www.elsevier.com/locate/catena

Catena 54 (2003) 637–649

Changes of pore morphology, infiltration and

earthworm community in a loamy soil under

different agricultural managements

Mathieu Lamandea, Vincent Hallairea,*, Pierre Curmia,b,Guenola Peresc, Daniel Cluzeauc

a INRA-Centre de Rennes, Unite Sol et Agronomie Rennes Quimper, 65, route de Saint-Brieuc,

35042 Rennes, FrancebFrench Institute of Pondicherry, 11, Saint-Louis Street, PB 33, Pondicherry 605001, India

cCNRS, UMR 6553 ‘‘Ecobio’’—Laboratoire d’Ecologie du Sol et de Biologie des Populations,

Station Biologique, 35380 Paimpont, France

Abstract

Earthworm activity produces changes at different scales of soil porosity, including the

mesoporosity (between 1.000 and 30 Am eq. dia.) where both water retention and near-saturated

infiltration take place. At this scale, the structural changes are poorly described in temperate

agricultural systems, so we do not yet fully understand how these changes occur. The present study

was conducted to determine the relationships between the morphology of the mesopores, which is

mainly affected by earthworm activity, and the hydrodynamic behaviour (near-saturated infiltration)

of topsoil under different agricultural managements inducing a large range of earthworm

populations.

Investigations were carried out at the soil surface in three fields under different management

practices giving rise to three different earthworm populations: a continuous maize field where pig

slurry was applied, a rye-grass/maize rotation (3/1 year, respectively) also with pig slurry, and an old

pasture sown with white clover and rye-grass.

Pore space was quantified using a morphological approach and 2D image analysis.

Undisturbed soil samples were impregnated with polyester resin containing fluorescent pigment.

The images were taken under UV light, yielding a spatial resolution of 42 Am pixel� 1. Pores were

classified according to their size (which is a function of their area) and their shape. Hydraulic

conductivity K(h) was measured using a disc infiltrometer at four water potentials: � 0.05, � 0.2,

� 0.6, and � 1.5 kPa. The abundance and ecological categories groups of earthworms were also

investigated.

0341-8162/$ - see front matter D 2003 Elsevier B.V. All rights reserved.

doi:10.1016/S0341-8162(03)00114-0

* Corresponding author. Tel.: +33-223-485-429; fax: +33-223-485-430.

E-mail address: hallaire@roazhon.inra.fr (V. Hallaire).

M. Lamande et al. / Catena 54 (2003) 637–649638

Continuous soil tillage causes a decrease in both abundance and functional diversity (cf. maize

compared with old pasture) when soil tillage every 4 years causes only a decrease in abundance (cf.

rotation compared with old pasture). There were no relationships between total porosity and effective

porosity at h =� 0.05 kPa. Image analysis was useful in distinguishing the functional difference

between the three managements. Fewer roots and anecic earthworms resulted in fewer effective

tubular voids under maize. There were fewer packing voids in the old pasture due to cattle trampling.

Greater hydraulic conductivity in the pasture phase of rotation may arise from a greater functional

diversity than in the maize and absence of cattle trampling compared with the pasture. We point to

some significant differences between the three types of agricultural management.

A better understanding is required of the influence of agricultural management systems on pore

morphology. This study provides a new methodology in which we consider the earthworm activity as

well as community in order to assess the effects of agricultural management on soil structure and

water movement.

D 2003 Elsevier B.V. All rights reserved.

Keywords: Soil structure; Hydraulic conductivity; Image analysis; Cropping systems; Earthworms

1. Introduction

Understanding the role of fauna on soil physical properties is important in developing

sustainable agricultural managements, and during the last decade, important efforts were

devoted to the description and quantification of the direct and indirect effects of soil

invertebrates on the major processes of the soil, in particular, the formation and

conservation of the physical structure. In temperate regions, the earthworms in term of

biomass constitute the principal component of the total faunal biomass (Lee, 1985).

Earthworm populations are affected by agricultural management (Binet et al., 1997;

Paoletti et al., 1998; Chan, 2001), and earthworms have a large influence on soil physical

properties through their burrowing and casting activities. Also known as ‘‘ecosystem

engineers’’ (Jones et al., 1994), earthworms produce structural features at three different

scales of soil porosity. Much work deals with the characterisation of burrow networks

created by earthworm species (Capowiez et al., 1998; Jegou et al., 1999). In relation to

macropore space (>1 mm), burrow networks act as preferential flow paths (Bouche and

Al-Addan, 1997; Trojan and Linden, 1998). At a smaller scale, earthworms may change

the pore space between mineral and organic particles, i.e. the microporosity, and the

stability of soil structure (Shipitalo and Protz, 1989; Blanchart et al., 1993; Chauvel et al.,

1999). Packing voids within cast deposits control soil mesoporosity, in which large

amounts of water and solutes are transported and retained. Because these structural

features have been little studied in temperate agricultural systems, we are here primarily

concerned with the mesoscale aspects of pore morphology.

