Geomorphic controls on aluminium in acid soils of the Axe Creek catchment, Victoria

Abstract

This study investigates the influence of terrain, including steepness and position in slope, on soil pH, extractable aluminium (Al), and organic carbon (OC) in the Axe Creek catchment, Victoria. Both soil pH and Al were determined by use of 1 : 5 soil : 0·01 M CaCl₂ extracts, with Al measured colorimetrically using a modified pyrocatechol violet method. Although all soils were acidic, the Al concentration was highest on the hilltops (>10 mg/kg) and lowest at base-of-slope sites (<1 mg/kg). The concentration of Al was generally inversely related to soil pH. However, on average, a lower Al concentration was found in the top 10 cm than in the interval from 10 to 30 cm, even though the soil pH remained relatively constant throughout the top 30 cm. The lower Al concentration in the surface layer corresponded to a substantially higher level of OC near the surface, suggesting the formation of Al-organic matter complexes.