Cotton

Water Management

Water requirement

• Till square formation, it requires 20-25 cm.
• From squaring to first blooming, 20-25 cm water is required by cotton.
• Remaining, 10-20 cm is required during boll development.

• Total 50-70 cm of water is required for cotton crop.
• The moisture stress at critical stages drastically reduces the growth and yield of cotton.
• The moisture stress during boll development will not only reduce the yield but substantially affect the quality of fibres.

Problems due to excess water

• The seasonal water use of the crop ranges from 70-110 cm depending on location, type of soil time of sowing, and duration of the crop and management practices.
• When the number of irrigations are less, the root development will be deeper which absorbs moisture from duper layers as compare to frequent irrigation. The crop is susceptable for moisture stress during flowering. With regard to irrigation, 3 periods can be distinguished.
• From sowing to flowering
• From flowering to active boll development
• Period of renewed vegetative growth and boll production.

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Critical stages of Water Requirement

• Seedling emergence
• Square formation
• Flowering
• Peak boll development

Water Requirement

• Moisture requirement till first bloom peak 30-40 cm
• From first peak to first boll opening 30-35 cm
• There after 10 cm

• Total - 70-80 cm of water is required for cotton crop.
• In red sandy to loamy soil cotton takes 40 per cent of its moisture from 30 cm depth and then remaining 32 per cent from 30-60 cm. whereas in black soil 60-65 per cent of its moisture from top 30 cm and then remaining 20-25 per cent from 30-60 cm.

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Methods of irrigation

Nitrogen

• The best method of irrigation for cotton is ridges and furrows. It is suitable for all the situations and reduces the wastage of water. It is also suitable for deep rooted crop like cotton.
• Ridges and furrow irrigation is also suitable for alternate furrow irrigation during water shortages. 30-35% water could be saved by alternate furrow irrigation.
• Use of sprinklers is an efficient method of irrigation for cotton cultivation. It can increase irrigation efficiency by 50-60% as compared to surface methods.
• Recently, drip method of irrigation is tried widespread for hybrid cotton. It can increase the irrigation efficiency by 80-90% as compared to surface methods.
• In Karnataka, most irrigated cotton area lies in command areas. The farmers in command area tend to use the irrigation water indiscriminately with no regard to the requirement of crops.

Drip irrigation in cotton:

• Cotton being a commercial crop, drip irrigation has been adopted in this crop in zone 3 and 8. This method of irrigation not only save 50 per cent of water, but also save the electricity and expenditure incurred on labours. In case of hybrid seed production, drip irrigation helps in the crossing activities. Though initial investment is too high, but the cost incurred could be recovered with in 3-4 years by increasing the area under irrigation and the production. Where the water, electricity and labour is the problem, drip irrigation is bless for them to adopt.
• Water saving is under drip irrigation is more than alternate furrow irrigation. Hybrids like DHH-11 and Sahana varieties are most suitable for drip irrigation. In addition to above, in zone-2 ACP-71 and AH-107 varieties are recommended for drip irrigation. Pair row (60-120 cm) system of sowing or dibbling and adaption of drip irrigation can save expenditure on lateral pipes by 50 per cent.
• Drip irrigation should be given once in 2 to 3 days or depending upon the evaporation rate and water requirement of crop. Crop should be irrigate if evaporation rate is 75 per cent for hybrids and 50 per cent for varieties. Irrigation also depends upon the number of lateral pipes, drippers, rate of flow through dripper and water requirement of the crop.
• In intra specific hybrids and varieties, apply 10 per cent of fertilizers at the time of sowing and rest of the dose applied between 30 to 120 days as top dressing in 10 - 15 days intervals. For fertigation, instead of high cost liquid fertilizers, other fertilizers like urea and DAP can be used as fertigation after dissolving them in water.
• In developed countries, yield obtained per ha in drip irrigation varies from 40-50 q/ha but in India due to high insect pest infestation on the crop, yield is restricted to only 15-30 q/ha.

