PHOSPHORUS LOADING POTENTIAL OF U.S. SOILS

Eutrophication and the contaminating of surface waters with phosphorus (P), continues to be 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 to better identify areas that are at highest risk to deliver excess P to surface waters. 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, and the data from this study will also be used to improve soil, water, and nutrient movement models, such as APEX. Key aspects to this study 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 297 of the most common agricultural soils in the U.S., and the desorption results have been compared to the clay content, carbon content, calcium carbonate content, pH, acid ammonium oxalate extractible aluminum and iron contents, Mehlich-3 P, and oxalate P characteristics of these soils. This presentation will summarize these 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.