Enzyme activities in a limed agricultural soil

This study assessed the effect of eight lime application rates, with four field replications, on the activities of 14 enzymes involved in C, N, P, and S cycling in soils. The enzymes were assayed at their optimal pH values. The soil used was a Kenyon loam located at the Northeast Research Center in Nashua, Iowa. Lime was applied in 1984 at rates ranging from 0 to 17,920 kg effective calcium carbonate equivalent (ha(-1)), and surface samples (0-15 cm) were taken after 7 years. Results showed that organic C and N were not significantly affected by lime application, whereas the soil pH was increased from 4.9 to 6.9. The activities of the following enzymes were assayed: alpha- and beta-glucosidases, alpha- and beta-galactosidases, amidase, arylamidase, urease, L-glutaminase, L-asparaginase, L-aspartase, acid and alkaline phosphatases, phosphodiesterase, and arylsulfatase. With the exception of acid phosphatase, which was significantly (P < 0.001) but negatively correlated with soil pH (r = -0.69), the activities of all the other enzymes were significantly (P < 0.001)and positively correlated with soil pH, with r values ranging from 0.53 for the activity of alpha-galactosidase to 0.89 for alkaline phosphatase and phosphodiesterase. The Delta activity/Delta pH values ranged from 4.4 to 38.5 for the activities of the glycosidases, from 1.0 to 107 for amidohydrolases and arylamidase, 97 for alkaline phosphatase, 39.4 for phosphodiesterase, and 11.2 for arylsulfatase. This value for acid phosphatase was -35.0. The results support the view that soil pH is an important indicator of soil health and quality.