- Number porcelain crucibles with wax pencil. Weigh crucibles to 4 decimal places. Scoop dried and ground samples into crucibles using 5 g soil scoop. Put crucibles plus samples on tray in furnace. Set temperature to 105 degrees C. Ash at this temperature for 2 h. (It takes 15 minutes for the furnace to reach this temp, so set the dial at 105 for a total of 2 h and 15 min.)
- Remove samples from furnace with tongs, place in desiccator, and weigh to 4 decimal places immediately while still warm so moisture won’t be absorbed. Replace crucibles plus samples in furnace. Turn dial up to 360 degrees C.
- Ash at this temp for 2 hours. (It takes ½ hour for the furnace to reach this temperature, so set the dial at 360 for a total of 2½ hour.) Turn furnace off and open door. Place samples in desiccator with tongs and allow samples to cool. Weigh samples to 4 decimal places.
- Calculate OM% and record on data sheet with one decimal.
- Crucible wt = a
- Crucible wt + sample wt after 105 heating = b
- Crucible wt + sample wt after 360 heating = c
%OM = ((b-a)-(c-a))(100)/(b-a)
- E. E. Schulte, Recommended Soil Organic Matter Tests.