The response of new, high-yielding rice cultivars to varying barnyardgrass control levels and rice plant densities is not well understood. Studies were conducted in 2002 through 2004 at the Rice Research and Extension Center near Stuttgart, AR, to evaluate three new rice cultivars at plant densities ranging from 79 to 392 plants/m2 grown in competition with barnyardgrass. Representatives from each of the three classes of long-grain rice produced in the United States were selected. ‘Wells’ represented conventional, long-grain rice, ‘CL161’ represented semidwarf, imidazolinone-tolerant, long-grain rice, and ‘XL8’ represented hybrid, long-grain rice. Rice density and barnyardgrass control affected rice total aboveground biomass production, panicle weight, and harvest index. As rice density decreased or barnyardgrass control increased, total aboveground biomass production and harvest index increased. Rice density had no effect on panicle density or yield. Panicle density increased 14 panicles/m2 for every 10% increase in barnyardgrass control. Cultivar yields were affected similarly by barnyardgrass control, and increased 750 kg/ha for each 10% increase in barnyardgrass control. XL8 and Wells produced the highest average yields, with CL161 producing the lowest over the three-year experiment. XL8 yield components fluctuated more than CL161 or Wells over the range of rice densities and barnyardgrass control levels, indicating that XL8 is highly sensitive to intra- and interspecific competition at high plant populations.
Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, rice, Oryza sativa L. ‘CL161’, ‘Wells’, ‘XL8’