The adoption of new weed management methods for flooded rice, aiming to reduce the use of herbicides requires quantitative knowledge about the weed-crop interference relations. The objectives of this research were to evaluate flooding start timing influence on the rice crop and barnyardgrass interference in the crop, as well as to compare the explicative variables plant population, dry weight, soil covering and leaf area to identify the one providing a better data adjustment to the model. Thus, a trial was carried out during the 2005/2006 growing season, arranged in a completely randomized design, with no replication. The treatments were flooding timing at: 1, 10 and 20 days after herbicide treatment (DAT), and barnyardgrass populations of 0, 6, 8, 14, 20, 28, 42, 66 and 200; 0, 4, 6, 50, 66, 88, 92 and 200; 0, 10, 12, 32, 42, 74, 166, 174 and 178 plants m-2, for flooding at 1, 10 and 20 DAT, respectively, resulting in 26 experimental units. Crop yield loss in function of the explicative variables population, canopy dry mass, leaf area and soil coverage of barnyardgrass plants were related by the rectangular hyperbole non-linear regression. The rectangular hyperbole appropriately estimates crop yield loss of flooded rice due to barnyardgrass interference. Flooding anticipation modifies the competitive ability of rice plants cv. BRS-Pelota in relation to barnyardgrass plants. The variable plant population fits better to the model, when compared to the other variables.
competition; integrated managements; nonlinear models
