evaluation of soil compaction effects on soil biota and soil biological processes in soils

11
Evaluation of soil compaction effects on soil biota and soil biological processes in soils Anneke Beylich a , Hans-Rudolf Oberholzer b , Stefan Schrader c , Heinrich Ho ¨ per d , Berndt-Michael Wilke e, * a IFAB Institut fu ¨r Angewandte Bodenbiologie GmbH, Sodenkamp 59 D-22337 Hamburg, Germany b Reckenholz-Ta ¨nikon ART Research Station, Reckenholzstrasse 191, CH-8046 Zu ¨rich, Switzerland c Johann Heinrich von Thu ¨nen Institut, Bundesforschungsinstitut fu ¨r La ¨ndliche Ra ¨ume, Wald und Fischerei, Institut fu ¨r Biodiversita ¨t, Bundesallee 50, D-38116 Braunschweig, Germany d Landesamt fu ¨r Bergbau, Energie und Geologie, Geozentrum Hannover, Stilleweg 2, D-30655 Hannover, Germany e Berlin University of Technology, Institute of Ecology, Franklinstr. 29, D-10587 Berlin, Germany 1. Introduction Soil compaction is a worldwide environmental problem of increasing importance occurring in arable and grassland as well as in forest soils. It is caused by the use of heavy machinery (Soane and van Ouwerkerk, 1994; Horn et al., 2000), but also by livestock trampling (Murphy et al., 1995; Chan and Barchia, 2007) and human leisure activities (Piz ˇl and Schlaghamersky ´ , 2007; Kissling et al., 2009). Soil compaction mostly means modification of soil structure and soil pore system geometry on the bulk soil and profile scale (Wiermann et al., 1999; Werner and Werner, 2001), as well as on the soil aggregate scale (Larink et al., 2001). Generally, soil compaction affects soil physical properties by increasing soil bulk density and by changing the size distribution as well as the tortuosity and connectivity of soil pores (Richard et al., 2001; Pagliai et al., 2003, 2004; Scha ¨ ffer et al., 2008a,b). As a result macropore functions like water infiltration, hydraulic conductivity, air permeability (Horn et al., 1995; Richard et al., 2001) and aeration (Czyz et al., 2001; Czyz, 2004) are especially decreased, leading to an increased potential for surface water runoff, soil erosion and unfavourable effects on plant growth (Soane and van Ouwerkerk, 1994; Horn et al., 2000). Up to now investigations have mainly focused on effects of soil compaction on soil physical parameters and on plant growth. Nevertheless, a substantial number of papers deal with effects of soil compaction on soil organisms (soil fauna, soil microorganisms) Soil & Tillage Research 109 (2010) 133–143 ARTICLE INFO Article history: Received 27 October 2009 Received in revised form 4 May 2010 Accepted 24 May 2010 Keywords: Bulk density Soil porosity Soil structure deterioration Soil organisms Soil biodiversity Threshold values ABSTRACT Investigations on soil compaction focused mainly on effects on soil physical parameters and on plant growth. Nevertheless, a substantial number of papers deal with effects of soil compaction on soil organisms (soil fauna, soil microorganisms) and biologically driven processes in soils (e.g., macropore formation, respiration rates, N-mineralisation). In view of soil and soil functions protection, there is an essential need to identify soil compaction threshold values with respect to soil biota and soil biological processes. No such values are currently available. Thus the aim of our study was to evaluate literature on the effects of soil compaction mainly in agricultural soils on soil organisms and soil biological processes (e.g., respiration, nitrification); to identify relevant parameters which are helpful for assessing soil compaction from the soil biological point of view; and to find out whether threshold values of soil structure parameters proposed by soil physicists correspond to harmful impacts on soil organisms and biological processes in soils. Our literature review showed that due to the high variability of experimental situations and conditions in the evaluated papers, especially in papers describing field investigations, no general effect of soil compaction was found. Negative and positive effects occurred with slight compaction as well as with strong compaction. A verification of the thresholds published to date for soil compaction was not possible based on the data evaluated. However, the fact that above an effective bulk density of 1.7 g cm 3 , only negative effects on microbial biomass and C-mineralisation were found confirms this value, proposed by soil physicists, also from the soil biological point of view. In order to provide a scientifically meaningful data base for the assessment of soil compaction, effects on soil biodiversity, related functions and processes, we recommend considering the following site and soil properties as essentials: land use, climate, soil type, texture, bulk density; soil organic matter content; pH value; soil moisture (water content/water tension); pore volume; macroporosity and air and/or water conductivity. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +49 30 314 736 85; fax: +49 30 314 736 90. E-mail address: [email protected] (B.-M. Wilke). Contents lists available at ScienceDirect Soil & Tillage Research journal homepage: www.elsevier.com/locate/still 0167-1987/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2010.05.010

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Soil & Tillage Research 109 (2010) 133–143

Evaluation of soil compaction effects on soil biota and soil biological processesin soils

Anneke Beylich a, Hans-Rudolf Oberholzer b, Stefan Schrader c, Heinrich Hoper d, Berndt-Michael Wilke e,*a IFAB Institut fur Angewandte Bodenbiologie GmbH, Sodenkamp 59 D-22337 Hamburg, Germanyb Reckenholz-Tanikon ART Research Station, Reckenholzstrasse 191, CH-8046 Zurich, Switzerlandc Johann Heinrich von Thunen Institut, Bundesforschungsinstitut fur Landliche Raume, Wald und Fischerei, Institut fur Biodiversitat, Bundesallee 50, D-38116 Braunschweig, Germanyd Landesamt fur Bergbau, Energie und Geologie, Geozentrum Hannover, Stilleweg 2, D-30655 Hannover, Germanye Berlin University of Technology, Institute of Ecology, Franklinstr. 29, D-10587 Berlin, Germany

