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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 phosphodiesterase, and from 0.66*** to 0.97*** for arylsulfatase. The Δ activity/Δ 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 (Cmic), with r values ranging from 0.28 (not significant) to 0.83*** and with microbial biomass N (Nmic), 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 Corg h^–1).

Abstract. The enzyme β-glucosaminidase (EC 3.2.1.30) is involved in C and N cycling in soils. The effects of crop rotations and N fertilization on β-glucosaminidase activity and its relationship to N mineralization were studied in soils of two long-term field experiments involving different cropping systems at the Northeast Research Center (NERC) and Clarion-Webster Research Center (CWRC) in Iowa that were initiated in 1978 and 1954, respectively. Surface soil samples (0-15 cm) were taken in 1996 and 1997 in corn (Zea mays L.), soybean [Glycine max (L) Merr.], oats (Avena sativa L.), or meadow (alfalfa; Medicago sativa L.) plots that received 0 or 180 kg N ha^-1 before corn and an annual application of 20 kg P and 56 kg K ha^-1. The β-glucosaminidase activity in the soils was assayed at optimal pH (acetate buffer, pH 5.5); microbial biomass C (C_mic) and N (N_mic) were determined by chloroform-fumigation methods; N mineralization was studied in leaching columns under aerobic conditions at 30°C for 24 weeks. The activities of β-glucosaminidase were significantly affected by crop rotation (P <0.001) and N fertilization (P ranging from 0.05 to 0.001). Generally, the highest enzyme activity was obtained in soils under 4-year corn-oats-meadow rotations taken under meadow, and the lowest under continuous mono-cropping systems. The activity of this enzyme was significantly correlated with C_org (r ranging from 0.42** to 0.76***), N_org (ranged from not significant at one site one year to r =0.76***), C_mic (r ranging from 0.44** to 0.71***), and N_mic (r ranging from 0.33* to 0.76***) in soils, and with cumulative N mineralized (r >0.84*** and r >0.79*** at the NERC and CWRC sites, respectively). The results suggest that β-glucosaminidase plays a major role in N mineralization in soils and is affected by cropping systems, i.e. ecosystem function and health.