Soil & Tillage Research 105 (2009) 209–216

The effect of tillage type and cropping system on earthworm communities,macroporosity and water infiltration

Yvan Capowiez a,*, Stephane Cadoux b, Pierre Bouchant b, Stephane Ruy c, Jean Roger-Estrade d,Guy Richard e, Hubert Boizard b

a INRA, UR 1115 Plantes et Systemes Horticoles, Domaine Saint Paul, 84914 Avignon Cedex 09, Franceb INRA, US 1158 Agro-Impact, 2 Chaussee Brunehaut, Estrees-Mons, BP 50136, 80203 Peronne Cedex, Francec INRA, UMR Climat-Sol-Environnement, Domaine Saint Paul, 84914 Avignon Cedex 09, Franced AgriParisTech, departement SIAFEE, Batiment EGER, BP 01, 78850 Thiverval-Grignon, Francee INRA, UR 0272 Science du Sol, 45166 Olivet, France

A R T I C L E I N F O

Article history:

Received 21 January 2009

Received in revised form 27 August 2009

Accepted 2 September 2009

Keywords:

Compaction

Tillage

Earthworm communities

Macroporosity

Infiltration

A B S T R A C T

To test the assumption that changes to earthworm communities subsequently affect macroporosity and

then soil water infiltration, we carried out a 3 year study of the earthworm communities in a

experimental site having six experimental treatments: 2 tillage management systems and 3 cropping

systems. The tillage management was either conventional (CT; annual mouldboard ploughing up to

�30 cm depth) or reduced (RT; rotary harrow up to �7 cm depth). The 3 cropping systems were

established to obtain a wide range of soil compaction intensities depending on the crop rotations and the

rules of decision making. In the spring of 2005, the impact of these different treatments on earthworm

induced macroporosity and water infiltration was studied. During the 3 years of observation, tillage

management had a significant effect on bulk density (1.27 in CT and 1.49 mg m�3 in RT) whereas

cropping system had a significant effect on bulk density in RT plots only. Tillage management did not

significantly affect earthworm abundance but significantly influenced the ecological type of earthworms

found in each plot (anecic were more abundant in RT). On the contrary cropping system did have a

significant negative effect on earthworm abundance (104 and 129 ind. m�2 in the less and most

compacted plots, respectively). Significantly higher numbers of Aporrectodea giardi and lower numbers

of Aporrectodea caliginosa were found in the most compacted plots. CT affected all classes of porosity

leading to a significant decrease in the number of pores and their continuity. Only larger pores, with a

diameter superior to 6 mm, however, were adversely affected by soil compaction. Tillage management

did not change water infiltration, probably because the increase in macroporosity in RT plots was offset

by a significant increase in soil bulk density. However, cropping system had a significant effect on water

infiltration (119 vs 79 mm h�1 in the less and most compacted plots, respectively). In RT plots, a

significant correlation was observed between larger macropores (diameter > 6 mm) and water

infiltration illustrating the potential positive effect of earthworms in these plots.

� 2009 Elsevier B.V. All rights reserved.

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1. Introduction

With the intensification of arable land use over the last fourdecades, deterioration of soil fertility has emerged as a major issue.There is therefore a need for sustainable farming systems withpractices that exploit the natural biotic mechanisms to maintain soilstructure, fertility and drainage (Pfiffner and Luka, 2007). Presentlythere is an increasing interest in new soil conservation managementpractices such as minimum or zero-tillage or control traffic farming.There is some evidence that these practices can lead to increased

* Corresponding author. Tel.: +33 4 32 72 24 38; fax: +33 4 32 72 22 82.

E-mail address: capowiez@avignon.inra.fr (Y. Capowiez).

0167-1987/$ – see front matter � 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.still.2009.09.002

earthworm populations because earthworms are substantiallyinfluenced by changes in their habitat (mainly soil structure andsoil organic matter content). In particular, it is well known thattillage (type and intensity) and soil compaction have a large impacton soil structure and subsequently affect earthworm communities.

