Plant and Soil (2005) 278:33–41
Springer 2005

DOI 10.1007/s11104-005-2379-0

Uprooting of vetiver uprooting resistance of vetiver grass

(Vetiveria zizanioides)

S.B. Mickovski1,3,4, L.P.H van Beek2 & F. Salin1

1
LRBB, Domaine de l’Hermitage, 69, rte d’Arcachon, 33612, Cestas cedex, France. 2IBED–Physical
Geography, University of Amsterdam, Nieuwe Achtergracht 166, NL 1018, WV Amsterdam, The Netherlands.
3
Current address: Civil Engineering Department, University of Dundee, Dundee DD1 4HR, Scotland, UK.
4
Corresponding author*

Received 7 October 2004. Accepted in revised form 15 February 2005

Key words: pullout resistance, root system morphology, roots, uprooting, vetiver, Vetiveria zizanioides

Abstract
Vetiver grass (Vetiveria zizanioides), also known as Chrysopogon zizanioides, is a graminaceous plant native
to tropical and subtropical India. The southern cultivar is sterile; it flowers but sets no seeds. It is a densely
tufted, perennial grass that is considered sterile outside its natural habitat. It grows 0.5–1.5 m high, stiff
stems in large clumps from a much branched root stock. The roots of vetiver grass are fibrous and reported
to reach depths up to 3 m thus being able to stabilize the soil and its use for this purpose is promoted by the
World Bank. Uprooting tests were carried out on vetiver grass in Spain in order to ascertain the resistance
the root system can provide when torrential runoffs and sediments are trying to uproot the plant.
Uprooting resistance of each plant was correlated to the shoot and root morphological characteristics. In
order to investigate any differences between root morphology of vetiver grass in its native habitat reported
in the literature, and the one planted in a sub-humid environment in Spain, excavation techniques were
used to show root distribution in the soil. Results show that vetiver grass possesses the root strength to
withstand torrential runoff. Planted in rows along the contours, it may act as a barrier to the movement of
both water and soil. However, the establishment of the vetiver lags behind the reported rates in its native
tropical environment due to adverse climatic conditions in the Mediterranean. This arrested development is
the main limitation to the use of vetiver in these environments although its root strength is more than
sufficient.

Introduction habitat. It is reported that vetiver grows 0.5–

1.5 m high, stiff stems in large clumps from a
Vetiver grass (Vetiveria zizanioides), also known much branched root stock (Erskine, 1992; Tru-
as Chrysopogon zizanioides, is a graminaceous ong, 1999). The use of vetiver grass hedges
plant native to tropical and subtropical India. against soil erosion increased following several
The southern cultivar is sterile; it flowers but sets key papers promoting vetiver grass planting as
no seeds. It is a densely tufted, perennial grass an effective and inexpensive erosion protection
that is considered sterile outside its natural measure and the publication of World BankÕs
manual in 1990 (for a review see Grimshaw,
*E-mail: s.b.mickovski @dundee.ac.uk 1989). Vetiver grass has wider applications due
34