A R T I C L E I N F O

Article history:

Received 27 October 2009

Received in revised form 4 May 2010

Accepted 24 May 2010

Keywords:

Bulk density

Soil porosity

Soil structure deterioration

Soil organisms

Soil biodiversity

Threshold values

A B S T R A C T

Investigations on soil compaction focused mainly on effects on soil physical parameters and on plant

growth. Nevertheless, a substantial number of papers deal with effects of soil compaction on soil

organisms (soil fauna, soil microorganisms) and biologically driven processes in soils (e.g., macropore

formation, respiration rates, N-mineralisation). In view of soil and soil functions protection, there is an

essential need to identify soil compaction threshold values with respect to soil biota and soil biological

processes. No such values are currently available. Thus the aim of our study was to evaluate literature on

the effects of soil compaction mainly in agricultural soils on soil organisms and soil biological processes

(e.g., respiration, nitrification); to identify relevant parameters which are helpful for assessing soil

compaction from the soil biological point of view; and to find out whether threshold values of soil

structure parameters proposed by soil physicists correspond to harmful impacts on soil organisms and

biological processes in soils. Our literature review showed that due to the high variability of

experimental situations and conditions in the evaluated papers, especially in papers describing field

investigations, no general effect of soil compaction was found. Negative and positive effects occurred

with slight compaction as well as with strong compaction. A verification of the thresholds published to

date for soil compaction was not possible based on the data evaluated. However, the fact that above an

effective bulk density of 1.7 g cm�3, only negative effects on microbial biomass and C-mineralisation

were found confirms this value, proposed by soil physicists, also from the soil biological point of view. In

order to provide a scientifically meaningful data base for the assessment of soil compaction, effects on

soil biodiversity, related functions and processes, we recommend considering the following site and soil

properties as essentials: land use, climate, soil type, texture, bulk density; soil organic matter content;

pH value; soil moisture (water content/water tension); pore volume; macroporosity and air and/or

water conductivity.

� 2010 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Soil & Tillage Research

journal homepage: www.elsev ier .com/ locate /s t i l l

1. Introduction

Soil compaction is a worldwide environmental problem ofincreasing importance occurring in arable and grassland as well asin forest soils. It is caused by the use of heavy machinery (Soaneand van Ouwerkerk, 1994; Horn et al., 2000), but also by livestocktrampling (Murphy et al., 1995; Chan and Barchia, 2007) andhuman leisure activities (Pizl and Schlaghamersky, 2007; Kisslinget al., 2009). Soil compaction mostly means modification of soilstructure and soil pore system geometry on the bulk soil andprofile scale (Wiermann et al., 1999; Werner and Werner, 2001), as

* Corresponding author. Tel.: +49 30 314 736 85; fax: +49 30 314 736 90.

E-mail address: [email protected] (B.-M. Wilke).

0167-1987/$ – see front matter � 2010 Elsevier B.V. All rights reserved.

doi:10.1016/j.still.2010.05.010

well as on the soil aggregate scale (Larink et al., 2001). Generally,soil compaction affects soil physical properties by increasing soilbulk density and by changing the size distribution as well as thetortuosity and connectivity of soil pores (Richard et al., 2001;Pagliai et al., 2003, 2004; Schaffer et al., 2008a,b). As a resultmacropore functions like water infiltration, hydraulic conductivity,air permeability (Horn et al., 1995; Richard et al., 2001) andaeration (Czyz et al., 2001; Czyz, 2004) are especially decreased,leading to an increased potential for surface water runoff, soilerosion and unfavourable effects on plant growth (Soane and vanOuwerkerk, 1994; Horn et al., 2000).

Up to now investigations have mainly focused on effects of soilcompaction on soil physical parameters and on plant growth.Nevertheless, a substantial number of papers deal with effects ofsoil compaction on soil organisms (soil fauna, soil microorganisms)

A. Beylich et al. / Soil & Tillage Research 109 (2010) 133–143134

and biologically driven processes in soils (e.g., macroporeformation, respiration rates, N-mineralisation). In this regard,positive as well as negative effects have been reported (Brussaardand van Faassen, 1994; Whalley et al., 1995).

Soil is essentially a non-renewable resource hosting the soilbiodiversity pool and delivering goods and services vital to humanwell-being and to the survival of ecosystems (Oberholzer andHoper, 2006; European Soil Framework Directive, 2006). In view ofsoil protection and the protection of soil functions, there is anessential need for the identification of soil compaction thresholdvalues with respect to soil biota and soil biological processes.Several concepts for ecological classification and assessment of soilquality that are mainly based on soil biodiversity have beendeveloped during the last two decades (Breure et al., 2005). Theywould also provide tools for the assessment of compaction inducedeffects on soil biodiversity and thus for a validation of a soilcompaction threshold value relevant for soil organisms.

