MODELING LEACHING AND RECHARGE IN A BARE TRANSITIONAL RED-BROWN EARTHPONDED WITH LOW-SALINITY WATER IN SUMMER

A modelling study was conducted to evaluate water and salt movement wi thin a transitional red-brown earth with saline B horizon soil when su ch waters are used for ponding in summer. The model was calibrated usi ng previously published experimental data. The calibrated model was us ed to evaluate the effect of depth to watertable, saturated hydraulic conductivity, and ponding water salinity on infiltration, water and sa lt movement within the soil profile, and recharge. The study showed th at when initial soil water content and the saturated hydraulic conduct ivity (K(s)) are low, infiltrating water will be stored within the soi l profile even in the absence of a shallow watertable. Once the soil w ater content is high, however, recharge will be significant in winter, even if there is no net infiltration at the soil surface. Infiltratio n rates depend more on K(s) than the depth to watertable if it is at, or below, 1.5 m from the soil surface. When K(s) is high, recharge und er ponding will be higher than that under winter fallow. Subsequent po nding in summer and fallow in winter tend to leach salts from the soil profile, the leaching rate dependent on K(s). During winter fallow, d ue to net evaporation, salts tend to move upwards and concentrate near the soil surface. In the presence of shallow watertables, leached sal ts tend to concentrate at, or near, the watertable.