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 rec lamation site, with the ultimate goal to stimulate microbial activity and improve the reclaimed soil's chemical and physical properties. Gro ss N transformation rates are indicators of microbial activity but are undocumented in such reconstructed ecosystems. We measured gross nitr ification, N mineralization and N immobilization in waste-amended and unamended soil using N-15 pool dilution techniques. Measurements were made in June, July and November 1993 at the reclamation site in wester n Kentucky, and compared to net N transformation rates. The premise th at 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-a mended soil than unamended soil. Gross N mineralization and nitrificat ion rates and gross NH4+ and NO3- immobilization rates were significan tly 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 prac tices created soil environments in which gross N transformation rates were of the same magnitude as those measured for less disturbed soil e cosystems. (C) 1998 Elsevier Science Ltd. All rights reserved.