Enchytraeids as indicator of soil quality in temporary organic grass-clover leys under contrasting management: A feasibility study

One objective in organic farming is to sustain the quality of the soil resource. Because enchytraeids are an important soil faunal component, they stand as bioindicators of soil quality. We tested this candidature in a field experiment on loamy sand soil with 1- and 4-year old grass-clover leys subject to contrasting management regimes (cutting, slurry injection, grazing). Enchytraeid density, biomass and species composition was determined in 0-18 cm soil sampled in October, and again in March and May before and after slurry application, respectively. For soils retrieved in October, ley age had no consistent impact on enchytraeid density and biomass. Injection of slurry significantly affected the enchytraeid community at one sampling only but tended to sustain higher enchytraeid abundance in 1-year old leys throughout the year. One persistent feature was a larger enchytraeid community in the autumn than in the spring, regardless of management regime. Compared with leys used for cutting, grazed leys had consistently lower enchytraeid density and biomass. This was ascribed to soil compaction induced by heifer trampling. The number of species ranged from 11 to 18 in the autumn and from 7 to 13 in the spring with no distinct relation to management. Simpson's index of diversity did not differ among sampling dates and management regimes, including ley age. Although the enchytraeid community to some extent reflected differences in management regime, the patchy distribution and management induced interactions among soil physical, chemical and biological properties suggest that enchytraeid abundance is not a feasible stand-alone indicator of management impacts on soil quality in temporary grass-clover leys but may candidate as one of several biological key parameters in more comprehensive soil quality assessment schemes.