The effect of tillage on earthworm communities was previouslydocumented in a large number of studies and most of thesereported (i) changes in earthworm diversity and (ii) higherearthworm numbers under no or reduced tillage compared toconventional tillage systems (see the review of Chan, 2001).However, as stated by Chan in this review, ‘‘(the) ecological andagronomic significance of such increases is not clear’’. The effect oftillage on macroporosity and subsequently water infiltration wasalso studied by many authors who described a decreasing number

Y. Capowiez et al. / Soil & Tillage Research 105 (2009) 209–216210

of macropores and decreased water infiltration in ConventionalTillage (CT) compared to Reduced Tillage (RT) or conservationtillage systems (Ehlers, 1975; Edwards et al., 1990; Shipitalo et al.,1990; Chan, 2004). Most of these studies focused on burrows madeby anecic species (L. terrestris for Edwards et al., 1990 andSpencerellia hamiltoni for Chan, 2004, for instance) since theseearthworms make large and vertical burrows often open to thesurface. However this ecological type of earthworm is rarelydominant in abundance in arable lands (Lee, 1985). The role ofendogeic earthworm burrows in water infiltration has beenstudied less (Zachmann et al., 1987; Trojan and Linden, 1992).

With regards to soil compaction, a large number of studiesreported that increases in soil bulk density caused a decrease inearthworm abundance in arable lands (Sochtig and Larink, 1992;Hansen and Engelstad, 1999; Radford et al., 2001), forests (Jordanet al., 2000), orchards (Pizl, 1992), pastures (Chan and Barchia,2007) and urban parks (Smetak et al., 2007). These negative effectsdepend on the ecological type (epigeic species are more sensitive),species and age/size of earthworms under consideration (Pizl,1992; Cluzeau et al., 1992; Jordan et al., 2000). Thus, soilcompaction decreases earthworm quantities directly (crushing)and indirectly (habitat modification). The same is true formacroporosity, which is also affected directly (macropore destruc-tion) or indirectly (limitation of earthworm burrowing activity(Rushton, 1986; Joschko et al., 1989; Stovold et al., 2004)). In thefirst case, the effect of soil compaction depends on macroporediameter and orientation (Blackwell et al., 1990; Pagliai et al.,2000). Soil compaction was also reported to have adverse effects onwater infiltration (Servadio et al., 2001).

In the present study, we aimed to examine and compare theeffect of a wide range of soil compaction and fragmentationintensity on earthworm communities in arable land and thendemonstrate the possible outcome of changes in these commu-nities on macroporosity and water infiltration. For this, wefollowed the approach outlined by Davidson and Grieve (2006)and investigated the relationships between earthworm commu-nities and soil structure and functions. To reach this objective, wefirst thoroughly characterised the consequences of these agricul-tural practices on soil structure. Moreover, in order to avoidtransient effects resulting from only recent modifications (John-son-Maynard et al., 2007), the INRA long-term experimental fieldsite at Estrees-Mons (Boizard et al., 2002) with a long history ofconsistent management was chosen.

2. Materials and methods

2.1. Site and experimental design

The field trial comprising 24 plots of 0.4 ha each (80 m � 48 m)was initiated in 1989 in northern France (Estrees-Mons, 508Nlatitude, 38E longitude, 85 m elevation) and modified in 1999 toinclude RT (on half of the experimental site). The soil is a silt loam(Orthic Luvisol following FAO classification with 19% clay, 76% silt,5% sand and 1.7% organic C) and has a pH of 7.6. Soil water contentsat �10, �32, �50, �100 and �1500 kPa were 0.253, 0.229, 0.208,0.175 and 0.084 g g�1, respectively. Water content at field capacity,measured during winter in field 2–3 days after excess water hasdrained away, was 0.24 g g�1 (Hillel, 1971). The average airtemperature is 9.6 8C and the annual rainfall is 667 mm. Theclimate was very dry from 2003 to 2006 with annual rainfall of 414,499, 483 and 614 mm, respectively. Two tillage types werecompared: a CT system with annual mouldboard ploughing anda RT system with only superficial tillage. In CT system, each plotunderwent mouldboard ploughing every year at 30 cm depth andseed bed preparation was made with a rotary or a combinedharrow at 7 cm maximum depth. In RT system, seed bed

