Submitted to: Applied Soil Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/26/2006
Publication Date: 1/1/2007
Citation: Acosta Martinez, V., Cruz, L., Sotomayor-Ramirez, D., Perez-Alegria, L. 2007. Enzyme activities as affected by soil properties and land use in a tropical watershed. Applied Soil Ecology. 35(1): 35-45. Interpretive Summary: Soil enzymes are important in how the soil function because of their participation in soil biochemical reactions where compounds added to soils are degraded, organic matter is formed and degraded, and nutrients become available to plants. Thus, knowledge about enzyme activities involved in C, N, P, and S cycling in soil can be used to describe changes in soil functioning and its quality. This study reports the values of enzyme activities in different soil order classifications (Oxisols, Ultisols, Inceptisols) and as affected by land uses (pasture, forest and agriculture) in a watershed in north-central Puerto Rico (Caribbean). We found higher enzyme activities involved in C, N, P, and S cycling in soils classified as Oxisols compared to soils classified as Inceptisols. Enzyme activities involved in P (acid phosphastase) and S (arylsulftase) cycling were similar in the Oxisols and Ultisols, which were higher than in the Inceptisols. Oxisols and Ultisols are low fertility soils, but they have higher organic matter and finer texture than the Inceptisols in the watershed. In general, lower soil enzyme activities were found under agriculture compared to pasture, and those involved in P (acid phosphastase) and S (arylsulftase) cycling were similar under pasture and forest. Our findings demonstrate that the enzyme activities of Inceptisols under agriculture can be increased to levels comparable to other soil orders with conservative practices similar to those under pasture and secondary forest growth.
Technical Abstract: Enzyme activities play key roles in the biochemical functioning of soils, including soil organic matter formation and degradation, nutrient cycling, and decomposition of xenobiotics. Knowledge of enzyme activities can be used to describe changes in soil quality due to land use management and for understanding soil ecosystem functioning. In this study, we report the activities of the glycosidases ('-glucosidase and '-galactosidase), '-glucosaminidase, acid phosphatase, and arylsulfatase, involved in C, N, P and S cycling, respectively, as affected by soil order and land use within a watershed in north-central Puerto Rico (Caribbean). Representative surface soil (0-15 cm) samples were taken from 84.6% of the total land area (45,067 ha) of the watershed using a completely randomized design. The activity of '-galactosidase was greater in soils classified as Oxisols than in soils classified as Ultisols and Inceptisols, and it was not affected by land use. The activity of '-glucosidase was greater in Oxisols compared to the Inceptisols and Ultisols, and it showed this response due to land use: pasture> forest> agriculture. The activity of '-glucosaminidase was higher in Oxisols than the other soil orders, and it was higher under pasture compared to forest and agriculture. Acid phosphatase and arylsulfatase activities were greater in Oxisols and Ultisols than in Inceptisols, and they were decreased in this order due to land use: forest= pasture > agriculture. As a group, '-glucosaminidase, '-glucosidase, and acid phosphatase activities separated the sites under forest and pasture from those under agriculture in a three-dimensional plot. Thus, enzyme activities in Inceptisols under agriculture could be increased to levels comparable to other soil orders with conservative practices similar those under pasture and secondary forest growth. Our findings demonstrate that within this watershed, acid and low fertility soils such as Oxisols and Ultisols have in general higher enzyme activities than less weathered tropical soils of the order Inceptisols, probably due to their higher organic matter and finer texture; and that these enzyme activities respond to management with agricultural practices decreasing key soil biochemical reactions of soil functioning.