Diversifying crop rotations with perennial forage crops: potential benefits for weed management & farmland biodiversity

Abstract : Crop rotation may be used to prevent the continuous selection of weed species adapted to one crop type. However, today’s crop rotations are often very short and simple. We studied the impacts of introducing perennial forage crops into cereal-based crop rotations on weed vegetation. Large-scale weed surveys in 632 fields in western France suggested that the weed species composition varied most strongly between perennial alfalfa forage crops and six annual crops[1]. Comparisons of wheat fields before, during, and after perennial alfalfa suggested that weed communities vary in a cyclic way during such crop rotations. This may be beneficial for weed management (suppression of weed species problematic in annual crops) and for plant diversity[2]. Field experiments in Dijon, eastern France, largely confirmed the negative impacts of perennial crops on the population dynamics of major noxious weed species. Moreover, contrasting crop management options permitted investigating the underlying mechanisms. The absence of soil tillage in perennial crops reduced weed emergence, but increased the survival of established weed plants. Additionally, the temporally extended vegetation cover and the frequent hay cuttings reduced the vegetative weed growth and seed production.