DSpace at VNU: Impact of fodder cover on runoff and soil erosion at plot scale in a cultivated catchment of North Vietnam

Geoderma 177–178 (2012) 8–17

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Geoderma
journal homepage: www.elsevier.com/locate/geoderma

Impact of fodder cover on runoff and soil erosion at plot scale in a cultivated
catchment of North Vietnam
Hai An Phan Ha a, b, Sylvain Huon b,⁎, Thierry Henry des Tureaux c, Didier Orange c, Pascal Jouquet c,
Christian Valentin c, Anneke De Rouw c, Toan Tran Duc d
a

Vietnam National University (VNU), Faculty of Chemistry, 19 Le Thanh Tong, Hanoi, Viet Nam
Université Pierre et Marie Curie (UMPC), UMR 7618 Bioemco, Case 120, 4 place Jussieu, 75 252 Paris Cedex 05, France
IRD, UMR 7618 Bioemco, 32 Avenue Henri Varagnat, 93143 Bondy Cedex, France
d
Soil and Fertilizer Research Institute (SFRI), Dong Ngac Tu Liem, Hanoi, Viet Nam
b
c

a r t i c l e

i n f o

Article history:
Received 21 May 2010
Received in revised form 19 January 2012
Accepted 23 January 2012
Available online 5 March 2012
Keywords:

Soil conservation
Paspalum atratum
Panicum maximum
Stylosanthes guianensis
Slope length
Plant cover

a b s t r a c t
In Vietnam soil erosion is a major environmental problem with respect to soil fertility, water quality and
downstream property damages and involves 40% of total land surface. Due to a continuous and persistent decrease of soil quality under annual crops, farmers gradually convert their fields to grazing lands and their
crops to fodder cultures or tree plantations. Experimental 1-m2 field plots with three replicates each were
monitored for two years (2006–2007) to evaluate the impact of three different fodder treatments (Paspalum
atratum, Panicum maximum and Stylosanthes guianensis) on runoff and soil detachment in a cultivated catchment of North Vietnam. These experiments were designed to monitor at local scale the protective effect of
vegetation cover against splash and rain-impacted erosion. The lowest runoffs (ca. 3.0–4.4%), sediment yields
(ca. 14–19 g m − 2 yr − 1) and soil organic carbon losses (ca. 0.7 g C m − 2 a− 1) were obtained for P. maximum
that provided the best soil protection with respect to the two other treatments. These values were low as
compared to cultivated crops (cassava and rainfed rice). Soil surface characteristics (mainly biological activity
and crusting) did apparently not play a key role, most likely because each plant cover provided, with its own
efficiency, protection against rainfall erosivity and rapid plant regrowth wiped out traces of flow detachment.
The extent of soil detachment and sediment export, mainly controlled by cut and carry operations of fodder
management, was reduced by increasing slope length from 1 to 5 m. The choice of dense fodders such as P.
maximum appears to be, in terms of improved livelihood and environment sustainability, an interesting
issue for uplands farmers.
© 2012 Elsevier B.V. All rights reserved.

1. Introduction
In South-East Asian regions runoff and soil erosion are significantly
related to agricultural land use in particular on sloping lands of headwater catchments (i.e., Sidle et al., 2006; Valentin et al., 2008). The amplitude of erosion seems to be more related to anthropogenic factors
such as land use change, deforestation, cultivation practice and crop
type than to climatic conditions (Chaplot et al., 2005; Craswell and