preparation was made using a rotary or disc harrow at 7 cmmaximal depth. Additionally, one or two additional pass of discwas made for weed control or stubble mixing between two crops.Three cropping systems (systems I, II and III) were established toobtain a wide range of soil compaction intensities depending onthe crops rotation and the rules of decision making. The rules fordecision making in each cropping system were built to combinecrop physiology requirements and soil workability. The rulesconcerning soil workability were based on soil water content at thetime of cultural operation were built from references obtainedduring preliminary experiments (Boizard et al., 2002). The croprotation in cropping system I was pea (Pisum sativum)/winterwheat (Triticum aestivum)/linen (Linum usitatissimum)/winterwheat. Harvesting and sowing were mainly carried out in summeror early autumn, i.e. during the dry period of the year, except forpea and linen sowings. Pea and linen sowings were made when soilwater content was lower than 0.22 g g�1 (water suction of 35 kPa)in the 0–20 cm layer to limit soil compaction. The rotation incropping systems II and III was sugar beet/winter wheat/maize/winter wheat. Cropping system II was managed to avoid wetconditions as much as possible during sowing and harvesting.Sowing were made when soil water content was lower than0.22 g g�1 in the 0–20 cm layer and sugar beet and maizeharvesting were made in early autumn. In contrast, croppingsystem III was managed so as to maximise light interception by thesugar beet and maize canopies by sowing in early spring andharvesting in late autumn, without taking into account the possiblesevere compaction caused by machinery traffic during these wetperiods of the year, which are generally wet in this region. Thus,winter wheat sowing dates were later in cropping system III thanin cropping systems I and II. The effect of the crop rotation and therules for decisions making on the compaction intensity underwheel tracks was evaluated in CT from 1990 to 1999 (Boizard et al.,2002). Annual compaction intensity depended to a large extent onthe cropping system with increasing compaction intensity fromcropping system I to III. Maximum compaction occurred duringharvesting in wet conditions because of high axle loads but theinter-annual variation of compaction was high due to variation inweather conditions and then soil water contents.

Each crop of each cropping system was grown every yearleading to 12 plots for each tillage management. Among these, 6plots (2 tillage managements � 3 cropping systems) were used forthis study with tillage management as main plots and croppingsystem as sub-plots. Wheel traffic was not confined and thelocation of wheel tracks was recorded after each operation. The soilwater content of each plot was measured before each tillage andharvest operation. A description of the decision rules and the maincharacteristics of the machinery used in each cropping system canbe found in Boizard et al. (2002; Tables 1 and 2). Because, the cropsare not the same in the rotation and because sowing dates can vary,pesticides application is different between the three croppingsystems (but is identical for RT and CT). None of the pesticide usedwas classified as to be toxic or very toxic to earthworms (Edwardsand Bohlen, 1996 and internet databases). Regarding fertilisation,the same quantity of P2O5 was applied in all plots whereasquantities of K2O and NO3 were adapted to the needs of each crop.

2.2. Characterisation of soil structure

We measured the soil bulk density after each sowing outsidewheel tracks at seedbed preparation and sowing, using atransmission gamma ray probe (10 replicates) at three depths(0.125, 0.175 and 0.225 m). We directly observed the soilmacrostructure from a soil pit with 3-m wide and 0.8-m depth.The pit was dug perpendicularly to the traffic and tillage direction.This observation was carried out on each plot, each year after

Y. Capowiez et al. / Soil & Tillage Research 105 (2009) 209–216 211

sowing of the different crops. The pit was randomly located in theexperimental plots. For this description, we adopted the methodfully described in Boizard et al. (2002). We focused on a particularstructural type, the highly compacted zones and clods labeled D byRoger-Estrade et al. (2004). D clods and zones were visuallyidentified on the basis of specific morphological features: no visiblemacroporosity, aspect of the breaking surface, constitutiveaggregates not discernable). D zones are created by compactionunder the wheel tracks. In tilled plots, those zones are displacedand fragmented into clods by the plough. In RT plots only the partof the D zones which are near soil surface are fragmented.

Clods and D zones were picked out with a knife in slight reliefon the observation face, so that they could be recognizable on aphotograph, taken 1 m from the face. The total area of D clods andzones was then measured using image analysis. Roger-Estradeet al. (2004) proposed to use the relative proportion of D clods andzones (evaluated as the ratio of the total D surface by the totalsurface of the layer) as an indicator of the compaction degree of thetilled layer in ploughed fields. We also evaluated this criterion inreduced tilled plot on the same soil volume (i.e. the formerploughed layer). Creation of D zones during each field operation(tillage, sowing and harvesting) was theoretically evaluated by themethod proposed by Boizard et al. (2002) from empiricalrelationship between the relative area of D zones created duringtraffic and the soil water content at the time of traffic.

