关键词: 无机碳, 气量法, CO₂吸收法, 间接法, 元素分析仪, 滨海土壤, 互花米草盐沼, 重铬酸钾氧化

Abstract:

【Objective】 Inorganic carbon constitutes a large proportion of soil carbon storage in the coastal area of northern Jiangsu; therefore, estimating the soil inorganic carbon (SIC) content with precision and accuracy is a prerequisite for further study.【Method】Soil samples at different depths (i.e., 0-10, ≥10-20, ≥20-40, ≥40-60, ≥60-80, and ≥80-100 cm) were collected from a poplor plantation and a Spartina alterniflora wetland. The SIC content as well as its recovery rate were then estimated using a calcimeter, carbon dioxide (CO₂) absorption and indirect methods, respectively. This was done to compare the precision and accuracy of the three methods. 【Result】 The ranges of the SIC content estimated by the calcimeter, CO₂ absorption and indirect methods were 4.25-9.93, 6.18-11.50 and 5.50-12.60 g/kg with the average of 8.11, 9.58 and 9.54 g/kg, respectively. When the amendment rate of exogenous calcium carbonate was 2.35-12.90 g/kg, the averaged recovery rates of SIC content estimated by the calcimeter, CO₂ absorption and indirect methods were 96.9%, 105.0% and 71.5%, respectively. According to the SIC content corrected by the recovery, the SIC contents measured by the indirect method were significantly higher than those measured by the other two methods, indicating that the recovery of SIC measured by the indirect method was underestimated. The coefficients of variation of the SIC content in the parallel soil samples estimated by the calcimeter, CO₂ absorption and indirect methods were 1.19%-4.99%, 0.52%-3.34% and 1.51%-6.79% with averages of 2.44, 1.36 and 3.25 g/kg, respectively. 【Conclusion】 The calcimeter, CO₂ absorption and indirect methods can all be used to determine the SIC content of coastal soils from Northern Jiangsu, although the SIC estimated by the CO₂ absorption and indirect methods were both higher than those measured by the calcimeter method. However, the SIC recovery rate estimated by the indirect method was underestimated, and this was mainly due to the overestimation of the organic carbon content of the acid-treated soils by the potassium dichromate oxidation method. The accuracy of the CO₂ absorption method was the highest, followed by that of the calcimeter and indirect methods. However, the calcimeter method is time-saving, whereas the indirect method can quantify the contents of soil organic carbon and SIC simultaneously. In the future, researchers should choose a method that is in line with their specific research purposes.

Key words: inorganic carbon, calcimeter method, CO₂ absorption method, indirect method, coastal soil, Spartina alterniflora salt marsh, potassium dichromate oxidation