Threshold values for soil physical properties have beenproposed by soil physicists in order to identify deleterious effectsof soil compaction on plant growth, crop yield as well as on the airand water regime of soils. Relevant criteria (see Table 1) werecompiled by Lebert et al. (2006). According to this paper, soilstructure is severely compacted, potentially affecting soil func-tions, when the volume of macropores (the ‘‘air capacity’’) is below5 vol.% (see also Blume, 1968; Fluhler, 1973; Dumbeck, 1986;Werner and Paul, 1999), the saturated water permeability is lessthan 10 cm d�1 (Zakosek, 1960; Blume, 1968; ATV-DVWK, 1999;Werner and Paul, 1999) or the effective bulk density BDeff (bulkdensity BD (g cm�3) + 0.009% clay) exceeds the value of 1.8–2.0 g cm�3 (corresponding to LD 4; German Guideline for SoilMapping, Ad-hoc-AG Boden, 2005). Similar values, assigned asaction values, were also identified in Switzerland: Buchter et al.(2004) proposed an effective bulk density of 1.85 g cm�3 (foragricultural soils) and 1.65 g cm�3 (upper horizon of forest soils),and air capacities of 5 vol.% (agricultural soils) and 7 vol.% (in upperlayers of forest soils). Moreover, penetration resistance greaterthan 3.5 MPa (in agricultural soils) and 3.0 MPa (in forest soils)indicate severe structural damage.

More recently, Horn and Fleige (2009) proposed test and actionvalues to assess harmful subsoil compaction. Test values are usedwhen there is concern about the development of ‘‘harmful soilchanges’’, action values indicate that ‘‘harmful changes of a soil’’ doexist and measures are required in order to avert danger or toinitiate restoration.

So far, no threshold values were identified with respect toadverse affects of soil compaction on soil organisms and on soilbiological processes. A general demand on threshold values forconservation purposes was identified by Sutherland et al. (2009) to

Table 1Critical values to evaluate soil physical parameters with respect to potential damage b

Parameter Dimension Threshold value

Macropore volume Vol.% 5

5

72

Saturated hydraulic conductivity cm d�1 10

Air conductivity �10�4 cm s�1

Infiltration rate mm d�1

Effective bulk density (BDeff) g cm�3 >2.0

>2.0

Penetration resistance MPa �3.5

3.01

1 Test and action values according to Horn and Fleige (2009).2 Forest soils.3 Hydromorphic soils.

guide policy makers in decision-making. Threshold values arevaluable tools for farmers, management consultants and policymakers to identify detrimental impacts and to take appropriatemeasures for at least mitigation or, better, avoidance of detrimen-tal impacts. Soil biodiversity as well as soil faunal and soilmicrobial processes may respond more sensitively to soilcompaction than plant growth and crop yield. According to thedraft European Soil Framework Directive (2006) soil compactionand loss of soil biodiversity are among the main threats of soildegradation. They are interdependent as soil compaction affectssoil biodiversity while simultaneously soil organisms can coun-teract compaction. Also from this point of view threshold valuesestablished with respect to soil compaction should also account foreffects on the soil biocoenosis to sustain the soils ability forregeneration.

The present study is mainly focused on data from agriculturalsoils. Our objectives were (1) to evaluate literature on effects of soilcompaction on soil organisms and soil biological processes (e.g.,respiration, nitrification); (2) to identify relevant parameterswhich are helpful for assessing soil compaction from the soilbiological point of view; and (3) to find out whether thresholdvalues of soil structure parameters proposed by soil physicistscorrespond to harmful impacts on soil organisms and biologicalprocesses in soils.

2. Effects of soil compaction on soil organisms

In most cases, soil compaction decreases the macropore volumeand, thus, affects the relative proportions of the water and airvolumes in soil (Ruser et al., 2006). This strongly determines theliving conditions for soil organisms, especially the oxygen andcarbon dioxide concentrations in soil air and the redox potential.Nevertheless, the effects of soil compaction on soil organisms arestrongly influenced not only by the structural soil properties butalso by the site-specific hydrological and climatic conditions(Brussaard and van Faassen, 1994). Basic results on this topic showthat limitations of aeration may occur at different degrees of watersaturation, depending on soil properties (Doran et al., 1988).

2.1. Soil fauna

Negative effects of soil compaction on various soil faunal groupsare reported from compaction studies in the field as well as fromlaboratory experiments. In compacted treatments often the biomassor the population density (abundance) of soil animals wasconsiderably reduced (Schrader and Lingnau, 1997; Rohrig et al.,1998; Langmaack, 1999). Further, a decrease in species number wasshown in field experiments (Heisler, 1993). Mesofaunal organisms

y soil compaction.

Test value1 Action value1 Source

Lebert et al. (2006)

Buchter et al. (2004)

<8 <5 Horn and Fleige (2009)

<123 <83

Lebert et al. (2006)

<20 <10 Horn and Fleige (2009)

<12 <5.5 Horn and Fleige (2009)

<5 <3 Horn and Fleige (2009)

Lebert et al. (2006)

>1.7 Not suitable Horn and Fleige (2009)

Buchter et al. (2004)

>2 Not suitable Horn and Fleige (2009)

A. Beylich et al. / Soil & Tillage Research 109 (2010) 133–143 135

with a body diameter of about 0.1–2.0 mm (e.g., Collembola(springtails), Acari (mites), Enchytraeidae (potworms)) inhabitmainly macropores and often show no or a restricted ability toburrow through the mineral soil by themselves also underuncompacted conditions. A decrease of the macropore class, whichcorresponds to their body diameter, thus reduces their habitablespace. Effects are partly species specific and can result in furtherindirect effects, e.g., changed competition relationships caused byspecies loss. For burrowing species like earthworms, belongingmainly to the macrofauna, burrowing is impeded by soil compaction(Kretzschmar, 1991). Thus, even if the abundance remainsunchanged, activity can be restricted. Burrow volume and totalburrow length, for instance, can be drastically reduced as a result ofheavy mechanical loads (Langmaack et al., 1999). A decline inabundance and/or activity of key species, like deep burrowingearthworms, which remarkably contribute to habitat formation insoil, may result in detrimental soil functional changes (Brussaardand van Faassen, 1994). An indirect effect of soil compaction issometimes the occurrence of waterlogging due to reduced hydraulicconductivity. The decrease of O2-levels in the soil to the point ofanaerobic conditions also affects soil fauna activity (Whalley et al.,1995).

