Improving Irrigated Agriculture: How Far Can We Go?

The last decade has seen the nexus between increasing world population and the area of irrigated land broken, indicating that further population will need to be fed by improved water productivity rather than through increased irrigated area. But how much improvement is possible? This paper systematically considers irrigated agriculture from the plant through to a catchment, and from production and natural resource use perspectives. While there is some evidence of improvement in transpiration productivity (yield per unit of transpired water) of our common irrigated crops, it seems we have reached the limit of potential improvement. Opportunity still exists to increase economic yield while containing seasonal water use through manipulation of vegetative and reproductive growth phases. For crops, the opportunity for improving water productivity largely involves decreasing soil surface evaporation relative to crop transpiration. There are still gains to be made in this area from both improved irrigation system design and agronomic practice. Farm layout, distribution and application systems can be significantly improved to increase water use efficiency. However, given the relative costs of water, earthworks, labour and equipment, there is often little financial incentive to reduce total water use for marginal gains in yield. Audits of many distribution systems show considerable opportunity for improvement and also highlight the inadequacy of current measurement systems. There is generally good opportunity to decrease water losses in these distribution systems but a significant limitation is securing the immediate and ongoing financial resources needed to upgrade. Given the demand for water and the constraints on availability, we need improvement in financial and ecological productivity. Our purpose is therefore to seek increased multi-purpose water use productivity. There is good evidence that this can be achieved through irrigated regional engagement and a much greater emphasis on irrigation within a business context.