LOSS-ON-IGNITION AS AN ESTIMATOR OF SOIL ORGANIC-CARBON IN A-HORIZON FORESTRY SOILS

The determination of soil organic matter by wet digestion techniques is a slow and laborious analysis. Loss-on-ignition (LOI) provides a simple alternative technique for the estimation of soil organic carbon in non-calcareous A horizon soils of the Natal midlands and Zululand forestry regions. Using multiple regressional techniques, the relationships between loss-on-ignition, Walkley organic carbon and soil texture for 55 soils were determined over a range of ignition temperatures. The relationships hold best for soil samples with relatively low organic carbon contents ( < 5%). The optimum temperature for ignition was found to occur at 450-degrees-C and resulted in the relationship: Soil organic carbon = 0.284*LOI percent. No advantage is gained through ignition at higher temperatures due to the loss of clay mineral structural water, even if the soil texture is accurately known.