Midterm effects of irrigation with desalinated seawater on soil properties and constituents in a Mediterranean citrus orchard

Desalinated seawater (DSW) is the newest source of water for irrigated croplands, although its use could lead to soil degradation and crop phytotoxicity, due to its high concentrations of boron, sodium and chloride. However, the impacts of DSW on soil properties have not been thoroughly investigated, with more research needed to fully understand how DSW affects soil health. This study presents the effects of irrigating with DSW, mixed water (50 % desalinated seawater + 50 % fresh water) and DSW treated on-farm to reduce its boron concentration on soil properties and constituents, compared to fresh water. Soils were monitored at two depths (0–25 cm and 25–50 cm) every four months for six years, and soil physicochemical characteristics were analyzed. DSW presented low salinity (0.9 dS m –1 ), basic pH (8.4), high concentrations of Na, Cl, and B, and low concentrations of Ca and Mg. The results showed that soil nutrients, organic/inorganic carbon, pH, cation exchange capacity, and soil texture were not affected by the irrigation water used. However, after about three years of DSW application, soil accumulation of boron and sodium began to rise, with a clear tendency to increase over time, reaching concentrations of 2.3 mg kg −1 and 699 mg L −1 , respectively, after six years. Conversely, the concentration of chlorides did not increase in soils irrigated with DSW, due to the high mobility of that element. Although no risk of salinization was observed with the use of DSW (mean value of 2.6 dS m −1 ), the risk of soil alkalinization increased, as the sodium absorption ratio rose from 4 to 6 and the exchangeable sodium percentage from 6.2 % to 10.2 %. The treatment involving on-farm B reduction provided the most suitable irrigation water, with the lowest concentrations in soil of available boron (1.4 mg kg −1 ), water-soluble chlorides (143 mg L −1 ) and sodium (129 mg L −1 ), and presented no risk of soil salinization (2.1 dS m −1 ) or alkalinization. Long-term DSW application could cause phytotoxicity and soil alkalinization. Therefore, strategies to mitigate those risks must be implemented, such as blending DSW with other water sources or on-farm DSW treatment to reduce its ionic load. • Desalinated seawater did not affect soil nutrients, organic and inorganic carbon, pH, cation exchange capacity and texture • No risk of salinization was observed with the use of desalinated seawater • Desalinated seawater increased boron and sodium in soil over time • Risk of soil alkalinization was observed with the use of desalinated seawater • On-farm B reduction proved to be the most suitable irrigation water