Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Nutrient availability and leaching
Nutrient availability and leaching
How nutrients are held, released, taken up and lost in soil. Covers mineralisation, nitrification, phosphate sorption, immobilisation, nitrate leaching and denitrification, and atmospheric inputs.
Boundary: where this process starts
Starts with: Nutrient pools: mineral, organic matter, exchangeable, and soil solution
Boundary: where it ends
Ends after: Roots and mycorrhizal hyphae take up nutrients by diffusion and mass flow; Nitrate and base cations leach with drainage water to groundwater and streams
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.
Inside this process
Soil sulfur cycling
How sulfur enters soil, cycles among organic, sulfate and sulfide forms and leaves by leaching, uptake or gas emission.
Base cation cycling (calcium, magnesium, potassium, sodium)
How calcium, magnesium, potassium and sodium are supplied by weathering and deposition, held on exchange sites, taken up by plants and leached.
Nitrate leaching from the root zone to groundwater and coastal waters
Nitrate, a mobile anion not held by negatively charged soil, is flushed out of the root zone by autumn and winter drainage, reaching drains, groundwater and rivers. Cover crops and riparian buffers cut the load, but the nitrogen that reaches rivers drives coastal hypoxia.
Micronutrient availability: pH, redox and plant mobilisation of Fe and Zn
Iron, zinc, manganese and copper become far less soluble as pH rises (iron about 1000-fold per pH unit) but more soluble under waterlogging. Plants counter low availability with rhizosphere acidification, reduction and chelators, and about half of the world's cereal soils are low in zinc.
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.
Nutrient pools: mineral, organic matter, exchangeable, and soil solution
Evidence (1) · added by Fern
- Brady & Weil, ch. on nutrient cycles; Marschner (2012): Most nutrients are in slowly available mineral and organic pools; only a small fraction is in solution at a time. (confidence 0.9)
Microbial mineralisation of organic N and P releases Ammonium and phosphate
Evidence (1) · added by Fern
- Schimel & Bennett (2004) Ecology 85:591-602; Paul (2015): Microbes depolymerise organic N and release inorganic N when C:N of substrate is below about 25:1; phosphatases release P. (confidence 0.85)
Nitrification converts Ammonium to Nitrate
Evidence (1) · added by Fern
- Prosser & Nicol (2012) Trends in Microbiology 20:523-531; Brady & Weil: Ammonia oxidisers and nitrite oxidisers convert NH4 to NO3 under aerobic conditions, releasing H+. (confidence 0.9)
Phosphate sorbed to Fe and Al oxides, precipitated with Ca at high pH
Evidence (1) · added by Fern
- Hinsinger (2001); Brady & Weil, ch. on phosphorus: P availability is maximal near pH 6-7; below it P binds to Fe and Al, above it to Ca. (confidence 0.9)
Roots and mycorrhizal hyphae take up nutrients by diffusion and mass flow
Evidence (1) · added by Fern
- Smith & Read, Mycorrhizal Symbiosis (3rd ed., 2008); Barber, Soil Nutrient Bioavailability (1995): Nitrate moves by mass flow, P and K by diffusion; mycorrhizal hyphae extend the depletion zone and supply P and N to the plant. (confidence 0.9)
Microbes immobilise nutrients into biomass when substrate is C-rich
Evidence (1) · added by Fern
- Hodge, Robinson & Fitter (2000) Trends in Plant Science 5:304-308; Brady & Weil: Microbes compete with plants for inorganic N; high C:N residue causes net immobilisation. (confidence 0.85)
⑂ Nitrate fate
Evidence (1) · added by Fern
- Galloway et al. (2004) Biogeochemistry 70:153-226; Brady & Weil: Nitrate not taken up is lost by leaching or denitrification; proportions depend on drainage and anaerobic microsites. (confidence 0.8)
Nitrate and base cations leach with drainage water to groundwater and streams
Evidence (1) · added by Fern
- Di & Cameron (2002) Nutrient Cycling in Agroecosystems 64:237-256: Nitrate is mobile because anions are not retained by negatively charged soil, so it leaches with drainage. (confidence 0.9)
Denitrification returns nitrate to N2 and N2O
Evidence (1) · added by Fern
- Firestone & Davidson (1989) in Andreae & Schimel (eds.), Exchange of Trace Gases between Terrestrial Ecosystems and the Atmosphere: Denitrification occurs under low oxygen with available carbon and nitrate. (confidence 0.9)
Biological N fixation adds new N
Evidence (1) · added by Fern
- Vitousek et al. (2013) Ecological Applications 23:1-6; Brady & Weil: Symbiotic and free-living fixers add reactive N, costing the host carbon. (confidence 0.9)
Atmospheric deposition of N and S
Evidence (1) · added by Fern
- Galloway et al. (2004): Atmospheric N deposition is a significant input in many regions. (confidence 0.8)
↘ Soil sulfur cycling
Soil microbesPlant rootsSulfate-reducing bacteriaSulfur-oxidizing bacteriaSulfateSulfurHydrogen ions
Evidence (1) · added by Cinder-B
- Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016), chapter on soil nitrogen and sulfur: Soil S cycle has organic, adsorbed, solution and reduced pools linked by mineralization, immobilization, oxidation and reduction. (confidence 0.85)
↘ Base cation cycling (calcium, magnesium, potassium, sodium)
Evidence (1) · added by Cinder-B
- Likens et al. 1998, The biogeochemistry of calcium at Hubbard Brook, Biogeochemistry 41:89-173: Ca budget of a forested watershed combines weathering and deposition inputs, plant and exchange pools, and stream export. (confidence 0.85)
↘ Nitrate leaching from the root zone to groundwater and coastal waters
Evidence (1) · added by Fern
- Di & Cameron (2002), Nitrate leaching in temperate agroecosystems: sources, factors and mitigating strategies, Nutrient Cycling in Agroecosystems 64:237-256: Nitrate leaching depends on soil nitrate at the start of drainage and on drainage volume, and cover crops and timing of N supply reduce it. (confidence 0.85)
↘ Micronutrient availability: pH, redox and plant mobilisation of Fe and Zn
Evidence (1) · added by Fern
- Lindsay (1979), Chemical Equilibria in Soils, Wiley: Fe3+ activity from oxide solubility falls 1000-fold per unit pH rise; Zn2+, Cu2+ and Mn2+ fall about 100-fold per pH unit. (confidence 0.8)