to its unique morphological, physiological and even forestry (Meyer et al., 1995). Being a low
ecological characteristics that highlight its adapt- cost, natural and environmentally friendly method
ability to a wide range of environmental and soil for erosion control (Truong, 1999), the efficiency of
conditions. Currently used in more than 120 such contour hedges for soil and water conserva-
countries, vetiver grass applications include soil tion have been studied inter alia by Mishra et al.
and water conservation systems in agricultural (1997), and Hellin and Haig (2002).
environment, slope stabilization, rehabilitation of The versatility of vetiver has led to its appli-
mines, contaminated soil and saline land, as well cation outside its original zones of provenance.
as wastewater treatment (Truong and Loch, Currently it is successfully used in Africa, Asia,
2004). In addition, vetiver has added commercial Central and South America, southern Europe
value as its roots yield aromatic compounds that and Australia for stabilisation of steep batters of
are applied for domestic and cosmetic use. How- roads and railway embankments. For example,
ever, there is an argument that when the plant is in China in the last 5 years it has been used for
harvested for this purpose it may actually in- erosion and sediment control on more than
crease erodibility because the process loosens the 150 000 km of embankments (Truong and Loch,
soil (Smith 2000). 2004). In principle it would be possible to apply
The most impressive characteristic of the veti- it also in the European Mediterranean basin
ver grass is its root system that consists of although the soil and climatic conditions are
fibrous roots reported to reach depths up to 3 m harsh. Therefore, a modest field trial was set up
(Erskine 1992; Hellin and Haigh 2002). Such in the Alcoy region (Spain) to evaluate its perfor-
roots extend deep enough in the soil to provide mance within the framework of the EcoSlopes
the grip and anchorage needed to prevent surfi- project. Two plots on the riser of a cultivated
cial slip in the event of heavy prolonged rain- bench terrace were planted with vetiver and com-
storm (Hengchaovanich, 1999). This is the major pared to similar plots under different treatments:
reason why the use of vetiver grass for slope pro- Spanish cane (Arrundo donax), natural cover and
tection is promoted by the World Bank (1990) regrowth after complete stripping. In the area
and The Vetiver Network (Paul Truong personal bench terrace risers are left unarmored and are
communication, www.vetiver.org). subject to erosion and failure despite their cover
Planted in rows along slope contours, vetiver is with natural vegetation (mainly Brachypodium sp.)
able to quickly form a narrow but very dense Previous studies have reported on the growth
hedge. Reported to tolerate adverse growing condi- and the use of vetiver grass in its natural environ-
tions (e.g. winters with ground temperatures as low ment (Salam et al., 1993; Erskine, 1992; Hengcha-
as )14 C) (Truong, 1999), its stiff foliage is able to ovanich, 1999, Hellin and Haigh, 2002, Truong
block the passage of soil and debris in cases of tor- and Loch, 2004) but the properties of vetiver root
rential rains (Dalton et al., 1996; Hengchaovanich systems have not been investigated in European
1999), in the same time allowing the trapped sedi- context. In this study the mechanical properties of
ment to form a terrace upslope the hedge. Vetiver vetiver roots and their architecture are studied in
hedge is also able to slow down any surface runoff order to evaluate its capacity to withstand torren-
which, in turn, gives the rainfall a better chance of tial rain, ponding and sediment pressure (Hengcha-
percolating into the soil instead of running off ovanich, 1999; Cheng et al., 2003), as well as its
downslope and potentially creating rills and gullies, potential for application in eco-engineering.
in the same time contributing to the increased yield
of crops planted on the slope (Truong and Loch,
2004). If the sediment is not removed vetiver will Materials and methods
continue to grow up and adjust itself in tandem
with it on the newly formed terrace (Truong, 1999; Site characteristics
Hengchaovanich, 1999) which, rises as the soil
accumulates behind the hedges, thus converting Experimental plots of vetiver grass were planted
highly erodible slopes into relatively more stable on a site near Almudaina, Spain (X = 729275;
terraces able to support sustainable agriculture or Y = 4293850 and Z = 480 m on UTM 30s) in
 35

