Wallumbilla agricultural catchment study 1982-2000 (Queensland, Australia)

A catchment study was established in 1983 on one of the major soil types (a brigalow brown clay) of the western Darling Downs. The objective of this 18 year duration study was to explore changes in soil water, catchment hydrology and water quality associated with different soil surface conditions i.e. tillage, stubble management, gypsum, roughness. The site was chosen to represent clay soils with high water holding capacity in the Maranoa region, where fallowing to store water for later crop growth is an essential risk management tool.
Rainfall, soil water, runoff, suspended sediment concentration, cover and all agronomic operations were monitored on four contour bay catchments. Different tillage practices and a pasture were used to create a range of soil cover and roughness conditions in order to explore functional relationships between land management, soil conditions, hydrology and water quality. This study aimed to compliment similar studies at Greenmount and Greenwood on the eastern Darling Downs.
This dataset provides benchmark data for further hydrologic and water quality studies.

Key findings
Daily runoff was determined strongly by soil water content which was strongly influenced by antecedent rainfall, water use and evaporation patterns. Surface cover and roughness had subtle influences on runoff, and a greater effect on suspended sediment concentrations. Runoff and suspended sediment movement was considerably lower under pasture than cropping.
Accumulation of soil water in fallows was inefficient, with fallow efficiencies ranging from -7 to 40% due to high evaporation and runoff losses.
Runoff and sediment concentration were both inversely related to surface cover and total soil movement was greatly reduced by surface cover. Greater than 75% of the variance in soil movement from single events was explained by surface cover and peak runoff rate.
Differences in hydrology and water quality associated with different management (tillage) were more subtle than experienced on two similar sites on the eastern Darling Downs (Greenmount and Greenwood), mainly due to the lower levels of stubble available after winter crops due to the drier climate. Tillage (roughness) was equally influential as cover on runoff.