Sodic soil reclamation: Modelling and field study

Reclamation of sodic soils has traditionally been undertaken using calculat ion of gypsum or Ca requirement assuming 100% exchange efficiency and negle ct of the contribution of calcium carbonate in the profile. The UNSATCHEM m odel is reviewed and then evaluated for its ability to predict field reclam ation of a sodic saline soil. The 40-ha field site was initially at an elec trical conductivity (EC) of 50 dS/m and a sodium absorption ratio (SAR) of 144 in the top 30 cm. After installation of a drainage system, 24 Mg/ha of gypsum was applied to a depth of 15 cm in the soil. Subsequently, 114 cm of water was applied by almost continuous ponding for 3 months. Model simulat ions were made based on infiltration of 70-80 cm of water, correcting for t he estimated evaporation of 41 cm of water. These infiltration estimates ar e consistent with the good fit between the measured Cl concentrations after reclamation and the model predicted values after 70-80 cm of infiltrated w ater. Model predictions of EC and SAR after reclamation gave a satisfactory fit to the measured values. The effectiveness of mixing gypsum to various depths was evaluated in terms of the predicted SAR profiles. Alternative ma nagement practices of green manuring in presence of calcite were simulated and appeared feasible. In this instance it appears likely that the field co uld have been reclaimed either with less water or without the addition of g ypsum.