Remediation measures for mitigating degraded properties of a clayey soil caused by treated wastewater irrigation.

Abstract Long-term irrigation of clayey soils with treated wastewater (TWW) has significant negative effects on soil physicochemical properties and the performance of various orchards, including avocado. The objectives of the study were to investigate the effects of four different mitigation practices on the dynamics and the spatial changes in selected soil properties, following long term irrigation with TWW. The experiment was conducted in a commercial fruit-bearing 'Hass' avocado orchard ( Persea americana Mill.) grown on a clayey soil irrigated with TWW since 2009. The mitigation measures, each in 6 replicates, were implemented in 2016 and included the following treatments: freshwater (FW), blended TWW: FW in a 1:1 ratio (MIX), low-frequency TWW-irrigation (LFI), TWW irrigated tuff trenches (TUF) and TWW as the control treatment. The results showed that FW and MIX significantly reduced total salinity (EC), specific salinity related ions (Na and Cl), sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) to (i) a depth of 90 cm and 30 cm under drippers, respectively, and (ii) a depth of 60 cm except for chloride and 30 cm between drippers, respectively compared with TWW. Moreover, FW significantly increased aggregate stability to a depth of 30 cm. TUF and LFI reduced soil salinity and sodicity under drippers but not between drippers compared with TWW. TUF increased oxygen concentration in the root zone (35-cm depth) compared with all other treatments. Considering the scarcity of FW, MIX and TUF can be suggested as mitigating measures for reducing soil salinity and sodicity, and increasing poor aeration of clayey soil under long term irrigation with TWW, respectively.