Organic soil materials are characterized by the National Cooperative Soil Survey as fibric, hemic, or sapric, using the rubbed fiber volume and the sodium pyrophosphate extract color (SPEC) as differentiae. The U.S. Department of Energy (DOE) defines fuel-grade peat as having a minimum gross calorific value of 8000 Btu/oven-dry lb (18.6 J/kg), and a maximum ash content of 25% by weight. The object of this study was to determine the nature of the correlations between the unrubbed and rubbed fiber volume, SPEC, calorific value, and percent ash parameters for selected organic soil materials.

Thirty-four samples of the most common kinds of materials collected as part of the Peat Resource Estimation in Michigan research project were selected for characterization. Fiber volumes and pyrophosphate solubility were determined in duplicate after procedures of the National Soil Survey Laboratory of the Soil Conservation Service. Calorific value and ash content were determined in accordance with ASTM Test for Gross Calorific Value of Solid Fuel by the Isothermal-Jacket Bomb Calorimeter (D 3286-77) and ASTM Test for Ash in the Analysis Sample of Coal and Coke (D 3174-73). Correlation analyses were performed between these five data sets.

The correlation between rubbed fiber and calorific value was not significant (α = 0.05). Unrubbed fiber and SPEC were significantly correlated with calorific value (r = 0.363, r = 0.530), while a much stronger correlation existed between the ash content and calorific value (r = −0.869). The results suggest that the ash content of the materials is a very useful indicator of the calorific value, much more so than the other parameters studied.

Other systems of characterizing organic soil materials for fuel used by other peat resource estimation projects are compared with the system used in Michigan. Ash content and calorific value data reported by these projects are compared with the aforementioned findings.