Adsorption and Persistence of Metalaxyl in Soils

The adsorption of metalaxyl was mainly influenced by clay content of the soils. Freundlich equation provided a good fit (R²>0.9) for adsorption of metalaxyl in all the soils. The Freundlich constant K values for metalaxyl ranged from 5.87–7.28. The values for 1/n were less than unity indicated non-linear relationship. The sorption coefficients for organic carbon (K_oc) ranged from 362–2275. The Gibb's free energy (“G°) was negative indicating that the adsorptton reaction is exothermic. The degradation pattern of metalaxyl residues indicated a close correspondence to first order exponential degradation kinetics in soils. The rate of degradation was faster at lower compared to higher appllcation rate. Among the factors studied, the soil moisture at field capacity and temperature of 25°C were found to accelerate the degradation of metalaxyl in the soils. However, the persistence of metalaxyl residues was higher at air-dry moisture, 15°C temperature and sterile soil conditions. Slower degradation of metalaxyl was noticed in the soils and their half-life values ranged from 41.2–165.1 days.