phosphorus behavior in soils

Phosphorus Behavior in Phosphorus Behavior in SoilsSoils

Phosphorus Behavior in Phosphorus Behavior in SoilsSoils

Plant and Soil Sciences Plant and Soil Sciences DepartmentDepartment

Oklahoma State UniversityOklahoma State University

Plant and Soil Sciences Plant and Soil Sciences DepartmentDepartment

Oklahoma State UniversityOklahoma State University

G.V. JohnsonG.V. JohnsonG.V. JohnsonG.V. Johnson

Understanding phosphorus Understanding phosphorus behavior in soilsbehavior in soils


Start with “stripped” down, bare P.Start with “stripped” down, bare P.““P” stands for Norwegian Goddess P” stands for Norwegian Goddess

Phyllis.Phyllis.Like elemental phosphorus, we Like elemental phosphorus, we

remember the ancient story of Phyllis, remember the ancient story of Phyllis, and how violent she reacted when she and how violent she reacted when she swam to shore and, as she stepped swam to shore and, as she stepped onto the beach, found herself naked!onto the beach, found herself naked!

Start with “stripped” down, bare P.Start with “stripped” down, bare P.““P” stands for Norwegian Goddess P” stands for Norwegian Goddess

Phyllis.Phyllis.Like elemental phosphorus, we Like elemental phosphorus, we

remember the ancient story of Phyllis, remember the ancient story of Phyllis, and how violent she reacted when she and how violent she reacted when she swam to shore and, as she stepped swam to shore and, as she stepped onto the beach, found herself naked!onto the beach, found herself naked! PP PP



Phyllis (P) ran to the nearest beach-Phyllis (P) ran to the nearest beach-front store and quickly bought a two-front store and quickly bought a two-piece bathing suit (Opiece bathing suit (O22) and matching ) and matching

beach sandals (Obeach sandals (O22). ).

Phyllis (P) ran to the nearest beach-Phyllis (P) ran to the nearest beach-front store and quickly bought a two-front store and quickly bought a two-piece bathing suit (Opiece bathing suit (O22) and matching ) and matching

beach sandals (Obeach sandals (O22). ).

PP + O + O22 + O + O22 = PO = PO443-3- PP + O + O22 + O + O22 = PO = PO443-3-

She was much more comfortable. She was much more comfortable. She was much more comfortable. She was much more comfortable.



But, Phyllis was chilled when it got But, Phyllis was chilled when it got cloudy and the wind blew, so she cloudy and the wind blew, so she went back to the store and bought a went back to the store and bought a “beach –wear” cover (H“beach –wear” cover (H++)and )and matching shoes (2 Hmatching shoes (2 H++).).

But, Phyllis was chilled when it got But, Phyllis was chilled when it got cloudy and the wind blew, so she cloudy and the wind blew, so she went back to the store and bought a went back to the store and bought a “beach –wear” cover (H“beach –wear” cover (H++)and )and matching shoes (2 Hmatching shoes (2 H++).).

POPO443- 3- + H+ H++ +2 H +2 H++ = H = H33POPO44

POPO443- 3- + H+ H++ +2 H +2 H++ = H = H33POPO44

Now she was comfortable Now she was comfortable anywhere along the beach. anywhere along the beach.

Now she was comfortable Now she was comfortable anywhere along the beach. anywhere along the beach.

Understanding phosphorus behavior in soilsUnderstanding phosphorus behavior in soilsUnderstanding phosphorus behavior in soilsUnderstanding phosphorus behavior in soils

Even a Norwegian Goddess can’t spend Even a Norwegian Goddess can’t spend all her time at the beach. Phyllis needed all her time at the beach. Phyllis needed to move about the land. to move about the land. – She was conspicuous in her beach-She was conspicuous in her beach-

wear. It rained a lot. People were wear. It rained a lot. People were always staring at her.always staring at her.

Even a Norwegian Goddess can’t spend Even a Norwegian Goddess can’t spend all her time at the beach. Phyllis needed all her time at the beach. Phyllis needed to move about the land. to move about the land. – She was conspicuous in her beach-She was conspicuous in her beach-

wear. It rained a lot. People were wear. It rained a lot. People were always staring at her.always staring at her.

