Earthworm communities are supported by perennial bioenergy cropping systems

Abstract

During the last decade a variety of perennial bioenergy crops (PECs) have been introduced into European agriculture. This study was designed to investigate the impact of various PECs on earthworm community patterns (species composition, numbers, biomass, α-diversity, life-form categories) at a landscape scale in Western Germany. The PECs investigated were cup plant (CP), tall wheatgrass (TW) and giant knotweed (GK). In total, 4 field replicates of each perennial crop were investigated at 9 study sites with the exception of CP, for which only 3 replicate sites were available. PECs were compared with silage maize as an annual bioenergy crop (AEC) and permanent grasslands (PGL). The earthworm community of the study area consisted of 13 species in total. Mean species number ranged from 2.7 (AEC) < 2.8 (GK) < 3.8 (TW) < 3.9 (PGL) < 4.2 (CP). Overall, PECs took an intermediate position between AEC and PGL concerning earthworm population data including α-diversity and community structure as indicated by Shannon-Weaver index (H’), species number and Evenness (E). There was a clear and close to significant (p < 0.1) increase in the mean total earthworm number in the range AEC (43.3 ind. m−2) – PECs (86.7 ind. m−2) – PGL (114.4 ind. m−2). Fresh earthworm biomass varied from 21.1 g m−2 (AEC) to 35.7 g m−2 (PGL) to 40.1 g m−2 (PECs), however, this difference was only significant for mean biomass of juveniles. Endogeic species were highly dominant in soils cultivated with PECs. Generalized linear mixed models revealed that soil pH, amounts of soil organic carbon and plant available soil water content were partly significant environmental driving variables for the improvement of the earthworm community in soils cultivated with PECs.