Sorption – desorption of imidacloprid insecticide on Indian soils of five different locations

Sorption-desorption processes govern the movement of all chemicals including pesticides in soils. The present investigation was undertaken to study the sorption-desorption of imidacloprid, using a batch method, on soils of five different location of India. Sorption data were fitted to Freundlich isotherm. The log K value was the highest for loam type soil (1.830) and the lowest for clay type soil (1.661). The value of 1/n was the maximum for silt loam soil (0.909) but minimum for loam soil (0.723). Simple correlation analysis indicated that among soil properties only electrical conductivity showed a higher but marginally non-significant negative correlation with log K (r = -0.826) indicating that higher concentration of solutes solutes are conducive to low sorption capacity of soil. The desorption data conformed to two surfaces Freundlich desorption isotherm. The values of 1/n1' corresponding to easily desorbed fraction of imidacloprid showed significant negative correlation with soil pH (r = -0.886, significant at p ≤0.05) but significant positive correlation with clay content (r = 0.980, significant at p ≤0.01). The desorption index for easily desorbed fraction of imidacloprid (n1’/n) also had significant negative correlation with soil pH (r = 0.953, significant at p ≤0.05). From cumulative desorption data, it appeared that bioavailability of imidacloprid would be lower in neutral soil than acidic or alkaline soils.