Soil compaction controls the abundance, biomass and distribution of earthworms in a single dairy farm in south-eastern Australia

To harness the benefits of earthworms in agro-ecosystems, it requires better knowledge of their ecology particularly their relationship with soil properties. Earthworm species distribution, abundance and biomass were surveyed in a single dairy farm (238 ha) in Camden, New South Wales, Australia, and the results were related to a range of soil physical and chemical properties, namely pH, texture, bulk density, soil organic carbon and nutrient status. A 33.7-fold variation in total earthworm abundance (40–1347 m−2) was found in the different fields of the single dairy farm, a magnitude of difference similar to those reported in regional surveys covering hundreds of square kilometres. Diversity was, however, low with mean number of species per field = 2.1. Our results highlight soil compaction and pH as soil factors affecting earthworm abundance and biomass, with compaction being a more important factor. The earthworm population was dominated by two introduced species, Aporrectodea trapezoides and Aporrectodea caliginosa which are also commonly found in pasture and cropping soils elsewhere in southern Australia. There was evidence suggesting that A. trapezoides has greater capacity to survive under harsher environments (drier and more compacted soil) than A. caliginosa. Native species were rare, averaged only 3.6% of the total earthworm population and were only found in the Alfisols.