Marginal quality waters: Adequate resources for sustainable forage production in saline soils?

The increasing utilization of non-conventional water sources, particularly in arid regions, necessitates strategies for effectively harnessing these resources. This study examines the impacts of using marginal quality waters, including recycled wastewater (RW) and brackish groundwater (BW), compared to those using desalinated brackish water (DW) as a control, on alfalfa cultivation in Fuerteventura, Canary Islands, over four years. Employing a 25 % leaching fraction in addition to organic amendments and gypsum application, the study evaluates the effects on alfalfa biomass production, mineral composition, and soil quality on two soil types (sandy-loam and clay-loam) affected by salinity. Initial and post-treatment analyses of the topsoil and soil profile revealed significant improvements in soil quality such as reductions in electrical conductivity (ECe), sodium absorption ratio and boron content, especially with RW irrigation. For instance, ECe decreased by 51 % and 26 % in the first 30 cm under irrigation with RW and BW, respectively, with regard to its initial soil conditions. Alfalfa yields under RW and BW reached 97 % and 79 % relative to those irrigated with DW in sandy-loam soil, and 92 % and 73 % in clay-loam soil, respectively. This demonstrates the capability of RW to sustain productivity levels close to those achieved with DW, highlighting its potential as a viable irrigation alternative in arid conditions. Nevertheless, irrigation with BW led to a significant reduction in alfalfa yields after the second year, which could become more pronounced over a longer period of use. Mineral analysis of alfalfa showed that irrigation water quality significantly affects the accumulation of nutrients such as iron and boron, which exceeded adequate levels for optimal livestock nutrition. The study's findings underline the importance of tailored water management strategies that optimize the use of marginal waters, ensuring sustainable agricultural practices in water-scarce environments while mitigating potential risks associated with soil salinization and nutrient imbalances.