HH33POPO44 + Al + Al3+3+ = AlPO = AlPO4 4 + 3 H+ 3 H++ HH33POPO44 + Al + Al3+3+ = AlPO = AlPO4 4 + 3 H+ 3 H++

She bought a jump-suit (AlShe bought a jump-suit (Al3+3+) and got rid ) and got rid of the beach-wear. of the beach-wear.

She bought a jump-suit (AlShe bought a jump-suit (Al3+3+) and got rid ) and got rid of the beach-wear. of the beach-wear.

She went shopping again.She went shopping again. She went shopping again.She went shopping again.

Now she was comfortable anywhere on Now she was comfortable anywhere on land along the beachland along the beach

Now she was comfortable anywhere on Now she was comfortable anywhere on land along the beachland along the beach



CaHPOCaHPO44CaHPOCaHPO44

In time Phyllis became lonely, she In time Phyllis became lonely, she missed her family, especially her twin missed her family, especially her twin sister Phylline.sister Phylline.

Phylline lived in dry, southern California, Phylline lived in dry, southern California, but not too far from the beach.but not too far from the beach.

She was quite stylish, but unstable, and She was quite stylish, but unstable, and wore OSU sweats (Cawore OSU sweats (Ca2+2+) and OU ) and OU running shoes (Hrunning shoes (H++).).

In time Phyllis became lonely, she In time Phyllis became lonely, she missed her family, especially her twin missed her family, especially her twin sister Phylline.sister Phylline.

Phylline lived in dry, southern California, Phylline lived in dry, southern California, but not too far from the beach.but not too far from the beach.

She was quite stylish, but unstable, and She was quite stylish, but unstable, and wore OSU sweats (Cawore OSU sweats (Ca2+2+) and OU ) and OU running shoes (Hrunning shoes (H++).).



CaHPOCaHPO4 4 + AlPO+ AlPO4 4 CaHPOCaHPO4 4 + AlPO+ AlPO4 4

Phyllis went to visit her sister Phylline.Phyllis went to visit her sister Phylline. Phyllis went to visit her sister Phylline.Phyllis went to visit her sister Phylline.

At first they weren't comfortable At first they weren't comfortable together. Their styles clashed.together. Their styles clashed.

At first they weren't comfortable At first they weren't comfortable together. Their styles clashed.together. Their styles clashed.



With time the sisters learned to With time the sisters learned to overcome their differences.overcome their differences.

Phyllis finally found a sweat-suit like Phyllis finally found a sweat-suit like Philline’s (CaPhilline’s (Ca2+2+), and a two-for-one sale ), and a two-for-one sale for matching (OSU) shoes (Cafor matching (OSU) shoes (Ca2+2+) )

With time the sisters learned to With time the sisters learned to overcome their differences.overcome their differences.

Phyllis finally found a sweat-suit like Phyllis finally found a sweat-suit like Philline’s (CaPhilline’s (Ca2+2+), and a two-for-one sale ), and a two-for-one sale for matching (OSU) shoes (Cafor matching (OSU) shoes (Ca2+2+) )

The sisters became inseparable and The sisters became inseparable and went everywhere together.went everywhere together.

The sisters became inseparable and The sisters became inseparable and went everywhere together.went everywhere together.

CaHPOCaHPO4 4 + AlPO+ AlPO4 4 + 2 Ca+ 2 Ca2+2+ Ca Ca33(PO(PO44))22CaHPOCaHPO4 4 + AlPO+ AlPO4 4 + 2 Ca+ 2 Ca2+2+ Ca Ca33(PO(PO44))22



In nature, P always exists In nature, P always exists in combination with in combination with oxygen (O) in the form of oxygen (O) in the form of phosphates.phosphates.

POPO443-3-

In nature, P always exists In nature, P always exists in combination with in combination with oxygen (O) in the form of oxygen (O) in the form of phosphates.phosphates.

POPO443-3-

ReviewReviewReviewReview

--O - P - OO - P - O----O - P - OO - P - O--

OOllllOOllll

llOO--

llOO--

Three separate sites Three separate sites for reaction with a for reaction with a single charge cation single charge cation (H(H++,, KK++,, NHNH44

++).).

Three separate sites Three separate sites for reaction with a for reaction with a single charge cation single charge cation (H(H++,, KK++,, NHNH44

++).).



POPO443-3- will react with: will react with:

whatever cation is in greatest abundance whatever cation is in greatest abundance and,and,

whatever cation is held with the strongest whatever cation is held with the strongest bond.bond.

