Determination of organic carbon in aqueous extracts of soils and fertilizers

A simple and accurate method for the routine determination of organic carbon in aqueous extracts of soils and fertilizers is described. Samples are oxidized for exactly 10 minutes with a mixture of 5 mL of 2N potassium dichromate plus 20 mL of concentrated sulphuric acid at 160 ± 2°C, and the excess dichromate is titrated either potentiometrically or manually with iron (II) sulphate. An appropriate correction factor (1.05) is suggested for aqueous extracts from humic acid.