Three-Year Cereal: Field Bean Intercropping Greatly Reduced Weed Abundance with Small Changes in Functional Composition

Weeds reduce crop yield but may also support agroecosystem biodiversity. The biomass and functional composition of weed communities were evaluated in cereal–field bean intercrops and sole crops, with and without NP fertilization. Intercrops were repeatedly grown in the same plots using 1:1 and 2:1 cereal:field bean row ratios, while sole crops were sown at low or high density and rotated. Weeds were sampled at cereal flowering and maturity stages. Fertilization had little effect on weed biomass but tended to reduce species richness and favor cosmopolitan species. Intercropping reduced weed biomass two- to sevenfold compared with high-density cereal and legume sole crops. Plot richness was 39% lower in intercrops than in field bean and low-density cereal crops. Over three years, weed functional composition was influenced more by year than by crop system or fertilization. However, the contribution of tall weeds increased in intercrops: 51% compared to 42% in high-density sole crops and approximately 31% in low-density ones. The average frequency of types indicated early shifts in weed community structure. In conclusion, continuous cereal–field bean intercropping controlled weeds more effectively than rotated sole crops, with a slight decline in species richness and minor shifts in functional composition.