| Elevated phosphorus (P) from manure application field (MAF) soils transported to surface waters is a concern throughout the world due to its role in eutrophication. Our goal was to determine why the common labile extractants Olsen, DTPA, and Mehlich-III produce different (P) 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 among the labile P were variable. Mehlich-III extracted more plant labile P at neutral and above to slightly alkaline pH. Mehlich-III also dissolved more carbonates. Therefore, assessment of the fraction of labile P that Mehlich-III extracts in excess of Olsen and DTPA may warrant further characterization of the carbonate associated P to assess its role in plant nutrition and environmental quality regulation. |
