Utilization of near infrared reflectance
Catena 81 (2010) 113–116
Contents lists available at ScienceDirect
Catena
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c a t e n a
Utilization of near infrared reflectance spectroscopy (NIRS) to quantify the impact of
earthworms on soil and carbon erosion in steep slope ecosystem
A study case in Northern Vietnam
Pascal Jouquet a,b,⁎, Thierry Henry-des-Tureaux a,b, Jérôme Mathieu b,c, Thuy Doan Thu a,
Toan Tran Duc a, Didier Orange a,b
a
b
c
SFRI – IWMI – IRD, Dong Ngac, Tu Liem, Hanoï, Vietnam
IRD, UMR 211 Bioemco, Equipe Transferts, Centre IRD Bondy, 32 Avenue H. Varagnat, 93143 Bondy Cedex, France
UPMC – UMR 7618 Bioemco, NCEAS, 735 State Street, Santa Barbara, 93101-5504 California, USA
a r t i c l e
i n f o
Article history:
Received 10 September 2009
Received in revised form 18 January 2010
Accepted 28 January 2010
Keywords:
Soil erosion
Carbon loss
Earthworm activity
Near Infrared Reflectance Spectroscopy
Vietnam
Amynthas khami
a b s t r a c t
This work focuses on a new approach to quantify the effects of above-ground earthworm's activity on soil
erosion in steep slope ecosystems such as in Northern Vietnam. In these areas and in many others in the world,
soil erosion becomes a major issue while the factors that determine it are still misunderstood. Earthworm's
activity is believed to influence soil erosion rate, but we are still unable to precisely quantify their contribution
to soil erosion. In this study, we used Near Infrared Reflectance Spectroscopy (NIRS) to quantify the proportion
of soil aggregate in eroded soil coming from earthworm activity. This was done by generating NIRS signatures
corresponding to different soil surface aggregates (above-ground soil casts produced by earthworms vs.
surrounding topsoil).
In order to test the proposed approach, we compared the NIRS-signature of eroded soil sediments to those of
earthworms' casts and of the surrounding soils. Our results strongly supported that NIRS spectra might be used
as “fingerprints” to identify the origin of soil aggregates. Although earthworms are generally assumed to play a
favorable role in promoting soil fertility and ecosystem services, this method shows that cast aggregates
constitute about 36 and 77% of sediments in two tropical plantations, Paspalum atratum and Panicum maximum
plantations, respectively. In light with these results, we estimated that earthworms led to an annual loss of 3.3
and 15.8 kg of carbon ha− 1 yr− 1, respectively in P. atratum and P. maximum agroecosystems.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Darwin published “The formation of vegetable Mould through the
action of worms, with some observations of their habits” (Darwin,
1881) 128 years ago. Although less known than his scientific masterwork “on the origin of species” (Darwin, 1859), this scientific book
was considered as a “best-seller” at its time. This book might be
considered as the first scientific essay stressing the importance of
earthworm activity on soil dynamic, and especially the topsoil
formation (i.e., the vegetable mould). With this work, Darwin also
highlighted the influence that earthworms might have on landscape
evolution through their effects on erosion–sedimentation cycle via
the creation of surface casts which might be eroded by wind and/or
⁎ Corresponding author. SFRI – IWMI – IRD, Dong Ngac, Tu Liem, Hanoï, Vietnam.
E-mail address: pascal.jouquet@ird.fr (P. Jouquet).
0341-8162/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catena.2010.01.010
water. Yet on the 200th anniversary of his birth, controversy still
surrounds exactly how earthworms affect soil erosion.
Soil erosion is a worldwide environmental and public health
problem leading to direct losses of soil fertility and other on-site and
off-site negative impacts such as dam siltation and biodiversity loss
(Pimentel, 2006). It is especially a problem in sloping lands of the
tropics which are characterized by rapid biogeochemical cycling.
When earthworms are abundant it is clear that they can significantly
affect soil erodibility and erosion through their burrowing activities
and especially the creation of vertical galleries that enhance water
infiltration (Blanchart et al., 2004; Shipitalo and Le Bayon, 2004).
Earthworms also produce deposit stable above-ground casts that
increase soil surface roughness and then can both decrease runoff
water velocity, and increase soil detachment and erosion (Blanchart
et al., 2004; Shipitalo and Le Bayon, 2004; Jouquet et al., 2008a). The
net influence of earthworms on soil erosion and nutrient losses,
however, remains unclear and is probably site specific (e.g., dependent
on the earthworm species, soil properties and land slope).
