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)