Adsorption-desorption, Mobility and Degradation behaviour of Kresoxim-methyl and acid Metabolite in Delhi Soil

Kresoxim-methyl, a new broad spectrum foliar-applied strobilurin group of fungicide, undergoes rapid transformation in soil to form acid metabolite. In this paper, adsorption-desorption, leaching and persistence behaviour of kresoxim-methyl and its acid metabolite in Delhi (Inceptisol) soil has been investigated. The adsorption studies were carried out at initial concentrations of 1.5, 1, 0.8, 0.5 and 0.2 μg ml for kresoxim-methyl and 5, 2, 1, 0.5 and 0.2 μg ml for acid metabolite. The Kd values for kresoxim-methyl and acid metabolite varied from 3.72-14.58 and 1.34-2.84 in test soils. On the basis of 1/n values, adsorption isotherms were classified as Stype. Around 11.626.8% and 38.1-80.4% of kresoxim-methyl and acid metabolite were desorbed in three desorption cycles. Lower values of Kd, KF and higher values of hysteresis coefficients observed for acid metabolite indicate its leaching potential. Leaching studies revealed that in column soil >90% of the kresoxim-methyl undergo hydrolysis and changed into acid metabolite. Acid metabolite showed more leaching potential than the parent molecule. Increasing the organic matter content of the soil by sludge amendment (5%) reduced the leaching potential of both the compounds. Degradation of kresoxim-methyl in Inceptisol was studied under different moisture regimes. In the present study, quantification has been done on the basis of residues of kresoxim methyl alone and the total residues (sum of parent + acid metabolite), because for the purpose of monitoring of soil, residues of acid metabolite were also considered along with the residues of parent molecule. In dissipation studies, faster dissipation of kresoxim-methyl and total residues was observed in submerged soil conditions (T1/2 0.5 and 5.2 days) followed Ashish Khandelwal et al 212 by field capacity (T1/2 0.9 and 33.8 days) and air dry (T1/2 2.3 and 51.0 days) conditions.