Perennial clover strips improve nitrogen synchrony and winter wheat productivity in the humid continental climate of southwestern Ontario

In southwestern Ontario’s humid continental climate, improving nitrogen (N) use efficiency requires balancing crop demand against overwinter leaching. This study evaluated a perennial clover strip intercropping system, using white clover (Trifolium repens L.) and subterranean clover (T. subterraneum L.), as a strategy to synchronize N supply with winter wheat (Triticum aestivum L.) demand. The research was conducted at an on-farm Living Lab (Agriculture and Agri-Food Canada) site in Dresden, Ontario, in a strip-plot arrangement comparing perennial clover strips established in 2020 with a conventional system without clover, with and without N fertilization. Soil N pools and soil health indicators were assessed from early spring through autumn to evaluate seasonal N dynamics and their impact on wheat productivity. Under zero applied N, perennial clover produced 57% more grain than conventional management, whereas the two systems did not differ where fertilizer was applied. Soluble N pools showed a significant cropping system × sampling stage interaction, and the direction of the perennial clover effect reversed over the season. While wheat was growing, NO₃⁻–N was 49% higher under perennial clover at mid-summer in fertilized plots. After harvest, autumn NO₃⁻–N was 45% to 54% lower under perennial clover at both fertilization levels. Water-extractable total N was 20% and 45% higher under clover in early spring and 23% and 32% lower in autumn in fertilized and non fertilized plots, respectively. These findings suggest that perennial clover can maintain winter wheat yield at reduced N input while lowering the residual NO₃⁻–N most vulnerable to overwinter loss, before any measurable change in bulk soil health.