Comparison of Adsorption Models for Determining Potassium Behavior in of Some Selected Soil Series

Potassium (K) availability to plants varies with the adsorption characteristics of soil, to evaluate the adsorption capacity, five soil series of different characteristics were used. K adsorption isotherms were performed by equilibrating 2.5 g soil samples with 10 levels of K (30-300 mg kg-1) as KCl in 0.01 CaCl2 solutions and shaken for 24 h at 25oC. The amount of K adsorbed ranged from 33.2 to 94.9% of added K. Freundlich model explained K adsorption behavior better than the other two equations. Higher coefficient of regression values 0.99, 0.97 and 0.96 were recorded in Sultanpur (Silt loam), Naivela (Fine sandy loam) and Bhutesar (Clay loam), respectively. The highest 1/n value 1.54 kg mg-1 and kf value 31.47 mg kg-1 of Freundlich isotherm were observed in Sultanpur (silt loam) due to high pH, high OM and high clay contents, lowest values of constants were observed in Wajan (loamy sand) with 1/n value 0.44 kg mg-1 and kf value 0.28 mg kg-1 might be due to high EC, high CaCO3 and sand contents. The K adsorption of soil varied with physico – chemical characteristics of soil, especially clay content, alkaline pH and organic matter content.