土壤溶解性有机碳四种测定方法的对比和转换

针对土壤溶解性有机碳(DOC)不同测定方法之间可比性较差的问题,应用TOC仪法、容量法、紫外分光光度法和比色法分别测定了中亚热带丘陵山地6个土属共46个新鲜土壤样品的DOC含量。结果表明:参照TOC仪法测得的DOC数据,容量法一致性地低估20%~67%;比色法测定DOC含量较低的底土时(200 mg/kg)仅低估7%~27%,但在分析DOC含量较高的表土(600 mg/kg)时最不敏感,低估达53%~93%;紫外分光光度法在DOC含量较高时也存在一定的低估,但在DOC含量较低时高估65%~189%。4种方法测得的DOC数据均呈极显著正相关关系(P0.01)。统计分析获得的线性或指数方程可应用于将容量法、紫外分光光度法和比色法的测定结果向TOC仪法的数据转换,而且有必要针对表土和底土使用不同的转换方程或参数,这些经验转换方程的建立有助于增强不同研究结果之间DOC数据的可比性,也有利于推动土壤DOC测定标准的完善。

Comparison and Transform of Soil Dissolved Organic Carbon Measured by Four Methods

Soil dissolved organic carbon (DOC) is essential for soil fertility and environmental health. However, there is still no unified standard procedure to measure soil DOC and several measuring methods are available. The application of various methods leads to poor comparability among DOC levels. Thus we employed four methods, including total organic carbon (TOC) analyzer method, volumetry method, ultraviolet absorption and colorimetric methods, to determine DOC concentration in fresh soil extracts. Totally 46 fresh soil samples at profiles belonged to 6 soil genus developed in mid-subtropical hills and mountains were collected by digging soil profiles. Results showed that comparing with DOC data from TOC analyzer method, the measured soil DOC concentration with volumetry method and colorimetric method was underestimated by 20%-67% and 7%-93%, respectively. It was also underestimated for topsoils whereas overestimated by 65%-189% for subsoils with UV absorption method. The correlations of DOC data among four methods were highly significant (P < 0.01). Linear or non-linear equations were developed to transform DOC data with volumetry, ultraviolet absorption and colorimetric methods to that with TOC analyzer method. It was necessary to apply specific equation and parameters for top- and subsoils. These empirical equations and parameters are useful for enhancing comparability of soil DOC data from different studies, and improving the standard of soil DOC measurement.