Vol. 10(50), pp. 4584-4590, 10 December, 2015
Article Number: F8E66CB56337
Author(s) retain the copyright of this article
African Journal of Agricultural
Full Length Research Paper
Effect of stocking rate on biomass variation and lamb
performances for barley stubble in Tunisian semi arid
region and under conservation agriculture conditions
Nizar MOUJAHED1*, Sourour ABIDI2, Salah BEN YOUSSEF2, Cyrine DAREJ1, Mohamed
CHAKROUN2 and Hichem BEN SALEM3
1LRGAA, Institut National Agronomique de Tunisie, 43 AV. Ch. Nicolle, 1082, Tunis, Tunisia.
2Institute National de Recherche Agronomique de Tunisie, Rue HédiKarray 2049 Ariana, Tunisia.
3ICARDA Bldg No. 15, Khalid Abu Dalbouh St. Abdoun. P. O. Box 950764, Amman 11195, Jordan.
Received 17 September, 2015; Accepted 15 October, 2015
The integration of livestock in the practices of conservation agriculture (CA) was assessed in Tunisian
semi-arid conditions. Forty five Barbarine lambs (aged 220 ± 10 days, average body weight 20 ± 2.5 kg)
were used in a performance trial, carried out in the experimental station of INRAT. During the
experiment, lambs were grazing on a plot of barley stubble cultivated according to CA was divided into
6 fenced equal subplots and to each subplot was assigned a stocking rate of animals (15 and 30 lambs
per hectare, SR15 and SR30 respectively). The biomass of stubble and its botanical composition were
estimated 2 times, using quadrats sampling technique. Live weight was determined 3 times after the
start of the experiment (three 15-days successive periods) to calculate live weight gain (LWG) and daily
live weight gain (DLWG). The amount of biomass varied (P <0.05) from 2204 to 2067 kg DM / ha for SR15
plots and from 2404 to 1826.5 kg DM/ha for SR30 ones. This decrease was higher with SR30 (P<0.05).
Heads proportion decreased first, then leaves and finally stems. Biomass chemical composition
declined with sampling period. During the first grazing period, lambs assigned to both treatments lost
LW (P<0.001), mainly SR30 lambs as compared to SR15 (P<0.05, -610 and -110 g, respectively). The
same trend was observed in DLWG (P<0.05). In the second period, the two groups exhibited similar
LWG (about 2 kg) and DLWG (about 171 g/d). In the third period, SR15 lambs maintained their body
weight, while SR30 group lost (P<0.001) about 400 g comparatively to the second period. It was
concluded that under the studied feeding system, stubble grazing without supplementation allowed
Barbarine sheep to maintain body conditions.
Key words: Lambs, barley stubble, stocking rate, conservation agriculture.
In the Mediterranean Basin, livestock production and crop
farming have always co-existed. Cereal stubble and straw are important feed resources mainly during
summer season. A major concern for the crop/livestock
*Corresponding author. E-mail: email@example.com. Tel: +216 98225949.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution
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systems in the arid or semi-arid lands is the competition
for natural resources, especially for crop and other
biological residues. In Tunisia, sheep husbandry (about
3.84 million ewes; OEP, 2013) is still playing an important
role in rural population. Local sheep breeds are often
assigned to extensive management system (OEP, 2013)
including local feed resources such as crop residues (e.g.
cereal straws and stubbles: about 1.5 million and 500 000
tones/year). These practices might not be independent of
farming system evolution and development. In this
connection, conservation agriculture (CA) based mainly
on zero tillage is increasingly developed in the world
(Valipour, 2014) and more and more adopted in Tunisia
as it improves profitability of cereal and forage cropping.
The total area cropped under CA context, mainly no-
tillage increased from 27 ha 1999 to nearly 12 000 ha
(INGC, 2014). The benefits from CA include social and
economic advantages and combine production and
environment protection. It promotes minimal disturbance
of the soil (zero tillage), balanced application of chemical
inputs and careful management of crop residues
(Dumanski et al., 2006). In its compilation of definitions
on sustainable agriculture, Gold (2007) reported that CA
practices leave residue cover on the soil surface,
substantially reducing the effects of soil erosion from
wind and water. They also minimize nutrient loss,
decreased water storage capacity, crop damage, and
decreased farmability. The soil is left undisturbed from
harvest to planting except for nutrient amendment. The
same author reported that weed control is accomplished
primarily with herbicides, limited cultivation, and with
cover crops. The concept of CA is somewhat in line with
other sustainable practices such as the low-input
sustainable agriculture (LISA). Indeed, according to Parr
et al. (1990), LISA are systems how “seek to optimize the
management and use of internal production inputs (that
is, on-farm resources) and to minimize the use of
production inputs (that is, off-farm resources), such as
purchased fertilizers and pesticides, wherever and
whenever feasible and practicable, to lower production
costs, to avoid pollution of surface and groundwater, to
reduce pesticide residues in food, to reduce a farmer's
overall risk, and to increase both short- and long-term
farm profitability”. This suggest that LISA will have a
physical productivity limited by the maximum on-farm
resources that can be mobilized and that LISA can then
be associated with lower output (Poux, 2008).
