The rate of herbicide required to reduce growth of grain sorghum (Sorghum vulgare, Per. ‘Pioneer 8417′) by 50% (GR50) and soil adsorption coefficients (Ka) were determined for the experimental herbicide, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, in 14 soils. A linear correlation analysis was conducted between GR50 values and the chemical and physical properties and fluridone absorption coefficient (Ka) for 14 soils. The GR50 values were significantly correlated to soil organic matter and Ka. A stepwise regression analysis suggests that Ka or organic matter content can be used to predict the rate of fluridone application required for herbicidal activity.
