Soil compaction as a driving force for changes in soil functions

Beata HouskovaSoil & Waste Unit

Institute of Environment & Sustainability

JRC Ispra

2nd European Summer School on Soil Survey

12-16 June 2004

European Summer School on Soil Survey

Soil degradation process – deterioration of all soil properties: directly (physical properties), indirectly (chemical and biological properties)

• natural origin (typical - change in aggregates arrangement)• human origin (typical – change in particles arrangement)• the integration of natural and human origin

Definition of Soil Compaction

Common features of compacted soil

• Formation of compacted layer (plough pan);• Unfavourable water regime (stagnation of water on soil surface,

runoff, wetting, higher wilting point in comparison with notcompacted soil);

• Significant bulk density increase and total porosity decrease incomparison with natural one;

• Low aeration. generally below 10 % of volume (e.g. formicroorganisms activity 20 % is optimum);

• Compacted soils have different heat regime. Generally, wetsoils warm more slowly in comparison with dry ones;

• Nutrients are concentrated in top layer. lower parts are almostwithout nutrients available for plants;

• Yields, even soil fertility decreasing;• Acceleration of the other degradation processes mainly water

and wind erosion;• Decreasing of soil biodiversity by affecting the habitat of soil

organisms; Soil compaction affects plants roots also indirectlythrough affecting soil microorganisms habitat.

Dep

th (

cm)

025

5075

100125

025

5075

100125

compacted layer

percolation /infiltration

runoff[erosion.

seepage

to groundwater

pollution]

to surface water

buffering

Impacts of Compaction:

non-compacted soil compacted soil

filtering

Bulk density higher than 1.9 g.cm-3 stops the ability of plant roots to grow

Common causes of soil compaction

Naturally induced soil compaction• Main factors: textural category (amount of clay>35%) and soil

morphological unit (argillic horizon, illimerisation, gleying, podsolization)

Soil compaction induced by human activities• Induced by intensive or incorrect land use (agriculture. forest

management);• Low amount of deep rooting structure forming plants in crop

rotation, e. g. fodder crops;• High amount of root crops (soil properties worsen plants: root

system, agrotechnics with high amount of crossing on the field);• Low amount of organic residues.

Soil morphological units according to their susceptibility to natural compaction

highStagnosols

highAlbic Luvisols and Glossisols

highPlanosols

highPodzols

highThe other Gleysols

mediumHaplic Luvisols

mediumDystric Cambisols and Umbrisols

mediumEutric Cambisols

mediumThe other Fluvisols

mediumMollic Fluvisols and Mollic Gleysoils

lowPhaeozems

lowChernozems

lowArenosols

lowAndosols

lowother Leptosols

lowRendzic Leptosols

lowAnthrosols

lowHistosols

Susceptibility to natural compactionSoil units (WRB –1994)

Soil textural categories

Influence of compaction origin on the soil profile properties

Natural soil compaction

Bulk de ns ity (ρd g .c m-3) o f me dium he avy naturally c o mpac te d s o il

y = 0.063x + 1.395

R2 = 0.9992

1.35

1.40

1.45

1.50

1.55

1.60

1.65

1.70

1.75

1 2 3

de pth

ρg.(c

m-3

)

limit value

Influence of compaction origin on the soil profile properties

Soil compaction induced by human activities

Bulk De ns ity (ρd g .c m-3) o f s e c o ndary c o mpac te d s o il; Kľačany

y = -0.11x + 1.834

R2 = 0.9978

1.35

1.40

1.45

1.50

1.55

1.60

1.65

1.70

1.75

1 2 3

de pth

ρd (

g.c

m-3

)

limit value

Depth of compaction depending on axle load and soil moisture increases

(Soehne, 1958)

Approximate axle loads for field equipment

6.5MFWD Tractor. 150 HP. rear axle

7.54WD Tractor. 200 HP. front axle

134WD Tractor. 325 HP. front axle

17-20Grain cart. 1.200 bu.. 2 axles

35-40Grain cart. 1.200 bu.. 1 axle

24Beet cart. full

22720 bu grain cart. full. 1 axle

2412-row. full with head

1812-row combine. empty

106-row combine. empty

17-18Slurry tanker. 7.200 gal.

10-12Slurry tanker. 4.200 gal.

Axle Load(Tons/axle)

Equipment

Assessment of the soil susceptibility to compaction

Method of possible soil compaction determination

%clay)*(0.009ρPD d += [g.cm-3, kg.m-3]

Packing density categories

Class Confidence

L Low

M Medium

H High

European Soil Information

Subsoil Susceptibility to Compaction

Class SusceptibilityL LowM ModerateH High

VH Very High

Packing density g cm-3 Texture Low Medium High

Code Class < 1.40 1.40 – 1.75 > 1.75

1 Coarse VH H M1

2 Medium H M M 3 Medium fine M(H) M L3

4 Fine M2 L4 L3

5 Very fine M2 L4 L3

9 Organic VH H 1 except for naturally compacted or cemented coarse (sandy) materials that have very low (L) susceptibility. 2 these packing densities are usually found only in recent alluvial soils with bulk densities of 0.8 to 1.0 t m-3 or in topsoils with >5% organic carbon. 3 these soils are already compact. 4 Fluvisols in these categories have moderate susceptibility

Bendingearthwormchannels in theplaty structure

Soil Compaction

Indicators and methods of soil compaction assessment (The rule of textural dependence)

The limit values of soil physical properties according to textural units

SOILPROPERTY Clay Clayey Loam Sandy loam Loamy sand Sand

Bulk density

(g.cm-3)Penetrometricresistance (MPa) *according to soil moisture (% of weight)