the spring of 2002. The vetiver was planted on the yielded a significant root reinforcement in the
riser of a bench terrace (Figure 1) which parts are order of 2.7 kPa (ranging between 2.1 and 3.7 kPa)
potentially endangered by runoff and soil slippage when the shearing resistance derived from the lab-
after intense rainfall events. The local gradients on oratory tests was subtracted.
the riser ranged between 35 and 60 while a nurs- The climate at the site is continental and Mediter-
ery was established on the bench terrace. Cuttings ranean. It shows a strong seasonality in rainfall and
of vetiver were planted in rows on the riser with a temperature. Most rainfall occurs in the late autumn
spacing of 10–15 cm. Rows were placed at the and winter and to a lesser extent in early spring. The
crest, bottom and middle of the riser that was total annual rainfall amounts to 700 mm per year
between 1.75 and 2.25 m high (Figure 1). The ver- but the rainfall has a strong inter-annual variabil-
tical interval of the vetiver rows was approxi- ity with annual totals varying between 350 and
mately 40 cm and their length 3 m each. 1050 mm. Moreover, rainfall is erratic and excep-
The soil on the site derives from Miocene tional events occur throughout the wet season: a
marl. The marl have a high clay content, predom- 24 h total of 284 mm and an event total of 553 mm
inantly smectites, but, due to a carbonate content have been recorded at Almudaina (van Beek, 2002).
of 60 per cent or more, most of the particles fall The mean annual temperature is 16 C ranging
in the silt fraction. The dry bulk of the topsoil between a mean monthly temperature of 24 C in
14.6 kN m)3 and the porosity 0.413 m3 m)3. The summer and 7 C in winter. In winter, the variabil-
soil shear strength was determined in the labora- ity in the temperature and its diurnal course are the
tory by means of strain-controlled, consolidated- largest with night frost occurring regularly between
drained direct shear tests on saturated samples end December and April (van Beek, 2002). The cli-
(BS 1377). Sample size was 60 · 60 · 20 mm and matic conditions at the site fall within the toler-
the applied strain rate 0.2 mm h)1. Because of the ances of vetiver (World Bank 1990) and the
dominance of the silt fraction, the soil has a high conditions over the growing period of the vetiver
angle of internal friction of 34 and a cohesion did not, on average, deviate from them. However,
of a mere 4.8 kPa (N = 30). These strengths the summer of 2001 was characterised by a pro-
have been confirmed by two in situ consolidated- longed drought that was terminated by a 90 mm
drained direct shear tests on pristine soil with storm in August. Drip irrigation was applied over
field capacity of saturation with dimensions of this period to enable the plants to establish them-
32 · 32 cm in plan and 20 cm high, for which no selves. February 2003 experienced exceptional
substantial root reinforcement was found. In snowfall which cover persisted for several days. In
comparison, four tests on soil rooted with vetiver April 2003, a 146 mm event in 24 h occurred which
induced some small slips on slopes and risers. At
the test site damage was restricted to one plot plan-
2.50
ted with vetiver through which the overland flow of
2.00 the overlying bench terrace was routed.
Since most erosion and slippage occur in the
1.50 late autumn, the investigation of the uprooting
Z (m)

resistance of vetiver grass was carried out in

1.00
November 2003 when the ambient moisture con-
0.50
ditions were close to field capacity (observed vol-
II
umetric moisture content ranged between 0.25
I
0.00 and 0.35 m3 m)3). At that time, the plants were
0.00 0.50 1.00 1.50 0.00 0.50 1.00 1.50 well established and have proliferated multiple
X (m) X (m) stems from the cuttings planted in 2002.

N S Preliminary tests
Figure 1. Profiles of the bench terrace risers along the north
and south margins of the vetiver plots I and II. The toe is lo-
In order to investigate the morphological character-
cated on the abandoned terrace, the horizontal crest on the istics of vetiver roots, four plants were completely
cultivated terrace. excavated using the block excavation method (van
36

