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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Aggregate formation and pore structure / Soil compaction and loss of macroporosity

Soil compaction and loss of macroporosity

Wheel or hoof loads above the soil's precompression stress, worst when wet, collapse the largest pores, raise bulk density and strength, and cut air and water flow. Subsoil compaction persists for decades because biology and frost rarely reach it.

Boundary: where this process starts

Starts with: Wheel or hoof load exceeds the soil precompression stress, and wet soil is much weaker so compacts at a lower load

Boundary: where it ends

Ends after: Low air-filled porosity and conductivity slow infiltration and gas diffusion, raising runoff and anaerobic N2O production; Subsoil compaction persists for decades because few roots, worms and frost cycles reach below plough depth

PARTICIPANTSRESOURCESSoil aggregatesTractorsLivestockMacroporesPlant rootsOtherparticipantsPore spaceWaterOxygenNitrous oxideCarbonImpact -3 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.↻ reinforces · moderate · 0.35 Fewer roots aImpact -3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Wheel or hoof load exceeds the soil precompression stress, and wet soil is much weaker so compacts at a lower load: uses Pore spaceWheel or hoof load exceeds the soil precompression stress, and wet soil is much weaker so compacts at a lower load: uses WaterMacropores 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: uses up Pore spaceuses upMacropores 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: uses OxygenPenetration resistance climbs above 1 to 2 MPa and root elongation drops sharply: uses Pore spacePenetration resistance climbs above 1 to 2 MPa and root elongation drops sharply: uses WaterLow air-filled porosity and conductivity slow infiltration and gas diffusion, raising runoff and anaerobic N2O production: uses WaterLow air-filled porosity and conductivity slow infiltration and gas diffusion, raising runoff and anaerobic N2O production: uses OxygenLow air-filled porosity and conductivity slow infiltration and gas diffusion, raising runoff and anaerobic N2O production: makes Nitrous oxidemakesSubsoil compaction persists for decades because few roots, worms and frost cycles reach below plough depth: uses Pore spacePoor rooting means less root carbon and fewer biopores, leaving the soil more vulnerable to the next load: uses Pore spacePoor rooting means less root carbon and fewer biopores, leaving the soil more vulnerable to the next load: uses Carboncollapses under heavyloadPore space: collapses under heavy loadwet soil compacts atlower loadWater: wet soil compacts at lower loadmacropores collapsefirstPore space: macropores collapse firstsupply falls withair-filled porosityOxygen: supply falls with air-filled porosityresists root penetrationPore space: resists root penetrationaffects penetrationresistanceWater: affects penetration resistanceslows infiltrationWater: slows infiltrationdiffusion slowed bycompactionOxygen: diffusion slowed by compactionproduced in anaerobicconditionsNitrous oxide: produced in anaerobic conditionsstays compacted beneathploughPore space: stays compacted beneath ploughbiopores fail to formPore space: biopores fail to formroot carbon inputreducedCarbon: root carbon input reducedStart: Soil compactionand loss ofmacroporositySTARTStart: Soil compaction and loss of macroporosityEnd: Soil compactionand loss ofmacroporosityENDEnd: Soil compaction and loss of macroporosityWheel or hoof loadexceeds the soilprecompression stres…📄1Wheel or hoof load exceeds the soil precompression stress, and wet soil is much weaker so compacts at a lower loadMacropores collapsefirst: air-filledporosity falls and bu…📄1Macropores 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 texturePenetration resistanceclimbs above 1 to 2 MPaand root elongati…📄1Penetration resistance climbs above 1 to 2 MPa and root elongation drops sharplyLow air-filled porosityand conductivity slowinfiltration and g…📄1Low air-filled porosity and conductivity slow infiltration and gas diffusion, raising runoff and anaerobic N2O productionSubsoil compactionpersists for decadesbecause few root…📄1Subsoil compaction persists for decades because few roots, worms and frost cycles reach below plough depthPoor rooting means lessroot carbon and fewerbiopores, leaving t…📄1Poor rooting means less root carbon and fewer biopores, leaving the soil more vulnerable to the next load
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)
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Wheel or hoof load exceeds the soil precompression stress, and wet soil is much weaker so compacts at a lower load
TractorsLivestockSoil aggregatesWaterPore space
Evidence (1) · added by Fern
  • Hamza & Anderson (2005), Soil & Tillage Research 82:121-145: Soil water content strongly lowers soil strength, so the same axle load compacts wet soil far more. (confidence 0.8)
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
MacroporesSoil aggregatesPore spaceOxygen
Evidence (1) · added by Fern
  • Daddow & Warrington (1983), Growth-limiting soil bulk densities as influenced by soil texture, USDA Forest Service WSDG-TN-00005: Root-limiting bulk density ranges from about 1.4 g per cm3 in clays to about 1.8 g per cm3 in sands. (confidence 0.7)
Penetration resistance climbs above 1 to 2 MPa and root elongation drops sharply
Plant rootsCompacted soilPore spaceWater
Evidence (1) · added by Fern
  • Bengough, McKenzie, Hallett & Valentine (2011), Root elongation, water stress, and mechanical impedance, Journal of Experimental Botany 62:59-68: Root elongation rate falls as penetrometer resistance rises through about 1 to 2 MPa. (confidence 0.8)
Low air-filled porosity and conductivity slow infiltration and gas diffusion, raising runoff and anaerobic N2O production
Soil poresDenitrifying bacteriaOxygenNitrous oxideWater
Evidence (1) · added by Fern
  • Hansen, Maehlum & Bakken (1993), N2O and CH4 fluxes in soil influenced by fertilization and tractor traffic, Soil Biology and Biochemistry 25:621-630: Compaction by tractor traffic increased N2O emissions through reduced aeration. (confidence 0.75)
Subsoil compaction persists for decades because few roots, worms and frost cycles reach below plough depth
Compacted soilEarthwormsFrostPore space
Evidence (1) · added by Fern
  • Hakansson & Reeder (1994), Subsoil compaction by vehicles with high axle load: extent, persistence and crop response, Soil & Tillage Research 29:277-304: Compaction of the subsoil from heavy axle loads was found to persist for more than ten years. (confidence 0.8)
Poor rooting means less root carbon and fewer biopores, leaving the soil more vulnerable to the next load
Plant rootsSoil organic matterCarbonPore space
Evidence (1) · added by Fern
  • Hamza & Anderson (2005), Soil & Tillage Research 82:121-145: Reduced root growth and organic matter in compacted soil lowers structural resilience; gain is an estimate. (confidence 0.5)