barley–legumes rotations for semi-arid areas of lebanon

Barley�/legumes rotations for semi-arid areas of Lebanon

S.K. Yau a,*, M. Bounejmate b, J. Ryan b, R. Baalbaki a, A. Nassar c,R. Maacaroun d

a Department of Plant Sciences, Faculty of Agricultural and Food Sciences, American University of Beirut, P.O. Box 11-0236, Beirut,

Lebanonb International Center for Agricultural Research in the Dry Areas (ICARDA), P.O. Box 5466, Aleppo, Syria

c International Center for Agricultural Research in the Dry Areas (ICARDA), Terbol Experimental Station, Terbol, Bekaa, Lebanond Faculty of Agricultural Sciences, Lebanese University, P.O. 55-484, Sin El-Fil, Beirut, Lebanon

Received 15 May 2002; received in revised form 3 January 2003; accepted 16 January 2003

Abstract

In arid and semi-arid areas of West Asia and North Africa, including the northern Bekaa Valley of Lebanon, farmers

have been increasingly practicing continuous barley cultivation. The objectives of the study were to (1) determine

whether barley monoculture is unsustainable1, (2) ascertain if barley and total dry matter yields can be increased and

sustained by including a legume crop in the rotation, and (3) determine which barley�/legume rotations are more

productive. The trial was set up in a randomised complete block design with two replicates under rain-fed conditions in

1994�/1995 at the Agricultural Research and Educational Center (33856? N, 3685? E, 995 m above sea level). Eight two-

phase barley-based rotations were compared: barley in rotation with barley, lentil, common vetch, bitter vetch,

common vetch for grazing, medics for grazing, common vetch for hay, and common vetch with barley for hay. Seed and

straw were harvested from barley and legumes in the first four rotations. Relative to the trial mean, seed and straw yield

under barley monoculture slumped in 1997�/1998 and did not recover since then. Infestation of wild barley was a cause

of this yield decline. Barley�/legume rotations yielded 44�/80% more barley grain and 27�/53% more barley straw than

the barley monoculture over the 6 years (1995�/1996 to 2000�/2001). Furthermore, in the legume phase, common and

bitter vetch gave higher seed yield than barley monoculture. Thus, all barley�/legume rotations, except barley�/medics,

yielded more total dry matter than barley monoculture on the basis of per rotation cycle. Among the barley�/legume

rotations, the barley-common vetch for seed rotation gave the highest and most stable dry matter yield. In conclusion,

barley monoculture was unsustainable, but barley yields could be increased and sustained by including legumes in the

rotation. Farmers in semi-arid areas of Lebanon should discontinue practicing barley monoculture and adopt a barley�/

legume, such as common vetch, rotation.

# 2003 Elsevier Science B.V. All rights reserved.

Keywords: Grazing; Hay yield; Lentil; Medics; Protein content; Vetches; Yield stability

* Corresponding author. Tel.: �/961-8-345151; fax: �/961-8-345142.

E-mail address: [email protected] (S.K. Yau).1 Defined in this study as having a marked yield decline over years.

Europ. J. Agronomy 19 (2003) 599�/610

www.elsevier.com/locate/eja

1161-0301/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S1161-0301(03)00006-6

mailto:[email protected]

1. Introduction

In arid and semi-arid areas of West Asia and

North Africa (WANA), including the northern

Bekaa Valley of Lebanon, sheep husbandry and

barley (Hordeum vulgare L.) cropping are the two

most important agricultural activities. In such

environments, barley is the dominant winter crop

because of its versatility (Jones and Singh, 2000a).It is more tolerant to dryness, poor soils, and

salinity, and usually gives higher grain yield than

wheat. Barley grain is the traditional and predo-

minant feed for sheep. Barley straw and stubble

after grain harvest are also important feed sources

in the summer. In poor years, farmers may not

harvest the mature barley crop but just let sheep

graze on them.The numbers of sheep and goats kept in the

region has increased rapidly due to demographic

and economic reasons, causing a feed shortage

problem. In 1985�/1989, there was a total of 163

million sheep in WANA (Belaid and Morris,

1991). A recent survey of small ruminant produc-

tion systems in the Bekaa Valley of Lebanon

showed that inadequate feed supplies, and highprices of feeds were among the top problems

ranked by farmers (Hammadeh et al., 1994). The

increase in feed demand led farmers to grow

barley continuously instead of their customary

barley�/fallow rotations (Belaid and Morris, 1991).