By the other hand, the integration of crop-livestock
under CA holds promise to improve the efficiency and
sustainability of production systems, but this is
conditioned by good understanding of CA principals and
appropriate use of corresponding packages. The farmer
can introduce forage crops into the crop rotation, thus
extending it and reducing pest problems. Forage species
could be used as dual-purpose crops for fodder and soil
cover. However, conflicts between the use of stubbles in
livestock feeding or to cover the soil have to be resolved,
Moujahed et al. 4585
particularly in drylands where fodder potential is low
(FAO, 2006). This concept of CA seemed to be appa-
rently incompatible with livestock extensive system and if
it is adopted, competition with livestock feeding needs to
The current study is part of a research program on live-
stock management under the context of CA which is not
yet documented in the literature. Therefore, this experi-
ment was designed to study the effect of stocking rate on
stubble biomass variation and lamb growth.
MATERIALS AND METHODS
The trial was carried out in the experimental station of INRAT (24
km from Tunis, semi-arid: 350 mm of annual rainfall). Barley (variety
Manel) was cropped using CA package. Indeed, barley was drilled
(no tillage) in the 26th of December 2012 at a seeding rate of 100
kg/ha. A treatment by herbicide (glyphosate 100 g L-1/ha) was
applied in absence of later weeding. The plot was fertilized using
ammonitrate (150 kg/ha). The harvest was made on the 24th of
June 2013, at a cutting height of about 25 cm above ground. The
registered grain yield was 1.4 t/ha.
Forty five 7-month-old Barbarine lambs (initial average weight 20 ±
2.3 kg) raised in the experimental station of Oueslatia (INRAT) were
used for the experiment. They received an antiparasitic treatment
and were vaccinated against enterotoxaemia. They were housed in
collective boxes in a covered barn and marked on, using different
colors of painting to be easily identified and separated per
treatment and plot, before leaving for grazing. They had free
access to clean water 3 times a day.
Experimental design, sampling and measurements
The experimental plot of 22500 m2 was divided into 6 subplots of
3750 m2 each, assigned randomly to two stocking rates (15 and 30
lambs per hectare, respectively for SR15 and SR30). Each
treatment was triplicated using the six fenced subplots. Along with
the 46 day-trial, lambs grazed twice a day (from 5.00 h to 8.00 h
a.m. and from 16.00 h to 18.00 h or 17.00 h to 19.00 h) with a total
grazing duration of 5 h per day. The grazing practice covered the
period 19th July-3rd September 2013, with a total duration of about
The biomass of stubble and the removal of particular fraction
were estimated using quadrats sampling technique (0.25 m2, 5
quadrats per subplot placed in zigzag to have representative
samples) at the beginning of the trial and 14 days after. The cutting
height was at about 4 cm from the soil. It was not possible to take
samples at the end of the experiment because of the rain occurring
towards the end of August and the beginning of September and the
emergency of vegetation. Samples were immediately weighed and
transported to the laboratory for immediate dry matter (DM)
determination. Proportions of heads, leaves, stems and other
vegetation were evaluated and samples were stored for chemical
In order to control lamb growing, the animals were weighed early
in the morning (5.00 h am) before the start of grazing. Live weight
was determined 3 times after the start of the experiment (each 15
4586 Afr. J. Agric. Res.
Table 1. Variation of DM biomass with stocking rate and sampling period.
Biomass (kg DM/ha)
Biomass (kg DM/ha)
Biomass (kg DM/ha)
Biomass (kg DM/ha)
S0: Sampling at 0 days, S 14 : sampling after 14 days, a, b, c: Different letters in the same column mean different values; A, B, C: Different letters
in the same line mean different values; SEM: Standard error of the mean; *: P<0.05; **: P<0.01.
days) and then lamb growth was followed for 3 successive periods
of grazing. Live weight gain (LWG) and daily live weight gain
(DLWG) were calculated.
Biomass samples were dried at 50°C ground to pass through a 1
mm-screen then were analyzed for ash and crude protein
(Association of Official Analytical Chemists, 1984) and for
lignocellulose fraction ADF (Van Soset et al., 1991).
Data were subject to analysis of variance using GLM procedure,
(Statistical Analysis System software; SAS, 2002). The model
included stocking rate (S) and period (P) effects and the interaction
(S x P). SNK test was used to compare treatment effects. When P-
value is below 5%, the treatment effect was considered significant.
