Cadmium Sorption Behaviour of Coffee-growing Soils of South India

Cadmium (Cd), a potentially hazardous pollutant in the environment, finds its way into soil through phosphate fertilizers and sewage sludge applied for supply of essential nutrients to crop. Potential toxicity of a trace metal like Cd depends on its concentration, speciation and soil physicochemical properties. Application of rock phosphate as a phosphorus (P) source is a common practice in slightly acidic coffee-growing soils which invariably carries sufficient Cd to interfere with the normal growth and performance of coffee plants. In order to understand the adsorption pattern of externally applied Cd through fertilizers as influenced by soil physicochemical properties a laboratory experiment was conducted. Soils representing four major states of South India, viz. Karnataka, Kerala, Tamil Nadu and Andhra Pradesh were selected to represent the coffee bastion of the country. Batch equilibration technique was employed to study the adsorption pattern. The results indicated that Cd was adsorbed in very low quantities by all the four soils under study. Cadmium adsorption was highly dependant on soil pH, cation exchange capacity, clay content and oxides of iron and manganese. The Cd adsorption data fitted well to both the Langmuir and Freundlich equations.