Changes in soil salinity under treated wastewater irrigation: A meta-analysis

Abstract

In view of water shortages, the development and utilization of unconventional water resources have been studied extensively. Treated domestic or industrial wastewater used for agricultural irrigation is an unconventional water resource utilization method. Due to the particularities of water sources, previous studies have mainly focused on changes in soil heavy metals, microorganisms, and organic substances and crop responses to toxic elements; thus, attention to soil salinity is of secondary importance. After selecting qualifying research, a meta-analysis was performed to statistically analyze the data of seven variables (potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), electrical conductivity (EC), pH, and yield) to 1) estimate the mean effects of treated wastewater (TWW) irrigation on the soil salinity, soil pH and crop yield; and 2) identify the wastewater treatment grade (primary treated wastewater (PTW), secondary treated wastewater (STW), and tertiary treated wastewater (TTW)) and soil texture (sandy texture, loamy texture and clayey texture) that benefit TWW irrigation. The results showed that TWW irrigation caused a significant accumulation of soil salinity, and the increase in cation content from high to low was K (90.1%), Na (59.9%), Mg (25.2%) and Ca (17.3%). EC also increased significantly by approximately 57.2%, while there was no significant change in pH, and even the crop yield presented an average reduction of nearly 6.5%. PTW contributed to the largest salt accumulation, followed by TTW and STW. STW showed a significant increase in EC but did not show a significant change for the four ions. In terms of yield, STW can increase yield, while TTW has the opposite effect. In general, the sandier the soil texture, the higher is the salt content detected, although the retention of salt in loamy textured soil may differ depending on the ions. The yield of crops grown increased in the clayey textured soil and decreased in the loamy textured soil. Our study elucidated the response of soil salinity accumulation under TWW irrigation and could provide a reference for unconventional water resource utilization.