Cereal rye mulch biomass and crop density affect weed suppression and community assembly in no‐till planted soybean

The use of multiple ecological weed management tactics may be an effective solution to weed management challenges associated with reducing tillage. An experiment was conducted to assess how soybean Glycine max (L.) Merr. density and cereal rye Secale cereale L. mulch biomass affected weed suppression and community assembly in no‐till production. Soybean was planted at five rates from 0 to 74 seeds m⁻², and five cereal rye mulch levels were established from 0 to 2 times the ambient cereal rye biomass within each site–year. We assessed the effects of soybean density and cereal rye mulch biomass on weed suppression, weed community composition, and the functional structure of weed life cycle, emergence timing, seed weight, height, and specific leaf area traits. Weed suppression was influenced by a synergistic interaction between soybean density and cereal rye biomass. The functional dispersion (FDis) of all weed traits, when combined, was reduced by increased soybean density and mulch biomass, suggesting that high treatment intensities induced trait convergence. However, soybean density and cereal rye biomass had differing effects on the FDis and composition of individual traits, suggesting that these management practices represent unique filters during weed community assembly. Mulch biomass had a larger effect on annual weed suppression and weed community composition than soybean density. Farmers who utilize high biomass cover crop mulch for weed management may experience shifts in weed community composition toward an increased proportion of perennials and weeds with later emergence, heavier seeds, and shorter stature. Increasing soybean density may reduce perennial weed biomass, making it a valuable complement to high cereal rye mulch biomass. As such, weed management in no‐till soybean is enhanced by combining multiple practices, which can enable synergistic weed suppression and the management of diverse weed functional groups.