Runoff, soil loss and soil physical property changes of light textured surface soils from long term tillage treatments

Abstract

A long-term tillage trial was conducted (1981 to 1987) on loamy textured soils to quantify changes in runoff, soil loss and some soil physical properties due to conservation tillage practices. Two sites were established, one at Cowra on a sandy loam textured soil, and the other at Grenfell on a loamy textured soil. The tillage treatments imposed were direct drilling (DD), reduced tillage (RT) and traditional tillage (TT), with grazing at both sites, and a direct drilling ungrazed (NT) treatment at Cowra only. Runoff and soil loss were measured using a rainfall simulator, and sorptivity (S), saturated hydraulic conductivity (Ksat), bulk density to 40 mm (BD4) and 100 mm (BD10), organic carbon (OC) and water stable aggregates (WSA) were measured annually. Runoff decreased significantly in the minimum soil disturbance treatments (NT and DD) at Cowra. Runoff did not decrease in the stubble incorporation treatments despite a significant increase in OC and WSA. Decreases in runoff were due to the development and maintenance of porosity, particularly macropores. Changes in other soil physical properties were generally not significant owing to temporal variability. The regression relationship between OC and WSA, although significant, had little practical value because of high prediction error. Although improvements in soil physical properties were measured, a period of at least five years of cropping at both sites was required before they became significant and consistent.