Influences of Charcoal Amendment on Adsorption-Desorption of Isoproturon in Soils

In order to prevent pesticide leaching from soil, the effects of charcoal amendment on adsorption-desorption of isoproturon in soils were studied and the mechanisms in reducing the loss of isoproturon from soils were suggested. Adsorption-desorption of isoproturon in five different particle sizes of charcoals and three different soils were studied using batch equilibration technique. The results showed that the experimental data were well fitted by the Freundlich empirical equation. Charcoal had a great adsorption capacity for isoproturon, and the smaller the particle size of charcoal, the more the adsorption of isoproturon. The amendment with charcoal could greatly improve the adsorption of isoproturon in soils. The adsorption of isoproturon in soils increased with the rate of charcoal amended (r = 0.9568, P < 0.01). Desorption of isoproturon from charcoals and soils showed significant hystersis which was shown by the higher adsorption slope (1/n(ads)) compared to the desorption slope (1/n(des)). The hysteresis effects of charcoal on desorption of isoproturon were closely correlated with the content of charcoal in the soils, and the hysteresis index (H) increased with the rate of charcoal amended. Observation of environmental scanning electron microscopy (ESEM) exhibitted the fine pore structure and special surface characteristics of the tested charcoal. Analysis of Fourier transform infrared spectra (FTIR) of isoproturon adsorbed on charcoal suggested probable bonding interactions between isoproturon and charcoal. This research suggests that charcoal amendment may be an effective management practice for controlling pesticide desorption and leaching in soils.