GES175, Science of Soils
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GES175, Science of Soils. Lecture 10 Phosphorus. Slide 10.2. Phosphorus Soil-Plant Relations. * Energy and reproduction * Growth and development a root growth a maturity (seed set, flowering,...) * Maintained by organic matter cycling . Slide 10.3. Water Quality.

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GES175, Science of Soils

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Ges175 science of soils

GES175, Science of Soils

Lecture 10

Phosphorus


Phosphorus soil plant relations

Slide 10.2

Phosphorus Soil-Plant Relations

* Energy and reproduction

* Growth and development

aroot growth

amaturity (seed set, flowering,...)

* Maintained by organic matter cycling


Water quality

Slide 10.3

Water Quality

  • accelerated eutrophication

  • P (often) promotes algae growth

    - may promote anoxia and lead to ‘dead’ zones

  • P from point and nonpoint sources


Phosphorus fixation

Slide 10.4

Phosphorus Fixation

* Limited Biological Availability

• P reacts strongly with soil material

  • - limits bioavailability

  • - limits transport through soil

  • - movement occurs via erosion

  • • Adsorbs and precipitates


  • Adsorption reactions

    Slide 10.5

    Adsorption Reactions

    * Strong adsorption on soil minerals

    - adsorption on Fe- and Al-oxides

    - adsorption on ‘edge’ sites of silicate clays (dominantly kaolinite)


    Ges175 science of soils

    Slide 10.6

    Volcanic Ashëë


    Inorganic p compounds precipitates

    Slide 10.7

    Inorganic P Compounds(precipitates)

    Acid soils

    8Fe and Al phosphates

    FePO4l2H2O, AlPO4l2H2O

    Alkaline soils

    4 Ca and Mg phosphates


    Inorganic p compounds

    Slide 10.8

    Inorganic P Compounds

    decreasing solubility

    â Ca(H2PO4)2

    âmonocalcium phosphate

    â CaHPO4

    âdicalcium phosphate

    âCa3(PO4)2

    âtricalcium phosphate

    â3Ca3(PO4)2lCa(OH)2

    â hydroxyapatite

    â3Ca3(PO4)2lCaCO3

    â carbonate apatite

    6

    pH

    8


    Nomenclature

    Slide 10.9

    Nomenclature

    H3PO4 = phosphoric acid

    H2PO4- = monobasic

    HPO4-2 = dibasic

    PO4-3 = tribasic


    Phosphate ion protonation

    Slide 10.10

    Phosphate Ion: Protonation

    acid soils

    alkaline

    soils


    Most available p between ph 6 7

    Slide 10.11

    Most Available P between pH 6 - 7


    Organic soil phosphorus

    Slide 10.12

    Organic Soil Phosphorus

    * 20 - 80 % of total soil P is organic

    * Mostly inositol phosphates,

    C6H6(OH)6

    - 10 - 50 % of organic-P

    - some nucleic acid and phospholipids


    Ges175 science of soils

    Slide 10.13

    Cycling: A slow release mechanism

    Organic-P

    immobilization

    mineralization

    (available P)

    HxPO4x-3

    Solid Phase-PO4

    (unavailable)


    Symbiotic relation fungi and plants

    Symbiotic Relation:Fungi and Plants

    Mycorrhizae root infections, a key to phosphorus uptake

    Plant root

    Fungal hyphae

    mycorrihizae


    The end

    The End


    Reactions at high ph values

    Slide 10.11

    Reactions at High pH Values

    * P converts to less soluble

    Ca and Mg compounds

    Ca(H2PO4)2 + CaCO3 + H2O ® 2 CaHPO4·2H2O + CO2

    very less

    soluble soluble

    6 CaHPO4·2H2O + 3 CaCO3® 3 Ca3(PO4)2 + 3 CO2 + 5 H2O

    less

    soluble

    3 Ca3(PO4)2 + CaCO3® 3Ca3(PO4)2·CaCO3

    very insoluble

    - most serious in calcareous soils of arid regions


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