A study of soil erosion on vertisols of the eastern Darling Downs, Queensland .I. Effects of surface conditions on soil movement within Contour Bay catchments

Abstract

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.

A survey of dairy farmers' practices and attitudes towards some aspects of arable-land management in the Darling Downs and South Burnett regions of Queensland

“…It is clear that any development and extension project seeking to expand the role of pastures as a soil-fertility restorative practice will need to investigate and address these issues further with farmers. The strong indication from respondents is that benefits that come from pastures in terms of soil fertility gains (Littler 1984;Hossain et al 1996), soil structure (Dalal et al 1991;Waters and Oades 1991) and reduced erosion (Freebairn and Wockner 1986) will be offset by lower farm productivity and increased risk taking.…”

“…Minimal-and zero-tillage farming has been demonstrated to have both economic and soil conservation benefits in the subtropical cereal belt (Freebairn and Wockner 1986;Radford et al 1995).…”

“…This second group of planters are commonly known as trashseeders and are capable of planting through more stubble than a conventional combine (Crothers and Graham 1995). This ability makes them useful in a stubble-mulch system which can reduce erosion (Freebairn and Wockner 1986). However, similarly to conventional planters their row spacing is narrow (150-200 mm), which limits the use of press wheels.…”

“…This cropping has traditionally relied on the inherent fertility of the soil to provide most plant nutrient requirements and tillage to control weeds over the fallow and prepare a fine, residue-free seedbed. These practices expose the soil to erosion, particularly over the summer period (Osborn 1978;Freebairn and Wockner 1986;Marshall et al 1988;Wylie 1993), and contribute to fertility decline (Dalal and Mayer 1986;Thompson and Bywater 1987) and soil structural decline in some soils (Cook et al 1992;Bridge and Bell 1994). The decline in soil productive capacity is applicable to both grain and forage cropping lands of the study region and has been the focus of a number of studies to better understand and develop strategies to overcome both biophysical (Freebairn and Wockner 1986;Dalal et al 1995;Connolly et al 1998) and sociological (Chamala et al 1983;Blacket and Hamilton 1992;Hamilton 1995) constraints to improved farm practices.…”

“…These strategies include the use of ley pastures (Littler 1984;Dalal et al 1995), increased cropping intensity , zero tillage (Freebairn and Wockner 1986) and improved fertiliser management (Strong and Holford 1997). Following a number of research and extension activities to address fertility decline on cropping soils on the Darling Downs dairy farms through increased fertiliser rates (Thompson and Bywater 1987;Chataway et al 1994), it was determined that there was a need for a broader, more strategic approach to this problem.…”