Nonetheless, ecosystem engineers like earthworms are able topartly counteract detrimental effects caused by soil compactionwith time. Along with recovering of their population densities,earthworms force the regeneration processes of the soil structure byincreasing burrowing activity, which leads to newly formed soilmacropore systems and soil aggregates (Larink and Schrader, 2000).Just recently, Capowiez et al. (2009) found evidence from fieldexperiments conducted directly on wheel tracks and plough pansthat earthworms can contribute significantly to the regeneration ofthose compacted zones. Moreover, Barre et al. (2009) reported fromcast analyses that earthworms may maintain mechanical soilproperties at an intermediate state by compacting loose soil andloosening compacted soil. They concluded that earthworms mayprovide an efficient mechanical resilience to soils.

2.2. Soil microorganisms and microbial processes in soils

Effects of soil compaction on soil microorganisms and microbialprocesses in soils are complex and depend on many factors. Typicalfor the complexity of these relationships are the investigations ofJensen et al. (1996a): identical wheeling intensity results in soilcompaction at a pasture site with an original bulk density of1.0 g cm�3, but not at an arable site (corn production) with anoriginal bulk density of 1.3 g cm�3. Nevertheless, on both sites adecrease of CO2-efflux in the field and a decrease of net N-mineralisation in soil cores in a laboratory experiment weremeasured. However, soil microbial biomass did not changesignificantly and showed increasing or decreasing effects depend-ing on the method of determination. In a laboratory experimentwith soil material from three sites, different crops, threecompaction levels and three levels of soil moisture (waterpotential), Jensen et al. (1996b) found a correlation between C-mineralisation and soil water content. Yet, N-mineralisationshowed similar correlations only in slightly compacted soils,whereas in heavily compacted soils potential effects on N-mineralisation were nullified by the occurrence of soil denitrifica-tion. In this experiment, soil microbial biomass measured by thefumigation extraction method decreased with increasing soilmoisture, whereas soil microbial biomass measured by thesubstrate induced respiration method did not change. In alaboratory experiment with soil cores, Ruser et al. (2006) foundincreasing denitrification in samples of increasingly compactedplots in a potato field at more than 70% water-filled pore space,whereas CO2-production was only reduced at 98% water-filled

pore space in the most compacted treatment. As more fundamen-tal research about the factors causing these effects, Czyz (2004)measured redox potential and oxygen diffusion rate (ODR) assensitive indicators for soil aeration status in a field experiment. Asconsequences of soil compaction, Nevens and Reheul (2003)observed a delayed maturation and a reduced yield as well as alesser nitrogen uptake by plants caused by a reduced nitrogenmineralisation (compared to a normal plough treatment).

3. Basis and procedure of data assessment for derivingthreshold values

In order to get evidence on threshold values we screened in total240 peer-reviewed papers in relevant scientific journals publishedin the years 1963–2007 for data on effects of soil compaction on soilorganisms and soil biological processes. The results presented inthese papers were compiled in a data base. In total, 640 data recordson microorganisms and microbial activity and 332 data records onsoil fauna were evaluated. The number of datasets does notcorrespond to the number of papers evaluated, because one papermay comprise the data of one or more compaction treatments on oneor more parameters, species or functional group of organisms,respectively. Table 2 gives an overview of all information collected.Missing physical data were calculated from other physical soilproperties determined in the respective study.

The effective bulk density (BDeff) is originally a field parameterassessed during soil mapping. It integrates classified informationon macro- and micropore structure, degree of settlement, andshape and size of aggregates. If not assessed in the field, it iscalculated from the bulk density (BD) and the clay content (clay)using the following formula (Ad-hoc-AG Boden, 2005):

BDeff ¼ BDðg cm�3Þ þ 0:009 clay ð%Þ

Total porosity (TP) is calculated from the bulk density of the soil(BD) and the density of soil solid matter (DS) as following:

TP ¼ 1� BD

DS

� �� �� 100

The density of soil solid matter is calculated from the organicmatter content (OM, organic carbon content � 1.724), assuming amean density of organic matter of 1.4 g cm�3 and a density ofmineral substances of 2.65 g cm�3

DS ¼ 100

ðð100� OMÞ=2:65þ OM=1:4Þ

The air capacity, which is the air filled porosity in the soil at avolumetric water content corresponding to field capacity (waterpotential �63 hPa), is derived from the bulk density, the soilorganic matter content and the standard texture class followingthe German Guidelines for Soil Mapping (Ad-hoc-AG Boden, 2005).

In order to identify relationships between changes in physicaland biological soil parameters and to derive threshold values, thewhole data base was evaluated by regression analysis.

Out of the overall 240 papers, however, only 54 were suitablefor our purposes. The main criteria for the selection of data were:

� Data on the relevant physical soil parameters, especially(effective) bulk density and macropore volume, are presentedor can be derived,� Uncompacted control treatments are included� Original and raw data are given,� Effects of compaction can be distinguished from other effects

(e.g., effects of different tillage systems).

Thus only 22 papers dealing with effects of soil compaction onsoil fauna and 32 papers reporting effects on soil microorganisms

Table 2Structure of database.

