Responses of phosphatases and arylsulfatase in soils to liming and tillage systems

This study was carried out to investigate the long-term influence of lime application and tillage systems (no-till, ridge-till, and chisel plow) on the activities of phosphatases and arylsulfatase in soils at four research sites in Iowa, USA. The activities of the following enzymes were studied: acid and alkaline phosphatases, phosphodiesterase, and arylsulfatase at their optimal pH values. With the exception of acid phosphatase, which was significantly (P < 0.001) but negatively correlated with soil pH (r ranged from -0.65** to -0.98***), the activities of other enzymes were significantly (P < 0.001) and positively correlated with soil pH, with r values ranging from 0.65** to 0.99*** for alkaline phosphatase, from 0.79*** to 0.97*** for phosphodieste rase, and from 0.66*** to 0.97*** for arylsulfatase. The Delta activity/Delta pH values were calculated to determine the sensitivity of each enzyme to changes in soil pH. Acid phosphatase was the most sensitive and arylsulfatase the least sensitive to changes in soil pH. Activities of the enzymes were greater in the 0 - 5 cm depth samples than those in 0 - 15 cm samples under no-till treatment. With the exception of acid phosphatase, enzyme activities were mostly significantly (P < 0.001) and positively correlated with microbial biomass C (C-mic), with r values ranging from 0.28 (not significant) to 0.83*** and with microbial biomass N (N-mic), with r values ranging from 0.31 (not significant) to 0.94***. Liming and tillage systems significantly affected the activities of some enzymes but not others, as was evident from the specific activity values (g of p-nitrophenol released kg(-1) C-org h(-1)).