Quality of amended mine soils after sixteen years

Soil quality research has focused on intensively managed agricultural and forest soils, but the concept and importance of soil quality is also pertinent to reclaimed mine soils and other disturbed ecosystems. Adding organic amendments has been used as a means for ameliorating mine soils and improving their quality, but the long-term effects of amendments on soil quality are not known. In 1982, a mined site was amended with seven different surface treatments: a control (nothing added), 30 cm of native soil, 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. Each plot was split and planted with pitch x loblolly pine hybrid (Pinus rigida x taeda) trees and Kentucky-31 tall fescue (Festuca arundinacea Schreb.). During the 16-yr period, organic matter content, total organic N, N mineralization potential, aggregate stability, and other physical and chemical properties were measured as mine soil quality indicators. The comparative ability of these organic amendments to positively affect organic matter content, total N, and other parameters was most apparent and pronounced after 5 yr. However, after 16 yr, soil organic matter (SOM) content and total N appeared to be equilibrating at approximately equal to 10 000 and 750 kg ha(-1), respectively. Organic matter inputs by vegetation alone across the 16-yr period in the control plots resulted in organic matter and N mineralization potential values comparable to levels in the organically-amended plots, indicating the overriding importance of vegetation in the soil recovery process. After 16 yr, there appears to be no lasting soil quality improvements due to addition of organic amendments to this mine soil. Amendments improved short-term production, but their cost of transport and application may be difficult to justify based on long-term soil quality improvement.