Nitrogen mineralization was determined by subtracting the initial inorganic N concentration of nonincubated soil samples from soil N extracted after 56 d of incubation. Inorganic N was extracted from 7-g soil subsamples using 28 ml of 2 M KCl. Samples were shaken for 30 min on a reciprocal shaker and filtered, and the extracts were analyzed for NH4–N and NO2– plus NO3–N using an autoanalyzer(Technicon 1977a, 1977b). The sum of the above N forms was designated inorganic N.