Significance of Enzyme Activities in Soil Nitrogen Mineralization

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 degrees C for 20 weeks, and with the exception of N-aceyl-beta-D-glucosaminidase (NAGase; EC 3.2.1.30) activity, which was assayed at both temperatures, the enzyme activities were assayed at 30 degrees 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 degrees C (r = 0.87***) and at 30 degrees C (r = 0.95***). The cumulative amounts of N mineralized at 30 degrees 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 degrees C were also significantly correlated with the activities of beta-glucosidase (r = 0.80***) and beta-galactosidase (r = 0.58***). Activities of other N enzymes that were significantly correlated with the cumulative amounts of N mineralized at 30 degrees 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.