Wisconsin P Index Basics for Watershed Planning Laura Ward Good UW-Madison Soil Science Department February 8, 2011
Wisconsin P Index Basics for Watershed Planning What it is What makes it change How it varies across watersheds
Wisconsin P Index Calculated P lb/acre/year delivered with average weather Dissolved P soil Dissolved P manure/fertilizer Eroded sediment P Field Stream
County Soil Type Soil Test P and Organic Matter Rotation Average WI P Index Field Slope Field Slope Length Tillage Rotation oa o crops copsand yields Manure Applications P Fertilizer Applications Downfield Slope to Surface Water Distance to Surface Water Phosphorus Index County Relative indicator of the potential for runoff Pfromagivenfieldto field contaminate surface water (lbs P/ac/yr)
Phosphorus h Index Equations Dissolved P from soil Dissolved P from manure and fertilizer Eroded sediment P [P] x Transport = P delivered
County Soil Type Soil Test P and Organic Matter Field Slope Field Slope Length Available P on Field Surface Soil total P Soil soluble P Tillage Rotation oa o crops copsa and yields Manure Applications P Fertilizer Applications Downfield Slope to Surface Water Distance to Surface Water Manure & fertilizer soluble P
Field Transport Potential County Soil Type Soil Test P and Organic Matter Weather databases Erosion - RUSLE2 Field Slope Field Slope Length Tillage Rotation crops and yields Manure Applications P Fertilizer Applications Downfield Slope to Surface Water Distance to Surface Water Rainfall runoff Frozen soil runoff
County Soil Type Soil Test P and Organic Matter Field Slope Field Slope Length WI P Index Calculations for Nutrient Management Planning Field is uniform Dominant critical soil, slope, and slope length High erosion estimate Tillage Rotation crops and yields Manure Applications P Fertilizer Applications Field
Fields lose P with runoff and erosion Average winter (W, frozen soil) and nonwinter (NW) runoff, sediment and phosphorus loss for monitored fields and pastures, 2004 2007. Runoff inch Sediment T/a ton/acre inch Phosphorus lb/a lb b/acre 2.5 2.0 1.5 1.0 0.5 0.0 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 2.5 2.0 1.5 1.0 2004 2005 2006 2007 W NW W NW W NW W NW Dissolved Particulate 0.5 0.0
Testing Source Components of P Index Equations WI Total P Index compared to measured runoff losses for 86 site years using measured sediment and runoff volume in the equations 16 14 12 P Index WI 10 8 6 4 2 0 y = 0.81x + 0.12 R 2 = 0.82 0 5 10 15 20 Measured Measured total P in lb runoff acre -1 lb/acre/yr -1
Year-to-year variability in precipitation means annual P Index values will not match measured loads P Index WI 15 13 11 9 7 5 3 1 1 y = 0.28x + 1.69 r² = 0.24 0 5 10 15 20 Measured total P in surface runoff lb/p/yr Measured total P in runoff lb/acre/yr
P Index Varies with Management: Driftless Area Example Soil test P = 70 ppm Fall chisel in 10,000 gal/acre dairy manure 5 T/a/yr erosion No till, fall apply 10,000 gal/acre dairy manure 2 T/a/yr erosion No till, winter apply 7,000 gal/acre dairy manure 2 T/a/yr erosion
P Index Varies with Management: Eastern Wisconsin Example Soil test P = 70 ppm Fall chisel in No till, fall apply No till, winter apply 10,000 gal/acre 10,000 gal/acre 7,000 gal/acre dairy dairy manure dairy manure manure 1.3 T/a/yr erosion 0.5 T/a/yr erosion 0.5 T/a/yr erosion
P Index over time with continuous corn silage Marathon County, Loyal silt loam, 4% slope. Initial soil test P is 100 ppm. Corn silage, 18 in rows. Fall chisel plowed or no till. With and without 12,000 gallons/acre liquid dairy manure in Fall.
County Soil Type Soil Test P and Organic Matter Field Slope PD Delivery Factor Field Slope Length Tillage Rotation crops and yields Manure Applications P Fertilizer Applications Downfield Slope to Surface Water Distance to Surface Water Stream Field
P Index: P Index: Estimate of annual storm flow delivery potential to nearest surface water
P Loss Potential Varies Across A Watershed 2000 1500 Acres 1000 500 0 6 12 WI P Index
Similar watersheds have similar PI Index distribution Paired watersheds in Driftless Area cropland, intensive grazing Acr res 1000 800 600 400 13% acres above 6 Average soil test P: 34-37 ppm Average soil loss: ~ 2.5 T/acre/yr Average WI P Index: 4 200 0 1000 6 12 WI P Index 17% acres above 6 Acres 500 0 6 12 WI P Index
Dane County N. Fork Pheasant Branch Cropland Average soil test P: 93 ppm Average soil loss: 2.5 T/acre/yr Average WI P Index: 4 700 600 Acr res 500 400 300 20% of acres have PI greater than 6 200 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 WI P Index Source: Corey Anderson
Lake Montello, Marquette County Cropland Average soil test P: 64 ppm Average erosion: 1.2 T/a/yr Avgerage WI P Index:1 Acres 3000 2500 2000 1500 1000 500 0 1% of acres are over 6 1 2 3 4 5 6 7 8 WI P Index
Acres 7000 Initial distribution 6000 5000 4000 3000 2000 1000 0 6 12 WI P Index Acres 7000 All fields managed to PI of 6, Results in 26% load reduction 6000 5000 4000 3000 2000 1000 0 6 12 WI P Index
Need to quantify other sources of P delivery to stream Storm loads: Dry lots, night pastures Barnyards Bank erosion Base loads: Groundwater Cattle in stream channels Phosphorus sorption and release from sediments Tile drains
Wisconsin P Index Basics for Watershed Planning Reasonable field rating tool Fields vary Watersheds vary