Parameters

Reference Author, journal

Geographical background Location, mean precipitation and temperature, climate zone

Organisms Species or higher taxon, functional group

Soil data Soil type, clay silt sand content, SOM, pH value

Compaction treatment Treatment type, treatment name, crops, impact type, matric (water) potential, duration of impact

Physical soil data (only measured data) Sampling depth, bulk density, total porosity, field capacity, air capacity (macropores), air filled pores, air permeability,

water permeability

Physical soil data (calculated data) Air capacity, total porosity, effective bulk density

Biological endpoints Parameter, sampling-method, data type, replicates, result control, result compacted treatment, unit, change in % of

control, significance, remark on results

A. Beylich et al. / Soil & Tillage Research 109 (2010) 133–143136

and microbiologically driven processes were included in theevaluation. Most of the soil faunal studies were conducted in thefield addressing effects on earthworms (eight studies), enchy-traeids (four studies), collembolans (six studies), mites (three

Table 3Number of papers on soil zoological parameters used for compilation of datasets.

Parameter Field Laboratory Sum of papers

Abundance 16 1 17

Dominance 1 – 1

Species number 3 – 3

Biomass 7 – 7

Cast production – 2 2

Number of burrows – 2 2

Burrow length/volume – 2 2

Other 2 1 3

Table 4Number of papers on soil microbial parameters used for compilation of datasets.

Parameter Field Laboratory

Microbial biomass 13 8

C-mineralisation 6 9

N-mineralisation 4 8

Denitrification 3 1

qCO2 3 0

Total 29 26

Table 5Range and median of bulk density data in control and compacted treatments as w

microbiological and soil zoological studies.

Microbiology: bulk density [g cm�3]

Control Compact Change in % of cont

Median 1.20 1.42 21.5

Maximum 1.47 1.80 51.2

Minimum 0.75 0.92 0.01

n2 270 370 370

1 In some cases, compaction treatment did not cause a change in bulk density, so the v

the study was included in our analysis even if the effect on the soil physical paramete2 Number of data records.

Table 6Range and median of macropore volume data in control and compacted treatments as

microbiological and soil zoological studies.

Microbiology: macropore volume [%]

Control Compact Change in % of cont

Median 15.0 11.0 �30.4

Maximum 42.0 28.0 01

Minimum 2.5 0.8 �94.4

n2 243 343 343

1 In some cases, compaction treatment did not cause a change in macropore volum

parameters, the study was included in our analysis even if the effect on the soil physi2 Number of data records.

studies), microarthropods in general (one study) and nematodes(one study). Under controlled laboratory conditions only one andfive studies on collembolans and earthworms, respectively, metour criteria for data selection. The most commonly measuredbiological parameter was abundance (Table 3). Microbial inves-tigations mainly focussed on microbial biomass, followed by C-mineralisation (Table 4).

The bulk densities of control soils ranged from 0.75 to1.47 g cm�3 for microbial investigations and from 0.99 to1.66 g cm�3 for soil fauna experiments (Table 5). Compactedtreatments had bulk density values from 0.92 to 1.80 g cm�3 inexperiments with soil microorganisms and from 1.01 to1.81 g cm�3 in soil fauna experiments. Macropore volumes incompacted soils ranged from 0.8 to 28% (microbiology) and 1.3 to20% (fauna) (Table 6).

4. Results of data evaluation and discussion

In order to standardize the results of different publications, theeffect of soil compaction on soil biological parameters wasgenerally calculated as difference between the results of thecompacted and the control treatments in percentage of the controltreatment (relative change in percent). So, it is possible to comparethe results of different endpoint parameters or of differentanalytical procedures for the estimation of the same parameter,which may differ in absolute values.

ell as their relative difference compared to the corresponding control from soil

Fauna: bulk density [g cm�3]

rol Control Compact Change in % of control

1.30 1.50 13.8

1.66 1.81 50.0

0.99 1.01 0.9

135 197 197

alue is 0%. If the compaction treatment caused effects on soil biological parameters,

rs was 0.

well as their relative difference compared to the corresponding control from soil

Fauna: macropore volume [%]

rol Control Compact Change in % of control

14.0 14.0 �15.0

20.0 20.0 01

6.2 1.3 �79.0

23 61 61

e, so the value is 0%. If the compaction treatment caused effects on soil biological

cal parameters was 0.

[(Fig._1)TD$FIG]

Fig. 1. Change of soil zoological parameter (% of uncompacted control) in relation to

bulk density. Studies on cast production highlighted because of high number of

positive effects. r2 = 0.005, n.s. (all data, dotted line; y = �40.45x + 56.489) and

r2 = 0.222, p < 0.05 (cast production, black line; y = �763.67x + 1229.3).

[(Fig._2)TD$FIG]

Fig. 2. Abundance of three soil fauna groups in relation to bulk density. No controls,

treatment data only. r2 = 0.484, p < 0.001 (earthworms, grey line;

y =�640.09x + 1161.1), r2 = 0.124, n.s. (Collembola, black line; y =�34823x +

63984), r2 = 0.161, n.s. (Enchytraeidae, dotted line; y = �3173.2x + 5748.2).

A. Beylich et al. / Soil & Tillage Research 109 (2010) 133–143 137

4.1. Soil fauna

The soil zoological parameters investigated in field studies weremainly abundance and biomass, while laboratory experimentsinvestigated predominantly burrow formation and cast productionof earthworms in meso- and microcosms prepared with sieved soilcompacted artificially. Only one laboratory experiment usedundisturbed soil columns obtained in the field and compactedin the laboratory. Since only 6 out of 22 studies presented the claycontent, no effective bulk density was calculated.

