Short-term alfalfa phases enhance the resilience of annual grain systems under climate variability: evidence from a 20-year crop rotation experiment

The benefits of including perennials in crop rotations are well established, yet recently perennial forages such as alfalfa have declined in use across the Canadian Prairies. This is due to decoupling of livestock and grain systems and concerns over water use. The role of short-term alfalfa phases within diversified grain systems remains underexplored in sub-humid regions such as southern Manitoba. This study evaluated whether adding a two-year alfalfa phase to an annual grain rotation could provide agroecological benefits under Prairie conditions. A 20-year, fully phased, replicated field experiment at Glenlea, Manitoba compared a diversified annual rotation (wheat (Triticum aestivum L.) – flax (Linum usitatissimum L.) – oat (Avena sativa L.) – soybean (Glycine max (L.) Merr.)) with a perennial-inclusive rotation (wheat – flax – alfalfa (Medicago sativa L.) – alfalfa), alongside climatic covariates including precipitation and vapour pressure deficit (VPD). Analyses focused on wheat and flax , the common crop phases between rotations. The perennial system required 50% less synthetic N than the annual system, produced higher flax yield (997 kg ha-1 vs 725 kg ha-1, p < 0.0001), greater wheat grain protein (14.2% vs 13.6%, p < 0.0001), and lower weed biomass (7.2% vs 12.1%, p = 0.0013) and seedbanks (4.3 vs 8.3 plants 170 cm-3). Wheat yield was unaffected by rotation, except under high VPD conditions in the perennial system. Integrating short-term alfalfa phases into diversified annual rotations reduced fertilizer dependence and improved agroecosystem performance with limited yield penalties, supporting their role in enhancing resilience under Prairie climate conditions.