Irrigation with treated wastewater under two different irrigation methods: Effects on hydraulic conductivity of a clay soil

Abstract

Use of treated wastewater (TWW) for irrigation of semiarid and arid soils may lead to degradation of soil hydraulic properties, the magnitude of which may depend on the type of the irrigation system. Most studies evaluated the impact of irrigation with TWW on soil hydraulic conductivity (HC) using repacked samples, which do not necessarily represent soil field conditions. Our objectives were to (i) determine the effects of long term irrigation with TWW vs. fresh water (FW), and drip vs. microsprinkler method of irrigation on the saturated HC of intact and repacked soil samples, and (ii) establish possible relationship between saturated HC of intact and repacked soil samples, and aggregate stability. Samples (intact and disturbed) were taken from the upper soil layer (0–0.2 m) of FW- and TWW-irrigated by drippers and microsprinklers sections of an orchard, and adjacent TWW-irrigated cultivated and fallow fields of a clay soil. Saturated HC was determined by leaching with deionized water using a constant head device. Aggregate stability was determined on the disturbed samples using the high energy moisture characteristics method. Initial HC values were in the range of 0.025–0.25 mm h − 1 for the intact cores and 1.5–16 mm h − 1 in the repacked soil columns. In both types of measurement steady state HC was significantly lower than the initial HC. The effects of water quality and method of irrigation in determining the HC depended on the method of HC measurement; water quality had a greater impact when intact cores were used, while method of irrigation had a greater impact in the case of repacked soil columns. Irrigation water quality and method of irrigation did not have conclusive effects on aggregate stability. Significant relationships, between aggregate stability and steady state HC of the intact and repacked soil columns, were noted. Those suggested that aggregate stability determination could replace the more complicated and time consuming HC measurement in evaluating the impact of irrigation with TWW on soil HC.