Evaluation of Potassium Status Using Thermodynamic Relationships in some Soils of Ismailia Governorate, Egypt

Abstract

Quantity – intensity (Q/I) isotherms were used to evaluate the dynamics of potassium in eight soil samples of Ismailia Governorate, Egypt. The results showed that the potassium activity ratio (ARek) values for all soils increased as the K+ concentration of the equilibrating solutions increased. El Qantara West soil had the highest ARek value (12.0 (mole l-1)0.5 × 10-3) while Eltal Elkebier soil had the lowest value (3.20 (mole l-1)0.5 × 10-3). El Qantara West soil had the highest labile K value (0.56 cmole Kg-1 soil), while the Eltal Elkebier soil had the lowest labile K value (0.10 cmole Kg-1), and the exchangeable K in this sample was higher than the labile K. The results showed that the potassium potential buffering capacity (PBCk)values of the investigated soils ranged between 23.1 and 46.7 (cmole Kg-1) / (mole l-1)0.5. Free energy (-ΔG) values ranged between 4.36 - 5.70 Kcal mole-1. In addition, the results showed that the Gapon selectivity coefficient (KG) varied between 3.81 and 51.9. The exchangeable K and -ΔKeo had a positive correlation coefficient (r = 0.70). AReK values were highly correlated with logarithmic values (pK- 0.5pCa+Mg) obtained from equilibration of a single sample (r = -0.87). The potential buffering capacities were highly correlated with the exchangeable K (r = 0.83). Q/I parameters were influenced by soil properties and K forms. It could be used to sustained K fertilizer management in order to rationalize and increase fertilizer use efficiency (FUE).