Phosphorus Chemistry in Phosphorus Chemistry in Soils Soils andand

Response to Fertilizer and Response to Fertilizer and ManuresManures

April Leytem

USDA/ARS

The Phosphorus The Phosphorus CycleCycleThe Phosphorus The Phosphorus CycleCycle

Animalmanures

and biosolids Mineralfertilizers

Crop harvest

Runoff anderosion

Leaching

Organic phosphorus•Microbial•Plant residue•Humus

Primaryminerals(apatite)

Plant residues

Plantuptake

Soil solutionphosphorus•HPO4

-2

•H2PO4-1

Secondarycompounds

(CaP, FeP, MnP, AlP)

Mineralsurfaces

(clays, Fe and Al oxides,

carbonates)

Mineralsurfaces

(clays, Fe and Al oxides,

carbonates)

InputsComponent Outputs

Atmosphericdeposition

PPI

PrecipitationPrecipitation

DissolutionDissolution

DesorptionDesorption

AdsorptionAdsorption

Wea

ther

ing

Wea

ther

ing

Immobilization

ImmobilizationMineralization

Mineralization

• Estimates of 800 million hectares of calcareous soils worldwide

• Generally they are low in P due to fairly insoluble Ca-P minerals

• The concentration of available P continues to decrease over time

Facts About Calcareous Facts About Calcareous SoilsSoils

Soil P FractionsSoil P Fractions

MineralPi

MineralPi

Labile Pi & Po

Labile Pi & Po

SolutionPi & Po

SolutionPi & Po

Mineral P >>> Labile P >> Solution-PMineral P >>> Labile P >> Solution-P

0

20

40

60

80

100

0 200 400 600 800

Equilibrium P (mg P L-1)

So

rbe

d P

(mm

ol

P k

g-1

) Experimental Data

Freundlich

Precipitation

Phosphorus Sorption in Soils

0 ppm P0 ppm P

Calcite Equilibrat

ed for 10 Days

Calcite Equilibrat

ed for 10 Days

10 ppm P10 ppm P

Calcite Equilibrate

d for 10 Days

Calcite Equilibrate

d for 10 Days

50 ppm P50 ppm P

Calcite Equilibrate

d for 10 Days

Calcite Equilibrate

d for 10 Days

The quantity of P sorbed on calcite depends largely on its surface area

Pure calcite has low surface area (1 to 2 m2/g)

Soil calcite has surface area ranging from 16 to 200 m2/g

(due to ongoing dissolution, reprecipitation, and incorporation of impurities)

On pure calcite, sorption occurs on ~5% of the surface beforeadsorption clusters serve as nuclei for Ca-P precipitation

• First few weeks, P initially precipitates First few weeks, P initially precipitates as MCP…. Then DCPDas MCP…. Then DCPD

• After 3 to 5 months, octacalcium phosphate After 3 to 5 months, octacalcium phosphate precipitatesprecipitates

• After 8 to 10 months, tricalcium phosphate After 8 to 10 months, tricalcium phosphate formsforms

• Long periods (years) hydroxyapatite Long periods (years) hydroxyapatite minerals form…minerals form…

(mineral with lowest solubility controls P (mineral with lowest solubility controls P concentration- while intermediates are concentration- while intermediates are unlikely to persist)unlikely to persist)

Traditional ConceptsAdding P Fertilizer to High pH/ High Calcium Soils

Incubation Period (days)

Fert

iliz

er

P A

vailab

ilit

y

(Fra

cti

on

of

Ad

ded

P S

till E

xtr

acta

ble

)

(Sharpley et al., 1989)

Phosphorus Availability Decreases Over Time

Average of 44% P sorptionbetween 30 and 180 days following application

Potato P Recommendations

0

100

200

300

400

500

0 10 20 30 40

STPC

P R

ate

, lb

s P

2O

5/A

Soil Test Calibration Studies

0 Lime

12% Lime

P R

ate

, lb

s P

2O

5/A

UI, 2001

Relative Y ield Response, Potatoes

0

20

40

60

80

100

120

0 10 20 30 40

STPC

Re

lati

ve

Yie

ld, %

Soil Test Correlation Studies

0 Lime

12% Lime

UI, 2001

University of Idaho: Potato P Recommendations take into account the free lime content of the soil

Leytem and Westermann, 2003

Majority of the soils had a break-point at approx. 150 ppm.

