Fig. 4. Percent contribution to the pasture from quackgrass, white clover, and bluegrass in spring, summer, and autumn 1998 to 2000 and averaged over harvested herbage, total herbage, and tiller/leaf density estimates. a, b indicate seasons that differed significantly within methods (P < 0.05). Seasons within species with the same letter were not significantly different at P < 0.05.