Remote sensing to predict soil moisture tension in water saving rice systems of temperate South-Eastern Australia

Non-ponded aerobic rice offers the opportunity for substantial global savings of irrigated water. Site and environment specific soil tension thresholds have been identified for non-ponded rice production to save water without adverse yield consequences. However, soil tension readings are point-source measures that are not necessarily representative of a given irrigation area/paddy and become costly when required in each paddy. Remote sensing offers spatial advantages and has been demonstrated in many crops to accurately estimate crop evapotranspiration (ETc), which is often used to schedule irrigation. This study uses soil moisture tension (SMT) data measured in a commercial aerobic rice experiment conducted in temperate Australia on a heavy clay soil to demonstrate the relationship between soil tension and remotely sensed estimated cumulative ETc between irrigation events using open access satellite imagery. The model was used to predict SMT in the second growing season during the vegetative period after establishment until PI with a root mean squared error of +/- 5.8 kPa. This demonstrates the ability of irrigators to schedule irrigation in water saving rice using open satellite-derived data that can be incorporated into an automated irrigation system, without the need for costly in-field soil moisture sensors. Future research to integrate forecast crop evapotranspiration could enable soil moisture forecasting days in advance, providing irrigators more time to plan irrigation activities.