Soil Organic Carbon: Relating the Walkley-Black Wet Oxidation Method to Loss on Ignition and Clay Content

Accurate estimation of soil organic carbon (SOC) is needed in many fields of science including ecology, soil science and global climate change. Loss on ignition method (LOI) of estimating SOC has been proposed as rapid, accurate and cheap method but it has some limitations. Walkley-Black method is also widely used. For this study, 12 soil samples from 0-15 cm depth were collected from four sites of the Crop Plantation Section of the Department of Crop and Soil Sciences, KNUST. The amount of SOC (%) estimated by LOI and W-B methods, and clay content were used to develop simple and multiple linear regression equations to describe their relationships. The highest estimate of SOC (3.28%) was produced by Loss on ignition method, whereas W-B gave lower estimates with 1.35% being the highest produced by this method. The coefficient of determination, R 2 , for the equations ranged from 0.35 to 0.84. Very weak relationship was observed between LOI and W-B as evidenced by R 2 value of 0.35. The clay content had a strong positive correlation (r = 0.70, p < 0.001) with LOI and gave R 2