EFFECTS OF THE CENTRIFUGE DRAINAGE METHOD ON TOTAL ORGANIC CARBON CONCENTRATIONS IN SOIL SOLUTIONS FROM PEATY SOILS

摘要

This paper investigates the effects of centrifuge speed, time and different filter media at the base of the soil column on the concentrations of total organic carbon (TOC) in soil solutions extracted by the centrifuge drainage method. With increasing time at 1000 rev min(-1) centrifuge speed, the volume of solution extracted increased as a logistic growth curve, but TOC concentrations decreased from initial values of 28 mg l(-1) to 15 mg l(-1) after 60 min. Increased centrifuge speed, and therefore applied suction, resulted in increased volumes of solution but TOC concentrations decreased from 33 mg l(-1) at 500 rev min(-1) (equivalent to 15 kPa suction) to 12 mg l(-1) at 4000 rev min(-1) (948 kPa), These findings suggest that leaching of organics from roots or microbial matter with increasing pressure was not significant in the peaty soil examined. Rather, fine particulate carbon probably contributed to the larger measured TOC concentrations at low suctions. In a comparison of filters, mean TOC concentrations were approximately 1.5 times greater when the centrifuge tube contained a glass wool filter or no filter, as these transmitted more fine particulate carbon. Sodium concentrations were more than 3 times greater and pH 1.7 units greater in solutions extracted through glass wool due probably to ion exchange on the filter, No effects on calcium or magnesium concentrations were found. It was concluded that centrifuge extraction through glass fibre filters and applying suction of 60 kPa for 1 h is suitable for studies of TOC in peaty soils.