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 / Aluminium toxicity and liming of acid soils

Aluminium toxicity and liming of acid soils

Below about pH 5 Al3+ dominates the exchange complex, buffers pH through hydrolysis and damages root tips at micromolar concentrations. Lime neutralises acid and displaces Al3+, but acid inputs and base removal slowly bring the problem back.

Boundary: where this process starts

Starts with: Below pH 5.0 to 5.5 exchangeable Al3+ dominates the exchange complex

Boundary: where it ends

Ends after: Stunted roots take up less water, Ca, Mg and phosphate, lowering yield; Al3+ hydrolyses (Al3+ + H2O gives AlOH2+ + H+), so Al buffers pH between about 3 and 4.5

PARTICIPANTSRESOURCESAluminumLimePlant rootsSoil solutionClay mineralsOtherparticipantsAluminumHydrogen ionsWaterCalciumCalciteImpact -3 of 5. Click for details and evidence.Impact 03 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Farmer limesImpact +4 of 5. Click for details and evidence.↻ balances · strong · 0.6 Lime neutralises aImpact 02 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.↻ balances · moderate · 0.4 Acid inputs slowImpact -3 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Below pH 5.0 to 5.5 exchangeable Al3+ dominates the exchange complex: uses AluminumBelow pH 5.0 to 5.5 exchangeable Al3+ dominates the exchange complex: uses Hydrogen ionsAl3+ hydrolyses (Al3+ + H2O gives AlOH2+ + H+), so Al buffers pH between about 3 and 4.5: uses up Aluminumuses upAl3+ hydrolyses (Al3+ + H2O gives AlOH2+ + H+), so Al buffers pH between about 3 and 4.5: makes Hydrogen ionsmakesMicromolar Al3+ inhibits root elongation within hours by damaging the root apex cell wall and membranes: uses AluminumMicromolar Al3+ inhibits root elongation within hours by damaging the root apex cell wall and membranes: uses WaterStunted roots take up less water, Ca, Mg and phosphate, lowering yield: uses up Wateruses upStunted roots take up less water, Ca, Mg and phosphate, lowering yield: uses up Calciumuses upLime dissolves (CaCO3 uses 2 mol H+ per mol), Ca2+ displaces Al3+ and Al precipitates as Al(OH)3: uses up Aluminumuses upLime dissolves (CaCO3 uses 2 mol H+ per mol), Ca2+ displaces Al3+ and Al precipitates as Al(OH)3: uses up Hydrogen ionsuses upLime dissolves (CaCO3 uses 2 mol H+ per mol), Ca2+ displaces Al3+ and Al precipitates as Al(OH)3: makes CalciummakesLime dissolves (CaCO3 uses 2 mol H+ per mol), Ca2+ displaces Al3+ and Al precipitates as Al(OH)3: uses up Calciteuses upSurface-applied lime moves down slowly because of its low solubility, so subsoil acidity can persist: uses WaterSurface-applied lime moves down slowly because of its low solubility, so subsoil acidity can persist: uses CalciteNitrification, product removal and acid deposition re-acidify the soil over years: makes Hydrogen ionsmakesNitrification, product removal and acid deposition re-acidify the soil over years: uses up Calciumuses updominates exchangecomplexAluminum: dominates exchange complexcompete on exchangesitesHydrogen ions: compete on exchange siteshydrolysed and bufferspHAluminum: hydrolysed and buffers pHreleased by aluminumhydrolysisHydrogen ions: released by aluminum hydrolysisdamages root apex cellsAluminum: damages root apex cellsuptake impaired in rootsWater: uptake impaired in rootsuptake reduced bystunted rootsWater: uptake reduced by stunted rootsuptake reduced bystunted rootsCalcium: uptake reduced by stunted rootsprecipitated ashydroxideAluminum: precipitated as hydroxideneutralised by limeHydrogen ions: neutralised by limedisplaces aluminumCalcium: displaces aluminumdissolves to neutraliseacidCalcite: dissolves to neutralise acidlimits lime movementWater: limits lime movementmoves slowly down theprofileCalcite: moves slowly down the profilere-generated bynitrificationHydrogen ions: re-generated by nitrificationlost from exchange sitesCalcium: lost from exchange sitesStart: Aluminiumtoxicity and liming ofacid soilsSTARTStart: Aluminium toxicity and liming of acid soilsEnd: Aluminium toxicityand liming of acidsoilsENDEnd: Aluminium toxicity and liming of acid soilsBelow pH 5.0 to 5.5exchangeable Al3+dominates the exchan…📄1Below pH 5.0 to 5.5 exchangeable Al3+ dominates the exchange complexAl3+ hydrolyses (Al3+ +H2O gives AlOH2+ + H+),so Al buffers …📄1Al3+ hydrolyses (Al3+ + H2O gives AlOH2+ + H+), so Al buffers pH between about 3 and 4.5Micromolar Al3+inhibits rootelongation within hou…📄1Micromolar Al3+ inhibits root elongation within hours by damaging the root apex cell wall and membranesStunted roots take upless water, Ca, Mg andphosphate, loweri…📄1Stunted roots take up less water, Ca, Mg and phosphate, lowering yieldLime dissolves (CaCO3uses 2 mol H+ per mol),Ca2+ displaces Al3+ a…📄1Lime dissolves (CaCO3 uses 2 mol H+ per mol), Ca2+ displaces Al3+ and Al precipitates as Al(OH)3Surface-applied limemoves down slowlybecause of its l…📄1Surface-applied lime moves down slowly because of its low solubility, so subsoil acidity can persistNitrification, productremoval and aciddeposition re-acidi…📄1Nitrification, product removal and acid deposition re-acidify the soil over years
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.

