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The amounts of K release in successive extraction with hot 1N HNO3 decreased consistently and reached to plateau at 6th to 8th extractions in the soils. The K release in the 1 st extraction was 452.6 to 890.9 mg/kg, whereas at 9th extraction it was 8.2 to 13.1 mg/kg. The step K contents of the soils varied from 663.2 to 1452.7 mg/kg. The ratio of step K to non-exchangeable K of the soil was in the range of 1.22 to 1.38 which may be used as a better index of mobilization of non-exchangeable K reserves to plants. The constant rate K of the soils as a measure of availability index of K under long-term basis varied within the limit of 8.2 to 13.1 mg/kg which reached a constant level at the sixth to eighth extractions. Step K, constant rate K and cumulative K release had significant positive correlations with pH, EC, CEC, water soluble K, exchangeable K, available K, non-exchangeable K and lattice K. The K releasing power evaluated through step K and constant rate K could be meaningful for making fertilizer recommendation programme especially in the intensively cultivated areas. | Releasing characteristics of potassium in some coastal soils of west Bengal
