Occupancy and geometrical properties of Lumbricus terrestris L-burrows affecting infiltration

Substitution of conservation tillage for conventional tillage practices can greatly decrease runoff and losses of soil, nutrients, and pesticides in o verland flow. Earthworm populations also frequently increase with a reducti on in tillage: intensity, which suggests that their effects on soil structu re and porosity may contribute to the decrease in runoff. In particular, th e size and number of L. terrestris burrows found in some agricultural field s suggest that they may have a major impact on hydrology. In fact, a number of studies have documented rapid transmission of water and surface-applied agricultural chemicals in L. terrestris burrows. Most studies, however, ha ve been conducted on unoccupied burrows and the techniques used disrupt nat ural low, which raises concern that their contribution to water and chemica l movement may be overestimated. In this study, we used a Mariotte device t o measure infiltration into active L. terrestris burrows in Coshocton, Ohio , USA and Bilsborrow, Lancashire, UK. Earthworms were expelled from some of the burrows prior to conducting the infiltration experiments. Afterwards, plastic replicas of the burrows were made so depth, length, volume, and dia meter could be determined. Average infiltration rates were highly variable (19-1005 mt min(-1) per burrow), but greatly exceeded what would be expecte d under natural rainfall. The presence of a live L. terrestris had little, if any, effect on infiltration. No significant correlations (P less than or equal to 0.05) between infiltration rate and burrow geometrical properties or earthworm weight were detected. These results suggest that high infiltr ation rates measured in burrows via other methods are realistic, but that m odels based on burrow geometrical properties are unlikely to accurately pre dict infiltration for soils similar to those investigated.