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THE IMPORTANCE OF THE POTASSIUM BUFFER POWER ON THE CRITICAL POTASSIUM LEVEL IN SOILS

We studied the relationship between the K+ buffer power and the critical K+ concentration of the soil solution in pot experiments with Italian ryegrass. Critical K+ concentration is defined as that K+ concentration of the bulk soil solution below which plants respond by a yield increase when K fertilizer is applied. The K+ concentration of the soil solution was measured indirectly by means of the electro-ultrafiltration technique. The K+ buffer power was obtained by plotting the exchangeable K+ against the K+ concentration of the bulk soil solution. The steepness of the resultingcurve reflects the K+ buffer power. Nine soils differing widely in clay content, CEC, and K+ buffer power were used for the investigation. A very close correlation (r2 = 0.908) was found between the K+ buffer power and the critical K+ concentration of the soil solution. This relationship was reflected by a hyperbola (y = c/x), indicating that the critical K+ concentration was lower the higher the K+ buffer power was.