Wisconsin P Index BasicsWisconsin P Index Basicsfor Watershed Planning

Laura Ward GoodUW-Madison Soil Science DepartmentFebruary 8, 2011

Wisconsin P Index BasicsWisconsin P Index Basicsfor Watershed Planning

•What it isWhat makes it change•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/fertilizerDissolved P manure/fertilizerEroded sediment P

Field

Stream

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

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

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

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

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

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

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

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

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

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

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.

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

P Index:P Index:Estimate of annual storm flow delivery potential to nearest surface water

P Loss Potential Varies Across A Watershed

2000

1000

1500

Acres

0

500

WI  P Index

6 12

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

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

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

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

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

Wisconsin P Index BasicsWisconsin P Index Basicsfor Watershed Planning

• Reasonable field rating tool• Fields vary• Watersheds vary• Watersheds vary