Potential protocol for earthworm monitoring under adverse soil conditions or in small plots

Abstract

Many methods for earthworm sampling have been developed with various sample sizes and soil volumes for physical, chemical, and electrical extraction. Each method has its benefits and shortcomings, as for example, in hard and dry soils aestivating earthworms are often unrecorded with chemical or electrical sampling. However, this study tested an alternative physical sampling method (Cylinder) for dry soils or small plots with a sample area of 78.54 cm2 which was compared with a more universally-used Spade-method (400 cm2). The Cylinder method used six soil augers per plot of 10 cm diameter and 20 cm length, driven into the soil by a heavy-duty electrical demolition hammer. Each Cylinder sample was hand-searched for earthworms for 15 min. The Spade-method comprised four soil monoliths per plot of 20 × 20 × 20 cm, with each hand-sorted for 45 min. Earthworm parameters such as abundance and biomass of total, adult, juvenile and ecological groups were compared for each technique. The study was part of an on-farm research project in Austria and eight sites were selected due to different soil types, climate and management systems (conventional vs. conservation). Conventional field management included soil tillage (depth 20–25 cm) without cover cropping whereas conservation practices comprised of no-till and the use of cover crops. The results for Cylinder were similar to Spade for Shannon index, abundance and biomass of most earthworm parameters, except for adult biomass (Spade was 7 % higher than Cylinder). In addition, power analysis showed that both methods are comparable and can detect a difference of 99 earthworms m−2 with 6 subsamples for Cylinder and 4 subsamples for Spade with β = 80 %. Nevertheless, due to the smaller sample volume, soil from Cylinder can be transported more easily than that from Spade and examined in the laboratory under more comfortable working conditions. In addition, Cylinder is less destructive to plots and can therefore be used for specific research purposes or in plots <2 × 2 m. The results of Shannon index, abundance and biomass of total, adult, anecic and endogeic earthworms were higher for conservation than conventional for both sampling methods. Results from this study may assist decision-making on choice of technique, depending on specific research objectives.