This practice could have brought short-

term economical benefits but is expected to be

unsustainable. Cereal monoculture maydeplete soil nutrients (Jones and Singh, 2000c;

Weston et al., 2002), and increase pest (Miller et

al., 1994) and weed populations (Karlen et al.,

1994), leading to reduction in yield and

farmers’ profit. A sustainable and productive

option to replace barley monoculture is urgently

needed.

The planting of legumes in rotation with cerealshas been demonstrated to be beneficial in many

semi-arid areas within (Papastylianou, 1999; Jones

and Singh, 2000b) and outside WANA (Zentner et

al., 1987; Karlen et al., 1994; Rao and Mathuva,

2000) and should be applicable in Lebanon as well.

A study in Cyprus reported that barley�/vetch

rotations gave more stable and probably more

sustainable yields than the continuous barley

cropping (Papastylianou, 1999). In Syria, studies

showed that barley�/vetch and barley�/grass pea

rotations yielded more dry matter and crude

protein than barley�/barley or barley�/fallow rota-

tions (Jones and Singh, 2000b).

Feed legumes have not been widely adopted by

farmers in the region. Although lentil (Lens

culinaris Med.) straw is a valuable feed, lentil is

not really a feed legume. It is a traditional food

legume crop in many arid WANA areas. Common

vetch (Vicia sativa) is one of the leguminous feed

crops that has the potential for being used in

rotation with barley (Christiansen et al., 2000a).

Recent research found that vetch is a versatile

forage legume (Jones and Arous, 1999). Besides

harvesting seed and straw, vetch is well suited to

green-stage grazing, hay making and growing in

mixture with barley for hay production. Bitter

vetch (Vicia ervilia ) is another species found to be

productive in semi-arid areas.

Medics (Medicago spp.) are common forage

legumes of the self-regenerating ley system in

Australia where alkaline soils dominate (Cocks et

al., 1980). The ley system has been adopted

practically in every farm in South Australia. It

has contributed to yield increase of small grains

and soil fertility since its adoption (Donald, 1964;

Weston et al., 2002). This success generated much

interest in the WANA region.

Crop rotation has a substantial influence on

sustainability of any farming systems. However,

no research on crop rotation has been conducted

and no serious effort has been spent to introduce

new crops to increase diversity or sustainability in

Lebanon. To fill this gap of inadequacy, a long-

term rotation trial was set up to find a sustainable,

more profitable, and environment-friendly alter-

native to cereal monoculture for farmers in the

semi-arid northern Bekaa. The objectives of the

study were to (1) determine if barley mono-

culture is really unsustainable, (2) ascertain if

barley and total dry matter yields can be increased

and sustained by including a legume crop

in the rotation, and (3) determine which barley�/

legume rotations are more productive in dry

matter.

S.K. Yau et al. / Europ. J. Agronomy 19 (2003) 599�/610600

2. Materials and methods

2.1. Site information

The rotation trial was set up in the Bekaa Valley

under rain-fed conditions at the Agricultural

Research and Educational Center (33856? N,

3685? E, 995 m above sea level). The long-term

annual precipitation of the Center is 513 mm, 58%

of which falls in December to February. The long-

term mean annual temperature is 13.9 8C. The soilis an alkaline (pH 8.0), clayey, Vertic Xerochrept

(Ryan et al., 1980).

2.2. Treatments

Besides the barley�/barley monoculture, there

were seven 2-course (i.e., 2-year) barley�/legume

rotations. The facultative 6-row barley Rihane-03

was used for the trial. Four legumes, i.e., medics(mixture of Medicago spp.: 75% M. rigidula , line

1919; 25% M. rotata and M. noeana ), lentil

(variety Talia-2), bitter vetch (ICARDA accession

3030), and common vetch (variety Syrian Local,

ICARDA accession 2541) were studied. Medics

were used for green-stage grazing by ewes and

their lambs. Seed and straw were harvested from

lentil and bitter vetch. Common vetch was used fordifferent purposes: green-stage grazing by lambs

(Vg), hay production in pure stand (Vh) or in

mixture with barley ([V�/B]h), or seed and straw

production (Vs).

2.3. Experimental design

The trial was set up in 1994�/1995. Results from

1995�/1996 to 2000�/2001 were analysed and

reported here. The experiment was in a rando-mised complete block design with two replicates.

