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Soil organic carbon (SOC) is crucial for soil health, impacting physical, chemical, and biological properties. It improves soil structure, water retention, nutrient retention, and biological diversity, leading to better crop yields and reduced erosion. The Walkley-Black method is a standard technique for determining SOC. It involves oxidizing soil organic matter with potassium dichromate (K2Cr2O7) in the presence of sulfuric acid (H2SO4), then titrating the remaining dichromate with ferrous sulfate. The amount of dichromate consumed is inversely proportional to the SOC content.

Part I: Determination of Soil Organic Carbon Content by Walkley-Black Method Introduction: Soil carbon is probably the most important component in soils as it affects almost all soil properties. Carbon, as soil organic matter, alters the physical, chemical, and biological properties of soils. Soil organic matter refers to all decomposed, partly decomposed and undecomposed organic materials of plant and animal origin. It is generally synonymous with humus although the latter is more commonly used when referring to the well decomposed organic matter called humic substances. Soil organic matter is a primary indicator of soil quality. Improvements in soil organic matter create a more favourable soil environment, leading to increases in plant growth. Higher soil organic matter levels cause the soil to retain more water that results in better crop yields, reduces soil erosion, increases plant nutrient retention and increases biological diversity. Moreover, improved aggregation of soil particles results in better soil structure, allowing for movement of air and water through the soil, as well as better root growth. More stable soil structure results in less soil erosion, which retains nutrients on the land and protects water quality. Soil organic carbon contributes to the cation exchange capacity of a soil. These cation exchange sites are important for retention of nutrients such as calcium, magnesium and potassium. Soil organic carbon often also provides binding sites for many anthropogenic organo chemicals, thus minimizing leaching of hazardous chemicals through the soil profile or making them less bioavailable, which reduces toxicity. Principle: The determination of soil organic carbon is based on the Walkley-Black chromic acid wet oxidation method. Oxidisable matter in the soil is oxidised by IN K2Cr2O7 solution. The reaction is assisted by the heat generated when two volumes of H2SO4 are mixed with one volume of the dichromate. The remaining dichromate is titrated with ferrous sulphate. The titer is inversely related to the amount of C present in the soil sample.