Research on Analytical Methods of Readily Organic Carbon in Different Types of Soil

The readily oxidation organic carbon is the most active part of the soil organic carbon, which deeply participates in the dissolution, migration, transformation, absorption and other processes of nutrient elements in the soil. Accurately determines the content of readily oxidation organic carbon in the soil, which is of great significance to explore the circulation of carbon elements and the migration and transformation of nutrient elements in the soil. Since the concept of readily oxidation organic carbon were proposed, the determination method involves using 25 mL of 333 mmol/L KMnO₄ to oxidize soil samples containing 15 mg of carbon. The measurement is made by observing the change in KMnO₄ concentration at 565 nm. Due to the non-fixed solid-liquid ratio during oxidation and the unclear oxidation time, there are significant differences among different researchers when using this method. As a result, the consistency and validity of the determination results are difficult to guarantee. This paper determined the distribution characteristics of readily oxidation organic carbon in soil aggregates through particle size experiments, identified the optimal particle size for sample testing, and improved the oxidation efficiency of KMnO₄ for readily oxidation organic carbon. By the experiments on solid-liquid ratio and oxidation time, the sample processing procedure was refined, enhancing the stability of the determination results for easily oxidizable organic carbon. A method for determining readily oxidation organic carbon in soil was established by constant temperature oscillating oxidation-spectrophotometry. The surface soil samples with different land use status in Yunnan red soil, northeast black soil, Shanxi loess and Sichuan purple soil were selected to carry out experimental condition optimization research and method applicability research. After the conditions optimization, the method detection limit is 0.021%, and the method precision (RSD, n=6)≤8.56%. This method is suitable for the determination of soil readily oxidation carbon in projects such as natural resources surveys and ecological restoration of land space.