The aim of this study was to investigate the sorption behavior and mechanisms of the organic pesticides on soil. To establish the sorption isotherms of six commonly used pesticides (acetochlor, atrazine, diazinon, carbendazim, imidacloprid, and isoproturon), laboratory equilibrium studies were performed at extended concentration ranges on brown forest soil using the batch equilibrium technique. The pesticide concentrations in the equilibrated liquid phase were quantified with high-performance liquid chromatograph by ultraviolet detection. The adsorption processes could be described by a single-step (Langmuir) isotherm for acetochlor and carbendazim, by a two-step curve for diazinon, isoproturon, and atrazine, and by a three-step curve for imidacloprid. A nonlinear mathematical model-derived from the Langmuir equation-has been developed that represents well the detected single-step and multistep shaped adsorption isotherms. The interpreted model was found to fit the experimental data well and allows the description of the adsorption profile with great precision. The altered adsorption activity, which was indicated by the step arising on the plot, may represent the existence/occurrence of a different specific type of adsorption mechanism. This binding force starts to operate simultaneously at a critical concentration of solute in the studied soil-pesticide system. The parameters calculated from the equation provide an opportunity to estimate the extent of absorption constant, adsorption capacity, and concentration limit characteristic to the measured stepwise isotherms.

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A new, easily applicable soil extraction method has been developed using the coffee percolator principle. The hot water percolation method (HWP) was examined on 36 soils with different properties. During hot water percolation the available, desorbable, easily soluble elements are extracted by hot water (102-105°C) at 120-150kPa pressure. The average time for one extraction is 2.6mm. It is possible to carry out kinetic measurements too. Nearly every nutrient is extracted by this method in measurable quantities, and the macroelements in appreciable quantities. The variation coefficient ( C V % ) of the method is in average 11%. The results are in close correlation with those of conventional soil testing methods and with the nutrient uptake of the sunflower and ryegrass used as test plants.