Phosphorus Desorption Characteristics and Relationships of U.S. Soils – Preliminary Results.

Eutrophication and the contaminating of surface waters with P is a major environmental issue throughout the United States. In many cases, sediment attributed to runoff and erosion from agricultural lands has been noted as a source of the P degrading waters. However, in order to improve P management at the watershed and farm and field scales, more information is needed on the behavior of P in soil. Thus, the objective of this research is to evaluate P sorption and desorption for a range of soils in the U.S. to develop better estimates of their potential to contribute P to surface waters. Key aspects to this study during the first year have revolved around the development of desorption curves and their relationships to the physical characteristics of the soils. The double-point anion exchange resin extraction method was used to measure desorption on surface horizons from 300 of the most common agricultural soils in the U.S., and the preliminary results have been compared to the clay content, organic carbon content (OC), calcium carbonate (CaCO3) content, pH, acid ammonium oxalate extractible aluminum plus ½ iron (Al+1/2Fe) content, Mehlich-3 P, and oxalate P characteristics of these soils. This presentation will summarize these preliminary results, discuss the correlations between total P fixation capacity and other soil properties, and summarize the development of an initial set of P-behavior interpretive groups of soils.