Wisconsin’s Integrated Approach to Phosphorus Indexing Laura Ward Good, Larry Bundy, and Paul Kaarakka University of Wisconsin-Madison

For planning manure applications use: 1. Soil Test P: > 50 ppm – limit P applications to crop removal > 100 ppm – eliminate P applications if possible; cumulative P applications must be 25% less than crop removal 2. Wisconsin P Index Wisconsin’s Nutrient Management Standard

Field The P Index estimates total annual P delivery from a field to nearest surface water Wisconsin P Index Stream

Field P Index Edge of field P loss: Sediment-bound P + Dissolved P + Single-event P (surface appl.) Total P Delivery Ratio X = Stream P Index Components

Advantages to “Modeling” Approach Quantifying impacts allows better comparison of management practices and allows management flexibility in reaching goals It can be tested through watershed monitoring

Year-round Runoff Monitoring on Cropped Fields 18 fields 21 crop years Crops: Alfalfa, corn, corn silage Slopes: 4-13% Soils: silt loam, silty clay loam, loam Soil test P: 18 – 130 ppm Range of tillage practices, manure and fertilizer applications

Soil Test P and Runoff P

Row and Column P Index and Runoff P

P Index Values and Runoff P

The Implementation Problem Phosphorus planning requires Multi-year calculations Up-to-date assessment of soil loss But …. Statewide expectation of limited/declining local field staff

Solution Software integrating soil loss and P loss risk assessments with nutrient management planning

RUSLE2 P Index calculator SNAP-Plus Entry by field: County, Soil, Slope, Soil test, Crop rotation, Yields, Tillage, Manure, Fertilizer Output by field: Fertilizer and manure application plan, Rotation soil loss assessment, Rotation P Index Value, Rotation P and K balance Nutrient application calculator

Download from SNAP-Plus website:

How many years in a plan? Nutrient application plans - 1 year Soil loss – rotation (up to 8 years) P-based planning – 4 years (soil test frequency) or rotation Conceptual Hurdle

Wisconsin Solution Phosphorus planning is rotation-based

P Index Planning No manure can be applied to a field with a planned P Index value greater than 6 across the rotation

Current Program Status On-going field monitoring and research Equations will be refined Field testing on farms as nutrient management planning tool Program improvements based on user feedback, agency needs Field testing on farms as P and sediment delivery risk tool Planned features (near future): filter strips; incorporation of economic information for planning

Wisconsin Dairy Farms Preliminary Results If applying manure according N standards, not over-applying P to most fields Most farms have very few “problems”: Erosion (corn for silage) Unmanaged grazing on fragile lands Large winter manure applications High soil test P

“Most-Problems” Farm Daily Haul – Rotation 2 Corn silage – Oats – 3 Alfalfa – Spr. Chisel Plow

Same Farm as No-till

Summary Wisconsin is using a quasi-model-type P Index integrated with RUSLE2 in nutrient management planning software Will lead to: More planning flexibility for producers Greater reductions in P delivery to surface waters

Acknowledgements Wes Jarrell, U. of Illinois Kevin Erb, UW-Extension Dan Yoder and Jim Lyon, U. of Tennessee Kevin Beckard, Sue Porter, and Jim Vandenbrook; WI DATCP Judy Derricks, John Pingry, and Pat Murphy; WI NRCS Chris Baxter, Paul Kivlin, and Scott Sturgul; UW-Extension Peggy James and Mark Caine, WI DNR Jeff Topel Major funding contributors for SNAP-Plus or related research: UW College of Agricultural and Life Sciences (CALS), Department of Agriculture, Trade, and Consumer Protection (DATCP), Natural Resources Conservation Service (NRCS), Wisconsin Fertilizer Research Program (WFRP), Wisconsin Buffer Initiative (WBI), UW Consortium for Agricultural and Natural Resources Research Researchers Conducting Runoff Monitoring: Dave Owens, Todd Stuntebeck, and Matt Komiskey, USGS; Carlos Bonilla, John M. Norman, and Christine Molling, UW- Madison Soil Science Department; John Panuska, Paul Miller, and K.G. Karthikeyan, UW-Madison Biological Systems Engineering Department; Randy Mentz, Chris Baxter, and Tom Hunt, UW-Platteville Pioneer Farm; Dennis Frame and Fred Madison, UW- Discovery Farms.