114
P. Jouquet et al. / Catena 81 (2010) 113–116
An important obstacle for quantifying the influence of earthworms
on soil erosion is our limited ability to differentiate the old earthworm
casts and the soil matrix. When freshly emitted, earthworm casts
are usually easily discriminated from the surrounding soil aggregates
based on their rounded shapes compared to the angular to subangular aspect of soil aggregates that has not been processed by
earthworms for a long time. However, it remains impossible to
visually distinguish the two types of soil once they have become
fragmented (Jouquet et al., 2009). As a consequence, we are still
unable to quantify the role of earthworms on soil erosion and
resulting carbon losses. In order to overcome this problem, several
analytical approaches have been compared for identifying the origin
of soil aggregates and the Near Infrared Reflectance Spectroscopy
(NIRS) has emerged as a promising analytical tool to determine the
origin of soil macroaggregates (Hedde et al., 2005; Velasquez et al.,
2007; Jouquet et al., 2008c). Recently, Jouquet et al. (2009) also
showed that NIRS allowed clear discrimination of casts from their
surrounding soil regardless of size or appearance. This present study
aimed to answer essential questions raised from Darwin's study
(Darwin, 1881) using NIRS analyses: How much do earthworms
contribute to soil erosion? And what is the consequence in terms of
carbon loss?
2. Materials and methods
2.1. Study site
Our study was carried out in the experimental catchment (46 ha)
of the MSEC (Management Soil Erosion Consortium of the International Water Management Institute, IWMI) project (Valentin et al.,
2008). This study site is located in Dong Cao village, in north-eastern
Vietnam, approximately 50 km south-west of Hanoi (20° 57′N, 105°
29′E). The annual rainfall ranges from 1500 to 1800 mm, of which 8085% occurs from April to October. The air humidity is always high,
between 75 and 100%. The mean daily temperature varies from 15 °C
to 25 °C. The soil is an Acrisol (WRB, 2006) with more than 50%
clay, mainly kaolinite, with a low pH of around 5, and a low CEC
(b10 cmol kg− 1) (Jouquet et al., 2008a,b; Podwojewski et al., 2008).
Experiments were carried out in two fodder plantations: Paspalum
atratum and Panicum maximum, growing in steep plots with a 45%
slope. Cattle's grazing was excluded in the study site.
The most abundant earthworm species found at the study site is
Amynthas khami, which is considered an anecic earthworm sensu
Bouché (1977). A. khami varies in size and adults can reach up to more
than 50 cm in length. It builds casts that are first deposited on the soil
surface then enlarged by days of deposition of globular cast-units
at the top edge of the structure (Fig. 1). Casts are globular and
characterized by a very high soil structural stability (Jouquet et al.,
2008b). These biogenic structures can reach 20 cm in height but are
often slowly broken, probably by livestock trampling, human traffic
and raindrop impacts, and then release free water stable aggregates
on the soil surface.
2.2. Measurement of soil erosion and carbon loss
Soil detachment was assessed from 1-m² plots (n = 3 in each
fodder plantation) under natural rainfall, as described by Janeau et al.
(2003). Plots were bordered by rigid metal frames inserted to a depth
of 0.10 m. Runoff water and sediments were collected after each
rainfall event, from May to October 2008, in a collector at the outlet
each plot. Sediment loss was measured through the sediment weight
after filtration from runoff water and oven-drying at 105 °C. This
sediment weight is assumed to represent the quantity of soil lost
during the rainfall event on 1-m² plots.
The organic carbon (C) was determined by the dry combustion
method using a CHN elemental-analyser (CHN NA 1500, Carlo Erba)
Fig. 1. Casts produced by Amynthas khami at the base of Panicum maximum plants. New
fecal aggregates are deposited one on top of the other [photo, P. Jouquet, 2008].
on each soil sample after NIRS analyses. Analytical precision was
±0.1 mg for C.
2.3. Soil sampling and preparation
Soil aggregates were collected from May to October 2008, which
corresponds to the rainy season in northern Vietnam, in the two
fodder plantations. Soil aggregates were differentiated according
to their origin: (i) physicogenic: soil aggregates without obvious
visible biological activity collected by scraping the soil surface, and
(ii) biogenic aggregates: above-ground earthworm casts (Bullock
et al., 1985; Pulleman et al., 2005). Biogenic and physicogenic aggregates were mixed in order to generate samples which contained an
increasing proportion of cast-originating soil (0, 25, 50, 75 and 100% of
cast soil, n = 9 for 0 and 100% and n = 3 for the other classes).
2.4. NIRS analysis
Near Infrared Reflectance Spectroscopy (NIRS) analysis was used
to characterize the physicochemical signature of soil aggregates and
sediments (Cecillon et al., 2009). Soil aggregates and sediments were
air-dried, crushed and sieved at 250 μm. Five grams of each of the
samples were scanned with a FossNIRSystems 5000 spectrophotometer (FossNIRSystems, Silver Spring, MD, USA) in the 1100–2500 nm
spectral range. The spectral data obtained were recorded as the
logarithm of the inverse of reflectance [log (1/R)]. They were analyzed
using WinISI III-version 1.50e software (Foss NIRSystems, Infrasoft
International). A 20-nm sampling interval was used for data analysis.
