Earthworm responses to long term agricultural management practices: Spatial relationships with soil properties

We used a long-term arable cultivation experiment to investigate spatial relationships between earthworm populations and soil physico-chemical properties using Spatial Analysis by Distance Indices methods (SADIE). Red-blue analyses showed that soil C and N were both spatially heterogeneous (patchy) as were total and juvenile earthworm counts. In contrast, theta probe and shear vane measurements, adult earthworm counts and earthworm biomass did not exhibit patchiness. All potential relationships between data classes were analysed using SADIE spatial association tests. Soil chemical properties were generally dissociated from earthworms whereas physical properties were positively associated. These results were largely attributable to juvenile counts, suggesting that this age group may be a more sensitive indicator of spatial relationships between earthworms and soil properties than are adults. We also found that earthworm counts had stronger spatial associations with soil chemical properties than did biomass; the obverse was seen with the measures of soil physical properties. This may provide evidence that earthworm dynamic responses vary between different aspects of the soil environment.