Effects of tropical endogeic earthworms on soil erosion

Soil biota play a crucial role in influencing soil structure and related soil physical properties. In particular, an abundant literature shows that earthworms, through their burrowing and feeding activities, influence particle size distribution, organic matter content, organic matter location, soil aggregation, aggregate stability and tensile strength, soil roughness, and water infiltration. All those properties greatly influence soil erodibility and soil erosion. Nevertheless, there are few quantitative studies of the influence of earthworms on soil erosion. In some cases, earthworms are said to increase soil losses while other studies emphasize their control on structural stability inducing a reduction in soil erosion. This paper analyses the effects of endogeic earthworms on soil erosion, using recently published data collected in the humid tropics. Endogeics comprise two separate functional groups regarding their effects on soil physical properties, i.e. "compacting" and "decompacting" species whose effects on soil erosion may differ substantially. The effects of these earthworms on soil erodibility and erosion in the tropics ultimately depend on soil types and on the organic matter content in soils. In kaolinitic soils, irrespective of clay content, endogeics greatly influence aggregation, aggregate stability, total porosity and pore size distribution; whereas in smectitic soils (such as vertisols), earthworms have a smaller effect on soil erodibility than soil organic matter and cations. Some options for managing earthworms and organic matter in order to limit soil erosion are also discussed in this paper. (C) 2004 Elsevier B.V. All rights reserved.