Applied Engineering in Agriculture Vol. 24(3): 391‐397 2008 American Society of Agricultural and Biological Engineers ISSN 0883-8542 391 CONSTRUCTION OF AN ELECTRICAL DEVICE FOR SAMPLING EARTHWORM POPULATIONS IN THE FIELD S. L. Weyers, H. H. Schomberg, P. F. Hendrix, K. A. Spokas, D. M. Endale ABSTRACT. Methods for the estimation of earthworm population densities range from laborious handsorting, through chemical applications, to electrical extraction. Of these methods, only the electrical extraction allows for sampling of earthworms without detrimental soil disturbance or contamination. However, a device to extract earthworms under controlled electronic conditions is not readily available to researchers. An improved design on the long‐established electrical “octet” extraction device is presented. This improved design allows for hand‐built construction of an apparatus that can be connected to external drive controls, including data loggers and PC‐controlled drivers. This design also allows for modification of sampling settings to suit specific environmental conditions, with control of voltage, and operation with a static or dynamic electrical field being generated. Operational ability to extract earthworms was validated in field trials in both a forested area and an agricultural field. Earthworm sampling efficiencies calculated in comparison to hand‐sorting averaged around 90% for the electrical device; however, because of limited field use in this instance, these efficiencies support the general functioning of the apparatus rather than an absolute assurance of quality. In using this hand‐built device we established that this design is capable of extracting both native and exotic earthworms of various age and size class under various soil conditions, that soil disturbance and contamination can be avoided, and that the device can easily be transported into remote locations. Keywords. Octet, Earthworms, Electrical extraction, Sampling, Disturbance, Conservation management, No‐till. here are three commonly used methods for extracting earthworms from soil: irritant solutions, e.g. formaldehyde and `hot' mustard (Raw, 1959; Gunn, 1992; Lawrence and Bowers, 2002; Zaborski, 2003); handsorting (Schmidt, 2001a); and electrical stimulation (Satchell, 1955; Rushton and Luff, 1984; Thielemann, 1986). Use of solutes and handsorting may not always be appropriate because of certain constraints on time and effort, environmental pollution concerns, or a desire to avoid soil disturbance. As reviewed by Lee (1985) and Edwards and Bohlen (1996) no single sampling method is 100% efficient as biases by species, soil type, temperature Submitted for review in August 2007 as manuscript number IET 7126; approved for publication by the Information & Electrical Technologies Division of ASABE in April 2008. Mention of trade names or commercial products in this report is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. The USDA is an equal opportunity provider and employer. The authors are Sharon Lachnicht Weyers, Research Soil Scientist, USDA Agricultural Research Service, North Central Soil Conservation Research Laboratory, Morris, Minnesota; Harry H. Schomberg, Research Ecologist, USDA Agricultural Research Service, J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville, Georgia; Paul F. Hendrix, Professor, Institute of Ecology and Department of Crop and Soil Sciences, University of Georgia, Athens, Georgia; Kurt A. Spokas, Research Soil Scientist, USDA Agricultural Research Service, Soil and Water Management Research Unit, St. Paul, Minnesota; and Dinku M. Endale, ASABE Member Engineer, Agricultural Engineer, USDA Agricultural Research Service, J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville, Georgia. Corresponding author: Sharon Lachnicht Weyers, USDA Agricultural Research Service, North Central Soil Conservation Research Laboratory, 803 Iowa Ave., Morris, MN 56267; phone: 320‐589‐3411 ext. 146; fax: 320‐589‐3787; e‐mail: Sharon.Weyers@ars.usda.gov. and moisture conditions exist. Sampling with solutes give limited results because the solution has to pass through soil pores and reach the organisms in order to initiate the irritation that causes them to surface. Use of solutes has a tendency to bias the sampling by numbers or total biomass extracted (Zaborski, 2003), or by species through selection of species constructing soil channels open to the surface, such as anecic species, allowing the infiltration of the solution (Edwards and Bohlen, 1996). Handsorting has been cited to be the best technique for sampling most species (Edwards and Bohlen, 1996) and is often the preferred technique to use in diversity studies. However, handsorting is the most labor intensive and due to the aggregated nature of most earthworm populations, can be less productive when trying to establish densities. A recent improvement in the methodology has reduced the sampling time (Schmidt, 2001a), nevertheless limitations still exist. Handsorting or chemical applications, such as formaldehyde, can not be applied in situations where soil disturbance or ground water contamination is a concern, such as under no‐till treatments in an agricultural system or a protected watershed. Electrical stimulation, or “electroshocking,” is a non‐distructive method for sampling earthworms. Staddon et al. (2003) recognized the value of electroshocking in situations that can prohibit use of other sampling methodologies. In 1986, Uli Thielemann published a report (Thielemann, 1986) and filed a German patent (DE3612464, available at www.espacenet.com) for an electrical apparatus to sample earthworm populations, which was an improved methodology for the circular electrode configuration originally presented by Rushton and Luff (1984). Electrical extraction has been as basic as connecting two pitch forks to a 12‐V battery to as advanced as a commercially‐available “Octet” device constructed by a German manufacturer. The T