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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 Structure of P index

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L. Bundy, L.W. Good, P Kaarakka, W. Jarrell University of Wisconsin-Madison

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  1. 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

  2. The Wisconsin P Index • Structure of P index • Research basis for P index estimates of P loss • Application of P index

  3. 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

  4. Where does the P Index fit in nutrient management planning?

  5. 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

  6. Components of the Phosphorus Index (PI): PI = PP + SP PI =Total P index PP =Particulate P SP =Soluble P

  7. 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

  8. 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

  9. 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

  10. Natural rainfall runoff: • Alfalfa – 24 plots • Corn- 36 plots Research ongoing. Datasets growing.

  11. 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

  12. 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

  13. PP = Annual mass loss x sediment P concentration SP = Annual volume loss x runoff P concentration

  14. Soil water soluble P can be predicted from soil test P

  15. Runoff dissolved P can be predicted by soil test P and soil type Simulated rainfall runoff corn plots without manure applications

  16. Simulated rainfall runoff corn plots four to six months after incorporated manure

  17. 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

  18. Natural runoff results show average runoff dissolved P concentrations related to soil test P

  19. 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

  20. Particulate P concentrations can be predicted with soil test P PP concentration = STP x Enrichment ratio

  21. Relationship between soil test P and total P for soils from simulated rainfall runoff plots from three sites

  22. Enrichment ratio = Sediment P/Soil Total P

  23. Sediment P enrichment ratio for simulated rainfall runoff plot events No enrichment for simulated and natural runoff from corn!

  24. 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

  25. Single-event worst-case losses from surface manure applications are added to estimated annual P delivery

  26. Risks of manure P loss change by season of application: • Fall • Spring • Winter (frozen soil)

  27. 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) 

  28. 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.

  29. Putting it all together: The P Index shows the relative effects of different field management practices on P loads

  30. 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

  31. 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

  32. 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

  33. 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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