Considering all data, no clear relation between relative changeof zoological parameter and increase of bulk density is observed(Fig. 1). Furthermore, a differentiation into field and laboratorystudies gives no better relation (r2 near 0.00). About 30% of the datarecords show positive values, of which one third originate fromtwo studies examining the cast production in the laboratory(Kretzschmar, 1991; Buck et al., 2000). The cast production isobviously increased by soil compaction at most of the studiedendpoint bulk densities. Nevertheless, there is a significant effectof decreasing values with increasing bulk density (r2 = 0.22;p < 0.05). This result was obtained with the two deep-burrowingspecies Aporrectodea longa and Lumbricus terrestris, which con-struct permanent vertical burrows by pushing soil aside oringesting/egesting soil. Since higher spatial resistance hampersmovement through soil via body pressure forces, there is a higherneed to ingest soil material and to produce more casts incompacted soil than in the reference soil. With respect to soilstructure formation, total burrow length and volume tend todecrease with increasing bulk density (Joschko et al., 1993; Jegouet al., 2002), which diminishes the positive casting effect, i.e.biogenic soil aggregate formation. A change of earthwormbehaviour from pressing to ingesting soil may have effects ontheir energy budget and their performance in the soil system, or onsoil properties in general, but such issues were not investigated inthe cited studies. Further, not all species are able to adapt theirbehaviour in the same way to compensate for compaction, as Bucket al. (2000) showed in the same experiment: slightly negativeeffects of compaction on cast production were found for theendogeic species Octolasion cyaneum, a smaller topsoil species.

In conclusion, the experiments on cast production show that

1. effects of soil compaction are species dependent and2. increasing casting activity induced by soil compaction needs not

necessarily mean positive effects for the soil system.

In addition, the separate consideration of cast productionstudies showed that the relation between bulk density andzoological parameters might become clearer, if only dataconcerning one parameter is analysed at one time. This approachis limited by the fact that the fewer studies included in an analysis,the less convincing the analysis results become. As abundance wasthe parameter investigated most often in the papers considered, itwas used for further analysis. Fig. 2 shows that the abundances ofearthworms, collembolans and enchytraeids are generally corre-lated negatively with bulk density. However, the correlation israther weak, especially for collembolans and enchytraeids. This ispartly due to very low abundance values in the control(enchytraeid studies) or highly variable abundance values in thecontrol (earthworm studies).

The threshold values proposed by soil physicists (Table 1) couldneither be verified nor falsified by our analyses on soil fauna data.Apart from high variability of general soil properties and the soilphysical parameters measured (Tables 4 and 5), possible reasonsare (1) the assessment of different zoological parameters thatmight react differently to soil compaction and (2) various methodsto induce soil compaction (e.g., livestock trampling or wheelingmight have different effects on soil physical parameters due tokneading and shearing forces than artificial compaction of soilcolumns).

Consequently, the soil zoological data compiled were ratherheterogeneous, but heterogeneity might not be the only reason forthe lack of a detectable correlation between soil physics and soilfauna. The soil physical parameter measured most often was thebulk density. However, effects on soil fauna were found remark-ably often, although no or very small effects on bulk density weremeasured in the compacted treatments. Several authors point outthat bulk density is obviously not the adequate parameter toexplain compaction effects on soil fauna (Langmaack et al., 1996).Other parameters such as macropore volume might be moreappropriate, but were rarely measured. In field studies, the timecourse of the respective proportions of air and water-filled porespace, which is strongly dependent on weather conditions, willhave an important influence.

4.2. Soil microorganisms and microbial processes in soils

For data analysis, results were subdivided into those from fieldinvestigations or field trials and those from laboratory experi-ments. The criterion of this grouping was the moment ofcompaction impact. Measurement of the current state of biologicalsoil properties (e.g., microbial biomass or C-mineralisation

[(Fig._4)TD$FIG]

Fig. 4. Change of C-mineralisation (% of starting point before compaction) relative to

effective bulk density after compaction in laboratory experiments. r2 = 0.316,

p < 0.001.

A. Beylich et al. / Soil & Tillage Research 109 (2010) 133–143138

potential in soil samples) was performed after a certain time ofcompaction in the field or was done in the laboratory. Microbialbiomass, for example, was always measured in the laboratory,whereas C-mineralisation in field experiments was measured asCO2-emission in the field or as CO2-production either in soilsamples which were sieved and then repacked to field density, insamples divided into different aggregate sizes or as decompositionof added plant residues.

In laboratory experiments, both the incubation of compactedand control treatments as well as the measurements of biologicalparameters were done in the laboratory.

In our data set, 29 data records originating from six scientificpapers on C-mineralisation in field experiments or field studies werecompiled. The compaction effect measured as bulk density increasewas 14% on average. Bulk densities of the soils after compactionranged from 1.38 to 1.69 g cm�3. Air capacity (macropore volume)was on average reduced by 27% due to compaction. Values rangedfrom 5 to 13 vol.% in the compacted treatments. Although thesechanges seem to be substantial, it has to be stated, that the aircapacity was reduced below the threshold values of 5 and 7 vol.%,which has been proposed in Germany and Switzerland, in only twoand eight compaction treatments respectively (see Table 1). Incontrast, the effective bulk density was increased above theproposed test values of 1.7 g cm�3 in 15 out of the total 23compacted soils. Because effective bulk density could not becalculated for all experiments, results in Fig. 3 are presented asdiagram of C-mineralisation (change in % of control) vs. bulk density.

In spite of the important effects of compaction on physical soilproperties, effects on C-mineralisation were very variable (Fig. 3),with changes ranging from �47 to +51%. About half of the casesexhibited a negative effect. The overall relation between thecompaction-induced changes in C-mineralisation and bulk densityresulted in a significantly positive regression, which means that C-mineralisation is more likely enhanced with increasing bulkdensity or with soil compaction, if compaction results in higherbulk densities.