low P (<150 ppm), P sorption with oxides, clay surfaces, and organically-complexed metals (Fe & Mn)

high P (>150 ppm), precipitation reactions

0

30

60

90

0 200 400 600 800

0

30

60

90

0 200 400 600 800

Sorb

ed P

(m

mol P k

g-1)

Equilibrium P (mg P L-

1)

r2 = 0.860

10

20

30

40

0 300 600 900 1200 1500

NTA (Mn + Fe), mmol kg-1

Xt,

mm

ol P

kg-1

Leytem and Westermann, 2003

Organically complexed Mn and Fe were the primary factors controlling P sorption

0

20

40

60

80

100

0 200 400 600 800

Equilibrium P (mg P L-1)

So

rbe

d P

(mm

ol

P k

g-1

) Experimental Data

Freundlich

Precipitation

Phosphorus Sorption in Soils

How Can organically complexed metals affect P adsorption?

P is complexed with OM through metal bridges?

• OM interferes with Ca-P and metal oxide precipitation by coating the calcite surfaces?

PO4

Robbins and Westermann previously showed that organic carbon enhanced the solubility and extractability of added P in calcareous soils-

showing that there are many mechanisms regulating P sorption

and solubility

Organic ligands affect P sorption- they compete with orthoP for similar sites on the surface of oxides.

Organic matter may also chelate metals and prevent reactions between metals and P

How does this relate to Humic Acid additions?

Far West Fertilizer Meeting, 2004: “Never add P fertilizer to a Calcareous soil without adding Humic Acid with it”

Organic Matter and P Interactions

University of Idaho experience with Humic Acid (2003 report)

If Organically Complexed If Organically Complexed Metals Control P Solubility, Metals Control P Solubility,

What Happens When We Add What Happens When We Add Manure?Manure?

Myths About P and Myths About P and ManuresManures

• Manure P is organic PManure P is organic P

• Organic P is more soluble and Organic P is more soluble and more readily leached than more readily leached than inorganic Pinorganic P

• Manure is a greater threat to water Manure is a greater threat to water quality than fertilizer P because it quality than fertilizer P because it is organic Pis organic P

HO P OH

O

OH

HO P O

O

OH

P OH

O

OH

Organic P

Inorganic P

Phytic Acid ATP (monoester)

Inorganic Orthophosphate

Pyrophosphate

OPO3H2

H2O3PO OPO3H2

OPO3H2

H2O3PO

OPO3H2

Some Typical Organic P Compounds in Manures

0

100

200

300

400

500

600

0 50 100 150 200

Equilibrium P (mg P mL-1)

P So

rbed

(m

g P

kg-1)

Phytic Acid

ATP

ADP

AMP

OrthoP

P Sorption in Soils P Sorption in Soils

HO P OH

O

OH

HO P O

O

OH

P OH

O

OH

Organic P

Inorganic P

Phytic Acid ATP (monoester)

Inorganic Orthophosphate

Pyrophosphate

OPO3H2

H2O3PO OPO3H2

OPO3H2

H2O3PO

OPO3H2

Some Typical Organic P Compounds in Manures

0%

20%

40%

60%

80%

100%

120%

SL SS- HP DL BS- grass DC PL

OrthoP Monoesters PyroP Phytic Acid

Manure P CompositionManure P Composition

How does manure How does manure behave as a fertilizer behave as a fertilizer

compared to inorganic compared to inorganic fertilizer? fertilizer?

(Leytem & Westermann, 2005)

Soil Test P

0

25

50

75

100

125

RP

E O

lsen

P

BS DC DL POLYP MAP MCP

0

1

2

3

4

5

Dry

ma

tte

r (g

)

C BS MCP DL DC MAP POLYP

Response in STP and Plant Response in STP and Plant GrowthGrowth

Plant P UptakePlant P Uptake

Although the soil test P increased less when we applied manures….

The amount of P taken up by the plants was greater for some manures than fertilizers

0

2

4

6

8

10

P u

pta

ke (

mg

)

C BS MCP DC MAP DL POLYP

P SourceP SourceRPERPE

OlsenOlsen

RPRP

UptakUptakee

EfficiencyEfficiency

Dairy LiquidDairy Liquid 62.662.6 113.1113.1 1.81.8

Beef SolidBeef Solid 26.526.5 59.559.5 2.242.24

Dairy Dairy CompostCompost 49.049.0 149.9149.9 3.053.05

MCPMCP 100.0100.0 100.0100.0 1.01.0

MAPMAP 85.385.3 145.0145.0 1.691.69

Phosphorus Uptake EfficiencyPhosphorus Uptake Efficiency

Do these trends Do these trends change in the field? change in the field?

