American Journal of Plant Sciences, 2011, 2, 202-216
doi:10.4236/ajps.2011.22022 Published Online June 2011 (
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping
Systems on Wheat Yield Stability in a Semiarid
Mediterranean Clay Soil
Rachid Mrabet
Institut National de la Recherche AgroNomique (INRA), Regional Agricultural Research Centre of Tangier, Tangier, Morocco.
Received February 11th, 2011; revised April 4th, 2011; accepted April 10th, 2011.
Agriculture is the single biggest user of land and water in Morocco; however its performances are still low due to high
rainfall variation and rates of soil produ ctivity depletion. Increasing concerns about soil and environmen t quality deg-
radation have raised the need to review existing tillage management systems and develop new systems for seed-bed
preparation. Consequently, No-tillage is found a promising practice of so il management to impro ve simultaneously so il
quality and wheat production in semia rid Morocco. Ho wever, residue management under No-tilla ge was not yet studied
in conjunction with wheat rotation. Therefore, a field study was conducted in the semiarid Chaouia Plain of Morocco
during the period from 1994 to 2003, in order to evaluate the impacts o f different tillage practices (conventio nal tillage
(CT), No-tillage (NT)); No-tillage wheat residue management scenarios (total NTr, partial NTp and No-removal of
residues NTm) and crop rotations (continuous wheat (CW), Wheat-Fallow (WF), Wheat-Maize-Fallow (WMF),
Wheat-Lentil-Fallow (WLF) and Wheat-Barley-Fallow (WBF)) on wheat production. Over-years, conventional tillage
system permitted lower yield of wh eat while NT main tenance of crop residue at th e surface is needed to increase it. Ba -
sically, NTp could be adopted in mixed crop-livestock systems of semiarid areas for the purpose of guarantying grain
and feed. Wheat yields were the lowest under continuous wheat for all years. Wheat-fallow rotation is an important
option in dry years or areas, while wheat-fallow-lentil or barley rotations are recommended in better environments.
Stability analysis indicated that yields in the No-tillage system were less influ ence d by ad verse grow ing conditions than
conventional tillage system, particularly under low rainfall. These results indicate that improved soil quality under
No-tillage enhanced wheat yield stability by reducing the impact of adverse growing conditions.
Keywords: No-Tillage, Residue Management, Wheat, Cropping System, Stability Analysis, Morocco
1. Introduction
In the Mediterranean basin, water is the most limiting
factor. In fact, agriculture triggers drought, soil degrada-
tion and erosion processes [1]. Crop mis-intensification,
conventional tillage and over-grazing characterize agri-
cultural systems. These typical agricultural practices as-
sure some production and income in wet years, but low
average yields and low moisture utilization efficiency in
dry years. Moreover, current practices suffer from high
year-to-year variations in income and extreme fluctua-
tions in production with very little biomass and nutrient
returned to the soil and little protection provided from
endemic water and wind erosion. The population growth
in Morocco resulted in increased reliance upon continu-
ous cropping rather than conservation cropping systems
[2]. In fact, continuous wheat occupies 30% of arable
lands, even though it is a permanently stressed environ-
ment [3].
Soil degradation is both a cause and consequence of
the poor economical development and social environ-
ment in the country. Consequently, farming systems need
to be adjusted to face a range of challenges, especially
water shortage and scarcity and low fertility soils [4].
Morocco’s agriculture should experience a shift based
upon conservation and intensification. In the other side,
world-wide and in the Mediterranean basin, No-tillage
systems are among the top technologies to mitigate
drought, reduce tillage costs, conserve soil and water,
increase soil organic carbon pools, boost crop productiv -
ity and reduce net CO2 emissions, which contribute to
global warming attenuation [5-7]. Hence, under these
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a 203
Semiarid Mediterranean Clay Soil
environmental and weather conditions, to increase the
yield stability in cereal crops represents an important
objective for ag ricultural progress.
Winter cereals have shown better adaptability to No-
tillage techniques than other crops [8-13]. In Morocco,
early No-tillage research, which started in 1983, showed
superiority of No-tillage grain production compared to
convention al tillage production [14,15]. It was also found
that No-till soil conditions favour more vigorous and
healthier plants that are resilient to various types of stress
(either biotic or edaphic) [16]. A new soil ecosystem is
created with adoption of No-tillage systems c haracterized
mainly by higher sequestration of carbon, better aggrega-
tion and improved availability of essential elements to
crops (nitrogen, phosphorus and potassium) [17,18].