2.5. Statistical analyses
Principal component analysis (PCA) was done using the matrix
of 27 samples and 69 variables from NIRS wavelengths quantifying
P. Jouquet et al. / Catena 81 (2010) 113–116
the absorptions between 1100 to 2500 nm. Partial Least Squares
Regression (PLSR) was used for fitting NIRS absorbance to the
percentage of cast aggregates in the soil samples (0, 25, 50, 75 and
100%). All statistical calculations were carried out using R version
2.6.2 (R Development Core Team, 2008), packages ade4 and pls,
respectively for PCA and PLSR analyses.
Fig. 2. Results of the principal components analysis showing the eigenvalue diagram
(upleft) and the evolution of the absorbance in the NIR according to the concentration
in cast aggregates (0, 25, 50, 75 and 100% of casts) and that of sediments collected at the
outlet of the 1-m². Samples were collected in Paspalum atratum (A) and Panicum
maximum (B).
115
3. Results and discussion
Several studies emphasize the ability of NIRS analysis for the
prediction of many soil physical, chemical and biological properties
(Cecillon et al., 2009). In our study, this method was used to determine
the optical signature of soil aggregates and sediments. PCA performed
from the NIRS-data allowed casts to be clearly differentiated from the
surrounding soil (Fig. 2A,B). Biogenic (100% casts) and physicogenic
(0% casts) soil aggregates were clearly separated along the first axis
which explained 56 and 62% of the total variability, respectively for
soil samples collected under P. atratum and P. maximum. PLSR models
reached accurate prediction of the percentage of cast in the soil
samples (Fig. 3A,B), with cross-validation coefficients of determination above 0.90. The proportion of casts in the sediments was then
quantified from the PLSR models. Surprisingly, although A. khami is
considered to play a positive role in increasing water infiltration and
decreasing water runoff in this studied watershed area (Jouquet et al.,
2008a), our findings show that sediments contained a high proportion
of casts in P. atratum (36.42%, Standard Error, SE: 5.03) and were
almost entirely constituted of cast aggregates in P. maximum (85.06%,
SE: 18.71).
Fig. 3. Scatter plots of predicted vs. actual values for the percentage of cast weight in soil
samples. Abbreviation: Q², cross-validated R²; RMSECV, root mean squared error of
cross-validation. (A) In Paspalum atratum. (B) In Panicum maximum.
116
P. Jouquet et al. / Catena 81 (2010) 113–116
Table 1
Soil organic carbon content (mg C g− 1 soil) in casts and control soils in Paspalum
atratum and Panicum maximum plantations. Standard errors are in parentheses, n = 9.
Paspalum atratum
Panicum maximum
Control
Cast
3.22 (0.14)
3.14 (0.22)
3.44 (0.25)
3.20 (0.16)
Even if earthworms mostly play a favorable role in regards to soil
fertility, carbon sequestration and plant growth, this study highlights
that the influence of earthworms remains site specific. At our study site,
soil erosion was estimated to reach 2.89 Mg ha− 1 yr− 1 (SE: 1.38) in
P. atratum and 5.54 Mg ha− 1 yr− 1 (SE: 2.61) in P. maximum fields.
Considering an average of 3.33 mg C g− 1 soil in earthworm cast aggregates (Table 1), earthworms are estimated to lead to the loss of 3.34 and
15.85 kg of C ha− 1 yr− 1, respectively in P. atratum and P. maximum
fields. Introducing fodder crops on sloping lands is very effective against
runoff and soil erosion by locally reducing slope length and creating
steps that lower water velocity and favour sediment deposition (Karlen
et al., 2006). Thus, they are generally considered as interesting
alternatives to annual crop plantations, which are known to have
dramatic environmental consequences in sloping lands (Valentin et al.,
2008). In these ecosystems, earthworms appear to have both positive
and negative effects on ecosystem functioning. They probably improve
soil properties such as water infiltration and soil nutrient cycling, and
plants' growth like in many other regions of the world (Lavelle and
Spain, 2001) but they are also responsible for an important proportion
of soil and C loss via erosion. In order to optimise agro-ecosystem
functioning (to ensure plant growth, decrease soil erosion, favour C
sequestration in soil…), an understanding of the balance between the
positive and negative effects of earthworms is required.
Acknowledgements
We would like to thank Patrick Lavelle, Nicolas Bottinelli, Leigh
Gebbie, Didier Brunet and Pascal Podwojewski for constructive
discussions. We would like also to thank Mr Din Van Tuyen and Ms
Bui Thi Thu Hien from the National Institute of Animal Husbandry
(NIAH, Vietnam) who helped us with the NIRS analyses. This project was
financially supported by CNRS/INSU (VERAGREGAT research program
under the framework of the EC2CO program) and IRD (unit research
UMR 211 BIOEMCO) French institutes and the Management of Soil
Erosion Consortium (MSEC) from the International Water Management
Institute (IWMI).
References
Blanchart, E., Albrecht, A., Brown, G., Decaens, T., Duboisset, A., Lavelle, P., Mariani, L.,
Roose, E., 2004. Effects of tropical endogeic earthworms on soil erosion. Agriculture,
Ecosystem and Environment 104, 303–315.
Bouché, M.B., 1977. Stratégies lombriciennes. Ecological Bulletin (Stockholm) 25, 122–132.
