Soil Aggregate, Organic Matter and Microbial Dynamics under Different Amendments after 27 Years of Mine Soil Development

Physical and biological properties of soils developing from spoil material following surface coal mining in southwest Virginia are poorly understood. Additionally, the effects of various types of soil amendments such as sawdust, topsoil or biosolids on long-term soil development are lacking in the current literature. The objective of this study was to examine water stable aggregation, organic matter (OM) content and microbial biomass in a long-term experiment (27 yr) where various types (control-CON, topsoil-TS, sawdust-SD, and biosolids-B) and rates of soil amendments (biosolids: B-22, B-56, B-112 and B-224 Mg ha) were applied in 1982. Treatments were replicated four times in a randomized complete block design. Small macroaggregates (250-2000 μm) were higher on the B-224 rate plots compared to other treatments, while there were no differences in large macroaggregates (2000-8000 μm) or microaggregates (53-250 μm) among treatments. Aggregate associated OM, as indicated by carbon (C) and nitrogen (N) concentrations, was highly variable among treatments. Biosolids treatments were clearly higher in total aggregate C and N relative to the CON, TS, and SD treatments; however, these differences were not significant for each aggregate size class due to the variability observed among replicates. There were no significant differences in aggregate C and N among biosolids application rates after 27 years of soil development. However, microbial biomass C was higher in all biosolids treatments compared to the CON, TS, and SD treatments and was slightly higher on the B-56 treatments relative to other biosolids treatments. Despite the large variability in soil development observed in these relatively small research plots, higher rates of biosolids amendments slightly improved macroaggregate structure while application rates between 22 and 56 Mg ha appeared to improve aggregate associated C and N concentrations and soil biological properties. Additional