Niamskul, 1999). In Vietnam, a country covered at 75% by hills and
mountains, erosion involves 13 × 106 ha, that represents 40% of total
land surface (Vezina et al., 2006). A large part of the former rain forest
was lost between the 1970s and 1990s to expand cultivation of cassava, arrowroot, taro, maize or tree plantations (De Koninck, 1999;
Meyfroidt and Lambin, 2008; Sharma, 1992). Soil erosion involved
with cultivation affects the livelihood of farmers and thoroughly
⁎ Corresponding author. Tel.: + 33 1 44 27 72 82; fax: + 33 1 44 27 41 64.
E-mail addresses: (H.A. Phan Ha),
(S. Huon).
0016-7061/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.geoderma.2012.01.031

hinders the economic development of upland catchments (Bui, 2003;
Pimentel, 2006). Due to the continuous decrease of soil organic carbon
with soil erosion, farmers gradually tend to convert their fields formerly under annual crops, into grazing land, forage cultures or tree
plantations (Castella et al., 2006; Horne and Stür, 1997; Tran et al.,
2004). The introduction of fodders opens new perspectives in sustainable development as it responds to a political desire to integrate crops
and livestock in upland farming systems of South East Asian countries
(Clement and Amezaga, 2008; Orange et al., 2008).
Conversion of cultivated lands to forage is considered as a tool for
conservation and stabilization of soil resources (Karlen et al., 2006) as
well as for soil structure improvement and maintenance (i.e., Juo et
al., 1995; Stone and Buttery, 1989; Tisdall and Oades, 1979). Perennial
forages strengthen the soil structure and stability by reducing rainfall
kinetic energy, soil aggregates breakdown, splash and inter-rill erosion due to more efficient leaf cover whereas higher root density increases soil carbon storage capacity (Conant et al., 2001; Gebhart et
al., 1994; Lal, 2003; Reeder et al., 1998; Uri and Bloodworth, 2000).
Fodder cultivation is also effective for the reduction of runoff and


H.A. Phan Ha et al. / Geoderma 177–178 (2012) 8–17

rill erosion (Gilley et al., 2000; Rachman et al., 2008; Raffaelle et al.,
1997) by increasing surface roughness, lowering runoff velocity and
favoring infiltration and sediment deposition (Dabney et al., 1993;
Karlen et al., 2006). It is well established that soil physical properties
(Auzet et al., 1995) as well as surface characteristics such as crusting,
soil roughness and crop cover are major factors controlling runoff and
interrill erosion (Arnau-Rosalén et al., 2008; Durán-Zuazo and
Rodríguez-Plequezuelo, 2008; Le Bissonnais et al., 2005; Ribolzi et
al., 2011). Additional features particularly active in tropical environments, such as earthworm casts also decrease runoff (Bochet et al.,
1999; Jouquet et al., 2008; Podwojewski et al., 2008).
If the connections between soil surface characteristics, sediment
yield and runoff are well established (i.e., Janeau et al., 2003; Ribolzi
et al., 2011), the protective role of plant cover is not well constrained
at plot's scales where splash and rain-impacted flows are the dominant soil detachment processes (Bellanger et al., 2004; Chaplot and
Poesen, 2012; Wainwright et al., 2000). However, longer slope
lengths are also required to assess the impact of soil erosion at landscape's scale, mainly because additional processes such as runoff–
runon due to local variability of infiltration, rill and gullies erosion,
deposition along slopes as well as stream bank erosion control sediment transport and export across catchments (Chaplot et al., 2009;
Van Noordwijk et al., 2004; Wang et al., 2010). The main objective
of this study was to assess, within a small agricultural catchment in
North Vietnam, the impact of three different fodder types on runoff
and soil erosion and soil organic carbon erosion using experimental
field plots with two different slope lengths (1 m and 5 m). These experiments were designed to monitor at local scale the protective effect of plant type against splash and rain-impacted sediment
mobilization using 1 × 1 m microplots (splash and inter-rill erosion)
and to monitor with a slightly longer slope length (5 × 1 m microplots) the extent of flow detachment and sediment transport (incipient rill erosion). Because the comparison between the behavior of
fodders in terms of improved livelihood (i.e., biomass production for
cattle) and environment sustainability (i.e., soil protection) was the
major issue of this experimental study for uplands farmers, two
main questions have been addressed: 1) what fodder type among

the chosen species insured the best soil protection against splash
and rain-impacted erosion? and, 2) what was the local impact of
slope length on runoff and sediment yield?
2. Materials and methods
2.1. Site loca. 6).

