Impact of Coffee Management Practices on the Soil Ecosystem: Earthworm Community Function

Coffee (Coffea arabica L.) is the most economically important crop in the central mountainous region of Puerto Rico, where it is grown under shade or in full sunlight. The conditions under which coffee is grown may affect the long-term sustainability of this land use through effects on soil physical, chemical and biological properties. As ecosystem engineers, earthworms are known to have a profound effect on abiotic and biotic properties and processes in terrestrial ecosystems. We examined differences in earthworm communities as a function of ecosystem type (sun and shade coffee, forest) and soil order (Oxisols, Ultisols, Inceptisols) as part of a study of the effects of coffee production practices on the structure and function of coffee agroecosystems led by scientists in the Dept. of Agronomy and Soils of the University of Puerto Rico - Mayagüez. Ecosystem type significantly affected earthworm population density (Sun, 281/m2 > Shade, 125/m2 > Forest, 37/m2) and earthworm biomass (Sun, 71 g f.w./m2 > Shade, 34 g f.w./m2 > Forest, 12 g f.w./m2). In contrast, the specific biomass of earthworms was significantly affected only by soil order. In general, earthworm population density and biomass appeared to be a function of soil moisture, leaf litter biomass, and the mineral content of leaf litter. Analyses of 15N and 13C enrichment of earthworm tissues suggest that management practices affect the trophic level they occupy within an ecosystem. Examination of isotopic enrichment of soil and leaf litter is underway to help elucidate the role of earthworms in carbon and nitrogen cycling in these ecosystems.