Risk Assessment for Phosphorus Movement in Nutrient Management Planning in Mississippi

Oldham, L. J., Ramirez-Avila, J. J., Kingery, W., & Jackson, W. (2013). Risk Assessment for Phosphorus Movement in Nutrient Management Planning in Mississippi. 2013 Mississippi Water Resources Conference. Jackson, MS: MWRRI.

Nutrient Management develops blueprints for using the right amount of the right nutrient source at the right time in the right place. Using poultry litter as a nutrient source in pastures and forages results in increased soil test phosphorus (STP) levels when applications are based on crop nitrogen needs because more phosphorus (P) is provided in each unit of litter than the corresponding unit of grass removes. Increased STP in combination with site-specific soil and field characteristics may lead to P enrichment of surface and ground water. Phosphorus Indices (PI) are state-specific, site-specific algorithms to assess potential P loss that are used in the Nutrient Management Planning (NMP) process. These tools have been developed by individual state Natural Resource Conservation Service (NRCS) agencies under national policy guidance and integrated into the NRCS 590 Nutrient Management Conservation Standard since the late 1990\\\'s. Source factors such as STP, and nutrient source and management are used in combination with transport factors including soil characteristics, landscape characterization, and distance to nearest stream in various models to determine relative risk of P movement. Because of the leeway provided to the states, there are numerous versions of PI. Some are quantitative and predict P loss amounts; others, including Mississippi, are qualitative and assign relative risk. With higher risk of P movement to water as determined by PI categories, NMP preparation should assess potential mitigating Best Management Practices adoption. At issue are two recent published southern regional efforts that found differences in PI prediction capacity between state versions, including Mississippi. Individual state NRCS agencies, in cooperation with in-state partners, were asked to update their Nutrient Management Practice Standards in 2012, including reassessment of each state Phosphorus Index. In addition to the in-state standard revision with Mississippi NRCS, Mississippi State University is participating in a multistate effort under the national NRCS Conservation Innovation Grants to coordinate and advance P management in the southern region, ensuring that the PI have been tested based on new guidance in the NRCS 590 standard, and that tools produce more consistent results across physiographic regions in order to promote better consistency between southern state recommendations. This paper provides an overview of NMP, the factors used in the Mississippi Phosphorus Index, and additional efforts regarding NMP process in Mississippi.