Effects of surface management on the hydrology of a vertisol in semi-arid Australia

Abstract

Rapid expansion of cropping in semi-arid north-eastern Australia in recent years has led to major changes in catchment hydrology and the potential for erosion. Runoff volume and peak runoff rate are influenced by storm rainfall and its intensity, tillage practices, surface cover, surface roughness and surface soil water deficit, but the influences are not well defined for general use. Data were obtained on contour catchments varying from 8 to 16 ha under different tillage and crop treatments, over a 4-year period. The response of runoff and peak runoff rate to the interactive effects of the independent variables was examined using multiple-regression analysis. As expected the main factor affecting runoff volume was total rainfall, whilst peak runoff rate was mainly determined by rainfall intensity. The other variables had smaller, interactive effects. The major effects of the management practices were soil water deficit on total runoff and surface cover on peak runoff rate. The process of runoff generation is complex. Surface cover, surface roughness and soil water deficit can be managed to minimise both total runoff and peak runoff rate. Maintenance of surface cover by reduced or zero-tillage practices is the most stable and dependable approach during fallow, and early establishment of a growing crop will further decrease both runoff and runoff rate. Benefits from increasing surface roughness by cultivation are generally cancelled by the associated reduction in surface cover.