Organic amendment effects on carbon and nitrogen mineralization in an Appaplachian minesoil
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The use of blasted rock overburden as a topsoil substitute during surface-mined land reclamation is practiced in areas with thin, unrecoverable topsoil. The long-term productivity of topsoil substitutes has often been difficult to maintain under forage and row crops. The objective of this project was to evaluate the effectiveness of an unamended topsoil substitute as a tree growth medium compared to both topsoil- and organic matteramended minesoils based on the accumulation and mineralization of carbon and nitrogen pools. A factorial experiment was established in 1987; treatments (5 cm of a Jefferson series topsoil, 8 cm of whole-tree woodchips, and an unamended control) were assigned to lysimeters filled with blasted overburden. All lysimeters were planted with a treecompatible ground cover of grasses and legumes and 10 pitch pine x loblolly pine hybrid seedlings (Pinus rigida L. x P. taeda L.). The control treatment was designed based on principles hypothesized as necessary for the success of reclamation forestry; i.e., the selection of a suitable spoil material (slightly acid, low salt concentration), placing that material in an uncompacted (rough-graded) condition, and planting a tree-compatible ground cover of grasses and legumes. It was hypothesized that, under these conditions, C and N accumulation and N supply would be comparable to topsoil- and organic matteramended minesoils.
Two years after treatment, net accumulated total organic C in the fine-earth fraction was 4.4, 3.7, and 9.2 g kg-l for the control, topsoil, and woodchip treatments, respectively; after 8 years, concentrations were 12.7, 16.0, and 18.2 g kg-l. Net accumulated total Kjeldahl N after 8 years was 784, 1132, and 679 kg ha-l! for the control, topsoil, and woodchip treatments, respectively, but amended minesoils were not significantly different from the control. Total Kjeldahl N accumulation rates were 103, 149, and 89 kg N ha-l yr-l. Aerobic N mineralization potential after 1 year was 31, 63, and 56 mg kg-l for the control, topsoil, and woodchip treatments and increased to 112, 157, and 118 mg kg-l after 8 years.
The woodchip treatment seemed to confer no additional benefits, relative to N accumulation and cycling, compared to the control. The topsoil treatment increased the amount of N and the N mineralization capacity of the minesoil, but did not affect the N accumulation rate or the N mineralization rate relative to the control. While maximum plant productivity would probably be realized in a topsoil-amended minesoil, pine tree volume between the control and topsoil treatments was not significantly different after 5 years.
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