In nature, there is plenty of water around:In nature, there is plenty of water around:

HH22O O ====== H H++ + OH + OH--

Concentration of HConcentration of H++ = OH = OH- - = 10= 10-7-7

POPO443-3- will react with: will react with:

whatever cation is in greatest abundance whatever cation is in greatest abundance and,and,

whatever cation is held with the strongest whatever cation is held with the strongest bond.bond.

In nature, there is plenty of water around:In nature, there is plenty of water around:

HH22O O ====== H H++ + OH + OH--

Concentration of HConcentration of H++ = OH = OH- - = 10= 10-7-7



When the charges on phosphate are all When the charges on phosphate are all satisfied by Hsatisfied by H++, in the laboratory, the , in the laboratory, the compound phosphoric acid is formed.compound phosphoric acid is formed.

HH33POPO44

When the charges on phosphate are all When the charges on phosphate are all satisfied by Hsatisfied by H++, in the laboratory, the , in the laboratory, the compound phosphoric acid is formed.compound phosphoric acid is formed.

HH33POPO44

ReviewReviewReviewReview

HHO - P - OO - P - OHHHHO - P - OO - P - OHH

OOllllOOllll

llOOHH llOOHH



The The HH++ leave (dissociate from) phosphoric leave (dissociate from) phosphoric acid in a stepwise manner when the acid is acid in a stepwise manner when the acid is reacted with base, like sodium hydroxide reacted with base, like sodium hydroxide (NaOH).(NaOH).

HH33POPO4 4 H H++ + + HH22POPO44--

HH22POPO44-- H H++ ++ H HPOPO44

22--

HHPOPO4422-- H H++ ++ POPO44

33--

One or more of the phosphate forms will be One or more of the phosphate forms will be present in solution, depending upon the present in solution, depending upon the solution pH.solution pH.

The The HH++ leave (dissociate from) phosphoric leave (dissociate from) phosphoric acid in a stepwise manner when the acid is acid in a stepwise manner when the acid is reacted with base, like sodium hydroxide reacted with base, like sodium hydroxide (NaOH).(NaOH).

HH33POPO4 4 H H++ + + HH22POPO44--

HH22POPO44-- H H++ ++ H HPOPO44

22--

HHPOPO4422-- H H++ ++ POPO44

33--






Mole fraction of phosphate ionic species with pH.

0.00

0.20

0.40

0.60

0.80

1.00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Solution pH

Mo

le fr

act

on

P

H3PO4 H2PO4 HPO4 PO4



In the normal pH range of soils the In the normal pH range of soils the

concentration of Hconcentration of H++ in the soil solution is too in the soil solution is too weak to effectively compete for reaction with weak to effectively compete for reaction with phosphate anions.phosphate anions.

At pH 6, the HAt pH 6, the H++ concentration is 1 x 10 concentration is 1 x 10-6-6 mole/liter.mole/liter.= 0.000001 g/liter.= 0.000001 g/liter.= 0.001 ppm.= 0.001 ppm.= 0.001 milliequivalent weights.= 0.001 milliequivalent weights.

At pH 5 the HAt pH 5 the H++ concentration is 10 times concentration is 10 times greater and at pH 7 it is 10 less than at pH 6.greater and at pH 7 it is 10 less than at pH 6.

In the normal pH range of soils the In the normal pH range of soils the

concentration of Hconcentration of H++ in the soil solution is too in the soil solution is too weak to effectively compete for reaction with weak to effectively compete for reaction with phosphate anions.phosphate anions.

At pH 6, the HAt pH 6, the H++ concentration is 1 x 10 concentration is 1 x 10-6-6 mole/liter.mole/liter.= 0.000001 g/liter.= 0.000001 g/liter.= 0.001 ppm.= 0.001 ppm.= 0.001 milliequivalent weights.= 0.001 milliequivalent weights.

At pH 5 the HAt pH 5 the H++ concentration is 10 times concentration is 10 times greater and at pH 7 it is 10 less than at pH 6.greater and at pH 7 it is 10 less than at pH 6.



Since the HSince the H++ concentration is so low in the concentration is so low in the normal pH range of soils, the concentration of normal pH range of soils, the concentration of HH22POPO44

-- and HPO and HPO442-2- might also be expected to might also be expected to

be low.be low.

