Gross nitrogen transformation rates in soil at a surface coal mine site reclaimed for prime farmland use

Organic wastes were used to increase N fertility at a surface mine reclamation site, with the ultimate goal to stimulate microbial activity and improve the reclaimed soilʹs chemical and physical properties. Gross N transformation rates are indicators of microbial activity but are undocumented in such reconstructed ecosystems. We measured gross nitrification, N mineralization and N immobilization in waste-amended and unamended soil using 15N pool dilution techniques. Measurements were made in June, July and November 1993 at the reclamation site in western Kentucky, and compared to net N transformation rates. The premise that organic waste amendment stimulates microbial activity in reclaimed soils was supported by the data. Gross N mineralization, nitrification and immobilization rates were as much as 4.5 times greater in waste-amended soil than unamended soil. Gross N mineralization and nitrification rates and gross NH4+ and NO3− immobilization rates were significantly greater than net rates in waste-amended and unamended soil. There was net immobilization of NH4+ and NO3− in waste-amended soil, whereas there was net N mineralization in unamended soil. This was consistent with using substrates containing high C-to-N ratios. Reclamation practices created soil environments in which gross N transformation rates were of the same magnitude as those measured for less disturbed soil ecosystems.