Adsorption and ED₅₀ values of five soil‐applied herbicides

The soil partition coefficients ( K d values) and ED 50 values of carbetamide, isoproturon, propyzamide, trifluralin and pendimethalin were determined on various soil types. Adsorption increased in the order carbetamide < isoproturon < propyzamide < trifluralin < pendimethalin, whereas the influence of soil types on herbicide efficacy increased in the order isoproturon < carbetamide < pendimethalin < trifluralin < propyzamide. The relationship between adsorption and ED 50 values of the herbicides was examined by estimating the herbicide concentration in soil water solution. Adsorption and ED 50 values on common Danish soil types (0.6% carbon and 12% clay to 2.3% carbon and 4.4% clay) differed by factors of up to three and four, respectively, indicating a possibility of adjusting the herbicide dose according to soil factors.