Crop residues left on the surface under zero-tillage
protect the soil surface from water and wind erosion and
from the sun’s radiation, propitiating soil biological ac-
tivity and bio-diversity, while improving nutrient effi-
ciency, water economy and soil structure. Consequently,
the best practice is to leave a fraction of crop r esidues in
the field, where they serve as soil cover and organic
amendment. For achieving sustainable mixed agricultural
systems, crop residue should be managed to simultane-
ously increase water availability and satisfy soil quality
and productivity requirement as well as livestock fodder.
Global climate change scenarios predict that variation
in precipitation patterns will increase in Morocco result-
ing in frequent extreme events (drought and flood) [19].
For the transition and then the shifting from intensive to
No-tillage systems, enhanced yield stability is of para-
mount importance for sustainable agriculture [20,21]. In
addition, according to [22], a Non-decreasing trend in
yield is necessary to call a system sustainable. Hence, the
main objectives of this study are 1) to redu ce dependen ce
on tillage, while increasing the use of precipitation dur-
ing the wheat growth thr ough residue management, 2) to
propose appropriate cropping system for semiarid farm-
ers of Morocco and 3) to check on yield stability due to
crop management strategies vis-à-vis changing climate
and environmental contexts.
2. Materials and Methods
2.1. Site Description
A long-term field experiment was established at Sidi El
Aydi experimental station to compare the sustainability
of a range of rotation, tillage and stubble management
systems on a clay soil. This research site is located at the
Institut National de la Recherche Agronomique (INRA)
(33°00'N, 09°22'W, elevation 230 m a.s.l.) situated 45
km South of Casablanca, Morocco. The region, named
Chaouia, is the major cereal production in the country.
This experiment was set up from 1994 to 2003, with
the same treatments applied to the same plot year after
year. Precipitation was measured with a standard rain
gauge adjacent to the plots. The major characteristics of
the soil are given in Table 1. The soil of the experimen-
tal area is classified as Vertic Calcixeroll with little or No
slope, representing the major soil in the region. It is
characterized by cracking-swelling properties [16].
Long-term wheat growing season rainfall (1967-2003)
at Sidi El Aydi averages 308.9 mm, ranging from 113.5
mm to 740 mm, with about 53.5% received between
November and January (Table 2). Maximum tempera-
tures can reach up to 34.4˚C in July, while minimum
temperatures can drop to 6˚C in January. Summers are hot
and dry, whereas winters are cold and moist (Table 3).
2.2. Experimental Design and Treatments
Prior to the experiment commencement in 1994, the site
had a long history of continuous wheat cropping using
conventional tillage. The experimental design was a
two-factorial split-plot design with three replicates. Large
plots were 6 m wide and 20 m long, while sub-plots are 3
m wide and 20 m long. Large plots corresponded to rota-
Table 1. Selected soil properties of the test site at the start of
the experiment for 0 to 200 mm depth.
Property Value
Sand (%) 21
Silt (%) 28
Clay (%) 51
Quartz (%)
Montmorillonite (%)
Albite (%)
Calcium carbonate (%)
Organic carbon (%) 1.40
pH (1:2 soil:water) 8.2
Cation Exchange Capacity (meq·l–1) 50
Exchangeable bases (mg·kg–1)
K 319
Na 154
Ca 8040
Mg 351
Dry bulk density (g·cm–3) 1.28
Soil moisture at 1/3 bar (cm3·cm–3) 0.39
Soil moisture at 15 bars (cm3·cm–3) 0.20
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a
Semiarid Mediterranean Clay Soil
Copyright © 2011 SciRes. AJPS
Table 2. Wheat growing season monthly rainfall for the study period (1994-2003) and for the long-term records (1967-2003).
