Responses of earthworm species to long-term applications of slurry

Livestock farming produces slurry, which is normally recycled by land-spreading; but this raises questions about the long-term impact of slurry on soil fauna and soil processes. To examine the long-term effects of slurry on earthworms, cattle and pig excreta slurries and inorganic fertiliser were applied to a ryegrass silage sward for 33 years in a replicated experiment, and earthworms sampled for four consecutive years at three seasonal intervals (March, May and October). Animal slurries were applied at three rates (50, 100 and 200 m3 ha−1 yr−1) and inorganic fertiliser as 200 kg N, 32 kg P and 160 kg K ha−1 yr−1. Epigeic earthworms, Lumbricus rubellus, Lumbricus juveniles, and the endogeic Allolobophora chlorotica responded strongly and positively to cattle slurry inputs. In the case of L. rubellus, biomass was five times greater in the highest input cattle slurry plots than in the untreated controls. In contrast to Al. chlorotica adults, other endogeic earthworms and juvenile Allolobophora were more associated with the inorganic fertiliser treatment. Aporrectodea juveniles, in particular, had significantly greater biomass in the inorganic fertiliser treatment. However, no such response was demonstrated by adult Aporrectodea caliginosa, the commonest species found, suggesting niche separation between adults and juveniles. Pig slurry applications produced relatively little change in earthworm biomass compared to controls, despite residual copper concentrations; suggesting that organic matter input was counterbalancing the sublethal effects of copper.