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Wisconsin P Index BasicsWisconsin P Index Basicsfor Watershed Planning
Laura Ward GoodUW-Madison Soil Science DepartmentFebruary 8, 2011
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Wisconsin P Index BasicsWisconsin P Index Basicsfor Watershed Planning
•What it isWhat makes it change•What makes it change
•How it varies across watersheds
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Wisconsin P Index
Calculated P lb/acre/year delivered with average weather
Dissolved P soil Dissolved P manure/fertilizerDissolved P manure/fertilizerEroded sediment P
Field
Stream
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Rotation AverageCounty Rotation Average WI P Index Soil Test P and
Organic Matter
Soil TypeSoil Type
County
Organic Matter
Field Slope
Field Slope
Phosphorus Relative indicator of the potential for runoff P from a given field to
Length
Tillage
Rotation crops and Index P from a given field to
contaminate surface water (lbs P/ac/yr)
o a o c ops a dyields
Manure Applications
P F tiliP Fertilizer Applications
Downfield Slope to Surface Water
Distance to Surface Water
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Ph h I d E tiPhosphorus Index EquationsDissolved P from soilsso ed o so
Dissolved P from manure and fertilizer Eroded sediment P
[P] x Transport = P delivered
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Available P on Field SurfaceCounty
Soil total PSoil Test P and Organic Matter
Soil TypeSoil Type
Soil Test P and Organic Matter
Soil TypeSoil Type
Soil soluble P
Organic MatterOrganic Matter
Field Slope
Field Slope Soil soluble P
M & f tili
Tillage
Rotation crops and
Length
Tillage
Rotation crops and Manure & fertilizer soluble P
o a o c ops a dyields
Manure Applications
P F tili
o a o c ops a dyields
Manure Applications
P F tiliP Fertilizer ApplicationsP Fertilizer Applications
Downfield Slope to Surface Water
Distance to Surface Water
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Field Transport Potential
E i RUSLE2
County
Soil TypeSoil Type
Weather databasesCounty
Soil TypeSoil Type
Erosion - RUSLE2Soil Test P and Organic Matter
Field Slope
Soil Test P and Organic Matter
Field Slope
Field Slope Length
TillageRainfall runoff
Field Slope Length
Tillage
Rotation crops and yields
Manure
Frozen soil runoffRotation crops and yields
Manure ApplicationsApplications
P Fertilizer Applications
Downfield Slope toDownfield Slope to Surface Water
Distance to Surface Water
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CountyWI P Index Calculations for
Soil Test P and Organic Matter
Soil TypeSoil Type Nutrient Management Planning
Field is uniformField Slope
Field Slope Length
Field is uniformDominant critical soil, slope, and slope lengthHigh erosion estimate
g
Tillage
Rotation crops and yields
Field
yields
Manure Applications
P Fertilizer Applications
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2.5
2004 2005 2006 2007W NW W NW W NW W NWFields lose
1.0
1.5
2.0
inch
P with runoff and
Runoffinch
0.0
0.5
1.4Average winter (W
runoff and erosion
Sediment
0.6
0.8
1.0
1.2
ton/
acre
Average winter (W, frozen soil) and non-winter (NW) runoff,
di t d
Sediment T/a
DissolvedParticulate
0.0
0.2
0.4sediment and phosphorus loss for monitored fields and
1.5
2.0
2.5
b/ac
re
pastures, 2004 – 2007.
Phosphoruslb/a
0.0
0.5
1.0lb
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WI T t l P I d d t d ff l f 86 it
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
12
14
16
8
10
12
P In
dex
y = 0.81x + 0.12R2 = 0.82
2
4
6WI
0
2
0 5 10 15 20
Measured lb acre-1 yr-1Measured total P in runoff lb/acre/yr
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Year-to-year variability in precipitation means annual P Index values will notmeans annual P Index values will not
match measured loads
y = 0.28x + 1.69r² = 0.24
13
15
7
9
11
P Inde
x
1
3
5WI
‐1
1
0 5 10 15 20
Measured total P in surface runoff lb/P/yrMeasured total P in runoff lb/acre/yry
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P Index Varies with Management: Driftless Area Example
Soil test P = 70 ppmSoil test P = 70 ppm
Fall chisel in 10,000 gal/acre dairy manure
No till, fall apply 10,000 gal/acre dairy manure
No till, winter apply 7,000 gal/acre dairy manuredairy manure
5 T/a/yr erosiondairy manure2 T/a/yr erosion
manure2 T/a/yr erosion
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P Index Varies with Management: Eastern Wisconsin Example
Soil test P = 70 ppm
Fall chisel in 10,000 gal/acre dairy manure
No till, fall apply 10,000 gal/acre dairy manure
No till, winter apply 7,000 gal/acre dairy manurey
1.3 T/a/yr erosion 0.5 T/a/yr erosion 0.5 T/a/yr erosion
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P Index over time with continuous corn silage Marathon County, Loyal silt loam, 4% slope.y y pInitial 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.
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County
P D li F tSoil Test P and Organic Matter
Soil TypeSoil Type
P Delivery FactorField Slope
Field Slope Lengthg
Tillage
Rotation crops and yields
Field
yields
Manure Applications
P Fertilizer
Downfield Slope to Surface Water
Distance to Surface
Applications
Downfield Slope to Surface Water
Distance to Surface
Stream
Distance to Surface Water
Distance to Surface Water
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P Index:P Index:Estimate of annual storm flow delivery potential to nearest surface water
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P Loss Potential Varies Across A Watershed
2000
1000
1500
Acres
0
500
WI P Index
6 12
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Similar watersheds have similar PI Index distributionPaired watersheds in Driftless Area – cropland, intensive grazing
13% b 6 Average soil test P: 34 -37 ppmAverage soil loss: ~ 2.5 T/acre/yr Average WI P Index: 4
600
800
1000
res
13% acres above 6
0
200
400Acr
6 12
1000
s
WI P Index
17% acres above 6
0
500
Acr
es
WI P Index 6 12
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Dane CountyN Fork Pheasant BranchN. Fork Pheasant Branch
Cropland
Average soil test P: 93 ppmAverage soil loss: 2 5 T/acre/yr
600
700
Average soil loss: 2.5 T/acre/yrAverage WI P Index: 4
400
500
600
res
20% of acres have PI greater than 6
100
200
300Acr
0
100
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
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Lake Montello, Marquette CountyCropland
Average soil test P: 64 ppm Average erosion: 1.2 T/a/yrAvgerage WI P Index:1
2500
3000
1% of acres are over 6
1000
1500
2000
Acres
0
500
1 2 3 4 5 6 7 8
WI P Index
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6000
7000 Initial distribution
3000
4000
5000
Acres
0
1000
2000
6 12
WI P Index
6 12
5000
6000
7000 All fields managed to PI of 6,Results in 26% load reduction
1000
2000
3000
4000
Acres
0
1000
WI P Index
6 12
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Need to quantify other sources of P delivery to stream
Storm loads:Storm loads:
• Dry lots, night pastures
• Barnyards• Barnyards
• Bank erosion
Base loads:Base loads:
• Groundwater
• Cattle in stream channels• Cattle in stream channels
• Phosphorus sorption and release from sedimentsrelease from sediments
• Tile drains
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Wisconsin P Index BasicsWisconsin P Index Basicsfor Watershed Planning
• Reasonable field rating tool• Fields vary• Watersheds vary• Watersheds vary