Earthworm community and soil microstructure changes with long-term organic fertilization

The aim of this study was to evaluate the effects of sludge compost (SC) in two rates and pig slurry (PS) on soil quality, in the framework of a field experiment (19-year-old) in a Mediterranean rainfed system. The treatments were compared with mineral fertilization (MF) plus a control treatment (no N fertilization). Soil microstructure and types of voids, earthworm community and its bioturbation were studied using micromorphological methods. Two earthworm species, Koinodrilus roseus and Nicodrilus trapezoides were identified; the latter was not present in the SC treatments. Earthworm abundance and biomass were not affected by fertilization. Pig slurry increased bioturbation associated with earthworm activity, improved soil microstructure (crumb type) and increased the biopore presence (compound packing voids). The control and MF plots showed a platy to massive microstructure with an absence of faunal chambers. In SC plots, non-mixed soil-organic materials were observed and soil vughs were not visible. Composition differences between SC and PS and the total amount of OM applied may have had an impact on the activity and species of earthworms; such changes can be an early indicator of further potential impacts on soil quality, however further contaminant studies are needed to validate this initial assessment.