Corn growing in a field in Rosemount, MN.

2020-21 Rapid Ag: Providing Critical Support to Minnesota Farmers for Phosphorus Risk Assessment

May 9, 2019

Principal Leader

Lindsay Pease


Northwest Research & Outreach Center and Soil, Water and Climate

The Problem

This proposal addresses an urgent need to update and revise the Minnesota Phosphorus Site Risk Index (MNPI) tool. The MNPI, last updated in 2006, must be updated to correspond with a recent policy change by the USDA Natural Resources Conservation Service regarding how erosion is predicted across landscapes. While making this change, we propose to evaluate the overall performance of the MNPI across Minnesota to ensure its reliability as a way to estimate phosphorus loss. Inaccurate phosphorus risk assessment can have serious economic, environmental, and biological consequences. If risk assessment is too high, farmers may risk under-application and stunted yields. If risk assessment is too low, farmers risk losing phosphorus during runoff events and harming downstream ecosystems. High levels of phosphorus in freshwater lakes drive the development of harmful algal blooms (HABs). In Minnesota, HABs have led to serious incidents including human illness and death of pets. Increased pressure to limit phosphorus loss could lead to increased regulations on manure and fertilizer application in Minnesota. The proposed project aims to improve both the quality and usability of the MNPI. This work will provide critical support to farmers in voluntarily reducing nutrient losses while ensuring that they maintain adequate soil fertility.


Mismanagement of applied nutrients can have serious economic, environmental, and biological consequences. It is well known that inadequate soil fertility will limit crop growth and reduce yield. At the same time, relatively low P concentrations fuel algal growth in freshwater lakes (Carpenter et al., 1998). High-profile freshwater harmful algal blooms (HABs), such as in Lake Erie and Lake Winnipeg, have increased public attention on reducing P loss from agricultural landscapes (Daloglu et al., 2012; Schindler et al., 2012). Locally, Minnesota farmers face similar pressure. HABs in Minnesota lakes have been linked to human illness and pet deaths (Lindon and Heiskary, 2009; Heiskary et al., 2014). Despite an increasing need for P loss risk assessment, the Minnesota Phosphorus Site Risk Index (MNPI) was last updated in 2006 (Lewandowski et al., 2006). Thus, there is an urgent need to update the MNPI to assist farmers in nutrient application planning. The lack of an up-to-date, easy-to-use tool for Minnesota farmers is a critical gap in nutrient management planning. Without an accurate way to evaluate risk of P loss on a field-to-field basis, Minnesota farmers may be faced with uniform restrictions on nutrient application in the future. Improving both the quality and usability of the MNPI will provide critical support to farmers in voluntarily reducing nutrient losses while ensuring that they maintain optimum soil fertility.

The long-term goal of this project is to provide support to farmers in nutrient application planning to ensure soil fertility needs are met while minimizing the risk of nutrient loss. The objective of this application , which is the next step toward our long-term goal, is to revise the MNPI so that it can better meet the needs of Minnesota farmers. The central hypothesis of this work is that improved nutrient planning tools will provide a pathway toward voluntary reduction of nutrient losses without sacrificing crop fertility requirements. We have formulated this hypothesis based on: (1) the success of in-field nutrient management strategies for reducing P loss at the field scale (e.g., King et al. 2018); and (2) stakeholder feedback indicating that a lack of guidance in this area limits broader adoption of improved P management strategies (see attached letter of support). Improvements to the MNPI tool will provide a framework to address critical gaps in nutrient application planning. Extension programming will be built around this framework in order to increase awareness of the interactions between P management and water quality risk. In turn, this will enable farmers to better balance crop needs with environmental impact. The project team, where all members are part of the University of Minnesota Extension Nutrient Management Team, is well prepared to conduct this research and extension effort because of our collective experience in the areas of P management, soil fertility, manure management, water management, and row crop production.

The proposed research will be transformative to Minnesota agriculture by providing critically needed guidance on P management planning in the context of water quality improvement. This work will take advantage of scientific and technological advancements of the past decade to revive, update, and build upon the MNPI. We anticipate that this work will yield the following expected short-term outcomes : (1) critical assistance to farmers in transitioning to new USDA-NRCS policies; (2) training for farmers, technical service providers, and conservation planners on how to incorporate the MNPI into nutrient management plans; (3) increased awareness of the potential interactions of phosphorus management and water quality; and (4) improved accessibility of the MNPI tool for on-the go nutrient planning. This work is also anticipated to yield the following long-term outcomes : (1) improved ability to update the MNPI in response to future changes in nutrient recommendations and/or understanding of nutrient loss; (2) a platform for growers to demonstrate voluntary action to prevent phosphorus loss; and (3) increased resiliency of good actors and voluntary adopters to potential changes in nutrient application restrictions.

