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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Aggregate formation and pore structure / Soil compaction: stress, density, root limitation and recovery

Soil compaction: stress, density, root limitation and recovery

Wheel and hoof loads press soil into a denser state, closing macropores, raising strength and cutting infiltration and aeration, with effects that persist for years in the subsoil and are only slowly reversed by freeze-thaw, roots and fauna.

Boundary: where this process starts

Starts with: Axle and tyre loads or hooves apply stress; contact stress near the surface is about the tyre inflation pressure (roughly 50-250 kPa) and heavy axles above about 6 Mg compact subsoil below 0.4 m

Boundary: where it ends

Ends after: Controlled traffic farming confines wheels to permanent lanes covering roughly 15-20% of the field instead of most of it; Natural recovery by freeze-thaw, wet-dry cycles, deep perennial roots and earthworm burrowing slowly rebuilds pores

PARTICIPANTSRESOURCESMachineryPlant rootsLivestockSoil aggregatesSoil waterOtherparticipantsPore spaceWaterSoilOxygenSoil aggregatesImpact +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.Impact +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 -4 of 5. Click for details and evidence.Impact +3 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 -2 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact -2 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 · 0.25 Shallow rootsImpact -2 of 5. Click for details and evidence.↻ balances · weak · 0.15 Recovery agents looAxle and tyre loads or hooves apply stress; contact stress near the surface is about the tyre inflation pressure (roughly 50-250 kPa) and heavy axles above about 6 Mg compact subsoil below 0.4 m: uses SoilCompaction is greatest at an intermediate water content (Proctor optimum), where water lubricates grains but does not yet carry the load: uses Pore spaceCompaction is greatest at an intermediate water content (Proctor optimum), where water lubricates grains but does not yet carry the load: uses WaterBulk 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: uses up Pore spaceuses upBulk 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: uses Soil aggregatesPenetration resistance rises; root elongation is strongly limited above about 2 MPa and a penetrometer reads 2-8 times the pressure that roots experience: uses Pore spaceSaturated conductivity and air-filled porosity fall, often by one to two orders of magnitude, as continuous macropores are lost: uses up Pore spaceuses upSaturated conductivity and air-filled porosity fall, often by one to two orders of magnitude, as continuous macropores are lost: uses WaterSaturated conductivity and air-filled porosity fall, often by one to two orders of magnitude, as continuous macropores are lost: uses OxygenRoots stay shallow and take up less water and nutrients; reported yield losses range 2.5-50% across crops: uses up Wateruses upWet compacted soil turns anaerobic and emits more N2O by denitrification: uses up Oxygenuses upReduced infiltration raises runoff, ponding and erosion: uses WaterReduced infiltration raises runoff, ponding and erosion: uses up Soiluses upSubsoil compaction below the tilled layer persists for more than a decade because it escapes tillage and has little frost or biological action: uses Pore spaceNatural recovery by freeze-thaw, wet-dry cycles, deep perennial roots and earthworm burrowing slowly rebuilds pores: makes Pore spacemakesNatural recovery by freeze-thaw, wet-dry cycles, deep perennial roots and earthworm burrowing slowly rebuilds pores: uses WaterControlled traffic farming confines wheels to permanent lanes covering roughly 15-20% of the field instead of most of it: uses Pore spacecompressed by axle andhoof stressSoil: compressed by axle and hoof stresscollapses under loadPore space: collapses under loadlubricates grains atoptimumWater: lubricates grains at optimummacropores lost asdensity risesPore space: macropores lost as density risespacked into denserfabricSoil aggregates: packed into denser fabriccompacted, resistingroot penetrationPore space: compacted, resisting root penetrationcontinuous macroporesdisappearPore space: continuous macropores disappeardrains more slowlythrough soilWater: drains more slowly through soillimited by fewer airporesOxygen: limited by fewer air poresless taken up from depthWater: less taken up from depthdepleted in waterloggedsoilOxygen: depleted in waterlogged soilfails to infiltrate andruns offWater: fails to infiltrate and runs offeroded by runoffSoil: eroded by runoffpersists beneath thetilled layerPore space: persists beneath the tilled layerrebuilt by freeze-thawand rootsPore space: rebuilt by freeze-thaw and rootsdrives freeze-thaw andwet-dry cyclesWater: drives freeze-thaw and wet-dry cycleskept intact outsidepermanent lanesPore space: kept intact outside permanent lanesStart: Soil compaction:stress, density, rootlimitation and recoverySTARTStart: Soil compaction: stress, density, root limitation and recoveryEnd: Soil compaction:stress, density, rootlimitation and recoveryENDEnd: Soil compaction: stress, density, root limitation and recoveryAxle and tyre loads orhooves apply stress;contact stress near t…📄1Axle and tyre loads or hooves apply stress; contact stress near the surface is about the tyre inflation pressure (roughly 50-250 kPa) and heavy axles above about 6 Mg compact subsoil below 0.4 mCompaction is greatestat an intermediatewater content (Proct…📄1Compaction is greatest at an intermediate water content (Proctor optimum), where water lubricates grains but does not yet carry the loadBulk density rises andporosity phi = 1 -rho_b/2.65 falls (1…👍1📄1Bulk 