ALLELOPATHIC POTENTIAL OF SOME WARM-SEASON GRASSES

Aqueous extracts of tissue from the test species (giant foxtail, green foxtail, yellow foxtail, bahiagrass, barnyardgrass, Johnsongrass and large crabgrass) harvested at the vegetative and mature stages were tested for allelopathy on seed germination and seedling growth of the bioassay species (alfalfa and Italian ryegrass). Tissues harvested from large crabgrass and barnyardgrass were found not to be allelopathic; only tissue harvested from the five other test species during the mature stage of plant growth exhibited allelopathic characteristics. Extracts of stem material reduced seed germination and seedling growth for both bioassay species. It was estimated that 0.30/0.33, 0.23/0.18, 0.20/0.21, 0.31/0.32 and 0.38/0.19% aqueous extracts of mature Johnsongrass, bahiagrass, giant foxtail, green foxtail and yellow foxtail stem tissue resulted in a 50% reduction in seed germination/seedling growth of Italian ryegrass, respectively. Concentrations in a similar range resulted in 50% reduction in seed germination and seedling growth in the alfalfa bioassay. The potential concentration for foliage tissue in soil solution of the pasture ecosystem for Johnsongrass, bahiagrass, giant foxtail, green foxtail, and yellow foxtail foliage tissue would be 3.2, 1.0, 2.0, 1.4 and 1.4%, respectively. The allelopathic characteristics of these species could therefore be of economic importance in the pasture ecosystem when overseeding the pasture with grass and legume species.