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Bw

Phosphorus storage and release characteristics pertinent to watertable management and BMP

implementation for Okeechobee Basin soils

Vimala NairSoil and Water Science Department

University of Florida

June 04, 2008

22

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E

Bh

Bw

A

E

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BwOutline

• Phosphorus issues in the Lake Okeechobee Basin (LOB) and contributors to research activities

• Soils of the LOB• Soil test P as a risk assessment tool and the need for an

alternate protocol• A new concept – the “safe” soil P storage capacity

(SPSC)• Applications of SPSC• Our progress …• What needs to be done …• Other related research needs in the LOB

33

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Bh

Bw

A

E

Bh

BwPhosphorus Transfer

Wetlands & Streams

[sink/source]

LakeOkeechobee

Lake [sink]

Uplands[sink/source]

Fertilizers, Animal wastesBiosolids, Wastewaters

Credit: K. R. Reddy and P. Inglett

44

A

E

Bh

Bw

A

E

Bh

BwSoils of the Lake Okeechobee County

Histosols2%

Alfisols3% Mollisols

4%Inceptisols4%

Others 11%

Entisols12%

Spodosols64%

Source: Vickie Hoge

55

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E

Bh

Bw

A

E

Bh

BwSoils of Florida Watersheds

Sand grain coatings,

their presence or absence,

makes a bigdifference in

P retention capacity

A

E

Bh

Bw

Entisol

SpodosolCredit: Willie Harris

66

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Bh

Bw

A

E

Bh

BwThe Need for a New Protocol

• Low value of soil test P (STP) is not necessarily an indicator of low environmental risk if P is added to a soil

• Some sandy soils, such as the Spodosols of the LOB could have 99% quartz sand in the upper horizons and negligible P retention

• STP does not convey the amount of P that can be safely added to a soil in an absolute sense

Nair, V.D., and W.G. Harris. 2004. New Zealand J. Agric. Res. 47:491-497.

77

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A

E

Bh

BwDevelopment of a New Protocol

• Based on extractable P of soil• Also on P retention capacity of soil (related to Fe+Al)• New tool: “Safe” Soil P Storage Capacity (SPSC)• Calculations based on oxalate-extractable P, Fe and Al• Calculations can also be based on P, Fe and Al in

Mehlich 1 or Mehlich 3 solutions

USDA-IFAFS

88

A

E

Bh

Bw

A

E

Bh

BwP Saturation Ratio (PSR)

• Ex-P/ [ExFe + ExAl] (Ex = Extractable)

• Change point ~ 0.10• Confidence intervals: 0.05

– 0.15• Threshold PSR: 0.15

Nair, V.D., K.M. Portier, D.A. Graetz, andM.L. Walker. 2004. J. Environ. Qual. 33:107-113.

FDEP

0

5

10

15

20

25

0 .125 .025 .375 0.5 .625 .75 .875

Wat

er S

olub

le P

(mg

kg-1

)

Surface HorizonSubsurface Horizon

PSR M1

Change point = 0.1

0

5

10

15

20

25

0 0.125 0.25 0.375 0.5PSROX

Wat

er S

olub

le P

(mg

kg-1

)

Surface HorizonSubsurface Horizon

Change point = 0.1

99

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E

Bh

Bw

A

E

Bh

BwThe Approach – “Safe” Soil Phosphorus Storage Capacity (SPSC)

31*2756 ⎥⎦

⎤⎢⎣⎡ +

AlOxalateFeOxalateSPSC = (0.15 – Soil PSR) * 31*

2756 ⎥⎦⎤

⎢⎣⎡ +

AlOxalateFeOxalateSPSC = (0.15 – Soil PSR) *

Nair, V.D., and W.G. Harris. 2004. New Zealand J. Agric. Res. 47:491-497.

• SPSC can also be expressed in mmoles P kg-1, or kg P ha-1

• SPSC is additive; SPSC for horizons within a sandy soil can be added providing a single value for a designated depth

(mg P kg-1)

Sink when soil PSR < 0.15 (positive SPSC)Source when Soil PSR > 0.15 (negative SPSC)

1010

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SPSC Calculations using Soil Test Parameters

Why do we need conversion factors for SPSC calculations using STP?

(mg P kg-1)

(mg P kg-1)

31*2756 ⎥⎦

⎤⎢⎣⎡ + AlOxalateFeOxalate

SPSC = (0.15 – Soil PSR) * 31*2756 ⎥⎦

⎤⎢⎣⎡ + AlOxalateFeOxalate

SPSC = (0.15 – Soil PSR) *

56⎢⎣⎡

+Mehlich 1

SPSC = (0.15 – Soil PSR) * 56⎢⎣

⎡ Fe SPSC = (0.15 – Soil PSR) *

27AlMehlich 1 31*⎥⎦⎤⎥⎦⎤

* ?

