Remediation and mitigation measures to counteract orchard soil degradation by treated wastewater irrigation

Recent studies have shown that long-term irrigation with treated wastewater (TWW¹) can lead to land degradation and reduction of crop performance in clayey soils due to additions of salts and organic compounds. This study investigated the effects of two remediation and two mitigation methods intended to alleviate the damage to soil properties following long-term irrigation with TWW. The experiment was conducted in a ‘Hass’ avocado orchard (Persea americana Mill.) grown on a clayey soil irrigated with TWW since 2009. The treatments implemented in 2016 included: TWW (control), freshwater (FW), blended TWW:FW in a 1:1 ratio (MIX), low-frequency TWW-irrigation (LFI), and TWW irrigated tuff trenches (TUF). The results showed that FW and MIX significantly reduced total salinity, salinity-related ions (Na and Cl), and sodium adsorption ratio (SAR) to (i) depths of 90 cm and 30 cm under drippers, respectively, and (ii) depths of 60 cm (except for chloride) and 30 cm between drippers, respectively, compared with TWW. TUF and LFI reduced soil salinity and sodicity under drippers but not between drippers compared with TWW. Moreover, FW significantly increased aggregate stability to a depth of 30 cm. TUF had the highest oxygen concentration in the root zone (35 cm depth), followed by FW. Considering the scarcity of freshwater, MIX and TUF are suggested as possible measures for reducing soil salinity and sodicity, and increasing aeration of clayey soils under long-term irrigation with TWW, respectively. Our findings contribute valuable insights into strategies for remediating and mitigating the detrimental effects of TWW irrigation on soil, thus promoting sustainable agriculture in regions facing water scarcity.