Estimating Legacy Soil Phosphorus Impacts on Phosphorus Loss in the Chesapeake Bay Watershed

• Published in: Journal of environmental quality 2018-05, Vol.47 (3), p.480-486
• Main Authors: Vadas, Peter A., Fiorellino, Nicole M., Coale, Frank J., Kratochvil, Robert, Mulkey, Alisha S., McGrath, Josh M.
• Format: Article
• Language: English
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2017.12.0481

Agricultural nutrient management is an issue due to P loss from fields and water quality degradation. This is especially true in watersheds where a history of P application in excess of crop needs has resulted in elevated soil P (legacy P). As practices and policy are implemented in such watersheds to reduce P loss, information is needed on time required to draw down soil P and how much P loss can be reduced by drawdown. We used the Annual P Loss Estimator (APLE) model to simulate soil P drawdown in Maryland, and to estimate P loss at a statewide scale associated with different combinations of soil P and P transport. Simulated APLE soil P drawdown compared well with measured rates from three field sites, showing that APLE can reliably simulate P dynamics for Maryland soils. Statewide APLE simulations of average annual P loss from cropland (0.84 kg ha−1) also compared well with estimates from the Chesapeake Bay Model (0.87 kg ha−1). The APLE results suggest that it is realistic to expect that a concerted effort to reduce high P soils throughout the state can reduce P loss to the Chesapeake Bay by 40%. However, P loss reduction would be achieved gradually over several decades, since soil P drawdown is very slow. Combining soil P drawdown with aggressive conservation efforts to reduce P transport in erosion could achieve a 62% reduction in state‐level P loss. This 62% reduction could be considered a maximum amount possible that is still compatible with modern agriculture. Core Ideas APLE model can reliably simulate soil P drawdown and P loss for Maryland soils. Soil P drawdown efforts in Maryland could reduce P loss to the Chesapeake Bay by 40%. Soil P drawdown will require decades to fully achieve. Soil P drawdown combined with conservation to reduce erosion could reduce P loss by 62%.