Earthworms significantly alter the physical and chemical properties of soil, as their bioturbation and the metabolism of organic residues influence soil structure, aggregate stability, porosity, water infiltration, and nutrient dynamics. Changes in land use and soil management practices can adversely affect earthworm populations and thereby impair soil ecosystem functioning. In long-term field experiments conducted in Ljubljana and Moškanjci since 1999, we studied the impact of different tillage systems on earthworm (Lumbricidae) abundance, biomass, and species composition. Conventional tillage (CT), involving ploughing to a depth of 25 cm, was compared with minimum tillage (MT), involving soil loosening to a depth of 10 cm without soil inversion. Sampling was performed by hand-sorting soil from a 30 × 30 cm excavation to a depth of 20 cm, followed by application of a 0.5% formalin solution. Tillage method influenced both earthworm abundance and biomass. In most sampling events at both locations, higher numbers and biomass of earthworms were found under MT compared to CT, with the exception of the April sampling in Moškanjci. In the lighter-textured soils of Moškanjci, the average total number of earthworms under MT was 117 individuals/m², compared to 95 individuals/m² under CT. The average total biomass was 87.5 g/m² under MT and 58.9 g/m² under CT. In the heavier-textured soils of Ljubljana, the differences were even more pronounced: the average number of individuals was 179/m² under MT and 85/m² under CT, while the average biomass amounted to 80.2 g/m² under MT and 32.3 g/m² under CT. In Moškanjci, tillage did not have a statistically significant effect on earthworm abundance, biomass, or species composition, which we attribute to the timing of sampling and specific environmental conditions (temperature and soil moisture). Species diversity was higher under MT than under CT at both locations. Sampling date had a significant effect on earthworm populations at both sites. During periods of favourable conditions, the number of juveniles was three to four times higher than that of adults, confirming that seasonal temperature and soil moisture are key factors affecting earthworm abundance. The results indicate that the biomass of juvenile individuals is more strongly influenced by tillage system than by sampling date. Endogeic species of earthworms dominated at both locations, particularly Aporrectodea caliginosa, Aporrectodea rosea and Proctodrilus sp. In Moškanjci, the anecic species Lumbricus terrestris was also found and was dominant under MT. For a more precise assessment of the effects of different tillage systems on earthworm populations and soil fertility, more frequent seasonal monitoring and long-term observations would be necessary.
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