2.3. Earthworm sampling

Earthworm communities were sampled twice a year from all 6plots in November and April (when earthworm activity wasmaximal) for 3 years (from autumn 2003 to spring 2006). Inautumn, the sampling was always done after tillage had occurred(tillage occurred between the 10th of October and the 10th ofNovember depending on the year). In each plot and for each date,four PVC rings (diameter = 40 cm) were inserted in the soil 1 mapart from each other and 1 m in front of the pit when a pit wasopen (spring) or else at a randomly chosen location (autumn).Approximately 5 l of diluted mustard (15 g l�1) was poured intoeach PVC ring. The mustard used contained 12% vinegar and about0.4% allylisothiocyanate. All earthworms which came to thesurface were sampled. After 30 min, the soil was dug out(depth = 0.3 m) and earthworms were removed by hand sorting.Hand sorting was carried out to ensure the representativeness ofthe earthworm sample (especially for endogeic species) but as aconsequence it was not possible to carry out other measurements(macroporosity and water infiltration) in exactly the samelocation. Earthworms were identified using Bouche’s key (1972)but translated into the nomenclature of Sims and Gerard (1999). Inthe Estrees-Mons site, only four earthworm species (two anecicLumbricus terrestris, and Aporrectodea giardi, and two endogeicAporrectodea caliginosa and Aporrectodea rosea) were very commonand could be easily distinguished by the naked eye. Only a fewAllolobophora chlorotica and Octolasion sp. individuals were found.Very small endogeic earthworms (less than 0.1 g) that could not beclearly identified as either A. rosea or A. caliginosa species wereclassified as ‘unidentified juvenile endogeic’ (UJE).

2.4. Macroporosity and infiltration

In spring 2005, the consequences of earthworm activity on soilmacroporosity and water infiltration was determined in the 6plots. Firstly, 2–3 cm of the soil was removed using a spade and aflat horizontal plane was prepared and refreshed using a knife.Water infiltration was examined in each plot using the single-ringinfiltration method (Braud et al., 2005), which was preferred todouble-rings methods since it was less time-consuming and easier

to implement. This method was applied in this study to quite alarge area (0.125 m2) to take into account the heterogeneity of thespatial distribution of earthworm macropores. Four PVC rings(diameter = 0.4 m) were inserted in the soil to a depth of about 1–2 cm in front of the pit in each plot. A fixed volume of water waspoured into the ring at time zero and the time elapsed for theknown volume of water to infiltrate was measured. When the firstvolume had infiltrated completely, a second fixed volume of waterwas added. The pressure head imposed at the soil surface was‘‘almost’’ constant, ranging from 10 mm to 0 mm. In the following,a mean pressure head of 5 mm was considered. The procedure wasrepeated for a series of about 8–18 known volumes until anapparent steady state of infiltration (i.e. the time elapsed betweentwo volume additions was constant). Transient infiltration datawere analyzed with different physically based infiltration models:the Philip’s equation (1957) extended to a 3D infiltration bySmettem et al. (1994), the Talsma and Parlange model (1972) andthe Green and Ampt model (Touma et al., 2007). The first one iswidely used for infiltrometry studies and the two later arebounding cases of infiltration models (Braud et al., 2005). We facedseveral problems when fitting the data: the Philip’s equation led tounrealistic negative values of Ks (see Vandervaere et al., 2000) and‘‘ugly’’ fits were observed leading to unreliable Ks for some plots.We finally go back to a straight and simple approach: we computedthe final infiltration rate FIR (mm h�1) by estimating the slope(linear regression) of the relationships between cumulativeinfiltration and time elapsed at steady state. As the FIR wasanalysed on a relative basis (CT vs RT or effect of the croppingsystem), we assumed that conclusions made concerning the FIRcould be extended to the Ks values. Because we were interested incharacterising the macropores that contributed to this infiltration,methylene blue was added to the water (concentration = 0.01 M)as a dye tracer of conductive macropores (Hangen et al., 2002;Chan, 2004). At the end of the infiltration experiment, the soilbelow the PVC rings was excavated with a spade in order toprepare successive horizontal planes at 10, 20, 30 and 45 cm depth.The 30 cm depth plane was inside the plough pan in CT. For eachdepth, the plane was carefully refreshed with a knife and the soilwas removed using a vacuum cleaner. Macropores stained in bluewere marked with a pin. The surface was then photographed. Thepictures were analysed and each visible round-shaped macropore(stained or not) was traced manually using NIH-Image (Rasbandand Bright, 1995). Given the diameter of the PVC ring, the surface ofeach macropore was automatically computed and pores, whoseEquivalent Circular Diameter (ECD) was smaller than 2 mm werediscarded.

