Adsorption-desorption of tricyclazole: effect of soil types and organic matter.

Adsorption-desorption of tricyclazole was studied by batch equilibrium method in two soil types, varying in their physical and chemical properties. The adsorption of tricyclazole on the soil matrix exhibited low rate of accumulation with 18.24 ± 0.14 % in Ultisol and moderately high rate with 43.62 ± 0.14 % in Vertisol after 6 h of equilibrium time. For soils amended with farmyard manure (FYM), the adsorption percentage increased to 32.52 ± 0.14 % in Ultisol and 55.14 ± 0.14 % in Vertisol. The Freundlich model was used to describe the adsorption-desorption of the tricyclazole in two soils. The adsorption isotherm suggested a relatively higher affinity of tricyclazole to the adsorption sites at low equilibrium concentrations. Variation in sorption affinities of the soils as indicated by the distribution coefficient (K d) for sorption in the range of 0.78 ± 0.01-1.38 ± 0.03, 1.71 ± 0.03-2.99 ± 0.09, 2.75 ± 0.05-4.69 ± 0.01, and 4.65 ± 0.08-7.64 ± 0.01 mL/g for Ultisol, FYM-amended Ultisol, Vertisol, and FYM-amended Vertisol, respectively. Desorption was slower than adsorption, indicating a hysteresis effect. The hysteresis coefficient varied from 0.023 ± 0.15 to 0.160 ± 0.12 in two test soils. A good fit to the linear and Freundlich isotherms was observed with correlation coefficients >0.96. The results revealed that adsorption-desorption was influenced by soil properties and showed that the maximum sorption and minimum desorption of pesticide were observed in soils with higher organic carbon and clay content. Thus, groundwater contamination may be minimized, on application of tricyclazole in high-sorption soils of rice-growing regions.