Divergent weed control performance of wheat-legume and rapeseed-pea intercrops in conventional Mediterranean systems

Intercropping is increasingly promoted as a weed management strategy in temperate organic farming for cereal-legume combinations. However, its ability to fully replace herbicides under conventional Mediterranean conditions, particularly for grain production, and for oilseed-legume combinations, remains underexplored. This study evaluated the performance of three intercropping systems as herbicide replacement strategy under contrasting nitrogen (N) fertilisation levels and quantified the potentially associated grain yield losses. From 2021 to 2023, rapeseed/pea, durum wheat/pea, and durum wheat/faba bean, were tested alongside their respective sole crops under irrigated on-farm conditions in the Ebro Valley (NE Spain). A 50/50 row replacement design was used with two N levels (0 and 75 kg mineral N ha −1 ). Herbicide application (no vs. yes) was tested on intercrops. Weed density, coverage, Shannon diversity index, crop biomass and grain yield were measured. Yield losses in rapeseed/pea without herbicides relative to herbicide-treated controls ranged from −13% under good rapeseed establishment, due to early growth, tall height, and high LAI, to −30% under poor establishment with high weed pressure (316 ± 351 plants m −2 ). In contrast, durum wheat/pea and durum wheat/faba bean led to limited weed control, with yield losses reaching 37% and 62%, respectively, in the presence of competitive late-growing species like Cirsium arvense L. and Lolium rigidum Gaudin. Legume yields declined sharply beyond 23% weed coverage, compared to 38–56% for wheat. Higher weed diversity was linked to greater weed-related yield loss. Species selection and canopy complementarity are key for weed suppression. Rapeseed–pea proved greater resilience, while shorter wheat–legume intercrops were more vulnerable. In Mediterranean conventional systems, intercropping alone is insufficient: complementary strategies are needed to manage weeds effectively without herbicides.