Optimizing spring canola ( <i>Brassica napus</i> L.) fatty acid profiles and oil yield under late sowing stress through transplanting practices and planting densities in semi-humid climates

In the semi-humid Moghan region of Iran, delayed planting, water limitations, and seasonal environmental pressures limit canola yield, requiring enhanced agronomic tactics. This study examined how spring canola transplanting and planting density affected fatty acid profiles, oil content, and oil yield over two growing seasons (2019–2021). Direct seeding was compared with bare-root and potted-root transplanting at densities of 20, 30, and 40 plants/m2, using one or two seedlings per hole in a RCBD experiment. Transplanting significantly (p ≤ 0.01) outperformed direct seeding in oil quality and yield by reducing undesirable fatty acids (e.g. erucic, behenic, eicosenoic, arachidic) while increasing beneficial unsaturated fatty acids (e.g. linolenic, oleic), oil content, and oil yield. Bare-root transplanting increased oleic acid and oil yield compared to potted-root transplants, although oil content differences were non-significant (p > 0.05). Single-seedling transplants outperformed two-seedling setups (p ≤ 0.01) in fatty acid composition, oil content, and oil yield, reflecting reduced plant competition. MGIDI ranking identified potted-root, single-seedling transplants at 40 plants/m² and bare-root, two-seedling transplants at 30–40 plants/m² as the most promising treatments. This study uniquely integrated the MGIDI index with economic return analysis to rank transplanting treatments, providing a novel framework for agronomic decision-making in stressed environments.