Fig. 5. Precipitation (vertical bars) and cumulated runoff (top) and sediment yield
(bottom) for the three PM 1-m2 microplots in 2007. Dashed lines correspond to cutting
days. PM = Panicum maximum.

However a better management of the soil erosion risk by programming cutting operations during periods of low rainfall remains
difficult as the distribution of precipitation during the wet season
changes from year to year, i.e. as shown in this study for 2006 and
2007. Because of its tufted and dense structure (Fig. 2), PM acted as
a physical barrier that reduced runoff and improved water infiltration

Fig. 6. Plots of precipitation (vertical bars), cumulated runoff and sediment yield for PA,
PM and SG 1-m2 microplots in 2007. Open and closed squares refer to runoff and sediment
yield, respectively. Dashed lines correspond to cutting days. PA= Paspalum atratum,
PM= Panicum maximum, SG= Stylosanthes guianensis.


14

H.A. Phan Ha et al. / Geoderma 177–178 (2012) 8–17

by channeling rainwater via its root system. This fodder also provided
the best soil protection with respect to flow detachment and suspended particles transport as pictured by low sediment yields (ca.
14–19 g m − 2 a − 1, Table 2) and reported in other studies (Nyangito
et al., 2009; Rietkerk et al., 2000). Although its growth rate was equivalent, the distribution of PA sprouts (Fig. 2) had more limited influence

on runoff and soil detachment than PM. Accordingly interrill erosion
was responsible of higher sediment yields (ca. 100–250 g m − 2 a − 1,
Table 2). Lower plant height, leaf size and pedestal thickness for SG
provided even more limited shelter against raindrop impacts (Fig. 2).
With total sediment yields of ca. 70–120 g m− 2 a − 1 (Table 2) soil protection of SG was intermediate between the two others. This behavior
was supported by lower conductivities (K5, Table 1) in regard to those
measured in PA and PM plots, favoring runoff with respect to infiltration during rainfall events. The best soil protection was thus obtained
for PM with 5–20 times and 2–8 times lower yields than for PA and SG,
respectively.
The results of these experiments can be compared to those carried
out with 1-m 2 microplots in 2004–2005 in the Dong Cao watershed
(Podwojewski et al., 2008) and in 2003 in the Houay Pano watershed
in Laos (Chaplot and Poesen, 2012). Plot of annual mean runoff
against soil detachment highlights the impact of soil protection by
different plant covers and for different rainfall conditions but with
slightly steeper slopes than in our study (Fig. 7).
Mean annual runoff and sediment yield determined for PM are
consistent with those reported for Bracharia, another fodder that provides high plant cover of soil surface. The two other fodders, PA and
SG, with higher values fell in the range of young fallow and cassava
(for one of the two years) known to favor, due to weeding and to
its architecture, more soil erosion than other cultivated plants
(Putthacharoen et al., 1998; Valentin et al., 2008). However all three
fodders had much lower sediment yields than for rice, extensively
cultivated by slash and burn along steep slopes in Laos (Chaplot and
Poesen, 2012). As expected, tree covers provided a better soil protection than fodders because the canopy intercepts part of the raindrops
and reduces as much splash at ground level (Kozak et al., 2007), except for some species with large leaves (i.e. teak, Nair, 1993). In the
Dong Cao watershed Podwojewski et al. (2008) also showed a positive correlation between soil surface crusting and annual runoff
under cassava and Bracharia. Negative correlations between runoff
and earthworm cast surface cover were also reported by Jouquet et
al. (2008) for various soils under cassava, Bracharia and Eucalyptus.

