Sorption, Persistence and Movement of Oxyfluorfen In Soils of Andhra Pradesh, India.

Sorption, persistence and movement of oxyfluorfen was studied in soils collected from different agro climatic zones of Andhra Pradesh. Adsorption was studied by Batch equilibrium technique at five different initial concentrations of oxyfluorfen. Adsorption isotherms were conformed to the Freundlich equation. The desorption, persistence and movement process was studied in two selected soils with varying in physico-chemical properties. The desorption exhibited pronounced hysteresis in all the soils, which was more prominent when desorption was carried out at higher concentration of herbicide and the percent cumulative desorption was high in soils with low in organic carbon content of soil. The values of Freundlich constant, Kf were ranged from 0.30 to 3.21 for oxyfluorfen. Persistence of oxyfluorfen was studied at three moisture levels (at saturation, FC and 50 % FC) and at two temperature levels (10+ 2 0C and 27 + 2 0C ) for the period of 137 days in the laboratory. Degradation of oxyfluorfen was more rapid at high temperature and moisture levels. The disappearance curve / semi logarithmic plot followed first order kinetics with two distinct pathways, an initial faster rate followed by a slower and more gradual disappearance. The specific reaction rates and rate constants were calculated from model given by Hamaker and Goring (1976) and activation energy from Arrehenius Equation. Half life values for oxyfluorfen varied from 97.60 to 192.50 in Sandy loam soil and 90.05 to 147.44 in Clay loam soil. Movement studies were carried out using packed soil columns to know the distribution pattern of oxyfluorfen in Sandy loam and Clay loam under saturated and unsaturated conditions. Oxyfluorfen was applied at 20 mg/kg of soil and the soil columns were kept for movement studies at time intervals of 1,3,5,7,15,22 and 37 days. Oxyfluorfen remained primarily in the top soil layers. Under saturated conditions movement of oxyfluorfen was more in sandy loam as compared to Clay loam. Under unsaturated conditions, pendimethalin showed more mobility in Vertisol. The increase in herbicide movement was observed with increase in days.