Phosphorus (P) in soil solution at any given time is less than 5 mg kg^-1. Management of soil pH is, therefore, critical for optimizing plant availability and uptake. On the other hand, elevated soil P concentrations under certain conditions can be a potential threat to surface water quality leading to eutrophication. Multiple factors contribute to potential P losses from agriculture and urban regions. Soil test is the most common predictive or diagnostic approach due to its wide use, relatively low cost, and existence of accepted field calibration and test interpretations. However, over-fertilization is common, particularly, where commercially valuable crops are grown and on confined animal farms, where land application is the only feasible option. Co-precipitation with iron and aluminum into insoluble phosphates occurs in predominantly acid soils, particularly in southeastern USA. While the assessment tools for P losses from agricultural operations consider multiple factors, in coastal plain soils, particularly due to sandy textures and minimal elevational differences, leaching becomes the predominant mechanism for P moving beyond the rootzone. In soils with sodic horizons or having immediately succeeding soil layers with distinctly lower hydraulic conductivities, subsurface lateral drainage of water with P can be significant, leading to negative impact on surface waterbodies. To address this issue, even as soil test P values are considered, addition of factors such as storage capacity and capacity index have been suggested to the P-Index tool, where the proportion of extractable soil P vs. soil Fe and Al is estimated for coastal plain soils to help determine the sustainable amounts of P applications for both agriculture and environment.

Audience Take Away:

• Audiences will learn about the need for considering additional factors impacting the soil P losses from agricultural operations, primarily. Site specific conditions must be understood well for designing an effective strategy for limiting the P movement in soils. How the dynamics of soil physical and chemical properties and interdependence of water impact the agricultural production and environment will be discussed.
• Once an estimate of P storage capacity in the soils is made, an effective P fertilization and management plan can be made for an agricultural operation, watershed or region, etc. This will help develop sound nutrient management plan(s) and budgeting of nutrients, particularly P. Including the additional factors in view of inherent soil properties, will improve the long term sustainability planning efforts. 

Rao Mylavarapu is the Professor of Sustainable Nutrient Systems in the Soil and Water Sciences Department, University of Florida. He also serves as the Director of the statewide Analytical Services Laboratories. He has previously worked at the USDA-ARS, and Clemson University. He has published over 150 research and extension publications and book chapters. His mentored 16 graduate students as the Committee Chair. He served as President of Soil & Plant Analysis Council and as the Chair of Nutrient Management and Soil and Plant Analysis Division, Soil Science Society of America. He serves on the Editorial Boards of three international journals.