Modeling, Simulation and Control of Irrigation on Young Almond Trees

Almond is the third largest woody crop in Spain. Although traditionally it is considered as a highly drought-tolerant crop with a great adaptability to water shortage, under non-limiting conditions almond significantly improves its yield, generating higher economic profits and increasing irrigation water productivity. Adequate measurements of volumetric soil-water content (SWC) and physiological parameters are of critical importance in order to evaluate the water and energy levels and to understand the biological and chemical processes in the soil-plant system. A deficit irrigation trial was conducted in juvenile almond trees, measuring the SWC with a real-time monitoring of the gravimetric SWC and trunk diameter fluctuations (TDF), which acted as the input signals for an automated control system. A simple model of the soil-plant-atmosphere system was proposed, designed and tested using the collected information. Subsequently, the model was used to design an irrigation automatic control system and simulate its performance using Matlab (R) mathematical software. Aside from the simple hysteresis (Yes/No) controller which was used in the experiment, a classic optimal LQG controller for lineal (or linearized) systems was proposed. Results suggests that the application of an automatic irrigation control system can be used to optimize the use of irrigation water while keeping the soil and plant water content at optimal levels. Furthermore, the use of TDF measurements in addition to SWC improves the performance of the controlled system.