Assessing the Effectiveness of the Walkley-Black Method for Soil Organic Carbon Determination in Tephra Soils of Cameroon

Abstract

ABSTRACTThe Walkley-Black (WB) method has been widely used for soil organic carbon (SOC) determination with little attention on its reliability and effectiveness compared to the dry combustion (DC) method. This study compared SOC contents of some Cameroon tephra soils as determined by the WB and DC methods to assess the effectiveness of the WB method, using surface and subsurface soil samples. SOC contents by both methods were significantly different for both surface (t = 15.47, p < 0.001) and sub-surface (t = 12.35, p < 0.001) samples. The low carbon recovery of 45.36% (recovery factor of 2.38) and 35.87% (recovery factor of 3.34) for surface and subsurface samples, respectively indicates that the WB method greatly underestimates SOC contents in tephra soils. The higher positive significant correlation between both methods for surface samples (r = 0.83**, p < 0.01) compared to subsurface samples (r = 0.6*, p < 0.05) confirms high variability in subsurface samples. This study will guide the choice of method in SOC determination in the tropics where similar soils obtain and where cost constraints and the search for a more pollutant-free method for soil OC determination warrants an alternative method to the WB.