ALLELOPATHIC INFLUENCE OF GERMINATING-SEEDS AND SEEDLINGS OF COVER CROPS ON WEED SPECIES

Bioassays using binary mixtures that included a cover crop with known allelopathic potential and a weed species were employed to determine t he importance of allelopathy compared to resource competition as inter ference mechanisms. Responses of weed species germinated with cover cr ops in a petri dish were measured. Interference between weed and cover crop seedlings was determined in a greenhouse experiment using the ad ditive design, which included partitions to reduce above- and below-gr ound competition and used capillary mat subirrigation to control moist ure and fertilizer availability. Germinating sorghum reduced radicle l ength of weeds, whereas germinating rye tended to increase weed radicl e length. Methods limited above-ground competition, so likely interfer ence mechanisms were below-ground competition and allelopathy. Germina tion with a cover crop had little effect on germination and shoot leng th of weeds. Increased density of rye but not of sorghum reduced growt h of barnyardgrass seedlings, Reduced number of barnyardgrass leaves i n the presence of rye was likely due to allelopathy. Suppression of ba rnyardgrass dry weight attributed to allelopathic interference by rye was successfully separated and compared to the combined effects of com petition and allelopathy.