Effect of density of barnyard grass on the yield of irrigated rice.
Competition by weeds for light, water and nutrients, mainly N, was a major factor causing reduction in rice yield and barnyard grass (Echinochloa crus-galli) was one of the principal weeds of lowland rice in Rio Grande do Sul, Brazil. A field trial was carried out at Pelotas in 1980-1 to study the effect of different densities of barnyard grass on the yield of rice cv. Bluebelle. Yield decreased by 16% with 5 plants/m2, c. 25% with 10-20 plants, 70% with 40-60 plants and by up to 80% with 80-100 plants/m2.