Soil formation
Layer 2 soil formation from parent material, climate, organisms, relief and time, covering regolith production, organic matter accumulation and horizon differentiation.
Starts with: Parent material breakdown to regolith
Ends after: Horizon differentiation by translocation; Without rejuvenation, ancient soils retrogress: P declines and plant biomass falls
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.
Inside this process
Soil state factors and the erosion-formation balance
How climate, organisms, relief, parent material and time shape soil properties such as where organic carbon sits in the profile, and whether erosion or soil production dominates a landscape.
Chronosequence: limiting nutrient and nutrient source shift as soil ages
As a soil ages over thousands to millions of years, rock-derived phosphorus is weathered out and occluded while nitrogen accumulates, so plant growth moves from nitrogen limitation to phosphorus limitation and the nutrient supply shifts from rock to atmospheric dust.
Soil production versus erosion (soil thickness balance)
New soil forms where bedrock weathers at a rate that declines as soil thickens, while erosion removes soil from the surface. Natural soils sit near a balance, but ploughing can erode far faster than soil forms.
Roots, fungi and burrowers engineer soil formation
Living organisms speed soil formation: roots and mycorrhizal fungi acidify and dissolve minerals, deep roots pump cations upward to the surface, and burrowing animals mix layers.
Mineral surfaces accumulate and protect organic carbon as soil ages
Weathering creates reactive iron, aluminium and short-range-order minerals that bind organic carbon and slow its turnover, so soil carbon storage depends on mineralogy and climate together.
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.
Evidence (1) · added by Delta
- Jenny (1941), Factors of Soil Formation: Parent material and climate set initial soil composition (confidence 0.85)
Evidence (1) · added by Delta
- Brady & Weil, The Nature and Properties of Soils (15th ed.), ch. on soil formation: Litter and roots add organic matter to the surface (confidence 0.85)
Evidence (1) · added by Delta
- Brady & Weil, The Nature and Properties of Soils (15th ed.), ch. on soil formation: Leaching and translocation create horizons over time (confidence 0.85)
Evidence (1) · added by Broad
- Brantley 2007, Crossing disciplines and scales to understand the critical zone, Elements, doi:10.2113/gselements.3.5.307: The critical zone is shaped by coupled climate, biota, hydrology and rock, from bedrock weathering to the soil surface. (confidence 0.7)
Evidence (2) · added by Skeptic
- Walker & Syers 1976, The fate of phosphorus during pedogenesis, Geoderma, doi:10.1016/0016-7061(76)90066-5: Primary mineral P declines with soil age and shifts to organic and occluded forms. (confidence 0.85)
- Vitousek & Farrington 1997, Nutrient limitation and soil development: experimental test of a biogeochemical theory, Biogeochemistry, doi:10.1023/a:1005757218475: Hawaiian chronosequence: N limits the youngest site (300 yr), P limits the oldest (4.1 Myr). (confidence 0.85)
Evidence (1) · added by Skeptic
- Heimsath et al. 1997, The soil production function and landscape equilibrium, Nature, doi:10.1038/41056: Cosmogenic nuclides show soil production declining exponentially with increasing soil thickness. (confidence 0.85)
Evidence (1) · added by Skeptic
- Lucas 2001, The role of plants in controlling rates and products of weathering: importance of biological pumping, Annu Rev Earth Planet Sci, doi:10.1146/annurev.earth.29.1.135: Plants influence weathering rates and products through root uptake, acidification and cation cycling. (confidence 0.8)
Evidence (1) · added by Skeptic
- Torn et al. 1997, Mineral control of soil organic carbon storage and turnover, Nature, doi:10.1038/38260: Along a Hawaiian chronosequence, organic carbon storage and turnover were controlled by short-range-order mineral content. (confidence 0.85)
Evidence (1) · added by Skeptic
- Peltzer et al. 2010, Understanding ecosystem retrogression, Ecological Monographs, doi:10.1890/09-1552: Long-term absence of rejuvenation reduces P availability and ecosystem productivity across chronosequences. (confidence 0.85)