2.5. Statistical analysis

Because no significant depth effect was observed on soil bulkdensity values, data were pooled for each plot. Because we werenot interested in annual variations in soil bulk density, weperformed an ANOVA with two factors (tillage management andcropping system) on each year separately. Data on earthwormcommunities were log-transformed to gain homogeneity ofvariance. We then performed a split-plot ANOVA with 3 factors:date as blocks, tillage type as the main plot factor and croppingsystem as the sub-plot factor (Dagnelie, 2003). This kind of ANOVAwas applied for earthworm total abundance, biomass andabundance for each species. Numbers of macropores for eachclass of diameter were log-transformed to gain homogeneity ofvariance and then analysed using an ANOVA with 3 factors (tillagemanagement, cropping system and depth). The proportion ofcoloured (blue) macropores in RT and CT was analysed with thesame kind of ANOVA. Values of FIR, for water infiltration, wereestimated from the slope of the curve using linear regressions of

Table 1Mean (and standard deviations) of soil bulk density for depths of 12.5, 17.5 and 22.5 cm depending on system, tillage type and year (n = 30). For each year, tillage type and

cropping system had a highly significant effect (p<0.01). Comparisons of systems are shown for each year and each tillage type separately (values bearing the same letter

were not significantly different at the 5% significance level).

Year Conventional tillage Reduced tillage

System I System II System III System I System II System III

2004 1.18a (0.05) 1.18a (0.11) 1.19a (0.12) 1.41a (0.07) 1.46b (0.08) 1.51c (0.06)

2005 1.29a (0.07) 1.31a (0.10) 1.41b (0.08) 1.48a (0.07) 1.53b (0.07) 1.58c (0.04)

2006 1.26a (0.08) 1.36b (0.09) 1.27a (0.11) 1.46a (0.04) 1.48a (0.06) 1.52b (0.05)

Y. Capowiez et al. / Soil & Tillage Research 105 (2009) 209–216212

the steady-state infiltration. These values were then log-trans-formed and compared using an ANOVA with 2 factors (tillage typeand cropping system). Because data for infiltration and macro-porosity were obtained at the same location, multiple regressionsbetween FIR and different classes of porosity were attempted byconsidering tillage type separately (and by pooling depths). Incontrast, because earthworm communities were assessed using adestructive method, regressions between earthworm abundance(of any species) and macroporosity or FIR were not attempted.

3. Results

3.1. Estimation of the creation of D zones and characterisation of the

soil structure

Using the method proposed by Boizard et al. (2002) fromempirical relationship between the relative area of D zones createdduring traffic and the soil water content at the time of traffic, therewas almost no D zone creation from 2003 to 2006 whatever thecultural operation, except harvesting in 2005 for cropping system IIand III where D zones occupied less than 0.25 of the soil volume.

Every year, each tillage management and cropping system had astrong and significant influence on soil bulk density (p < 0.01)(Table 1). The soil bulk density was much higher under RT than CT(1.49 and 1.27, respectively, if the data from the 3 years are pooled).The effect of cropping system on bulk density was clear in RT withsignificantly higher values for system III and intermediate values forsystem II (except in 2006) (Table 1). In CT, the effect of croppingsystem on bulk density was minimal (except in 2005). As can beclearly seen in Fig. 1, RT systems II and III are characterised by a muchhigher percentage of highly compacted zones than RT system I andthe 3 systems under CT, which had almost the same value.

3.2. Earthworm communities

When the effects of the treatments on earthworm totalabundance were examined, only the factor ‘system’ had asignificant effect (p = 0.038; F = 3.35; df = 2), whereas tillage

Fig. 1. Percentage of D zones in vertical soil profiles depending on tillage

management and cropping system.

management and the interaction between these 2 factors werenot significant (Table 2). However, in Table 2, it can be seen that theeffect of system was more pronounced under RT where clearly lessearthworms were sampled in system III. When we then analysedearthworm abundance according to individual species, weobserved significantly lower quantities of both of the anecicspecies (L. terrestris and A. giardi) and higher number of A. caliginosa

earthworms under CT (Table 2). System had a significant influenceon A. giardi, which were less abundant and A. caliginosa which weremore common in cropping system I (Table 2). The interactionbetween the two factors was not significant except for A. giardi andA. caliginosa for which the significant effect of cropping system wasobserved mainly in RT (Table 2). Regarding total biomass ofearthworm communities, both factors were significant (p < 0.01,F = 42.39, df = 1 for tillage and p = 0.014, F = 4.42 and df = 2 forcropping system). A greater biomass was found in RT andconversely a lower biomass was found in cropping system I(Table 2). The percentage of juvenile earthworms was notsignificantly different in any case.

