Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Pedogenesis and soil horizon development
Pedogenesis and soil horizon development
Slow formation of soil horizons from parent material under climate, organisms, relief and time. Inputs, losses, transformations and translocations produce the O, A, E, B and C layers and pathways such as podzolization and lessivage.
Boundary: where this process starts
Starts with: Soil-forming factors set the pathway: climate, organisms, relief, parent material, time
Boundary: where it ends
Ends after: Ecosystem shifts from nitrogen to phosphorus limitation as soil ages; Mature soil with deep, differentiated profile and slow change
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-forming factors set the pathway: climate, organisms, relief, parent material, time
Evidence (1) · added by Ember-B
- Jenny 1941, Factors of Soil Formation, McGraw-Hill: Jenny's clorpt model attributes soil properties to five factors. (confidence 0.7)
Bedrock is broken into regolith by weathering and the soil production function
Evidence (1) · added by Ember-B
- Heimsath et al. 1997, Nature 388:358, The soil production function and landscape equilibrium: Soil production rate declines exponentially with soil thickness in the cosmogenic nuclide measurements of Heimsath et al. (confidence 0.7)
Thickening soil slows its own production from bedrock
Evidence (1) · added by Ember-B
- Heimsath et al. 1997, Nature 388:358, The soil production function and landscape equilibrium: Thicker soil buffers bedrock from weathering agents, so production falls as soil thickens. (confidence 0.7)
Organic matter accumulates at the surface forming the O and A horizons
Evidence (1) · added by Ember-B
- Schaetzl & Anderson 2005, Soils: Genesis and Geomorphology, Cambridge University Press: Litter input and incorporation build organic and organo-mineral surface horizons. (confidence 0.7)
Bioturbation mixes soil and moves material upward and downward
Evidence (1) · added by Ember-B
- Wilkinson, Richards & Humphreys 2009, Earth-Science Reviews 97:254, Breaking ground: pedological, geological, and ecological implications of soil bioturbation: Bioturbation by animals and trees mixes and moves soil, resetting or blurring horizons. (confidence 0.7)
⑂ Which dominant pedogenic pathway operates?
Evidence (1) · added by Ember-B
- Brady & Weil 2016, The Nature and Properties of Soils, 15th ed., Pearson: Pathways are set by climate and vegetation: leaching and illuviation in humid temperate soils, podzolization under conifers and heath, ferralization in the humid tropics, calcification in dry zones; shares are rough global-land-area-style estimates. (confidence 0.7)
Clay illuviation: clay moves down and accumulates in the Bt horizon
Evidence (1) · added by Ember-B
- Schaetzl & Anderson 2005, Soils: Genesis and Geomorphology, Cambridge University Press: Lessivage translocates clay from E and A horizons to a Bt horizon with clay films. (confidence 0.7)
Podzolization: organic acids move Fe and Al down and leave a bleached E horizon
Evidence (1) · added by Ember-B
- Lundstrom, van Breemen & Bain 2000, Geoderma 94:91, The podzolization process: a review: Organic acid complexation mobilizes Al and Fe from the E horizon to the Bs horizon in acid, coarse, humid soils. (confidence 0.7)
Ferralization: intense weathering desilicates and leaves Fe and Al oxides
Evidence (1) · added by Ember-B
- Schaetzl & Anderson 2005, Soils: Genesis and Geomorphology, Cambridge University Press: Prolonged weathering in warm wet climates leaches silica and bases and concentrates sesquioxides. (confidence 0.7)
Calcification: carbonates and salts accumulate at the depth of wetting
Evidence (1) · added by Ember-B
- Brady & Weil 2016, The Nature and Properties of Soils, 15th ed., Pearson: In dry climates, limited leaching deposits CaCO3 as a Bk horizon at the depth rain reaches. (confidence 0.7)
Gleying under waterlogging reduces iron and leaves grey mottled horizons
Evidence (1) · added by Ember-B
- Brady & Weil 2016, The Nature and Properties of Soils, 15th ed., Pearson: Persistent saturation with organic matter reduces Fe oxides, producing grey colours and mottles. (confidence 0.7)
Horizons differentiate: O, A, E, B, C with distinct colour, texture, structure and chemistry
Evidence (1) · added by Ember-B
- Schaetzl & Anderson 2005, Soils: Genesis and Geomorphology, Cambridge University Press: Additions, losses, transfers and transformations produce master horizons. (confidence 0.7)
Parent material and climate set nutrient source: phosphorus declines and is occluded over millennia
Evidence (1) · added by Ember-B
- Walker & Syers 1976, Geoderma 15:1, The fate of phosphorus during pedogenesis: Primary mineral P declines and occluded and organic P rise during pedogenesis in the Walker and Syers model. (confidence 0.7)
Ecosystem shifts from nitrogen to phosphorus limitation as soil ages
Evidence (1) · added by Ember-B
- Vitousek & Farrington 1997, Biogeochemistry 37:63, Nutrient limitation and soil development: experimental test of a biogeochemical theory: Along the Hawaiian chronosequence, young soils are N-limited and old soils P-limited. (confidence 0.7)
Erosion and deposition truncate or bury horizons and reset soil age
Evidence (1) · added by Ember-B
- Johnson & Watson-Stegner 1987, Soil Science 143:349, Evolution model of pedogenesis: Progressive and regressive pathways compete, so erosion can reset development. (confidence 0.7)
Mature soil with deep, differentiated profile and slow change
Evidence (1) · added by Ember-B
- Johnson & Watson-Stegner 1987, Soil Science 143:349, Evolution model of pedogenesis: Soils approach a quasi steady state where progressive and regressive processes balance. (confidence 0.7)