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Resource: used or used up in processesPore space
Appears in 34 processs and 85 steps. Everything below is linked: open a process to see it in context.
Top processes
- Compaction is greatest at an intermediate water content (Proctor optimum), where water lubricates grains but does not yet carry the load
- Bulk density rises and porosity phi = 1 - rho_b/2.65 falls (1.3 to 1.6 g/cm3 takes porosity from 51% to 40%), mostly at the expense of macropores
- Penetration resistance rises; root elongation is strongly limited above about 2 MPa and a penetrometer reads 2-8 times the pressure that roots experience
- and 4 more in this process
- Wheel or hoof load exceeds the soil precompression stress, and wet soil is much weaker so compacts at a lower load
- Macropores collapse first: air-filled porosity falls and bulk density rises toward root-limiting values of roughly 1.4 to 1.8 g per cm3 depending on texture
- Penetration resistance climbs above 1 to 2 MPa and root elongation drops sharply
- and 2 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 2 more in this process
- 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
- Surface seals, compaction or water repellency throttle the top boundary, so rain exceeding the seal conductivity runs off
- and 2 more in this process
Show 28 more processes
Soil gas exchange and redox
3 steps- Millington-Quirk model Ds/D0 = e^(10/3)/phi^2: at porosity 0.5, cutting air-filled porosity from 0.30 to 0.10 reduces Ds/D0 from about 0.07 to 0.002
- Aeration is adequate above about 10% air-filled porosity, equivalent to an oxygen diffusion rate above about 0.2 microgram per cm2 per minute
- Compaction and surface seals cut air-filled porosity and connectivity, lowering Ds and raising N2O emissions and lowering methane uptake
- 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)
- First rain after drought runs down cracks as bypass flow and wets the subsoil from below before the matrix swells
- 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
- Unsaturated hydraulic conductivity falls by orders of magnitude as soil dries, so supply to roots limits uptake before the wilting point
Salinity and sodicity
1 stepOften found with
Water 58Soil pores 21Soil water 19Plant roots 15Oxygen 13Capillary forces 10Soil organic matter 9Soil aggregates 9Macropores 8Earthworms 7Clay minerals 7Clay minerals 7
Known by 719 participants and resources across the map.