TESTING THREE DIFFERENT ANALYTICAL METHODS FOR ESTIMATING ORGANIC CARBON CONTENTS (SOC) OF SOILS

Soil quality is significantly influenced by its carbon content, impacting various aspects such as physical, chemical, and biological properties. Soil organic carbon (SOC) can be determined via several different techniques and often there is a variability in SOC contents among different methods. The present study compared three methods (loss on ignition, Walkley and Black, and Elemental Analyzer) for estimating organic carbon content with primary aim of evaluating their effectiveness and determining the optimal temperature for the loss on ignition method (LOI). We hypothesized that there is no difference in SOC content between three testing methods. The loss on ignition (LOI) method involved in igniting samples at different temperatures (350 – 650 ⁰C) while the Walkley and Black method involved in oxidizing oxidizable carbon by potassium dichromate solution in concentrated sulfuric acid. The Elemental Analyzer method involved in combusting the sample at higher temperature, isolating and measuring CO₂ gas using a thermal conductivity detector (TCD). The B horizon of the Frederick soil series was used as the soil sample since the low organic carbon content of the B horizon enable to have control over the methods used. Results indicted a high variability across the three methods, leading to the rejection of the null hypothesis. The Elemental Analyzer recorded significantly lower SOC content compared to the Walkley and Black method. The LOI method showed the highest calculated percentage, whereas the Elemental Analyzer recorded the lowest SOC content. Higher LOI temperatures were found to be suboptimal for determining SOC contents, evident from considerable losses. The study suggested that a temperature range of 450 – 550 ⁰C is likely adequate, however further experimentation with different times and soil types is necessary to validate this conclusion.