Assessment of Suitable Extractants for Predicting Plant-available Potassium in Indian Coastal Soils

The suitability of seven chemical extractants was evaluated on 24 Indian coastal soils for prediction of plant-available potassium (K) to rice (Oryza sativa L. var. NC 492) grown in modified Neubauer technique. Average amounts of soil K extracted were in descending order: 0.5 M NaHCO3 > neutral 1 N NH4OAc > 0.02 M CaCl2 > Bray and Kurtz No.1 > 1 N HNO3 > 0.1 N HNO3 > distilled water. The highest simple correlation with plant K uptake was obtained with 0.1 N HNO3-K (r = 0.848) and lowest with CaCl2-K (r = 0.805). Predictive models were developed using plant K uptake as the dependent variable and extractable soil K, sand, silt, soil pH, and electrical conductivity as the independent variables. Based on the final R-2 and ease of measurement, distilled water, 1 N NH4OAc, and 0.1 N HNO3 models were the best predictors of plant-available K in coastal soils when used along with sand or soil pH.