Rainfall (mm)
Month 1994-
1995 1995-
1996 1996-
1997 1997-
1998 1998-
1999 1999-2000 2000-
2001 2001-
2002 2002-
2003 Average Long-term
November 33 43.2 37 76.9 0 36 13.4 16.3 189.1 49.4 49.2
December 0 74.2 231.8 103.5 68.1 33.3 98.8 146.9 29.1 87.3 60.4
January 0.5 176 74.1 36.2 54.2 31 66.5 0 25.8 51.6 55.7
February 32 28.7 1 44.7 23.1 0 0 4 22.2 17.3 49.6
March 06 74.7 17.8 8.5 26 0 0 60.8 29.3 24.8 42.8
April 39.5 1.7 58.8 8.1 0 41.6 0 52.4 20.9 24.8 37.6
May 2.5 41.5 0 0 21 10.5 10 4.7 2.5 10.3 13.4
Total 113.5 440 420.5 277.9 192.4 152.4 188.7 285.1 318.9 265.5 308.7
Deviation of
total b –195.4 131.1 111.6 –31.0 –116.5 –156.5 –120.2 –23.8 10.0 –43.4
Phase c 57.70 73.20 81.80 94.00 75.60 65.81 94.70 58.65 83.47 77.44 69.61
Phase d 42.30 26.80 18.20 6.00 24.40 34.19 5.30 41.35 16.53 22.56 30.39
a Long-term rainfall average (1967-2003); b Deviation of growing season total from long-term total (1967-2003); cPhase assumed from November to February
(% of growing season rainfall); dPhase assumed from March to May (% of grow ing season rainfall).
Table 3. Long-term mean monthly minimum/maximum
temperature and pan evaporation at the experimental site
Temperaturea (˚C)
Month Minimum Maximum
Class A Pan
Evaporationb (mm )
January 6.0 20.0 78
February 7.2 21.3 89
March 8.7 23.7 112
April 10.3 25.3 138
May 12.7 27.4 206
June 15.9 30.6 219
July 18.0 34.4 308
August 20.2 31.8 294
September 18.2 31.6 225
October 12.8 28.7 157
November 10.1 24.1 100
December 8.4 21.4 72
Average 12.4 26.7
Total 1998
adata of 1967 to 1998. bdata of 1985 to 1996.
tion and sub-plot to tillage-residue management system.
Five rotations were studied (Table 4). All phases (rota-
tion-year) of each rotation were present each year and
each treatment was cycled on its assigned plot. Two till-
age systems were established: conventional tillage with
off-set disk (CT) and Zero-tillage system. The most
common tillage practice is to prepare a seedbed by disk
harrowing after stubble grazing along the summer.
Nearly all stubble and crop residues are normally re-
moved from the field (via grazing or ballin g). The use of
disk harrowing helped to break clods and make a proper
seedbed, which is believed to capture and store autumn
precipitation in soils. The number of off-set disk opera-
tions to prepare seedbeds differed among years and crops.
Tillage depth ranged from 100 to 150 mm, depending
upon the conditions of the soil at time of tillage. These
practices have been shown to exacerbate degradation of
soils, promote erosion and reduce production potential.
In this study, stubble and plant residues were totally in-
corporated with tillage tools (under CT).
The experimental design combined tillage and stubble
treatments to allow their separate effects on grain yield to
be assessed (Table 4). Here, “tillage-residue management”
denotes these combinations as shown in Table 4. Zero-
tillage system (NT) received No-tillage and the only soil
disturbance was for seeding and fertiliser banding.
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a 205
Semiarid Mediterranean Clay Soil
Table 4. Description of cropping sequences and tillage-
residue management systems used in the experiment and
their abbreviations.
Cropping system:
Abbreviation Sequence’s description
CW Continuous Wheat
WF Wheat-Fallow
WBF Wheat-Barley-Fallow
WMF Wheat-Maize-Fallow
WLF Wheat-Lentil-Fallow
Tillage and Residue Man-
agement System: Abbre-
viation System’s description
NTr Total or full removal of flat residues
in no-tillage wheat phase for fodder
use (no-mulch cover).
Partial removal of flat residues in
no-tillage wheat phase (50 - 60 per-
cent mulch cover) with uniform cover
of the soil.
Total maintenance of flat residues in
no-tillage wheat phase (full mulch
cover) with a layer of several centi-
meters in thickness.
CT Conventional tillage with off-set disk
harrows—biomass incorporated.
Note: After wheat harvest, stubble was approximately 10 - 15 cm tall and
was not removed from no-tillage treatments. Under no-tillage systems,
stubble and crop residue from other crops were maintained at the surface,
while under conventional tillage, this biomass was incorporated in the soil
with disking.
