I puzzled over the measurement of organic sources by volume in mixes, and the reporting of organic matter by weight in soil samples. How do you know if you are getting what you pay for? It can't be determined with certainty after the rootzone mix is blended.
Part of this problem comes down to the weight dilution of a low bulk density material such as sphagnum peat or reed-sedge peat, compared with a high bulk density material such as sand. Depending on the ratios of bulk densities, you are always going to see a much lower % organic matter by weight in the mix than the % organic source by volume. The other part of this problem is the starting organic matter content of the organic source which can be above 85% or 90% for the high quality fibric sources such as sphagnum to as low as 40% for the low quality sapric sources such as muck. Muck, which is plentiful in Florida, is a suitable material for agricultural and highway work but Ohio State's Dr. Ed McCoy says cause "dangerously low permeability." Best recommendation is to use sphagnum peat or reed-sedge peat and make sure your supplier understands that you want analysis of the peat before it is mixed.
Here's an article that explains this:
http://philbusey.com/sports_turf/organic_matter.htmlAnd an organic source converter:
http://philbusey.com/sports_turf/organi ... erter.html