Soil microbial activity in opencast coal mine restorations

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Abstract
A number of restored areas, a soil store and undisturbed areas on opencast coal mine sites, all of similar soil type, were sampled. The microbiological activity (dehydrogenase assay), nitrogen mineralization and nitrifying potentials and physico‐chemical characteristics of the soils were determined. Dehydrogenase activities ranged from 140 to 580 μg TPF g‐124 h‐1in undisturbed control soils, whereas the disturbed soils had activities of 10 to 220 μg g‐124 h‐1, with the smallest activities being recorded in the stored and most recently reinstated soil, indicating that disturbance has depressed microbial activity. Nitrogen mineralization potential was significantly affected by disturbance, with a value of 18 to 26 μg inorganic N g‐121 d‐1in the soil store and 38 μg‐121 d‐1in a soil reinstated for six months, although the values were less than this in soils reinstated for up to six years. Nitrifying potential was not significantly less in the stored soils, being within the range of 60 to 135 μg nitrate N formed g‐1soil 21 d‐1, which was similar to that found in the undisturbed control soil.The water‐holding capacity was less in the stored soil than the undisturbed controls, and was significantly less in soil reinstated for 1.5 to 2.5 years, being only 65% of the undisturbed value (0.66 g water g‐1soil). Ammonium content of the soil store was one hundred fold larger in the soil store than in the controls (0.6 to 1.7 μg ammonium N g‐1). The carbon contents in the control soils ranged from 4.5 to 7.2%, whereas the stored and reinstated soils had generally less amounts ranging from 1.6 to 5.8%. There was a significant and positive correlation between water‐holding capacity and nitrifying potential.The implications for long‐term restoration are discussed.