GES175, Science of Soils Lecture 10 Phosphorus. Phosphorus Soil-Plant Relations * Energy and...
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Transcript of GES175, Science of Soils Lecture 10 Phosphorus. Phosphorus Soil-Plant Relations * Energy and...
![Page 1: GES175, Science of Soils Lecture 10 Phosphorus. Phosphorus Soil-Plant Relations * Energy and reproduction * Growth and development a root growth a maturity.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c865503460f9493db94/html5/thumbnails/1.jpg)
GES175, Science of Soils
Lecture 10
Phosphorus
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Phosphorus Soil-Plant Relations
* Energy and reproduction
* Growth and developmentroot growth
maturity (seed set, flowering,...)
* Maintained by organic matter cycling
Slide 10.2
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Water Quality
• accelerated eutrophication
• P (often) promotes algae growth
- may promote anoxia and lead to ‘dead’
zones
• P from point and nonpoint sources
Slide 10.3
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Phosphorus Fixation
* Limited Biological Availability
• P reacts strongly with soil material - limits bioavailability - limits transport through soil - movement occurs via erosion
• Adsorbs and precipitates
Slide 10.4
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Adsorption Reactions
* Strong adsorption on soil minerals
- adsorption on Fe- and Al-oxides
- adsorption on ‘edge’ sites of silicate clays
(dominantly kaolinite)
Slide 10.5
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Volcanic Ash
Slide 10.6
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Inorganic P Compounds(precipitates)
Acid soils
Fe and Al phosphates
FePO42H2O, AlPO4
2H2O
Alkaline soils
Ca and Mg phosphates
Slide 10.7
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Ca(H2PO4)2 monocalcium phosphate
CaHPO4
dicalcium phosphate
Ca3(PO4)2
tricalcium phosphate
3Ca3(PO4)2Ca(OH)2
hydroxyapatite
3Ca3(PO4)2CaCO3
carbonate apatite
decreasing solubility
Inorganic P CompoundsSlide 10.8
pH
6
8
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Nomenclature
H3PO4 = phosphoric acid
H2PO4- = monobasic
HPO4-2 = dibasic
PO4-3 = tribasic
Slide 10.9
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acid soilsacid soils alkalinealkaline soilssoils
Phosphate Ion: ProtonationSlide 10.10
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Most Available P between pH 6 - 7Slide 10.11
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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
Slide 10.12
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Organic-P
Slide 10.13
(available P)
Cycling: A slow release mechanism
HxPO4x-3
mineralizationim
mob
iliza
tion
Solid Phase-PO4(unavailable)
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Symbiotic Relation:Fungi and Plants
Mycorrhizae root infections, a key to phosphorus uptake
Fungal hyphae
mycorrihizae
Plant root
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The End
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Reactions at High pH Values
* P converts to less soluble Ca and Mg compounds
Ca(H2PO4)2 + CaCO3 + H2O 2 CaHPO42H2O + CO2 very less
soluble soluble
6 CaHPO42H2O + 3 CaCO3 3 Ca3(PO4)2 + 3 CO2 + 5 H2O
less soluble
3 Ca3(PO4)2 + CaCO3 3Ca3(PO4)2CaCO3
very insoluble
- most serious in calcareous soils of arid regions
Slide 10.11