Water balance of annual and perennial pastures on a duplex soil in a Mediterranean environment

Dryland salinity in southern Australia is largely due to inadequate water u se by annual agricultural crops and pastures. Perennial pastures, such as l ucerne, have been proposed as a possible means of increasing water use whil st maintaining flexibility in agricultural rotations. In a trial located on a duplex soil near Katanning, Western Australia, lucerne and subterranean clover pastures both used water at rates indistinguishable from potential e vapotranspiration during the winter and early spring of 3 consecutive years (1995-97), and completely exhausted water stored in the A horizon. Lucerne , through a deeper rooting pattern and by maintaining activity in the summe r and autumn, used approximately 50 mm more water than the annual pasture d uring each 12-month period. This resulted in reduced deep drainage below 1. 2 m in the 1996 season (30 mm compared with 80 mm under annual pasture). Wi th average regional groundwater recharge in the range 10-50 mm, the reducti ons in drainage observed under lucerne show promise in reducing the regiona l impact of dryland salinity.