Soil enzyme response to vegetation disturbance in two lowland Costa Rican soils

Conversion of forests to intensive agriculture often leads to degradation o f weathered soils. The effects of two intensities of vegetation management on soil beta-glucosidase (beta-GLC) and phosphomonoesterase (PME) activitie s were studied on two river-terrace soils of differing fertility in Costa R ica. After approximately four years of annual harvest or continuous vegetat ion removal to bare soil, soil organic matter carbon (SOM-C), microbial bio mass carbon (Mb-C), beta-GLC and PME activity were reduced. Effects of cont inuous cropping to bare soil on Mb-C, beta-GLC and PME were greater in the more weathered, acidic, Al-rich, P-limited upper-terrace soil than in the m ore neutral, base cation-rich lower-terrace soil. In contrast, more SOM-C w as lost in the lower terrace. The annual harvest treatment produced interme diate decreases in SOM-C, Mb-C, beta-GLC and PME on upper-terrace soils, in termediate reduction in lower terrace beta-GLC, and no significant effect o n lower terrace Mb-C or PME. beta-GLC activity was the most sensitive indic ator of treatment effect and may be a suitable alternative to Mb-C or SOM-C as a measure of change in soil health. (C) 1999 Elsevier Science Ltd. All rights reserved.