Abstract
The stress on water resources and the need to maintain water quality and to protect the environment push for an efficient use of natural resources: irrigation water and nutrients (particularly nitrogen). Traditional surface irrigation areas (frequently located on saline materials) use huge amounts of these resources, contributing to the degradation of water bodies by salts and nitrate loads in Irrigation Return Flows (IRF), and also to soil salinization when salt leaching is constrained. In this respect, 1.5 Mha of irrigated lands in Spain have been modernized recently to more efficient systems. Such is the case of the Violada Irrigation District (VID; 4880 ha; Northeast Spain) modernized from surface to sprinkler irrigation. The availability of historical data under both irrigation systems in VID offered an ideal scenario to analyze the impact of the modernization process on water consumption and nitrogen management. The analysis was based on the water and salt balances, which showed that irrigation modernization triggered an alteration of the hydrological regime of the VID controlled by the irrigation system. The transformation to sprinkler irrigation resulted in high quality non-diverted water savings of 5536 m3/ha yr (19 h m3/yr for the whole VID) available for other uses downstream, triggering a reduction of the IRF from the VID to the Ebro River. In general, the modernization has brought about a clear reduction of all flows in the water balance (except ETa), together with a slight increase in salt and nitrate concentrations in IRF. Both changes entailed a reduction in salt and nitrate loads of 11.5 Mg/ha yr (44,889 Mg/yr; −60.4%) and 82.2 kg N/ha yr (301 Mg N/yr; −70.4%), respectively. The modernization also resulted in better water use and agronomic indices (drainage fraction, consumptive fraction and irrigation fraction). It was also concluded that at the moment, there is no risk of soil salinization in VID.
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