Influence of different factors on the adsorption of phosphamidon on soils

The effect of exchangeable cations (H⁺ and Na⁺), organic matter and temperature on the adsorption of phosphamidon on two different types of Indian soils was studied. The adsorption isotherms for all the effects/treatments were in close agreement with the Freundlich equation and yielded (S) shaped isotherms. The amount adsorbed in all the cases was lower in tarai loam soil than black silt clay loam soil and was related to organic matter content, clay content, CaCO₃ content, surface area and CEC of the soils. The adsorption on both the soils follows the order as H‐soil > Na‐soil > natural soil at 25°C > natural soil at 50°C > organic matter removed soil. This order of adsorption was in accordance with Freundlich constant K values and distribution coefficient K _d‐values. The adsorptive capacity of phosphamidon for organic matter and clay content for both the soils was. also evaluated by calculating K_om and K_c values and found that phosphamidon adsorption was slightly better correlated with clay content than organic matter content. On the basis of adsorption isotherms, various thermodynamic parameters such as thermodynamic equilibrium constant (K_o) standard free energies (?G°), standard enthalpies (?H°) and standard entropies (?S°) changes have been calculated for predicting the nature of isotherms.

Key Words:

• Phosphamidon
• organophosphate
• insecticide
• soil adsorption