Evaluation of organic carbon oxidation efficiencies of a modified wet combustion and Walkley‐black procedures in Nigerian soils

Abstract

The organic carbon (C) oxidation efficiencies of the Walkley‐Black and modified wet combustion procedures were evaluated in soil samples taken from different ecological zones and diverse parent materials in Nigeria. Dry combustion using a C analyzer was the standard to evaluate the efficiency of the modified wet combustion method. The efficiency of the Walkley‐Black method was later compared to that of the modified wet combustion procedure. The results indicated that the modified wet combustion and the dry combustion procedures were highly correlated (r=0.99**)‐Significant correlation (r=0.96**) was also found between the Walkley‐Black and the modified wet combustion procedures. There was no correlation between the C data obtained using the modified wet digestion method and the % DCB‐Fe₂O₃. These results suggest the absence of strong organo‐mineral complexes in these soils. Organic C recoveries by the Walkley‐black method were not affected by fine‐grinding (<0.5 mm) of the soil samples. It is suggested that both the modified wet combustion and the Walkley‐Black methods may be used without a correction factor in Nigerian soils. The modified wet combustion procedure was also found to be an adequate substitute for the dry combustion procedure.