Effects of liming and tillage systems on microbial biomass and glycosidases in soils

This study was undertaken to investigate the long-term influence of lime application and tillage systems (no-till, ridge-till and chisel plow) on soil microbial biomass C (C-mic) and N (N-mic) and the activities of glycosidases (alpha- and beta-glucosidases, alpha- and beta-galactosidases and beta-glucosaminidase) at their optimal pH values in soils at four agroecosystem sites [Southeast Research Center (SERC), Southwest Research Center (SWRC), Northwest Research Center (NWRC), and Northeast Research Center (NERC)] in Iowa, USA. Results showed that, in general, the C-mic and N-mic values were significantly (P <0.001) and positively correlated with soil pH. Each lime application and tillage system significantly (P <0.001) affected activities of the glycosidases. With the exception of alpha-glucosidase activity, there was no limextillage interaction effect. Simple correlation coefficients between the enzyme activities and soil pH values ranged from 0.51 (P <0.05) for the activity of alpha-glucosidase at the NWRC site (surface of the no-till) to 0.98 (P <0.001) at the SWRC site. To assess the sensitivity of the enzymes to changes in soil pH, the linear regression lines were expressed in Deltaactivity/DeltapH values. In general, their order of sensitivity to changes in soil pH was consistent across the study sites as follow: beta-glucosidase>beta-glucosaminidase>beta-galactosidase>alpha-galactosidase>alpha-glucosidase. Lime application did not significantly affect the specific activities (g p -nitrophenol released kg(-1) soil organic C h(-1)) of the enzymes. Among the glycosidases studied, beta-glucosidase and beta-glucosaminidase were the most sensitive to soil management practices. Therefore, the activities of these enzymes may provide reliable long-term monitoring tools as early indicators of changes in soil properties induced by liming and tillage systems.