High and dry: Barley (Hordeum vulgare) yield benefits from tree presence in a temperate alley cropping system during a drought year

Alley cropping systems (ACS) are promoted as sustainable, resilient and multifunctional land-use systems. However, concerns about yield reductions persist and whether these are driven by microclimate alterations or below-ground competition for water remains unclear. In this study, we measured wind speed, air temperature, and global radiation at seven positions within a 48 m wide crop alley of a short rotation ACS in Germany with summer barley (Hordeum vulgare) and poplar (Populus nigra × P. maximowiczii and P. trichocarpa Torrey & A. Gray) and on a treeless reference field (OF) during a particularly dry and warm year. Additionally, gravimetric soil water content and crop yield were assessed with high spatial resolution. Our results show that tree strips influenced all measured parameters. Global radiation and air temperature patterns varied dynamically with shading, while night-time air temperatures were unexpectedly highest on the OF. Wind speeds were reduced by up to 98% near tree strips and 81% further away. Soil water content displayed a U-shaped pattern, with higher values near tree strips, a rare observation in ACS. Crop yields in the ACS were twice as high as in the OF, despite being lower near tree strips. Yields were strongly correlated with global radiation but not with air temperature, wind speed, or soil water content. These findings provide preliminary evidence that tree presence in ACS can, under certain conditions, contribute to increased crop yields. The results suggest that ACS provide potential benefits for sustainable land-use, but further multi-year and multi-site studies are needed to validate the observed yield patterns across different environments and years, particularly under varying climatic conditions. Further research should also explore the indirect effects of microclimate modifications on soil water dynamics, including evapotranspiration.