Noordwijk et al., 2000) (Figure 2). These plants was assumed to represent the maximum rooting
were randomly selected from the plot, the soil sur- depth reached by the root itself.
face in a radius 30 cm around each plant was care-
fully cleared from the litter, and the soil block with Pullout resistance of vetiver grass
dimensions 0.3 m · 0.3 m and 0.5 m deep, contain-
ing their roots was manually excavated using a In order to investigate the pullout resistance of
spade. Excavated plants were then transferred to vetiver grass, 22 plants were randomly chosen
the in situ root washing facilities where, to mini- from the plantation and were used as a test sam-
mise root loss or damage, the plants together with ple. Before each pullout test the soil surface in a
their root systems were hand washed gently from radius 30 cm around the plant was carefully
the remains of the soil. Root systems were then cleared from the litter, exposing the stem base. A
sprinkled under a low water flow from a sprinkler. strong PVC rope (3 mm diameter) padded with
For separating the last remnants of soil on the soft tissue in order not to destroy the plant mate-
roots, it was necessary to soak the root systems in rial was then tied around the stem base of the
water basins and remove the soil by gently agitat- plant. The other end of the rope was connected
ing the sample after what the soil particles settled to a hand-held portable force gauge (Alluris
on the bottom of the basin, and the broken roots, FMI-100) for accurate measurement of uprooting
if any, floated on the surface. After the root sys- force. In order to mimic the forces applied to the
tems were thoroughly cleaned from the soil, they plant during runoff and sediment impoundment,
were placed on a paper mat and left to dry in the the pullout force was applied parallel to the slope
open air for half an hour and the maximum lateral in downslope direction. The force was applied
spread, and maximum rooting depth was measured manually with a rate of 10 mm min)1, recording
for each plant. All the primary lateral roots (Fig- the change in resistance along the way. The test
ure 2) were then carefully cut off from the plant was terminated once the resisting force dropped
base with scissors and the number of roots re- sharply and the plant was uprooted. Each plant
corded; root diameter at its base and near its tip was then carefully excavated, its roots washed
(di) was noted together with the length of the pri- from the soil remnants, and left on a paper mat
mary lateral root. The root cross sectional area to air dry for an hour.
(CSA) was calculated as an area of a circle with
radius di. Observing the strong geotropical ten- Plant morphological analysis
dency in the rooting pattern of vetiver, it was as-
sumed that all of the roots grow more or less Aboveground characteristics such as the plant
vertically downwards and the length of each root height and the average diameter at the base (Fig-

Figure 2. Morphological characteristics of a semi-excavated vetiver plant. Stiff stems grow upwards from the plant base, while pri-
mary lateral roots grow vertically down the soil. Primary lateral roots often branch into second/third, etc. order lateral roots.
 37

ure 2) were measured with measuring tape and specific plantation. Vetiver roots were shown to
callipers for each of the 22 uprooted plants. The originate from the base of the plant that had be-
number of stems growing from each stem base tween 8 and 10 stems on average (Figure 2). The
was also recorded. roots were numerous, pale yellow in colour and
Similarly as in the preliminary tests, the num- strongly geotropic. Having diameters at the base
ber of roots was recorded for each tested plant of the plant in the range between 0.3 and
and root system characteristics including the root 1.2 mm, the roots did not visibly taper and bran-
length, root system lateral spread and depth were ched to second and third order laterals of
measured with measuring tape (Böhm, 1979). decreasing diameters. None of the roots of the
The diameter of each root close to the stem base test plants had a lateral spread larger than
was measured with callipers. 0.25 m from the base of the plant, nor did the
Root systems were then separated from the depth of the excavated plants reach more than
stems using scalpel and sharp blade and placed 0.3 m. These parameters justified the chosen size
in an oven to dry over 24 h at 70 C, after which of the excavation block that provided that no
the root:shoot ratio of each uprooted plant was mechanical damage is incurred to the root systems.
calculated as the weight of dry root mass over
the dry weight of shoots (Böhm 1979). Plant morphology

Statistical analysis Morphological characteristics of investigated

vetiver plants are given in Table 1.
The results of the pullout tests were analysed
using the statistical package SPSS 10.0 (SPSS Inc, Pullout resistance
Chichago). A bivariate correlation analysis with
PearsonÕs coefficient was performed in order to The plant pullout method described in the Materi-
investigate any underlying relation between the als and methods section was suited to the objec-
uprooting force for each plant and the stem and tives of the investigation, and 19 out of 22 plants
root parameters measured during the investiga- could be uprooted using this method. The other
tion. A two-tailed test of significance was used to three plants were not uprooted because of the
identify the statistically significant correlations. rope failure or a snap through the plant stem.
The investigated vetiver plants did not show
any movement in the first several force/displace-
Results ment increments. With the increase of the force
applied, the plants started to rotate around a
Preliminary tests point close to the downslope end of the stem
base but under the soil surface, while the upslope
The tests to describe the overall morphological lateral roots were activated in tension and pro-
characteristics of vetiver grass worked well in this vided most of the resistance for the plant. In the

