Improving the suitability of desalinated water for irrigated agriculture using adsorbents based on clay and ash

Abstract

Water scarcity and high pressure over available water among productive sectors are one of the main limiting factors on the competitiveness of irrigated Mediterranean crop production. In addition to agronomic practices to improve water productivity, using non-conventional water sources, such as desalinated water (DW), could be an effective solution if its suitability for irrigation is improved, as it often presents constraints related to its mineral composition, particularly due to high concentrations of boron (B), which can reduce crop productivity. In this regard, treating DW with natural and cost-effective adsorbents, such as clay or carbon ash, offers a promising strategy to reduce water nutrient excess and enhance its suitability for irrigation. For this reason, the objective of our work was to evaluate the effectiveness of adsorbents on DW quality, and the response of winter lettuce grown in pots with coconut fiber irrigated with treated DW. Three randomized treatments (n = 5) were established according to the irrigation water source: (i) a control treatment (CTL), in which plants were irrigated with DW containing 1.2 mg L⁻¹ of B; (ii) T1, in which DW was treated by decantation with 20 g L⁻¹ of clay, mainly composed of kaolinite and sepiolite; and (iii) T2, in which DW was treated by filtration using 50 g L⁻¹ of carbon ash. In all treatments, irrigation was scheduled using a threshold corresponding to a maximum soil water depletion of 20% relative to field capacity. Crop physiological response was assessed as net photosynthesis (Pn) and leaf stomatal conductance (Lc), together with aerial fresh weight and the concentration of macro- and micro-nutrients in both leaves and roots. Prior to the ANOVA assumptions were tested and when differences were detected, means were separated by using LSD-Fisher test (p