Effects of Domestic Sewage Water and Ameliorant Effectiveness on Soil Hydraulic Conductivity

Abstract

Irrigation with domestic sewage water is a normal practice in developing countries, and its possible adverse effects on soil hydraulic conductivity are important for sustainable farmland management. The objective of this study was to assess (i) the influences of untreated raw domestic sewage water irrigation on hydraulic conductivity, and (ii) the effectiveness of soil ameliorants at various soil sodicity levels. The saturated hydraulic conductivity for soils that were equilibrated with Na adsorption ratios (SARs) of 0, 10, 20, and 30 (mmolc L−1)1/2 was measured in a laboratory under constant‐head ponding with raw domestic sewage water following gypsum and polyacrylamide application at rates of 5 and 0.1 g kg−1 soil, respectively. Compared with distilled water, raw domestic sewage water decreased the hydraulic conductivity of nonsodic soil but increased that of sodic soils. The influence of soil sodicity on hydraulic conductivity decreased under domestic sewage water. Additionally, gypsum application decreased leachate pH by about 0.5 pH units and increased hydraulic conductivity by up to 180%, with the exception of soil with a SAR of 20. In that case, the hydraulic conductivity decreased by about 50%. The influence of gypsum on hydraulic conductivity decreased with increasing soil sodicity levels. Application of gypsum by spreading generally resulted in a slightly greater leachate electrical conductivity and hydraulic conductivity than its application by mixing. Polyacrylamide application decreased leachate pH by 0.5 to 1.0 units and slightly decreased hydraulic conductivity. The adverse effect of domestic sewage water irrigation on soil hydraulic conductivity generally can be inhibited or ameliorated by gypsum application.