Water is the major factor limiting cotton production in Australia, with 70-90% of the cotton production area usually managed under an irrigated system. The Cotton Catchment Communities Cooperative Research Centre (Cotton CRC) placed a major emphasis on improving water use efficiency and productivity of irrigated cotton farming systems in Australia. This paper reviews the research and trends in the water use efficiency and productivity of irrigated cotton.

Cotton CRC research from 2006 – 2012 focused on promoting measurement of water use efficiency, optimising the performance of surface irrigation systems, investigating alternatives irrigation systems to the conventional furrow irrigation systems, understanding the movement of water through the soil and the potential of deep drainage, reducing water losses from on farm storages and better understanding of plant water relations

Surface irrigation systems are used on 80% of the irrigated Australian cotton crop and utilise 6-7 ML/ha depending on the amount of seasonal rain received. Over the past decade water use efficiency by Australian cotton growers has improved by 3-4% per annum, or by 40% increase in the water use productivity. This has been achieved by both yield production increases and more efficient use of applied irrigation water. The whole farm irrigation efficiency has improved from 57% - 70%, while crop water use index is above 3 kg/mm/ha and is high by international standards. The seasonal evapotranspiration of surface irrigated crops averages 729 mm over the last 20 years

Yield increases over the last decade can be attributed to plant breeding advances, the adoption of genetically modified varieties, and other agronomic research. There has been an increased use of irrigation scheduling tools and furrow irrigation system optimisation evaluations. This has reduced in field deep drainage losses. The largest losses of water on cotton farms is from evaporation from on farm water storages. Application efficiencies of over 90 per cent are achievable under well managed furrow irrigation. The greatest initial gains in water use efficiency can be achieved by improving the management of existing surface irrigation systems through this site specific optimisation. Growers are also making changes to alternative systems such as centre pivots and lateral move systems and it is expected there will be increasing numbers of these machines in the future. These systems achieve labour and water savings (30%), but have significantly higher energy costs associated with water pumping and machine operation.

The standardisation of water use efficiency measures and improved water measurement tools for surface irrigation have been important research outcomes to enable irrigation benchmarks to be established. While the Cotton CRC achieved important new research outcomes, its major effort was related to water extension projects, training of growers and advisers, capacity building, technology demonstrations and information packaging. The industry benchmarks indicate that Australian cotton irrigators should be producing >1.1 bales per ML water (total water, ie irrigation water applied, rainfall and soil moisture used) with surface irrigation systems and 1.3 bales/ML with centre pivots and lateral move machines.

Water use management performance is highly variable and site specific between cotton growers, farming fields and across regions. Therefore, site specific measurement is important. The range in the presented data sets indicates there remains potential for further improvement in water use efficiency and productivity.