Crop water use and water use efficiency on irrigated cotton farms in Australia

Increasing public debate regarding the allocation of water resources within Australia has introduced a new level of significance to the issue of water use efficiency (WUE). Irrigated crops have been criticised for inefficient water use, but there is little information available to quantify performance. Production and water use data were obtained from 25 cotton farms and over 200 individual fields representing the six largest production areas, which produce over 80% of the annual crop. A daily water balance was calculated for each crop to estimate evapotranspiration (ET). Irrigation efficiency (IE) was calculated as the proportion of irrigation water input to the farm for cotton production that was used by the crop as ET over the growing season. Crop water use efficiency (CWUE) was calculated as lint production per unit of ET. The average on-farm total water input was 12 Ml/ha including 7 Ml/ha of irrigation water. The estimated mean seasonal ET was 735 mm. The observed average CWUE was 2.5 kg/mm/ha and the average farm level IE was 57%, but both efficiency measures showed large variability. These values compare well with published data on cotton industries in other countries. The figures can be used as a basis for future water management activities of the cotton industry. The wide variation in both CWUE and IE indicates that there is significant potential for some producers to increase their efficiency under the current reduction in water allocation.