Potassium Quantity-Intensity Ratio of Some Soils of Iran and Correlation of its Parameters with Selected Soil Properties

Quantity-intensity (Q/I) curves and their derived parameters provide general information about soil K availability. This investigation was conducted to obtain Q/I parameters and to study the relationships between the Potassium Q/I parameters and the properties of 15 soils from central and northern Iran. Soil samples were equilibrated with solutions containing different potassium activity ratios (ARk). Changes in potassium concentrations in the equilibrium solution (ΔK) were plotted against activity ratio of K, and Q/I parameters were determined. Correlations between Q/I Parameters and some properties of soils were studied. The Q/I plots showed the common shapes described in the literature whereas high variations were observed in the soils with respect to AR°, ΔR°, BPCk and Kx. The potassium activity ratio at equilibrium ranged from 0.005 to 0.532 with an average of 0.02 (mmol L-1)0.5. The potassium potential buffering capacity (PBCk) ranged from 4.40 to 76.3 with an average of 16.2 (mmol kg-1) / (mmol L-1)0.5. The readily exchangeable potassium (ΔK°) ranged from 0.007 to 0.737 with an average of 0.25 cmol kg-1 and slowly exchangeable potassium (Kx) ranged from 0.023 to 0.55 with an average of 0.3 cmol kg-1. Highly significant linear correlations were found (α=0.01) between PBCk and CEC (r=0.66), AR° and exchangeable potassium percentage (r=0.76), AR° and solution potassium (r=0.89), and between ΔK° and exchangeable potassium (r=0.79). Because of high variations in physicochemical properties of soils, correlation coefficients between Q/I parameters and soil properties were not very high.