The effects of earthworm activity and agricultural management on soil physical

properties have been studied, but only in terms of preferential flow paths (Ehlers, 1975;

Sveistrup et al., 1997). Hallaire and Curmi (1994) and Kribaa et al. (2001) showed the

main role of morphology in linking the effective porosity with movement of water and

solutes. The effect of agricultural management systems on soil physical properties has

M. Lamande et al. / Catena 54 (2003) 637–649 639

often been quantified with near-saturated infiltration measurements (Ankeny et al., 1990;

Meek et al., 1992; Azevedo et al., 1998; Heddadj and Gascuel-Odoux, 1999; Angulo-

Jaramillo et al., 2000).

Our objective here is to evaluate the effect of various agricultural managements and

natural earthworm populations on the physical properties of topsoil. We looked for

relationships between the morphology of the mesopores and the rate of near-saturated

infiltration. We measured in situ hydraulic conductivity at multiple water potentials near

saturation with tension infiltrometers and characterised the morphology of a large part of

mesopores by image analysis of a soil affected by both agricultural treatments and

earthworm activity.

2. Materials and methods

2.1. The experimental design

The experiment was carried out at the experimental station of the Lycee Agricole de

Kerbernez, in western Brittany, France (latitude 47j57VN, longitude 4j8VW). Agriculture

in this region consists mainly of intensive milk production characterised by rotations of

maize and pasture. The climate is of temperate oceanic type, with an average annual

precipitation of 1200 mm and a mean annual temperature of 11.4 jC. The soil is a Humic

Cambisol (FAO) of loamy texture with a high concentration of organic matter in the first

30 cm (Table 1) developed on granitic saprolite.

The trial comprised three plots, each 9 m wide and 16 m long, that were managed as

follows: (i) continuous maize treated with pig slurry for 22 years, (ii) a pasture phase (1st

year) of a rye-grass/maize rotation (3/1 year) also with pig slurry for 22 years, (iii) old

pasture sown with white clover and rye-grass maintained over a period of 9 years. Physical

measurements and soil sampling were performed from soil surface on the most represen-

tative zone in the topsoil, determined by mapping the structural features of the given

ploughed soil horizon (Manichon and Roger-Estrade, 1990; Curmi et al., 1996) just before

maize seeding (March) after 6 months without tillage.

2.2. Earthworm community

Natural earthworm community was extracted in each field using the formaldehyde

method on 1 m2 (Bouche, 1972; Cluzeau et al., 1999); after three sprayings of

Table 1

Soil characteristics of the top soil in the three studied fields

< 2 Am(%)

2–20

Am (%)

20–50

Am (%)

50–200

Am (%)

200–2000

Am (%)

Organic matter

content (%)

pHwater

Maize 16.1 21.4 20.4 13.2 28.9 4.18 6.20

Rotation 17.7 19.6 23.6 13.1 26.6 4.43 5.65

Old pasture 17.0 17.5 17.5 18.0 30.0 4.20 5.90

M. Lamande et al. / Catena 54 (2003) 637–649640

formaldehyde solution (10 l per spraying with different concentrations: 0.25%, 0.25%,

0,4%), earthworms were collected at the soil surface. Three replicates were performed in

each field surrounding the sites chosen for physical measurement and soil sampling.

Earthworm communities were characterised by their abundance (number collected per

m2) and their ecological group. This last parameter is based on earthworm morphology

and behaviour (localisation in soil, feeding behaviour), and corresponds to three

ecological groups (Lee, 1959; Bouche, 1972, 1977) whose burrow systems were

described (Kretzschmar and Aries, 1990; Lee and Foster, 1991; Lavelle, 1997): epigeic

(range, 1–2.5 mm in diameter, live and feed above the soil surface, create no or few

burrows), anecic (range, 4–8 mm in diameter, feed at the ground surface, live in

semipermanent burrows, more or less vertical and opened to the soil surface), and

endogeic (range, 2–4.5 mm in diameter, ingeste soil, dig extensive systems of temporary

burrows that they immediately refill with their casts, the burrows are mostly subhorizontal

oriented and very ramified through the soil but rarely open to the surface). In order to link

earthworm activity to soil properties, the earthworm communities were also characterised

by their functional diversity that combines the ecological group and growth stage (juvenile,

adult) (Peres et al., 1998); six functional classes are defined.

