Alternatives for sustainable weed control in single- and double-cropped soybean: A case study for Mediterranean irrigated conditions

The irrigated cropping systems in South Europe could benefit from soybean [Glycine max (L.) Merr.] introduction in their maize (Zea mays L.)-based crop rotations. However, sustainable weed management strategies are needed for soybean growers under Mediterranean irrigated conditions. This work aimed to assess the weed control efficacy, and the soybean performance, of alternative management practices for single- and double-cropped soybean. Two field experiments were carried out in northeast Spain in the period 2019-2021. Row width narrowing (75-37.5 cm), herbicide application (yes/no), and roller-crimped rye [Secale cereal (L.) M.Bieb.] cover crop (yes/no) were assessed in the single cropping system experiment (SCS). In the barley-soybean double cropping system experiment (DCS), row width narrowing and herbicide application were assessed. In the SCS, the presence of rye cover crop reduced weed biomass up to 92% compared to the controls without herbicide and cover crop in 2020. In 2021, no effect of the cover crop on weed pressure was found due to the low amount of rye biomass accumulated (11.8 and 3.4 ton DM ha(-1) in 2020 and 2021, respectively). In the DCS, herbicide application attained the expected weed control. Row width narrowing to 37.5 cm did not have an impact on weed pressure nor on soybean yield in either experiment. We concluded that herbicide reduction for single-cropped soybean under Mediterranean irrigated conditions can be achieved by roller-crimping a rye cover crop, provided enough rye biomass is accumulated. In the DCS, our results indicated that further research is needed to find alternatives to chemical weed control.