Impacts of monoculture cropland to alley cropping agroforestry conversion on soil N2O emissions

Monoculture croplands are a major source of global anthropogenic emissions of nitrous oxide (N₂O), a potent greenhouse gas that contributes to ozone depletion. Agroforestry has the potential to reduce N₂O emissions. Presently, there is no systematic comparison of soil N₂O emissions between cropland agroforestry and monoculture systems in Central Europe. We investigated the effects of converting the monoculture cropland system into the alley cropping agroforestry system on soil N₂O fluxes at three sites (each site has paired agroforestry and monoculture) in Germany, where agroforestry combined crop rows and poplar short-rotation coppice (SRC). We measured soil N₂O fluxes monthly over 2 years (March 2018–January 2020) using static vented chambers. Annual soil N₂O emissions from agroforestry ranged from 0.21 to 2.73 kg N ha⁻¹ year⁻¹, whereas monoculture N₂O emissions ranged from 0.34 to 3.00 kg N ha⁻¹ year⁻¹. During the rotation of corn crop, with high fertilization rates, agroforestry reduced soil N₂O emissions by 9% to 56% compared to monocultures. This was mainly caused by low soil N₂O emissions from the unfertilized agroforestry tree rows. Soil N₂O fluxes were predominantly controlled by soil mineral N in both agroforestry and monoculture systems. Our findings suggest that optimized fertilizer input will further enhance the potential of agroforestry for mitigating N₂O emissions.