Comparing loss-on-ignition with dry combustion as a method for determining carbon content in upland and lowland forest ecosystems

Peat and forest floor samples (n = 307) from sites across continental western Canada are analyzed. to determine (a) Carbon/organic matter (C/OM) ratios for different peat and forest floor types, (b) variability in C/OM ratios, and (c) the influence of vegetation type and ash content on C/OM ratios. Measured C/OM ratios for different peat and forest floor types are between 0.50 and 0.56, with an average of 0.52 over all samples. C/OM ratios change with ash content, with a positive relationship between the two variables if ash content is < 20%. In samples with ash contents >20%, C/OM ratios are highly variable and our data suggest a slight decrease in average C/OM ratios with increased mineral content. Measurement error due to loss of structural water from clay minerals and the presence of inorganic C increasingly influence observed C/OM ratios as mineral content increases. While these problems can be partially overcome by use of appropriate analytical technique, LOI may not be a reliable measure of OM content in samples with very high mineral content.