Fig. 1. Effects of barnyard grass on allelopathic activity (A) and momilactone B concentration in rice (B). Fifty rice seedlings were incubated with (Mixed-) or without (Mono-) 50 barnyard grass seedlings for 10 days, and allelopathic activity of rice extract was determined by barnyard grass bioassay. Bioassay concentration was one rice plant equivalent extract/mL. Allelopathic activity (%) was determined by the formula: [(control plant length − plant length treated with rice extract)/control plant length] × 100. Control bioassays did not contain rice extract. The bioassay was repeated six times using a randomized design with 10 plants for each determination. Momilactone B concentration was also determined in rice seedlings. The experiment was repeated six times with three assays for each determination. Different letters show significant difference (P < 0.01) according to Tukey’s HSD test.