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Adsorption and desorption kinetics are essential components for modeling the fate of pesticides in soils. This study was conducted to characterize the kinetics of alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl) acetamide] adsorption and desorption in Gigger (fine‐silty, mixed, thermic Typic Fragiudalf) surface soil samples collected from long term no‐till and conventional tillage plots. A batch method was used to determine alachlor adsorption with time up to 528 h for a range of input concentrations from 0.5 to 50 mg/L. Successive dilution was used to quantify desorption kinetics following 16, 32, 64, 128, 256, and 512 h of adsorption. For both samples, alachlor time‐dependent results indicated initially fast adsorption followed by slow adsorption where kinetic reactions appeared dominant. Adsorption‐desorption showed extensive hysteretic behavior resulting from discrepancies between adsorption and desorption isotherms. Hysteresis was more pronounced with increased reaction time of adsorption. Four variations of a nonlinear multireaction kinetic model successfully described retention results. Adsorption and desorption, however, were best described by a model version incorporating nonlinear equilibrium, a kinetic reversible mechanism, and a consecutive irreversible mechanism. The model was successfully used in describing alachlor adsorption and desorption results. The model predicted the overall alachlor hysteresis satisfactorily except that, at large times, desorption isotherms were not considered adequate. The model also was capable of predicting alachlor desorption kinetics based solely on parameters obtained from adsorption experiments.

Several heat-based methods, such as soil solarization, are being developed as alternative practices for managing soil-borne pests and pathogens. The effectiveness of these practices is often inconsistent or marginal, thus commanding the need for their integration with other methods. The main objective of this study was to determine synergistic interaction between soil fumigants and temperature. Soil infested with citrus nematode Tylenchulus semipenetrans was exposed to methyl bromide or 1,3-dichloropropene at various temperatures. Fumigant degradation was concurrently measured and concentration-time index (ct) was calculated and correlated to the recovered nematode population. In untreated soil, nematode survival was not affected by temperatures of 20±30°C, but was strongly reduced at ! 40°C. In fumigated soil, nematode suppression was much greater at 30°C than at 20°C, and the ct required for nematode elimination at 30°C was`50% of that needed at 20°C for both fumigants. These results suggest that these fumigants became more active with increasing temperature in the sub-lethal temperature range. It also implies that, when integrated with a heatbased practice, reduced rates of fumigants may provide adequate pest control, thus minimizing the environmental input of chemical fumigants.

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