If there is not enough HIf there is not enough H++ to react with PO to react with PO443-3- in in

the soil, what else can POthe soil, what else can PO443-3- react with? react with?

Consider the lyotropic series and the Consider the lyotropic series and the relationship of soil pH and percent base relationship of soil pH and percent base saturation.saturation.

Since the HSince the H++ concentration is so low in the concentration is so low in the normal pH range of soils, the concentration of normal pH range of soils, the concentration of HH22POPO44

-- and HPO and HPO442-2- might also be expected to might also be expected to

be low.be low.

If there is not enough HIf there is not enough H++ to react with PO to react with PO443-3- in in

the soil, what else can POthe soil, what else can PO443-3- react with? react with?

Consider the lyotropic series and the Consider the lyotropic series and the relationship of soil pH and percent base relationship of soil pH and percent base saturation.saturation.

If there is not enough HIf there is not enough H++ to react with PO to react with PO443-3-

in the soil, what else can POin the soil, what else can PO443-3- react with? react with?



The lyotropic series is the order of adsorption The lyotropic series is the order of adsorption strength of cations adsorbed on soil colloids:strength of cations adsorbed on soil colloids:

AlAl3+3+ ~ H~ H++ > Ca > Ca2+2+ ~ Mg ~ Mg2+2+ > K > K++ ~ NH ~ NH44++ > Na > Na++

Soil pH and % base saturation are directly Soil pH and % base saturation are directly related:related:

The lyotropic series is the order of adsorption The lyotropic series is the order of adsorption strength of cations adsorbed on soil colloids:strength of cations adsorbed on soil colloids:

AlAl3+3+ ~ H~ H++ > Ca > Ca2+2+ ~ Mg ~ Mg2+2+ > K > K++ ~ NH ~ NH44++ > Na > Na++

Soil pH and % base saturation are directly Soil pH and % base saturation are directly related:related:

0 20 40 60 80 100

7

6

5

4

Percent Base Saturation

So

il pH

The lyotropic series also relates to acidic and The lyotropic series also relates to acidic and basic cations:basic cations:

AlAl3+3+ ~ ~ HH++ > > CaCa2+2+ ~ ~ MgMg2+2+ > > KK++ ~ ~ NHNH44++ > > NaNa++

Strongly acidStrongly acid================ Strongly alkaline: Strongly alkaline:

The lyotropic series also relates to acidic and The lyotropic series also relates to acidic and basic cations:basic cations:

AlAl3+3+ ~ ~ HH++ > > CaCa2+2+ ~ ~ MgMg2+2+ > > KK++ ~ ~ NHNH44++ > > NaNa++

Strongly acidStrongly acid================ Strongly alkaline: Strongly alkaline:

0 20 40 60 80 100

7

6

5

4


So

il pH





Above soil pH 5.5 there is an abundance of:Above soil pH 5.5 there is an abundance of:

CaCa2+2+ ~ ~ MgMg2+2+ > > KK++ ~ ~ NHNH44++ > > NaNa++

Below soil pH 5.5 there are increasing amounts Below soil pH 5.5 there are increasing amounts of of AlAl3+3+ ~ ~ HH++..

Above soil pH 5.5 there is an abundance of:Above soil pH 5.5 there is an abundance of:

CaCa2+2+ ~ ~ MgMg2+2+ > > KK++ ~ ~ NHNH44++ > > NaNa++

Below soil pH 5.5 there are increasing amounts Below soil pH 5.5 there are increasing amounts of of AlAl3+3+ ~ ~ HH++..

0 20 40 60 80 100

7

6

5

4


So

il pH





AlAl3+3+ + H + H33POPO4 4 ==== AlAlPOPO44

DAPDAP AlAl3+3+ + (NH + (NH44))22HPOHPO4 4 === = AlAlPOPO4 4 + 2 NH+ 2 NH44

++

MAPMAP AlAl3+3+ + NH + NH44HH22POPO4 4 === = AlAlPOPO4 4 + NH+ NH44

++

AlAlPOPO44 is very insoluble.is very insoluble.

The reaction rate depends on the concentrations The reaction rate depends on the concentrations of of AlAl3+3+ and H and H33POPO4 4 in the soil solutionin the soil solution..

27 lbs27 lbs AlAl3+3+ will react with about 71 lbs P will react with about 71 lbs P22OO5 5 to to

form form AlAlPOPO44..

