Soil Adsorption and Volatility of Dinitroaniline Herbicides

Abstract

Studies were conducted to determine both the extent and relative strengths of adsorption of twelve dinitroaniline herbicides to a Piano silt loam soil. The effects of soil on the growth of foxtail millet [Setaria italica(L.) Beauv.] in vitro on agar media containing 1.0 and 0.1-μM concentrations of the various herbicides and on the relative phytotoxicities of herbicide vapors arising from the agar media to the same species were also measured. Although considerable differences in the extents and strengths of adsorption of the respective herbicides to soil were noted, correlations with herbicide performance under field conditions were low. Extrapolation of laboratory results to a Piano silt loam soil under field conditions suggests that field applications of 0.32 kg/ha of the respective herbicides might result in herbicide concentrations between 0.00062 and 0.026 ppmw in the soil solution. These concentrations appeared to be less than those necessary to produce substantial plant injury from most of the dinitroaniline herbicides. High correlations between the effects of herbicide vapors on growth of the foxtail millet under laboratory conditions and the relative effectiveness of seven of the herbicides under field conditions suggest that absorption of vapors of the dinitroaniline herbicides by plants may be more important than absorption of the herbicides from soil solutions.