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GES175, Science of Soils PowerPoint Presentation
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GES175, Science of Soils

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  1. GES175, Science of Soils Lecture 10 Phosphorus

  2. Slide 10.2 Phosphorus Soil-Plant Relations * Energy and reproduction * Growth and development aroot growth amaturity (seed set, flowering,...) * Maintained by organic matter cycling

  3. 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

  4. 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

  5. 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)

  6. Slide 10.6 Volcanic Ashëë

  7. Slide 10.7 Inorganic P Compounds(precipitates) Acid soils 8Fe and Al phosphates FePO4l2H2O, AlPO4l2H2O Alkaline soils 4 Ca and Mg phosphates

  8. 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

  9. Slide 10.9 Nomenclature H3PO4 = phosphoric acid H2PO4- = monobasic HPO4-2 = dibasic PO4-3 = tribasic

  10. Slide 10.10 Phosphate Ion: Protonation acid soils alkaline soils

  11. Slide 10.11 Most Available P between pH 6 - 7

  12. 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

  13. Slide 10.13 Cycling: A slow release mechanism Organic-P immobilization mineralization (available P) HxPO4x-3 Solid Phase-PO4 (unavailable)

  14. Symbiotic Relation:Fungi and Plants Mycorrhizae root infections, a key to phosphorus uptake Plant root Fungal hyphae mycorrihizae

  15. The End

  16. 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