石灰性土壤有机碳和无机碳不同测定方法比较 postprint

Abstract: This study investigated whether different measurement methods for soil total carbon (STC), soil organic carbon (SOC), and soil inorganic carbon (SIC) yield varying results, which is essential for accurately assessing soil carbon pools in calcareous soils. A total of 793 soil samples from depths of 0–100 cm were collected in June 2019, June 2023, and September 2023 across grasslands, deserts, and farmlands in Xinjiang. This study compared four analytical methods for soil carbon research: dry combustion, wet oxidation, gas volumetric, and indirect methods. The compa rison focused on bulk soil and soil fractions with particle sizes below 53 μm. The study also established reliable conversion equations for correcting the results between these methods. According to the results, for STC determination, the dry combustion me thod was significantly superior to the indirect method in terms of accuracy and stability; the latter systematically underestimated STC by a range of 3%~11% in soils with high pH values and obvious salinization properties, which can be attributed to insufficient reaction time between high-carbonate soils and hydrochloric acid. For SOC determination, the tested methods exhibited good consistency in most practical measurement scenarios; however, the indirect method was significantly affected by the degree of soil salinization: it underestimated the SOC content in non-saline soils while overestimating it in slightly to moderately saline soils, a phenomenon closely related to salt ions inhibiting carbonate dissolution during the entire determination procedure. For SIC determination, the gas volumetric method was verified to be the most optimal and reliable approach, whereas the indirect method generally underestimated SIC by 20%~42%, and the extent of such estimation errors exhibited a clear and gradual increasing trend with increasing soil pH. In conclusion, it is strongly recommended to prioritize the dry combustion method for STC determination and the gas volumetric method for SIC determination in calcareous soil carbon assessments. In addition, adequate calibration of the results obtained using the indirect method based on specific soil pH values and salinization levels is essential to effectively improve the overall accuracy and interstudy comparability of carbon assessmen toutcomes. This study provides a solid and valuable scientific basis for the rational selection of analytical determination methods and the reliable calibration of test results in calcareous soil carbon storage evaluation, thereby supporting more consistent, accurate, and comparable soil carbon research globally.