Assessment of suitable extractants for predicting plant-available potassium in Indian coastal soils

Abstract

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 R2 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.