The misuse of permanganate as a quantitative measure of soil organic carbon
Andrew J. Margenot, Jordon Wade, Finnleigh S. Woodings
Abstract
Abstract In the last two decades, permanganate has been used to define what is assumed to be a labile or “active” soil carbon (C) pool, commonly referred to as “permanganate‐oxidizable carbon” (POXC). However, uncertainties in the reduction reaction (Mn 7+ → Mn 4+ /Mn 2+ ) and even greater uncertainties in the oxidation reaction (C ? → C ? ) as well as the reaction of non‐C reductants in the soil sample preclude the calculation of milligram C per kilogram of soil oxidized. Combined variation in the reduction–oxidation reactions can entail up to fivefold variation in how much soil organic C is oxidized per unit permanganate reduced. Without determining final reduction state of Mn and the initial and final oxidation states of C, the amount of C oxidized cannot be calculated. Unless a concrete understanding of the reduction and oxidation half‐reactions is achieved, an alternative expression of permanganate reactivity of a soil sample (i.e., not mg C kg −1 soil) is needed.