There is currently a shortage of irrigation water available for cotton production in Australia due to recent climatic and legislative conditions. Some growers have responded to this water shortage by changing from traditional furrow irrigation to alternative irrigation systems such as centre pivots and lateral move irrigations (collectively known as large mobile irrigation machines – LMIMs). Improved efficiency of irrigation application, as well as labour savings, have been the main reasons for the increased adoption of LMIMs. The use of LMIMs also enables a higher level of control in water application in terms of irrigation volume, timing and placement. As a result, growers now have much greater control over soil moisture conditions which enables the implementation of improved irrigation management strategies that have the potential for improved crop water use efficiency (WUE).

Two irrigation strategies which have been demonstrated to achieve benefits in terms of crop WUE are partial rootzone drying (PRD) and deficit irrigation (DI). PRD and DI involve manipulating the placement of irrigation water and the moisture deficit maintained in the root zone, respectively. Neither PRD nor DI is able to be applied easily under furrow irrigation. However, both PRD and DI may be able to be implemented under LMIMs within the cotton industry. Deficit irrigation has been shown to be effective at improving WUE in cotton, although it is not widely used within the Australian cotton industry. Similarly, there has been little research conducted to identify whether cotton responds to partial rootzone drying and there is currently little understanding of the way in which DI and PRD strategies could be implemented commercially using LMIMs.

This research investigated the response of cotton to a range of PRD and deficit irrigation strategies under LMIMs. Assessment of the biochemical and physiological response of cotton to irrigation strategies were conducted under glasshouse conditions. Field trials conducted under a commercial centre pivot and lateral move assessed the crop response, soil moisture movement, yield and WUE associated with the implementation of a range of PRD and deficit treatments. Modelling of rainfall probability and soil moisture movement were also undertaken to quantify constraints to the successful commercial implementation of irrigation management strategies such as PRD within the Australian cotton industry.