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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Cation exchange, pH and soil solution chemistry / Nitrification-driven acidification of ammonium fertilised soil

Nitrification-driven acidification of ammonium fertilised soil

How nitrification of ammonium fertiliser releases hydrogen ions, and how nitrate uptake, leaching and buffering determine whether the soil acidifies.

Boundary: where this process starts

Starts with: Ammonia oxidisers convert Ammonium to nitrite, releasing H+

Boundary: where it ends

Ends after: Plants take up Nitrate and release OH-/HCO3-, offsetting part of the acid; Nitrate leaches with Calcium and Magnesium, leaving net acidity

PARTICIPANTSRESOURCESAmmonia-oxidisingarchaeaPlant rootsNitrifyingbacteriaAmmonia-oxidisingbacteriaNitrite-oxidisingbacteriaOtherparticipantsNitrateOxygenHydrogen ionsAmmoniumNitriteImpact +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.Impact +2 of 5. Click for details and evidence.40% nitrate taken up by cropImpact -3 of 5. Click for details and evidence.60% nitrate leachedImpact +2 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.↻ reinforces · weak · 0.15 lost bases lower Ammonia oxidisers convert Ammonium to nitrite, releasing H+: uses up Oxygenuses upAmmonia oxidisers convert Ammonium to nitrite, releasing H+: makes Hydrogen ionsmakesAmmonia oxidisers convert Ammonium to nitrite, releasing H+: uses up Ammoniumuses upNitrite oxidisers produce Nitrate: makes NitratemakesNitrite oxidisers produce Nitrate: uses up Oxygenuses upNitrite oxidisers produce Nitrate: uses up Nitriteuses upSoil pH falls as acidity accumulates: makes Hydrogen ionsmakesPlants take up Nitrate and release OH-/HCO3-, offsetting part of the acid: uses up Nitrateuses upNitrate leaches with Calcium and Magnesium, leaving net acidity: uses up Nitrateuses upconsumed as oxidantOxygen: consumed as oxidantreleased as acidHydrogen ions: released as acidoxidized to nitriteAmmonium: oxidized to nitriteformed in final stepNitrate: formed in final stepconsumed as oxidantOxygen: consumed as oxidantoxidized to nitrateNitrite: oxidized to nitrateaccumulate and lower pHHydrogen ions: accumulate and lower pHtaken up by rootsNitrate: taken up by rootsleached with cationsNitrate: leached with cationsStart:Nitrification-drivenacidification …STARTStart: Nitrification-driven acidification of ammonium fertilised soilEnd:Nitrification-drivenacidification …ENDEnd: Nitrification-driven acidification of ammonium fertilised soilAmmonia oxidisersconvert Ammonium tonitrite, releasing H+👍1📄1Ammonia oxidisers convert Ammonium to nitrite, releasing H+Nitrite oxidisersproduce Nitrate📄1Nitrite oxidisers produce NitrateSoil pH falls asacidity accumulates📄1Soil pH falls as acidity accumulatesPlants take up Nitrateand release OH-/HCO3-,offsetting part of t…📄1Plants take up Nitrate and release OH-/HCO3-, offsetting part of the acidNitrate leaches withCalcium and Magnesium,leaving net acidity👍1📄1Nitrate leaches with Calcium and Magnesium, leaving net acidity
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)
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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.

Ammonia oxidisers convert Ammonium to nitrite, releasing H+
Ammonia-oxidising bacteriaAmmonia-oxidising archaeaAmmoniumOxygenHydrogen ions
Evidence (1) · added by Fern-B
  • Prosser & Nicol (2012), Archaeal and bacterial ammonia-oxidisers in soil: the quest for niche specialisation, Trends in Microbiology 20:523: Both AOB and AOA oxidise ammonia to nitrite, with AOA favoured in acidic, low-ammonia soils. (confidence 0.8)
Nitrite oxidisers produce Nitrate
Nitrite-oxidising bacteriaNitriteNitrateOxygen
Evidence (1) · added by Fern-B
  • Daims et al. (2015), Complete nitrification by Nitrospira bacteria, Nature 528:504: Nitrospira oxidise nitrite to nitrate, completing nitrification in soils and other habitats. (confidence 0.85)
⑂ Soil pH falls as acidity accumulates
Soil solutionHydrogen ionsBase cations
Evidence (1) · added by Fern-B
  • Bolan & Hedley (2003), Handbook of Soil Acidity: Outcome depends on buffering and on whether nitrate is taken up or leached; shares are an estimate (range 30-70% leached in humid, fertilised soils). (confidence 0.45)
Plants take up Nitrate and release OH-/HCO3-, offsetting part of the acid
Plant rootsNitrateHydroxide
Evidence (1) · added by Fern-B
  • Hinsinger et al. (2003), Origins of root-mediated pH changes in the rhizosphere and their responses to environmental constraints: a review, Plant and Soil 248:43: Anion uptake (NO3-) by roots is accompanied by net OH-/HCO3- release that raises rhizosphere pH. (confidence 0.8)
Nitrate leaches with Calcium and Magnesium, leaving net acidity
Drainage waterNitrateCalciumMagnesiumWater
Evidence (1) · added by Fern-B
  • Bolan & Hedley (2003), Handbook of Soil Acidity: Leached nitrate with base cations converts nitrification acid into permanent soil acidification. (confidence 0.8)