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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]

This study investigated the long-term effect of lime application and tillage systems (no-till, ridge-till and chisel plow) on the activities of arylamidase and amidohydrolases involved in N cycling in soils at four long-term research sites in Iowa, USA. The activities of the following enzymes were assayed: arylamidase, l-asparaginase, l-glutaminase, amidase, urease, and l-aspartase at their optimal pH values. The activities of the enzymes were significantly (P<0.001) and positively correlated with soil pH, with r values ranging from 0.42&ast; to 0.99&ast;&ast;&ast; for arylamidase, 0.81&ast;&ast;&ast; to 0.97&ast;&ast;&ast; for l-asparaginase, 0.62&ast;&ast;&ast; to 0.97&ast;&ast;&ast; for l-glutaminase, 0.61&ast;&ast;&ast; to 0.98&ast;&ast;&ast; for amidase, 0.66&ast;&ast; to 0.96&ast;&ast;&ast; for urease, and 0.80&ast;&ast;&ast; to 0.99&ast;&ast;&ast; for l-aspartase. The Δactivity/ΔpH values were calculated to assess the sensitivity of the enzymes to changes in soil pH. The order of the sensitivity of enzymes was as follows: l-glutaminase>l-asparaginase>amidase>arylamidase>urease>l-aspartase. The enzyme activities were greater in the samples of the 0–5 cm depth than those of the 0–15 cm samples under no-till treatment. Most of the enzyme activities were significantly (P<0.001) and positively correlated with microbial biomass C (Cmic) and N (Nmic). Lime application significantly affected the specific activities of the six enzymes studied. Results showed that soil management practices, including liming and type of tillage significantly affect soil biological and biochemical properties, which may lead to changes in nitrogen cycling, including N mineralization in soils. [Copyright &y& Elsevier]