The size of the plots was 0.1 ha (10 m by 100 m)

except for barley�/medics (100 m by 100 m) and

barley�/vetch for grazing (25 m by 100 m) rota-

tions. Both phases of each treatment were present

each year.

2.4. Field management

Sowing took place in November, which is the

optimal sowing time for the northern Bekaa, after

the first rain, except in 1998 and 1999 when rains

came unusually late in December. Seeds were sown

with a commercial drill in rows spaced 15 cm

apart. Sowing rates in kg ha�1 were: 120 for

barley, 100 for common vetch, bitter vetch, andlentil, 140 for barley/vetch mixture (2 vetch:1

barley) and 30 for medics. Medic seeds were

sown in 1994 only. For controlling grass weeds

in legume crops, except vetch and medics for

grazing, a pre-emergence herbicide, cyanazine,

was sprayed at the rate of 1 kg a.i. ha�1. In

March, cycloxidim at the rate of 200 g a.i. ha�1

was also sprayed. For barley, one spraying of 2,4-D at the rate of 660 g a.i. ha�1 was carried out in

March to control broad-leaf weeds.

Nitrogen was broadcasted by hand in the spring

as ammonium nitrate to the barley plots only. The

application rate was 60 and 30 kg N ha�1 in the

first 3 years and in the last 4 years, respectively.

The lower rate was considered adequate as the soil

mineral N level was �/20 mg kg�1 and close-bybarley yield trials did not response to 60 kg

N ha�1. Since the Olsen-P level was high (�/25

mg kg�1), no phosphate fertiliser was applied.

2.5. Sampling, grazing and harvesting

Unless specified, all samples were collected in a

fixed procedure. Three samples were collectedfrom each plot (6 for the medic plot). Each plot

was roughly divided into three equal-area sections

(6 for the medic plot). A sample was taken

randomly within each section. Samples of plants

were cut at ground level within the specific area,

collected, oven-dried at 80 8C for 48 h and

weighed.

Grazing of medics and vetch started around theend of March. Ewes (21�/35 ha�1) with their

lambs were used to graze the medics. The stocking

rates varied between years according to the carry-

ing capacity. The moving-cage technique was

followed to measure the dry matter yield. Samples

from inside and outside the ten evenly located

S.K. Yau et al. / Europ. J. Agronomy 19 (2003) 599�/610 601

cages (0.6 length, 0.6 m width, and 0.4 m height)were collected from the plot every 2�/3 weeks.

Weaned lambs (initial 28�/56, increased to 56�/

116 heads ha�1) were used to graze the vetch. The

stocking rates varied between years according to

availability of lambs and carrying capacity. Before

grazing, three samples were collected from and

three cages were installed at representative spots of

the plot to measure dry matter production. Graz-ing was stopped as soon as all the plant materials

were consumed practically. Then, samples were

collected from inside the cages. However, as plant

growth and availability of weaned lambs varied

between years, the growth stage at which grazing

was stopped also varied, from the end of flowering

to after maturity. In years in which grazing

continued longer, dry matter production wasprobably over-estimated. In the comparison be-

tween legumes, yield of vetch under grazing was

not included in the analysis.

From representative spots in the plots for hay,

three 0.5 by 0.5 m samples of plant materials were

collected when the vetch reached early-pod set in

late April to early May. After sampling, the plots

were cut by a windrower as close to the ground aspossible. The herbage was sun-dried in the field

before the hay was collected, baled, and weighed.

Three 1-m2 samples from representative spots in

each plot of lentil, common vetch for seed, and

bitter vetch were hand-harvested at ground level

before physiological maturity in May to prevent

seed shattering and leaf loss. Samples were dried

for 24 h in the oven at 80 8C before measuring dryweight and threshing. After samples were taken,

the whole legume plots were hand-harvested by

pulling up the plants (cut at ground level from

2000�/2001) and threshed using a stationary plot-

thresher.

For barley, three (6 for barley�/medics) 1-m2

samples from representative spots in each barley

plot were hand-harvested at ground level atmaturity in late May. Total weight was measured

before being threshed by a small-plot-thresher.

From 1996�/1997 onwards, the barley plots were

harvested with a commercial combine harvester in

June.

