Density and spatial interference of barnyardgrass (Echinochloa crus-galli) wih rice (Oryza sativa).
Field trials were conducted in 1987-88 to evaluate density and spatial interference of barnyardgrass with rice cv. Lemont and Newbonnet on silt loam. Barnyardgrass reduced grain yield of Lemont, a semi-dwarf cultivar, more than Newbonnet, a short-statured cultivar, 50% yield reduction to approx. 3000 and 4500 kg/ha, resp., due to approx. 19 and 22 barnyardgrass plants/m2, resp. Linear regression indicated that season-long interference of barnyardgrass at 1-20 plants/m2 reduced grain yields of cv. Lemont and Newbonnet by 301 and 257 kg/ha per barnyardgrass plant, resp. Grain yields of Lemont and Newbonnet were reduced by barnyardgrass densities of 40 plants/m2 but were not affected further if barnyardgrass density increased beyond this level. Barnyardgrass reduced straw yield of cv. Lemont more than that of cv. Newbonnet, 50% reduction to approx. 4000 and 4500 kg/ha, resp., due to approx. 23 and 42 barnyardgrass plants/m2, resp. Although barnyardgrass culms/m2 and straw yield increased as weed density increased, the weed produced more culms/ plant when present at 2 and 5 plants/m2 than at 20-80 plants. In a spatial interference experiment, Lemont grain yield reduction averaged 21% when plants were grown within 0-25 cm of a barnyardgrass plant group (group = 4 plants/140 cm2), but were not reduced when weed plant groups were 25-100 cm away. When Lemont grew between barnyardgrass groups spaced 20 or 40 cm apart, grain yields were reduced 40 and 27%, resp., compared with weed-free rice, but yield was not reduced when rice plants grew between weed plant groups spaced 100 cm apart.