Method 57a Determination of soil organic matter by loss on ignition

Procedure. Weigh approximately 10 g (±0.001 g) air-dry soil, sieved to ^2 mm, into an accurately weighed, oven-dried, 100-ml beaker. Dry at 105°C overnight, cool in a desiccator, and weigh beaker plus sample. Place the beaker in a cold muffle furnace, switch on and ignite at 400°C overnight. Transfer to an oven at 105°C for 15 min, then to a desiccator until cool, before weighing the beaker plus ignited soil.

Calculation. The percentage loss on ignition is calculated as:

oven-dry soil weight - ignited soil weight x 100% oven-dry soil weight

The weight of water (W) in the air-dry soil may also be calculated as:

(wt of beaker + air-dry soil) - (wt of beaker + oven-dry soil)

The weight of air-dry soil (S) is:

The percentage of water in the air-dried soil is therefore:

and the percentage of water relative to the oven-dry soil becomes: W

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