Smallholders in mixed crop-livestock systems consti-
tute a very large fraction of farming enterprises in Mo-
rocco. In those systems, crop residues are a strategic
production component. This study aims at better under-
standing the tradeoffs in crop residue uses in cereal based
systems. The major trade-off in most systems is the short
term benefits of using crop residues to feed livestock
versus leaving the crop residues in the field to improve
water management and availability as well as soil pro-
ductivity (nutrient balance, erosion control and soil
health). Consequently, in order to help devise these far-
mers for possibilities of integrating grain and livestock
production, three No-tillage wheat residue management
scenarios were investigated (total NTr, partial NTp and
No-removal of residues NTm). Because of the high op-
portunity cost of crop stubbles and straw in traditional
mixed farming systems, there may be a temptation to
adopt a No-tillage system (NTm) while persisting with
removal of stubble for other uses (livestock, fuel and
commodity). In the other two options, NT has to be
adopted as a system, combining both direct seeding and
either full or selective retention of crop residues at the
soil surface. The NTp help to explore sharing and opti-
mizing crop residues between No-tillage and traditional
or energy uses [2 3] .
2.3. Crop Management, Fertilization and Pest
In this study, we tested the performance of alternative
rotations to the typical wheat monoculture in a rainfed
Mediterranean semiarid area of south-western Morocco
under No-tillage (NT) and conventional tillage systems.
Hence, four other rotations were established and main-
tained over 9-yr period (1994-1995 to 2002-2003): a
wheat-barley-fallow rotation (W-B-F), a wheat-Maize-
Fallow rotation (W-M-F) and Wheat-Lentil-Fallow (WLF)
rotation (Table 4).
In 1995-1995 to 1996-1997, a No-till drill equipped
with coulters, double-disk openers and single press
wheels with 0.25 m row spacing (TYE, The TYE Com-
pany, Lockney, USA) was used to plant wheat, barley
and lentil in all plots. In 1997-1998 to 2002-2003, wheat
was planted in a 0.25 m spacing using a research proto-
type hoe-type No-till drill built at INRA-Dryland Re-
search Center, Settat, Morocco. This newly developed
drill permitted N and P fertiliser placement beneath the
seeds. Winter wheat (Triticum aestivum L. cv Achtar or
Tilila) and barley (Hordeum vulgare L. cv ACSAD 60,
Laanacer or Aglou) were sown 30 - 50 mm deep at a
seed rate of 120 kg·ha–1.
Like many leguminous crops, lentil (Lens culinaris L.
cv Bakria) plays a key role in crop rotation due to their
ability to fix nitrogen. It was seeded using the No-till
wheat drills at a rate of 60 kg·ha–1 at spacing of 0.50 m.
Corn (Zea mays L.) is cultivated throughout the
Chaouia region in rotation with wheat. Corn varieties
(Mabchoura and Doukkalia) were planted either using a
commercial 4-row No-till planter or manually in rows
spaced 0.60 m and thinned to 60 - 65 thousands plants
per hectare. Time of seeding for wheat, barley and lentil
crops varied from 20 November to 5 December. Corn
planting date ranged from mid-February to mid-March
depending on the soil moisture. All field-crop varieties
are adapted to the environment of Sidi El Aydi.
Soil analysis permitted the following fertilizer recom-
mendations: ammonium nitrate (33.5% N), at a rate of 75
kg·ha–1, and triple super phosphate (45% P2O5), at a rate
of 100 kg·ha–1, were placed in the seed row as starter
fertilizers for wheat, lentil and barley. Additional urea
fertilizer (46% N) was broadcast at the mid-tillering
stage of wheat (50 kg·ha–1). For Corn, ammonium nitrate
(100 kg of material per hectare) and triple super phos-
phate (50 kg of material per hectare) were applied at
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a
206 Semiarid Mediterranean Clay Soil
planting. Soil tests at Sidi El Aydi indicate high K and
therefore K fertilizer was not applied. These application
rates ensured that nutrients (N, P) were not limiting pro-
duction and crops did not exhibit any deficiency symp-
toms. No irrigation or farm manure was used in this ex-
Pre-plant herbicides were used for weed control in all
treatments. No-till treatments were sprayed with gly-
phosate at 2 - 3 L·ha–1 to control any standing vegetation
during the week before crop planting. Before seeding, all
wheat, barley and fallow plots were sprayed with chlo-
rosulfuron herbicide (10 to 20 g·ha–1). Corn and lentil
were sprayed at seeding with simazine at rate of 1.5 and
1 L·ha–1, respectively.
2.4. Measurements
Climatic data were collected between 1994 and 2003 at
the Sidi El Aydi Experimental Station, less than 1 km
from the experimental site. Precipitation data were col-
lected daily throughout the wheat growing season and
summarized as monthly means. Historical climatic data
were obtained from the same weather station.
