Soybean N2-fixation rates and yield in tree-based intercropping systems: Effects of water limitations and environmental modifications

In Ontario, where 80% of Canada's soybean crop is grown, a lack of reliable soil moisture during the growing season is an anticipated outcome of climate change. Di-nitrogen (N2) fixation rates in soybean are well known to be highly sensitive to water deficits. The objective of this study was to examine i) the effect of a full season water deficit on soybean N2-fixation rates and yield in the field, and ii) whether tree- based intercrops (TBI) could modulate the impact of a full season water deficit on these two parameters. This study used rainfall reduction shelters to reduce available soil moisture in monoculture and in a TBI agroforestry system in southern Ontario. Fixed N was significantly reduced in the water deficit treatment in both monoculture and TBI systems. Soybean yield was significantly reduced in the water deficit treatment but only in monoculture, not in the TBI system. Results demonstrate that important N pathways are restricted under water limitation but that TBI systems may induce yield stability under water deficit scenarios.