In our study, soil surface properties were not significantly different
between PA and PM treatments although contrasted runoff and sediment yields were determined. For both treatments, soil surfaces were

mainly occupied by free soil aggregates and the percentages of soil
surface cover by crusts, casts and vegetation residues were rather
low. It is also likely that root density (0.9–1.1 g cm − 3, Table 1) did
not play a key role with respect to infiltration and sediment transport
in our study as shown elsewhere with experimental and modeling
approaches (De Baets and Poesen, 2010; Zhou and Shangguan,
2008). The overall experiments showed that runoff and soil detachment were linked both to rainfall intensity (with a threshold effect
for soil detachment with respect to runoff) and vegetation cover.
Fig. 3 shows that erosion was detachment limited due to a densification of vegetation cover. Conversely, cutting operations of the fodder
enhanced soil losses but rapid regrowth limited soil losses over the
cycle (e.g., Durán-Zuazo and Rodríguez-Plequezuelo, 2008). It is possible that temporary rills not observed during soil surface surveys
appeared after major erosive rainfall events but were filled up or hidden by plant growth. The impact of fodder cultivation on soil erosion
is also supported by decreasing annual sediment yields at the outlet
of the Dong Cao watershed, from 3.6 Mg ha− 1 a − 1 before 2002 to
0.1–0.3 Mg ha− 1 a − 1 after 2004, following the replacement of cassava
by fodder and acacia in the catchment (Orange et al., 2008).
Low TOC/TN ratios for suspended organic matter recovered at the
outlet of the plots indicated that most of soil detachment originated
from the breakdown of surface soil aggregates. These ratios rather
matched the composition of fine sized clay-bound organic matter
than coarse vegetation debris (Feller and Beare, 1998) and were consistent with high occurrences of free soil aggregates. These aggregates
tend in turn to be embedded in packing crust when soil is bare or insufficiently covered (Janeau et al., 2003; Podwojewski et al., 2008;
Ribolzi et al., 2011) but resist here to crusting due to the dense vegetation cover of fodder crops. With high TOC enrichment ratios (1.4–
1.7, Table 3) suspended organic matter was also enriched in TOC
with respect to soil average TOC contents as shown for the Houay
Pano catchment in Laos (e.g., Rumpel et al., 2006). However in contrast, particle size sorting by rain-impacted erosion and runoff was
more likely responsible for the TOC enrichment of detached sediments than residual “charcoal fragments”. Light organic matter

bound to clay size fractions with low TOC:TN ratios was preferentially
released during the breakdown of soil aggregates (i.e., Bellanger et al.,
2004; Legout et al., 2005; Palis et al., 1990; Wan and El-Swaify, 1997).
Because TOC releases were proportional to sediment yields (e.g.,
Gregorich et al., 1998), lower TOC deliveries were found in 2007 for
PM treatments (ca. 0.65 g C m − 2 a − 1, Table 3) than for the two
others (ca. 3.3 and 4.7 g C m − 2 a − 1, for PA and SG, respectively,
Table 3). All soil organic carbon losses were low when compared to
1-m 2 experiments under rainfed rice carried out in Laos (11.2–

Fig. 7. Mean annual runoff and soil detachment determined for 1-m2 microplots with different plant covers in the Dong Cao watershed. Data for cassava, Bracharia, fallow, Eucalyptus and trees from Podwojewski et al. (2008). The values for rainfed rice in the Houay Pano watershed in Laos are from Chaplot and Poesen (2012).


H.A. Phan Ha et al. / Geoderma 177–178 (2012) 8–17

30.8 g C m − 2 a − 1, Chaplot and Poesen, 2012). These results indicate
that the decline of soil fertility (in terms of soil organic carbon content) will be more limited with fodders and in particular with PM as
compared to the two other plants.
4.2. Local impact of slope length on runoff and sediment yield
Field observations carried out in the course of this study showed
that the extension of plant cover was similar at 1-m 2 and 5-m 2 plot
sizes. Therefore the observed deviations were mainly linked to slope
length. It is known that when transport distance increases infiltration
along slope is favored, reducing as much runoff (Le Bissonnais et al.,
1998; Poesen et al., 2003). Moreover, grass pedestal bands also contribute to a reduction of runoff velocity and to trapping or sorting of
detached sediments. The scale ratios of 5-m 2 to 1-m 2 plots runoffs
and soil detachment are reported in Fig. 8 together with precipitation
and plant cover change.
Because scale ratios were always lower than 1.0 for the two treatments, our results showed that runoff and sediment yield were both
reduced when slope length increased from 1 m to 5 m. This effect

