Chlorimuron ethyl sorption and desorption kinetics in soils and herbicide-desiccated cover crop residues
1995
Reddy, K.N. | Locke, M.A. | Wagner, S.C. | Zablotowicz, R.M. | Gaston, L.A. | Smeda, R.J.
Interaction between a herbicide and plant residue on the soil surface in plant residue management systems such as no-tillage or cover crop is of interest in terms of environmental fate of the herbicide. This study was designed to evaluate sorption and desorption of chlorimuron ethyl (ethyl 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl) amino]carbonyl]amino]sulfonyl]benzoic acid) in herbicide-desiccated rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) residues and soils collected from a field. Sorption was determined by reacting 0.5 g of soil or plant residue with 6 mL of [14C]chlorimuron ethyl solution at five concentrations (0.06-12.04 micromoles 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 (0.81-1.03). The N values (0.88-0.95) for soils and plant residues indicated nearly linear sorption. Time course sorption data analyzed by an equilibrium/kinetic model indicated that sorption was initially rapid (within 1 h), followed by a negligible increase in soil or a slow increase in rye and hairy vetch residue. Chlorimuron ethyl Kf increased with increased decomposition of plant residue. 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 CaCl2-desorbable chlorimuron ethyl in two consecutive 24-h cycles ranged from 54 to 65% in soils and from 42 to 49% of that sorbed in plant residues. Two additional 24-h cycles with methanol/(NH4)2CO3 did not completely desorb the remaining chlorimuron ethyl. Under field conditions plant residues can apparently intercept and temporarily retain chlorimuron ethyl.
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