Bullock, P., Federoff, N., Jongerius, A., Stoops, G., Tursina, T., 1985. Handbook for Soil
Thin Section Description. Waine Research Publications, Albrighton, England.
Cecillon, L., Barthès, B.G., Gomez, C., Ertlen, D., Genot, V., Hedde, M., Stevens, A., Brun, J.J.,
2009. Assessment and monitoring of soil quality using near-infrared reflectance
spectroscopy (NIRS). European Journal of Soil Science 60, 770–784.
Darwin, C.R., 1859. On the Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life1st edition. John Murray,
London. 1st issue.
Darwin, C., 1881. The Formation of Vegetable Mould Through the Action of Worms with
Some Observations on Their Habits. John Murray, London.
Hedde, M., Lavelle, P., Joffre, R., Jimenez, J.J., Decäens, T., 2005. Specific functional
signature in soil macro-invertebrate biostructures. Functional Ecology 19, 785–793.
Janeau, J.L., Bricquet, J.P., Planchon, O., Valentin, C., 2003. Soil crusting and infiltration
on steep slopes in northern Thailand. European Journal of Soil Science 54, 543–553.
Jouquet, P., Podwojewski, P., Bottinelli, N., Mathieu, J., Ricoy, M., Orange, D., Tran Duc, T.,
Valentin, C., 2008a. Above-ground earthworm casts affect water runoff and soil
erosion in northern Vietnam. Catena 74, 13–21.
Jouquet, P., Bottinelli, N., Podwojewski, P., Hallaire, V., Tran Duc, T., 2008b. Chemical and
physical properties of earthworm casts a compared to bulk soil under a range of
different land-use systems in Vietnam. Geoderma 146, 231–238.
Jouquet, P., Hartmann, C., Chutinan, C., Hanboonsong, Y., Brunet, D., Montoroi, J.P.,
2008c. Different effects of earthworms and ants on soil properties of paddy fields in
North-East Thailand. Paddy Water Environment 6, 381–386.
Jouquet, P., Zangerlé, A., Rumpel, C., Brunet, D., Bottinelli, N., Tran Duc, T., 2009. Relevance
of the biogenic and physicogenic classification. A comparison of approaches to
discriminate the origin of soil aggregates. European Journal of Soil Science 60, 117–
1125.
Karlen, D.L., Lemunyon, J.L., Singer, J.W., 2006. Forages for Conservation and Improved
Soil Quality. In: Barnes, R.F., Nelson, C.J., Moore, K.F., Collins, M. (Eds.), Sixth Edition
of Forages, Volume II The Science of Grassland Agriculture. Blackwell Publishing,
Inc, pp. 149–166. IA.
Lavelle, P., Spain, A.V., 2001. Soil Ecology. Dordrecht, Netherlands, Kluwer Academic
Publishers. 654 pp.
Pimentel, D., 2006. Soil erosion: a food and environmental threat. Environment, Development
and Sustainability 8, 119–137.
Podwojewski, P., Orange, D., Jouquet, P., Valentin, C., Nguyen Van, T., Janeau, J.L., Tran
Duc, T., 2008. Land-use impacts on surface runoff and soil detachment within
agricultural sloping lands in Northern Vietnam. Catena 74, 109–118.
Pulleman, M.M., Six, J., Uyl, A., Marinissen, J.C.Y., Jongmans, A.G., 2005. Earthworms and
management affect organic matter incorporation and microaggregate formation in
agricultural soils. Applied Soil Ecology 29, 1–5.
R Development Core Team, 2008. R: a language and environment for statistical
computing. R Foundation for Statistical Computing, Vienna, Austria3-900051-07-0.
Accessed at www.R-project.org.
Shipitalo, M.J., Le Bayon, R.C., 2004. Quantifying the effects of earthworms on soil
aggregation and porosity, In: Edwards, C.A. (Ed.), Earthworm Ecology, 2nd ed. CRC
Press, Boca raton, London, New York, Washington, pp. 183–200.
Valentin, C., Agus, F., Alamban, R., Boosaner, A., Bricquet, J.P., Chaplot, V., de Guzman, T.,
de Rouw, A., Janeau, J.L., Orange, D., Phachomphonh, K., Phai, Do. Duy, Podwojewski,
P., Ribolzi, O., Silvera, N., Subagyono, K., Thiébaux, J.P., Tran, Duc T., Vadari, T., 2008.
Runoff and sediment losses from 27 upland catchments in Southeast Asia: impact of
rapid land use changes and conservation practices. Agriculture Ecosystem and
Environment 128, 225–238.
Velasquez, E., Pelosi, C., Brunet, D., Grimaldi, M., Martins, M., Rendeiro, A.C., Barrios, E.,
Lavelle, P., 2007. This ped is my ped: visual separation and near infrared spectra
allow determination of the origins of soil macroaggregates. Pedobiologia 51, 75–87.
WRB,: World Reference Base for Soil Resources, 2006. World Soil Resources Reports,
n°103. FAO, Rome, 145 pp.
