The researchers studied how different amounts of soybean seeds and timing of weed killer application affect weed control and soybean yields. They found that using more soybean seeds led to less weed biomass at harvest. At one location, lower seeding rates resulted in more weeds when the weed killer was applied early. However, at the location with the most weeds, no single weed killer application gave yields as high as a weed-free field. Overall, using 240,000 seeds per hectare led to lower soybean yields compared to using 420,000 seeds per hectare.