Discussion 57 Determination of soil organic matter

An approximate determination of soil organic matter is achieved by burning it off in a muffle furnace and measuring the weight loss. This 'loss on ignition' may overestimate the true content, especially with clay soils. The —OH groups of clay minerals dehydroxylate, as also iron and aluminium oxyhy-droxides and aluminium hydroxide, yielding H2O and therefore losing weight. Illite may lose structural water at temperatures around 150-250°C. Calcium carbonate loses CO2 when heated at 550°C to form CaO (Miall and Miall, 1956), therefore as low a temperature as possible is chosen (400°C), which will still achieve the oxidation of the organic matter.

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