| Abstract: | Glycosidases are a group of soil enzymes that play a major role in degradation of carbohydrates. This study was conducted to assess the impact of crop rotation and N fertilization on the activities of α‐ and β‐glucosidases and α‐ and β‐galactosidases in plots of two long‐term field experiments at the Clarion‐Webster Research Center (CWRC) and Northeast Research Center (NERC) in Iowa. Surface‐soil (0–15 cm) samples 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, applied as urea before corn, and an annual application of 20 kg P ha–1 and 56 kg K ha–1. Activities of the four glycosidases were significantly affected by crop rotations in both years at the two sites but not by nitrogen application. In general, higher activities were observed in plots under meadow or oat and the lowest in continuous corn (CWRC) and soybean (NERC). Four‐year rotation showed the highest activity, followed by 2‐year rotation and monocropping systems. Linear‐regression analyses indicated that, in general, the activities of the glycosidases were significantly correlated with microbial‐biomass C (r > 0.302, p ≤ 0.05) and microbial‐biomass N (r > 0.321, p ≤ 0.05), organic‐C (r > 0.332, p ≤ 0.05) and organic‐N (r > 0.399, p ≤ 0.01) contents of the soils. Results of this work suggest that multicropping stimulated the activities of the glycosidases. The specific activities of the glycosidases in soils of the two sites studied, expressed as g p‐nitrophenol released per kg of organic C, differed among the four enzymes. The lowest values were obtained for β‐galactosidase and α‐glucosidase, followed by α‐galactosidase and β‐glucosidase. |