AlAl3+3+ + H + H33POPO4 4 ==== AlAlPOPO44

DAPDAP AlAl3+3+ + (NH + (NH44))22HPOHPO4 4 === = AlAlPOPO4 4 + 2 NH+ 2 NH44

++

MAPMAP AlAl3+3+ + NH + NH44HH22POPO4 4 === = AlAlPOPO4 4 + NH+ NH44

++

AlAlPOPO44 is very insoluble.is very insoluble.

The reaction rate depends on the concentrations The reaction rate depends on the concentrations of of AlAl3+3+ and H and H33POPO4 4 in the soil solutionin the soil solution..

27 lbs27 lbs AlAl3+3+ will react with about 71 lbs P will react with about 71 lbs P22OO5 5 to to

form form AlAlPOPO44..

Below soil pH 5.5 there are increasing Below soil pH 5.5 there are increasing amounts ofamounts of AlAl3+3+ ~ ~ HH++..Below soil pH 5.5 there are increasing Below soil pH 5.5 there are increasing amounts ofamounts of AlAl3+3+ ~ ~ HH++..

27 lbs27 lbs AlAl3+3+ will react with about 71 lbs will react with about 71 lbs

PP22OO5 5 to form to form AlAlPOPO44..

When PWhen P22OO5 5 is banded with seed, is banded with seed,

the Pthe P22OO5 5 concentration is several concentration is several

times greater than the times greater than the AlAl3+3+ concentration in the band zone. concentration in the band zone.

The concentrations of HThe concentrations of H22POPO44-- and and

HPOHPO442-2- are very low in acid soils are very low in acid soils

because of their reaction with because of their reaction with AlAl3+3+. .

27 lbs27 lbs AlAl3+3+ will react with about 71 lbs will react with about 71 lbs

PP22OO5 5 to form to form AlAlPOPO44..

When PWhen P22OO5 5 is banded with seed, is banded with seed,

the Pthe P22OO5 5 concentration is several concentration is several

times greater than the times greater than the AlAl3+3+ concentration in the band zone. concentration in the band zone.

The concentrations of HThe concentrations of H22POPO44-- and and

HPOHPO442-2- are very low in acid soils are very low in acid soils

because of their reaction with because of their reaction with AlAl3+3+. .

Below soil pH 5.5 there are increasing Below soil pH 5.5 there are increasing amounts ofamounts of AlAl3+3+ ~ ~ HH++..Below soil pH 5.5 there are increasing Below soil pH 5.5 there are increasing amounts ofamounts of AlAl3+3+ ~ ~ HH++..

CaCa2+2+ + H+ H33POPO4 4 CaCa(H(H22POPO44))2 2 (0-46-0)(0-46-0)

DAPDAP CaCa2+2+ + (NH+ (NH44))22HPOHPO4 4 CaCaHPOHPO4 4 + 2 NH+ 2 NH44++

MAPMAP CaCa2+2+ + NH+ NH44HH22POPO4 4 CaCa(H(H22POPO44))2 2 + NH+ NH44++

CaCa(H(H22POPO44))2 2 and and CaCaHPOHPO4 4 are “highly” water soluble. are “highly” water soluble.

CaCa2+2+ + H+ H33POPO4 4 CaCa(H(H22POPO44))2 2 (0-46-0)(0-46-0)

DAPDAP CaCa2+2+ + (NH+ (NH44))22HPOHPO4 4 CaCaHPOHPO4 4 + 2 NH+ 2 NH44++

MAPMAP CaCa2+2+ + NH+ NH44HH22POPO4 4 CaCa(H(H22POPO44))2 2 + NH+ NH44++

CaCa(H(H22POPO44))2 2 and and CaCaHPOHPO4 4 are “highly” water soluble. are “highly” water soluble.

0 20 40 60 80 100

7

6

5

4


So

il pH

Above soil pH 5.5 there is an abundance of:Above soil pH 5.5 there is an abundance of:CaCa2+2+ ~ ~ MgMg2+2+ > > KK++ ~ ~ NHNH44

++ > > NaNa++


++ > > NaNa++

CaCa(H(H22POPO44))2 2 and and CaCaHPOHPO4 4 are highly water soluble. are highly water soluble. These phosphates revert to apatite (rock-phosphate).These phosphates revert to apatite (rock-phosphate).

