Allelopathic Effects of Tall Fescue on Birdsfoot Trefoil as Influenced by N Fertilization and Seasonal Changes1

Abstract Difficulties in obtaining successful establishment of birdsfoot trefoil (Lotus corniculatus L.) in sods of tall fescue (Festuca arundinacea Schreb.) cannot be fully explained by competition for water, nutrients, and light. The difficulty may be due to allelopathy that has been shown to exist in tall fescue. Laboratory and greenhouse experiments were conducted at Columbia, Mo., to characterize the influence of N fertilization and seasonal changes on the intensity of allelopathic effects of tall fescue on birdsfoot trefoil. Trefoil seeds were germinated in water extracts of fescue herbage (15 g herbage/100 ml H2O) applied to filter paper in a 23.3 C germination chamber and also in sand or soil (fine, montmorillonitic, mesic Udollic Ochraqualf) media in the greenhouse. Extracts of fresh herbage caused inhibition of germination and seedling growth, but ashing of the fresh herbage prior to extraction eliminated the inhibition. Previous N fertilization of tall fescue increased inhibition of germination and seedling growth. Percent germination and root and hypocotyl lengths of birdsfoot trefoil seedlings treated with the June through September extracts were 10, 13, and 7 times greater, respectively, than were those obtained from herbage sampled from January through May. Soil reduced the inhibitory effects of extracts, but root growth was still suppressed 54.7% in soil + extract as compared with the soil + water control. Growth of trefoil roots were reduced more by allelopathic substances than either germination or hypocotyl growth.