Evaluation of very high soil-water tension threshold values in sensor-based deficit irrigation systems

The variable and limited availability of water for irrigation in agriculture is a general challenge for farmers to cope with. Sophisticated irrigation strategies are needed that allow an efficient management of the available water resources, i.e., ensuring high water productivity (WP). Controlled deficit irrigation (DI) can be such a strategy in which soil-water status specific thresholds (in either soil-water tension or moisture) are used to trigger irrigation. For DI systems to be effective, irrigation control is of utmost importance, yet thresholds are likely to be chosen by trial and error. Hence, systematic investigations for deriving reliable thresholds are needed that account for different DI strategies. In this study a methodology is presented for evaluating the performance of sensor-based DI systems for very high soil-water tension threshold values. The study consists of three parts: a DI experiment with maize was carried out where a new sensor was employed that allowed measurement of high soil-water tensions and that was used to control irrigation. From that experiment, a crop growth model was calibrated, and finally the model was used in a simulation study to systematically investigate parameters for implementing effective setups of DI systems with high soil-water tension thresholds. Possibilities and limitation of this methodology are shown and discussed when applied for investigating and evaluating the potentials of sensor-based DI systems.