Agricultural intensification, soil biodiversity and agroecosystem function in the tropics: The role of earthworms

Earthworm biodiversity is modified when forests and natural savannas are replaced by agroecosystems; these changes can be studied from the taxonomic and functional point of view. In the first case the number and origin (native or exotic) of species is important, as well as the geographic scale of the study (local or regional), The functional approach considers the ecological groups (epigeic, endogeic, anecic), which have different effects on soil function, Studies in Mexico, Peru and India reveal that agroecosystem earthworm communities (as compared with those in the undisturbed ecosystem) have lower species richness, lower number of native species, lower number of ecological groups and a predominance of endogeics, Therefore the role of endogeic species in intensifying agroecosystems is likely to be more important for soil function, especially because they act as ecosystem engineers and through their mutualistic interactions with microflora, selective ingestion of soil particles, high rates of ingestion and production of casts, galleries, burrows and chambers can affect nutrient and organic matter dynamics and other pedological processes. Epigeic and anecic species do not appear to be as widespread in agricultural systems and their dependence on a litter layer for survival implies that litter management practices must be implemented for their role in soil function to be of importance. The role of earthworms in enhancing primary production depends on the synlocalization (in the same place) and the synchronization (at the same time) of their activities with the period and the sphere of active root growth and nutrient demands. Several field studies have found significant yield increases with earthworm inoculation, though more research is needed. Incorporation of information on earthworm life histories, field population variations, ecological strategies and short and long term effects on soil properties, in addition to plant and environmental factors (climate, soil, cropping period and management of the agroecosystem), are essential to properly assess the potential role of a particular earthworm species on plant production.