Comparison of Analytical Methods and Prediction of Soil Organic Carbon Content

Abstract

Soil organic carbon (SOC) can be analyzed in many methods, with different advantages and disadvantages. The objectives of this study were 1) to study the correlation between three SOC analysis methods and to predict the dry combustion-SOC with wet oxidation and Loss on Ignition (LOI) and 2) to study the correlation and predict the dry combustion-SOC with soil properties. One hundred fifty-eight soil samples were collected in lowland and upland soils and analyzed for soil properties. The SOC content was analyzed by 3 methods as follows: 1) wet oxidation method 2) dry combustion method and 3) LOI method. The results showed that the dry combustion-SOC had a statistically significant positive correlation with the wet oxidation-SOC and the LOI-SOC in both lowland and upland soils. The correlation coefficients (r) between the dry combustion-SOC with the wet oxidation-SOC in lowland and upland soils were 0.91** and 0.81**, while the r values with the LOI-SOC were 0.95** and 0.77**, respectively. The regression equation to predict the dry combustion-SOC in lowland and upland soils with the wet oxidation-SOC had a coefficient of determination (R²) of 0.83** and 0.66**, respectively. The R² of the regression equation to predict the dry combustion-SOC in lowland and upland soils with the LOI-SOC were 0.90** and 0.59**, respectively. However, an equation for converting wet oxidation-SOC and LOI-SOC to dry combustion-SOC were useful for interpreting the dry combustion-SOC testing. The correlation between the dry combustion-SOC and soil properties showed that lowland and upland were positively correlated with clay content and CEC and negatively correlated with sand content and bulk density.