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
and delivered to a nearby ditch, stream, or lake. It allows the user to
evaluate management options that can reduce the risk.
How to use the Index
Details about the model
Download the program
To install the Minnesota P Index:
- Download the setup program by right-clicking on the link above and
saving the file to your computer.
- Uninstall any previous versions of the MN P Index.
- Run the setup program by double-clicking on <MNPIndexSetup.exe> in your file manager.
The program will be installed, and a
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
- 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.
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.
- 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
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
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.