Degree of Phosphorus Saturation as Environmental Threshold for Acidic Soils of Eastern India

Abstract

Abstract An indicator is essential to predict the potential for phosphorus (P) movement from a nonpoint soil source to surface water bodies, causing environmental pollution. The present study was undertaken with terai and lateritic acidic soils of eastern India to estimate their environmental threshold degree of P saturation (DPS) values as an indicator of the potential risk for P loss. Comparisons of DPS with soil-test P and water-soluble P suggested that DPS could be a useful environmental indicator. The change point DPS with Bray-1 extractant were 17.8 and 19.8% and with Mehlich-1extractant were 16.9 and 18.3% for terai and lateritic soils, respectively. The water-soluble P at those corresponding change points were 2.94 and 3.42 mg kg-1 with Bray-1 and 2.83 and 3.34 mg kg-1 with the Mehlich-1 method for terai and lateritic soil, respectively. The relationship between DPS (%) estimated with Bray-1 extractant (DPSB-1) and Bray-1P (mg kg-1) revealed that agronomic optimum values of Bray-1 P could not indicate the environmental risk. Therefore, considering the change points, confidence intervals and agronomic soil test values, we can recommend replacing Bray-1P with three categories of DPSB-1: <20%, 20-40% and >40% as safe, warrant and critical levels of P loss from Indian soils, respectively.