Transport of Nicosulfuron in Soil Columns
Nicosulfuron (2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide) is a relatively new sulfonylurea promoted for weed control in corn (Zea mays L.). However, there are no published studies on its transport and mobility in soils. In this study, breakthrough curves (BTCs) were measured using soil columns for eight Iowa soils and four Oxisols from Brazil. Chloride (Cl−) and pentafluorobenzoic acid (PFBA) were used as nonreactive tracers. For the sandy Iowa soils and the Brazilian soils BTCs were symmetrical, while for the nonsandy Iowa soils BTCs were asymmetrical. Breakthrough curves were interpreted using convection-dispersion equation and equilibrium and nonequilibrium transport models. In Brazilian soils and sandy Iowa soils equilibrium models described the BTCs well. In nonsandy Iowa soils, where tailing was observed, the data were better described by a two-site/two-region model, indicative of nonequilibrium processes. A comparison with the Cl− and PFBA BTCs suggests that the nonequilibrium is not transport-related. This is also supported by the low correlation between the mass transfer parameters and the partition coefficients. It is proposed that the observed nonequilibrium in nonsandy Iowa soils is most likely due to nicosulfuron chemisorption on smectites. The results of this study indicate that due to rapid sorption of nicosulfuron on smectites its potential to leach to the groundwater should be relatively low in the loamy and clayey soils that contain expandable 2:1 layer silicates.
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