The Best Farm-Level Irrigation Strategy Changes Seasonally With Fluctuating Water Availability.

Around the globe farmers managing irrigated crops face a future with a decreased and more variable water supply. To investigate generic adaptation issues, a range of on-farm strategies were evaluated for apportioning limited water between fields and enterprises using a typical case-study farm from Australia’s Riverina region. These strategies are compared for a range of seasonal water availability levels. The analysis did not address investment in new irrigation technologies or new crops, but focussed on irrigation intensity and crop choice amongst existing enterprises. Participatory engagement and whole-farm simulation modelling were our primary tools of research. The adaptation options found to best suit irrigation farming in years of high water availability were substantially different to those when water supplies were low.   In circumstances when water is plentiful and land availability becomes the limiting factor in production, it makes economic sense to fully-irrigate and fertilize crops, selecting populations and varieties to maximize crop yields.  In this way, farmers maximize their return per ML, per hectare, and per farm. However, when water allocations are low, our analysis demonstrated that the best average returns per farm are obtained through strategies which ‘spread the water’ and focus on maximizing land utilization through partial irrigation of winter crops, capitalizing on the law of diminishing returns. These strategies aim for sub-maximal yields per hectare, but maximize returns per ML and per farm when land is not limiting. This illustrates strategic differences between irrigation farming in land-limited circumstances and water-limited circumstances. Our study indicates that the cropping and irrigation strategy leading to greatest farm returns changes on a season-by-season basis, depending primarily on the water availability level.