Table 1. Morphological characteristics of 22 investigated vetiver plants

Morphological characteristic Range Mean Standard error

Plant height [m] 0.74–1.08 0.925 0.035

Number of stems per plant 4–23 12.5 1.25
Plant diameter at base [m] 0.030–0.092 0.062 0.005
Maximum rooting depth [m] 0.110–0.275 0.219 0.018
Lateral root spread [m] 0.151–0.292 0.229 0.015
Root diameter at base[mm] 0.30–1.45 1.02 0.04
Dry root mass [g] 4.40–37.8 22.96 3.33
Dry shoot mass [g] 36.40–114.20 70.05 8.04
Root : shoot ratio 0.121–0.636 0.353 0.059
38

later stages, sporadic sounds of root snapping tics measured during the investigation is shown
were heard just before the plant was uprooted. in Table 2. Positive correlations were found be-
The plant pullout data showed that the plant tween the uprooting force and all other measured
resisting force increased with displacement until it parameters. However, only the correlation be-
reached the peak and then gradually started to tween the uprooting force and the plant height,
decrease as the roots started to break or slip from and between the uprooting force and lateral root
the soil. A typical pullout force–displacement spread was statistically significant (P < 0.05).
curve is shown on Figure 3. The slopes of the in- Figure 4 shows the dependency of the uproot-
crease in the force–displacement curve to the ing force on the plant height for the investigated
maximum load ranged from 0.29 to 9.33, or on plants. Taller plants show higher uprooting resis-
average 2.50 ± 0.36 (throughout this paper: tance and require higher pullout forces. Figure 5
mean ± SE). The maximum uprooting force ran- shows the relationship between the maximum
ged from 190 to 620 N, or on average uprooting force and the maximum lateral root
466.97 ± 31.25 N for the investigated plants. spread. Vetiver plants with root system that
The summary of the correlation analysis be- spread wider are able to resist uprooting better
tween the pullout resistance of the investigated than the plants with root systems that do not
plants and the other morphological characteris- reach far from the stem base.

180.0 D2

160.0

140.0

120.0
for c e [N]

100.0

80.0

60.0

40.0

20.0

0.0
0 50 100 150 200
displacement [mm]

Figure 3. Typical force–displacement curve for a pullout test on vetiver grass (sample D2). The uprooting force increased with dis-
placement to its peak value and then started to decrease due to root slippage or breakage.

Table 2. Correlation between the force necessary to uproot the plant and other morphological factors. Analysis based on n = 22
plants

Factor Correlation Significance Factor Correlation Significance

coefficient R2 coefficient R2

Plant height 0.598 0.019* Lateral root spread 0.517 0.048*

Number of stems 0.218 0.435 Root:shoot ratio 0.013 0.768
Plant diameter at base 0.130 0.644 Total CSA 0.236 0.397
Maximum rooting depth 0.201 0.472 Number of primary lateral roots 0.246 0.377
Average root length 0.378 0.165 Average root diameter 0.07 0.804

* significant at a 0.05 level.

 39

700

600
Maximum uprooting force [N]

500
y = 517.05x - 13.025
2
R = 0.598
400

300

200

100
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3
Plant height [m]

Figure 4. The relation between the maximum uprooting force and the plant height in the investigated vetiver grass (Vetiveria ziza-
nioides) plants. Taller plants resist uprooting forces better than shorter plants.

700
y = 1029.9x + 230.65
R2 = 0.517
600
Maximum uprooting force [N]

500

400

300

200

100
0.1 0.15 0.2 0.25 0.3 0.35 0.4
Lateral root spread [m]

Figure 5. The relation between the maximum uprooting force and the maximum lateral spread of root systems in investigated veti-
ver grass (Vetiveria zizanioides) plants. Plants with wider-spreading roots resist uprooting forces better than the plants with roots
systems that do not reach far from the stem base.

