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

ABSTRACT

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.

Abbreviations: CO: control; DM: dry matter; MF: mineral fertilizer; OM: organic matter; PS: pig slurry; SC: sewage sludge compost.

KEYWORDS:

• Dryland agricultural system
• pig slurry
• sludge compost
• soil bioturbation
• soil micromorphology

Acknowledgements

The authors thank Josep M. Llop and Stefania C. Maris for field assistance and Dr. Antonio Pérez Onteniente for his valuable help on earthworm classification. Alcira S. Valdez thanks Fundación Carolina for her PhD grant.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Spanish Ministry of Economy and Competitiveness and the Spanish National Institute for Agricultural Research and Experimentation (MINECO-INIA) through the projects RTA2013-57-C5-5 and RTA2017-88-C3-3. The field maintenance of the experimental site by the Ministry of Agriculture, Livestock, Fisheries and Food (Generalitat de Catalunya), in the framework of the improvement of fertilization practices in Catalonia (Spain), is fully acknowledged.