In 1999�/2000, barley samples were collected at

tillering for N analysis. Samples were also col-

lected after heading in early May in the barleymonoculture plots and the nearby barley�/lentil

plots. The numbers of 2- and 6-row heads were

counted, and the plant dry weights of the two

components were measured.

2.6. Chemical analysis

Soil samples were collected to 20-cm depth inSeptember (exception: on 2 April in 2000�/2001).

Olsen P, NH4-N, NO3-N, Kjeldahl-N and organic

matter were measured. In 1999�/2000, barley

samples collected at tillering stage, and grain and

straw at maturity were analysed for N% using the

Kjeldahl method.

2.7. Weather

The 6 years sampled a diverse spectrum with

respect to annual precipitation and temperature.

Precipitation ranged from 366 mm in 1999�/2000

to 593 mm in 1995�/1996 (Table 1). Mean tem-

peratures of the 6 years, except 1996�/1997, were

above the long-term average. 1998�/1999 was the

warmest year.

2.8. Statistical and stability analysis

The ANOVA directive of the GENSTAT package

(Genstat 5 Committee, 1993) was used for the

analysis of variance. In the combined ANOVA

analysis, the random-year and fixed-treatment

model was adopted (McIntosh, 1983). MS of

years, treatments, and year�/treatment weretested against the MS of blocks/years, year�/

Table 1

Annual precipitation and mean temperature of each year

Year Precipitation (mm) Temperature (8C)

1995�/1996 593 11.9

1996�/1997 541 11.4

1997�/1998 560 12.3

1998�/1999 382 13.8

1999�/2000 366 12.2

2000�/2001 425 12.3

Long-term averagea 518 11.3

a 45 years (1957�/2001).


treatment, and pooled error, respectively. Barlett’stest of homogeneity of variances was applied to

error MS from individual ANOVAs of the 6 years

when the year�/treatment interaction was signifi-

cant. For those traits that showed heterogeneity of

variance, the loge or the square root transforma-

tions were found to be effective in removing or

reducing the heterogeneity. Since results of the

ANOVAs using transformed or original data wereessentially the same, the original data were pre-

sented.

The coefficient of variation on treatment yield

relative to the year mean (Yau and Hamblin, 1994)

was used as an agronomic type of stability measure

across years. Farmers’ main concern is the low

yields of poor years, but they always welcome high

yield. The use of an agronomic stability, which iscloser to a farmer’s perception of yield stability

(Becker and Leon, 1988), is more desirable than a

biological stability.

Simple linear regressions were also carried out

using the barley relative yield of the different

treatments as response variable and year as

explanatory variable. A significant, negative re-

gression coefficient, which showed a decliningyield trend on advancing years, was considered

as an indication of un-sustainability.

3. Results

3.1. Random sampling versus combine harvesting

There was a strong linear correlation in meanbarley grain yield of the treatments between

random sampling and bulk harvesting (r�/0.91,

df�/6, PB/ 0.01). Correlation within years ranged

from 0.52 to 0.94. In legume seed yield, the two

harvesting procedures gave the same ranking to

the three rotations. Since there were no major

differences in rankings of treatments between the

two procedures, and straw yield and one more yearof grain yield data were measured by random

sampling, only results from random sampling will

be presented.

Mean barley grain yield from combine harvest-

ing was lower than that from random sampling

(Table 2). Bulk harvesting was carried out later,

thus more seed loss caused by shattering or stem

breakage most probably had occurred. The loss of

shrivelled or small seed from the combine could be

another main cause of difference in barley. The

finding that the percentage difference was larger in

low yielding than in high yielding years supports

this explanation. A similar result was obtained in

mean legume seed yield.

3.2. Yield decline under barley monoculture

The grain yield of barley monoculture was close

to the average of the different rotations in the first

3 years (Fig. 1). However, its yield dropped

sharply from 1997�/1998 onwards to 48% of the

trial mean in the last 4 years. It was the only

treatment that had a significant negative regres-

sion coefficient. In contrast, the three barley-pure

common vetch rotations all had a positive regres-

sion.

3.3. Barley yields under the different rotations

Differences between rotations and years were

significant, but not for rotation-by-year interac-

tion, in barley grain and straw. Mean grain yield of

barley monoculture was lower than all the other

rotations except barley�/vetch for grazing (Table

3). Furthermore, the barley monoculture had the

highest CV, showing that it gave the most unstable

yield across years. There were no significant

differences between the barley�/legume rotations

in mean grain yield. The barley yield under the

barley�/lentil rotation had the lowest CV. Mean

grain yield in 1997�/1998 was higher than all the

other five years, which were not different among

themselves (Fig. 1).

