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 rain-fall 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 irri-gation. This is essential to guarantee that use of TWW irrigation does not cause irreversible damage to farmlands potentially threatening soil health and food security.