Skip to content

Latest commit

 

History

History
71 lines (34 loc) · 4.19 KB

Soil Organic Matter Loss On Ignition.md

File metadata and controls

71 lines (34 loc) · 4.19 KB
Raw

Soil Organic Matter

Loss on Ignition Method

Hailin Zhang, Tony Provin and Jim Wang

Application and Principle

This method determines the organic matter by oxidation at an elevated temperature in a muffle furnace and measuring the weight loss. The heating temperature is critical to record an accurate weight loss due to organic matter oxidation because the weight loss can be affected by loss of hydroscopic water in gypsum if the initial temperature is not high enough and calcium carbonate in the soil if the final temperature is too high. The initial temperature was modified to 150C to minimize the gypsum effect (Combs and Nathan, 1998; Schulte and Hopkins, 1996), while the final temperature was set at 360C to avoid CaCO3 loss. This method is a good alternative to the Walkley-Black method which generates hazardous waste and the dry combustion method which may get interference from the presence of inorganic carbonates and structural water in the soil.

Equipment and Apparatus

  1. Analytical balance: 100g capacity, resolution ±0.001g

  2. Muffle furnace capable of heating to 400C

  3. Drying oven, 105C

Procedure

  1. Number metal tins

  2. Weigh tins to 3 decimal places (W1).

  3. Weigh 5.000 to 10.000 g of wet soil samples into tins.

  4. Put tins plus samples on tray in a standard drying oven set at 105C.

  5. Dry at this temperature for 24 hrs.

  6. Weigh.

  7. Place tins plus samples in a muffle furnace preset at 360C.

  8. Combust at this temperature for 2 h. It may take some time to reach this temperature, therefore, extra time, e.g., 30 min to 1 hour, may be added if the furnace is just turned on.

  9. Weigh samples to 3 decimal places (W3). Note; be consistent when weighing samples after they are removed from the oven or furnace either warm or cooled from desiccator.

Calculations

  1. OM% = [(W2-W3)/(W2-W1)] x 100

Analytical Performance

  1. The estimation of organic matter (OM) by loss on ignition (LOI) is generally done by regression between LOI and wet chemistry method such as the Walkley-Black method. The OM regression slope between LOI and the Walkley-Black method ranged from 0.66 to 1.04 and intercept ranged from 0.04 to -0.36 at 360oC combusting temperature (Combs and Nathan, 1998). Other combusting temperatures, such as 400, 450, 500, and 600oC, have been reported (Nelson and Sommers, 1996; David, 1988; Storer, 1984; Goldin, 1987). They were generally correlated with but different from the standard wet chemical method. Therefore, the accuracy of LOI may not be as good as the wet chemistry method. The method is considered reproducible within ±20% (Gavlak, R. et al., 2003).

  2. The 150oC initial temperature was intended to remove water molecules associated with gypsum, but this temperature may not be high enough to remove structural waters in smectite (Tony Provin, unpublished). Therefore, this method may not suitable for soils with high clay contents.

  3. Calcium carbonate should be included as a method check. If the weight loss of calcium carbonate is > 0.05%, the temperature calibration of the muffle furnace should be checked.

References

Combs, S.M., and M.V. Nathan. 1998. Soil organic matter. In Recommended chemical soil test procedures for the North Central Region. Missouri Agricultural Experiment Station SB 1001.

David, M.E. 18988. Use of loss-on-ignition as an estimate of soil organic carbon in forest soils. Comm. Soil Sci. Plant Anal. 19:1593-1599.

Goldin, A. 1987. Reassessing the use of loss-on-ignition for estimating organic matter in non-calcareous soils. Comm. Soil Sci. Plant Anal. 18:1111-1116.

Gavlak, R, D. Horneck, R.O. Miller, and J. Kotuby-Amacher. 2003. Soil, Plant and Water Reference Methods for the Western Region. 2nd Edition.

Nelson, D.W., and L.E. Summers. 1996. Total carbon, organic carbon, and organic matter. In Sparks et al. (eds.) Methods of Soil Analysis. Part 3, Chemical methods. SSSA, Madison, WI.

Schulte, E.E., and B.G. Hopkins. 1996. Estimation of soil organic matter by weight-loss-on-ignition. In F.R. Magdoff et al. (eds.) Soil organic matter: analysis and interpretation. SSSA Spec. Publ. 46, Madison, WI.

Storer, D.A. 1984. A simple high volume ashing procedure for determining soil organic matter. Comm. Soil Sci. Plant Anal. 15:759-772.