Earthworm populations in twelve cover crop and weed management combinations

- Cover crop type and weed management had significant effects on earthworms.
- A pea cover crop supported the largest mean earthworm populations.
- Mustard yielded the largest mean cover crop biomass.
- Cover crop biomass was not correlated with earthworm population size.

Earthworm communities were assessed in twelve agronomic treatment combinations at the cessation of a three year winter cover crop-spring barley main crop in Ireland. Agronomic treatments had statistically significant effects on earthworm abundance and biomass; the above-ground biomass of cover crops species and other weed species was also significantly affected. A pea cover crop supported the largest earthworm communities, 221 ± 55 (±SD) individuals m−2 and live biomass 67.4 ± 12.0 g m−2, while having the smallest overall mean yield for cover crop biomass, 56.8 ± 56.7 g dry matter m−2. By contrast, a mustard cover crop had the largest overall mean yield for cover crop biomass, 195 ± 82.7 g m−2, but earthworm populations similar to those in other cover crops and under natural regeneration. The lowest overall mean earthworm biomass (23.1 ± 1.8 g m−2) of all agronomic combinations was recorded in a bare fallow treatment which had no overwinter vegetation. Earthworm species numbers between treatments were similar, with endogeic species such as Allolobophora chlorotica, Aporrectodea caliginosa and A. rosea being dominant. The pea cover crop probably supported the largest earthworm populations due to a high quality food supply. Conversely, brassicaceous cover crops such as mustard, while producing large above-ground biomass, did not support larger earthworm populations, but a biofumigation effect was not evident either. In conclusion, various winter cover crops as well as natural regeneration supported similar earthworm populations after a three year cover crop-spring barley main crop cycle, with some evidence for larger and more species-rich populations under some cover crops such as pea and oat, and somewhat smaller populations where no overwinter vegetation was present.