Soil organic carbon recovery by the Walkley-Black method in a Typic Hapludoll

Organic carbon (C) levels in a Typic Hapludoll under four management systems [moldboard plowing, chisel plowing, no-tillage, and perennial fescue (Festuca arundinacea) pasture] were determined by two methodologies: wet oxidation with potassium dichromate (K2Cr2O7) and dry combustion with a carbon analyzer. The correlation between organic C levels obtained by both methodologies (r=0.87, n=48, p<0.01) rose when agricultural and pasture systems were considered separately. Carbon recovered by Walkley-Black method under pasture was 15% lower than that under the agricultural systems. This difference was attributed to greater amounts of chemical stable organic compounds in pasture residues than in crop residues.