Abbey F. Wick

SOIL AGGREGATE, ORGANIC MATTER AND MICROBIAL DYNAMICS UNDER DIFFERENT AMENDMENTS AFTER 27 YEARS OF MINE SOIL DEVELOPMENT 1

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 -1 ) 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 -1 appeared to improve aggregate associated C and N concentrations and soil biological properties.

EFFECTS OF PRIME FARMLAND SOIL RECONSTRUCTION METHODS ON POST-MINING PRODUCTIVITY OF MINERAL SANDS MINE SOILS IN VIRGINIA 1

Significant areas of prime farmland in the upper Coastal Plain of Virginia have been disturbed by heavy mineral sands (Ti/Zr-bearing ilmenite, rutile, zircon) mining over the past 15 years. Mine soils created by the deposition of tailings and slimes in dewatering pits exhibit physical and chemical properties that limit agricultural use due to abrupt textural changes, heavy compaction from grading and the inherently low pH and available P of the processed subsoils. In 2004, the Carraway-Winn Reclamation Research Farm (CWRRF) was developed with Iluka Resources Inc. in Dinwiddie County to evaluate reconstruction strategies for returning mined land to agricultural production. In 2004, row crop plots were established in a randomized complete block design with 4 replications of 4 treatments: 1) LBS-CT - lime-stabilized biosolids (78 dry Mg ha -1 ) with conventional tillage, 2) LBS-NT - lime-stabilized biosolids (78 dry Mg ha -1 ) with no tillage, 3) TS - 15 cm of topsoil replacement with lime+NPK, and 4) C - control (tailings+lime+NPK). All treatments were deep ripped to 90 cm following grading and limed and fertilized annually to optimal levels. Two additional study sites, managed similarly to the treatment plots, included a compacted (no ripping) area (COMP) and a nearby unmined prime farmland (Orangeburg series) field (UM). Between 2005 and 2008, the plots were managed with a corn-wheat/double crop soybean rotation. In 2009, the plots were managed with cotton and in 2010 with wheat/double crop soybeans. During the initial four year corn-wheat/double crop soybean rotation, the two LBS treatments produced significantly higher yields than the TS or C treatments. No significant differences were observed among treatments for the 2009 cotton yield; however, erratically distributed settlement depressions adversely affected crop growth and harvest and led to high variability within each treatment. Similarly, no significant differences were observed for the 2010 wheat and soybean yields in a low rainfall year. Overall, yields from all four treatments typically exceeded 5-year local county averages, but were 25 to 40% lower than yields from the local prime farmland soil under identical management. Relatively low COMP yields illustrated the need for initial deep ripping and periodic tillage to improve physical conditions of these mine soils.

ECOSYSTEM RECOVERY ON RECLAIMED SURFACE MINELANDS 1

The ultimate goal of mineland reclamation is reestablishment of a productive, functional, and sustainable ecosystem suitable for postmining land use. Evaluation of reclamation success for bond release, however, is limited to examination of the reestablished plant community with emphasis also placed on soil erosion protection and landscape hydrologic function. Most ecosystem components and processes of the reclaimed site are not examined but are crucial to ecosystem function and sustainability. The objective of this paper is to present data from our work on recovery of ecosystem structure (e.g. organisms, soils, mycorrhiza) and function (e.g. biomass production, carbon cycling, nitrogen cycling) on reclaimed surface coal mines in Wyoming. Our studies of chronosequences of reclaimed sites indicate increasing productivity through time in all groups of organisms monitored (plants, bacteria, fungi, nematodes and arthropods) as well as increasing concentrations of soil organic matter, rapid incorporation of organic carbon into soil aggregates, redevelopment of mycorrhizae, and reformation of carbon and nitrogen pools. Although the precise trajectory of the restored ecosystems are very difficult to predict because of changing control variables such as potential biota (invasive species) and climate, our data indicates ecosystem structure and function is recovering on reclaimed surface minelands.

AGGREGATE SIZE DISTRIBUTION AND STABILITY UNDER A COOL SEASON GRASS COMMUNITY CHRONOSEQUENCE ON RECLAIMED COAL MINE LANDS IN WYOMING 1

Evaluation of mine reclamation success is based on examination of aboveground ecosystem components. Recovery of belowground constituents and processes, such as soil structure and nutrient cycling, is crucial to successful reclamation of disturbed lands. Inadequate recovery of belowground ecosystem structure and function during reclamation can lead to future site degradation. Our objective in this study was to test the hypothesis that recovery of plant community properties on reclaimed surface mine land accurately reflect recovery of soil structure, more specifically aggregate size distribution. In this study, above- and belowground constituents were sampled on reclaimed mine sites representing various ages (native rangeland, a 4 month old topsoil stockpile, 14, 26, and 29 year old reclamation) located in northeastern Wyoming. Cool-season grass (native and reclaimed) communities were sampled for aboveground biomass production, cover and species diversity according to Wyoming Department of Environmental Quality standards. Soil samples were analyzed for water stable aggregate size distribution with wet sieving. Soil structure appears to be recovering through time. An increase in macroaggregates (250-2000µm) on a weight basis and a decrease in free microaggregates (53-250 µm) and free silt and clay (<53 µm) on reclaimed sites with time was observed, indicating incorporation of free silt and clay and free microaggregates into macroaggregates. Aboveground biomass production and macroaggregate formation showed a significant relationship (R 2 = 0.457); however, no relationship was evident for microaggregate formation. No significant relationship existed among total cover and species diversity with respect to macro- and microaggregate formation. These preliminary results suggest that soil structural recovery is most closely related to plant biomass production, while other plant community properties do not necessarily reflect this recovery.

SOIL AGGREGATE AND AGGREGATE ASSOCIATED CARBON RECOVERY IN SHORT-TERM STOCKPILES 1

Soil organic matter (OM) is drastically reduced by various processes (erosion, leaching, decomposition, dilution through soil horizon mixing etc.) typically associated with topsoil salvage prior to surface mining activities. Of these processes, loss of physical protection of OM through the breaking up of soil aggregation can result in up to 65% of soil carbon (C) reductions. Objectives of this research were to monitor soil aggregate size distribution and associated C throughout short-term stockpiling and subsequent utilization of topsoil for reclamation. Soil samples were collected from the top 5 cm of a stockpile over a 3 year period (<1, 1.5, 3 yrs) and an adjacent undisturbed, native site. Surface stockpile soils were then tracked to a temporary location following stockpile removal and sampled again. Samples were analyzed for aggregate size distribution, fractions, associated C, and OM turnover with 13 C natural abundance. Macroaggregation increased and microaggregation decreased after 3 yrs of storage, indicating recovery of aggregation in 3 yrs. Following the second removal, macroaggregate proportions decreased and silt and clay fractions were greater than that observed in the native site soils. The second disturbance resulted in greater destruction of aggregate structure than the initial disturbance during topsoil salvage. Carbon increased significantly between <1 and 1.5 yrs in both aggregate size classes. Macro- and microaggregate light fraction (LF) C decreased with storage time as this material was available for utilization by microbes. Aggregate δ 13 C values indicated up to 65% new C associated with aggregate structure. Topsoil storage was beneficial for aggregation and associated C in the surface layers only where plant roots and microbial communities are active; however, the second movement of the topsoil resulted in loss of soil aggregation without impact to soil C.