Abstract: Environmentally sustainable weed management is crucial to meet the increasing demand for food. Previous studies have demonstrated that improving spatial uniformity and planting density can effectively suppress weeds. However, research on how planting patterns (PPs) affect the functional traits of crops and weeds is limited. In 2019 and 2021, we conducted a field experiment to compare the functional traits and biomass of Glycine max and Amaranthus retroflexus in two PPs—row (R) and equidistant (E)—with varying combinations of G. max and A. retroflexus densities. We found that the equidistant planting pattern (EPP) amplified the competitive ability of G. max in size-asymmetric competition with A. retroflexus, and this advantage increased alongside higher G. max density, primarily due to functional traits related to light acquisition. In the EPP, G. max established a closed canopy during the early growth stage, reducing light availability to A. retroflexus. This advantage was reflected in higher leaf area index (LAI) and leaf dry weight for G. max in the EPP than in the row planting pattern (RPP), while A. retroflexus experienced reduced LAI and plant height due to increased shading in the EPP. Consequently, the EPP enhanced the total biomass and yield of G. max by an average of 40.8% and 37.7%, respectively, while the biomass of A. retroflexus decreased by an average of 34.5% compared with the RPP. These results suggest that adopting an EPP with a high density of G. max, could be an effective strategy for suppressing A. retroflexus and improving crop yield.

Key words: planting pattern, functional traits, crop-weed competition, Glycine max, Amaranthus retrofexus