The effect of grassland management intensity on earthworms and leatherjackets

Grasslands play an important role in the provisioning of ecosystem services like biodiversity. Species-rich grasslands are important for aboveground biodiversity; however, it is unclear whether this also results in increased belowground biodiversity. The objective of our study was to assess earthworm (Lumbricidae) and leatherjacket (Tipulidae) populations in permanent grasslands with a gradient of grassland management intensity. In an on-farm research we compared intensively managed permanent grasslands (INT, n=12) with three types of extensively managed grasslands (EXT, n=3×12=36) varying in the degree of herb-richness, on sea clay soils in the Province of Friesland, The Netherlands. The intensively managed permanent grasslands had high fertilizer inputs (361 kg N ha–1 year–1) and a high mowing frequency (4–5 cuts year–1). The extensively managed grasslands received only solid farm-yard manure and the mowing date was postponed until the 15th of June (1–2 cuts year–1). In March 2022, soil samples were taken in each field for soil chemical analysis, and to detect earthworms and leatherjackets. The number of adult and anecic earthworm numbers as well as the biomass of earthworms were significantly higher in the case of INT, and were positively correlated with N-fertilization and pH. There were no significant differences in the number of earthworms between the three types of EXT sward. The results of the abundance of leatherjackets showed a similar (non-significant) tendency as for earthworms, however the variation between fields was large. Our results show that there is a positive relationship between management intensity and earthworm abundance and biomass.