Another collection method is application of an electrical current to the soil. This method is attractive as little or no damage is done to the area sampled and only fallen leaves and overgrown vegetation need be removed prior to sampling to assist earthworm detection. To date only limited work has been undertaken with this method, specifically in agricultural soils [21] possibly because equipment is expensive as an extraction unit to sample 0.2 at a time will cost (at 2009 prices) in excess of $3000.
Having determined which earthworms are present in a given habitat, if desired, it is then possible to experimentally manipulate the earthworms themselves or resources, such as food, in the habitat. Several studies have used field enclosures to investigate the effects of earthworms on soil properties and plants [22, 23]. Such enclosures can be formed with PVC walls, buried in slit trenches to a depth of up to 45 cm and a height of 15 cm above the soil surface. These have been shown to act as effective barriers to lateral earthworm movements. Results have suggested that both earthworm removal and addition of field-collected earthworms within enclosures can be an effective and useful approach for assessing the influence of earthworms on ecosystem processes