Phosphorus lability across diverse agricultural contexts with legacy sources

Authors: Simpson, Zachary; Mott, Joshua; Elkin, Kyle; Buda, Anthony; FAULKNER, JOSHUA - University Of Vermont; Hapeman, Cathleen; McCarty, Gregory; FOROUGHI, MARYAM - University Of Maryland; HIVELY, W. DEAN - Us Geological Survey (USGS); King, Kevin; Osterholz, William; Penn, Chad; Williams, Mark; Witthaus, Lindsey; Locke, Martin; PAWLOWSKI, ETHAN - Oak Ridge Institute For Science And Education (ORISE); Dalzell, Brent; Feyereisen, Gary; DOLPH, CHRISTINE - University Of Minnesota; Bjorneberg, David; Nouwakpo, Sayjro; Rogers, Christopher; SCOTT, ISIS - Kansas State University; Bolster, Carl; DURIANCIK, LISA - Natural Resources Conservation Service (NRCS, USDA); Kleinman, Peter

Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2024
Publication Date: 9/29/2024
Citation: Simpson, Z.P., Mott, J.D., Elkin, K.R., Buda, A.R., Faulkner, J., Hapeman, C.J., Mccarty, G.W., Foroughi, M., Hively, W., King, K.W., Osterholz, W.R., Penn, C.J., Williams, M.R., Witthaus, L.M., Locke, M.A., Pawlowski, E., Dalzell, B.J., Feyereisen, G.W., Dolph, C., Bjorneberg, D.L., Nouwakpo, S.K., Rogers, C.W., Scott, I., Bolster, C.H., Duriancik, L., Kleinman, P.J. 2024. Phosphorus lability across diverse agricultural contexts with legacy sources. Environmental Quality. 1-19. https://doi.org/10.1002/jeq2.20632.
DOI: https://doi.org/10.1002/jeq2.20632

Interpretive Summary: Phosphorus (P) from past nutrient management can contribute to water quality concerns decades after it was applied as fertilizer or manure: a dynamic known as ‘legacy P’. Legacy P presents a long-lasting obstacle for P management. The USDA Legacy P project was created to provide critical research on legacy P dynamics across a variety of agricultural settings and scales. Here, we analyzed more than 600 soils and sediments from seven sites where legacy P is a concern. Across all sites, potentially mobile P stores could supply significant dissolved P losses for decades. We built a model to predict the potential of soil or sediment P to release to water; this model, based on fundamental P sorption chemistry, proved highly predictive across the diversity of physical and chemical characteristics studied. These findings can guide the future generation of P transport models, meaning that we can better predict the impacts of legacy P on water quality such as harmful algal blooms.

Technical Abstract: The buffering of phosphorus (P) in the landscape delays management outcomes for water quality. If stored in labile form, P may readily pollute waters. Herein, we studied P lability for more than 600 soils and sediments across seven study locations in the USA. Labile P stocks were large enough to sustain high P losses for decades, indicating the transport-limited regime typical of legacy P. Sediments were often more sorptive for P than nearby soils. Soils in the top 5 cm had 1.3 to 3.0 times more labile P than soils at 5–15 cm. Stratification in soil test P and total P was, however, less consistent. As environmental P exchange via sorption follows the difference in intensity between solution and the surface of soil or sediment, we built a model for the equilibrium phosphate concentration at net zero sorption (EPC0) as a function of labile P quantity and buffer capacity. Despite widely varying properties across sites, the model generalized well for all soils and sediments: EPC0 increased sharply with more labile P and to greater degree when buffer capacity was low or sorption sites were likely more saturated. This quantity-intensity-buffer relationship is central to the P transport models we rely on today. Our data inform the improvement of such P models, which will be necessary to predict the impacts of legacy P. Further, this work reaffirms the position of labile P as a key focus for environmental P management.