Field trial and modelling of different strategies for remediation of soil salinity and sodicity in the Lower Murray irrigation areas

Abstract

Rising saline groundwatertables and drought in the Lower Murray Reclaimed Irrigation Area (LMRIA) has created soil salinity and sodicity conditions, which has resulted in a decline in agricultural production. A 2 month field experiment was conducted at Mobilong irrigation area using a randomised block design with trial plots (4 m2) in each of the three blocks containing the following six treatments: (1) control (not irrigated), (2) irrigation (River Murray water) only, (3) gypsum application (1.5 kg/m2) and irrigation, (4) limestone application (1.5 kg/m2) and irrigation, (5) seawater (source of dissolved Ca2+) application (100 mm depth) and irrigation and (6) acid (pH 3) drainage (to dissolve CaCO3 in soil to release Ca2+) application (100 mm irrigation water depth) and irrigation. Soil electrical conductivity (EC), pH, exchangeable cations (Ca2+, Mg2+, Na+, K+), exchangeable sodium percentage (ESP) and saturated hydraulic conductivity were measured. The decrease in EC was greatest in the irrigation only treatment followed by the gypsum and limestone treatments. At the end of the trial, the EC in the irrigation only treatment was about one-quarter of the control, in which the EC increased. The seawater and acid drainage treatments reduced the soil EC relative to the control but the EC was 2–3 dS/m higher than the irrigation, gypsum and limestone treatments at the end of the trial. The gypsum, irrigation only and limestone treatments approximately doubled the exchangeable Ca relative to the control and exchangeable Na was reduced. Unsaturated water and solute transport model (HYDRUS-UNSATCHEM) simulations were able to represent the general trends in the field results. The results suggest that only River Murray water irrigation and drainage could be effective for the management of soil salinity and sodicity in the LMRIA but further research is required to establish the threshold electrolyte concentration to prevent soil dispersion.