Phosphorus in the Environment

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Phosphorus Index Based Management
Douglas Beegle Dept. of Crop and Soil
Sciences Penn State University dbb_at_psu.edu http/
/panutrientmgmt.cas.psu.edu
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Why do we need a P Index?Why not just agronomic
recommendations?
¼
Nutrient flows in modern ag
¾
?
P Index
Manure
P Index
Eutrophication
Regional P Balance
Field P Balance
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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
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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
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Managing Phosphorus Pollution
Transport
Sources
Runoff
Erosion
Leaching
Tile flow
Subsurface flow
Water Body
Hydrology
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Soil Test vs P Loss
P loss, lb P2O5/A
P Threshold
Crop P Optimum
No recent P inputs
R20.80
Mehlich-3 soil P, mg/kg
Sharpley, USDA-ARS
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Managing Phosphorus Pollution
Transport
Sources
Runoff
Erosion
Leaching
Tile flow
Subsurface flow
Water Body
Hydrology
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Soil Test vs P Loss - with applied P
For all data points R20.40
P loss, lb P2O5/A
75 kg P/ha TSP 112 kg P/ha swine slurry 150 kg
P/ha poultry manure
Soil Only R20.80
Mehlich-3 soil P, mg/kg
Sharpley, USDA-ARS
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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

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Managing Phosphorus Pollution
Transport
Sources
Runoff
Erosion
Leaching
Tile flow
Subsurface flow
Water Body
Hydrology
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Phosphorus Transport by Erosion
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Managing Phosphorus Pollution
Transport
Sources
Runoff
Erosion
Leaching
Tile flow
Subsurface flow
Water Body
Hydrology
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Zone of Interaction with Runoff

• 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.

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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
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Managing Phosphorus Pollution
Transport
Sources
Runoff
Erosion
Leaching
Tile flow
Subsurface flow
Water Body
Hydrology
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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
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P Loss is a Complex Landscape Process
Transport
Sources
Runoff
Erosion
Leaching
Tile flow
Subsurface flow
Water Body
Hydrology
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Landscape Transport
Hydrology
Modified Connectivity Direct Connection
Modified Connectivity Riparian Buffer
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Phosphorus Index

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

Drainage
Distance
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PA Phosphorus Index v 2.0
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P Index describes P loss potential
High
Very high
Medium
Low
P loss, kg/ha
75 kg P/ha TSP 112 kg P/ha swine slurry 150 kg
P/ha poultry manure
R20.79
P index value for the site
Sharpley, USDA-ARS
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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.

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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 _at_ N rate, excess P
• Unacceptable Risk
• Modify N based plan, where necessary, to address
  P loss risk

or
or
NONE
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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

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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

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College of Agricultural Sciences
Department of Crop and Soil Sciences