Intensification of pastoral systems influence earthworm populations

Agriculture occurring on much of New Zealand’s pasture land is becoming increasingly intensified. This often involves the introduction of irrigation, increased nitrogen inputs, and a change in grazing species from sheep to cattle. These changes have the potential to affect soil quality, and earthworms are a critical component of the soil biota that can be affected by these changes. Over four 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, to determine the impact of these three factors on earthworm populations. Irrigation had the greatest influence on both pasture production and earthworm abundance. N fertiliser tended to increase pasture production under irrigation but this did not increase earthworm abundance. Defoliation regime also influenced pasture production and earthworm abundance, with lower values recorded under irrigated cattle grazed pastures compared to sheep grazed pastures. These opposing influences 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 environment.