Phosphorus Phosphorus Index Based Index Based ManagementManagement
Phosphorus Phosphorus Index Based Index Based ManagementManagement
Douglas Beegle Dept. of Crop and Soil Sciences
Penn State University
[email protected]://panutrientmgmt.cas.psu.edu
Why do we need a P Index?Why not just agronomic recommendations?
N P2O5 K2O
Nitrogen BasedCorn/Dairy
Manure
Regional P Balance
¼
¾
ManureManure
Crops
Soil
AnimalsFeed
EutrophicatioEutrophicationn
Nutrient flows in
modern ag
P Index
?
Field P Balance
N P2O5 K2O
Phosphorus Based
Corn/Dairy Manure
P Index
Source Transport
Critical Source Area
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 Areas of P Export
90% of annual P export comes from 10% of land area
Mahantango Creek Watershed, USDA-ARS
90% of P Loss comes from 10% of the watershed
Managing Phosphorus Pollution
Subsurfaceflow
Tile flow
Leaching
Sources Transport
Erosion
Runoff
N P K
Hydrology Water Body
Mehlich-3 soil P, Mehlich-3 soil P, mg/kgmg/kg
00 200200 400400 600600 800800
P loss,P loss,
lb Plb P22OO55/A/A
Soil Test vs P Loss
R2=0.80
0.80.8
00
1.61.6
2.42.4
Sharpley, USDA-ARS
Crop POptimum
P Threshold
No recent P inputs
Managing Phosphorus Pollution
Subsurfaceflow
Tile flow
Leaching
Sources Transport
Erosion
Runoff
Hydrology Water Body
N P K
Mehlich-3 soil P, Mehlich-3 soil P, mg/kgmg/kg
00 200200 400400 600600 800800
P loss,P loss,
lb Plb P22OO55/A/A
75 kg P/ha TSP
112 kg P/ha swine slurry
150 kg P/ha poultry manure
75 kg P/ha TSP
112 kg P/ha swine slurry
150 kg P/ha poultry manure
Soil Test vs P Loss - with applied P
Soil OnlyR2=0.80
For all data points R2=0.40
0.80.8
00
1.61.6
2.42.4
Sharpley, USDA-ARS
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
Managing Phosphorus Pollution
Subsurfaceflow
Tile flow
Leaching
Sources Transport
Runoff
N P K
Hydrology Water Body
Erosion
Phosphorus Transport by Erosion
Erosion reduced 95%
1980 1985 1990 1995
Conventionaltill wheat
Convertedto no-till
Total P
mg/L
6
4
2
0
-
-
Sharpley, USDA-ARS
Managing Phosphorus Pollution
Subsurfaceflow
Tile flow
Leaching
Sources Transport
Erosion
N P K
Hydrology Water Body
Runoff
Zone of Interaction with Runoff
100
0 100 200 300 400 500 600
0
20
40
60
80
Mehlich 1 P (mg/kg)
Dep
th (
cm)
Data from Mozaffari and Sims, 1994
Zone of interaction with runoff
Plow depth
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.
Soluble P Transport in Runoff
Conventionaltill wheat
1980 1985 19951990
Alg
al-
availa
ble
P, m
g/L
0.5
1.0
0
Convertedto no-till
Sharpley, USDA-ARS
Managing Phosphorus Pollution
Subsurfaceflow
Tile flow
Sources Transport
Erosion
Runoff
N P K
Hydrology Water Body
Leaching
Soluble P Loss by Sub-surface flowVery 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
P Loss is a Complex “Landscape” Process
Subsurfaceflow
Tile flow
Leaching
Sources Transport
Erosion
Runoff
N P K
Hydrology Water Body
Modified Connectivity:
Direct Connection
Landscape Transport
Modified Connectivity:
Riparian Buffer
DistanceRunoff Return Period Hydrology
Phosphorus Index
• P Transport Site Characteristics
– Soil Erosion
– Runoff Class
– Leaching Potential
• Sub-surface Drainage
– Contributing Distance
– Modified Connectivity
Erosion
Runoff
Drainage
Distance
PA
Phosphorus
Index
v 2.0
0.40.4
00
0.80.8
1.21.2
P loss,P loss,
kg/hakg/ha
P index value for the siteP index value for the site
00 5050 100100 150150 200200
75 kg P/ha TSP
112 kg P/ha swine slurry
150 kg P/ha poultry manure
75 kg P/ha TSP
112 kg P/ha swine slurry
150 kg P/ha poultry manure
P Index describes P loss potential
Very highVery highHighHighMediumMediumLowLow
Sharpley, USDA-ARS
R2=0.79
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.
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
N P2O5 K2O
Nitrogen BasedCorn/Dairy
Manure
N P2O5 K2O
Phosphorus Based
Corn/Dairy Manure
or
or
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
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
College of Agricultural Sciences
Department of Crop and Soil Sciences