Living mulches as a strategy for weed control and improved Nigella sativa L. production in salt-affected soils☆

Expanding the cultivation of underutilized oilseed crops on marginal lands necessitates innovative agronomic strategies to maintain lipid quality while ensuring stable yields. This study explored the use of living mulch systems for the sustainable production of black cumin (Nigella sativa L.), a promising yet weed-sensitive oilseed crop, in salt-affected soils in Iran. Through a two-year field experiment, the effectiveness of berseem clover (Trifolium alexandrinum L.) and barley (Hordeum vulgare L.) mulches, paired with strategic mowing timings, was evaluated. The results showed that berseem clover mulch significantly reduced the biomass of dominant weeds including Amaranthus retroflexus, Chenopodium album, and Portulaca oleracea, by 47–74.3% compared to weedy control plots. The highest reduction (74.3%) observed in plots with T. alexandrinum living mulch mowed before the black cumin flowering stage. The oil yield of black cumin cultivated under berseem clover living mulch (with post-establishment mowing) increased by 12.4% relative to weed-free control plots. Concurrently, the fatty acid profile improved, with a 3.47% increase in unsaturated fatty acids and a 13.35% higher unsaturated-to-saturated fatty acid ratio compared to the control. These results demonstrate a dual improvement in both oil yield and quality under the living mulch system. The optimal management strategy involved removing berseem clover after crop establishment, which led to a 12.4% and 45.7% increase in oil yield compared to the weed-free and weedy plots, respectively. These findings provide the first evidence-based protocol for managing weeds in black cumin under saline conditions, offering oilseed producers an ecological alternative to herbicides that maintains both yield quantity and lipid quality in marginal environments.