Date of this Version
Young, R.A.P. 2015. Phosphorus Release Potential of Agricultural Soils of the United States. PhD dissertation. University of Nebraska - Lincoln.
Phosphorus (P) is one of the leading causes of surface water quality decline in the United States, leading to algal blooms and hypoxia in lakes and streams. Decreasing conservation funds dictate that agencies such as the Natural Resources Conservation Service, maximizes its effectiveness and efficiency in implementing practices to address P management and runoff on agricultural lands. Additional information on P behavior in soil is needed to improve P management plans to reduce pollution risk at the watershed, farm, and field scales. This research focuses on the development of total soil P release models, to be included into assessment and management tools to better identify agricultural soils that pose the greatest threat to surface water if eroded, and to improve existing nutrient loss models.
Soil P sorption behaviors and relationships with other soil properties were investigated on 313 agricultural surface soils from across the U.S. Different soil grouping schemes were investigated when analyzing and modeling soil P sorption behaviors at the national-level. Three large watershed areas with known P issues were also investigated to compare watershed-specific models to overall national-level models.
Overall results showed that, (a) oxalate extractable and Mehlich-3 extractable P tests are the most appropriate soil P tests for estimating total P release and P adsorption in most soils, (b) total P release prediction models improve when soils are grouped based on their calcium carbonate content and degree of weathering or modeled at a large watershed level, than at a general national-scale, (c) the majority of statistically significant and reliable total P release prediction models include clay and either oxalate or Mehlich-3 extractable Al, (d) potential risk models can differ greatly within a given area or watershed, depending on the employed modeling scheme (i.e. area-specific vs. national-level), and that (d) with further research and refinement, the relationships and models developed in these studies have the potential of improving current P Indices and assessment tools, and subsequent management recommendations and practices.
Advisor: Mark S. Kuzila