Contents lists available at ScienceDirect
Catena
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c a t e n a
Utilization of near infrared reflectance spectroscopy (NIRS) to quantify the impact of
earthworms on soil and carbon erosion in steep slope ecosystem
A study case in Northern Vietnam
Pascal Jouquet a,b,⁎, Thierry Henry-des-Tureaux a,b, Jérôme Mathieu b,c, Thuy Doan Thu a,
Toan Tran Duc a, Didier Orange a,b
a
b
c
SFRI – IWMI – IRD, Dong Ngac, Tu Liem, Hanoï, Vietnam
IRD, UMR 211 Bioemco, Equipe Transferts, Centre IRD Bondy, 32 Avenue H. Varagnat, 93143 Bondy Cedex, France
UPMC – UMR 7618 Bioemco, NCEAS, 735 State Street, Santa Barbara, 93101-5504 California, USA
a r t i c l e
i n f o
Article history:
Received 10 September 2009
Received in revised form 18 January 2010
Accepted 28 January 2010
Keywords:
Soil erosion
Carbon loss
Earthworm activity
Near Infrared Reflectance Spectroscopy
Vietnam
Amynthas khami
a b s t r a c t
This work focuses on a new approach to quantify the effects of above-ground earthworm's activity on soil
erosion in steep slope ecosystems such as in Northern Vietnam. In these areas and in many others in the world,
soil erosion becomes a major issue while the factors that determine it are still misunderstood. Earthworm's
activity is believed to influence soil erosion rate, but we are still unable to precisely quantify their contribution
to soil erosion. In this study, we used Near Infrared Reflectance Spectroscopy (NIRS) to quantify the proportion
of soil aggregate in eroded soil coming from earthworm activity. This was done by generating NIRS signatures
corresponding to different soil surface aggregates (above-ground soil casts produced by earthworms vs.
surrounding topsoil).
In order to test the proposed approach, we compared the NIRS-signature of eroded soil sediments to those of
earthworms' casts and of the surrounding soils. Our results strongly supported that NIRS spectra might be used
as “fingerprints” to identify the origin of soil aggregates. Although earthworms are generally assumed to play a
favorable role in promoting soil fertility and ecosystem services, this method shows that cast aggregates
constitute about 36 and 77% of sediments in two tropical plantations, Paspalum atratum and Panicum maximum
plantations, respectively. In light with these results, we estimated that earthworms led to an annual loss of 3.3
and 15.8 kg of carbon ha− 1 yr− 1, respectively in P. atratum and P. maximum agroecosystems.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Darwin published “The formation of vegetable Mould through the
action of worms, with some observations of their habits” (Darwin,
1881) 128 years ago. Although less known than his scientific masterwork “on the origin of species” (Darwin, 1859), this scientific book
was considered as a “best-seller” at its time. This book might be
considered as the first scientific essay stressing the importance of
earthworm activity on soil dynamic, and especially the topsoil
formation (i.e., the vegetable mould). With this work, Darwin also
highlighted the influence that earthworms might have on landscape
evolution through their effects on erosion–sedimentation cycle via
the creation of surface casts which might be eroded by wind and/or
⁎ Corresponding author. SFRI – IWMI – IRD, Dong Ngac, Tu Liem, Hanoï, Vietnam.
E-mail address: pascal.jouquet@ird.fr (P. Jouquet).
0341-8162/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catena.2010.01.010
water. Yet on the 200th anniversary of his birth, controversy still
surrounds exactly how earthworms affect soil erosion.
Soil erosion is a worldwide environmental and public health
problem leading to direct losses of soil fertility and other on-site and
off-site negative impacts such as dam siltation and biodiversity loss
(Pimentel, 2006). It is especially a problem in sloping lands of the
tropics which are characterized by rapid biogeochemical cycling.
When earthworms are abundant it is clear that they can significantly
affect soil erodibility and erosion through their burrowing activities
and especially the creation of vertical galleries that enhance water
infiltration (Blanchart et al., 2004; Shipitalo and Le Bayon, 2004).
Earthworms also produce deposit stable above-ground casts that
increase soil surface roughness and then can both decrease runoff
water velocity, and increase soil detachment and erosion (Blanchart
et al., 2004; Shipitalo and Le Bayon, 2004; Jouquet et al., 2008a). The
net influence of earthworms on soil erosion and nutrient losses,
however, remains unclear and is probably site specific (e.g., dependent
on the earthworm species, soil properties and land slope).