Objectives and Goals

The overall goal of the proposed work is to revise the Minnesota Phosphorus Site Risk Index (MNPI) to improve its ability to meet the needs of Minnesota farmers. We plan to accomplish the overall objective of this application by pursuing the following specific aims :

  1. Revise the MNPI to correspond with changes to USDA-NRCS conservation planning requirements The MNPI currently uses the Revised Universal Soil Loss Equation (RUSLE2) to estimate soil erosion and risk of sediment-bound phosphorus (P) loss. NRCS has recently announced transition from RUSLE2 to the new Water Erosion Prediction Project (WEPP) in its policies and conservation planning. For the MNPI to remain compatible with NRCS policies and conservation plans, RUSLE2 must be replaced by WEPP within the MNPI. We plan to work closely with NRCS to ensure a smooth transition for Minnesota farmers who rely on the MNPI for P risk assessment.
  2. Translate the Minnesota P Index into a format that will be compatible with the University of Minnesota Extension Website and facilitate future updates and improvements to the model. The current MNPI desktop application is written in an outdated computer programing language. This presents a dual challenge; the application is neither developer-friendly (e.g., it is not easy to update) nor user-friendly (e.g., it is not easily accessible for online and/or mobile use). These challenges are key factors in the limited use of the current MNPI tool. Rewriting the application in a more common programming language, such as Python, will make the MNPI easier to update, maintain, and transfer into new formats in the future.

  3. Improve prediction of P loss and assessment of water quality risk from across Minnesota’s diverse agricultural regions. The current version of MNPI was last updated in 2006. Since that time, our understanding of—and ability to monitor—phosphorus (P) loss in agricultural systems has improved substantially. Based on our project team’s collective expertise in nutrient management, we hypothesize that the addition of P loss risk in subsurface drainage discharge will improve performance of the MNPI. We plan to test this hypothesis by compiling existing water quality data collected within the state of Minnesota and evaluating the performance of the MNPI across Minnesota’s agricultural regions.

  4. Train farmers to incorporate the MNPI into nutrient management planning through Extension and outreach programming. We plan to conduct five regional workshops throughout the state (Twin Cities, Northwest, Central, Southwest, and Southeast regions) to train farmers, NRCS agents, certified crop advisors, and technical service providers to use and incorporate the MNPI into their nutrient management planning. We will build interest in these workshops by sharing details on the redevelopment of the MNPI at field days, presentations, and through online media outlets (University of Minnesota Extension website, Twitter, Facebook). Following the conclusion of the workshops, we will develop an online, self-paced course to reach more individuals over time.


  1. Carpenter, S.R., N.F. Caraco, D.L. Correll, R.W. Howarth, A.N. Sharpley, and V.H. Smith. 1998. Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen. Ecol. Appl. 8(3): 559–568.
  2. Daloğlu, I., K.H. Cho, and D. Scavia. 2012. Evaluating causes of trends in long-term dissolved reactive phosphorus loads to Lake Erie. Environ. Sci. & Technol. 46(19): 10660–6.
  3. Heiskary, S., M. Lindon, and J. Anderson. 2014. Summary of microcystin concentrations in Minnesota Lakes. Lake and Reservoir Management 30(3): 268–272.
  4. King, K.W., M.R. Williams, G.A. LaBarge, D.R. Smith, J.M. Reutter, E.W. Duncan, and L.A. Pease. 2018. Addressing agricultural phosphorus loss in artificially drained landscapes with 4R nutrient management practices. J. of Soil and Water Conserv. 73(1): 35–47.
  5. Lewandowski, A., J. Moncrief, M. Drewitz. 2006. The Minnesota phosphorus index: Assessing risk of phosphorus loss from cropland. AG-BU-08423. University of Minnesota Extension Service: St Paul.
  6. Lindon, M., and S. Heiskary. 2009. Blue-green algal toxin (microcystin) levels in Minnesota lakes. Lake and Reservoir Management 25(3): 240–252.
  7. Schindler, D.W., R.E. Hecky, and G.K. McCullough. 2012. The rapid eutrophication of Lake Winnipeg: Greening under global change. J. of Great Lakes Res. 38(3): 6–13.