Abstract

Weed competition, persistent seed banks, and management costs can limit crop productivity in organic farming. A two-year field experiment was conducted in southern Finland to evaluate the effects of pea (Lathyrus oleraceus Lam.), oats (Avena sativa L.), and camelina (Camelina sativa (L.) Crantz.), grown as pure stands and as three-crop mixtures at varying seeding densities, on weed diversity and suppression. The seeding densities (%) were 50:20:30 and 33:33:33 of the pure stand density of pea, oats, and camelina in 2022 and 50:50:50 and 33:33:33 of the pure stand density in 2023. Weed diversity was assessed at five sampling times, species were identified and analyzed for biomass, richness, Shannon-Wiener index (H), evenness, and dominance. Weed diversity and suppression varied with crop composition, growth stage, and seasonal conditions. In 2022, the 33% mix had the highest H (2.22) and evenness (0.77), enhancing weed suppression while controlling dominance. In 2023, pure oats had the highest H (1.65) and evenness (0.87), and pure peas had the lowest H (1.41) and evenness (0.67). Although pure oat stands provided the strongest weed suppression, crop mixtures enhanced species diversity and evenness, suggesting potential for more balanced weed management in organic systems, with short-term results indicating potential benefits for weed control.

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