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Department of Soil, Water, and Climate




For more information about the Minnesota Phosphorus Index, contact:

John Moncrief
Department of Soil, Water, & Climate
Borlaug Hall
1991 Upper Buford Circle
St. Paul, MN 55108
Phone: 612.625.1244
Fax: 612.625.2271


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Phosphorus Loss Assessment

The Phosphorus Source Assessment Tool

The Phosphorus Source Assessment Tool is used to estimate the relative contributions of various land uses and point sources to P loading in a watershed.

The Minnesota Phosphorus Index

The Minnesota Phosphorus Index (P Index) is a management tool to estimate the relative risk that phosphorus is being lost from an agricultural field and delivered to a nearby ditch, stream, or lake. It allows the user to evaluate management options that can reduce the risk.

Brief descriptions

How to use the Index

Details about the model

Download the program

    To install the Minnesota P Index:

  1. Download the setup program by right-clicking on the link above and saving the file to your computer.
  2. Uninstall any previous versions of the MN P Index.
  3. Run the setup program by double-clicking on <MNPIndexSetup.exe> in your file manager. The program will be installed, and a icon will be placed on your desktop or in your start menu. The default folder location for the program is: C:\Program Files\Minnesota P Index\.

    Some of the program changes from the previous version:

  • Corrected some errors in the reports and data export functions.
  • Updated RUSLE2 to the June 2006 version.
  • Anhydrous ammonia injections are now accounted for in estimating the fall soil condition. Previously, anhydrous ammonia was only considered when estimating fall residue cover.

Screening Tool

The Rapid Phosphorus Index (RPI) is a small set of indicators and thresholds based on the MN P Index. It can be used as a screening tool to eliminate the lowest risk sites or highlight the highest risk sites where the full MN P Index should be applied.

The inputs needed for the RPI are manure and fertilizer application rates and method, soil test P, erosion rate, distance to water, and whether the soil is poorly drained.

The RPI is three separate screening tools of varying sensitivity. Choose the one appropriate for your goals. The high sensitivity version identifies sites likely to have a MN P Index value greater than 2; the medium sensitivity version identifies sites likely to be greater than 4; and the low sensitivity version only identifies sites likely to have a MN P Index value greater than 6. The RPI will occasionally mis-identify a field as either higher or lower risk. Consider which type of error you can tolerate. For example, if it is important not to miss any high risk sites, choose a higher sensitivity tool. If it is important to minimize the number of fields analyzed with the MN P Index, choose a lower sensitivity tool.


Workshops and Presentations

  • Presentation for Soils 3416, 5Dec06, Phosphorus Index. Lewandowski.pdf
    Key points:
    • Phosphorus sources and transport mechanisms
    • Structure of the MN P Index
    • How to interpret MN P Index results
    • Where and how is the MN P Index used?
    • What inputs is the MN P Index sensitive to?
  • Minnesota Phosphorus Index Workshop Presentations. Updated 02/28/06.


Initial funding for development of the Minnesota Phosphorus Index came from the Minnesota Environmental Quality Board and the University of Minnesota Extension Service in response to the results of the Generic Environmental Impact Statement (GEIS) on Animal Agriculture. Current funding is from a U.S. Environmental Protection Agency 319 grant sponsored by the Minnesota Department of Agriculture.

The Phosphorus Index Development Team:

John Moncrief, Paul Bloom, Dave Mulla, Neil Hansen,
Gyles Randall, Carl Rosen, Ed Dorsey, and Ann Lewandowski
University of Minnesota

Input and Critique:

Matt Drewitz and Mark Dittrich
Minnesota Department of Agriculture

Jeff St.Ores, Pete Cooper, and Robin Martinek
Natural Resources Conservation Service

Chris Zadak, Jim Klang, and Dave Wall
Minnesota Pollution Control Agency

Greg Larson
Board of Water and Soil Resources


Surface water quality is an important issue in a state where this resource provides a major economic engine. Phosphorus can be a major factor in lake eutrophication. Phosphorus (P) is the nutrient limiting algae growth in most fresh water systems. When P in runoff is allowed to enter surface waters the resultant algal bloom leads to depleted dissolved oxygen levels and the associated degradation in water quality. Phosphorus is also an important plant nutrient. Fertilizer, manure, and other organic P sources are land applied to support adequate plant growth. The challenge for people who make land use decisions is to balance economic and environmental risks.

The Minnesota Phosphorus Index can be used to determine the relative risk posed by farm fields on the landscape and how to reduce the risk. The P Index is a management tool for individual fields or landscapes that provides a relative (unitless) assessment of the risks to surface waters of P losses from erosion, rainfall runoff, and snowmelt runoff. It allows the user to evaluate management options that can reduce the risk. It is not intended to be used as a regulatory tool, nor to estimate changes in surface water quality measurements. The Minnesota P Index does not consider the sensitivity of the receiving waters nor the environmental costs of entry of P to surface waters. It also does not consider the cost of adoption of different practices to reduce P losses from specific fields.

Other states have developed similar tools. As with other states, Minnesota’s P Index addresses its unique climate, soils, landscapes, and land use practices to develop a risk assessment. For example, it assesses the risk associated with snowmelt P losses. This would have little value in Florida or Texas but in Minnesota snowmelt can be a major source of P entering surface waters.

Three pathways are considered in the Minnesota approach. The first is the transport of sediment-bound P associated with the eroded particles in rainfall runoff. The second is the transport of dissolved P by rainfall runoff. The third is the transport of dissolved P by snowmelt. Losses from these three pathways are added, giving a total P index (unitless) for the given site. This index value represents the relative long-term average risk of P losses for a given site and set of management practices

Evaluation of test scenarios revealed that there are multiple ways to lower the P Index. Best management options can be evaluated for a specific site using the Minnesota P Index. P losses can be lowered using some combination of reduced P application rates, improved methods of P application, or adoption of practices such as conservation tillage or buffer strips that reduce the risk of P transport across the landscape. Usually one pathway (erosion, rainfall runoff, or snowmelt runoff) is more important than other pathways, and management changes that address that pathway will be the most effective method for reducing the overall risk.

Page updated May 19, 2007