The researchers studied how different crop mixtures can help control weeds in fields. They tested barley and pea mixtures in Sweden and Poland to see how well they suppressed weeds compared to pure crops. In Sweden, barley and pea mixtures were better at stopping weed growth than peas alone. In Poland, mixtures with more barley were more effective at weed control. The crops did not affect seed yield significantly. In controlled experiments, crops reduced the growth of a common weed called Elytrigia repens. Overall, crop mixtures can help reduce weed growth and improve crop yield in fields.