Tuesday, 8 November 2005
9

Comparison of Phosphorus Fractions in Calcareous Soils Characterized by Different Fractionation Schemes.

Jim J. Wang and Dustin E. Harrell. Louisiana State University, Dept. of Agronomy and Environmental Management, 104 Sturgis Hall, Baton Rouge, LA 70803

Adequate phosphorus (P) fractionation is important in understanding soil P chemistry and mobility. In this study, the redistribution of P due to the additions of NaHCO3 (for labile P) and citrate-bicarbonate (CB) and replicated extractions to a common P frasctionation scheme along with the effect of salt washing on ICP analysis of P fractionation extracts was investigated. The P chemical fractionation experiment was carried out with surface and subsurface samples of five calcareous soils. Spike recovery of P by ICP analysis was near 100 % for the NaHCO3, CB and HCl fractions while the recovery in the NaOH and CBD fractions was 81 and 61 %, respectively. The loss of P recovery in NaOH-P and CBD-P were determined to originate from the high NaCl concentrations in the final extracts caused by washing the soil residues between samples with NaCl solutions between fractions. The addition of the NaHCO3 for labile P and the CB for recovering P reabsorbed to CaCO3 caused a redistribution of P from the residual-P fraction to the NaHCO3-P, NaOH-P, CB-P, and CBD-P fractions. The HCl-P fractions were generally unaltered by the addition of the NaHCO3-P or CB-P fractions or by replicating extractions. It was concluded that the caution should be taken when interpreting P fractions from experiments using differing fractionation procedures.

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