3.3. Macroporosity

We found that depth had a significant effect on porosity for allpore classes under study (2–4, 4–6 and >6 mm ECD). There weresignificantly less pores in the �30 cm depth plane (plough pan)than in those from �10 and �45 cm depth. On the other hand,there were significantly more pores in the �45 cm depth planethan in those from �20 to �30 cm depth (Fig. 2). For all classes ofporosity, we observed significantly more pores in plots under RTthan CT. The system effect depended on the pore class. System IIIappeared to have led to a significantly higher number of pores ofthe intermediate ECD and a lower number of bigger pores (Table 3).

Tillage had a significant effect (p < 0.01) on the relativeproportion of pores coloured with methylene blue. The resultsclearly showed that, except for in the first plane (�10 cm), therewas a much higher proportion of coloured pores under RTcompared to CT (Fig. 3). In CT, the proportion of coloured poresdecreased regularly with depth whereas it remained constant inRT. Cropping system did not have a significant effect on theproportion of coloured pores (not shown).

3.4. Water infiltration and correlation with macroporosity

Differences in FIR are mainly due to soil bulk density (and thensoil fragmentation), macroporosity (earthworm communities) butas well to initial difference in soil water content. These ones wereindeed limited since experiments were carried out under wetconditions.

Unexpectedly, water infiltration (FIR) was not significantlyinfluenced by tillage management (mean value of 81.8 and96.0 mm h�1 in CT and RT, respectively; F = 0.98; p = 0.33;df = 1). On the other hand, the factor ‘system’ affected the finalwater infiltration rate (F = 5.29; p = 0.032; df = 2) with significantlyhigher values for system I (118 mm h�1) compared to system II andIII (68 and 78 mm h�1, respectively).

Table 2Mean values of total and species relative abundance and total biomass depending on tillage management and cropping system compared with a split-plot ANOVA (results for

UJE are not presented). Values bearing different letters are significantly different at the 5% significance threshold (tillage and cropping systems were compared separately).

The S letter in the last row means that the interaction between the 2 factors is significant.

Tillage management Cropping system Interaction

CT RT I II III

Abundance (no. m�2) 110.6a 116.2a 122.7A 122.1AB 95.6B

L. terrestris (no. m�2) 10.1b 22.5a 14.0A 19.7A 15.2A

A. giardi (no. m�2) 2.2b 27a 6.1B 20.8A 16.8A S

A. caliginosa (no. m�2) 54.2a 23.9b 56.5A 31.3B 29.5B S

A. rosea (no. m�2) 16.6a 19.6a 14.4A 24.3A 15.6A

Biomass (g m�2) 36.9b 76.8a 46.9B 62.4A 61.1A

Percentage of juveniles 51.03a 49.29a 47.78A 53.35A 49.44A

Fig. 2. Mean cumulative number of the three classes (2–4, 4–6 and above 6 mm equivalent diameter) of macropores (m�2) with depth (cm).

Y. Capowiez et al. / Soil & Tillage Research 105 (2009) 209–216 213

Table 3Mean number of pores (m�2) for the 3 factors (tillage management, cropping system and depth). Values bearing different letters (within a diameter class) are significantly

different at the 5% significance threshold.

ECD Depth Tillage System

�10 cm �20 cm �30 cm �4 cm CT RT I II III

2–4 mm 265.6c 247.9b 121.9a 252.6bc 190.6A 340.6B 279.7a 229.7a 285.5a

4–6 mm 64.1b 59.9b 38.0a 114.6c 36.5A 91.7B 45.3a 67.2a 79.7b

>6 mm 35.9b 26.6ab 21.9a 96.9c 15.6A 56.2B 40.6b 45.3b 21.9a

Y. Capowiez et al. / Soil & Tillage Research 105 (2009) 209–216214

Even if tillage management did not have a significant effect,multiple correlation procedures led to improved results when thetwo tillage managements were considered separately. In this case,we observed a significant positive correlation for RT between FIRand the number of pores larger than 6 mm ECD (p = 0.038 andmultiple R-squared = 0.645). If the same kind of multiple correla-tion was applied on stained pores only, we observed a significantrelationships with the number of larger coloured pores (p = 0.046and multiple R-squared = 0.564). No significant correlation wasobserved in any case between FIR and any class of porosity underCT (p = 0.18).