2.3. Physical measurements

Hydraulic conductivity K(h) was measured using a disc tension infiltrometer with an

80-mm-diameter base, which determined tension at the soil surface as described in Ankeny

et al. (1990, 1991). Steady-state infiltration rates were measured at four soil water

potentials h: � 0.05, � 0.2, � 0.6, and � 1.5 kPa. Flow was measured from � 1.5 to

� 0.05 kPa. The disc of the infiltrometer was positioned on the undisturbed surface

covered with a thin layer of sand to obtain a flat surface in the soil with maize. We gently

removed the upper root zone in the rotation and old pasture fields in order to place the disc

of the infiltrometer (respectively, 2 and 3 cm from the surface). The flow was measured at

a given potential for about 1 h to reach steady state. We used methylene blue in water (0.4

g l� 1) to dye the effective porosity at water potential h =� 0.05 kPa. We estimated the

unsaturated hydraulic conductivity curve at several tensions by computing multiple supply

potentials with the same disc, as proposed by Reynolds and Elrick (1991) and Ankeny et

al. (1991), assuming Wooding’s solution for three-dimensional axisymmetric infiltration

(Wooding, 1968). We estimated total porosity from measurements at the same sites by

weighing cylindrical samples having a volume of 250 cm3 (four replicates) assuming a

solid density of 2.65 g cm� 3.

2.4. Image analysis of macropore space

Pore space descriptions were made using undisturbed soil blocks (10� 10� 8 cm)

taken vertically beneath the locations of the infiltration measurements. Soil samples were

dried and impregnated with a polyester resin containing fluorescent dye (Ringrose-Voase,

1996). The blocks were then cut in four horizontal polished sections (7� 7 cm) at four

depths (1, 3, 5, and 7 cm). For each section, four areas (2.2� 3.1 cm) were analysed using

OPTIMAS software with a spatial resolution of 42 Am pixel� 1. We chose a spatial

M. Lamande et al. / Catena 54 (2003) 637–649 641

resolution corresponding to the pore space involved in infiltration measurements (pore size

between 0.018 and 28.3 mm2), so we cannot measure the smallest part of the meso-

porosity. One grey-level image was taken with a CCD camera under UV light on which the

Fig. 1. Method of image treatment (magnification � 2.5): (a) grey-level image acquired under UV light (the

porosity is bright and the solid material is dark); (b) grey-level image acquired under white light (quartz, feldspar,

and plagioclase are bright, the porosity and solids are dark); (c) segmented image of quartz, feldspar, and

plagioclase; (d) intersection of images (c) and (a); (e) segmented image of (d); (f) segmented image of (d) only

stained pores.

Table 2

Pores classification according to size and shape

Shape classes Size classes (10� 6 m2)

1 2 3 4

[0.018; 0.031] [0.032; 0.196] [0.197; 1.77] >1.77

Tubular void Is< 38 T1 T2 T3 T4

Crack Isa[38; 89] C1 C2 C3 C4

Packing void Is>89 P1 P2 P3 P4

Is: elongation index.

M. Lamande et al. / Catena 54 (2003) 637–649642

solid phase appears dark and the porosity bright. Because some mineral fragments (quartz,

feldspar) appear bright under UV light, another grey-level image was taken under white

light on which the porosity is dark and coarse fragments are bright. We segmented and

inverted the image with coarse fragments and masked the coarse fragments on the grey-

level UV image. We then segmented the grey-level UV image into a binary image and

removed the porosity unaffected by methylene blue using a hand-made mask (Fig. 1). The

stained pores were classified from the final binary image according to their size and shape.

Pore size was measured from surface area on the binary image. Four size classes were

determined, corresponding to the effective pore size at the water potentials used for

infiltration measurement: from 0.018 to 0.031, from 0.032 to 0.196, from 0.197 to 1.77,

and up to 1.77 mm2. Pore shape was measured using the elongation index Is (perimeter2/

area), and three shape classes were determined to distinguish between tubular voids,

cracks, and packing voids (Hallaire and Curmi, 1994). The thresholds used for the size and

shape classes are given in Table 2.

