Arylamidase and amidohydrolases in soils as affected by liming and tillage systems

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∗ to 0.99∗∗∗ for arylamidase, 0.81∗∗∗ to 0.97∗∗∗ for l-asparaginase, 0.62∗∗∗ to 0.97∗∗∗ for l-glutaminase, 0.61∗∗∗ to 0.98∗∗∗ for amidase, 0.66∗∗ to 0.96∗∗∗ for urease, and 0.80∗∗∗ to 0.99∗∗∗ 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.