The objective of this study was to evaluate the effect of spatial variation of pH and organic matter of a Dark Red soil, under different managements, on imazaquin herbicide sorption. Soil-water sorption partitioning coefficient (Kd) was used in surface soil samples collected at 0-15 cm layer in a 38 ha area, under central pivot irrigation and with till and no-till management. Herbicide sorption was most strongly related to soil organic matter content and pH, revealing greatest sorption in lower pH values with greater soil organic matter content. These samples were collected at no-till management area. The pH effects on imazaquin retention occur either by controlling the organic matter ionization form as also its speciation. The clay content in the whole area had no variation, however, it didn't affect the Kd values. Using multivariate regression and two independent variables (soil organic matter content and pH), the prediction of herbicide sorption by soil was good (R² = 0.91).
imidazolinone; site-specific management; organic matter; pH; conventional-tillage
