苏北滨海土壤无机碳含量的测定方法比较

Comparison of three methods for inorganic carbon in coastal soil from northern Jiangsu

【目的】无机碳是苏北滨海土壤碳库的重要组成部分,探索其含量的精准测定方法,以期为深入认识土壤无机碳(SIC)的形成和转化提供基础。【方法】在苏北地区野外选取杨树人工林和互花米草湿地作为样地,采集0~10、≥10~20、≥20~40、≥40~60、≥60~80和≥80~100 cm深度的土壤样品,在实验室分别使用气量法、二氧化碳(CO_(2))吸收法和间接法测定SIC含量及其回收率,比较3种方法的精准性。【结果】使用气量法、CO_(2)吸收法和间接法测得的SIC含量的变化范围分别为4.25~9.93、6.18~11.50和5.50~12.60 g/kg,平均值分别为8.11、9.58和9.54 g/kg。当外源碳酸钙添加梯度为2.35~12.90 g/kg时,气量法、CO_(2)吸收法和间接法的回收率的平均值分别为96.9%、105.0%和71.5%。根据回收率校正后的SIC含量,间接法的结果明显高于其他两种方法,这表明间接法的回收率被低估。气量法、CO_(2)吸收法和间接法测定平行土壤样品无机碳含量的变异系数分别为1.19%~4.99%、0.52%~3.34%和1.51%~6.79%,平均值分别为2.44%、1.36%和3.25%。【结论】气量法、CO_(2)吸收法和间接法均能用于苏北滨海SIC含量的测定,CO_(2)吸收法和间接法的测定结果均高于气量法,但间接法回收率明显被低估,这主要是由于重铬酸钾氧化法高估了酸处理后土壤的有机碳含量。CO_(2)吸收法测定的精确性最高,气量法次之,间接法最低,但气量法的耗时短,间接法能同时获得土壤有机碳和SIC的含量,研究者可以根据具体的研究目的选择合适的方法。

【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(CO_(2)) 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, CO_(2)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, CO_(2)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, CO_(2)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, CO_(2)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 CO_(2)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 CO_(2)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.