RESULTS AND DISCUSSION
Estimated biomass yields are reported in Table 1. At the
beginning of the experiment (S0), no difference was
observed in biomass between the plots reserved to the 2
stocking rates (averaged 2304 kg DM/ha). Subplots
assigned to the two stocking rates exhibited substantial
decrease of biomass yield (P<0.05) in the second
sampling time (S14: -137 and -577.5 kg DM/ha
respectively with SR15 and SR30). Proportions of
biomass components indicated in Table 1 showed that
the proportions of heads decreased (P<0.05) in SR30
plots, but was maintained in SR15 ones. This decrease
could be due to the sorting exerted by lambs which
preferred heads while grazing (Brand et al., 1993). The
same trend was observed by Yiakoulaki and
Papanastasis (2005) who mentioned that sheep grazing
on cereal stubble tend to consume heads first. Heads are
selected first by sheep because they are higher in energy
than the other parts of the stubbles (Houmani, 2002).
Leaves proportions were not affected after 14 days of
grazing in both SR15 and SR30 plots, while stems
proportions increased (P<0.05) in SR30.
The observed values of stubble biomass are in the
same range of that reported by Valderrabano (1991) and
Cabello et al. (1992). It worthy to note that wide variation
in stubble biomass amounts were observed in the
literature and that several factors could affect the
precision of measurements, mainly the size of quadrat.
Moujahed et al. 4587
Table 2. Chemical composition of biomass according to stocking rate and sampling period (% DM).
S0: Sampling at 0 days, S 14: sampling after 14 days, a, b, c: Different letters in the same column mean different
values; A, B, C: Different letters in the same line mean different values; SEM: Standard error of the mean; *: P<0.05.
Indeed, according to Treacher et al. (1996), a comparison
of samples cut, using quadrats of 1.0 x 1.0 m (S) and
4.25 x 0.47 m (R), showed a large reduction in the
coefficient of variation from 23% with S to 9% with R. The
absence of later sampling times in our study did not allow
to better understanding grazing evolution. Treacher et al.
(1996) conducted a similar experiment on stubble grazing
ewes. They noted that heads were selected first and
disappeared after 4 to 8 days of grazing at stocking rates
of 20 to 60 sheep/ha. They also recorded an increase of
stems intake when most of the leaf had been removed.
Houmani (2002) mentioned that the consumption of high-
energy diets encouraged sheep to consume more stems.
When the stems become very hard, sheep then tend to
Chemical composition variation
Nutrient contents of stubble are presented in Table 2. Dry
matter proportion of stubble was similar among sampling
times and stocking rates. Ash content did not change
between S0 and S14 in both SR15 and SR30. However,
it decreased (P<0.05) with the increase of the stocking
rate in S0. Similar trends of contents were reported by
Ben Said et al. (2011) in semi-arid regions from Tunisia.
CP contents are relatively high in the beginning of the
experiment in all the plots comparatively to literature.
Indeed, the average content of this nutrient (4.9% DM at
S0) is higher than which found by Avondo et al. (2000) for
barely stubble (3.4% DM) and values relative to cereal
straws (Houmani and Tisserand, 1999). This may be
related to the richness of biomass in heads and thereby
grains. The CP content was maintained in SR15 treat-
ment, but decreased (P<0.05) by about one percentage
unit 1% in SR30, 14 days after the beginning of the
grazing period. Houmani (2002) conducted a similar
experiment on ewes and concluded that the content of
CP decreased with grazing frequency by the animals (-
1.3 percentage unit), 16 days after the beginning of the
experiment. This variation of the CP content of stubble is
likely due to its level in grains, which decreases with the
grazing duration. Also,the relatively high content of CP,
even in the second sampling time, may indicate once
more that the studied stocking rates were not very high.
Rihani et al. (1991) suggested that the lower is the
stocking rate, the higher is the digestibility and the CP
content of the stubble.
The content of ADF seems relatively low (averaged
45.9% DM in S0) when compared to that of fibrous
4588 Afr. J. Agric. Res.
Table 3.Variation in LW according to stocking rate and period (kg).
a, b, c: Different letters in the same column mean different values; A, B, C: Different letters in the same line mean
different values; SEM: Standard error of the mean; *: P<0.05; **: P<0.01; ***: P<0.001.
feedstuffs including cereal straws in Mediterranean
regions (generally ADF content is above 50%, Susmel et
al., 1994). This observation is in line with the relatively
high content of CP and confirms the negative correlation
between CP and ADF shown by Avondo et al. (2010).
