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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