Enhancing winter canola integration into soybean cropping systems through relay intercropping

Abstract

Winter canola ( Brassica napus L.) has the potential to enhance the sustainability of soybean‑based cropping systems when integrated as a relay‑intercropped winter oilseed. A critical factor for successful overwinter survival is timely seeding that allows sufficient rosette development before dormancy. This study evaluated relay intercropping across eight environments in southwestern Ontario during the 2022/2023 and 2023/2024 growing seasons, testing three winter canola planting dates and two seeding methods (broadcast vs. planted). A complementary experiment assessed the effect of soybean plant population density on system performance. Early winter canola planting significantly increased grain yield (up to 3.6 Mg ha ⁻¹ ) compared with late planting ( p ≤ 0.02), but was associated with a non‐significant (∼8%–10%) reduction in soybean yield at some site‑years ( p ≤ 0.06), a magnitude that may still be agronomically or economically relevant. Seeding method significantly affected fall canola establishment, with planted treatments producing higher fall plant densities than broadcast seeding across most environments ( p < 0.001). Although later planting dates often resulted in higher fall stand counts, they also experienced greater winterkill (up to 65%) and lower canola yields ( p ≤ 0.001). Soybean plant population density did not significantly affect fall canola establishment among soybean‑planted treatments; however, fallow plots had higher fall stands ( p  < 0.001). Lower soybean densities reduced winterkill ( p ≤ 0.03) and increased winter canola yield ( p ≤ 0.001). Overall, results indicate that relay intercropping can successfully integrate winter canola into soybean systems when planting date, seeding method, and soybean density are optimized. Targeted management strategies that balance fall establishment with overwinter survival are essential to maximize system productivity.