Characterization of clay bound organic matter using activation energy calculated by weight loss on ignition method

Soil organic matter (SOM) through intimate associations with clay particles forms clay bound organic matter (CBO), which contributes mainly to long-term stability of SOM in most soils. The CBO fraction contributes mainly to more meaningful carbon sequestration due to their long-term stability and hence storage. The formation and stabilization of CBO is a complex process and studies on determination of the exact composition of this fraction are meagre. In this study, an attempt was made to characterize the CBO of a soil in terms of the other SOM fractions such as fulvic fraction (FF), humic fraction (HF) and fine soil litter. The weight loss on ignition (LOI) data of extracted SOM fractions and fine soil litter were used to characterize CBO. Rate constants (k) of the oxidation reactions during the LOI were calculated using percentage weight losses at different temperatures of the FF, HF and fine soil litter. Calculated activation energies (E a ) of the other SOM fractions at different temperatures were used in a multiple regression analysis to predict the E a of the CBO fraction. The results showed that the activation energy of the CBO [E a (CBO)] was positively related to that of the fine soil litter [E a (fine soil litter)] and the FF [E a (FF)]. The relationship indicates that the CBO of the soil is composed of a mixture of fine soil litter and the FF, as also proposed in the literature.