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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Cation exchange, pH and soil solution chemistry / Salinity and sodicity

Salinity and sodicity

How soluble salts and sodium accumulate in soil, raise osmotic stress and disperse clay, and how leaching or amendments reverse it.

Boundary: where this process starts

Starts with: Salts accumulate where evapotranspiration exceeds leaching

Boundary: where it ends

Ends after: Microbial respiration and decomposition decline under salt stress; Dispersed clay clogs pores and crusts; infiltration drops, runoff and erosion rise

PARTICIPANTSRESOURCESSoluble saltsSodiumIrrigationwaterClay mineralsSoil solutionOtherparticipantsWaterSodiumChlorideCationsSaltsImpact +3 of 5. Click for details and evidence.Impact +2 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.Impact -3 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.↻ reinforces · strong · 0.4Impact -2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.↻ balances · strong · 0.5Impact -2 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.Salts accumulate where evapotranspiration exceeds leaching: uses up Wateruses upSalts accumulate where evapotranspiration exceeds leaching: makes SodiummakesSalts accumulate where evapotranspiration exceeds leaching: makes ChloridemakesShallow water table rises by capillary action; salt is left at the surface: uses WaterShallow water table rises by capillary action; salt is left at the surface: makes SodiummakesClassify salt-affected soil by EC_e and ESP: uses SodiumClassify salt-affected soil by EC_e and ESP: uses CationsSaline soil: osmotic stress reduces water uptake: uses WaterSaline soil: osmotic stress reduces water uptake: uses SaltsSodic soil: Na on exchange sites disperses clay when electrolyte is low: uses SodiumDispersed clay clogs pores and crusts; infiltration drops, runoff and erosion rise: uses WaterReclamation: gypsum supplies Calcium and leaching removes Na: uses WaterReclamation: gypsum supplies Calcium and leaching removes Na: uses up Sodiumuses upevaporates and leavessaltsWater: evaporates and leaves saltsconcentrates at surfaceSodium: concentrates at surfaceaccumulates in the rootzoneChloride: accumulates in the root zonerises by capillaryactionWater: rises by capillary actionleft at the surfaceSodium: left at the surfacemeasured via ESPclassificationSodium: measured via ESP classificationexchangeable poolmeasuredCations: exchangeable pool measureduptake reduced byosmosisWater: uptake reduced by osmosislower osmotic potentialin soilSalts: lower osmotic potential in soiloccupies exchange sitesSodium: occupies exchange sitesinfiltration drops,runoff risesWater: infiltration drops, runoff risesleaches sodium from soilWater: leaches sodium from soilleached from exchangesitesSodium: leached from exchange sitesStart: Salinity andsodicitySTARTStart: Salinity and sodicityEnd: Salinity andsodicityENDEnd: Salinity and sodicitySalts accumulate whereevapotranspirationexceeds leaching📄1Salts accumulate where evapotranspiration exceeds leachingShallow water tablerises by capillaryaction; salt is left …📄1Shallow water table rises by capillary action; salt is left at the surfaceClassify salt-affectedsoil by EC_e and ESP📄1Classify salt-affected soil by EC_e and ESPSaline soil: osmoticstress reduces wateruptake📄1Saline soil: osmotic stress reduces water uptakeSodic soil: Na onexchange sitesdisperses clay wh…📄1Sodic soil: Na on exchange sites disperses clay when electrolyte is lowDispersed clay clogspores and crusts;infiltration drop…📄1Dispersed clay clogs pores and crusts; infiltration drops, runoff and erosion riseMicrobial respirationand decompositiondecline under sa…📄1Microbial respiration and decomposition decline under salt stressReclamation: gypsumsupplies Calcium andleaching removes Na📄1Reclamation: gypsum supplies Calcium and leaching removes Na
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.

Salts accumulate where evapotranspiration exceeds leaching
Soluble saltsSunIrrigation waterWaterSodiumChloride
Evidence (1) · added by Fern
  • Rengasamy 2006, Journal of Experimental Botany 57:1017: Salinity develops in arid zones and under irrigation or rising saline water tables where leaching is limited. (confidence 0.7)
Shallow water table rises by capillary action; salt is left at the surface
GroundwaterSoluble saltsWaterSodium
Evidence (1) · added by Fern
  • Ghassemi, Jakeman & Nix 1995, Salinisation of Land and Water Resources (CAB International): Capillary rise and evaporation concentrate salts in the root zone and surface. (confidence 0.6)
Classify salt-affected soil by EC_e and ESP
Soil solutionExchange sitesSodiumCations
Evidence (1) · added by Fern
  • Richards 1954, USDA Handbook 60: Saline: EC_e above 4 dS/m and ESP below 15; sodic: ESP above 15; saline-sodic: both. (confidence 0.8)
Saline soil: osmotic stress reduces water uptake
Plant rootsSoil solutionWaterSalts
Evidence (1) · added by Fern
  • Maas & Hoffman 1977, Journal of the Irrigation and Drainage Division ASCE 103:115: Yield thresholds differ: wheat about 6.0 dS/m and maize about 1.7 dS/m, with yield loss per dS/m above the threshold. (confidence 0.7)
Sodic soil: Na on exchange sites disperses clay when electrolyte is low
SodiumClay mineralsSodiumClay minerals
Evidence (1) · added by Fern
  • Quirk & Schofield 1955, Journal of Soil Science 6:163: Permeability falls sharply when ESP is high and electrolyte concentration is low. (confidence 0.75)
Dispersed clay clogs pores and crusts; infiltration drops, runoff and erosion rise
Dispersed claySoil poresWaterPore space
Evidence (1) · added by Fern
  • Shainberg & Letey 1984, Hilgardia 52(2):1: Response of soil hydraulic properties to dispersion and swelling at high ESP and low salinity. (confidence 0.7)
Microbial respiration and decomposition decline under salt stress
Soil microbesCarbon dioxideSoil organic matter
Evidence (1) · added by Fern
  • Rath & Rousk 2015, Soil Biology and Biochemistry 81:108: Review: salinity reduces microbial biomass and activity and carbon turnover. (confidence 0.65)
Reclamation: gypsum supplies Calcium and leaching removes Na
GypsumDrainage waterCalciumGypsumSodiumWater
Evidence (1) · added by Fern
  • Ayers & Westcot 1985, FAO Irrigation and Drainage Paper 29 Rev. 1: Gives the leaching requirement LR = EC_iw / (5 EC_e - EC_iw) and gypsum as an amendment for sodicity. (confidence 0.75)