Zinc Adsorption Isotherms of Soils as Related to Soil Properties

The Langmuir constants describing adsorption sites of dual mechanism for zinc on 10 surface samples covering five major soil types of Karnataka region were investigated. Adsorption maxima at b₁ and b₂ ranged from 0.13 to 0.49 and 0.54 to 3.69 with an average of 0.29 and 1.45 mg/g, respectively. On an average, the b₁ and b₂ values were equivalent to 3.7 and 18.3%, respectively of the cation exchange capacity (CEC). The values of adsorptive bond k₁ and k₂ varied from 0.220 to 1.026 and 0.012 to 0.068 with a mean of 0.454 and 0.037 ppm, respectively. With increased adsorption capacity there is a relative decrease in bonding energy coefficient and vice-versa. Inverse relations, C/C/x/m called as ‘breaks’ or inflection point of part I with part II of these soils expressed in μg/ml are 85 for saline, 124 and 138 for laterite, 180 and 204 for red, 218 and 227 for alluvial, 290 and 334 for black and 292 for sodic soils showing the direct relationship and ability of the soils to adsorb zinc. The Langmuir adsorption maxima (b₂) were related to the soil properties viz, CEC, pH, clay content, organic carbon and calcium carbonate content in a decreasing order of significance.