Availability and fixation of added potassium in rice soils of West Bengal

An incubation experiment on potassium fixation and availability in six rice soils of West Bengal was conducted at varying levels of added K. Amount of K fixed increased in all the soils with the increase in applied K from 15 to 240 mg kg-1 soil, however, the percentage of added K fixed decreased gradually. The K fixation could still increase upon addition of higher levels of added K beyond 240 mg kg-1 soil. Illite and smectite dominant Inceptisols with high available and reserve K showed a lower K fixation (4.9 to 39.6 mg kg-1 soil) as compared to illite dominant Entisols (5.5 to 41.0 mg kg-1 soil) containing moderate available and reserve K. Conversely, kaolinite dominant Alfisol with low available and reserve K registered the lowest amount of K fixation (2.5 to 14.9 mg kg-1 soil). Maximum per cent K fixation was observed at 15 mg kg-1 of added K in all the soils, the more so in Entisols than in Inceptisols and Alfisol. Fertilizer K requirement per unit increase in available K in soil was relatively higher in Entisols and Inceptisols (1.15 to 1.19) and lower in Alfisol (1.06).