ALLELOPATHIC CHARACTERISTICS OF 3 COOL-SEASON GRASS SPECIES IN THE FORAGE ECOSYSTEM

Allelopathy, the direct or indirect effect of one plant on another thr ough the production of chemical compounds that escape into the environ ment, occurs widely in natural plant communities and is postulated to be one mechanism by which weeds interfere with crop growth. The purpos e of this research was to determine the potential allelopathic influen ce of selected cool-season grass species on species interseeded into t he pasture ecosystem. Aqueous extracts of tall fescue (Festuca arundin acea Schreb.), Italian ryegrass (Lolium multiflorum Lam.), and little barley [Critesion pusillum (Nutt.) A. Love; syn. Hordeum pusillum Nutt .] leaf and stem tissue harvested at the mature stage of plant develop ment reduced seed germination and seedling growth of alfalfa (Medicago sativa L.) and Italian ryegrass. It was estimated that 2.8 and 2.5 g L-1 aqueous extracts of mature tall fescue stem tissue, resulted in a 50% reduction in alfalfa seed germination and seedling growth, respect ively. For the extracts from Italian ryegrass and little barley, it wa s estimated that tissue concentrations of near 5.0 g L-1 resulted in a 50% reduction in seed germination and seedling growth for the two bio assay species. leaf and stem tissue concentrations of the three grasse s >7.0 g L-1, resulted in complete inhibition of alfalfa seedling grow th. The potential concentration for foliage tissue in soil solution of the pasture ecosystem for tall fescue, Italian ryegrass, and little h arley would be 28, 23, and 9 g dry wt. L-1, respectively. Therefore, t he allelopathic characteristics of these species could be of economic importance in the pasture ecosystem when overseeding the pasture with annual ryegrass or alfalfa.