Estimating episodic recharge under different crop/pasture rotations in theMallee region. Part 2. Recharge control by agronomic practices

Much environmental degradation, including salinity in the Mallee region of southeastern Australia, is associated with the loss of native vegetation an d increased recharge. As a result, various agronomic practices have been pr oposed to reduce groundwater recharge. This study was conducted to evaluate the impact of these practices on recharge, in particular episodic recharge . A biophysically based model (WAVES) was used to estimate recharge rates u nder some typical crop and pasture rotations in the region using long-term meteorological data. Results show that: (1) recharge just below the root zo ne was episodic and that just 10% of annual recharge events contributed ove r 85% of long-term totals. Management options such as incorporating lucerne and deep-rooted non-fallow rotations can reduce both, mean annual recharge , and the number of episodic events, but not eliminate recharge completely; (2) winter fallows increased soil-water storage and some of the additional water was stored in the lower portion of the root zone or below it. This c an increase the risk of recharge to groundwater system; (3) changes inland management may take a considerable period of time (>10 years) to have any n oticeable impacts on recharge; and (4) recharge under lucerne was approxima te to 30% of that under medic pasture. (C) 1999 Elsevier Science B.V. All r ights reserved.