Enhancing soybean (Glycine max L.) yield and quality through optimized weed-free periods and sowing techniques

Soybean ( Glycine max L.) yield is sensitive to early weed competition, yet optimal weed control timing and sowing methods remain unclear. Although early-season weed interference is widely recognized as detrimental, critical knowledge gaps persist regarding the precise weed-free period required and how sowing configuration affects weed dynamics and crop performance. Hence, this study aimed to clarify the effects of different weed-free durations and sowing methods (flat vs . bed) on soybean growth, yield, and seed quality. Over two years, a split-plot randomized block design with three replications was used to examine 16 treatments, including two sowing methods (bed sowing and flat sowing) with weed competition and weed-free periods of up to 25, 40, and 55 days after sowing (DAS), along with full-season competition and a weed-free period. Data were recorded to evaluate weed density, growth, yield, and quality parameters, including protein and oil content. Results showed that maintaining a weed-free window between 25–40 DAS was critical to minimizing yield losses. Weed competition throughout the season caused 57–62% yield loss in flat sowing and 58–60% in bed sowing, while weed-free management during 25–40 DAS maximized grain yield and improved seed protein and oil content. Flat sowing consistently outperformed bed sowing due to better canopy closure, reduced weed pressure, and improved resource capture during the critical weed-free period. In conclusion, maintaining a weed-free environment during the 25–40 DAS window, particularly under flat sowing, optimizes soybean growth, yield, and quality under non-GMO conditions. Future research should prioritize integrated, site-specific weed management strategies and assess their long-term impacts on economic returns, soil health, and environmental sustainability.