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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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slide1

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)

slide6

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

â monocalcium phosphate

â CaHPO4

â dicalcium phosphate

â Ca3(PO4)2

â tricalcium phosphate

â 3Ca3(PO4)2lCa(OH)2

â hydroxyapatite

â 3Ca3(PO4)2lCaCO3

â carbonate apatite

6

pH

8

nomenclature

Slide 10.9

Nomenclature

H3PO4 = phosphoric acid

H2PO4- = monobasic

HPO4-2 = dibasic

PO4-3 = tribasic

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

slide13

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

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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