Do fields with elevated soil test phosphorus disproportionately contribute to western Lake Erie basin dissolved phosphorus loading?

Authors: Nottingham Byers, Emily; JOHNSON, LAURA - Michigan Department Of Agriculture; King, Kevin; Penn, Chad; Williams, Mark

Submitted to: Agricultural & Environmental Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2025
Publication Date: 7/7/2025
Citation: Nottingham Byers, E.R., Johnson, L.T., King, K.W., Penn, C.J., Williams, M.R. 2025. Do fields with elevated soil test phosphorus disproportionately contribute to western Lake Erie basin dissolved phosphorus loading?. Agricultural & Environmental Letters. Article 10:e70024. https://doi.org/10.1002/ael2.70024.
DOI: https://doi.org/10.1002/ael2.70024

Interpretive Summary: Agricultural crop production fields with elevated concentrations of soil test phosphorus have been reported as a primary risk factor for increasing occurrences of harmful and nuisance algal blooms in Lake Erie. However, results showed that while fields with high soil test phosphorus (> 75 mg/kg) disproportionately contributed to watershed phosphorus loads, they do not solely explain the increases in the phosphorous loads within the Western Lake Erie basin. To help reduce phosphorus losses on crop production fields, producers should implement targeted conservation practices despite their soil phosphorous concentrations. For fields with elevated soil phosphorus, producers should combine upland field practices such as nutrient management, harvesting cover crops, and a one-time soil inversion with edge-of-field practices like phosphorous removal structures to help account for increased risks of phosphorus loss from their field. Policy makers should take into consideration that managing soil phosphorus concentrations alone will not solely reduce the risk of harmful and nuisance algal blooms in Lake Erie. Policies and management programs need to consider the broad spectrum of phosphorus concentrations in soils when recommending conservation practices.

Technical Abstract: Crop production fields with elevated soil test phosphorus (STP) concentrations are often purported as the primary contributor to dissolved reactive P (DRP) loads in the Western Lake Erie Basin (WLEB). Analysis of annual DRP loading from 41 fields categorized into low (<75 mg kg-1), high (75-150 mg kg-1), and very high (>300 mg kg-1) STP were upscaled to the WLEB. An estimated 31.2% (±4.8%) of annual DRP loading originated from elevated STP fields when assuming 10% of the WLEB had STP>75 mg kg-1. Assuming 5% of the WLEB had STP>75 mg kg-1, the contribution reduced to 17.7% (±3.4%). Elevated STP fields disproportionately contribute to WLEB DRP loads, but do not solely explain the increase in DRP leading to harmful and nuisance algal blooms. Targeted upland (e.g., nutrient management) and edge-of-field (e.g., P removal structures) practices are needed across the broad spectrum of STP concentrations to meet WLEB loading goals.