Release Kinetics of Nonexchangeable Potassium in Some Soils under Pistachio of Rafsanjan Region

Nonexchangeable potassium has a critical role in crops nutrition, therefore the study of nonexchangeable release rate in cultivated lands is necessary. Information about release kinetics of nonexchangeable potassium in Kerman province soils is limited. In this research 15 soil samples were collected from Rafsanjan lands under pistachio trees and mineralogical properties and release kinetics of nonexchangeable potassium using successive extraction with 0.01 M CaCl2 were determined. In order to determine correlation coefficient between the constant rate of kinetics equation and potassium concentration in pistachio leaf, leaf samples were collected from studied sites. Results indicated that montmorilonite, illite and chlorite clays are present in studied region and between kinetics equations including zero order, first order, second order, parabolic diffusion, power function(two constant rate) and elovich, according to R2 and SE values, power function model is able to describe nonexchangeable release rate satisfactorily. Constant rate values for this model varied between 57.83- 107.86. Constant rate of studied equations have not significant correlation with the potassium concentration of pistachio trees. It is recommended that release rate of nonexchangeable potassium be studied with other methods and extractants.