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Title: CHLORIMURON SORPTION AND DESORPTION KINETICS IN SOILS AND HERBICIDE DESICCATED COVER CROP RESIDUES

Author
item Reddy, Krishna
item Locke, Martin
item Wagner, Stephen
item Zablotowicz, Robert
item Gaston, Lewis
item Smeda, Reid

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Herbicide interactions with plant residues on the soil surface in a no-tillage or a cover crop system is of interest in terms of efficacy and environmental fate of herbicide. Chlorimuron sorption and desorption in herbicide-desiccated rye and hairy vetch residues and soils collected from a cover crop system was evaluated. The sorption of chlorimuron was highest in hairy vetch followed by rye and soils from no cover crop or beneath plant residue. Time- course sorption data analyzed by an equilibrium/kinetic model indicated that sorption was initially rapid (within 1 h), followed by negligible increase in soil or increase in rye and hairy vetch. Chlorimuron sorption increased with increased residue decomposition. Sorption for rye and hairy vetch residued sampled at 11 weeks after soybean planting increased by 54% and 49%, respectively, compared with residues sampled at planting. Four, 24-h desorption with CaCl2 and methanol:(NH4)2CO3(2 cycles each) did not completely desorb the chlorimuron. Under field conditions, any plant residue on the soil surface can intercept and retain chlorimuron. Partial retention of chlorimuron by plant residues may retard lateral and downward movement of herbicide, thus reducing off-site movement and subsequent adverse impact on the environment.

Technical Abstract: Interaction between a herbicide and plant residue on soil surface in plant residue management systems such as no-tillage or cover crop is of interest in terms of efficacy and environmental fate of herbicide. Study was designed to evaluate sorption and desorption of chlorimuron in herbicide-desiccated rye and hairy vetch residues and soils. Sorption was determined by reacting 0.5 g soil or plant residue with 6 mL of 14**C-chlorimuron solution at five concentrations (0.06 to 12.04 umol L**-1) for 72 h. Freundlich Kf was highest in hairy vetch (6.33) followed by rye (3.95) and soils from no cover crop or beneath plant residue (0.81 to 1.03). The N values (0.88 to 0.95) for soils and plant residues indicated nearly linear sorption. Time-course sorption data analyzed by kinetic model indicated that sorption was initially rapid (within 1 h), followed by negligible increase in soil or slow increase in rye and hairy vetch residue. Chlorimuron Kf increased with increased residue decomposition. The Kf for rye and hairy vetch residues sampled at 11 weeks after soybean planting increased by 54% and 49%, respectively, compared with residues sampled at planting. Two 24-h desorptions with either CaCl2, or methanol:(NH4)2CO3 did not completely desorb all the chlorimuron. Under field conditions, plant residues can apparently intercept and temporarily retain chlorimuron