Higher earthworm abundance in conventionally managed agricultural fields than ecologically managed fields

Agricultural activities affect soil fauna and may thus impede biological soil functions. In the field of soil biology, uncertainty remains about which specific activity adversely affects biological soil functions.  This study aimed: (i) to quantify the effect of ploughing activity on earthworm abundance in an experimental farm of the University of Göttingen, Reinshof, and (ii) to compare the earthworm abundance between an ecologically managed field vs. a conventionally managed field. Earthworm sampling, using the mustard method, was done between the 22^nd of April and 3^rd of May 2021. Three differently managed fields were sampled: ecologically managed with ploughing, conventionally managed with ploughing and conventionally managed without ploughing. Earthworms were collected in 30 locations per field. Soil organic matter contents, penetrometer resistance, and soil moisture were also measured. The conventionally managed ploughed field exhibited a mean earthworm abundance of 98.9 individual per square metre, which was more earthworms than the ecologically managed field that showed a mean earthworm abundance of only 7.86 individuals per square metre. The highest mean earthworm abundance of 160.8 individual per square metre was observed in the conventionally managed non-ploughed field. Species richness of earthworms was also higher in the conventionally managed fields compared to the ecologically managed field. The conventionally managed non-ploughed field had the highest soil organic matter content, moisture status, nitrogen content, and penetrometer resistance, in contrast to the ecological ploughed field, which showed the lowest values for all these parameters. The findings of this study are consistent with previous studies that the non-ploughed fields provide a suitable environment for earthworm communities, as perturbation of earthworms is avoided and soil organic matter levels are maintained, which is a key requirement for earthworms’ survival, therefore increasing their abundance. The very low earthworm abundance of the ecologically managed field was unexpected, but might be explained by the frequent ploughing, used for weed control instead of herbicides. We concluded that ploughing is an important activity that impacts the abundance of earthworms.

Keywords: soil, earthworms, conventional farming, ecological farming, ploughing