Effects of farming practices on the structure of earthworm communities in kiwifruit orchards

In Galicia (north-west Spain), growing kiwifruit is an important economic activity, since more than 15,000 t of fruit are produced every year. Conventional farming practices have been traditionally employed to maximize yield; however, they involve the use of large amounts of inorganic fertilizers, pesticides, herbicides and plant-growth regulators, which have negative effects on the soil environment. Earthworms play a key role in soil organic matter transformations, soil fertility and nutrient cycling. Their low mobility and strong sensitivity to environmental perturbations make them a suitable group for investigating the effects of management practices on agro-ecosystem function. In this study, we determined the abundance, biomass, diversity and structure of earthworm communities in two orchards where kiwifruit is grown either conventionally (CONV) or organically (ORG). Earthworms were hand-sorted in the field (quadrats: 50×50×20 cm) and identified to species level. Results showed that earthworm abundance and biomass as well as biodiversity exhibited important changes in response to farming practices. Accordingly, the earthworm populations in the CONV soils were less numerous and more species poor, whereas ORG practice promoted earthworm abundance and biomass and the presence of those species with greater bioturbation effects (burrowing and soil mixing), such as Lumbricus friendi. Fertility losses and impoverished soil structure are anticipated in the CONV treatments as a result of these profound alterations in earthworm community structure.