Ash and organic matter content
A crucible was pre-heated in a muffle furnace at 500°C, cooled in desiccator and weighed. 2 g of the sample was transferred into the crucible and weighed. The crucible and its content were kept in the muffle furnace at 525°C until white ash was obtained after twelve hours. The organic matter content was calculated by subtracting the percent ash content from 100 following the standard methods of the Association of Official Analytical Chemists (1990).