Dynamics and Characterization of Soil Organic Matter on Mine Soils 16 Years after Amendment with Topsoil, Sawdust, and Sewage Sludge

The present state and future prospect of the world's soil resources has prompted scientists and researchers to address the issue of soil quality and sustainable land management. Soil quality research has focused on intensively-managed agricultural and forest soils, but the concept and importance of soil quality is also pertinent to disturbed systems such as reclaimed mine soils. The restoration of soil function and mine soil quality is essential to long-term ecosystem stability. The objectives of this study were (i) to determine the comparative ability of topsoil, sawdust, and sewage sludge amendments, after 16 years, to positively affect mine soil quality using the following key soil quality variables: organic matter content, aggregate stability, and mineralizable nitrogen, (ii) to determine the effects of these key soil quality variables on plant productivity, and (iii) to determine the comparative ability of trees and herbaceous plants to persist and to conserve or maintain mine soil quality. In 1982, a mined site was amended with seven different surface treatments: a fertilized control (2:1 sandstone:siltstone), 30 cm of native soil + 7.8 Mg ha-1 lime, 112 Mg ha-1 sawdust, and municipal sewage sludge (SS) at rates of 22, 56, 112, and 224 Mg ha-1. Four replicates of each treatment were installed as a randomized complete block design. Whole plots were split according to vegetation type: pitch x loblolly pine hybrid (Pinus rigida x taeda) trees and Kentucky-31 tall fescue (Festuca arundinacea Schreb.). Soil analyses of composite samples for 1982, 1987, and 1998 were evaluated for changing levels of mine soil quality. The positive effect of these organic amendments on organic matter content, total nitrogen, and other soil parameters was most apparent and pronounced after 5 growing seasons. However, after 16 years, soil organic matter content and total nitrogen appear to be equilibrating at about 4.3 and 1.5%. There was a significant difference in organic matter content and nitrogen mineralization potential between vegetation types. Organic matter inputs by vegetation alone over the 16-yr period in the control plots resulted in organic matter and nitrogen mineralization potential values comparable to levels in the organically amended plots. The results suggest that about 15 years is needed for climate, moisture availability, and other edaphic features to have the same influence on overall organic matter decomposition, N accretion, organic nitrogen mineralization levels, system equilibrium, and overall mine soil quality as a one-time 100-Mg ha-1 application of organic amendment. Tree volume and biomass were measured as indices of the effects of organic matter content 16 years after initial amendment. Individual tree volumes of the sawdust, 22, 56, and 112 Mg ha -1 SS treatments retained 18 to 26% more volume than the control, respectively. Overall, fescue production was the same among treatments. Organic amendments improved initial soil fertility for fescue establishment, but it appears that they will have little or no long-lasting effect on plant productivity.