SORPTION AND DESORPTION OF ATRAZINE BY SLUDGE-AMENDED SOIL - DISSOLVED ORGANIC-MATTER EFFECTS

Addition of insoluble and soluble organic C to soil through management practices, such as sewage sludge (SS) application, may greatly alter pesticide sorption-desorption in soil. Ratch equilibrium techniques me re used to determine the effects of four sewage sludges (liquid-SS, so lid-SS, limed-SS, and composted-SS) and their water dissolved organic matter (DOM), on the sorption-desorption of atrazine loro-4-ethylamino -6-isopropylamino-1,3,5-triazine) by a silt loam soil. Atrazine sorpti on on the sludges increased in the order: limed-SS < liquid-SS < solid -SS < composted-SS. Sludge addition to soil increased atrazine sorptio n in the same order, although the effectiveness of the mixtures to sor b atrazine was lower than expected from the sorption capacity of the i solated soil and sludges. The effects of the DOM extracted from the di fferent sludges on atrazine sorption varied with sewage sludge, For li quid-, solid-, and limed-SS, DOM reduced atrazine sorption on soil. A low association between these DOMs and atrazine was measured In soluti on by dialysis technique, and indicated that processes st the soil/sol ution interface may have contributed to reduce atrazine sorption, In c ontrast, enhanced atrazine sorption in the presence of DOM extracted f rom composted-SS indicated atrazine was hound by DOM associated with t he soil. Atrazine desorption from sail increased in the presence of DO M from all four sludges; however, DOMs had little effect on atrazine d esorption from sludge and from sludge-amended soil. Interactions of so il surfaces with organic amendments and their DOM are shown in this wo rk as a major process determining atrazine sorption-desorption in amen ded soil.