Disentangling the contribution of trait plasticity to improve the productivity of a maize-soybean intercrop system for the Midwest, USA

Crop yields in intercropping systems are the result of a combination of factors dominated by plastic responses in plant traits to the heterogeneity associated with the intercrop design and the row configuration of the intercrop. Disentangling their relative influence is infeasible in situ but crucial for cultivar selection and intercrop design. Using functional-structural plant (FSP) modelling, these effects can be separated in silico. Here, a mechanistic FSP model was developed, including three-dimensional aboveground plant architecture of maize and soybean, radiation distribution, and assimilate allocation. The model was used to explore the potential to improve yields in a simultaneous intercrop by disentangling the contribution of three plastic traits related to photosynthesis, leaf thickness and plant height. The improved phenotypes were then simulated in two intercrop configurations, single- and twin-rows of maize, for potential increases in land-use efficiency. The study revealed that for maize, photosynthesis had the greatest contribution (+78%), followed by plant height (+31%) and leaf thickness (+6%) where the total maize monoculture phenotype produced the greatest maize yield without affecting the yield of intercropped soybean. However, soybean trait plasticity had a negligible effect on soybean yield, but the soybean monoculture phenotype with a low light-saturated photosynthetic rate resulted in the greatest intercropped maize yield. These improved phenotypes may increase land-use efficiency by 1-3% relative to the standard monoculture systems of the Midwest, USA. Together, these results could aid the selection of maize and soybean germplasm that could improve the productivity of a simultaneous intercrop.