Soil Organic Matter by Loss on Ignition

Procedures for Loss on Ignition determination of Organic Matter (5A)

Environmental Soils and Biogeochemistry Soil Characterization Laboratory

Follows the Survey Laboratory Method Manual (2004) with adaptions.

April 28, 2011

Revised March 17, 2014

This method is used with Organic Matter that is greater than eight percent (8%). If less than 8% other methods might be more appropriate.

The mineral content is the plant ash and soil particles that remain after organic matter removal. The percentage of organic matter lost on ignition can be used to define organic soils in place of organic matter estimates by the Walkley-Black organic C method. The determination of organic matter by loss on ignition is a taxonomic criterion for organic soil materials (Soil Survey Staff, 1999). Organic C data by Walkley-Black are generally considered invalid if organic C is > 8%.

Dry sample overnight at 110° C in moisture can. Cool and weigh. Place sample in a cold muffle furnace and raise the temperature to 400° C. Heat sample overnight (16 h), cool, and weigh. The ratio of the weights (400° C ÷ 110° C) is the mineral content fraction (multiply by 100 to achieve percentage) of organic matter. The sample must be placed in a cold muffle furnace to prevent rapid combustion and sample splattering.

  1. Record weight of weighing tin.
  2. Place a 10 to 15 g sample in weighing tin and record weight and weighing tin number.
  3. Dry sample at 110° C overnight.
  4. Remove sample from oven, cap, and cool in a desiccator.
  5. When cool, record weight to at least the nearest 0.01 g.
  6. Place sample and weighing tin in a cold muffle furnace. Raise temperature to 400° C. Heat overnight (16 h).
  7. Remove sample from oven, cap, and cool in a desiccator.
  8. When cool, record sample weight to at least the nearest 0.01 g.

Oven dry weight is obtained by subtracting the weighing tin weight from step 1 from the weight of the weighing tin and oven dried soil in step 5.

The weight of the soil without organic matter is the weight of the tin and soil after 16 hours of 400° C less the weight of the tin.

References

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys, USDA-NRCS Agric. Handb. 436. 2nd ed. U.S. Govt. Print. Office, Washington, DC.

Soil Survey Staff. 2004. Soil Survey Laboratory Methods Manual – Soil Survey Investigations Report No. 42 Ver. 4.0. USDA-NRCS. Lincolin, Nebraska, USA. 

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