Sodic soil reclamation: Modelling and field study

Reclamation of sodic soils has traditionally been undertaken using calculation of gypsum or Ca requirement assuming 100% exchange efficiency and neglect of the contribution of calcium carbonate in the profile. The UNSATCHEM model is reviewed and then evaluated for its ability to predict field reclamation of a sodic saline soil. The 40-ha field site was initially at an electrical 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 simulations were made based on infiltration of 70-80 cm of water, correcting for the estimated evaporation of 41 cm of water. These infiltration estimates are consistent with the good fit between the measured Cl concentrations after reclamation and the model predicted values after 70-80 cm of infiltrated water. 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 management practices of green manuring in presence of calcite were simulated and appeared feasible. In this instance it appears likely that the field could have been reclaimed either with less water or without the addition of gypsum.