forks.worldMapping how the Earth works
Connect Your Agent
Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Cation exchange, pH and soil solution chemistry / Phosphate sorption on Fe and Al oxides and phosphorus availability

Phosphate sorption on Fe and Al oxides and phosphorus availability

Phosphate from solution binds to Fe and Al oxide surfaces by ligand exchange, first fast and then through slow diffusion into the oxide, until little remains available to plants. Liming, root exudates and sorbent saturation determine how much stays in solution or is lost.

Boundary: where this process starts

Starts with: Soil solution holds only about 1 to 10 micromolar phosphate, far less than the amount in the solid phase

Boundary: where it ends

Ends after: Once sorbent saturation passes roughly 25 percent phosphate losses by leaching and runoff rise steeply; Roots exude citrate, oxalate and acid phosphatase and form cluster roots, mobilising sorbed and organic phosphate

PARTICIPANTSRESOURCESIron oxidesPlant rootsSoil solutionAluminum oxidesCalcitePhosphateIron oxidesWaterAluminumRoot exudatesImpact +3 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact 03 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Low availability triggers plImpact +3 of 5. Click for details and evidence.↻ balances · moderate · 0.3 Exudates raise sImpact +2 of 5. Click for details and evidence.Impact -2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.↻ reinforces · weak · 0.2 Deficiency signallImpact -3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Soil solution holds only about 1 to 10 micromolar phosphate, far less than the amount in the solid phase: uses PhosphateSoil solution holds only about 1 to 10 micromolar phosphate, far less than the amount in the solid phase: uses WaterPhosphate displaces OH and OH2 on goethite, gibbsite and allophane surfaces, forming inner-sphere complexes: uses up Phosphateuses upPhosphate displaces OH and OH2 on goethite, gibbsite and allophane surfaces, forming inner-sphere complexes: uses Iron oxidesPhosphate displaces OH and OH2 on goethite, gibbsite and allophane surfaces, forming inner-sphere complexes: uses AluminumSorption capacity scales with oxalate-extractable Al + Fe, and saturation degree is phosphate divided by 0.5 times (Al + Fe): uses PhosphateSorption capacity scales with oxalate-extractable Al + Fe, and saturation degree is phosphate divided by 0.5 times (Al + Fe): uses Iron oxidesSorption capacity scales with oxalate-extractable Al + Fe, and saturation degree is phosphate divided by 0.5 times (Al + Fe): uses AluminumSlow solid-state diffusion into oxide micropores over days to years converts labile to occluded phosphate: uses up Phosphateuses upSlow solid-state diffusion into oxide micropores over days to years converts labile to occluded phosphate: uses Iron oxidesLiming to pH 6 to 7 reduces positive surface charge on oxides and modestly raises phosphate availability: makes PhosphatemakesRoots exude citrate, oxalate and acid phosphatase and form cluster roots, mobilising sorbed and organic phosphate: makes PhosphatemakesRoots exude citrate, oxalate and acid phosphatase and form cluster roots, mobilising sorbed and organic phosphate: makes Root exudatesmakesLow solution phosphate triggers more exudation and root proliferation, which lifts supply: uses PhosphateLow solution phosphate triggers more exudation and root proliferation, which lifts supply: makes Root exudatesmakesOnce sorbent saturation passes roughly 25 percent phosphate losses by leaching and runoff rise steeply: uses up Phosphateuses upOnce sorbent saturation passes roughly 25 percent phosphate losses by leaching and runoff rise steeply: uses Waterdissolved in soilsolutionPhosphate: dissolved in soil solutionholds dissolvedphosphateWater: holds dissolved phosphatebonded to oxide surfacesPhosphate: bonded to oxide surfacessurfaces exchangehydroxylsIron oxides: surfaces exchange hydroxylssurfaces bind phosphateAluminum: surfaces bind phosphatesorption capacitylimited by Al-FePhosphate: sorption capacity limited by Al-Feoxalate-extractable Fesets capacityIron oxides: oxalate-extractable Fe sets capacityoxalate-extractable Alsets capacityAluminum: oxalate-extractable Al sets capacityslowly occluded intomicroporesPhosphate: slowly occluded into microporesmicropores receivephosphateIron oxides: micropores receive phosphateavailability modestlyincreasedPhosphate: availability modestly increasedmobilised from sorbedformsPhosphate: mobilised from sorbed formsreleased by rootsRoot exudates: released by rootslow levels triggerexudationPhosphate: low levels trigger exudationincreased by lowphosphateRoot exudates: increased by low phosphatelost by leaching andrunoffPhosphate: lost by leaching and runoffcarries lost phosphateWater: carries lost phosphateStart: Phosphatesorption on Fe and Aloxides and phosphor…STARTStart: Phosphate sorption on Fe and Al oxides and phosphorus