CaCa(H(H22POPO44))2 2 and and CaCaHPOHPO4 4 are highly water soluble. are highly water soluble. These phosphates revert to apatite (rock-phosphate).These phosphates revert to apatite (rock-phosphate).


++ > > NaNa++


++ > > NaNa++

Mineral

Reversion Reversion timetime

Chemical formula Ca/P

Solubility

g/100 mL

Monocalcium phosphate Ca(H2PO4)2

. H2O 0.5 1.8

Dicalcium phosphate

33++ weeks weeks CaHPO4 1.0 0.03

Octacalcium phosphate 2 to 5 mo.2 to 5 mo.

Ca4H(PO4)3 . 2.5

H2O 1.33

Tricalcium phosphate

8 to 10 8 to 10 mo.mo. Ca3(PO4)2 1.5

0.002

(4 ppm)

Hydroxyapatite 1 to 2 yr.1 to 2 yr. Ca5(PO4)3OH 1.66

Understanding phosphorus Understanding phosphorus behavior in soils: Fertilizersbehavior in soils: FertilizersUnderstanding phosphorus Understanding phosphorus behavior in soils: Fertilizersbehavior in soils: Fertilizers

Phosphate fertilizers Phosphate fertilizers dissolve slowlydissolve slowly, but react , but react quicklyquickly in soils to form in soils to form solidsolid calcium and aluminum calcium and aluminum phosphates, which, in time become very insoluble.phosphates, which, in time become very insoluble.

DAP (solubility = 23g/100mL)DAP (solubility = 23g/100mL)

100 H100 H22O + 23 (NHO + 23 (NH44))22HPOHPO4 4 (dissolves slowly)(dissolves slowly) ==> > HPOHPO44

2-2-

+ 2 NH+ 2 NH44++

((solid)solid)((solution)solution)

CaCa2+ 2+ + + HPOHPO442-2-

<<====

==((precipitates quickly)precipitates quickly)CaCaHPOHPO44 Equilibrium P concentration is Equilibrium P concentration is ~ 60 ppm~ 60 ppm

Equilibrium Equilibrium CaCa2+ 2+ concentration is concentration is ~ 70 ppm.~ 70 ppm.

Most soil Most soil CaCa2+ 2+ concentrations will be > > 400 ppmconcentrations will be > > 400 ppm

Phosphate fertilizers Phosphate fertilizers dissolve slowlydissolve slowly, but react , but react quicklyquickly in soils to form in soils to form solidsolid calcium and aluminum calcium and aluminum phosphates, which, in time become very insoluble.phosphates, which, in time become very insoluble.

DAP (solubility = 23g/100mL)DAP (solubility = 23g/100mL)

100 H100 H22O + 23 (NHO + 23 (NH44))22HPOHPO4 4 (dissolves slowly)(dissolves slowly) ==> > HPOHPO44

2-2-

+ 2 NH+ 2 NH44++

((solid)solid)((solution)solution)

CaCa2+ 2+ + + HPOHPO442-2-

<<====

==((precipitates quickly)precipitates quickly)CaCaHPOHPO44 Equilibrium P concentration is Equilibrium P concentration is ~ 60 ppm~ 60 ppm

Equilibrium Equilibrium CaCa2+ 2+ concentration is concentration is ~ 70 ppm.~ 70 ppm.

Most soil Most soil CaCa2+ 2+ concentrations will be > > 400 ppmconcentrations will be > > 400 ppm

Understanding phosphorus Understanding phosphorus behavior in soils: Fertilizersbehavior in soils: FertilizersUnderstanding phosphorus Understanding phosphorus behavior in soils: Fertilizersbehavior in soils: Fertilizers

Phosphate fertilizers Phosphate fertilizers dissolve slowlydissolve slowly, but , but reactreact quicklyquickly in soils to form in soils to form solidsolid calcium and calcium and aluminum phosphates, which, in time become aluminum phosphates, which, in time become very insoluble.very insoluble.

Phosphate fertilizers Phosphate fertilizers dissolve slowlydissolve slowly, but , but reactreact quicklyquickly in soils to form in soils to form solidsolid calcium and calcium and aluminum phosphates, which, in time become aluminum phosphates, which, in time become very insoluble.very insoluble.

0

20

40

60

80

100

120

140

0.000 0.025 0.050 0.075 0.100

Soil solution P (ppm)

% R

ela

tive

Yie

ld

phosphorus behavior in soils

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