AASHTO T 194-22

The Wet Combustion method for the determination of soil organic matter is most applicable when it is desired to determine the humus-like, easily oxidized organic material to provide information relating to the suitability of the soil for plant growth. The method provides a good estimate of this type of organic matter, and, when the soil contains only this type, it can also provide a good estimate of the total organic content. However, the reagents used react only very slightly with fresh plant materials such as wood, roots, grass, and weed tops, etc., or with hydrocarbons, charcoal, lignite, coal, and the organic remains in ancient sediments. If such materials are present and the total organic matter is to be determined, the Loss on Ignition method found in AASHTO T 267 must be used.