Effects of catchment management on runoff, water quality and yield potential from vertisols

Abstract

To determine the effect of soil surface cover and antecedent moisture on catchment yield of water and sediment; runoff, soil moisture, and soil erosion were monitored on vertisols at two sites on the eastern Darling Downs, Qld., Australia. Stubble or crop cover reduced runoff volumes by 40% and peak discharge rates by 70–85% compared to bare soil. Contour banks trapped 80–90% of the eroded soil from paddocks. Suspended sediment discharged from contour banks into grassed waterways was reduced from a mean of 1.3% from bare soil to 0.2% where stubble was retained as a surface mulch. Cropping patterns planned to maximise the use of available soil water and rainfall reduced runoff. Using a water balance model to predict long-term runoff, it was shown that farm dams can be used to store a signifiant portion of the excess rainfall for later irrigation use while reducing total runoff and peak discharges. The combination of techniques viz. contour banks, stubble retention, optimised crop water use patterns and on-farm water storage significantly reduce flood flows and improve water quality from upland catchments, as well as improving productivity. Results from this study are directly relevant to many cracking clays in the semi-arid tropics.