The click bait title is unfortunate because it's a really interesting study. TLDR: It's different to a polyculture, where species complimentarity is the aim. Basically, different cereal species and varieties are sown in a mix. They all have slightly different growing requirement/preferences, making the overall productivity of the system more stable in the face of seasonal climatic variability. Modern grain handling, and different end uses for species/varieties, makes such a system impractical. However, planting multiple pasture species is (or should be) standard practice for exactly this reason.