Effects of winter wheat and endogeic earthworms on soil physical and hydraulic properties

Earthworms directly and indirectly affect soil physico-hydraulic properties. We studied interactions between winter wheat and the common European earthworm Allolobophora chlorotica, testing for impacts upon soil physico-hydraulic properties. Column experiments with three different soil textures and field-relevant earthworm densities were conducted. Saturated hydraulic conductivity (Ks)increased over time in earthworm treatments, with the increase occurring most rapidly in the plant plus earthworm treatment. After 16 weeks Ks had increased in the treatment comprising both plants and earthworms by factors of 12, 34 and 39 in the loam, silt-loam and sandy-loam soils respectively relative to controls. The presence of earthworms resulted in an 88.5% increase in the contribution of pores >3mm diameter to water flow. In the majority of treatments, soil water-holding capacity and percentage water-stable aggregates of the 5 cm topsoil in both the plant and the earthworm treatments increased significantly compared to controls with the plant plus earthworm treatment showing the greatest increase. Plant growth was greater in the presence than absence of earthworms. Our study shows synergistic and additive effects on soil physical properties in the presence of both earthworms and plants compared to when only earthworms or plants are present. It shows that it is not just vertical-burrowing anecic earthworms that can have a significant effect on soil hydraulic properties but that field-relevant densities of endogeic earthworms such as A.chlorotica can also contribute to soil water flow regulation.