Earthworm communities under boreal grass and legume bioenergy crops in pure stands and mixtures

Crop mixtures can impact soil properties through their effect on earthworm communities. Earthworm abundance and species number in a bioenergy crop mixture can therefore provide valuable information about its stability and sustainability. In the context of developing sustainable bioenergy farming methods, this experiment aimed to determine the effects of pure stands of reed canary grass (Phalaris arundinacea) (RCG), the legume forage galega (Galega orientalis) and their mixture on earthworm populations, with bare fallow controls. Twice in each growing season in 2011 and 2012, soil blocks 25 cm × 25 cm × 25 cm were extracted from each plot, earthworms were manually separated from the soil and mustard oil was used to extract those from soil underlying the block. Four earthworm species were collected: Aporrectodea caliginosa, A. rosea, Lumbricus rubellus, and L. terrestris. Earthworm abundance ranged from no individuals in bare fallow in summer 2011 to 364 individuals m−2 in galega in spring 2012. Biomass of the worms ranged from 0 to 188 g m−2 and had the same trend as abundance. Of the cropped treatments, pure galega supported the greatest earthworm numbers and biomass, although being significant only in summer. Treatment effects were weak in most sampling periods but differed between seasons and this should be investigated in future studies. Our results demonstrate that specific plant species can have positive effects on the earthworm community under certain environmental conditions, which should be considered in bioenergy cropping.