Phosphorus Index-Based Management in Agriculture: Strategies for Nutrient Balancing

1. Phosphorus Index Based Management Douglas Beegle Dept. of Crop and Soil Sciences Penn State University dbb@psu.edu http://panutrientmgmt.cas.psu.edu

2. Animals Feed Crops Soil P2O5 P2O5 K2O K2O Why do we need a P Index?Why not just agronomic recommendations? ¼ Nitrogen Based Corn/Dairy Manure Nutrient flows in modern ag ¾ ? N P Index Manure P Index Phosphorus Based Corn/Dairy Manure Eutrophication Regional P Balance N Field P Balance

3. P Index Critical Source Area Management • Overlap of Source & Transport Indicators • Identify and manage the critical source areas • Evaluate environmental risk • Target effort and resources Critical Source Area Source Transport

4. Critical Areas of P Export 90% of annual P export comes from 10% of land area 90% of P Loss comes from 10% of the watershed Mahantango Creek Watershed, USDA-ARS

5. N P K Managing Phosphorus Pollution Transport Sources Runoff Erosion Leaching Tile flow Subsurface flow Water Body Hydrology

6. 2.4 1.6 0.8 0 400 600 800 200 0 Soil Test vs P Loss P loss, lb P2O5/A P Threshold Crop P Optimum No recent P inputs R2=0.80 Mehlich-3 soil P, mg/kg Sharpley, USDA-ARS

7. N P K Managing Phosphorus Pollution Transport Sources Runoff Erosion Leaching Tile flow Subsurface flow Water Body Hydrology

8. 2.4 1.6 0.8 0 400 600 800 200 0 Soil Test vs P Loss - with applied P For all data points R2=0.40 P loss, lb P2O5/A 75 kg P/ha TSP 112 kg P/ha swine slurry 150 kg P/ha poultry manure Soil Only R2=0.80 Mehlich-3 soil P, mg/kg Sharpley, USDA-ARS

9. Phosphorus Index • P Source Site Characteristics • Environmental Soil Test P • Same soil test different interpretation • Sampling Questions? • P Saturation? • P Fertilizer • Rate and Appl. Method • Organic P • Rate and Appl. Method • P Source Coefficient (PSC) • Direct availability of manure P to runoff • Based on WEP in manure

10. N P K Managing Phosphorus Pollution Transport Sources Runoff Erosion Leaching Tile flow Subsurface flow Water Body Hydrology

11. 6 - 4 Total P mg/L Conventional till wheat - 2 Converted to no-till 0 1980 1985 1990 1995 Erosion reduced 95% Sharpley, USDA-ARS Phosphorus Transport by Erosion

12. N P K Managing Phosphorus Pollution Transport Sources Runoff Erosion Leaching Tile flow Subsurface flow Water Body Hydrology

13. Zone of Interaction with Runoff Mehlich 1 P (mg/kg) • Location of applied P • Interaction with runoff • P on surface • Soil test at surface • High P Saturation at surface Psat = P / Al + FeOxalate extr. or Mehlich 3 extr. 0 100 200 300 400 500 600 0 20 40 Depth (cm) Zone of interaction with runoff Plow depth 60 80 Data from Mozaffari and Sims, 1994 100

14. 1980 1985 1990 1995 Soluble P Transport in Runoff 1.0 Algal-available P, mg/L Converted to no-till 0.5 0 Conventional till wheat Sharpley, USDA-ARS

15. N P K Managing Phosphorus Pollution Transport Sources Runoff Erosion Leaching Tile flow Subsurface flow Water Body Hydrology

16. Soluble P Loss by Sub-surface flow Very Dependent on soil properties • Hydrology • Piston flow • Macro pores • Texture • Soil Chemistry(Fe, Al, Ca) • P loading/saturation • Artificial Drainage Data from: Bolton et al., 1970 Culley and Bolton, 1983

17. N P K P Loss is a Complex “Landscape” Process Transport Sources Runoff Erosion Leaching Tile flow Subsurface flow Water Body Hydrology

18. Distance Runoff Return Period Landscape Transport Hydrology Modified Connectivity: Direct Connection Modified Connectivity: Riparian Buffer

19. Erosion Runoff Phosphorus Index • P Transport Site Characteristics • Soil Erosion • Runoff Class • Leaching Potential • Sub-surface Drainage • Contributing Distance • Modified Connectivity Drainage Distance

20. PA Phosphorus Index v 2.0

21. 1.2 0.8 0.4 0 100 150 200 50 0 P Index describes P loss potential High Low Medium Very high P loss, kg/ha 75 kg P/ha TSP 112 kg P/ha swine slurry 150 kg P/ha poultry manure R2=0.79 P index value for the site Sharpley, USDA-ARS

22. Phosphorus Index • Low P Index • N Based Management • Medium P Index • N Based Management • High P Index* • P Based: Crop removal • Very High P Index* • No P: Manure or Fertilizer • High and Very High* • Modify Management based on P • No or reduced manure • Change time or method of application • Conservation practices • Buffers • Etc.

23. P2O5 P2O5 K2O K2O Phosphorus Nutrient Management Plan • Develop N based plan • Usually means excess P will be applied • Use P Index to evaluate the N based plan • Is the risk of P loss acceptable • Acceptable risk • Apply @ N rate, excess P • Unacceptable Risk • Modify N based plan, where necessary, to address P loss risk Nitrogen Based Corn/Dairy Manure or N Phosphorus Based Corn/Dairy Manure or N NONE

24. P Index Application • Eventually, all fields will have a high P index • P Index is not the solution • Tool to buy time to solve problem • Minimizes negative impact of P while we come up with a sustainable solution • We need to get the system into better balance

25. NRCS/EPA P Index Issues • Proposed change in NRCS 590 Std. • P soil test only – No more P Index • Easy to regulate • Very strict limits • Not supported by the science - Source/Transport • Unrealistic for animal agriculture to comply with in short term • Better soil P balance is a good long term goal • Withdrawn, under further review

26. College of Agricultural Sciences Department of Crop and Soil Sciences