The high variability (heterogeneity) of effects is explained bythe fact that soil respiration is a general activity of allmicroorganisms, and that this activity is influenced by manyfactors, depending on organism and situation. The pore volume ofthe soil is principally changed by soil compaction. Thereby thehabitable pore space is changed. Often the volume of smaller soilpores, which are the main living space for microorganisms isincreased. Negative effects of a change in pore volume may becaused by inaccessibility of organic substances (energy, nutrients)(Van Veen and Kuikman, 1990; Kretzschmar and Ladd, 1993) or[(Fig._3)TD$FIG]

Fig. 3. Change of C-mineralisation (% of starting point before compaction) relative to

bulk density after compaction in field investigations. r2 = 0.373, p < 0.001.

reduction of the gas exchange between soil and free atmosphere(CO2, O2). Depending on the situation when effects of compactiontake place, these factors or combinations of factors may lead topositive or negative overall effects on C-mineralisation. Finally,even the method used for conditioning or measuring soil samplescan lead to a positive, negative or no effect (Ruser et al., 2006).

For the evaluation of compaction effects on C-mineralisation inlaboratory experiments, 68 data records from nine papers wereavailable. In these experiments bulk density was increased as amedian by 20% due to compaction, resulting in bulk densities up to1.80 g cm�3, effective bulk densities up to 1.99 g cm�3 and aircapacities (macropore volume) as low as 0.8 vol.%. In 11 cases theproposed threshold value for the effective bulk density(1.7 g cm�3) and in 7 cases the threshold values for air capacity(5 and 7 vol.%, Table 1) was reached.

The correlation coefficient (r2) between changes in C-miner-alisation (in % of control) and effective bulk density or bulk densitywas 0.32 or 0.17, respectively (Figs. 3 and 4). All compactiontreatments resulting in an effective bulk density of more than1.70 g cm�3 lead to a decrease of CO2-production. In all theseinvestigations, the bulk density of the control treatment wasbelow 1.7 g cm�3 and compaction increased bulk density between14 and 50%.

Microbial biomass was estimated in most investigations bymeans of the substrate induced respiration method (SIR) or thefumigation extraction method (CFE), in single cases it wascalculated from the number of bacteria (direct counts or CFU’s)or determined as amount of PLFA’s extracted from soil samples.Results concerning microbial biomass in field studies wereextracted from 13 papers and comprised 60 data records. In theseexperiments compaction resulted in an increase of bulk density byup to 50% and of air capacity by above 60%, with an averageincrease of 20 and 33%, respectively. In one case the compactedtreatment had a lower bulk density and higher air capacity than thenon-compacted control. No relation was found between thecompaction induced relative change of microbial biomass andthe endpoint of compaction (Fig. 5). The high variability in thechange of microbial biomass due to compaction is also accompa-nied by a high variability between the investigations. In the fieldinvestigations very often only one or two compactions intensities(steps) within a small impact range were established.

Nine laboratory experiments with microbial biomass as amicrobial parameter were included in our data base with 85 datarecords. Compaction increased bulk density by up to 45% and air

[(Fig._5)TD$FIG]

Fig. 5. Change of microbial biomass (% of starting point before compaction) relative

to bulk density after compaction in field investigations. r2 < 0.001, n.s.

A. Beylich et al. / Soil & Tillage Research 109 (2010) 133–143 139

capacity by up to 90% (with a median of about 30%). The changes inmicrobial biomass were between �94 and +70%, with a medianvalue of �13%.

The correlation coefficient between the relative changes ofmicrobial biomass as a consequence of compaction and the bulkdensity was 0.42 with a significantly negative slope (Fig. 6). Thisresult is primarily achieved by the data of Nadian et al. (1998),because this investigation and those of Jordan et al. (2000) werethe only works with compactions to an effective bulk density ofmore than 1.7 g cm�3. Without these data the correlation is 0.01.On the contrary, the correlation coefficient between the change ofmicrobial biomass and the change of bulk density was, even withthe data of Nadian et al. (1998), much lower (0.18). Therefore, thehigher the bulk density resulting from compaction, the strongerthe microbial biomass was reduced, independently of the intensityof compaction, i.e. the difference between the bulk densities of thecontrol and the compacted treatment. Also, the duration ofcompaction, varying between 21 and 180 days, had no effect.

Variability of laboratory experiments related to soil propertiesand compaction intensity was on a similar scale as in fieldinvestigations, but the duration of the laboratory experiments was[(Fig._6)TD$FIG]

Fig. 6. Change of microbial biomass (% of starting point before compaction) relative

to effective bulk density after compaction in laboratory experiments. r2 = 0.417,

p < 0.001.

clearly shorter. While interpreting the results of the differentcompaction experiments, it is important to bear in mind that theconditions between the laboratory experiments were variable, but,in contrast to the field investigations, the conditions were keptconstant within a single experiment.

Compaction leads to similar effects on microbial biomass thanon C-mineralisation: whereas in field experiments compactioninduced a rather slight increase of the biological parameters, inlaboratory experiments a clear decrease was found. Above acompaction level indicated by an effective bulk density of morethan 1.7 g cm�3, all effects on microbial biomass were negative. Incontrast, in the experiments with a bulk density in the compactedtreatments below 1.7 g cm�3, effects on microbial biomass wereboth negative and positive not only between but also within theexperiments.

