Phosphorus Index Based Management

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