3. Results and discussion

3.1. Earthworm community

Earthworm abundances are significantly different in the three treatments (Student’s t-

test, p = 0.05) (Fig. 2): the highest abundance of earthworms is found in the old pasture and

lowest in the maize; the increase of anthropic constraints is associated with a decrease in

earthworm abundance and species diversity. In the old pasture, the community is

dominated by endogeic earthworms (48%) and especially by Aporrectodea caliginosa

(Savigny, 1826) (juveniles and adults) and Allolobophora c. chlorotica (Savigny, 1826)

(adults). Anecic earthworms are also found (42%), especially Lumbricus friendi (Cognetti,

1904) (juveniles and adults). The low abundance of epigeic species in the old pasture

(10%) compared to the pasture phase of rotation (52%) may be explained by cattle

trampling (Cluzeau et al., 1992). Although land management conditions associated with

maize culture (tillage, pesticide use, and low organic matter return) affect all the

earthworm communities, the changes mainly concern the anecic (6%) and epigeic species

(4%); tillage may affect the largest individuals (anecic adults and juveniles, and endogeic

adults), while the soil cover may affect the epigeic species. In fact, the community under

Fig. 2. Earthworm communities in the studied three fields: (a) continuous maize, (b) pasture phase of rotation, (c)

old pasture.

M. Lamande et al. / Catena 54 (2003) 637–649 643

maize is dominated by endogeic species (90%), especially by A. caliginosa observed

mainly at the juvenile stage, while both juvenile and adult anecic are almost totally absent.

Pasture after maize especially favours the epigeic species (52%), which are dominated by

Lumbricus castaneus (Savigny, 1826) and Lumbricus rubellus castenoides (Bouche, 1972)

(observed at the adult stage), as well as anecic species (33%) dominated by L. friendi. This

specific structure could be explained by (1) the high rate of reproduction of the epigeic

species, (2) the maintenance of some earthworm species via the cocoons during the maize

phase, (3) the restauration of the anecic species due to better environmental conditions

(grass cover, no more tillage), and (4) the recolonisation of the site by exogenic

earthworms.

Thus, functional diversity is higher in the two pasture soils than under maize. Anecic

(juvenile and adult) and endogeic (juvenile and adult) species are present in the two

pastures, but there are more individuals of the three ecological groups in the old pasture

than under the rotation system.

3.2. Bulk density

The Student’s t-test on the mean at the 95% confidence interval shows that bulk density

is not significantly different between maize (1.21 g cm� 3) and the pasture phase of rotation

(1.26 g cm� 3) (Fig. 3). We expected a higher bulk density with rotation than maize due to

‘‘natural’’ compaction and the lack of tillage. The biological activity is more intense with

the rotation and could account for the better aggregation and porosity. Bulk density is

significantly higher in the old pasture (1.43 g cm� 3) (Fig. 3). We observed a compacted

layer on the top of the soil profile in the old pasture that was attributed to cattle trampling.

3.3. Near-saturated infiltration

The results of near-saturated infiltration measurements are presented in Fig. 4. We

estimate a high hydraulic conductivity in the rotation fields at the two water potentials

Fig. 3. Bulk density (g cm� 3) for the three fields: (a) continuous maize, (b) pasture phase of rotation, (c) old

pasture. Circles represent means that are significantly different, which either do not intersect at all or intersect

only slightly so that the external angle of intersection is less than 90j.

M. Lamande et al. / Catena 54 (2003) 637–649644

nearest to saturation (K(� 0.05) = 1.85� 10� 4 m s� 1 and K(� 0.2) = 1.16� 10� 5 m s� 1).

There were many new effective pores with equivalent diameters up to 0.5 mm. Only a few

new pores become effective at conditions near saturation in the maize field and the old

pasture. At the two water potentials nearest to saturation, water flow is controlled more by

gravity than by capillarity. The water potential corresponding to the change of gravity/

capillarity ratio is between � 0.35 and � 0.3 kPa in the three fields. Jarvis and Messing

(1995) estimated this break point between � 0.6 and � 0.25 kPa, depending on the soil

texture, and at � 0.25 kPa for a loamy soil. They suggested that this water potential could

be used as an operational boundary between mesoporosity and macroporosity (Luxmoore,

1981). Although reducing the bulk density, ploughing did not increase the hydraulic

Fig. 4. Hydraulic conductivity at four water potentials near saturation in the three fields.

