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...
GES175, Science of Soils
Lecture 10
Phosphorus
Phosphorus Soil-Plant Relations
* Energy and reproduction
* Growth and developmentroot growth
maturity (seed set, flowering,...)
* Maintained by organic matter cycling
Slide 10.2
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
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
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
Volcanic Ash
Slide 10.6
Inorganic P Compounds(precipitates)
Acid soils
Fe and Al phosphates
FePO42H2O, AlPO4
2H2O
Alkaline soils
Ca and Mg phosphates
Slide 10.7
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
Nomenclature
H3PO4 = phosphoric acid
H2PO4- = monobasic
HPO4-2 = dibasic
PO4-3 = tribasic
Slide 10.9
acid soilsacid soils alkalinealkaline soilssoils
Phosphate Ion: ProtonationSlide 10.10
Most Available P between pH 6 - 7Slide 10.11
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
Organic-P
Slide 10.13
(available P)
Cycling: A slow release mechanism
HxPO4x-3
mineralizationim
mob
iliza
tion
Solid Phase-PO4(unavailable)
Symbiotic Relation:Fungi and Plants
Mycorrhizae root infections, a key to phosphorus uptake
Fungal hyphae
mycorrihizae
Plant root
The End
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