Intensification of pastoral systems influences earthworm populations

Agriculture is becoming increasingly intensified through irrigation, increased nitrogen inputs and a change in grazing animal from sheep to cattle. These changes have the potential to affect earthworms, an important component of the soil biology. Over 4 years, this study compared earthworm populations under sheep or cattle grazing, mowing or no harvesting of pasture and with or without combinations of nitrogen fertiliser and irrigation. Irrigation had the greatest influence on both pasture production and earthworm abundance, also changing the earthworm species composition, with epigeic Lumbricus rubellus becoming more abundant. Nitrogen fertiliser increased pasture production under irrigation in both the sheep grazed and mown treatments, but not under cattle grazed treatments. The opposing influences of increasing pasture production and physical pressures mean that moving from dryland sheep to irrigated cattle grazing may have a minimal overall effect on earthworm numbers, while irrigated sheep grazing provides an ideal earthworm habitat.