| The exploitation of production factors is essential for sustainable agriculture. Sustainability is very important in productive systems of irrigated lands in semiarid regions, where water is scarce and expensive, and optimisation is essential.; Irrigation water optimisation should be considered from different points of view: (1) irrigation programming; (2) application efficiency improvement of the irrigation systems; and (3) election of crops that allow obtaining maximum profitability (economic, social, etc.).; The developed model considers the crops in a district, determining net irrigation requirements for different productive strategies. Economic information is added, obtained by valorising the technical itinerary of each productive strategy. With these data, and by means of the crop production function (including the effect of water application efficiency of the irrigation system on yield), the model relates gross margin for each crop to discharged gross depth.; Finally, this function (polynomial) that relates gross margin with gross irrigation water depth is obtained, and considered in a global optimisation process, where other variables can be included and the restrictions necessary to define the reference scenario. This non-linear optimisation system is based on genetic algorithms, analysing different combinations (as in a natural selection process) to reach the optimum solution.; The model can be applied on either a farm or a large irrigated area using representative farms. Thus, it is an interesting decision-support system (hydrologic planning, alternative analysis in engineering projects, prices, climatic variability effect, etc).; In this work, the developed model is applied to the 08.29 Hydrogeological System located in semi-arid Spain, whose resources supply 120000 ha of irrigated lands.; Among the fundamental results, it is important to highlight that optimum water depth is below the necessary for maximum yield, and that the cropping alternatives that maximise gross margin are mainly integrated by horticultural crops.; Other interesting conclusion when including crops in the alternatives to maximise gross margin in the farm is that water depths obtained, in the optimisation process, are between optimum irrigation depth of each species and water depth allowing maximum economic efficiency (gross margin/m 3). Water depth obtained is closer to economic efficiency depth the lower water availability is. |
