Efficiency of two widespread non-destructive extraction methods under dry soil conditions for different ecological earthworm groups

Reliable non-destructive extraction methods are required for the assessment of the size and composition of earthworm communities where physical disturbances are not acceptable. The aim of the present study was to investigate the efficiency of the electrical octet method and the mustard extraction method for sampling of different ecological groups of earthworms (anecics, endogeics and epigeics) under dry soil conditions. We hypothesized that: (1) the extraction efficiency of the mustard method and the octet method will vary with ecological earthworm group; and (2) beforehand water addition to dry soil will increase the extraction efficiency of the octet method but not that of the mustard method. Endogeic earthworm species were extracted in low numbers irrespective of the extraction method indicating their inactivity during dry periods. The mustard method was more efficient for the extraction of anecic earthworms even under dry soil conditions, whereas the octet method was inappropriate in reflecting the actual earthworm community structure. Surprisingly, the efficiency of both methods was not improved by beforehand water addition. These findings are essential to be considered when working under dry soil conditions e.g. in the context of environmental monitoring.