Numerical Simulation and Evaluation of a Soil Profile Subjected to Rehabilitation Techniques Using a One-Dimensional Water and Solute Transport Model.

Saline-sodic soils can be rehabilitated through revegetation using halophytes. However, poor soil structure can restrict leaching salts from the soil and so limit the plant germination and establishment. Addition of organic and inorganic amendments may ameliorate and accelerate leaching of salts through improving the soil physical conditions and creating favourable conditions for plant establishment. For the purpose of the evaluation of reclamation of saline-sodic soils using amendments under typical climatic scenarios of semi-arid environments, a one-dimensional water and solute transport model (HYDRUS-1D) was evaluated. Columns of a length of 30 cm (7cm diameter) were filled with a saline-sodic soil at the lower end (10-30 cm) and then covered with the soil amended with 40% (wt/wt) fine sand and 20% (wt/wt) wood chips, respectively. A control column was filled with saline-sodic soil, only. A rainfall scenario with 50% probability of annual exceedance for a location in south-west Queensland (Australia) was applied to the columns. The hydrological performance was monitored as water potential for three depths (3.5, 12 and 25 cm) using tensiometers and including information from outflow from the columns and inflow as precipitation. Soil solutions were collected after each rainfall event. The concentrations of individual cations (Na⁺, Ca²⁺, Mg²⁺ and K⁺) and electrical conductivity of the soil solution were monitored. The numerical simulations of the solute transport resulted generally in good agreement with the observed values for all investigated columns. The RMSE values for cations were between 0.002 and 0.175 g/L for the soil substrates. The simulated water potentials also confirmed the observed results (R² ranged between 0.80 and 0.98). The study showed that HYDRUS-1D was able to simulate water and solute transport within the soil profile subject to rehabilitation techniques, and can be used for the prediction of the reclamation of saline soils under climatic conditions of semi-arid environments.