1111

A

E

Bh

Bw

A

E

Bh

BwConversion Factors for A & E Horizons

y = 2.24x - 2.92R² = 0.84n = 760

-1000

-800

-600

-400

-200

0

200

400

-300 -200 -100 0 100 200

SPSC-M1 (mg kg-1)

SPSC

-Ox

(mg

kg-1

)

Okeechobee A & E horizons

1212

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E

Bh

Bw

A

E

Bh

BwSPSC and Water Soluble P (WSP)

• Soil is a P sink when SPSC is positive and a source when SPSC is negative

• Similar observation under field conditions

• 95% of samples with positive SPSC (soil is a P sink) indicate less than 0.1 mg L-1 P in solution

Chrysostome, M, V.D. Nair, W.G. Harris, and R.D. Rhue. 2007. Soil Sci. Soc. Am. J. 71:1564–1569.

Column Study Set-up

y = -65.89x - 25.41R2= 0.88

-600

-500

-400

-300

-200

-100

0

100

200

300

0 1 2 3 4 5 6

Average leachate P concentration (mg L -1)

Initi

al S

PSC

(mg

P kg

-1)

Lab

P source

P sink

y = -11.6x –0.9R2 = 0.84n = 147

-600

-500

-400

-300

-200

-100

0

100

200

300

400

0 10 20 30 40 50 60

WSP (mg kg-1)

SPSC

(mg

kg-1

)

n = 604

y = -11.6x –0.9R2 = 0.84n = 147

600

500

400

300

200

100

0

100

200

300

400

0 10 20 30 40 50 60

WSP (mg kg-

y = -11.6x –0.9R2 = 0.84n = 147

-

-

-

-

-

- 0 10 20 30 40 50 60

-1 )

SPSC

(mg

kg-1

) n = 604

Field

P source

P sink

1313

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Bw

A

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Bh

BwApplication: Soils of LOB

A

E

Bh

Bw

Spodosol Profile

SFWMD; FDACS

SPSC (kg haSPSC (kg ha 1- )0 1000 2000 3000 4000 5000 6000

Dep

th (c

m)

AE

Bh

Bw2

Bw1

B ’h

a

0

20

40

60

80

100

-400 -200 0 200 400 600 800 1000

E1

BhBw

E2

0

20

40

60

80

b

0 1000 2000 3000 4000 5000 60000 1000 2000 3000 4000 5000 6000A

EBhBh

Bw2

Bw1Bw1

B ’hB ’h

a

AAE

E1

BhBw

E2

0

20

40

60

80

b

AAE

0

20

40

60

80

100

-400 -200 0 200 400 600 800 1000

Dep

th (c

m) E1

BhBw

E2

0

20

40

60

80

b

AAAE

0

100

-400 -200 0 200 400 600 800 1000

E1

Bh

Bw

E2

0

20

40

60

80

b

Minimally impacted

Impacted

0

20

40

60

80

100

P sink

P source

1414

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A

E

Bh

BwApplications

0102030405060708090

100

0 200 400 600 800 1000 1200 1400

Dep

th, c

m0

102030405060708090

100

- 200 0 200 400 600 800 1000 1200 1400D

epth

, cm

0102030405060708090

100

- 200

Soil P Storage Capacity, kg P ha-1

Dep

th, c

m0

102030405060708090

100

Dep

th, c

m

Tree-based vs tree-less pasture

Nair, V.D. P.K.R. Nair, R.S. Kalmbacher, and I.V. Ezenwa. 2007. Ecol. Eng. 29:192-199. Michel, G.-A., V.D. Nair, P.K.R. Nair. 2007. Plant Soil. 297:267-276.

USDA/IFAFS, through the Center for Subtropical Agroforestry

SPSC=1495 kg P ha-1

SPSC=370 kg P ha-1

SPSC increased by ~ 60 kg P ha-1 yr-1 in presence of trees

1515

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A

E

Bh

BwUse of SPSC for Watertable Monitoring

FDACS

E1

Bh

Bw

E

2

0

20

40

60

80

b

A

AE

0

20

40

60

80

100

-400 -200 0 200 400 600 800 1000

Dep

th (c

m)

E1

Bh

Bw

E

2

0

20

40

60

80

b

AA

AE

0-400 -200 0 200 400 600 800 1000

E1

Bh

Bw

E2

0

Water table

SPSC (kg haSPSC (kg ha 1- )

P sink

P source

1616

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Bw

A

E

Bh

BwSoil Series and Watertable

Water table BhBh

Bh

Bh

Ona Myakka Immokalee Pomello

If the “safe” soil P storage capacity above the Bh is the same …..