Discussion reached the values reported in earlier studies

(Salam et al., 1993, Mishra et al., 1997, Truong,
The morphology of the investigated plants did 1999). Possible causes for the ÔunderdevelopmentÕ
not confirm findings on the plant morphology of of the root system might be the soil type and the
vetiver grass in earlier studies. While the plant severity of climatic conditions over the growth
height reached almost the average reported for period (Paul Truong, personal communication).
the vetiver in its natural environment (Erskine, The topsoil is more structured and stores most
1992; Mishra et al., 1997; Hengchaovanich, 1999), water and nutrients available to the plant as the
neither the number nor the length of the roots underlying marl has a dense structure. Moreover,
40

during the short growth season under the Medi- plot withstood the rain and hardly any sediment
terranean climate the soil dries out and becomes was collected. The other vetiver plot, however, re-
more hard. While the local availability of water ceived most of the overland flow generated on the
due to drip irrigation also prevents root expan- overlying terrace and the riser failed as a slump
sion. Hence, the full root development, particu- with the slip plane at 30–40 cm, below the roots
larly in length and abundance observed in deeper, of the established vetiver.
drainable soils such as present in the Tropics have The investigation of Vetiver zizanioides plan-
not been achieved at the time of testing. ted for soil and water conservation on a bench
In Mediterranean environments therefore, terrace riser in Spain showed that soil depth, wa-
where soils are shallow and water is scarce over ter availability and to a lesser extent temperature,
the growing season, it would be more economical adversely influence root development in Mediter-
for plants to have the roots closer to the soil sur- ranean environments. Competition between na-
face. This would explain the biased investment in tive vegetation and vetiver highlights the poor
aboveground biomass of vetiver observed at this adaptation of the vetiver, and shows that the
site when water is available. This leads to suc- dense, deep and columnar root systems can not
cessful growth as long as irrigation is applied develop to the same extent as under its native
over the growing season but when dependent on tropical and subtropical environment (Figure 6).
natural rainfall that often falls outside the grow- Rooting depth is therefore the crucial factor for
ing season of vetiver, it loses the competition to the performance of vetiver on steep slopes in
endemic species that are better adapted. Mediterranean environments as the event in
Despite the poor root development, correla- April 2004 showed. Still, the uprooting force of
tion and regression analysis showed that taller the vetiver is high and sufficient to withstand the
plants will resist uprooting better than the short- water and sediment loads that would apply dur-
er ones, which was to be expected given the rela- ing torrential runoff for which it may remain of
tively constant root:shoot ratio. Plants that interest for soil and water conservation in Medi-
invest more in their above ground parts would terranean environments. However, because of its
also invest more in the proliferation of their root dependence on irrigation and advantageous soil
systems. Furthermore, the increase in uprooting conditions, vetiver seems more suitable for use in
resistance of plants that have root systems with engineering solutions when sites are carefully pre-
extensive lateral spread can be explained by the pared and maintained rather than as a species
fact that larger lateral spread also means larger amenable to low cost vegetative solutions.
anchoring length of the lateral roots. Bearing in
mind that the lateral roots, especially the upslope
ones (opposite of the side where the uprooting
force was applied) provided most of the resis- Acknowledgements
tance for the plant resisting in tension, it is clear
that larger anchorage length will provide better The work on this paper was funded under the
friction on the root–soil contact thus increasing framework of the ECOSLOPES project (EU,
the overall resistance of the root to pullout QLK5-2001-00289). Planting material was kindly
(Cheng et al., 2003). The differences in lateral provided by Mike Pease, the European and Medi-
root spread can be explained in terms of local terranean Vetiver Network Coordinator.
differences in water and nutrient availability.
Even the limited root systems of the investi-
gated vetiver grass proved able to withstand rela- References
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