β-Glucosaminidase activity of soils: effect of cropping systems and its relationship to nitrogen mineralization

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.