Below pH 5.0 to 5.5 exchangeable Al3+ dominates the exchange complex
AluminumClay mineralsAluminumHydrogen ions
Evidence (1) · added by Fern
  • Kamprath (1970), Soil Science Society of America Proceedings 34:252-254: Exchangeable Al appears in quantity below pH 5.5 in mineral soils and is the main acidity. (confidence 0.8)
Al3+ hydrolyses (Al3+ + H2O gives AlOH2+ + H+), so Al buffers pH between about 3 and 4.5
AluminumSoil solutionAluminumHydrogen ions
Evidence (1) · added by Fern
  • Bloom, McBride & Weaver (1979), Aluminum organic matter in acid soils: buffering and solution aluminum activity, Soil Science Society of America Journal 43:488-493: Al hydroxy species and Al-organic matter complexes buffer soil pH over this range. (confidence 0.75)
Micromolar Al3+ inhibits root elongation within hours by damaging the root apex cell wall and membranes
AluminumPlant rootsAluminumWater
Evidence (1) · added by Fern
  • Kochian (1995), Cellular mechanisms of aluminum toxicity and resistance in plants, Annual Review of Plant Physiology and Plant Molecular Biology 46:237-260: Root growth inhibition by Al occurs at micromolar activities in the root apex. (confidence 0.85)
Stunted roots take up less water, Ca, Mg and phosphate, lowering yield
Plant rootsPlantsWaterCalciumPhosphate
Evidence (1) · added by Fern
  • Kochian, Hoekenga & Pineros (2004), How do crop plants tolerate acid soils? Annual Review of Plant Biology 55:459-493: Al-damaged roots have reduced nutrient and water acquisition, a major yield limit on acid soils. (confidence 0.75)
Lime dissolves (CaCO3 uses 2 mol H+ per mol), Ca2+ displaces Al3+ and Al precipitates as Al(OH)3
LimeAluminumCalciteHydrogen ionsCalciumAluminum
Evidence (1) · added by Fern
  • Kamprath (1970), Soil Science Society of America Proceedings 34:252-254: Liming to neutralise exchangeable Al raises pH to about 5.5 and removes Al toxicity. (confidence 0.8)
Surface-applied lime moves down slowly because of its low solubility, so subsoil acidity can persist
LimeSoil solutionCalciteWater
Evidence (1) · added by Fern
  • Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016), ch. 9 on soil acidity: Lime is sparingly soluble and moves little below the zone of incorporation without incorporation. (confidence 0.55)
Nitrification, product removal and acid deposition re-acidify the soil over years
Nitrifying bacteriaCrop harvestHydrogen ionsCalcium
Evidence (1) · added by Fern
  • Helyar & Porter (1989), Soil acidification, its measurement and the processes involved, in Soil Acidity and Plant Growth, Academic Press: Agricultural soils acidify by nitrification, removal of alkaline product and leaching; acidification rates are of order several kmol H+ per ha per year. (confidence 0.6)