INFLUENCE OF SOIL PROPERTIES ON THE POPULATION AND ACTIVITY OF GEOPHAGOUS EARTHWORMS AFTER 5 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 b are at one site in large plots (3 Mg soil per plot) to liminate crop a nd weather interference and to isolate the dominating mechanisms of ea rthworm effects. Earthworm density, biomass, and tunnelling activity w ere assessed after 5 years of bare fallow. All earthworm parameters va ried strongly. Earthworms increased soil respiration by their tunnelli ng activity, and in turn increased microbial activity and propagated t he 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 abu ndance was mainly caused by variations in the numbers of juveniles. Th e average soil moisture content was the only soil property among the m any properties investigated that was consistently correlated with eart hworm abundance and biomass. Even after 5 years of bare fallow with al most 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 c onsumption by productive crops may degrade the habitat for geophagous earthworms.