At harvest, wheat grain was harvested at 10 - 15 cm
above ground from the plot area to determine grain yield
(GY), reported at 130 g·kg–1 moisture concentration. Th e
above-ground dry matter or wheat biomass (TDM) was
determined from hand samples taken from two 1-m2
quadrats of each plot at harvest.
2.5. Data Analysis
2.5.1. Analysis of Variance
All data were subjected to an analysis of variance using
the procedures of SAS [24-26] for each variable. The
analysis of variance was carried out for each year as well
as over years. This combined variance analysis provided
an overview of the magnitude of variation among years
and treatments and especially the treatment * year inter-
action. When the F-test indicated statistical significance
at 5%, treatment means were separated by Least Signifi-
cant Difference (LSD) test.
2.5.2. Stability Analysis
The significance of the interactions of treatment x years
can be interpreted using stability analysis. It is the linear
regression of treatment yield on the year environment
mean yield (average yield of all comparable treatments in
a given year). This analysis is carried out without the use
of data transformation. High yield stability usually refers
to a crop’s ability to perform consistently, whether at
high or low yield levels, across a wide range of environ-
ments [27]. The regression tests were carried using SAS
statistical package. A regression coefficient (slope, b) > 1
is indicative of below average stability while a regression
coefficient < 1 is indicative of above average stability.
Specific tillage-residue management and cropping sys-
tems can be considered stable if variation is low over
years (i.e. Low Coefficients of Variation, CVs) [28].
3. Results
This field study assessed average wheat yields and tem-
poral yield variability over a 9 -year period in agricultural
management systems that are part of a long-term crop-
ping systems experiment at Sidi El Aydi Station (SEAS)
in south-western Morocco.
Table 5 presents pooled (averaged over the nine years)
analysis of variance of the experiment. Significant year
effects were noticed for all management systems. Table
5 indicates significant Tillage x years and Rotation x
years interactions (P < 0.001) and showed the influence
of changes in environments on the yield performance of
the various tillage-residue management and cropping
systems evaluated.
It is also worth noting that during the course of the
experiment, soil quality attributes have changed or been
altered by tillage, residue management and cropping sys-
tems. These modifications in soil porosity and organic
matter, stable aggregates, nitrogen and phosphorus con-
tents of the soil surface (0 - 5 cm) were reported by sev-
eral authors [29,30].
Table 5. Degree of freedom and Mean square error (MSE)
for wheat grain and biomass yields as affected by year, till-
age-residue management and cropping systems (Combined
ANOVA) at Sidi El Aydi (Morocco); 1994-2003.
Source of variation df Biomass Grain yield
Year (Y) 8 735.4 99.47
Block (B) 2 32.89 2.53
Error a 16 5.159 0.68
Rotation (R) 4 5.159 16.088
Y * R 32 1 12. 8 2.018
Error b (Y * R * B) 72 0.134 0.028
Tillage-residue management (T) 3 18.32 2.79
Y * T 24 5.6 1.25
R * T 12 0.18 ns 0.03 ns
Y* R* T 96 0.09 ns 0.019 ns
Error c 270 0.12 0.025
ns = Not significant. All other factors or interactions were highly significant
(P < 0.001).
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a 207
Semiarid Mediterranean Clay Soil
3.1. Growing Conditions
The semiarid climate, gently sloping topography and
slowly permeable clay soils are important characteristics
of the western plains of Morocco. Humid winters and dry
summers c ha racterize the c limate of Sidi El Aydi (Chaouia).
Table 2 gives wheat growing season monthly rainfall for
the study period (1994-2003) and for the long-term re-
cords (1967-2003).
As reported in Table 2, during the nine years of the
experiment, about 77% of the 265.5 mm mean growing
season rainfall (GSR) for wheat occurs from November
through February and about 23% from March to May.
However, for the 1967-2003 records, the two phases re-
ceived 70 and 30% amount of rainfall for the two grow-
ing periods respectively. Exceptionally, in 1997-1998
and 2000-2001, most rain fall occurred in the period from
November to January (94%), leaving the rest of the
growing season almost dry. At the opposite, in the driest
year (1994-1995), almost 60% of received rainfall oc-
cu rre d i n t he rep rod uctive period of wheat (Table 2). The
wettest year (1996-1997) corresponded to the average
year with 82 and 18% of rainfall received in the vegeta-
tive and reproductive phase, respectively.
