The role of agroforestry and perennial pasture in mitigating water logging and secondary salinity: summary

Clearing of native vegetation for annual crops and pastures is recognised as a major cause of water logging and secondary salinity in southern Australia. A study was commenced in 1995 to evaluate the role of belts of trees, drains and perennial pasture on the water balance, hydrology, water logging and secondary salinity in a duplex-soil subcatchment located in the rejuvenated landscape of southwestern Australia. This summary paper reports on the findings of the integrated research reported in full in this special publication. The belts of trees used an estimated 150 mm more water than was received through rainfall, approximately 30 mm from the surrounding crop and the remainder from groundwater. Lucerne was shown to remove 50–100 mm more water from the soil profile than annual pasture, reducing average annual drainage beyond the root zone throughout the 5-year rotation from 45 mm to 17 mm. At this location, reverse interceptor drains had little impact on water flows at the field scale, but they may have been more effective in other parts of the subcatchment. Calculations suggest that in this region a combination of belts of trees and perennial pasture, such as lucerne, can mitigate and even reverse water logging and secondary salinity while maintaining crop production at near-current levels.