Deficit Irrigation of Cereals and Horticultural Crops: Simulation of Strategies to Cope with Droughts

To cope with droughts and water scarcity in semi-arid to sub-humid climates require the development of preparedness measures. For irrigated agriculture these include the identification of irrigation scheduling strategies that minimize the water demand with acceptable impacts on yields Those strategies may be produced by simulation and focus on different levels of water demand, from average to drought conditions. The irrigation scheduling simulation model ISAREG, first calibrated in Portugal and later validated for Tunisia, is used to simulate those strategies. Results for validation in Tunisia are given in this paper. The generated irrigation scheduling strategies to cope with droughts are applied to the deficit irrigation of winter wheat, tomato, and potato crops, both in Tunisia and in Portugal. The alternatives are evaluated through the combined use of indicators relative to the reduction in demand for irrigation water and the consequent yield reduction. An economic analysis applied to the Tunisian case study is presented in a companion paper. Results show the technical feasibility of reducing the water demand for supplemental irrigation of the wheat crop, including when large water deficits are considered. Results show that crop responses are more favorable when the crop season is relatively short. Also shown that center-pivot systems are less appropriate when deficit irrigation aims at large reductions in the water demand. Results for tomato, cropped out of the irrigation season, evidence that only mild deficits are acceptable and it is less appropriate to adopt large water deficits. In case of the potato crop, it was observed that deficit irrigation is easier to be adopted when early planting is practiced; for late planting, this crop behaves like the tomato crop, thus showing large yield losses when heavy deficits are considered.