Don’t P in the Lake

Knowing when a phosphorus (P) fertilizer application is warranted can be a good first step towards a much larger concern – the quality of our nation’s water supply.

Whether for drinking, recreation, fishing, irrigation, or aesthetics, the quality of our water supply impacts us all. A series of phosphorous (P) induced algal blooms over the last several years in the western Lake Erie Basin continues to raise concern as to the cause of the eutrophication issues and how to fix them. While sediment and sediment movement in surface runoff waters has generally been identified as a major P contributor, more recent evidence suggests conservation practices aimed at curbing sediment-bound P (i.e., particulate P) may in fact increase the availability of other forms of P, particularly dissolved P which tends to be more bioavailable. Due to fertilizer P additions continuing to be a primary target from a regulatory standpoint, understanding when to apply or not apply P fertilizer can promote both economic gain and environmental stewardship simultaneously. At MSU Agriculture Innovation Day – Focus on Soil on Aug. 24 in Frankemuth, MI, attendees will learn to better understand when's the best time to test their soil.

Don’t Guess, Soil Test!

The complexity of the P cycle and the interconnectedness to water eutrophication reach well beyond fertilizer P additions as other factors have changed as production agriculture has evolved. Land use, the amount of impervious surface, the rate of water removal from both urban and agricultural landscapes, population densities and wastewater treatment are merely a few examples that may influence the retention time and sorption ability of water and some nutrients under certain flow conditions. However, a key factor in nutrient management is to avoid building-up nutrients in excess of crop demand and this principle may serve a key strategy in targeting dissolved P losses. Two complicating factors involved in soil P management are:

  1. Soil test P levels represent merely a fraction of the total P in the soil which can create difficulties when interpreting a soil test report
  2. The loss of dissolved P may be considered invisible as compared to sediment loss creating further uncertainty with regard to actual losses and impact control measures.

Nutrient management strategies, particularly phosphorus, will continue to be at the forefront of water quality concerns. At the MSU Agriculture Innovation Day: Focus on Soils field tour, discussion, demonstration, and effectiveness of multiple P fertilizer management strategies will be reviewed in addition to soil test P stratification within the soil profile and principles used to determine P application. While multiple conservation and management strategies will be required to address the water eutrophication issue and may depend upon individual agricultural operations, the decision on whether a P application is warranted for your crop can be a good start.

MSU Agriculture Innovation Day is slated to become an annual event that will focus on in-depth education on a single topic. The event will rotate to various locations throughout the state. Experts will deliver innovative information to help producers take the next step in improving their bottom line while maintaining environmentally sound practices on their farms. 

To learn more, visit the MSU Agriculture Innovation Day website or contact Ron Bates at

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