IMPACT OF MINERALOGY ON FIXATION AND RELEASE OF POTASSIUM IN SOILS FROM THREE AGROECOLOGICAL REGIONS OF BANGLADESH

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The impact of mineralogical composition of soil on potassium (K) fixation and release was studied with nine selected soils from three important Agroecological Regions of Bangladesh : Old Himalayan Piedmont Plain, Old Brahmaputra Floodplain and High Ganges River Floodplain. Mica, in variable amounts, was the most dominant mineral in all soils. In addition to mica, smectite and vermiculite were present in considerable amounts in the High Ganges River Floodplain and Old Brahmaputra Floodplain soils, respectively, while the Old Himalayan Piedmont Plain soils contained none of them. In the study of K fixation, three levels (0.3, 0.6 and 0.9 cmol_c kg^<-1>) of K were added to soils for three periods of incubation (15, 30 and 45 days) at two moisture conditions (continuous waterlogging and alternate wetting and drying). Potassium release was studied by successive extractions using three concentrations of the HNO_3 solution (1.0 M, 0.1 M and 0.01 M). Both the K fixation rate and K release potential were the highest in the High Ganges River Floodplain soils followed by the Old Brahmaputra Floodplain soils while the lowest were in the Old Himalayan Piedmont Plain soils. The K fixation and release behaviors of the soils could be related to their mineralogical make-up.
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