2.2 Field trials
A paddy field was selected at the experimental station during the 2020 growing season. The paddy had previously been planted with rice for several seasons. Several weeds occurred in the paddy, includingEchinochloa crusgalli (barnyardgrass), Leptochloa chinensis , Cyperus difformis and Eclipta prostrata but barnyardgrass was dominant. Other weedy species such asAlternanthera sessilis and Monochoria vaginalisoccasionally occurred in the field. The field was divided into a series of 3×5 m plots arranged in a completely randomized design with four replicates of each treatment or control. Each plot was separated by trenches with at least 30 cm discard strips on each side. Each focal cultivar ‘Huagan-3’ or ‘Lingyou-6173’ was paired with itself, or with a closely or distantly related cultivar, and planted at a density of 50 m-2 by direct seeding at a 1:1 proportion. Plots not planted with rice served as controls for weed growth. All plots received fertilizer (nitrogen, phosphorus pentoxide, and potassium oxide at the rates of 7.5 g m-2, 9.0 g m-2 and 8.5 g m-2 respectively) 1 day before the plots were saturated with water. All other field management followed the rules of the rural administration in Anhui Province, China except chemical or hand weeding. After 50 days, weed species and numbers in each plot were identified and their aboveground biomass dry weights measured.