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Resource: used or used up in processesWater
Appears in 136 processs and 457 steps. Everything below is linked: open a process to see it in context.
Top processes
Living soil system
18 steps- Mineral weathering and parent material
- Water infiltration, retention and movement
- Soil gas exchange and redox
- and 15 more in this process
- Capillary and adsorptive forces bind water to particles, giving soil water a negative matric potential
- Pore radius sets suction by capillarity, h(cm) = 0.15/r(cm): pores of 15 micrometre radius empty near -10 kPa while 0.1 micrometre pores hold water to about -1.5 MPa
- Texture shapes the curve: sands release most water by -10 kPa while clays hold much water below -1.5 MPa
- and 6 more in this process
- Flux follows Buckingham-Darcy, q = -K(h) times the gradient of total potential, and combined with mass balance gives the Richards equation
- Flow through a pore scales with radius to the fourth power, so doubling radius gives 16 times the flow and large pores dominate conductivity
- Saturated conductivity spans about three orders of magnitude by texture: sand about 20 cm/h, silt loam about 0.7 cm/h, clay about 0.03-0.1 cm/h
- and 6 more in this process
Show 130 more processes
Water movement
8 steps- Infiltration of water into soil
- Plant root uptake and transpiration
- Drainage, runoff and evaporation
- and 5 more in this process
- Capillary fringe above the water table: rise follows Jurin h = 0.15/r cm, about 0.3-0.5 m in fine sand and 1-2 m in silt
- Evaporation and root uptake pull water up when K at the table depth permits: the maximum steady upward flux falls roughly as depth to the table raised to a power of 2-4
- Shallow groundwater can supply tens of percent of crop water use where the table is within about 1-2 m
- and 5 more in this process
- Capillary and adsorptive forces hold water: by the Young-Laplace law pores wider than about 10 to 30 micrometres empty at field capacity (-10 to -33 kPa) and pores narrower than about 0.2 micrometres hold water beyond -1.5 MPa
- Field capacity is reached when downward drainage becomes negligible, about 2 to 3 days after wetting
- Texture sets the available water: roughly 0.05-0.10 m3 per m3 in sand and about 0.15-0.20 in silt loam
- and 4 more in this process
- Stage 1: a wet surface evaporates at the atmospheric demand rate, typically 3-8 mm per day in sunny weather
- Evaporating 1 mm of water absorbs about 2.45 MJ per square metre, cooling the surface
- Stage 1 ends when the readily evaporable water is used: about 2-7 mm for sand and 8-12 mm for loam and clay
- and 4 more in this process
- Wetting hydrates the cations between smectite layers: Ca-smectite swells to about 1.9 nm basal spacing, whereas Na-smectite at low salt swells osmotically beyond 4 nm
- Shrinkage curve: after a structural phase, volume loss in the proportional phase equals water loss (slope near 1), then residual and zero shrinkage
- Drying shrinks the soil, first as vertical subsidence then as cracks; total shrinkage is split between subsidence and crack volume by a geometry factor between 1 (vertical only) and 3 (isotropic)
- and 4 more in this process
- Primary production
- Soil formation
- Water movement
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Bacteria and archaea
6 stepsWeathering
5 stepsRoots and rhizosphere
5 stepsWater cycle
5 stepsOcclusion in aggregates
5 stepsSalinity and sodicity
5 steps- Stage I: evaporation runs near the potential rate while capillary flow keeps the surface wet; readily evaporable water is about 2-7 mm in sand, 8-10 mm in loam, 8-12 mm in clay
- A dry surface layer forms and stage II starts: loss is limited by vapour diffusion through the dry layer and falls to a small fraction of potential
- Organic mulch or litter cover cuts soil evaporation, by about 5 percent per 10 percent of surface covered
- and 2 more in this process
- Water raises volumetric heat capacity (water 4.18, mineral about 2.0, air about 0.001 MJ per m3 per K), so wet soil warms more slowly than dry soil
