EXTRACTION METHODS AND ADSORPTION KINETICS OF POTASSIUM IN CALCAREOUS SOILS OF MULTAN

Abstract

Understanding the dynamics of potassium (K) and its availability is fundamental in its efficient use as an important nutrient. The objectives of present study were to compare standard K extraction methods for extractable K and kinetics of K adsorption on five different textured soils. The soils were analyzed for physico-chemical properties, extractable K contents and kinetics of K adsorption. The soils had variable contents of soluble (8-52mg kg^-1), exchangeable (13-215mg kg^-1), fixed (488-1836mg kg^-1), structural (2936-26362mg kg^-1) and total K (3438-28517mg kg^-1). Except soluble K, the amount of K in different forms was significantly (P?0.05) correlated with clay contents, electrical conductivity (EC), cation exchange capacity (CEC) and calcium carbonate in soils. Different methods variated the extracted K in different textured soils. Mehlich-III, ammonium acetate, AB-DTPA, and calcium chloride extracted K was maximum in sandy clay loam (298mg kg^-1, 267mg kg^?1, 226mg kg^-1, and 113mg kg^-1) and lowest was in loamy sand (33mg kg^-1, 24mg  kg^-1, 30mg kg^-1, and 24mg   kg^-1) respectively. Elovich and power function models best explained the K kinetics adsorption, as rate of adsorption constants were negatively correlated with sand contents in the soil type. Pearson correlation showed that the extractability of K by different methods and kinetics of K adsorption were dependent on soil texture EC, CEC and calcium carbonate contents. Hence, soil physico-chemical properties should be considered in recommending rate of K fertilization along with crop K demand and soil extractable K.