Note:

• Drip irrigation should be given as per the following table.
• Evaporation rate 75 and 50 per cent is recommended for hybrids and varieties respectively.

• Water flow rate – 4 lit / dripper / hour
• Wetting area – 60%
• Distance between two dripper – 60 cm
• Distance between two laterals – 60 cm

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Water required from sowing to flowering

• The ridges are laid out so as to adjust with row spacing. The slope in the furrow should not be more than 1 to 2%.
• The height of ridge should not be less than 30 cm.
• Each furrow should not be irrigated directly by opening the feeder channel at required place. But, each furrow may be irrigated by siphon tube from feeder channel or alternatively a control channel may be created inside the plot – from where openings can be made at required places.
• Water should not be allowed to be stagnated at any stage for more than a day. A proper drainage should be arranged.
• The seeds can be placed on dry ridge and irrigation can be provided in furrows so that ridges are moistened with adequate water and help in good germination.
• Do not irrigate the crop – whenever the water is available. But, irrigate the crop when the soil is dry or crop shows wilting symptom. Including the critical stages, cotton require 5-6 irrigation in black soils 10-12 irrigation in red loamy/red sandy soils.
• Avoid irrigation at boll bursting stage – (after 150-160 days in hybrids; 130-140 days in varieties).
• Adjust the irrigation schedule to critical stages like germination, squaring, flowering, boll development stages.
• In case, deep presoaking irrigation is given before sowing, crop need not be irrigated for first 40-50 days

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Water required from flowering to active boll development

• A deep ploughed and well pulverised soil can retain large quantity of water in it. Hence, full ploughing (immediately after earlier crops) or ploughing at the time of first shower is most essential step.
• A proper contour bunding (preferably live) structure is also essential for better moisture conservation.
• The crop rows should be established across the slope and not along the slope.
• In heavy rainfall tracts, laying out the land in ridges and furrow will help in ensuring that crop is grown with good areation.
• Application of atleast a kg of FYM at each spot of irrigation helps the crop establish better and hold the moisture for a long time.
• It is advisable to collect extra rainwater in the farm pond and utilize the same for protective irrigation during the drought period.

Table : Every day water requirement of cotton crop (Zone 2 and 8)

Period of renewed vegetative growth

• Most cultivated cotton varieties have retained their perennial habits in part. Hence, supply of moisture at late stages (either by rain or irrigation) can result into post maturity vegetative growth.
• Post maturity vegetative growth is at cost of process of fibre maturity of late formed bolls.
• It is necessary to discourage it, when it occurs by rains, it is desirable to defoliate the plants.
• Under no circumstances, the renewed vegetative growth should be encouraged to lead to flowering and fruiting – by supplemental fertilizer application because such practice leads to perpetuation of pests.

Ratooning

• Dry land farmers have the practice of cutting the plant at base or retaining the entire plant till next monsoon and allow a ratoon crop. Irrigated farmers can also practice it to grow two crops of cotton in one year.
• Though this appears to reduce the cost of seed, cost of land preparation but it is not desirable in the long run interest.
• Some farmers have success stories are found in farming community, whenever yield of ratoon crop is recorded to be more than main crop itself.

But, a closer scientific observation has shown that ratooning is a dangerous practice because:

• It perpetuates the polyphagous pest like helicoverpa armigera.
• Usually in South India, pink bollworm attack is at late stages and thus damage is minimum. By ratooning, this pest is invited from 3rd or 4th week of crop itself.
• The cut at the base promotes profuse growth of lateral branches, this leads to difficulties in inter cultivation.
• If the crop is left uncut and later vegetative growth is allowed, the potentiality to bear the foliage and flowers is limited as new leaves/flowers should appear at the apex of each branch.
• The quality of fibres in ratoon crop is not good because the bolls will not gain advantage of continued nutrition by normal growth of leaves.

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