The most common and widespread of the country’s
natural hazards is drough t. It is a country-spread problem
seriously influencing wheat production and quality.
Drought may occur early in the season as in 1998-1999,
in mid-season as in 1996-1997, 1999-2000 and 2000-
2001 or in later season as in 1997-1998. It may also oc-
cur at combination of stages such as in 1994-1995.
Weather conditions in the nine seasons from 1994-1995
to 2002-2003 spanned much of the variability, which
characterizes rainfall records for this area (Table 2). The
growing-season rainfall (GSR) for the 9-year study pe-
riod averaged 265.5 mm per year, 43.4 mm lower than
the long-term average; thus conditions were unfavour-
able for dryland cropping. In fact, the deviation of GSR
from the long-term rainfall average varied from –195.4 to
+131.1, which shows the large variation of rainfall pat-
tern of Chaouia region (Table 2).
Growing season rainfall varied from as low as 113.5
mm (1994-1995) to 440 mm (1995-1996), with an aver-
age over the 9 years of 265.5 mm (Table 2). Only 3
years (1995-1996, 1996-1997, and 2002-2003) were
above long-term average (1967-2003) that is 308.9 mm.
Hence, differences in rainfall contributed to different
yield respon ses, as shown by the variou s treat ment * year
interactions (Table 5).
3.2. Wheat Yields
Seasonal and annual variations in rainfall strongly influ-
enced wheat responses to tillage-residue management and
cropping systems in this experiment. Rainfall amount
and distribution are critical for proper wheat perform-
ances. Moisture stress at critical physiological stages
could inhibit crown roots, reduce effective tillers, dimin-
ish wheat vegetative growth and number of grains per ear
and cause poor grain-filling. Generally, in semi-arid ar-
eas, wheat under No-till conditions are under high avail-
able water content during most the growing season and
lower temperatures [16].
The long-term effects of tillage and wheat residue
management on wheat grain yields are summarized in
Table 6. Complete crop failure was observed in the first
and the sixth year of the experiment for all tillage-residue
management systems and rotations. At the research site,
cumulative growing season rainfall was 113.5 and 152.4
mm for the two years, respectively. There is a need of at
least 190 mm of moisture during the wheat growing sea-
son to garanty wheat grain production in semi-arid re-
gions as noted by [14].
3.2.1. Tillage—Residue Management Effects
When averaging over th e nin e years, No -tillag e system in
its 3 variants guarantied higher grain yields than the
convention al tillage system (Table 6). Within the 3 vari-
ants of residue cover, it is clear that NTp should be the
logical choice for mixed farming systems, since it per-
mitted identical yield as NTm. This is due to the need to
export partially biomass for livestock feeding. It is also
important to Note that grain yield was significantly lower
under CT than bare No-till (NTr). Hence, it is evidently
recommended to support No-tillage for higher and stab le
yields of wheat; which is a leeway to adapt under con-
trasting climates.
The effect of tillage system was significant in all years
at the exception of 1996-1997 and 1999-2000. In addi-
tion, CT was permitting higher yields than NT in one
year (1997-1998) (Table 6). Residue management under
NT did not show effects in 4 contrasting years (1994-
1995; 1996-1997; 1998-1999 and 1999-2000). In the
other 5 years, either NTp or NTm or both out-yielded NTr.
Hence, when analyzing the performances of wheat yield
under the various tillage-residu e management options for
the 9-year, it is clear that No-tillage either equalled or
exceeded CT. Particularly for NTp, wheat yields were
largely greater than CT in 1995-1996; 2000-2001 and
2002-2003 as shown by the high yield ratios of Table 6.
These trends were also reported by [13]. However, [31]
did not find any difference between the two tillage sys-
tems in Northern Syria for barley production.
The type of drill used in No-tillage systems changes
the growing environment ann thereby impact the d ca
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a
Semiarid Mediterranean Clay Soil
Copyright © 2011 SciRes. AJPS
Table 6. Effect of tillage and wheat residue management on wheat yields (Mg·ha–1).
