Quantification of the effects of organic carbon (OC) addition to reclaimed soils is an important reclamation issue. Such effects on soil texture, field capacity (FC), wilting point (PWP) and water-hold- ing capacity (WHC), all expressed both on a gravimetric and volumetric basis, were quantified using both in situ soil samples and laboratory-prepared peat:mineral mixes. Soil samples were collected from both natural and reclaimed areas within the Oil Sands region of Alberta; peat was obtained from the same area. Organic carbon was determined for laboratory-created mixtures and expressed as volume ratios; for the in situ samples it was expressed as % OC. Bulk density, an important factor in the effects of OC on water retention, was measured in situ.
Water retention parameters of in situ samples on a gravimetric basis were significantly related to % OC, but those on a volume basis were not. Trends in volumetric WHC for in situ, coarse-textured samples were similar to those for gravimeteric WHC, due to similar bulk densities ranging from 1.30 to 1.40 Mg m–3. However, for in situ peaty soils, trends in volumetric water retention did not mimic those expressed on a gravimetric basis due to low and irregular bulk densities. For laboratory-constructed peat:min- eral mixes, FC and WHC were significantly impacted by % OC, however, PWP was not.
The addition of peat material resulted in minor textural changes for sand and loamy sand; hence, the change in texture could not be responsible for the increases in WHC as the result of peat additions. The results for sandy loam were variable.