Deficit Irrigation Optimization of Cotton with AquaCrop

Given the current pressures to reduce irrigation water use, it is important to optimize the use of water in irrigated agriculture. This work was aimed at determining the optimum level of applied irrigation water (AIW) for cotton (Gossypium hirsutum L.) production in southern Spain under several climatic and agricultural policy scenarios. To generate the yield response to variations in AIW, we used the FAO crop water productivity (WP) model, AquaCrop. Model calibration and validation using four experiments conducted in the region showed that AquaCrop adequately simulated the yield response to AIW. The model was then used to determine the yield–AIW functions for different scenarios, assuming the best deficit irrigation (DI) strategy. An economic optimization procedure showed that maximum profits occurred at AIW values between 540 and 740 mm, depending on the climatic scenario. However, profits stayed close to the maximum (above 95%) for AIW levels exceeding 300–350 mm, indicating that under DI, AIW may be reduced significantly with little impact on profits. A sensitivity analysis suggested that increasing the price of water above the current level will have only a limited impact on optimum AIW, and that the current Common Agricultural Policy (CAP) of the European Union does not encourage water conservation in cotton irrigation. We conclude that AquaCrop is a useful tool to assist managers for making decisions in cotton irrigation under water supply restrictions.