Weed‐Crop Competition Models and Response‐Surface Analysis of Red Rice Competition in Cultivated Rice: A Review

Models that predict crop yield based on crop and weed densities are valuable for estimating yield losses and devising weed control strategies. Field experiments were conducted in 1987 and 1989 to evaluate a model describing the competitive interaction between red rice ( Oryza sativa L), a weedy variety, and the commercial cultivar, Mars. The response‐surface model consisted of nonlinear yield‐density equations where average per‐plant yield was the dependent variable and the densities of the competing plant varieties were the independent variables. Yield was measured as both grain yield and the number of seeds. The model predicted the maximum yield of an isolated plant, the area associated with the maximum yield per plant, and competitive ability. Each year, the predicted maximum yield of an isolated red rice plant was greater than that for Mars. Similarly, the parameter describing the area associated with maximum yield per plant was larger for red rice. Red rice was the dominant competitor; the model indicated that it took approximately three Mars plants to have the same effect on the grain yield of Mars as only one red rice plant. With respect to red rice, competition was primarily with plants of the same variety, whereas for Mars, competition with plants of the other variety was more important.