IrriSAT – weather based scheduling and benchmarking technology

IrriSAT is a weather based irrigation management and benchmarking technology that uses remote sensing to provide site specific crop water management information across large spatial scales. Developed in partnership with the CRC for Irrigation Futures, IrriSAT uses satellite imagery to estimate crop coefficients (Kc) at a 30 m resolution. IrriSAT calculates Kc from a linear relationship with satellite derived Normalised Difference Vegetation Index (NDVI). Daily crop water use is determined by simply multiplying Kc and daily reference evapotranspiration (ETo) observations from a nearby weather station. A seven day forecast of ETo is also produced. A delivery platform is being developed using the Google App Engine. The app will provide easy access to the IrriSAT crop water use data, which coupled with weather and crop water use (ETc) forecasts will enable irrigators to track their soil moisture deficit and better manage irrigation schedules. Spatial crop water use information determined by IrriSAT is also available through the IrriSat app and will allow users to investigate water use difference within and between fields. This information can be used for changing management decisions along with investigating the impacts of these decisions. Introduction Irrigation water is scarce, there are competing needs between the environment, urban communities and agricultural uses (Roth et al. 2013). In the Gwydir Valley in Northern NSW, on average irrigators only receive about 30 per cent of their water entitlement (NSW Office of Water 2015). Therefore, maximising onfarm water use efficiency is vital to farm profitability. Irrigation scheduling matches the timing and volume of irrigation water supplied for crop needs (Wigginton et al. 2012). Of Australian cotton growers, 70 per cent use soil moisture monitoring to assist their irrigation decisions (Roth 2014). This technique often relies on one soil water content profile to represent very variable fields. Weather based irrigation scheduling estimates crop water use (ETc) as the proportion of reference evapotranspiration (ETo), calculated from climate parameters using a multiplier or crop coefficient (Kc), which varies with the stage of crop growth (Allen et al. 1998), where ETc = ETo x Kc. The weakness in this approach is in estimating the crop coefficient (Trout and Johnson 2007) and often generic Kc curves do not match the actual crop water use. Weather based scheduling techniques have not been widely adopted in the cotton industry due to the problem of determining site specific crop coefficients. Kc is related to crop light interception and canopy cover which can be estimated from remotely sensed observations of the normalised difference vegetation index (NDVI) (Trout and Johnson 2007). IrriSAT is a weather based irrigation service driven by satellite data to estimate Kc and ETc at the same 30m resolution as the satellite (Hornbuckle et al. 2009). IrriSAT was successfully used in the Murrumbidgee Irrigation Area by grape and citrus irrigators to estimate daily crop water use and provide irrigation scheduling information to growers (Hornbuckle et al. 2009). It was first trialled in the cotton industry by two consultants in the Gwydir Valley in Northern NSW during 2009/10. In 2010/11 it was trialled by ten cotton consultants in Northern NSW over 20,000 ha. In 2011/12 the IrriSAT technology was applied over 75,000 ha. Although developed primarily as an irrigation scheduling tool, IrriSAT data also provide a means of benchmarking crop water productivity at field, farm and regional scales.