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This study was undertaken to assess the relationship between nitrogen (N) mineralization in soils treated with eight lime application rates, with four field replications, and the activities of six amidohydrolases involved in N cycling and four glycosidases involved in carbon (C) cycling in soils. Nitrogen mineralization was studied at 20 or 30 °C for 20 weeks, and with the exception of N-aceyl-β-D-glucosaminidase (NAGase; EC 3.2.1.30) activity, which was assayed at both temperatures, the enzyme activities were assayed at 30 °C at their optimal pH values. Results showed that among the eight enzyme activities studied, NAGase activity was the most significantly correlated with the cumulative amounts of N mineralized in 32 soil samples at 20 °C (r = 0.87***) and at 30 °C (r = 0.95***). The cumulative amounts of N mineralized at 30 °C were also significantly correlated with arylamidase and L-aspartase activities, with r values of 0.61*** and 0.52**, respectively. Because NAGase activity is involved in both N and C cycling, the cumulative amounts of N mineralized at 30 °C were also significantly correlated with the activities of β-glucosidase (r = 0.80***) and β-galactosidase (r = 0.58***). Activities of other N enzymes that were significantly correlated with the cumulative amounts of N mineralized at 30 °C in 20 weeks were those of L-asparaginase (r = 0.61***), urease (r = 0.57***), amidase (r = 0.54**), and L-glutaminase (r = 0.41*). It seems that the activity of NAGase can be used as an index of N mineralization in soils. [ABSTRACT FROM AUTHOR]

N-Acetyl-β-d-glucosaminidase (NAGase, EC 3.2.1.30) is one of three enzymes that catalyze the hydrolysis of chitin. This hydrolysis is important in carbon (C) and nitrogen (N) cycling in soils because it participates in the processes whereby chitin is converted to amino sugars, which are major sources of mineralizable N in soils. This study investigated the relationship between N mineralization indexes and activity of β-glucosaminidase in soils from six agroecological zones of the North Central region of the United States. Nitrogen mineralization was studied by using short-term laboratory incubations under aerobic and anaerobic conditions and by hydrolysis of soil organic N by steam distillation with chemical reagents. Enzyme activity was assayed at its optimal pH value. The amounts of N mineralized by all the biological and chemical methods studied were significantly correlated with β-glucosaminidase activity, with r values of 0.73*** and 0.76*** for the amounts of released by steam distillation with PO4-B4O7 for 4 or 8 min, respectively; of 0.69*** and 0.74*** for the amounts of released with Na2B4O7 for 4 or 8 min, respectively; of 0.47*** for the amounts of inorganic N produced under aerobic incubation; of 0.80*** for amounts of inorganic N produced by incubation under anaerobic conditions of field-moist soils; and of 0.86*** for anaerobic incubation of air-dried soils. There was a significant correlation between β-glucosaminidase activity and organic C (r = 0.56***), total N (r = 0.60***), and fixed of the soils (r = 0.79***). The amounts of inorganic N released by the methods, with the exception of those under aerobic incubation, were significantly (P < 0.001) correlated with organic C and total N contents of the soils, with r values ranging from 0.65*** to 0.78*** and from 0.62*** to 0.80*** for organic C and total N, respectively. [ABSTRACT FROM AUTHOR]

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 (Cmic) and N (Nmic) 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 Corg ( r ranging from 0.42** to 0.76***), Norg (ranged from not significant at one site one year to r =0.76***), Cmic ( r ranging from 0.44** to 0.71***), and Nmic ( 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. [ABSTRACT FROM AUTHOR]