Allelopathy in forage crop systems

Secondary plant metabolites and their degradation products are important in all agroecosystems including those with forage crops. Allelopathy affects cropping systems and interseeding of one species into established sods of another. Autotoxicity and heterotoxicity are types of allelopathy. Alfalfa (Medicago saliva L.) has been investigated as both an autotoxic and heterotoxic species. Reestablishment of alfalfa immediately after alfalfa has usually resulted in poor stands due to autotoxicity, and several other forage species also exhibit autotoxicity. Many forage species have shown heterotoxicity, both between forage species and weed species. Several investigators have identified various allelochemicals and/or families of allelochemicals as being responsible for allelopathic reactions. Identifying such chemicals would aid in developing resistant forage cultivars and in maintaining a productive and profitable crop. Crop rotation, cover-crop management, interplanting, double cropping, no-till planting, and nonrotational cropping systems are involved with allelopathic effects. Some alfalfa cultivars possess some resistance to these allelochemicals. Therefore, a breeding program could provide resistant germplasms. Various forage grasses and some weed species have demonstrated allelopathic effects on alfalfa, and alfalfa has allelopathic effects on some weed species. This alone may provide an insight for herbicide studies in alfalfa production.