Nonequilibrium transport of pesticides is frequently reported to greatly affect their transport and mobility in soil.Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) is a kind of herbicide that is widely used for selective control of grassy weeds in corn production but poses potential danger to the quality of ground water in China.Consequently, there is interest in predicting its mobility in agricultural soils.The objective of the present study was to apply the one-dimensional convection-dispersion equation based on the local equilibrium assumption model (LEA model) and nonequilibrium assumption model (NEA model, including the two-site model and two-region model) for describing nonequilibrium sorption characteristics of atrazine during miscible displacement in water-saturated homogeneous soil.Soil column experiments were conducted in duplicate with a sandy loamy soil under steady-state flow at a specific pore water velocity.A nonlinear least-squares optimization approach (CXTFIT 2.0) was used to fit breakthrough curves (BTCs) for bromide and atrazine in Exp.1.The symmetrical BTC for tracer bromide was best described by the LEA model, indicating that there were no significant effects of immobile water on transport of bromide (i.e., no significant physical nonequilibrium in this system).The asymmetrical shape and tailing of atrazine BTC showed that atrazine was mainly influenced by chemical nonequilibrium during transport and the best fit to observed atrazine BTC was obtained with the two-site model.Model verification procedures were based on bestfit parameters optimized from the first displacement experiment (Exp.1), and then these fitted parameters were used to simulate the transport of atrazine in the duplicate experiment (Exp.2) by the chemical nonequilibrium model.The results showed that there was a good agreement between measured and simulated concentration variations for atrazine leaching in this soil column.In addition, dynamics of the flux concentration and the cumulative leaching quantity of atrazine at different depths of the soil column in Exp.2 were simulated.This study suggests that the two-site model based on the nonequilibrium theory can be used as a useful approach to better quantifying environmental fate of atrazine in a given scenario.