114
P. Jouquet et al. / Catena 81 (2010) 113–116
An important obstacle for quantifying the influence of earthworms
on soil erosion is our limited ability to differentiate the old earthworm
casts and the soil matrix. When freshly emitted, earthworm casts
are usually easily discriminated from the surrounding soil aggregates
based on their rounded shapes compared to the angular to subangular aspect of soil aggregates that has not been processed by
earthworms for a long time. However, it remains impossible to
visually distinguish the two types of soil once they have become
fragmented (Jouquet et al., 2009). As a consequence, we are still
unable to quantify the role of earthworms on soil erosion and
resulting carbon losses. In order to overcome this problem, several
analytical approaches have been compared for identifying the origin
of soil aggregates and the Near Infrared Reflectance Spectroscopy
(NIRS) has emerged as a promising analytical tool to determine the
origin of soil macroaggregates (Hedde et al., 2005; Velasquez et al.,
2007; Jouquet et al., 2008c). Recently, Jouquet et al. (2009) also
showed that NIRS allowed clear discrimination of casts from their
surrounding soil regardless of size or appearance. This present study
aimed to answer essential questions raised from Darwin's study
(Darwin, 1881) using NIRS analyses: How much do earthworms
contribute to soil erosion? And what is the consequence in terms of
carbon loss?
2. Materials and methods
2.1. Study site
Our study was carried out in the experimental catchment (46 ha)
of the MSEC (Management Soil Erosion Consortium of the International Water Management Institute, IWMI) project (Valentin et al.,
2008). This study site is located in Dong Cao village, in north-eastern
Vietnam, approximately 50 km south-west of Hanoi (20° 57′N, 105°
29′E). The annual rainfall ranges from 1500 to 1800 mm, of which 8085% occurs from April to October. The air humidity is always high,
between 75 and 100%. The mean daily temperature varies from 15 °C
to 25 °C. The soil is an Acrisol (WRB, 2006) with more than 50%
clay, mainly kaolinite, with a low pH of around 5, and a low CEC
(b10 cmol kg− 1) (Jouquet et al., 2008a,b; Podwojewski et al., 2008).
Experiments were carried out in two fodder plantations: Paspalum
atratum and Panicum maximum, growing in steep plots with a 45%
slope. Cattle's grazing was excluded in the study site.
The most abundant earthworm species found at the study site is
Amynthas khami, which is considered an anecic earthworm sensu
Bouché (1977). A. khami varies in size and adults can reach up to more
than 50 cm in length. It builds casts that are first deposited on the soil
surface then enlarged by days of deposition of globular cast-units
at the top edge of the structure (Fig. 1). Casts are globular and
characterized by a very high soil structural stability (Jouquet et al.,
2008b). These biogenic structures can reach 20 cm in height but are
often slowly broken, probably by livestock trampling, human traffic
and raindrop impacts, and then release free water stable aggregates
on the soil surface.
2.2. Measurement of soil erosion and carbon loss
Soil detachment was assessed from 1-m² plots (n = 3 in each
fodder plantation) under natural rainfall, as described by Janeau et al.
(2003). Plots were bordered by rigid metal frames inserted to a depth
of 0.10 m. Runoff water and sediments were collected after each
rainfall event, from May to October 2008, in a collector at the outlet
each plot. Sediment loss was measured through the sediment weight
after filtration from runoff water and oven-drying at 105 °C. This
sediment weight is assumed to represent the quantity of soil lost
during the rainfall event on 1-m² plots.
The organic carbon (C) was determined by the dry combustion
method using a CHN elemental-analyser (CHN NA 1500, Carlo Erba)
Fig. 1. Casts produced by Amynthas khami at the base of Panicum maximum plants. New
fecal aggregates are deposited one on top of the other [photo, P. Jouquet, 2008].
on each soil sample after NIRS analyses. Analytical precision was
±0.1 mg for C.
2.3. Soil sampling and preparation
Soil aggregates were collected from May to October 2008, which
corresponds to the rainy season in northern Vietnam, in the two
fodder plantations. Soil aggregates were differentiated according
to their origin: (i) physicogenic: soil aggregates without obvious
visible biological activity collected by scraping the soil surface, and
(ii) biogenic aggregates: above-ground earthworm casts (Bullock
et al., 1985; Pulleman et al., 2005). Biogenic and physicogenic aggregates were mixed in order to generate samples which contained an
increasing proportion of cast-originating soil (0, 25, 50, 75 and 100% of
cast soil, n = 9 for 0 and 100% and n = 3 for the other classes).
2.4. NIRS analysis
Near Infrared Reflectance Spectroscopy (NIRS) analysis was used
to characterize the physicochemical signature of soil aggregates and
sediments (Cecillon et al., 2009). Soil aggregates and sediments were
air-dried, crushed and sieved at 250 μm. Five grams of each of the
samples were scanned with a FossNIRSystems 5000 spectrophotometer (FossNIRSystems, Silver Spring, MD, USA) in the 1100–2500 nm
spectral range. The spectral data obtained were recorded as the
logarithm of the inverse of reflectance [log (1/R)]. They were analyzed
using WinISI III-version 1.50e software (Foss NIRSystems, Infrasoft
International). A 20-nm sampling interval was used for data analysis.