Barley monoculture also yielded the least straw

and had the largest CV in straw yield (Table 3).

The barley�/bitter vetch rotation gave the highest

straw yield, while barley�/lentil rotation had the

lowest CV. Unlike grain yield, the warm 1998�/

1999 gave the highest straw yield and the cool

1995�/1996 and 1996�/1997 gave the lowest.


3.4. Legume yields

In the combined analysis of variance of seed

yield in the legume phase, differences between

rotations and years were significant, but not for

rotation-by-year interaction. Mean seed yields of

bitter and common vetch were higher than that of

lentil and barley monoculture (Table 4). The bitter

vetch yield had the lowest CV as well. Mean yield

was highest in 1997�/1998 (1140 kg) and lowest in

1998�/1999 (540 kg).

There was a significant rotation-by-year inter-

action in straw yield. Straw yield of barley mono-

culture was lower than the legumes in 1997�/1998

but not in the other 3 years (Table 4). Differences

between rotations were not significant but years

were significant different. Straw yield of 1997�/

1998 was higher than that of 1998�/1999, which

Table 2

Comparison of mean seed yield obtained by random sampling with bulk harvesting in barley (1996�/1997 to 2000�/2001) and in legume

(1997�/1998 to 2000�/2001) phases

Rotation Seed yield (kg ha�1)

Barley phase Legume phase

Random sampling Combine harvest Random sampling Bulk hand-harvest

Barley�/barley 510 260 510 260

Barley�/lentil 1040 530 590 320

Barley�/vetch (s)a 1140 670 1010 590

Barley�/bitter vetch 1030 660 1220 680

Barley�/vetch (g)a 860 450 �/ �/

Barley�/vetch (h)a 1100 660 �/ �/

Barley�/[V�/B]ha 950 410 �/ �/

Barley�/medics 790 370 �/ �/

LSD (P�/0.05) 273 202 369 156

Mean 930 500 820 470

a (s): for seed, (g): for grazing, (h): for hay, [V�/B]h: vetch/barley mixture for hay.

Fig. 1. Mean barley grain yield of the trial and yield of barley monoculture relative to the trial mean over the years (1994�/1995 to

2000�/2001).


was higher that those of 1999�/1900 and 2000�/

2001. Bitter vetch had the lowest CV in straw

yield.

The rotation-by-year interaction was significant

for dry matter yield in the combined analysis of the

seven rotations and 4 years. Lentil, vetch for seed,

and bitter vetch gave much higher yield in 1997�/

1998 than in the other years (Table 5). Unlike the

other rotations, barley monoculture yielded the

highest dry matter in the warm 1998�/1999.

Differences between rotations were non-signifi-

cant. Dry matter yield in 1997�/1998 was higher

than that of 1998�/1999, which was higher than

those of 1999�/2000 and 2000�/2001.

3.5. Total dry matter yield per cycle

The combined analysis of variance on total dry

matter yield per cycle for the different barley�/

legume rotations showed that the rotation-by-

year interaction was not significant, but rotation

and year main effects were significant. Barley�/

medic gave poorer yield than the other five

rotations (Fig. 2), which were not significantly

different. Barley in rotation with vetch for seed

gave the highest yield and the lowest CV. The

mean dry matter yield was 9840, 7960, 6220, and

6710 kg ha�1 for 1997�/1998, 1998�/1999, 1999�/

2000, and 2000�/2001, respectively.

3.6. Weed infestation under barley monoculture

There was an apparent increase in infestation of

2-row wild barley (Hordeum spontaneum ) under

the barley monoculture over the years. In 1999�/

2000, there were 952 and 320 heads m�2 of 2-row

wild barley and 6-row Rihane, respectively. The

number of 6-row heads was similar to that under

the barley�/lentil rotation, but that of 2-row heads

was more than six times higher. The mean dry

weight of 2 versus 6-row plants was 1300 and 710

kg ha�1, respectively. Relative to the barley�/lentil

rotation, there was 900 kg ha�1 more in 2-row

plants, but 1070 kg ha�1 less in 6-row plants.