M. Lamande et al. / Catena 54 (2003) 637–649 645

conductivity. Kooistra et al. (1984) suggested that ploughing produces a disconnected

macroporosity, while some earthworms produce a more continuous type of porosity.

Hydraulic conductivity shows that mesopores formed by settling and biological activity

with rotation are more continuous than mesopores formed by settling under maize after 11

months without tillage. Chan (2001) suggested that preferential flow paths (related to deep-

burrowing earthworm species) are the most important factors controlling water movement

in soil (preventing flooding and erosion). Since the connections between macropores are

strongly dependent on the presence of mesopores, endogeic species should be as important

as deep-burrowing species. The beneficial effect of biological activity on near-saturated

infiltration observed in the rotation compared with the maize (where K(� 0.05) is divided

by a factor 17) could have been reduced by cattle trampling in the old pasture (where

K(� 0.05) is divided by a factor 19).

Near-saturated hydraulic conductivity is useful for evaluating the effect of agricultural

management systems on soil hydraulic properties. It provides information on soil

infiltration capacity as well as the amount of effective pores of different sizes.

3.4. Morphology of the effective mesoporosity

Total effective mesoporosity at water potential h =� 0.05 kPa as measured by image

analysis (surface of the total dyed porosity) was compared with total porosity estimated from

bulk density measurements, assuming 2.65 g cm� 3 as solid density (Fig 5). There were no

relationships between effective mesoporosity and total porosity for the three fields. The

difference in hydraulic conductivity at h =� 0.05 kPa between the three fields was not

related to a difference in total porosity or in effective porosity. There is no correlation

between total porosity and effective porosity. In this case, image analysis is useful in

distinguishing the functional difference between those two managements.

Fig. 5. Total porosity estimated from bulk density measurements and effective porosity at water potential

h=� 0.05 kPa.

Fig. 6. Pore classification according to size and shape for the three fields: (a) continuous maize, (b) pasture phase

of rotation, (c) old pasture. Means of the 16 images (4 images per level� 4 levels).

M. Lamande et al. / Catena 54 (2003) 637–649646

M. Lamande et al. / Catena 54 (2003) 637–649 647

Effective pore size distribution increases sharply from size 1 to size 4 in the three

treatments (0.018 mm2 to more than 1.77 mm2, corresponding to efficient pores size at the

water potentials used for infiltration measurement) (Fig. 6). This increase was mainly due to

packing voids. Packing voids decrease in the old pasture compared with the rotation and

partly transformed into cracks due to cattle trampling (Fig. 6). There are more tubular voids

in the old pasture and in the rotation than in maize. Tubular voids are almost negligible in the

maize, where biological activity (roots and fauna) is lower. Although very few anecic

earthworms are present in the maize, they are responsible for most of the tubular voids larger

than 2mm in horizontal 2D sections. Such anecic species live in permanent vertical burrows.

The distribution of effective pores coincides well with the hydraulic conductivity curve.

Packing voids seem to have a major role in water flow at conditions near saturation (size

classes 3 and 4). At lower potentials, water flow is controlled by tubular voids and cracks.

The effective porosity at water potential h =� 0.05 kPa was two times less in maize than in

the old pasture, while the hydraulic conductivity was similar. In maize, most of the water

flow occurs through the pores of equivalent diameter smaller than 200 Am. These pores are

not all quantified by image analysis (42 Am pixel� 1 resolution) but are taken into account in

infiltration measurements at water potential h =� 1.5 kPa. These pores correspond to the

porosity observed within earthworm casts, but theymay correspond also to porosity between

enchytraeid casts (Dawod and FitzPatrick, 1993). In cultivated soil at low level of earthworm

densities, the enchytraeids can play an important role in creating a stable soil structure and

porosity (Topoliantz et al., 2000). But the high pH value in maize (6,2) is not favourable to

enchytraeid development (Gorny, 1984).

4. Conclusion

The types of agricultural management and earthworm community both induce changes

in the structural features and physical properties of soil. To propose sustainable agricultural

management systems, we need to improve our understanding of the processes controlling

these changes. In this study, we compare pore morphology, infiltration rate, and earthworm

community under three different agricultural managements. We show it is necessary to

consider the functional diversity of earthworms as well as their abundance. The packing

voids are important in controlling water flow and retention, especially when preferential

flow paths such as earthworm burrows or cracks are disconnected by tillage. The present

study provides a new methodology that may be used to assess the effects of agricultural

managements on soil structure and water movement. In particular, we consider the type of

earthworm community as a factor influencing the changes in soil physical properties.

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