Considering the discussion about deriving threshold values forphysical soil parameters based on effects on biological soilparameters, it must consequently be concluded that only fewclear scientifically demonstrated arguments were found. Effects ofsoil compaction on microbial parameters may generally be positiveas well as negative, depending on the initial state of soil structureand on microclimatic soil conditions during the experimentalperiod. If in laboratory experiments the final effective bulk densityafter compaction was greater than 1.7 g cm�3, exclusively negativeeffects on C-mineralisation and microbial biomass were observed.Because evaluated papers show this observation to be true for bothmicrobial parameters, they make a strong argument for proposingthis as a threshold value for the effective bulk density. However,two facts weaken these arguments: (1) The single investigationsdid not include compaction levels of bulk density in smaller stepsbelow and above this threshold value, and (2) a part of the resultswas generated by laboratory experiments, using disturbed sievedsoil and artificially compacted soil cores; this type of compactioncertainly differs from the field compaction of structured field soils,especially regarding the continuity of the pore system. Thus, theseresults cannot fully support the observed threshold values becauseof their limited applicability to real situations with structured soils.

4.3. General discussion

The high variability in the change of biological parameters dueto compaction is accompanied by a high variability between theinvestigations. This concerns different aspects:

- The variability in the properties of the analyzed soils with respectto clay content, carbon content and pH values;

- The extent of compaction from 0 to 50% of the initial bulk densityor from 0 to 60% of the initial air capacity.

- The time of observations after compaction, varying from 3 weekto 9 years,

- Climatic and soil conditions during and after compaction differedconsiderably and in most cases varied over the experimentalperiod.

General statements regarding compaction effects on bothmicrobial and zoological soil parameters are:

- Due to the high variability of experimental situations andconditions in the evaluated papers, especially in papers describ-ing field investigations, no general effect of soil compaction wasfound.

- The generation of sub-data sets, grouping results obtained undersimilar conditions (e.g., soil texture, duration) was not possiblebecause the number of valid cases was too small.

- Consequently, using existing data it seems that not only inscientific investigations, but also in reality it is not generally

A. Beylich et al. / Soil & Tillage Research 109 (2010) 133–143140

possible to predict effects of compaction on biological param-eters, because influencing factors and their interactions arenumerous and the corresponding knowledge is only marginaland selective. Considering these influencing factors is essential.

5. Conclusions and recommendations

Common target parameters, enabling comparison of results, arefundamentally important for the collective exploration andanalysis of results from different investigations. A main result ofour literature evaluation was that soil zoological studies collectinsufficient soil physical data, even if the experiments include soilphysical impacts. The situation is similar for field investigations forsoil microbial studies, while laboratory experiments mostlyprovide sufficient information with regard to soil properties. Itis crucial that either soil physical parameters be measured ordetailed information on soil properties such as texture and Corg begiven so that soil physical parameters can be derived for thecomparison of studies. Information concerning texture can alsopose comparability problems due to different internationalparticle-size class definitions.

Negative and positive effects occurred with slight compactionas well as with strong compaction for soil zoological as well as forsoil microbiological parameters. Apart from compaction itself,hydrology and oxygen levels were of major importance for adverseeffects, especially for microbiological parameters. A verification ofthe thresholds for soil compaction published so far was notpossible based on the data evaluated. However, the fact that onlynegative effects on microbial biomass and C-mineralisation werefound above an effective bulk density of 1.7 g cm�3 in laboratorystudies confirms this value, proposed by soil physicists, also fromthe soil biological point of view.

The threshold value for air capacity proposed by soil physicistscould not be verified because this parameter was not analysed inmany investigations, and the values calculated by pedotransferfunctions are not sensitive enough to derive threshold values (aircapacity estimated by pedotransfer functions in control andcompacted treatment often resulted in identical values).

Finally it must be stated that the two parameters bulk densityand estimated air capacity, are not sensitive enough in describingthe physical environment of soil organisms and generally not verysignificant parameters in describing functional aspects of soilstructure. Moreover, both parameters are – above all taken asconstant values – only indirectly related to physiological require-ments of soil organisms. The use of physical parameters with theconsideration of the dynamics of soil structure as well as a closerlink to the physico-chemical properties of the soil environmentand needs of soil organisms would be very helpful in future studies.This would include a deepened study and a more functionalcharacterisation of the soil pore system, mainly by usingparameters directly describing pore size distribution, poreconnectivity and tortuosity, and the transport properties of soilstructure regarding soil gases and soil solution (Assouline, 2006;Novosad and Kay, 2007).

With regard to the relevance of this topic for soil protection andtrace-gas emission from agricultural soils, an intensification ofresearch on relations between physical impacts on soil andconsequences for soil organisms and functions is necessary. Inorder to provide a scientifically meaningful data base for theassessment of soil compaction effects on soil biodiversity, relatedfunctions and processes, we recommend considering the followingabiotic parameters as essentials:

� Site properties (land use, climate)� Soil properties (soil type, texture (clay, silt and sand fraction in

%), (effective) bulk density, soil organic matter content, pH value)

� Soil water retention characteristics (water content/water ten-sion)� Soil porous system characteristics, macroporosity� Air and/or water conductivity

Acknowledgements

All results published in this paper were established by theworking group ‘‘Biological assessment of soils’’ of the German SoilAssociation (Bundesverband Boden). The authors would like tothank G. Broll, H. Brauckmann, H.-C. Frund, Th. Gartig, U. Graefe, K.Rahtkens and A. Ruf for their participation in the work. Moreover,we would like to thank the Federal Institute for Materials Researchand Testing and the German Environmental Protection Agency forfinancial support under Grant FKZ 35013009.

Appendix A

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