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Nutrient management tools for protecting environmental quality while maintaining economic sustainability: Tools that meet a regulatory requirement – The Wisconsin P Index L. Bundy, L.W. Good, P Kaarakka, W. Jarrell University of Wisconsin-Madison The Wisconsin P Index Structure of P index

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l bundy l w good p kaarakka w jarrell university of wisconsin madison
Nutrient management tools for protecting environmental quality while maintaining economic sustainability:Tools that meet a regulatory requirement – The Wisconsin P Index

L. Bundy, L.W. Good, P Kaarakka, W. Jarrell

University of Wisconsin-Madison

the wisconsin p index
The Wisconsin P Index
  • Structure of P index
  • Research basis for P index estimates of P loss
  • Application of P index
the wisconsin p index3
The Wisconsin P Index
  • Indicates potential of a field to deliver P to surface water
  • P index values used to rank fields for P loss
  • Identifies management options for reducing P loss
the p index and nutrient management planning
The P Index and Nutrient Management Planning
  • Tool for implementing P-based planning
  • Options for P applications:
    • Use Wisconsin P index
    • Rates based on soil test P values
components of the phosphorus index pi
Components of the Phosphorus Index (PI):

PI = PP + SP

PI =Total P index

PP =Particulate P

SP =Soluble P

slide7
Sediment delivered to edge of field calculated by RUSLE2 Assumes no concentrated flow in field, but includes effects of in-field deposition if multiple field slope or management segments are entered in the program.

Field

Delivery point for P Index calculation: perennial or intermittent stream

Sediment travels via concentrated flow from edge of field to waterway

Particulate P Movement

Particulate P = Sediment loss x Sediment P concentration x Sediment delivery ratio

slide8
Dissolved P Movement

Soluble P = Annual runoff volume x Dissolved P concentration

Dissolved P delivered to edge of field calculated as annual rainfall plus snowmelt runoff volume times the average runoff P concentration

Field

No off-field infiltration. Volume of runoff and concentration of P in the runoff does not change with distance to delivery point.

Delivery point for P Index calculation: perennial or intermittent stream

slide9
Wisconsin Datasets used for P Index

Development

  • Simulated rainfall runoff:
  • Alfalfa – 20 events
  • Corn – 267 events, 4 sites

Varying:

    • Tillage
    • Manure applications
    • Timing
    • Soil test P
slide10
Natural rainfall runoff:
    • Alfalfa – 24 plots
    • Corn- 36 plots

Research ongoing. Datasets growing.

parameters needed to calculate p index values
Soil hydrol. group

Field slope (%)

Soil group

Contour, Terrace,

Residue Mgt.

Crop

Distance (Field to H2O) & Ave. Dist. slope (%)

Erosion rate

Bray P-1 soil test

Manure rate & type

Avail. P2O5

Month of manure application

Fert. Rate, P2O5 %

Incorporated (X)

Frozen ground (X)

Parameters needed to calculate P index values
slide12
The Interpretation of the Wisconsin PI - field basis

0 - 2: Minimal risk, N-based management

2 - 6: PI should not increase over 4 years or length of average rotation

6 -10: Implement plans to decrease PI to <6 over two rotations (max. 6 years)

> 10: Lower PI to <10 over one rotation or 4 years, anddecrease PI to <6 over two additional rotations or 6 years

slide13
PP = Annual mass loss x sediment P concentration

SP = Annual volume loss x runoff P concentration

slide15
Runoff dissolved P can be predicted by soil test P and soil type

Simulated rainfall runoff corn plots without manure applications

slide17
New P additions to a field can be accounted for in P Index calculations adjusting soil test P concentrations used in dissolved P concentration calculations
slide18
Natural runoff results show average runoff dissolved P concentrations related to soil test P
slide19
Relationship between average runoff dissolved P concentrations and soil test P on corn plots at Arlington, April through July, two soils, varying manure history and tillage
slide20
Particulate P concentrations can be predicted with soil test P

PP concentration = STP x Enrichment ratio

slide21
Relationship between soil test P and total P for soils from simulated rainfall runoff plots from three sites
slide22
Enrichment ratio

= Sediment P/Soil Total P

slide23
Sediment P enrichment ratio for simulated rainfall runoff plot events

No enrichment for simulated and natural runoff from corn!

slide24
PP = Annual mass loss x sediment P concentration

SP = Annual volume lossx runoff P concentration

Concentrations are only half of the story!

P Index web site

http://wpindex.soils.wisc.edu/

has more information

slide25
Single-event worst-case losses from surface manure applications are added to estimated annual P delivery
slide27
Runoff dissolved P and particulate P from simulated rainfall event one week after a 32 ton per acre dairy manure surface applicationto silt loam soil in the Spring (Lancaster) and Fall (Arlington) 
slide28
The additional SP load from
      • Spring manure = 0.5 %
      • Fall manure = 3.7 %
  • of the manure water soluble P.
  • The additional PP load from
        • Spring manure = 0
        • Fall manure = 2.9 %
  • of the manure total P.
slide29
Putting it all together:

The P Index shows the relative effects of different field management practices on P loads

slide30
Improved management practices to decrease PI if values are too high

Lower Bray PI (see above for particulate P)

Low-disturbance

manure incorporation

Eliminate mineral

P supplements

Soluble P

too high

Decrease soluble P

in manure

Chemically sorb or

precipitate P

Change winter

spreading

Storage

Spread on low-risk

sites

slide31
P Index Values for Grant County Corn Field

Rozetta silt loam soil, 6% slope, Bray P 50 ppm

7

6

Winter Manure

Fall Manure

Winter Manure

5

No Manure

4

Fall Manure

Spring Manure

P Index

3

Spring Manure

No Manure

2

1

0

Chisel Plow

No - till

Particulate P

Soluble P

the p index and nutrient management planning32
The P Index and Nutrient Management Planning
  • P index is not the ultimate solution to nutrient management
  • Balancing nutrient inputs and removals is the ultimate goal
  • Using the P index can minimize environmental problems until balance is achieved
slide33
SNAP-Plus

Output: Field by field fertilizer and manure application plan, P Index value, soil loss estimate

Nutrient application

calculator

Entry: Field by field crop manage-ment info

P Index calculator

RUSLE2 soil

loss calculator

The SNAP-Plus program will produce field-by-field nutrient management plans that will meet the 590 Nutrient Management Standard with a P Index value and soil loss estimate for each field

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