ADSORPTION-DESORPTION KINETICS OF CHLORPYRIFOS INSECTICIDE IN MOLLISOLS

The kinetics of adsorption and desorption of chlorpyrifos in soils of Himalayan tarai (mollisols) were studied using the miscible displacement technique under the laboratory conditions. The adsorption data of chlorpyrifos conformed to the first order kinetics and the computed values of adsorption rate constant (k(ads)) increased with depth and had a significant negative correlation with soil E.C.. The desorption data of chlorpyrifos also fitted well to two phase first order kinetics. However, no soil property individually showed any significant simple correlation with the desorption rate constant of chlorpyrifos (k(1 des)). Adsorption rate constant (k (ads)) could be successfully predicted on the basis of soil sand; clay; organic C; and free iron oxide contents contents and soil E.C.. The faster desorption rate constant (k(1 des)) of chlorpyrifos could be predicted on the basis of soil sand; clay; and organic C contents and soil pH and E.C. while the slower desorption rate constant (k(2 des)) could be estimated using sand; organic C; and free iron oxide contents and soil pH and E.C..