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Abstract
Herbicide retention by residue mulch in vegetative filter strips could be an effective attenuation mechanism for removing herbicides from runoff. Adsorption studies were conducted to quantify the amount of atrazine and metolachlor that can be adsorbed and removed from runoff by thatch or fresh switchgrass residue. Adsorption of C14‐atrazine and metolachlor on thatch or fresh switchgrass residue was conducted by using concentrations of 2.5, 7.5, 13.2, and 26.4 µmol L−1 and a 24‐h equilibration period. Adsorption coefficients (Kd) decreased in the order, atrazine sorption on fresh switchgrass residue (81.1 L−1 kg−1), metolachlor sorption on fresh residue (32.9 L−1 kg−1), atrazine sorption on thatch residue (21.4 L−1 kg−1), and metolachlor sorption on thatch switchgrass residue (15.1 L−1 kg−1). On a volumetric basis (Kd-vol), only atrazine showed a significantly greater Kd-vol value on fresh residue than on the thatch residue. Absorption through cut ends of the residues (especially the fresh residue) may have produced adsorption capacities that would not be observed under field conditions. Fresh or thatch switchgrass residue in vegetative filter strips can help abate atrazine and metolachlor by intercepting and sorbing some of the herbicides.