Efficacy of Soil Extracting Solutions for Assessing Potential Phosphorus Loss from a Dairy Waste Application Field Soil in North Central Texas

Elevated phosphorus (P) from manure application field (MAF) soils transported to surface waters is a concern throughout the world because of P's role in eutrophication. Our goal was to determine why the common labile extractants alkaline-buffered sodium bicarbonate (Olsen), ammonium bicarbonate-diethylenetriaminepentaacetic acid (DTPA), and dilute acid-fluoride (Mehlich III) produce different values given the same soil sample. Ten sites within a dairy MAF were sampled by genetic horizons from fine, mixed, Thermic, Udic Paleustalf (Windthorst) map units. In addition to determining plant labile P, soluble and total P were determined. All P pools decreased with depth, but concentrations between the labile P were variable. Mehlich III extracted more plant labile P at neutral and slightly alkaline pH values. Mehlich III also dissolved more carbonates. The fraction of labile P that Mehlich III extracts in excess of Olsen and DTPA warrants further characterization of carbonate associated P to assess its role in plant nutrition and environmental quality regulation.