was more pronounced for PA (in average 80% and 90% for runoff
and sediment yield, respectively, Table 2) than for PM (in average
30% for runoff and sediment yield, Table 2). The combined impact of
rainfall intensity and plant cover on scale ratios is difficult to assess
because only a limited number of surface cover surveys was performed (Fig. 8). However, the lower ratios were found for PA at the
end of the rainy season when vegetation growth and cover were
low and precipitation still important. These results are in agreement
with those displayed by Stomph et al. (2002) who observed a reduction of runoff on bare soil experiments with increasing 1.5, 3, and 6 m
slope lengths. Equivalent conclusions are drawn for splash erosion
and sediment yields reported by Chaplot and Poesen (2012) when
plot size increased from 1 to 2.5 m 2. However lower runoff and soil
detachment values for 1-m 2 than for 5-m 2 experiments were also observed, when vegetation cover was reduced and accompanied by the

15

extension of structural crusts and small temporary ponds along
slopes (Chaplot and Le Bissonnais, 2003). It was not the case in our
study because crusted areas always represented less than 10% of soil
surface within each plot favoring infiltration whereas plants acted
as physical barriers against splash and rain impacted soil detachment
and sediment transport.
5. Conclusion
A two years' monitoring of runoff and sediment yield from 1-m 2
microplots under different fodder cover, set up on moderate 15%
slopes of the Dong Cao catchment in North Vietnam, showed that P.
maximum provided the best soil protection with respect to splash
and rain-impacted soil detachment compared to P. atratum and S.
guianensis, the two other fodders tested. These differences are most
likely linked to the morphological characteristics of the plant species
in terms of soil cover. Because total soil organic carbon losses were

proportional to sediment yields, soil quality (in terms of total organic
carbon content) should also be better preserved with P. maximum.
This fodder also provided a better protection compared to other vegetation covers (young fallow, cassava and rainfed rice) tested with
comparable experiments. In this study, runoff and sediment yields
were mainly controlled by rainfall intensity and soil cover extension
with a threshold when plant covers exceeded 40% of plot surface.
Changes in soil surface characteristics (mainly biological activity and
soil surface crusting) did apparently not play a key role, most likely
because plant covers favored infiltration and reduced soil detachment
by rainfall. Maximum runoff and suspended sediments yields were
recorded when the cut and carry operations of fodder management
were followed by heavy rainfalls. Cutting of the fodder enhanced
soil losses but rapid regrowth limited soil losses over the cycle. The
increase from 1 to 5 m in slope length contributed to reduce runoff
and sediment yield by favoring sediment deposition and water infiltration, in particular for P. atratum that involved higher flow and
soil detachments than P. maximum. The integration of crops and

Fig. 8. Plots of precipitation and plant cover (upper graphs), runoff (middle graphs) and sediment yield (bottom graphs) 5-m2 to 1-m2 scale ratios in 2007 for PA and PM treatments. Vertical bars are for precipitation, runoff and sediment yield, open and black circles for plant cover. The dashed line refers to cutting operations. PA = Paspalum atratum,
PM = Panicum maximum.


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H.A. Phan Ha et al. / Geoderma 177–178 (2012) 8–17

livestock in upland farming systems should be better supported by
the use of dense fodders with high soil cover capacities.
Acknowledgments
This study is part of H.A. Phan Ha doctorate thesis (UMPC, Paris,
France) and was supported by a PhD grant from AUF (Agence Universitaire de la Francophonie). This work was also integrated in the

Management of Soil Erosion Consortium (MSEC) activity and the
DURAS program supported by the French Ministry of Foreign Affairs.
The authors are grateful to Dr P. Podwojewski (IRD), Nicolas Péchot
(UMR Bioemco), MSEC team members for their help during fieldwork and two anonymous reviewers for their comments of a former
version of this manuscript.
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