POTASSIUM STATUS IN SOME LEBANESE SOILS

This study was conducted to evaluate K content and availability in Lebanese soils using the traditional methods of K measurement, K-thermodynamics and K-kinetics measurements. Nine surface soil samples (0-30 cm) were collected from major agricultural regions in Lebanon and were later exposed to the following laboratory measurements. Extraction of K with H2O, 1N NH4OAc and 1N HNO3, and calculation of: K-fixation capacity, ionic strength, K-activity ratio, free energy of replacement (- ∆F), Q/I relationship. Five K-kinetic equations were compared by applying the least square regression analysis to determine the suitable ones for describing K release from soils. The results showed that the tested soil samples varied widely in K contents and K supplying power to plants. According to NH4OAc and HNO3 extraction methods, the K levels of samples 5 is high, 7 is medium, 9 is medium/low and the other 6 samples are low. The values of H2O-K didn’t follow the same order. The values of KSP were low in all samples except 5 & 6. The amounts of fixed K in the studied samples varied from 1.53 Cmol.Kg-1 to 5.02 Cmol.Kg-1. The activity ratio values ranged between 0.0008 and 0.018. The values of free energy of replacement (- ∆F) showed that soils 5 and 6 have medium K supplying power. The values of K-buffering capacity ranged between 22.0 Cmol.Kg-1/mol/L and 297.8 Cmol.Kg-1/mol/L. The values of labile K were lower than those of available K. This means that a part of exchangeable K exists on sites with high bonding energy. The release capacity ranged between 9.5 % and 59.1%. From the five mathematical models which were tested, the first order equation was the most suitable and was selected to determine the release rate coefficient of K. The results show that K content in Lebanese soils differs widely and the results of soil testing should be compared to field responses