Allelopathic Influence of Nine Forage Grass Extracts on Germination and Seedling Growth of Alfalfa

Poor establishment of alfalfa (Medicago sativa L.) often results when the alfalfa is sown with cool-season perennial grasses. This study was conducted to screen the inhibitory characteristics of grasses that are often grown in combination with alfalfa in grass swards. Laboratory and greenhouse studies were conducted to determine the allelopathic potential of nine grasses to alfalfa germination and seedling growth. Alfalfa seeds were germinated in aqueous extracts of nine grasses, using distilled water as a control. Measurements were taken to determine the effect of the extracts on germination, seedling length, and weight. Alfalfa germination ranged from 64% for tall fescue (Festuca arundinacea Schreb.) extracts to 91% for the control. Total alfalfa seedling length was reduced by 39% for grain sorghum [Sorghum bicolor (L.) Moench] extracts. Dry weights of alfalfa cotyledons, hypocotyls, and radicles were reduced significantly by several grass extracts. Smooth bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), and grain sorghum extracts were more inhibitory than other grass extracts. Alfalfa seedling emergence and survival percentage was affected by various grass root residues. Timothy (Phleum pratense L.) extracts caused the lowest survival percentage of 59% compared to the control of 88%. Redtop [Agrostis gigantea Roth; syn. Agrostis alba L. sensu auct. (American)] and reed canarygrass (Phalaris arundinacea L.) extracts had no effect on alfalfa seedling emergence and survival. Leached and nonleached residues significantly inhibited alfalfa height, leaf area, and dry weights of leaves and stems. The extent of reduction was greater in nonleached than in leached residues. These results suggest that grass residues may affect alfalfa growth and development because of inhibitory effects of allelochemicals present in grass residues. Exp. Stn. Project 1-6-55179.