- Thermal conductivity rises steeply with water: dry sand about 0.3 W/m/K versus about 2-2.5 when saturated (quartz 7.7)
- Evaporation removes 2.45 MJ per mm, so wet bare soil stays cooler than dry soil, whose surface can exceed 50 C in summer sun
- and 2 more in this process
- Compaction is greatest at an intermediate water content (Proctor optimum), where water lubricates grains but does not yet carry the load
- Saturated conductivity and air-filled porosity fall, often by one to two orders of magnitude, as continuous macropores are lost
- Roots stay shallow and take up less water and nutrients; reported yield losses range 2.5-50% across crops
- and 2 more in this process
- Active protists reach about 10^4-10^6 per gram of soil, mostly flagellates and naked amoebae, with fewer ciliates and testate amoebae
- Which protist group dominates the grazing in the pore
- Flagellates (Cercomonas, Spumella) graze suspended bacteria in water films and move through narrow pores
- and 2 more in this process
Decomposition
4 stepsSoil formation
4 stepsSoil gas exchange and redox
4 stepsSoil fauna
4 stepsNitrogen cycling
4 steps- Glass hydrolyses within centuries in humid, well-drained conditions, releasing Al3+ and Si(OH)4
- Al and Si co-precipitate as allophane spherules (about 3.5 to 5 nm) and imogolite tubes (about 2 nm outer diameter)
- Open allophane aggregates give bulk density below 0.9 g per cm3 and very high water retention
- and 1 more in this process
- Soil with 30 percent or more clay dominated by smectite holds water between the layers of expandable clay
- Drying shrinks the matrix: Vertisols have linear extensibility of 6 cm or more in the upper metre
- Cracks open to 0.5 m or more; first rain bypasses the matrix through them into the subsoil
- and 1 more in this process
Mycorrhizal fungi network
3 stepsOrganic matter decomposition
3 stepsPhosphorus cycling
3 steps- Dormant spore germinates in a wet, nutrient-rich pulse and sends out a germ tube
- Gram-positive thick walls and spores allow activity at low water potential, so actinobacteria are enriched in drying soil
- Aerial hyphae produce spore chains; geosmin released attracts springtails that eat and disperse spores
- Rain beyond infiltration capacity or on saturated soil produces runoff and subsurface drainage
- Runoff and erosion carry particles; rivers deliver about 12-13 Gt of sediment per year to the ocean
- Drainage leaches dissolved organic carbon from organic horizons; rivers carry about 0.2-0.4 Gt C per year to the ocean
- Virus-like particles number about 10^8-10^9 per gram dry soil, usually exceeding or matching bacterial counts
- Contact is limited to connected water films; clay and organic matter adsorb phage and can protect or inactivate them
- Stress (DNA damage, starvation, drying and rewetting) can induce prophage and switch cells to the lytic cycle
- Cell response to starvation or drying: sporulate, enter reversible non-spore dormancy, or die
- Rewetting of dry soil or a substrate pulse produces a CO2 flush (Birch effect) from released osmolytes and revived cells
- Reactivation proceeds in sequence: phylogenetically clustered groups resuscitate at different times over hours to days after rain
- Wheel or hoof load exceeds the soil precompression stress, and wet soil is much weaker so compacts at a lower load
- Penetration resistance climbs above 1 to 2 MPa and root elongation drops sharply
- Low air-filled porosity and conductivity slow infiltration and gas diffusion, raising runoff and anaerobic N2O production
- Nitrate is not adsorbed by net-negative soil surfaces and moves with drainage water, taking base cations with it
- Most leaching occurs in autumn and winter, when the crop is gone, mineralisation continues and drainage is highest
- Nitrate reaches drains and groundwater; the US drinking-water limit is 10 mg nitrate-N per litre
Plant-mediated water flux
3 stepsSoil sulfur cycling
2 stepsBiochar and charcoal in soil
2 stepsOften found with
Plant roots 70Soil water 67Plants 63Pore space 58Soil 55Carbon dioxide 45Rain 37Oxygen 33Heat 29Drainage water 26Nitrogen 24Nitrate 24
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