The ADF contents of stubble in the 3 plots in the first
sampling time are similar (Table 2). In both treatments,
ADF content increased by 2.6 and 2.1% units (P<0.05)
for SR15 and SR30 plots respectively. This result is
related to the changes in botanical composition between
the 2 sampling time, exhibiting decreasing trends of head
and leave proportions and a decrease in steam ones,
mainly in SR30. The higher lignocellulosic fraction in
steams comparatively to heads and leaves may be
reflected in which of biomass. Our results confirmed the
cell wall variation trends observed in Tunisia by Ben Said
et al. (2011), for cereal stubble produced in CA condition.
Controversial literature data on the nutritive value of
stubble are reported. Some differences are noted
comparatively with results found by Ben Said et al. (2011)
for barley stubble variation between June and September
in Tunisian semi-arid regions and by Avondo et al. (2000)
for the same speciesin southern Italy. Chemical compo-
sition of cereal stubbles is related to different factors such
as region, cereal species and varieties and climate (Rao
and Dao, 1994). The compilation of chemical composition
results, mainly the relatively high content of CP and the
low content of ADF are in line with morphological compo-
sition of stubbles which were especially high in heads
and leaves as compared to data reported in Cobarellero
et al. (1992) and Ben Said et al. (2011). Differences in
head proportions are mainly related to the control level of
the harvesting process and used machines. Variation in
chemical composition between the two sampling times
especially noted in SR30 may be due to selective
behavior of lambs during grazing, which induced changes
in morphological composition of stubbles and thereby in
chemical composition (Ben Said et al., 2011). Indeed,
animals start the grazing period by sorting heads and
LWG and DLWG according to stocking rate and period
are presented in Tables 3 and 4 respectively. During the
first grazing period, lambs from the both treatments lost
Live weight (P<0.001), but this loss was higher (P<0.05)
for SR15 than SR30 group (-610 and -110 g,
respectively). The same trend was observed in DLWG (-
23.3 and -4.1 g/d, respectively for SR15 and SR30,
P<0.05). This result couldn’t be ascribed to the nutritive
value of stubbles but likely to the initial body conditions of
lambs and the first period represents, actually, an adap-
tation period for experimental conditions. Also, it is not
excluded that the sorting by lambs of high amounts of
heads and grains in stubble biomass could have induced
some digestive disturbances in this first period
particularly rich in grains. These hypotheses are
confirmed in the second period, since the two groups
performed similarly as reflected by the LW (around 2 kg,
Table 3) and the DLWG (171 g/d, Table 4). The last
finding suggests that the biomass in the plots was not
limiting and was sufficient for animals assigned to the two
treatments. As expected, in the third period SR15 group
conserved their body weights, while SR30 group lost
(P<0.001) about 400 g comparatively with the second
period (Tables 3 and 4).
Biomass estimation seemed to be in line with sheep
performances. In addition, data presented in Table 5
indicated that generally in this feeding system, body state
of animals was preserved. Furthermore, animals in both
treatments registered a similar total LWG (around 1.5 kg).
Thus, stubbles have contributed to safeguard livestock
even in absence of supplementation. Similar findings
were reported by Treacher et al. (1996) on ewes grazing
barley stubbles at different stocking rates.
These results obtained under CA conditions, should be
translated in terms of stubble management strategies to
comply with CA principles and objectives, including soil
cover (Abbas and Zitouni, 2010). Indeed, the effect of
livestock is closely related to the rate of vegetation cover
before grazing (Masmoudi, 2012), the stocking rate and
the duration of grazing. Köller (2003) claimed that
livestock could be fully integrated into conservation
agriculture, when more than 30% of the residues from the
previous cropare left on the ground as mulch. Also, the
study of Masmoudi (2012) showed that the integration of
livestock at different levels of stocking rates requires a
rate of biomass cover higher than 78% before grazing.
Moujahed et al. 4589
Table 4. Variation in DLWG according to stoking rate and period (g/d).
a, b, c: Different letters in the same column mean different values; A, B, C: Different letters in the same line mean different values;
SEM: Standard error of the mean; *: P<0.05; **: P<0.01; ***: P<0.001.
Table 5.Effect of stocking rate on total TLWG and DLWG.
SEM: Standard error of the mean.
Further studies are needed in different conditions and
with different crops and animal species before claiming
suitable residues amounts, as related to both animal and
Irrespective of the stocking rate, lambs grazing barley
stubbles for one month and half after harvest were able
to meet their maintenance requirements and even to
grow at a rate of 30 g/day. Under the experimental
conditions of the current work, the two stocking rates
resulted in similar performances of Barbarine lambs. This
suggests that the available biomass could support higher
Conflict of Interests
The authors have not declaredanyconflict of interests.
This study is part of the IFAD-ICARDA CLCA Project. We
are in debt to all students who contributed in this
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