Soil properties as factor influencing the adsorption and mobility of penconazole in vineyard soils

Resumen

A study was made of the adsorption and mobility of the fungicide penconazole (1-[2-(2,4-dichlorophenyl)pentyl]-1H-1,2,4-triazole) in 19 vineyard soils with low organic matter contents (0.31-1.98%) and in seven uncropped soils from oak and beech forests or grasslands with higher organic matter contents (3.30-8.24%). Adsorption isotherms were obtained using the batch equilibrium technique, and mobility was studied using soil thin layer chromatography. The aim of this study was to evaluate the adsorption and mobility behavior of this relatively new fungicide in vineyard soils. The adsorption isotherms fit the Freundlich adsorption equation, the Kf values ranged between 10.3 and 151, and the nf values were always lower than unity. The Kf constants were correlated positively with the soil organic matter content. According to the r2determination coefficients, the organic matter content accounted for 85% of the variance in adsorption when all soils were considered together and for 76% and 36%, respectively, when considering the natural and vineyard soils. In no case was any influence of clay or silt contents on adsorption observed. According to the Rf values obtained, penconazole is immobile in 8% of soils and slightly mobile in 92% of soils. Adsorption of the fungicide by individual soil components, clay minerals and humic acid, confirms the importance of the organic matter fraction as the only soil parameter that affects adsorption. The results obtained indicate that vertical leaching of penconazole is low. The fungicide may, however, cause surface pollution of the soil because of its accumulation. If its degradation rate is low, this accumulation may lead to the pollution of surface water through runoff of the sorbed pesticide. (Soil Science 2000;165:951-960).