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

Organic carbon (C) levels in a Typic Hapludoll under four management system s [moldboard plowing, chisel plowing, no-tillage, and perennial fescue (Fes tuca arundinacea) pasture] were determined by two methodologies: wet oxidat ion with potassium dichromate (K2Cr2O7) and dry combustion with a carbon an alyzer. The correlation between organic C levels obtained by both methodolo gies (r=0.87, n=48, p<0.01) rose when agricultural and pasture systems were considered separately. Carbon recovered by Walkley-Black method under past ure 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.