Effects of converting a temperate short-rotation coppice to a silvo-arable alley cropping agroforestry system on soil quality indicators

Short-rotation coppices (SRC) and alley cropping agroforestry systems (ACS) provide ecosystem services and environmental benefits. Particularly, their role in improving soil quality has frequently been emphasised. However, the economic lifetime of fast growing tree plantations may be limited, making a transition indispensable. Since information on effects of such land-use changes on soil microbial properties is scarce, the aim of this study was to assess effects of converting a German poplar-based SRC to a silvo-arable ACS, comprising rootstock incorporation and reduced tillage, on soil quality indicators after one year. Soils were sampled under poplars and within the re-converted alleyway. Distance transects were considered to further include potential beneficial effects of remaining trees on alleyway topsoil quality. We analysed soil organic carbon (SOC), total nitrogen, soil microbial biomass C and N, ergosterol, microbial activity (enzyme activities, multi-substrate-induced respiration rates), ratios relative to SOC, fungal abundance and microbial functional diversity at two topsoil depths (0-5, 5-20 cm). Repeated measures mixed effects models were calculated for each depth, considering spatial dependence structures and potential heterogeneity of abiotic factors (pH, clay contents). SRC to ACS conversion decreased SOC, microbial biomass and activity in upper topsoils within the arable alleyway, irrespective of tree distance. Furthermore, shifts in the composition of main microbial groups towards a lower fungal abundance and functional diversity were observed. Reductions of fungal indices were also identified in lower topsoils. Unexpectedly, results demonstrated that partial conversion of a SRC back to arable cropping decreased soil quality within as little as one year.