Olsen P with Depth in Field Olsen P with Depth in Field Plots Plots

0

10

20

30

40O

lse

n P

(p

pm

)

0-6" 6-12" 12-18"

Control

Compost

Manure

Fertilizer

aa

b

c

a

b

b

c ab ab ab

Fertilizer and manure behave similarly in the topsoil, but fertilizer P enriched STP in the subsurface compared to manure

and compost

Runoff P from Field Plots Runoff P from Field Plots

0

50

100

150

200

250

Ru

no

ff P

(m

g)

ControlCompostManureFertilizer

a

c

bcab

Fertilizer and manure had similar runoff P while compost and control were lower but similar

r2 = 0.82

0

50

100

150

200

250

0 10 20 30 40

Olsen P (ppm)

Ru

no

ff P

(m

g)

Cumulative runoff P was closely correlated with the bicarbonate STP

P Uptake from Field Plots P Uptake from Field Plots

0

10

20

30

P u

pta

ke

(k

g)

Control

Compost

Manure

Fertilizer

a

b

a a

The addition of fertilizer, manure and compost increased the P uptake by the crop, but they did not differ significantly

STP over 20 ppm does not require fertilizer addition

Is it really all just Is it really all just about the P in about the P in

manures or is there manures or is there something else going something else going

on? on?

1313C NMR of WS-CarbonC NMR of WS-Carbon

Chemical shift (ppm)

050100150

050100150

050100150

Dairy Compost

Dairy Manure

Dairy Liquid

Solid manures dominated by aromatic and

aliphatic compounds (larger more

stable)

Liquid manures dominated by

carbonyl functional groups

(smaller more reactive)

r2 = 0.90

0102030405060708090

0 50 100 150

C:P Ratio of Manures

Ols

en

P (

mg

kg-1

)

The Carbon in Manures The Carbon in Manures Influences the P solubility of Influences the P solubility of

the Soil the Soil

r2 = 0.71***

0

20

40

60

r2 = 0.75***

0

20

40

60

0 20 40 60

Microbial P mg kg-1

Ols

en

P m

g k

g-1

W

SP

mg

kg

-1

Effect of Microbial P on WSP and Effect of Microbial P on WSP and Olsen POlsen P

P Release Over Growing Season From P Release Over Growing Season From Manure, Compost and FertilizerManure, Compost and Fertilizer

0

10

20

30

40

50

0 2 4 6 8 10 12 14

Weeks

RPE

PRS

pro

bes

compost

manure

fertilizer

C:P = 15

C:P = 45

C:P = 0

SummarySummary

• Manure with similar P composition applied at Manure with similar P composition applied at same total P ratessame total P rates• Differences in P solubility dominated by the Differences in P solubility dominated by the

amount of C added with the manure treatmentamount of C added with the manure treatment

• Manures increase STP less than fertilizer Manures increase STP less than fertilizer treatments but have a greater plant P uptake than treatments but have a greater plant P uptake than fertilizerfertilizer

ImplicationsImplications

• We need to consider the amount of C in We need to consider the amount of C in calcareous soils when determining P calcareous soils when determining P sorption/availabilitysorption/availability

• When we make P risk assessments in When we make P risk assessments in calcareous soils with manure incorporation, calcareous soils with manure incorporation, we need to consider the effects of the C we need to consider the effects of the C content and composition of manures content and composition of manures

• Microbial P has a large influence on soluble P Microbial P has a large influence on soluble P and this needs to be further exploredand this needs to be further explored

So Why the P Problems with So Why the P Problems with Manures?Manures?

N:P ratios don’t match upN:P ratios don’t match up Crops want a ratio of about 5:1Crops want a ratio of about 5:1 Manure ratios are typically closer to 2:1Manure ratios are typically closer to 2:1 Therefore when applying manure on an N based Therefore when applying manure on an N based

rate we are always over applying Prate we are always over applying P Overfeeding of P in animal operationsOverfeeding of P in animal operations

Low P availability of feeds in monogastrics leads to P Low P availability of feeds in monogastrics leads to P supplementationsupplementation

Dairies traditionally overfeed P for insurance Dairies traditionally overfeed P for insurance Cost of transporting manuresCost of transporting manures

Over application of manures on sites closest to manure Over application of manures on sites closest to manure generation/storagegeneration/storage

Northwest Irrigation and Northwest Irrigation and Soils Research LaboratorySoils Research Laboratory

Kimberly, IdahoKimberly, Idaho

USAUSA