The soil microbial biomass C (BC) and N (BN) were obtained by the fumigation–extraction method (Vance et al., 1987) and determined with an automatic analyser for liquid samples (TOCV CSN +TNM-1 Analyzer, Shimadzu), being calculated as BC = 2.22 (fumigated soil C - unfumigated soil C) and BN = 2.22 (fumigated soil N - unfumigated soil N), according to Jenkinson (1988) and Wu et al. (1990), respectively.