FDACS

1717

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E

Bh

Bw

A

E

Bh

BwBh Horizons and the “Change point”

y = 104.71x - 1.16R2 = 0.64

n = 37

y = 65.541x - 0.9138R 2 = 0.2956, n = 78

0

20

40

60

80

100

120

140

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

PSR -Ox

WSP

(mg

kg-1

)

Change point = 0.10

0

20

40

60

80

100

120

140

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

PSR ‐M1

WSP

 (mg kg

‐1)

Change point = 0.10

y = 26.2 + 0.08; R2 = 0.53

y = 79.8 + 1.47; R2 = 0.71

• Change point is 0.1using either oxalate orMehlich 1- P, Fe and Al• The value is the same as that for A & E horizons

FDACS

1818

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A

E

Bh

BwOur progress …

• Protocol for SPSC calculation established (using oxalate P, Fe and Al) for A, E, and Bh horizons

• Need to establish protocol for SPSC calculation using easily determined parameters in soil test solutions (Mehlich 1 and Mehlich 3)

• Conversion factor for SPSC calculation That factor is ~2.25 for A and E horizons using Mehlich 1 parametersConversion factor for Bh horizons is on-going (using Mehlich 1)Need to obtain conversion factors for both A & E, and Bhhorizons using Mehlich 3

1919

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Bh

BwThe End Product …..

• Protocol for determining SPSC will be available using Mehlich 1 and Mehlich 3 solutions obtainable in soil testing laboratories in Florida

• The SPSC concept, and alternate procedures for its calculation will be available as an EDIS publication, and also available in our soil testing lab

• Able to calculate SPSC to any desired soil depth (Note: SPSC is additive)

• Able to determine if a given soil volume (or mass) is an environmental risk (positive SPSC: P sink; negative SPSC: P source)

2020

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Bh

Bw

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Bh

BwUses of SPSC for Okeechobee Soils

• Predict P release from a soil within the LOB that can be used to project consequences of water-table manipulations for P control

• Evaluate amount of P that can be safely applied to a soil if manure application is based on N requirements of a crop instead of P requirements

• Calculate the amount of an iron or aluminum- based amendment to be added to a soil as a BMP

31*2756 ⎥⎦

⎤⎢⎣⎡ +

AlOxalateFeOxalateSPSC = (0.15 – Soil PSR) * 31*

2756 ⎥⎦⎤

⎢⎣⎡ +

AlOxalateFeOxalateSPSC = (0.15 – Soil PSR) *

(mg P kg-1)

2121

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Bw

A

E

Bh

BwUses of SPSC cont.

• Predict reduction in SPSC with time if the P loading to a soil is known

• Identify suitable areas for location of animal-based agriculture by selecting soils with greater SPSC

• Verify suitability of potential locations for the construction of stormwater treatment areas.

2222

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BwPlanned Activities

• Set up lab experiment to evaluate:P release rates from Bh horizons as a function of P loading as measured by i) Mehlich extractable P and ii) SPSC determine if a relationship exists between SPSC and the amount of releasable P in Bh materials.

• Iron-oxide strips as a measure of releasable Pphytoremediationwatertable management

(to control P loss in drainage water from upland soils).

2323

A

E

Bh

Bw

A

E

Bh

BwResearch Areas not Addressed so Far• Use SPSC as a quantitative

approach for concurrently determining crop P requirement while minimizing environmental risks associated with offsite P movement

• Calculate the amount of aluminum or iron based amendment to be added to a soil to maintain near “zero”SPSC to allow unnecessary additions of the material

• SPSC for organic and calcareous soils

y = -11.6x –0.9R2 = 0.84n = 147

-600

-500

-400

-300

-200

-100

0

100

200

300

400

0 10 20 30 40 50 60

WSP (mg kg-1)

SPSC

(mg

kg-1

)

n = 604

y = -11.6x –0.9R2 = 0.84n = 147

600

500

400

300

200

100

0

100

200

300

400

0 10 20 30 40 50 60

WSP (mg kg-

y = -11.6x –0.9R2 = 0.84n = 147

-

-

-

-

-

- 0 10 20 30 40 50 60

-1 )

SPSC

(mg

kg-1

)

n = 604

5%0%

2%

61%

32%

24%

3%

2%

37%

34%Labile-P

Fe/Al-P

Organic-P

Ca/Mg-P

Residual P

Dairy manure Beef manure

TP = ~6000mg/kgTP = ~8000mg/kg

Nair, V.D., D.A. Graetz, and D.O. Dooley. 2003. J. Food Agric. Environ. 1: 217-223

• SPSC and P source effects

P sink

P source

2424

A

E

Bh

Bw

A

E

Bh

Bw

Thank you!