• Michigan Sea Grant's HABs 101: Provides resources and factsheets to learn more about harmful algal blooms
• Cooperative Lakes Monitoring Program Total Phosphorus Fact Sheet (PDF)

• USDA Legacy Phosphorus Assessment Project: provides information about Legacy P, ongoing USDA work to investigate legacy P, and phosphorus modeling

• MSU Precision Agriculture Resources
• Soil Microbial Community Dynamics Across Michigan Farms

• 4R Plus: Features an overview and resources for the 4R's of Nutrient Stewardship: right source, right time, right rate, right place
• Video series on 4R nutrient application
• BMP Funding Sources WLEB (Google Doc): Includes financial resources - both broad and Western Lake Erie Basin specific - for producers looking to implement best management practices.
• Find your local Natural Resources Conservation Service office here.

Soil test labs that service Michigan:

• A&L Great Lakes Laboratory
• Midwest Laboratories
• Michigan State University Soil Test

• Tri-State Fertilizer Recommendations: The Tri-State Field Crop Fertilizer Recommendations for Indiana, Michigan, and Ohio recommends soil sampling and provides recommendations for how much phosphorus to apply to maintain yield up to a limit.
• Sheet about law changes with phosphorus fertilizer (PDF)

Zhou, S., & Margenot, A. J. (2023). Muddied Waters: The Use of “Residual” And “Legacy” Phosphorus. Environmental Science & Technology, 57(51), 21535-21539.

• The authors explain the history and purpose of the terms 'residual' and 'legacy' phosphorus, asserting that these terms should remain different.
  • 'Residual phosphorus' represents the phosphorus added by humans, mainly in agriculture, and refers to how much phosphorus builds up in the soil.
  • 'Legacy phosphorus' refers to tracking P movement through water systems / the landscape and its impact on water quality.

This paper is cited on the Legacy Phosphorus page.

Turner, B. L., & Kim, P. J. (2024). Terminology for residual and legacy phosphorus. Plant and Soil, 1-3.

• The authors note that agronomists and soil scientists use 'residual phosphorus' distinctly -these uses don’t match up. They suggest using three specific terms:
  • Legacy phosphorus: Phosphorus in the soil from human activities.
  • Residual phosphorus: Phosphorus in soil that can't be removed after a specific extraction process.
  • Surplus phosphorus: Extra phosphorus from fertilizer that plants don't absorb.

This paper is cited on the Legacy Phosphorus page.

Rowe, H., Withers, P. J., Baas, P., Chan, N. I., Doody, D., Holiman, J., ... & Weintraub, M. N. (2016). Integrating legacy soil phosphorus into sustainable nutrient management strategies for future food, bioenergy and water security. Nutrient Cycling in Agroecosystems, 104, 393-412.

• The authors view legacy phosphorus as a useful, accessible resource, but note that using it well depends on its distribution, what crops are available, and how fast crops use it up.
• They suggest a comprehensive method called 'agro-engineering' to help better utilize legacy phosphorus. 'Agro-engineering' includes:
  • Advanced nutrient management based on precision farming
  • New plant breeding techniques
  • Microbial engineering
  • Using more recycled and recovered phosphorus

This paper is cited on the Legacy Phosphorus and Reducing Phosphorus Application pages.

Doydora, S., Gatiboni, L., Grieger, K., Hesterberg, D., Jones, J. L., McLamore, E. S., ... & Duckworth, O. W. (2020). Accessing legacy phosphorus in soils. Soil systems, 4(4), 74.

• The authors examine what is known about different types of phosphorus, how legacy phosphorus changes when different fertilizers are used, and the challenges of using natural phosphorus.
• They highlight ways to use legacy phosphorus for growing crops.

This paper is cited on the Legacy Phosphorus, Reducing Phosphorus Application, and the Soil Test Methods pages.

Smith, D. R., Wilson, R. S., King, K. W., Zwonitzer, M., McGrath, J. M., Harmel, R. D., ... & Johnson, L. T. (2018). Lake Erie, phosphorus, and microcystin: Is it really the farmer's fault? Journal of Soil and Water Conservation, 73(1), 48-57.

• The authors highlight that phosphorus agricultural runoff contributes to water pollution in Lake Erie, stressing that we need to rethink how we manage soil fertility and conservation to protect the environment.
• Based on two farmer surveys, they found that most farmers use phosphorus fertilizers at or below recommended levels. The authors emphasize the need to better understand how phosphorus behaves in the environment, to reconsider traditional advice, and to use better farming practices.

This paper is cited on the Legacy Phosphorus page.

Sharpley, A., Jarvie, H. P., Buda, A., May, L., Spears, B., & Kleinman, P. (2013). Phosphorus legacy: overcoming the effects of past management practices to mitigate future water quality impairment. Journal of environmental quality, 42(5), 1308-1326.

• The authors note that water quality isn't improving as quickly as hoped because of leftover phosphorus from past practices. They stress the need to recognize this 'legacy phosphorus' in order to better manage nutrients and make restoration efforts more effective.
• They examine how past land management has increased soil phosphorus levels and changed how it moves through waterways. Through examples, they show that legacy phosphorus still affects lakes and rivers, making restoration harder. They call for better management of these old phosphorus sources in future conservation efforts.

This paper is cited on the Legacy Phosphorus and Reducing Phosphorus Application pages.

Baker, D. B., Johnson, L. T., Confesor, R. B., & Crumrine, J. P. (2017). Vertical stratification of soil phosphorus as a concern for dissolved phosphorus runoff in the Lake Erie basin. Journal of environmental quality, 46(6), 1287-1295.

• The authors look into why dissolved reactive phosphorus levels are rising in Lake Erie. They attribute the trend to phosphorus building up in the topsoil, which is 55% higher than traditional farming measurements show.
• They find that most fields, even those with normal soil-test phosphorus levels, still pose a high risk of dissolved reactive phosphorus runoff, especially fields within maintenance ranges.
• The study suggests that turning over the soil to reduce this buildup could lower dissolved reactive phosphorus runoff more effectively and quickly than just reducing the overall soil phosphorus levels.

Jankowiak, J., Hattenrath‐Lehmann, T., Kramer, B. J., Ladds, M., & Gobler, C. J. (2019). Deciphering the effects of nitrogen, phosphorus, and temperature on cyanobacterial bloom intensification, diversity, and toxicity in western Lake Erie. Limnology and oceanography, 64(3), 1347-1370.

• The authors find that while nutrients and elevated temperatures promote cyanobacterial harmful algal blooms, specific combinations of nitrogen, phosphorus, and temperature selectively favor certain cyanobacterial genera, suggesting that effective management of both nutrients is crucial to control cyanobacterial harmful algal blooms as lake temperatures rise.

Environmental Protection Agency (EPA) 1978 - Method 365.3: Phosphorus, All Forms (Colorimetric, Ascorbic Acid, Two Reagent)

• EPA Method 365.3 may be used to determine dissolved, total, and hydrolyzable phosphate, as well as all forms of phosphorus (including particulate and dissolved) in waters and wastes. The original operational definitions of total phosphorus, dissolved reactive phosphorus/soluble reactive phosphorus, and the other related phosphorus terms were developed in the 1940s: this approach is used in Method 365.3.
• Dissolved phosphorus, or “un-bound phosphorus,” is defined by the EPA methods as the form of phosphorus that passes through a 0.45 µm filter.