Conservation of mineral nitrogen in restored soils at opencast coal mine sites: I. Results from field studies of nitrogen transformations following restoration

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Abstract
Summary: One of the characteristics of soils located within the cores of stockpile storage mounds at opencast mine sites is their accumulation of ammonium‐nitrogen. Two areas of restored land were constructed from soil stockpiled for 3 years; one consisted of mound‐surface (‘aerobic zone’) soil, and the other of deeply buried (‘anaerobic zone’) soil. In that constructed from mound‐surface soil, concentrations of both ammonium‐ and nitrate‐nitrogen remained fairly stable throughout the first 6 months of restoration at about 12–20 μg g−1, but in the site constructed from deeply buried soil, concentrations of ammonium‐N decreased from an initial high of 160 to 14 μg N g−1 soil after 14 weeks, and increased again to 42 μg N g−1 soil by week 29. In contrast, concentrations of nitrate‐nitrogen at the latter site increased from an initial 9 μg to a maximum recorded level of 77 μg N g−1 soil by week 14, before subsiding to 9 μg N g−1 soil by week 29. Nitrate was considered to have been lost from the restored soils by a combination of leaching and denitrification, as no vegetation was established at these sites. After a short‐term stimulation following restoration, soil microbial biomass levels remained fairly constant, though soils (up to 3 years after restoration) were characterized by a very small ratio of biomass C: organic C.

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