Legumes and Water Stress: Soybean Performance Under Rainfall Reduction in a Tree-Based Intercropping System.

In southern Ontario, where 80% of Canada’s soybean (Glycine max (L) Merr.) crop is grown, a lack of reliable soil moisture during the growing season is one of the anticipated impacts of climate change. A decline in available soil moisture during the growing season may have profound implications for soybean performance. By offering beneficial microclimatic modifications and potential synergies via pathways such as fixed N deposition, annual intercropping as well as agroforestry systems may be viable agricultural management options for soybean production in water stressed environments.

In this study we use rainfall reduction canopies to simulate a full season (12 week) drought under soybean monoculture and soybean-wheat intercropping systems during field trials in Southern Ontario. These two cropping systems are grown in both an open field and in a tree-based intercropping system with Silver Maple (Acer saccharinum).

Our objective is to determine the impact of water stress on soybean yield, plant nutrition, dinitrogen (N₂) fixation and phenotypic trait plasticity, under these four cropping systems. Data collection focuses specifically on biological nitrogen fixation using the ¹⁵N natural abundance method, bi-weekly measurements of plant morphological traits and mineral nutrition as well as final yield analysis this summer. Environmental sensors are used to couple environmental conditions (e.g. soil moisture, temperature) to our response variables.

Building on previous research, we anticipate that tree-based intercropping systems will modulate microclimatic conditions and thus limit the impact of water limitations on soybean performance. This soybean response is expected to be even greater under annual intercropping with wheat given established facilitative interactions in cereal-legume intercrops. Our work will benefit farm managers with in-situ diagnosis of alternative soybean production systems for use in water stressed environments.