2.5. Statistical analyses
Principal component analysis (PCA) was done using the matrix
of 27 samples and 69 variables from NIRS wavelengths quantifying
P. Jouquet et al. / Catena 81 (2010) 113–116
the absorptions between 1100 to 2500 nm. Partial Least Squares
Regression (PLSR) was used for fitting NIRS absorbance to the
percentage of cast aggregates in the soil samples (0, 25, 50, 75 and
100%). All statistical calculations were carried out using R version
2.6.2 (R Development Core Team, 2008), packages ade4 and pls,
respectively for PCA and PLSR analyses.
Fig. 2. Results of the principal components analysis showing the eigenvalue diagram
(upleft) and the evolution of the absorbance in the NIR according to the concentration
in cast aggregates (0, 25, 50, 75 and 100% of casts) and that of sediments collected at the
outlet of the 1-m². Samples were collected in Paspalum atratum (A) and Panicum
maximum (B).
115
3. Results and discussion
Several studies emphasize the ability of NIRS analysis for the
prediction of many soil physical, chemical and biological properties
(Cecillon et al., 2009). In our study, this method was used to determine
the optical signature of soil aggregates and sediments. PCA performed
from the NIRS-data allowed casts to be clearly differentiated from the
surrounding soil (Fig. 2A,B). Biogenic (100% casts) and physicogenic
(0% casts) soil aggregates were clearly separated along the first axis
which explained 56 and 62% of the total variability, respectively for
soil samples collected under P. atratum and P. maximum. PLSR models
reached accurate prediction of the percentage of cast in the soil
samples (Fig. 3A,B), with cross-validation coefficients of determination above 0.90. The proportion of casts in the sediments was then
quantified from the PLSR models. Surprisingly, although A. khami is
considered to play a positive role in increasing water infiltration and
decreasing water runoff in this studied watershed area (Jouquet et al.,
2008a), our findings show that sediments contained a high proportion
of casts in P. atratum (36.42%, Standard Error, SE: 5.03) and were
almost entirely constituted of cast aggregates in P. maximum (85.06%,
SE: 18.71).
Fig. 3. Scatter plots of predicted vs. actual values for the percentage of cast weight in soil
samples. Abbreviation: Q², cross-validated R²; RMSECV, root mean squared error of
cross-validation. (A) In Paspalum atratum. (B) In Panicum maximum.
116
P. Jouquet et al. / Catena 81 (2010) 113–116
Table 1
Soil organic carbon content (mg C g− 1 soil) in casts and control soils in Paspalum
atratum and Panicum maximum plantations. Standard errors are in parentheses, n = 9.
Paspalum atratum
Panicum maximum
Control
Cast
3.22 (0.14)
3.14 (0.22)
3.44 (0.25)
3.20 (0.16)
Even if earthworms mostly play a favorable role in regards to soil
fertility, carbon sequestration and plant growth, this study highlights
that the influence of earthworms remains site specific. At our study site,
soil erosion was estimated to reach 2.89 Mg ha− 1 yr− 1 (SE: 1.38) in
P. atratum and 5.54 Mg ha− 1 yr− 1 (SE: 2.61) in P. maximum fields.
Considering an average of 3.33 mg C g− 1 soil in earthworm cast aggregates (Table 1), earthworms are estimated to lead to the loss of 3.34 and
15.85 kg of C ha− 1 yr− 1, respectively in P. atratum and P. maximum
fields. Introducing fodder crops on sloping lands is very effective against
runoff and soil erosion by locally reducing slope length and creating
steps that lower water velocity and favour sediment deposition (Karlen
et al., 2006). Thus, they are generally considered as interesting
alternatives to annual crop plantations, which are known to have
dramatic environmental consequences in sloping lands (Valentin et al.,
2008). In these ecosystems, earthworms appear to have both positive
and negative effects on ecosystem functioning. They probably improve
soil properties such as water infiltration and soil nutrient cycling, and
plants' growth like in many other regions of the world (Lavelle and
Spain, 2001) but they are also responsible for an important proportion
of soil and C loss via erosion. In order to optimise agro-ecosystem
functioning (to ensure plant growth, decrease soil erosion, favour C
sequestration in soil…), an understanding of the balance between the
positive and negative effects of earthworms is required.
Acknowledgements
We would like to thank Patrick Lavelle, Nicolas Bottinelli, Leigh
Gebbie, Didier Brunet and Pascal Podwojewski for constructive
discussions. We would like also to thank Mr Din Van Tuyen and Ms
Bui Thi Thu Hien from the National Institute of Animal Husbandry
(NIAH, Vietnam) who helped us with the NIRS analyses. This project was
financially supported by CNRS/INSU (VERAGREGAT research program
under the framework of the EC2CO program) and IRD (unit research
UMR 211 BIOEMCO) French institutes and the Management of Soil
Erosion Consortium (MSEC) from the International Water Management
Institute (IWMI).
References
Blanchart, E., Albrecht, A., Brown, G., Decaens, T., Duboisset, A., Lavelle, P., Mariani, L.,
Roose, E., 2004. Effects of tropical endogeic earthworms on soil erosion. Agriculture,
Ecosystem and Environment 104, 303–315.
Bouché, M.B., 1977. Stratégies lombriciennes. Ecological Bulletin (Stockholm) 25, 122–132.