4. Discussion

We observed clear differences with both methods used tocharacterise the effects of tillage management and croppingsystem on the soil structure in the 6 experimental plots.Nevertheless the creation of D zones was almost zero between2004 and 2006. So the differences in soil structure were induced bysevere compaction events before 2004.

As expected with the dry conditions from 2003 to 2006, the soilbulk density was lower in the CT treatment, which also exhibitedthe lower proportion of D zones. Boizard et al. (2002) showed thatD zones could rapidly disappear from the ploughed layer. Indeedthe plough fragments the D zones and, when inversing the soil,brings D zones close to the soil surface where weathering andtillage at seed bed preparation make them disappear.

This process did not occur in RT plots where the D zonesdisappeared more slowly, essentially due to the effect of weath-ering and soil fauna (Roger-Estrade et al., 2009). As a consequence,the effects of cropping system on soil structure were more obviousin RT and almost negligible under CT where soil bulk density wasnot affected by crop management systems. Indeed, we clearlydemonstrated that under RT the three cropping systems sig-nificantly altered soil bulk density and influenced the proportion ofD zones. Due to these large effects on soil structure, it was assumedin the present study that the effect of the crop management systemon earthworm communities would be mainly related to compac-tion intensity but cropping system I had a different rotation

Fig. 3. Percentage (mean and standard deviation) of coloured macropores (whose

ECD > 2 mm) in function of depth and tillage management.

schedule to cropping systems II and III and thus the pesticidesapplied and possibly the residues which remained in the soil werealso different.

We confirmed that the effect of tillage type is clearly differentdepending on the two ecological types of earthworms (Edwardsand Lofty, 1982; Chan, 2001). CT had pronounced negative effectson anecic earthworms. This can be explained by direct physicaldamage, or indirect effects on food resources (burial of surfaceorganic matter) or habitat (destruction of burrows). For endogeicspecies, tillage type did not affect A. rosea but the number of A.

caliginosa earthworms significantly increased in CT. The positiveeffect on the A. caliginosa population could be due to a directincrease in food resources (burial of organic matter) or an indirectdecrease in competition for food with anecic species. As a result,tillage type had a significant effect on earthworm biomass becauseanecic species, which are larger earthworms, were more abundantunder RT.

We showed that earthworm abundance was significantlyhigher (mean increase of 30%) in cropping system I, which hadthe lowest soil bulk density and smallest number of compactedzones, compared to cropping system III. We also determined thatonly the quantities of A. caliginosa and A. giardi were distinctlyinfluenced by compaction especially in RT. Consequently, earth-worm biomass was higher in cropping systems II and III due to thehigher abundance of these larger A. giardi in these plots. Previousstudies reported that larger species were less sensitive to soilcompaction (Cluzeau et al., 1992) and that A. nocturna (a speciesclosely related to A. giardi) was more abundant in compacted areas(Cuendet, 1992). More recently Chan and Barchia (2007) showedthat A. caliginosa was highly affected by soil compaction. Howeverknowledge on the sensitivity of different earthworm species to soilcompaction are too scarce and observations were often made invery different compaction intensity.

Overall we observed that soil compaction (cropping system) ortillage management have effects with the same order ofmagnitude. This is somewhat unexpected since compaction inplots is characterised by high spatial variability linked to pathwaysand wheel tracks, as reported by Binet et al. (1997) in maize fields.Most of the effects of compaction detected were more obvious inRT plots. This observation is in agreement with recent findings byOuellet et al. (2008) who reported higher correlations betweenearthworm biomass and soil characteristics (with bulk density asthe most important factor) in no-till plots compared to tilled plots.

The first functional consequence of these changes to thecomposition of earthworm communities in the plots was a changein macroporosity. However, regardless of pore size, the minimumnumber of macropores was found in the�30 cm depth plane, i.e. inthe plough pan. This is another obvious effect of compaction andeven after 5 years of RT, the adverse effect of the ancient ploughpan could still be observed in RT plots. In contrast, the maximumnumber of macropores was almost always found in the �45 cmdepth plane, as was previously observed by Sveistrup et al. (1997)in a site dominated by deep burrowing earthworm species. Thisraised the question of the ecological significance of these deepmacropores for which we could assume that a proportion are infact ‘‘ghost burrows’’, i.e. burrows no longer occupied by an active

Y. Capowiez et al. / Soil & Tillage Research 105 (2009) 209–216 215

earthworm. It should be noted however that in RT plots most ofthese burrows were still conductive since the percentage ofcoloured macropores between �30 and �45 cm did not show amarked decrease (Fig. 3). CT had a strong negative impact onmacropore number, for all pore classes, clearly illustrating thedisruptive effect of tillage. The coloured macropore data from theCT plots also provided further evidence of this and definitivelyshowed that CT leads to decreased burrow continuity.

