Thus, the loss of volatile organic dry matter in the drying step is rarely a significant factor. However, dry weight is used as the basis for determining concentrations of nutrients, heavy metals, and microorganisms. Inaccuracies in measuring moisture contents could overstate these qualities. What differs among the various gravimetric methods is how samples are dried, how long they are dried, and, in some cases, what the sample size is. Drying methods include air drying, oven drying at various temperatures, and microwaves.
Microwaves are quickest and most convenient but also the least accurate.
Air drying is painfully slow but most accurate if the material is not actively decomposing. Oven drying is the middle ground and tends to be the standard. Standard oven-drying procedures exist for analytical laboratories. The primary intent is to insure accuracy in determining dry weights, as the basis for calculating concentrations, rather than managing moisture during processing. Again, determining moisture content for the purpose of managing the composting process or the handling characteristics of compost does not merit great accuracy and precision.