Plant height under the barley monoculture was

non-significantly lower than that in other rotations

in March, but this difference turned significant

Table 3

Mean barley grain and straw yield of different rotations with

coefficients of variation over the years (1995�/1996 to 2001�/

2002)

Rotation Grain yield Straw yield

kg ha�1 CV (%) kg ha�1 CV (%)

Barley�/barley 590 45.1 2010 28.5

Barley�/lentil 1010 15.4 2620 6.8

Barley�/vetch (s)a 1050 23.8 2800 20.1

Barley�/bitter vetch 1060 21.0 3070 22.1

Barley�/vetch (g)a 830 18.2 2800 13.4

Barley�/vetch (h)a 1060 20.5 2850 18.7

Barley�/[V�/B]ha 970 19.2 2580 11.7

Barley�/medics 850 25.3 2560 18.8

Mean 930 23.5 2660 17.5

LSD (P�/0.05) 244 449

a (s): for seed, (g): for grazing, (h): for hay, [V�/B]h: vetch/

barley mixture for hay.

Table 4

Seed yield and straw yield of lentil, common vetch and bitter vetch compared to barley monoculture

Rotation Seed yield Straw yield (kg ha�1)

kg ha�1 CV (%) 1997�/1998 1998�/1999 1999�/2000 2000�/2001 Mean CV (%)

Barley�/barley 450 1430 3120 1600 1740 1970

Barley�/lentil 590 19.8 5880 2890 1520 1780 3020 8.6

Barley�/vetch 1010 24.1 5320 2700 2070 1890 3000 10.0

Barley�/bitter vetch 1220 11.5 5990 2820 1760 1840 3100 2.5

Mean 820 4650 2880 1740 1810

LSD (P�/0.05) 369 rotation 932; year 386;

rotation-year 1631,

for same year 1864


from mid-April. Weeds other than wild barley

were present in a negligible frequency.

3.7. Nitrogen content of barley in 1999�/2000

Rotations of barley with vetch for hay and vetch

for grazing gave the highest N content in barley

dry matter at tillering (Table 6). Barley mono-

culture had the lowest N content that was non-

significantly different from barley�/lentil and

barley�/bitter vetch but was lower than the other

five rotations.

Barley after lentil gave the highest but barley

monoculture gave the lowest N content in grain.

Barley�/lentil was the only rotation that gave

higher grain N content than barley monoculture.

There were no significant differences in straw N

content at maturity.

Table 5

Mean dry matter yield of the legume phase under different rotations with coefficients of variation over the years

Rotation Dry matter yield (kg ha�1) CV (%)

1997�/1998 1998�/1999 1999�/2000 2000�/2001 Mean

Barley�/barley 1980 3640 1830 2250 2430

Barley�/lentil 6690 3350 2160 2220 3600 21.7

Barley�/vetch (s)a 6750 3090 3340 2830 4000 13.2

Barley�/bitter vetch 7760 3620 3290 2640 4330 17.0

Barley�/vetch (h)a 4460 2890 1880 2770 3000 14.7

Barley�/[V�/B]ha 3800 3620 3040 3410 3460 22.4

Barley�/medics 2990 2620 2380 n.a. 2660 23.5

Mean 4920 3260 2560 2530 3320

LSD (P�/0.05) rotation 819; year 194;

rotation-year 1523,

for same year 1639

a (s): for seed, (h): for hay, [V�/B]h: vetch/barley mixture for hay. n.a.: not available.

Fig. 2. Mean total dry matter yield of barley and legumes per rotation cycle under the different rotations (1997�/1998 to 2000�/2001)

with coefficients of variation over the years (error bar indicates LSD; (s): for seed, (h): for hay, [V�/B]h: vetch/barley mixture for hay).


3.8. Soil fertility

Rotations did not differ significantly in soilnitrate, ammonium, Kjeldahl N and organic

matter level in 2000�/2001. The combined analysis

over years also did not detect significant rotation

and year-by-rotation interaction effects.

4. Discussion

Under the conditions of this study, barley

monoculture was clearly a non-sustainable farm-

ing system. Relative to the trial mean, seed and

straw yield of barley under continuous barley

slumped just 3 years after the establishment of

the trial. Our results on the poor performance ofbarley monoculture supported those obtained in

arid or semi-arid areas of neighbouring countries

by Papastylianou (1990), Jones and Singh (1995),

Christiansen et al. (2000a) and Jones and Singh

(2000b). However, the 29�/44% lower barley grain

yield after barley monoculture than in barley�/

legume rotations found in this study was much

higher than those reported by Christiansen et al.(2000a) and Jones and Singh (2000b).