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 macroporesPenetration resistancerises; root elongationis strongly limit…👍1📄1Penetration resistance rises; root elongation is strongly limited above about 2 MPa and a penetrometer reads 2-8 times the pressure that roots experienceSaturated conductivityand air-filled porosityfall, often by one …📄1Saturated conductivity and air-filled porosity fall, often by one to two orders of magnitude, as continuous macropores are lostRoots stay shallow andtake up less water andnutrients; report…📄1Roots stay shallow and take up less water and nutrients; reported yield losses range 2.5-50% across cropsWet compacted soilturns anaerobic andemits more N2O …📄1Wet compacted soil turns anaerobic and emits more N2O by denitrificationReduced infiltrationraises runoff, pondingand erosion📄1Reduced infiltration raises runoff, ponding and erosionSubsoil compactionbelow the tilled layerpersists for more th…📄1Subsoil compaction below the tilled layer persists for more than a decade because it escapes tillage and has little frost or biological actionNatural recovery byfreeze-thaw, wet-drycycles, deep perenni…📄1Natural recovery by freeze-thaw, wet-dry cycles, deep perennial roots and earthworm burrowing slowly rebuilds poresControlled trafficfarming confines wheelsto permanent lan…📄1Controlled traffic farming confines wheels to permanent lanes covering roughly 15-20% of the field instead of most of it
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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Axle and tyre loads or hooves apply stress; contact stress near the surface is about the tyre inflation pressure (roughly 50-250 kPa) and heavy axles above about 6 Mg compact subsoil below 0.4 m
MachineryLivestockSoil
Evidence (1) · added by Fern-C
  • Soane & van Ouwerkerk 1994, Soil Compaction in Crop Production, Elsevier; Hakansson & Reeder 1994, Soil & Tillage Research 29:277-304: Surface stress approximates tyre inflation pressure; stress penetrates deeper with axle load, so high axle loads compact the subsoil. (confidence 0.55)
Compaction is greatest at an intermediate water content (Proctor optimum), where water lubricates grains but does not yet carry the load
Soil waterMachineryWaterPore space
Evidence (1) · added by Fern-C
  • Proctor 1933, Engineering News-Record 111:245-248; Soane et al. 1981, Soil & Tillage Research 1:207-237: Dry density after a given compactive effort peaks at the optimum water content and declines on either side. (confidence 0.75)
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
Soil aggregatesMacroporesPore spaceSoil aggregates
Evidence (1) · added by Fern-C
  • Brady & Weil, The Nature and Properties of Soils, 15th ed., ch. 4; Alaoui, Lipiec & Gerke 2011, Soil & Tillage Research 115-116:1-15: Porosity follows from bulk density and a particle density of 2.65 g/cm3; compaction collapses the largest pores first. (confidence 0.8)
Penetration resistance rises; root elongation is strongly limited above about 2 MPa and a penetrometer reads 2-8 times the pressure that roots experience
Plant rootsPore space
Evidence (1) · added by Fern-C
  • Bengough & Mullins 1990, Journal of Soil Science 41:341-358: Penetrometer resistance exceeds root growth pressure by a factor of 2-8; 2 MPa commonly marks severe restriction. (confidence 0.7)
Saturated conductivity and air-filled porosity fall, often by one to two orders of magnitude, as continuous macropores are lost
MacroporesSoil waterWaterPore spaceOxygen
Evidence (1) · added by Fern-C
  • Alaoui, Lipiec & Gerke 2011, Soil & Tillage Research 115-116:1-15: Compaction reduces macroporosity, pore continuity and saturated hydraulic conductivity, sometimes by orders of magnitude. (confidence 0.65)
Roots stay shallow and take up less water and nutrients; reported yield losses range 2.5-50% across crops
Plant rootsCropsWaterNitrogen
Evidence (1) · added by Fern-C
  • Hamza & Anderson 2005, Soil & Tillage Research 82:121-145: Review of compaction effects on crop growth reports yield reductions between about 2.5% and 50%. (confidence 0.6)
Wet compacted soil turns anaerobic and emits more N2O by denitrification
Denitrifying bacteriaNitrateNitrous oxideOxygen
Evidence (1) · added by Fern-C
  • Ball, Scott & Parker 1999, Soil & Tillage Research 53:29-39: Field N2O fluxes were higher in compacted soil because of reduced aeration. (confidence 0.65)
Reduced infiltration raises runoff, ponding and erosion
Overland flowSoil surfaceWaterSoil
Evidence (1) · added by Fern-C
  • Batey 2009, Soil Use and Management 25:335-345: Compaction lowers infiltration and increases surface runoff and erosion risk. (confidence 0.7)
Subsoil compaction below the tilled layer persists for more than a decade because it escapes tillage and has little frost or biological action
SubsoilPore space
Evidence (1) · added by Fern-C
  • Hakansson & Reeder 1994, Soil & Tillage Research 29:277-304: Effects of heavy-axle compaction below the plough layer remained after many years. (confidence 0.6)
Natural recovery by freeze-thaw, wet-dry cycles, deep perennial roots and earthworm burrowing slowly rebuilds pores
Plant rootsEarthwormsFrostPore spaceWater
Evidence (1) · added by Fern-C
  • Dexter 1991, Soil & Tillage Research 20:87-100, Amelioration of soil by natural processes: Wetting-drying, freezing-thawing and biological activity are the natural agents loosening compacted soil. (confidence 0.65)
Controlled traffic farming confines wheels to permanent lanes covering roughly 15-20% of the field instead of most of it
MachineryFarmersPore space
Evidence (1) · added by Fern-C
  • Tullberg, Yule & McGarry 2007, Soil & Tillage Research 97:272-281: Controlled traffic confines wheel compaction to permanent lanes and reduces trafficked area to a small fraction of the field. (confidence 0.5)