Influence of soil properties on the population and activity of geophagous earthworms after five years of bare fallow

Many soil properties influence earthworm populations and activity. To determine which properties are of significance, a broad collection of soils was investigated. Samples from these different soils were kept bare at one site in large plots (3 Mg soil per plot) to liminate crop and weather interference and to isolate the dominating mechanisms of earthworm effects. Earthworm density, biomass, and tunnelling activity were assessed after 5 years of bare fallow. All earthworm parameters varied strongly. Earthworms increased soil respiration by their tunnelling activity, and in turn increased microbial activity and propagated the loss of organic C. Earthworm abundance ranged from 12 to 274 m^-2 and was about 10 times greater than on cropped soils. The range in abundance was mainly caused by variations in the numbers of juveniles. The average soil moisture content was the only soil property among the many properties investigated that was consistently correlated with earthworm abundance and biomass. Even after 5 years of hare fallow with almost no addition of fresh plant biomass and with little water loss by plant transpiration, the earthworm population was controlled by water stress and not by food stress. We therefore conclude that high water consumption by productive crops may degrade the habitat for geophagous earthworms.