The substantially lower yields of barley mono-

culture in our study most probably were due to

infestation of the 2-row wild barley. The spikes of

the wild barley shattered when matured, either

before or during harvesting. This wild barley was

not a problem in barley plots after legumes

because it was controlled by herbicide under the

legume phase. However, it could not be effectively

controlled under barley monoculture. The cultiva-

tion just before planting killed the early emerged

wild barley, but many seedlings emerged after. The

problem was aggravated in the two consecutive

dry years of 1998�/1999 and 1999�/2000, in which

seeds were sown before the first rain that came as

late as December. Such an outcome was not

unexpected as monoculture cropping often results

in greater weed density (Karlen et al., 1994).

Studies in Canada showed that downy brome

densities drastically increased over years in the

continuous winter wheat and caused yield reduc-

tion (Blackshaw, 1994; Larney and Lindwall,

1994). This study probably is the first report to

highlight the problem of infestation by H. sponta-

neum under barley monoculture in the region,

where the wild species still exists widely.

Crop rotation can be a key component of an

integrated management program for wild barley

control. Wild barley data collected on the contin-

uous barley and barley�/lentil rotation indicated

that adopting legumes in the rotation was effective

in controlling the wild barley. In Canada, it was

found that rotating winter wheat with canola was

effective in checking the population of downy

brome (Blackshaw, 1994). Cereal�/fallow is effec-

tive in controlling weeds, however it probably

gives less yield and economic return per rotation

Table 6

Nitrogen content of barley dry matter at tillering, and grain and straw at maturity under the different rotations in 1999�/2000

Rotation Nitrogen content (%)

Dry matter at tillering Grain at maturity Straw at maturity

Barley�/barley 2.3 1.5 0.6

Barley�/lentil 2.8 1.9 0.6

Barley�/vetch (s)a 2.9 1.7 0.7

Barley�/bitter vetch 2.8 1.8 0.7

Barley�/vetch (g)a 3.3 1.7 0.6

Barley�/vetch (h)a 3.5 1.8 0.6

Barley�/[V�/B]ha 3.1 1.8 0.7

Barley�/medics 3.0 1.6 0.7

LSD (P�/0.05) 0.52 0.33 ns

Mean 3.0 1.7 0.7

a (s): for seed, (g): for grazing, (h): for hay, [V�/B]h: vetch/barley mixture for hay.


cycle than a cereal�/legume rotation (Christiansenet al., 2000a).

After weed infestation, soil moisture supply

could be the second most important factor limiting

grain yield under barley monoculture in our study.

Soil moisture availability after barley and legumes

was not measured here but other studies showed

that legumes use less soil moisture than barley and

the moisture stored in the soil translates to higheryield in the following barley crop (Jones and

Arous, 1999; Jones and Singh, 2000a). Inadequate

N fertilization probably was not a main cause

leading to low yield of barley monoculture. This

view was supported by the finding that soil N level

in the barley monoculture plots was not lower than

the other rotations after 7 years. Monoculture is

expected to increase pest infestation (Karlen et al.,1994). However, minimal foliage diseases and

insects were observed in this trial. Root diseases

and nematodes are more insidious. It was reported

that gall nematode has become quite widespread

and devastated barley yield (Christiansen et al.,

2000a). Research will be conducted to investigate

whether nematodes contributed to the yield decline

of the barley monoculture.Besides giving lower barley yields, barley mono-

culture had the highest CV among the eight

rotations, indicating that it was unstable in yields.

This result was similar to that reported by

Papastylianou (1999) and Brandt and Zentner

(1995), who found that yield was more stable

under rotations involving other crops than in

cereal monoculture. Studies in neighbouring Syriashowed that barley monoculture gave higher

annual variability than barley�/vetch rotation in

the wetter site but not in the drier site (Jones and

Singh, 2000b). Such an inconsistency in results

could be due to the fact that in their (Jones and

Singh, 2000b) study, CV was calculated on raw

data, thus a biological stability was used. Under

such a measurement, any yield response to favour-able conditions would score negatively on stability.

In our study, CV was converted to an agronomic

type of stability as relative yield (Yau and Ham-

blin, 1994) was used.

