Assessing crop productivity, grain quality, and soil labile carbon and nitrogen in pea-based intercrops under low nitrogen input

Pea-based intercrops provide nitrogen (N) benefits and often improve land productivity through functional diversification. However, their impact on grain quality and soil health remains unclear. We conducted a 2-year (2021 and 2022) intercrop study at Swift Current and Melfort, Saskatchewan, assessing productivity, grain quality, and soil water-extractable organic carbon (WEOC) and water-extractable dissolved N (WEDN). Nine treatments included pea–oat (PO) intercrops with three N rates (0, 1/4, and 1/2 of full recommended N rate for oat monocrop), pea–canola (PC) intercrops with three N rates (0, 1/4, and 1/2 of full recommended N rate for canola monocrop), and three monocrops (pea, oat, and canola). Pea monocrop received no N fertilizer, while oat and canola monocrops received the full recommended N rate. In intercrops, pea was seeded at 2/3 and the companion crop at 1/2 of their recommended rates. PO intercrops consistently produced higher energy-based yields than PC intercrops. Intercrops outperformed monocrops at Melfort but not at Swift Current. Intercropping reduced canola protein content by 6–9% and oat protein content by 6–8%, compared to monocrops. PO intercrops increased WEOC level by 5%–9% compared to monocrops. PC intercrops resulted in 10% higher WEDN than PO intercrops, attributed to a higher pea plant stand in PC. Nitrogen fertilizer rates in intercrops did not affect yields or soil labile C and N. The results showed that applying N fertilizers to pea-based intercrops did not improve productivity, but seeding rate ratio in intercrops should be finetuned based on crop competitiveness to improve overall performance.