Effect of long-term treated wastewater irrigation on soil sodium levels and table grapevines' health

The use of treated wastewater (TWW) for irrigation is constantly on the rise, while the long-term impacts are not in consensus. In this study we examined the impact of 9 years of municipal TWW irrigation on sodium (Na) and sodium adsorption ratio (SAR) in a vineyard soil and consequently on table grapevines. Our objectives were to: 1) quantify multiannual temporal trends of Na and SAR; 2) construct a regression model to define the relative contribution of various factors on Na and SAR levels in the soil; and 3) determine Na and SAR accumulation impact on the grapevines’ health state (healthy, damaged, or dead). Our analyses indicated that long-term irrigation with TWW resulted in Na accumulation in the soil, with enhanced effects attributed to higher rainfall levels (precipitation levels). Applying TWW for irrigation was also found to affect vines as evident with observations of damaged and dead vines after 9 years, ranging between 25% and 40% mortality rates depending on the treatment used. These observations were found to be directly and significantly associated with higher Na concentrations (p-values of 0.008 and 0.011 compared to damaged and healthy vines, respectively). Our results, although specific to the region, raise a warning sign and merit further long-term investigations of TWW irrigation. This is essential to guarantee that use of TWW irrigation does not cause irreversible damage to farmlands potentially threatening soil health and food security.