Cropping system (or compaction) only had significant ramifica-tions on macroporosity in the two higher pore classes. Weobserved significantly more macropores belonging to the inter-mediate diameter (between 4 and 6 mm ECD) in cropping systemIII plots. This could be related to the high abundance of A. giardi incropping system III since Bouche (1972) stated that the meandiameter of A. giardi was between 5 and 7 mm. However, the morea plot was compacted, larger macropores (>6 mm ECD) becamescarce. This result seems surprising because we did not observehigher numbers of anecic earthworms in system I plots. It couldeither be due to higher macropore destruction by compaction or toa lower burrow length made by each earthworm in croppingsystem II and III. Indeed many authors showed, that undercontrolled conditions, higher compaction could result in smallerburrow length (Rushton, 1986; Joschko et al., 1989; Stovold et al.,2004). This means that the direct relationship between earthwormabundance and macropore number should be studied with caution.

Water infiltration is also known to be influenced by earthwormmacropores (Ehlers, 1975; Zachmann et al., 1987; Wuest, 2001)but the relationships is not always straightforward since (i) not allmacropores contributed equally to water infiltration (Trojan andLinden, 1992) and (ii) part of the flow is inside the soil matrix,either through cracks (other macropores) or poroid voids (microand mesopores). Even if macropores can play a role in waterinfiltration, once they are full of water (after a few minutes) thenthe most likely limiting factor is water flow through the burrowwalls (Bastardie et al., 2005), which is also influenced by bulkdensity at least for the first 30 cm. Although mean soil bulkdensities were significantly lower in CT plots (between �10 and�30 cm depth), tillage type was not observed to significantly affectwater infiltration. This suggests that the higher number ofmacropores and their increased continuity in RT offset thenegative effect of soil matrix bulk density. Conversely, soilcompaction has a significant negative impact on water infiltration,mainly because of increased soil bulk density but also possibly dueto the prevalence of pores with an ECD > 6 mm in less compactedareas (cropping system I). Because tillage type strongly affects soilstructure and therefore water infiltration, the correlations betweenFIR and macropores should be tested separately on data from RTand CT plots. Indeed, when correlations were examined on RT plotdata only, positive correlations were found between FIR and thedensity of larger macropores. Earthworm macropores are thereforethought to play a limited role in water infiltration in CT plots but agreater role in RT plots on the Estrees-Mons site. Indeed under RT,the significantly higher abundance of anecic earthworms was ableto counteract the negative impact on water infiltration caused bythe increase in soil bulk density.

In conclusion, the findings of this study are in agreement withpreviously published results, however our findings also bring tolight new complementary information of importance for thedesign of soil conservation land use management practices. Firstly,we confirmed that the main effect of conventional tillagecompared to reduced tillage is not necessarily a decrease inearthworm abundance but a clear modification in the structure ofearthworm communities with an important decrease in anecicearthworms. Secondly, we revealed that, under realistic fieldconditions with a clear characterisation of the consequences onsoil structure, soil compaction can have important effects on

earthworm abundance especially under RT (mean reduction ofabout 30% between cropping system I and III). Interestingly, theconsequences of these changes in the earthworm communitieswere not straightforward. We confirmed that tillage has a clearnegative effect on macroporosity both in terms of abundance andcontinuity. This did not result, however, in decreased waterinfiltration since the decrease in macroporosity was offset by thesignificant decrease in soil bulk density in CT plots due tomouldboard ploughing. On the other hand, soil compactionsignificantly decreased water infiltration due to the combinedeffect of the decrease in number of larger macropores and theincrease in soil bulk density.

Acknowledgments

Bertrand Chauchard is thanked for his help in field experiments.This work was carried out with the financial support of the «ANR-Agence Nationale de la Recherche—The French National ResearchAgency» under the «Programme Agriculture et DeveloppementDurable», ‘‘ANR-05-PADD-013, DST’’ and of the ‘‘MEDD – TheFrench Ministry of Environment and Sustainable Development’’under the ‘‘Programme Gessol2’’.

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