Study on the Threshold Values of Soil Potassium Parameters for Release and Fixation: A Prognostic Approach to Improve the Use Efficiency of Soil and Fertilizer Potassium

The reserve of nonexchangeable potassium (K), threshold levels for release and fixation of intermediate K, and the Gapon exchange selectivity coefficient for K to calcium (Ca) and magnesium (Mg) exchange were studied in soils of widely varying properties, with a view to optimize the efficiency of native as well as added fertilizer K for plant uptake. The illite-dominated soils recorded greater reserve of nonexchangeable K and showed greater cumulative K release. The threshold values of soil K parameters for release and fixation of intermediate K were found to vary with the change in background electrolyte concentration. The soils dominated by illite were found to possess greater K threshold release and fixation values. In general, the fixation threshold level was greater than release threshold level. The Gapon exchange selectivity coefficient for K to Ca exchange revealed that K ions were more tightly held in the specific sites than in planar sites.