The wet dichromate methods for the quantification of soil organic carbon on the basis of the reductant ability of soil organic matter have been widely used and they are still nowadays. The results obtained with these methods depart from the reference dry combustion with CO₂ measurement and the discrepancies are interpreted in terms of incomplete oxidation under the wet dichromate conditions. However, in the calculations accompanying the dichromate methods a carbon valence (V_C) equal to four is systematically used, even though the actual V_C could be different. To assess the importance that an actual V_C different from four could have in the mismatch between the wet dichromate methods and the reference dry combustion, the relationship between V_C and the average formal oxidation state of carbon (z_C) in soil organic matter should be known. On the basis of the definition of the equivalent weight and the average formal oxidation state, it is shown that a simple linear expression of the form V_C = 4 – z_C relates both concepts in carbon-hydrogen-oxygen-nitrogen-phosphorus-sulphur compounds, which are representative of soil organic matter. On the basis of this equation the actual V_C in soil organic matter can be assessed, thus helping in the interpretation of soil organic carbon determinations with the wet dichromate methods and, therefore, in the comparison between the dichromate methods and the reference dry combustion.

中文翻译：

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从土壤有机质中的平均形式氧化态估算碳价

基于土壤有机质还原能力的湿重铬酸盐法定量土壤有机碳已被广泛应用，至今仍在使用。使用这些方法获得的结果与使用 CO ₂测量的参考干燃烧不同，并且根据湿重铬酸盐条件下的不完全氧化来解释差异。然而，在伴随重铬酸盐方法的计算中，系统地使用等于 4的碳价 ( V _C )，即使实际的V _C可能不同。评估实际V _C的重要性不同于四种可能存在于湿法重铬酸盐法与参考干法燃烧之间的不匹配，应了解V _C与土壤有机质中碳的平均形式氧化态 ( z _C )之间的关系。根据当量和平均形式氧化态的定义，表明V _C  = 4 – z _C形式的简单线性表达式将碳-氢-氧-氮-磷-硫中的两个概念联系起来代表土壤有机质的化合物。在这个方程的基础上，实际的V _C 可以评估土壤有机质，从而有助于解释湿重铬酸盐法测定土壤有机碳的结果，因此有助于比较重铬酸盐法和参考干法燃烧。