A comparative study of titrimetric and gravimetric methods for determination of organic carbon in soil

Two gravimetric procedures for determining carbon in soil, one a dry combustion method and the other a wet oxidation method, were compared with seven variants of the titrimetric method, all based on titrimetric determination of the dichromate consumed when soil is heated with dichromate and acid. The coefficients of variation of the methods were, as percentages: dry combustion, 0.76; wet combustion, 1.1; Tinsley I, 1.3; Tinsley II, 1.8; Tinsley III, 0.8; Anne, 1.3; Mebius, 1.8; Walkley and Black, 1.6 and Tyurin, 8.5. Taking the dry combustion method as standard, the percentage recovery of organic carbon from 22 soils was 99 for wet combustion, 95 for Tinsley I, 95 for Tinsley II, 97 for Tinsley III, 93 for Anne, 95 for Mebius, 77 for Walkley and Black and 93 for the Tyurin method. A variant of the Tinsley method (Tinsley III) is proposed as a quick procedure when the accuracy of dry combustion is not essential.