A 20-g subsample of field-moist soil per sample was placed in a 125-ml specimen cup, which was then closed with a perforated plastic cap to allow gas exchange while minimizing evaporation. These subsamples were incubated for 30 days at room temperature (approximately 24 °C). NH4+−N and NO3−−N concentrations were determined by extracting inorganic N at 100 rpm for 2 h from subsamples with 100 ml of 2 mol L−1 KCl before and after incubation. The extract was subjected to colorimetric determination on a 2300 Kjeltec Analyzer Unit (FOSS, Höganäs, Sweden). Net N mineralization was calculated as the change in total inorganic N content from the start until the end of incubation. The changes in NH4+−N and NO3−−N concentrations over one month were obtained by subtracting the initial concentration from the corresponding final concentration, and the resultant values are referred to as net ammonification and net nitrification rates. Net N mineralization was calculated as the sum of ammonification and nitrification rates over one month (Evans et al., 2001)