SORPTIVE BEHAVIOR OF THE NEEM-BASED BIOPESTICIDE, AZADIRACHTIN, IN SANDY LOAM FOREST SOIL

Adsorption-desorption of azadirachtin-A (AZ-A) was studied at pH 4.0 a nd 7.0 in sterilized and unsterilized sandy loam forest soil, by batch equilibrium method, using RH-9999(R), an experimental wettable powder (WP) formulation containing 20% of AZ-A. Data generated were fitted t o linear, Freundlich and Langmuir adsorption isotherms. Adsorption of AZ-A to the soil was not high and decreased with increasing pH. Differ ences observed in the adsorption between sterilized and unsterilized s oil were attributed to alterations in soil porosity and aggregation of soil particles. The K-D and K-F parameters, and the Freundlich expone ntial term (1/n) were low, indicating that the interactions between th e soil particles and AZ-A molecules were weak due to physical forces a nd H-bonding. Desorption studies showed that the adsorbed AZ-A was not firmly retained by the soil particulates and was reversible, If micro bial degradation is not high, desorbed AZ-A leaching to lower soil hor izons is possible. The soil parameters, K-OC and K-OM, were calculated using the K-D and the measured percent OC and OM values. Also, K-OC w as computed by using the K-OM and the Van Bemmelen factor, and the two K-OC values were compared.