Quantification of field earthworm burrowing rates using repeated X-ray scanning of open soil cores

• Field earthworm burrowing was monitored by repeatedly scanning open soil cores. • Volumes of created, maintained and collapsed earthworm burrows were analysed. • Burrowing rates were obtained from temporal dynamics of burrow volumes. • Burrows created by anecic and endogeic earthworms was separated by burrow diameter. Earthworms contribute to soil functioning by burrowing through soil, but quantitative knowledge of their burrowing activities and how environmental factors influence it under field conditions is still limited. The objectives of this study were to test a method for quantification of the temporal dynamics of in-situ earthworm burrowing rates, and to investigate links between variations in burrowing rates and soil moisture and temperature. Specially designed perforated cylinders repacked with soil were installed in an arable field with a known earthworm community in Uppsala, Sweden, and repeatedly removed, X-ray scanned, and re-installed, during May-October 2023. Earthworm burrow volumes and characteristics of burrow networks were derived from the X-ray images. Burrows were classified into burrows likely originating from endogeic earthworms (burrow diameter ≤ 4 mm) and anecic earthworms (> 4 mm). We tested two methodological approaches, using either new repacked soil after each scan or re-installing the same soil cylinder. We also employed two soil moisture treatments (with and without rainout shelters). In-situ soil moisture and temperature were monitored using sensors. The results showed that burrowing rates in newly repacked soils were higher than in the soil columns with the same soil. Depending on treatment and the time of the year, mean burrowing rates varied between 0.05 and 0.64 cm 3 day −1 . On average, we estimated that topsoil turnover rate by earthworm burrowing is about 21–42 years in this field where the earthworm abundance was 81 individuals per m 2 . The data from the “same soil” treatment indicates that a steady state in earthworm burrow volume was achieved after five months, indicated by the balance between burrow creation and disappearance. In our study, soil moisture appeared to be a more important driver for earthworm burrowing than soil temperature. We show that about 40% of the earthworm burrow volume was classified as anecic earthworm burrows in the topsoil. We conclude that the proposed method using perforated cylinders with repeated scans is suitable for seasonal monitoring and to quantify earthworm burrowing rates under field conditions.