ADSORPTION OF IMAZETHAPYR TO AMENDED AND NONAMENDED SOILS AND HUMIC ACIDS

Soil amendment with municipal sewage sludge affects the total amount a nd chemical nature of soil organic matter, including its humic acid (H A) component. These effects are expected to modify the quantitative an d mechanistic aspects of herbicide adsorption to soil. The magnitude a nd mechanisms of adsorption of the imidazolinone herbicide, imazethapy r, to sewage-sludge amended and nonamended soils, and their HA compone nts, were studied using a batch equilibrium method coupled with high-p ressure liquid chromatography, and by Fourier-transform infrared (FT-l R), fluorescence and electron spin resonance (ESR) spectroscopic techn iques. Sludge-amended soils exhibited nonlinear, L-shaped adsorption i sotherms, and much higher adsorption capacity than nonamended soils, w hich had linear isotherms. Soil-isolated HAs had nonlinear, L-shaped i sotherms and adsorbed imazethapyr in amounts much higher than the corr esponding whole soils. Spectroscopic data indicate that imazethapyr ma y interact with HAs through multiple-binding mechanisms including ioni c, charge-transfer, and hydrogen bonds. Results of this work indicate that organic matter applied as sludge amendment to soil is able to inc rease the magnitude and modify the mechanism of imazethapyr adsorption to soil, and confirms the prominent role played by HAs in this proces s.