28 - 24 24 - 20 18 - 16 15 - 13 12 10

Porosity(% of volume)**Minimal air capacity(% of volume)Maximal capillary capacity (% of volume)

>35 >35 >35 - - -

Clay content (< 0.001 mm) >30 >30 - - - -

Plasticity index >25 >25 >25 - - -

3.7 - 4.2 4.5 - 5.0

SOIL TEXTURAL CATEGORY

>1.35 >1.40 >1.45 >1.55 >1.60 >1.70

5.5 6

< 48 < 47 < 45 < 42 < 40 < 38

2.8 - 3.2 3.2 - 3.7

< 10 < 10< 10 < 10 < 10 < 10

Notes:* if the actual soil moisture content does not fit to the given moisture interval it is necessary to add 0.25 MPa to the measured resistance value (in case of higher soil moisture) or to take away 0.25 MPa (in case of lower moisture content) for every 1% (of weight) difference** 10 % of volume is the average value of air capacity. For different crops this value changes:

root-crop - limit air capacity is 12 % of volumecereal - limit air capacity is 10 %fodder - limit air capacity is 8 %.

Average annual losses of organic carbon (t/C.ha-1) from the soil according to the productivity

potential and crops

1 2 3I 2.25 2.81 3.09II 3.42 4.27 4.7III 3.67 4.59 5.05

Soil category according to productivity potential

Plant groups

Soil category: 1 – soils with high productivity potential2 – soils with medium3 – soils with low productivity potentialPlant group:

1. fodder crops; inhibitor of organic matter mineralization and soil erosion and compaction2. cereals. peas. lupin. soya. colza; neutral plants (neutral plants)3. sugar beet. mangel-wurzel. potatoes. corn. sunflower. chicory. poppy. tobacco;

increased intensity of organic matter mineralization leading to losses of organic C in soil profile, increase of soil susceptibility to erosion and compaction

(source: Jurcova. Bielek. 1997)

• Field observations;

• Field measurements (penetrometric resistance, hydraulic conductivity);

• Laboratory measurements (core samples for bulk density, porosity and capillarycapacity determinations)

Methods of soil compaction investigation

• Occurrence of areas with water stagnation on the soil surfacemainly in tracks of agricultural machinery after precipitations, irrigations or snow melting

Field observations

• Slow and irregular plants grow

Field observations

Crop height 2.3-2.7 m at maturity Crop height 1.8-2.2 m

at maturity

Crop height 1.2-1.7m at maturity

Field observations• Plants distribution

Field observations

•Yellowed leaves of vegetation

• Crust and cracks formation

Field observations

• Roots deformation

Field observations

Field measurements

• Penetrometric resistance

Field Distance of individual measurements· homogeneous 200 - 300 m; i.e. cca 5 ha· heterogeneous 100 - 300 m; cca 1 - 3 ha· hill side 20 - 50 m; cca 1 ha

The number of punctures is on the homogeneous field from 5 to 10, on the heterogeneous one it is from 10 to 15. It is necessary to execute the correction of field measurements according to actual moisture content in the profile.

Evaluation of penetrometric measurementsSoil compaction is detected on 15 to 20 % of investigated field: ameliorative measure is not necessary;· Soil compaction is detected on 20 to 40 % of the field: ameliorative measure is necessary on compacted part of field;· Soil compaction is detected on more than 40 % of field: it is necessary to execute the ameliorative measure on the whole field.

Field measurements

Penetrometric resistance (MPa) of secondary compacted soil.

y = 0,0027x2 - 0,176x + 4,8698

R2 = 0,8706

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

5,51 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61

depth (cm)

MP

a

average

STD

critical value

Poly. (average)

Field measurements

• Hydraulic conductivity determination

o Saturated hydraulic conductivity Ks [LT-1]

o Unsaturated hydraulic conductivity K(h) [LT-1]

K(h) = Ks exp (αh), α = ln [Q(h2)/Q(h1)]/h2 – h1

α − parameterQ(h1), Q(h2) - water flow at tension 1, 2

o Preferential flow, bypassing ratio (Br) [%]

BR = [Ks – K(-3 cm)] / Ks * 100 K (-3 cm)– non saturated hydraulic conductivity at tension -3 cm

Prevention and sanation

Prevention• Use of the agrotechnics with lower weight• Decreasing of the number of operations• Crop rotation• Increasing of soil structure stability (manure)

Sanation• Deep tillage/Subsoiling (+,- effects)• Reduced tillage/No till (+,- effects)

Driving Forces

Pressures

State

Impacts

ResponsesAgricultureintensification

Land use practicescontinuous cultivation

deforestation

European soil protection policy

On-site: soil degradationcompaction

loss of structure

Good agricultural practice- low ground pressures- timing of cultivations- alleviation measures- conservation tillage

On-site- reduction in water

storage capacity- increased soil

erosion

Off-site- pollution of surface waters

- effects on regional drainage- flooding

Soil Protection Strategy

Framework (DPSIR) for Soil Compaction

Sources of pictures, maps, tables and graphs

• CETS, University of Minnesota Extension Service

• Bielek, P.- Jurcova, O. SSCRI, Bratislava. Slovakia

• Houskova, B. SSCRI, Bratislava. Slovakia

• Lhotský, J. et al. 1984. Methods of compacted agricultural soils reclamation.• ÚVTIS, Praha.

• Shepherd, G. (2000): Visual Soil Assessment. ISBN 1-8772214-92-9. New Zeeland

• Soil Science and Conservation Research Institute, (SSCRI). Bratislava. Slovakia