Cotton is considered as a ‘xerophyte’, meaning a plant that needs less water. Cotton is basically tolerant to drought and heat. The plants circumvent adverse weather due to their well-distributed root system and indeterminate growth habit. Based on the crop evapotranspiration ETc rates, water requirement of cotton crop was reported to be 2.0 mm per day (20,000 litres per hectare) during the vegetative stage and 6-8 mm per day during flowering and early green boll formation stage (critical window). Research reports show that cotton crop needs about 80-85% of the total water requirement during the critical window; and moisture stress during this time causes serious yield losses. Excessive water during vegetative and boll opening stages cause lower yields. Irrigation and rainfall data were obtained from 44 main cotton-growing countries and analysed by the ICAC to estimate water productivity. The following results were obtained:
1. The global average irrigation water usage was 1214 litres to produce 1.0 Kg lint + 2.0 Kg seeds.
2. The global area under rain-fed cotton is 16.9 million hectares, which is equivalent to 55.7% of the total cotton acreage.
3. Rain-fed area contributed to 10.22 million tonnes of lint, which is equivalent to 41.3% of the total global cotton production.
4. About 21.42 million tonnes of lint, which is equivalent to 87.0% of the total global cotton was produced by using only 644 litres irrigation water per Kg lint.
Water productivity can be enhanced by water harvesting, irrigation with precision timing based on evapotranspiration measurements and optimizing the methods of water delivery through alternate furrows, or sprinklers or sub-surface drip irrigation. Soil and moisture conservation methods such as minimum tillage, mulching, cover crops or intercrops, efficient pest and weed management were reported to enhance yields, thereby greatly enhancing water use efficiency and water productivity.