Influence of Drying Temperature and Duration on the Quantification of Particulate Organic Matter

Abstract

Various drying conditions, temperatures (40 to 80°C) and durations (overnight to 72 hrs), for the particulate organic matter (POM) fraction after wet-sieving size fractionation have been applied for determination of POM contents in the weight loss-on-ignition method. In this study, we investigated the optimum drying condition for POM fraction in quantification of POM and/or mineral-associated organic matter (MOM; usually indirectly estimated). The influence of the drying conditions on quantifying POM was dependent upon soil properties, especially the amount of soil organic components. In relatively high organic soils (total carbon > 40 g/kg in this study), the POM values were significantly higher (overestimated) with drying at 55°C than those values at 105°C, which were, for example, 173.2 and 137.3 mg/kg, respectively, in a soil studied. However, drying at 55°C for longer than 48 hrs of periods produced consistent POM values even though the values were much higher than those at 105°C. Thus, indirect estimates of MOM (MOM = SOM POM) also tended to be significantly impacted by the dry conditions. Therefore, we suggest -- - POM fractions should be dried at 105°C for 24 hrs as determining POM and MOM contents. If the POM fraction is needed to be dried at a lower temperature (e.g. 55°C) with a specific reason, at least 48 hrs of drying period is necessary to obtain consistent POM values, and a moisture correction factor should be deter- mined to adjust the values back to a 105°C weight basis.