Abstract

Sorption kinetics studies of herbicides, using different models, are an important tool for determining the mechanisms and kinetic parameters that explain the bioavailability and environmental behavior of these compounds. However, little is known about the combined effects of fertilizers and herbicides and how it could modify these processes on the soil. The aim of this study was to evaluate the sorption kinetics of diuron and 2,4-D in an Andisol treated with urea using various kinetic models. The experiments were carried out in batch, independently for each herbicide, with urea application in an equivalent dose of 200 kg N ha(-1) and artificial pH modifications. The results showed no differences in sorption kinetics due to urea for diuron; however 2,4-D showed differences with urea and changes in pH conditions. The data fitted well with the pseudo-second-order model (R-2 > 0.996), showing a maximum soil adsorption capacity of 11.9, 10.8, and 9.61 mg kg(-1) for diuron, 2,4-D, and 2,4-D-urea, respectively. The initial adsorption rate was similar for both herbicides, but a significant increase in the rate constant was observed for 2,4-D at acid pH. We conclude from the Elovich and Weber-Morris models that both herbicides were adsorbed mainly during the first stage, followed by lower adsorption in the slower second stage. According to these models, mass transfer across the boundary layer, and to a lesser degree intraparticle diffusion mechanisms, controlled sorption kinetics for both herbicides. The results suggest that urea application could influence sorption process of acid herbicides for pH changes in soils.