Arylsulfatase activity of microbial biomass in soils as affected by cropping systems

The impacts of crop rotations and N fertilization on different pools of ary lsulfatase activity (total, intracellular. and extracellular) were studied in soils of two long-term field experiments in Iowa to assess the contribut ion of the microbial biomass to the activity of this enzyme, Surface-soil s amples were taken in 1996 and 1997 in corn, soybeans, oats, or meadow (alfa lfa) plots that received 0 or 188 kg N ha(-1) before corn, and an annual ap plication of 20 kg P ha(-1) and 56 kg It ha(-1) The arylsulfatase activity in the soils was assayed at optimal pH (acetate buffer, pH 5.8) before and after chloroform fumigation; microbial biomass C (C-mic) and N (N-mic) were determined by chloroform-fumigation methods. All pools of arylsulfatase ac tivity in soils were significantly affected by crop relation and plant cove r at sampling time, but not by N fertilization. Generally the highest total , intracellular, and extracellular arylsulfatase activities were obtained i n soils under cereal-meadow relations, taken under oats or meadow, and the lowest under continuous crapping systems. Total intracellular, and extracel lular arylsulfatase activities were significantly correlated with C-mic (r> 0.41, P<0.01) and N-mic(r>0.38, P<0.01) in soils. The averages of specific activity values, i.e., of arylsulfatase activity of the microbial biomass, expressed per milligram C-mic, ranged from 315 to 407 mu g p-nitrophenol h( -1). The total arylsulfatase activity was significantly correlated with the intracellular activity, with r values >0.79 (P<0.001), In general, about 4 5% of the total arylsulfatase activity was extracellular, and 55% was assoc iated with the microbial biomass in soils, indicating the importance of the microflora as an enzyme source in soils.