Submitted to: Pedobiologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/1999
Publication Date: N/A
Citation: Interpretive Summary: When conservation tillage practices are used by farmers increased earthworm populations are frequently noted. These earthworms can benefit the soil and crop in a number of ways such as improving soil structure and the cycling of nutrients. One species of earthworm, the common nightcrawler, also creates and lives in large diameter, permanent, burrows that penetrate ethree feet or more into the soil. These burrows may rapidly transmit rainwater from the soil surface to the subsoil, thereby reducing the losses of soil and agrochemicals in runoff. Assessing how effective these burrows are in conducting water in the field is difficult because most methods have the potential to exaggerate the amount of flow and ignore the possibility that a live earthworm in the burrow could act as an effective plug. In experiments conducted in Ohio and in England we found that nightcrawler burrows rapidly transmitted water regardless of whether a worm was in the burrow. There was little relationship between burrow size and shape and th amount of water that a particular burrow would accept. Thus, it is more efficient and just as effective to measure earthworm populations to estimate infiltration rate in burrows than to painstakingly measure the size and shape of burrows. Farmers can look for nightcrawlers, or signs as of their activity, as a way of determining how effective their management practices are in promoting healthy worm populations and reducing runoff.
Technical Abstract: Substitution of conservation tillage for conventional tillage practices can greatly decrease runoff and losses of soil, nutrients, and pesticides in overland flow. Earthworm populations also frequently increase with a reduction in tillage intensity, which suggests that their effects on soil structure and porosity may contribute to the decrease in runoff. In particular, the size and number of L. terrestris burrows found in some agricultural fields suggest that they may have a considerable effect on hydrology. In fact, a number studies have documented rapid transmission of water and surface-applied agricultural chemicals in L. terrestris burrows. Most of these studies, however, have been conducted on unoccupied burrows and the sampling techniques disrupt the natural flow. In this study, we used a Mariotte device to measure infiltration into active L. terrestris burrows in Coshocton, Ohio, USA and Bilsborrow, Lancashire, UK. Earthworms swere expelled from some of the burrows prior to conducting the infiltratio experiments. Afterwards, plastic casts of the burrows were made so that burrow depth, length, volume, and diameter could be determined. Average infiltration rates into burrows were highly variable (range 19-1005 mL min**-1), but greatly exceeded what would be expected under natural rainfall conditions. The presence of a live L. terrestris in the burrows had little, if any, affect on infiltration. No significant relationships between infiltration rate and burrow geometrical properties or earthworm size were detected. These results suggest that high infiltration rates measured in burrows in the field are realistic, but that models of infiltration based on burrow geometrical properties are unlikely to accurately predict infiltration for soils similar to those investigated.