Analytical Methods:LOI

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Loss-On-Ignition
Loss-on-ignition is the most straightforward method of analysing soil organic matter content. The organic matter is burnt off at high temperature and the loss in mass (weight) is recorded. At very high temperatures calcium carbonate in the soil and structural waters in clay minerals are also lost, so the usual method is to use a lower temperature burn for a longer period of time; typically 425oC for 8 hours (or overnight). There may still be some inaccuracy, however, in soils with a high clay content or significant amounts of limestone or other carbonates (including lime based mortars and plasters, and bone).

Method

 * Air dry soil and sieve to 2 mm, discard the greater than 2 mm fraction.
 * Weigh to 0.01 grams a clean, dry crucuible and record this weight (W1).
 * Place approximately 10 grams of the less than 2 mm soil into the crucible and oven dry at 105oC. Store these samples in a dessicator until cool.
 * When cool reweigh the crucibe and soil to 0.01g (W2).
 * Using tongs and taking extreme care place the sample in a furnace set at 425oC. Make a note of exactly where each sample is placed in the furnace as markings on the crucibles will often burn off.
 * Leave for 8 hours or overnight. Then using tongs and taking extreme care remove the samples from the furnace and place them straight into a dessicator. Again make a note of exactly where each sample is placed.
 * Leave the samples to cool in the sealed dessicator.
 * Once cool reweigh the crucible and soil (W3).

&#37; Loss on ignition = ((W2 - W3) &divide; (W2 - W1)) x 100

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