Potassium Fixation Characteristics of Major Benchmark Soils of India

Fixation of added fertilizer potassium (K) is an importanl reaction in the dynamics of soil K and it affects availability of K to crop plants. Twenty two major benchmark soils of India were studied for their K fixation characteristics. Fixation of added K increased with the rate of added K irrespective of soil mineralogy and depth. Surface soils of smectitic Vertisols and vertic sub-groups showed greater K fixation (26 to 32%), followed by illitic Inceptisols, Alfisols, Entisols and Aridisol (23 to 29%) whereas lower fixation values were found for kaolinitic Alfisols and Inceptisols (17 to 23%). In case of subsurface soils, illitic group showed the maximum K fixation followed by smectitic and kaolinitic soils. The overlapings among the soils belonging to different mineralogical groups as regard to the extent of K fixation were ascribed to the composition of the associated minerals in silt and clay fractions of soils. The study highlights the need for more studies on K fixation in relation to the associated minerals in addition to the dominant mineral in a particular soil.