LAUSR

Abstract Desalinated sea water (DSW) is increasingly being used as an alternative source of irrigation in dry coastal areas. Owing to its high price and singular composition, it is often blended with other water resources to curb costs. Although this is a common practice, limited resources are available to manage the increased agro-economic complexity required to balance several water sources with heterogeneous quality, price, and availability restrictions. To support the management of fertigation with DSW, in this study, we present an open-source decision support tool (DST), Irriblend-DSW. The DST has been designed to identify potentially profitable fertigation options for different water and fertiliser availability scenarios. To demonstrate the key features of the tool, we applied it to two actual case study scenarios in south-eastern Spain, where severe water scarcity led to massive seawater desalination for agricultural supply. The information provided by the DST enabled the assessment of the viability of different water blending options and the selection of an optimal combination of water and fertilisers. The simulation results showed that the fertigation costs of the studied crops, hydroponic lettuce, and greenhouse tomato substantially increased with the integration of DSW. The DST output showed how water price rises, and how additional types and amounts of fertilisers are required when more DSW is used. However, because the salinity of the blend is also reduced with the use of DSW, the yield outcome improves and, thus, to some extent, compensates for the increased cost. In fact, despite higher costs, the studied crops were found to be very profitable when the optimised solutions computed by the DST were selected. Moreover, the optimum fertigation solutions not only reduced costs but also decreased nutrient leaching in areas of severely polluted aquifers.