Similar spatial patterns of soil quality indicators in three poplar-based silvo-arable alley cropping systems in Germany

Abstract

Alley cropping systems (ACS) are regarded as a sustainable land-use alternative that provides ecosystem services, assuming that beneficial tree effects extend towards crop alleys. However, the spatial range of these effects has rarely been considered. The objective of this study was to investigate soil quality indicators at different distances from trees in three German silvo-arable ACS. We analysed soil microbial biomass C and N, ergosterol, microbial activity (enzyme activities, substrate-induced respiration rates) and their functional diversity (MicroResp™ method) in topsoils. Furthermore, fungal abundance and fungal and bacterial contribution to microbial residues (amino sugars) were determined. Tree effects on soil quality indicators were estimated for each depth, for the first time considering both, spatial dependence and abiotic factors (pH, clay content) using mixed effects models with repeated measures. Additionally, differences between soil depths were tested. Analysis combining the three ACS revealed a generalisation of effect sizes and spatial range of tree effects on soil quality indicators. Tree implementation in arable systems increased SOC, microbial biomass and activity in upper topsoils and shifted the composition of main microbial groups towards a higher fungal abundance and functional diversity. Soil quality indices decreased with increasing depth. However, in alleys, no differences between distances from trees were observed. Results demonstrate that ACS are capable to enhance soil quality mediated by microorganisms under trees within 5–8 years. Long-term studies are required to estimate whether beneficial tree effects extend towards crop alleys and deeper soil layers when systems are mature.