Importance of Volumetric Expression of Water Contents of Organic Soils

Methods for evaluating water contents and bulk densities of several different peats are compared. Because bulk densities (saturated volume basis) of moss, herbaceous, and aggregated peats varied from 0.028 to 0.249 g. per cc., a highly distorted impression of the amount of water actually held under field conditions is given if water values are expressed on an oven‐dry weight basis. On a wet‐volume basis, moss peat held only 10 to 20% more water at saturation than did herbaceous and aggregated peat and retained less water than they did at higher suctions. Between 0.1 and 15 bars, moss peat retained about one‐quarter the volume of water of a medium‐textured mineral soil, Barnes loam. Since considerable volume reduction occurs on drying, bulk density of oven‐dry peat, D b (dry volume basis), represents an artificial condition rarely, if ever, occurring in undrained bogs. Bulk densities must, therefore, be calculated on the basis of the wet bulk volume and are referred to as D b (wet bulk volume). A more precise expression of degree of wetness may be substituted for “wet” in the wet volume basis term.