Bullock, P., Federoff, N., Jongerius, A., Stoops, G., Tursina, T., 1985. Handbook for Soil
Thin Section Description. Waine Research Publications, Albrighton, England.
Cecillon, L., Barthès, B.G., Gomez, C., Ertlen, D., Genot, V., Hedde, M., Stevens, A., Brun, J.J.,
2009. Assessment and monitoring of soil quality using near-infrared reflectance
spectroscopy (NIRS). European Journal of Soil Science 60, 770–784.
Darwin, C.R., 1859. On the Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life1st edition. John Murray,
London. 1st issue.
Darwin, C., 1881. The Formation of Vegetable Mould Through the Action of Worms with
Some Observations on Their Habits. John Murray, London.
Hedde, M., Lavelle, P., Joffre, R., Jimenez, J.J., Decäens, T., 2005. Specific functional
signature in soil macro-invertebrate biostructures. Functional Ecology 19, 785–793.
Janeau, J.L., Bricquet, J.P., Planchon, O., Valentin, C., 2003. Soil crusting and infiltration
on steep slopes in northern Thailand. European Journal of Soil Science 54, 543–553.
Jouquet, P., Podwojewski, P., Bottinelli, N., Mathieu, J., Ricoy, M., Orange, D., Tran Duc, T.,
Valentin, C., 2008a. Above-ground earthworm casts affect water runoff and soil
erosion in northern Vietnam. Catena 74, 13–21.
Jouquet, P., Bottinelli, N., Podwojewski, P., Hallaire, V., Tran Duc, T., 2008b. Chemical and
physical properties of earthworm casts a compared to bulk soil under a range of
different land-use systems in Vietnam. Geoderma 146, 231–238.
Jouquet, P., Hartmann, C., Chutinan, C., Hanboonsong, Y., Brunet, D., Montoroi, J.P.,
2008c. Different effects of earthworms and ants on soil properties of paddy fields in
North-East Thailand. Paddy Water Environment 6, 381–386.
Jouquet, P., Zangerlé, A., Rumpel, C., Brunet, D., Bottinelli, N., Tran Duc, T., 2009. Relevance
of the biogenic and physicogenic classification. A comparison of approaches to
discriminate the origin of soil aggregates. European Journal of Soil Science 60, 117–
1125.
Karlen, D.L., Lemunyon, J.L., Singer, J.W., 2006. Forages for Conservation and Improved
Soil Quality. In: Barnes, R.F., Nelson, C.J., Moore, K.F., Collins, M. (Eds.), Sixth Edition
of Forages, Volume II The Science of Grassland Agriculture. Blackwell Publishing,
Inc, pp. 149–166. IA.
Lavelle, P., Spain, A.V., 2001. Soil Ecology. Dordrecht, Netherlands, Kluwer Academic
Publishers. 654 pp.
Pimentel, D., 2006. Soil erosion: a food and environmental threat. Environment, Development
and Sustainability 8, 119–137.
Podwojewski, P., Orange, D., Jouquet, P., Valentin, C., Nguyen Van, T., Janeau, J.L., Tran
Duc, T., 2008. Land-use impacts on surface runoff and soil detachment within
agricultural sloping lands in Northern Vietnam. Catena 74, 109–118.
Pulleman, M.M., Six, J., Uyl, A., Marinissen, J.C.Y., Jongmans, A.G., 2005. Earthworms and
management affect organic matter incorporation and microaggregate formation in
agricultural soils. Applied Soil Ecology 29, 1–5.
R Development Core Team, 2008. R: a language and environment for statistical
computing. R Foundation for Statistical Computing, Vienna, Austria3-900051-07-0.
Accessed at www.R-project.org.
Shipitalo, M.J., Le Bayon, R.C., 2004. Quantifying the effects of earthworms on soil
aggregation and porosity, In: Edwards, C.A. (Ed.), Earthworm Ecology, 2nd ed. CRC
Press, Boca raton, London, New York, Washington, pp. 183–200.
Valentin, C., Agus, F., Alamban, R., Boosaner, A., Bricquet, J.P., Chaplot, V., de Guzman, T.,
de Rouw, A., Janeau, J.L., Orange, D., Phachomphonh, K., Phai, Do. Duy, Podwojewski,
P., Ribolzi, O., Silvera, N., Subagyono, K., Thiébaux, J.P., Tran, Duc T., Vadari, T., 2008.
Runoff and sediment losses from 27 upland catchments in Southeast Asia: impact of
rapid land use changes and conservation practices. Agriculture Ecosystem and
Environment 128, 225–238.
Velasquez, E., Pelosi, C., Brunet, D., Grimaldi, M., Martins, M., Rendeiro, A.C., Barrios, E.,
Lavelle, P., 2007. This ped is my ped: visual separation and near infrared spectra
allow determination of the origins of soil macroaggregates. Pedobiologia 51, 75–87.
WRB,: World Reference Base for Soil Resources, 2006. World Soil Resources Reports,
n°103. FAO, Rome, 145 pp.