The yield decline due to a build-up of weeds,

lower dry matter yield and N content, and higher

yield instability under continuous barley clearly

show that farmers in northern Bekaa of Lebanonshould be encouraged to discontinue practising

barley monoculture and adopt a barley�/legume

rotation. Furthermore, we showed in our earlier

report (Yau et al., 2001) that despite the higher

cost for hand harvesting of legume seed, the net

incomes from barley�/legume rotations were much

higher than that from barley monoculture. Among

the different feed legume crops, we are moreinclined to support common vetch. The barley�/

vetch for seed rotation produced the highest and

most stable dry matter yield in this study. Besides,

common vetch is a versatile crop suitable to meet

different farmers’ demands (Jones and Arous,

1999).

In contrast to the finding of Jones and Arous

(1999) and Jones and Singh (2000a), barley seedand straw yields after vetch for grazing, hay and

seed were found to be non-significantly different in

this study. Barley after vetch for grazing out-

yielded barley after vetch for hay and seed in the

study by Jones and Arous (1999), and they

suggested that better performance of the barley

after vetch for grazing was due to the lesser soil

water usage and the enhanced N availability undergrazing. This suggestion was supported by crop

water-use data of Jones and Singh (2000a). The

mode of grazing might have caused the difference

in the results between our and their studies. In

their studies, vetch was clipped at the ground level

at the early flowering stage. In our study, lambs

grazed until practically all plant materials were

removed, a stage that varied from the end offlowering to after maturity. As grazing was

completed late in the year, the effect on moisture

and N probably would not differ greatly from that

of harvesting for hay or seed.

Our result, that there was no significant differ-

ence in hay yield between the two rotations:

barley�/vetch and barley�/vetch/barley mixture,

supported the findings of Jones and Singh(1995). In both studies, barley�/vetch for hay

gave higher barley yields than barley�/vetch/barley

mixture for hay, but lower dry matter yield in the

legume phase. Thus, there was only a marginal

difference in dry matter production per rotation

cycle. The growing of a mixture of vetch and

barley may be less costly and more environment


friendly since no herbicide is registered for suchconditions. However, there was less N produced in

the vetch/barley mixture than in a pure stand of

vetch (Jones and Singh, 1995). Besides, growing a

legume/cereal mixture will not allow easy weed

control. If there is wild barley in the field, farmers

need to make sure that the hay is cut well before

the wild barley plants are mature enough to shed

their seeds. If the field is weedy, we believe thatgrowing vetch for hay is safer than growing a

mixture of vetch and barley.

The performance of the barley�/medic rotation

was disappointing. Although yields of barley after

medics were higher than that after barley mono-

culture, they were the lowest among the barley�/

legume rotations. Similarly, dry matter yield of

medics were the lowest among the legumes. (Thesampling management of the study might have

underestimated the productivity of medics, since

no more samples were collected after flowering

when grazing was stopped.) These results provide

another possible explanation on why projects on

introducing ley farming in Syria and other WANA

countries failed (Christiansen et al., 2000b). Ap-

parently, the ley farming is well suited to theconditions in Australia, where farms are big and

sheep are left to graze inside fenced paddocks.

However, we believe that it is not suitable for the

WANA region where farm size is small, farmers

are practising intensive agriculture to get the

maximum dry matter yield, and there are other

more profitable and easily managed crops.

In our study, soil NH4�, NO3

� and Kjeldahl-Nand organic matter contents were not significantly

different under barley�/legumes rotations and

barley monoculture. This result differed from

those reported by Rao and Mathuva (2000) and

Weston et al. (2002). The monoculture in their

studies received no N fertiliser, thus an increase in

inorganic N under cereal�/legume rotations was

not unexpected.

5. Conclusion

This study clearly showed that barley mono-

culture is a non-sustainable farming system. As

barley�/legume rotations gave higher and more

stable dry matter with higher N content, farmers innorthern Bekaa of Lebanon should be encouraged

to discontinue practising barley monoculture and

adopt a barley�/legume rotation. The barley-com-

mon vetch rotation could be recommended since

common vetch is a versatile feed legume that can

meet different farmers’ demands.

Acknowledgements

Our thanks go to S. Christiansen, M. Sugh-

ayyar, and N. Nersoyan for their enthusiastic

guidance in the initiation of the project and helpduring the early stage. Comments and suggestions

from the reviewers were much appreciated.

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