….
15. As a general rule, crops obtain about 40% of their total water requirement from the one fourth of the root zone. The depth that soil moisture is managed in irrigation is referred to as the effective root zone or effective rotting depth. Allowable depletion percentage for cotton is 50 – 65% and root zone depth normally irrigated in deep soils is 3 – 4 feet.
16. Cotton cultivation under flood irrigation Cotton cultivation under drip irrigation Sprinkler irrigation in cotton Alternate furrow irrigation in cotton
17. A good yield of a 160 to 180 day cotton crop under irrigation is 4 to 5 ton/ha seed cotton of which 35 percent is lint. Water utilization efficiency for harvested yield (Ey) for seed cotton containing about 10 percent moisture is 0.4 to 0.6 kg/m3. Boll and fibre properties such as lint to seed ratio, and length, strength and fineness of lint, are primarily determined by the variety and to a lesser extent by irrigation and fertilizer practices. In general, the boll size, and the seed and lint index (weight per 100 seeds) increases under adequate water supply. However, the lint percentage (the ratio lint to seed) tends to decrease. Low soil water depletion levels during yield formation (3) tend to result in longer and finer fibre of decreased strength. The direct effect of water deficits on fibre properties, however, appears to be small because of the shedding of bolls which would have produced inferior fibre when allowed to mature.
18. Normally cotton seed contains 35 percent oil and 35 percent protein. Under irrigation there is an indication that severe water deficits substantially reduce the oil percentage in the seed, and more fibrous material with 20 percent lower oil and protein content is produced compared to an adequately irrigated crop
19. Mc Michael et.al. 2010
20. Increase of production and water saving through furrow irrigation Singh (2002)
21. K. Sankaranarayanan et
22. Seed cotton yield, water applied and yield per unit water used for different treatments T1 - 100 per cent ETc and 100 per cent Pw, T2 - 100 per cent ETc and 75 percent Pw, T3 - 75 per cent ETc and 75 percent Pw, T4 - 100 per cent ETc and 50 percent Pw, T5 - 75 per cent ETc and 50 percent Pw, T6 - 50 per cent ETc and 50 percent Pw Shirahatti et al.,2007
23. Onder et al.,2009
24. Sivanappan et al.,1998