Forage Evaluation Support Laboratory (FESL)

Dry Matter and Organic Matter

Dry matter (DM) is that which remains after redrying at 105°C for 15h a previously dried and ground sample. Dry matter is expressed as a percentage of the sample at the time of the analysis. Dry matter changes over time even in plastic bags, so the DM value from FESL may not be the same as the DM concentration of your sample at some previous or subsequent time.

Where:

• W1 = tare weight of container in grams.
• W2 = dry weight of sample as received in grams
• W3 = dry weight of sample and container in grams

Organic Matter is the loss in weight of DM after 15h at 550°C expressed as a percentage of DM.

• OM = 100 - Ash
• Ash = 100 - OM

Note: Ash is not the difference between the DM and OM values reported to you by FESL because DM is on an "as received" basis and OM is on a "dry" basis.

Suggested text statement: "Dry matter was determined by drying sample for 15h at 105°C and organic matter by ashing for at least 4h at 500°C."