Organic Matter Pools in Reclaimed Soils: Quantification Using Biological, Chemical and Physical Fractionation Methods.

Long-term assessment of soil amendments used to enhance not only soil properties, but also carbon (C) storage in reclaimed mine soils is of interest.  Furthermore, the stability of C associated with various amendments is important for estimating C storage potential.  To evaluate these dynamics, long-term experimental plots were sampled where a series of treatments (control, topsoil, biosolids and sawdust) were applied over a mixture of sandstone and siltstone overburden in southwest Virginia.   As a second component to this study, samples from these four treatments were analyzed using different laboratory fractionation methods for C stability to illustrate the impact of sample preparation and method selection on interpretation of results.  Labile and recalcitrant C concentrations were similar across soil treatments after 28 yrs when using physical and chemical fractionation methods. However, differences were observed when using a biological method for separation (incubation), where pool sizes among treatments varied and the mineralization rate for the recalcitrant pool was higher under the biosolids and topsoil treatments.  When using a physical fractionation technique (density floatation), labile C constituted a greater portion of total C (67-72%) than the recalcitrant fraction.  This was similar regardless of sample preparation (sieving to 2 mm or 8 mm).  Chemical fractionation (acid hydrolysis) indicated 30 - 38% of total C in the labile fraction with the remainder in the recalcitrant pool.  The selection of fractionation technique for assessing soil C pools in various reclamation treatments is vital for the interpretation of treatment effects, where the proportion of pools and differences among treatments may vary greatly depending on the method used.