Coping with drought: Deficit irrigation strategies for cereals and field horticultural crops in Central Tunisia

Preparedness measures to cope with droughts and water scarcity in semi-arid climates in irrigated agriculture include the identification of irrigation scheduling strategies that minimize the water demand with acceptable impacts on yields. nose strategies may be produced by simulation and focus on different levels of water demand. The irrigation scheduling simulation model ISAREG, validated for Tunisia, is used to simulate those strategies. The generated irrigation scheduling strategies are applied to deficit irrigation of winter wheat, tomato and potato crops under semi-arid conditions in Central Tunisia. The alternative schedules are evaluated through the combined use of indicators relative to the reduction in demand for irrigation water, the consequent yield reduction and the impacts on farmer's income. The economic evaluation of those strategies is performed with the help of a linear programming model. Results indicate that, when there is limited water availability, each crop reacts differently to the water restrictions applied in terms of yield decrease and gross margin per unit surface and unit of water applied. For average demand, the adoption of deficit irrigation is generally feasible for all crops considered. However, for the tomato crop, there is a trend to restrict the cultivated surface when water scarcity increases. Under high and very high demand conditions, the gross margin per unit of water applied decreases for the potato and the tomato crops but increases for the wheat crop. Then, adopting deficit irrigation is not feasible for the tomato and potato crops, the option being to decrease the cultivated surface. On the contrary, the wheat crop responds well to deficit irrigation, with a good water valorisation, including under drought conditions.