Effects of soil surface conditions on runoff and soil loss were studied on two major cracking clay soils of the Darling Downs, Queensland. Techniques used to measure soil loss between field contour bays under natural rainfall are described, and the results from 10 contour bay catchments (66 plot years) are presented. Soil movement was separated into rill, interrill, suspended sediment and channel deposition. Two slope lengths were considered (60 and 35 m), and interrill erosion appeared to be the major source of soil loss. Runoff and sediment concentration were both inversely related to surface cover and total soil movement was greatly reduced by surface cover. In an annual winter-wheat, summer-fallow system, removal of stubble resulted in soil movement of 29-62 t ha-1 year-1. Retention of stubble (stubble mulching) reduced soil movement to less than 5 t ha-1 year-1. Greater than 75% of the variance in soil movement from single events was explained by surface cover and peak runoff rate. Surface cover is a measure of the surface area protected from soil detachment and entrainment. Peak runoff rate describes the amount of energy or stream power available for detachment and entrainment.
Runoff water was sampled as it discharged through weirs installed at the outlet of 1 ha contour bay catchments. Cover, rainfall intensity, and soil tilth were important factors determining the concentration of suspended sediment in runoff. Mean delivery ratios for a grey clay, and a black earth, were 0.19 and 0.13 respectively. Contour banks reduced sediment loads reaching the bottom of slopes by at least six-fold. Three methods of calculation of total sediment loss were assessed. It was found that a flow-weighted mean of rising stage samples, and the arithmetic mean of sequential samples, were adequate in most cases for determining sediment losses. However, sequential samples weighted for discharge between samples were necessary for reliable measurements, especially during complex events.
Abstract. Hydrology and water quality impacts of alternative land management practices are poorly quantified for semi-arid environments in the northern Australia cropping zone, yet wide-scale changes in tillage practices and land use were being recommended based on experience from other environments.The objective of this study was to explore changes in soil profile and catchment hydrology and water quality associated with different soil surface conditions created by different tillage and grazing practices. Soil water, runoff, and suspended sediment concentrations were monitored on 4 contour bay catchments over an 18-year period. Soil conditions were described by soil moisture, soil cover, and surface roughness in order to explore functional relationships between management, hydrology, and water quality. The site was chosen to represent the drier margins of cropping in southern Queensland where clay soils with high water-holding capacity, in conjunction with fallowing to store water for later crop growth, are an essential risk management tool.Accumulation of soil water in fallows was inefficient, with fallow efficiencies ranging from -7 to 40% due to high evaporation and runoff losses. Runoff amount was determined 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 concentration. Runoff and suspended sediment losses were considerably lower under pasture than cropping.A participative approach between farmers and scientists was demonstrated to be an efficient method to carry out an extensive and long-term catchment study at a remote location. This study provides benchmark data for future hydrologic and water quality investigations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.