An incubation study was continued in the net house of the Department of Soil Science, Bangladesh Agricultural University, Mymensingh during Boro season (31 December 2013 to 10 March 2014) to judge the distribution of native and added K in soils and its effect on rice. Seven soil samples viz: BAF (Brahmaputra Alluvial Flooded), BANF (Brahmaputra Alluvial Non-flooded), LBT (Level Barind Tract), GTF (Ganges Tidal Floodplain), OHPP (Old Himalayan Piedmont Plain), NEBT (North Eastern Barind Tract) and MT (Madhupur Tract) were collected from six different AEZs of Bangladesh. In this study, the water soluble, exchangeable and non-exchangeable K of the different soils ranged from 2.30 to 23.40, 27.30 to 163.80 and 234.0 to 877.50 mg kg-1, respectively in non-treated samples. The addition of 100 mg K per kg soil increased the different forms of K. The percent increase here 12.30 to 73.33 for water soluble K, 6.42 to 78.75 for exchangeable K and 6.9 to 35.0 for non-exchangeable K over the initial status. The dry matter yield of different non-treated and treated pots ranged from 2.08 to 4.4 and 3.77 to 5.48 g pot-1. The highest dry matter yield was found in LBT soil for non-treated pots and the lowest in BAF. In case of treated soil, the highest dry matter yield found in OHPP and the lowest in GTF soil.

Key words: K content, soils, AEZ, rice yield.