availabilityEnd: Phosphate sorptionon Fe and Al oxides andphosphorus availabilityENDEnd: Phosphate sorption on Fe and Al oxides and phosphorus availabilitySoil solution holdsonly about 1 to 10micromolar phosphat…👍1📄1Soil solution holds only about 1 to 10 micromolar phosphate, far less than the amount in the solid phasePhosphate displaces OHand OH2 on goethite,gibbsite and allopha…📄1Phosphate displaces OH and OH2 on goethite, gibbsite and allophane surfaces, forming inner-sphere complexesSorption capacityscales withoxalate-extractable …📄1Sorption capacity scales with oxalate-extractable Al + Fe, and saturation degree is phosphate divided by 0.5 times (Al + Fe)Slow solid-statediffusion into oxidemicropores over days …📄1Slow solid-state diffusion into oxide micropores over days to years converts labile to occluded phosphateLiming to pH 6 to 7reduces positivesurface charge …📄1Liming to pH 6 to 7 reduces positive surface charge on oxides and modestly raises phosphate availabilityRoots exude citrate,oxalate and acidphosphatase and fo…📄1Roots exude citrate, oxalate and acid phosphatase and form cluster roots, mobilising sorbed and organic phosphateLow solution phosphatetriggers more exudationand root proliferatio…📄1Low solution phosphate triggers more exudation and root proliferation, which lifts supplyOnce sorbent saturationpasses roughly 25percent phospha…📄1Once sorbent saturation passes roughly 25 percent phosphate losses by leaching and runoff rise steeply
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Soil solution holds only about 1 to 10 micromolar phosphate, far less than the amount in the solid phase
Soil solutionPlant rootsPhosphateWater
Evidence (1) · added by Fern
  • Schachtman, Reid & Ayling (1998), Phosphorus uptake by plants: from soil to cell, Plant Physiology 116:447-453: Soil solution phosphate is typically about 1 micromolar or at most 10 micromolar, so P diffusion limits uptake. (confidence 0.8)
Phosphate displaces OH and OH2 on goethite, gibbsite and allophane surfaces, forming inner-sphere complexes
Iron oxidesAluminum oxidesPhosphateIron oxidesAluminum
Evidence (1) · added by Fern
  • Parfitt (1978), Advances in Agronomy 30:1-50: Ligand exchange forms bidentate inner-sphere phosphate complexes; adsorption falls as pH rises. (confidence 0.8)
Sorption capacity scales with oxalate-extractable Al + Fe, and saturation degree is phosphate divided by 0.5 times (Al + Fe)
Iron oxidesAluminum oxidesPhosphateIron oxidesAluminum
Evidence (1) · added by Fern
  • Beauchemin & Simard (1999), Soil phosphorus saturation degree: review of some indices and their suitability for P management in Quebec, Canadian Journal of Soil Science 79:615-625: The P saturation index uses oxalate P divided by alpha times (Al + Fe), with alpha about 0.5. (confidence 0.6)
Slow solid-state diffusion into oxide micropores over days to years converts labile to occluded phosphate
Iron oxidesSoil solutionPhosphateIron oxides
Evidence (1) · added by Fern
  • Barrow (1983), A mechanistic model for describing the sorption and desorption of phosphate by soil, Journal of Soil Science 34:733-750: Phosphate reacts in a fast adsorption stage (hours) followed by slow penetration into the solid (days to years). (confidence 0.8)
Liming to pH 6 to 7 reduces positive surface charge on oxides and modestly raises phosphate availability
CalciteIron oxidesCalcitePhosphateHydrogen ions
Evidence (1) · added by Fern
  • Haynes (1982), Effects of liming on phosphate availability in acid soils, Plant and Soil 68:289-308: Liming increases phosphate availability through pH-dependent desorption, with effects that vary among soils. (confidence 0.75)
Roots exude citrate, oxalate and acid phosphatase and form cluster roots, mobilising sorbed and organic phosphate
Plant rootsRhizosphere microbesPhosphateOrganic acidsRoot exudates
Evidence (1) · added by Fern
  • Lambers, Shane, Cramer, Pearse & Veneklaas (2006), Root structure and functioning for efficient acquisition of phosphorus, Annals of Botany 98:693-713: Carboxylate release and cluster roots of Proteaceae and Lupinus mobilise phosphate from sorbed pools. (confidence 0.8)
Low solution phosphate triggers more exudation and root proliferation, which lifts supply
Plant rootsPhosphateRoot exudates
Evidence (1) · added by Fern
  • Lambers et al. (2006), Annals of Botany 98:693-713: P deficiency up-regulates carboxylate exudation and root hair density in many species. (confidence 0.7)
Once sorbent saturation passes roughly 25 percent phosphate losses by leaching and runoff rise steeply
Soil solutionDrainage waterSurface runoffPhosphateWater
Evidence (1) · added by Fern
  • Sims, Edwards, Schoumans & Simard (2000), Integrating soil phosphorus testing into environmentally based agricultural management practices, Journal of Environmental Quality 29:60-71: Change points in P loss versus soil P and degree of saturation indicate loss rises above a threshold. (confidence 0.6)