1994-1995 1995-1996 1996-1997 1997-19981998-19991999-20002000-20012001-2002 2002-2003 AverageYielda
NTr 0 3.37c 2.69a 1.11d 2.98a 0.26a 1.91b 3.25bc 3.32a 2.10B
NTp 0 3.57b 2.72a 1.31c 2.93ab 0.28a 2.30a 3.42a 3.36a 2.21A
NTm 0 3.94a 2.65a 1.62b 2.86ab 0.26a 2.27a 3.31ab 2.94b 2.21A
CT 0 2.60d 2.73a 1.75a 2.76c 0.28a 1.01c 3.16c 2.85b 1.90C
Average 0F 3.37A 2.70C 1.44E 2.88BC 0.27F 1.87D 3.29A 3.11AB 2.10
NTr /CT - 1.30 0.98 0.63 1.08 0.93 1.89 1.03 1.16 1.13
NTp/CT - 1.37 1.00 0.75 1.06 1.00 2.28 1.08 1.18 1.21
NTm/CT - 1.51 0.97 0.93 1.04 0.93 2.25 1.05 1.03 1.21
athe ratio of NT to CT not including the 1994-95 year in averaging over years. NTr = Full removal of flat residues in no-tillage, NTp = Partial removal of flat
residues in no-tillage, NTm = Total maintenance of flat residues in no-tillage, CT = Conventional tillage. In the column (small or italic letters) or row (capital
letters), means followed by the same lette rs do not differ by LSD test at p = 0.05.
physiology of the cr op. Th ese facts may have so me nega-
tive outcomes on crop growth. Use of the double-disk
type drill, during the first 3 years, had various disadvan-
tages, including surface application of P fertilizer, weak
penetration through thick residues and dry soil, and in-
ability to adequately cut through residues. Under NTm,
seeds were also in close contact with the straw which
reduced early vigour and growth [16]. The high residue
cover could delay emergence, seedling development and
retard tillering of wheat seeded with disk drills [32].
The hoe-type drill, used during the 6 last years, pro-
duced more soil disturbance along seeding row than TYE
drill, and was needed fo r better seeding of wheat into dry
soil surface. It also permitted localisation of P and N fer-
tilisers in proximity to the seeds, which helped wheat to
grow more vigorously and produce m ore biomass [33,34].
3.2.2. Cropping System’s Effects
Wheat is an important part of the cropping system in
semiarid Morocco. Yielding of dryland wheat depends
enormously on the amount of profile-stored water and/or
precipitation during the growth period. Wheat is very
responsive to crop rotation. The long-term effects of
cropping systems on wheat grain are shown in Table 7.
The continuous wheat rotation had the lowest yields
irrespective of the treatment and years (Table 7). Not
including 1994- 1995, wheat yields varied from as low as
0.05 Mg/ha under WLF in 1999-2000 to as high as 3.83
Mg/ha under WMF in the year (2001-2002).
On average, it is s hown from Table 7 that wheat yields
are the highest under WF; WBF and WLF. Wheat yield
under WMF is intermediary and higher than CW. The
WLF could be more performing if Not the low wheat
yielding in 1999-2000 due to residual effect of herbicide
(Simazine) used for controlling weeds in lentil. The per-
cent increase in wheat yields when comparing biennial or
triennial rotations to CW varied from 84% under WF to
59% under WMF (Table 7).
3.3. Above-Ground Biomass Yield
Grain yield is the product of plant b iomass and partition-
ing of that biomass to the harvested components. Hence,
in uncovering the impact of tillage systems on yield, it
would be necessary to determine whether NT limits plant
biomass accumulation or Not. In other terms, although
much work has been conducted on the impact of NT on
wheat yield, there is little information on the impact of
NT on above-ground biomass accumulation. A reduction
in biomass may occur due to poor stand establishment or
reduced tillering [16].
3.3.1. Tillage—Residue Management’s Effects
In Table 8, tillage and residue management system’s
effects on wheat above-ground biomass are presented.
NT production systems did not generally red uce the abil-
ity of wheat cultivars to accumulate biomass. The NT
treatment impacted biomass yields of wheat, but this re-
sponse was dependent on the environment. According to
Table 8, the three variants of NT helped accumulation of
higher biomass than CT. It is also reported in the same
Table that biomass yield increases with residue cover
under the soil, on average and by year. At the exception
of 1996-1997 where NTp was permitting higher biomass
yield of wheat, NTm was showing the highest biomass. In
fact, it has reached 12.67 Mg·ha–1 in 1995-1996. Not
considering the driest year of 19 94-95, in other dry years
(<200 mm), NT out-yield ed CT by 1.11 to 2.07 as shown
in Table 8. Especially, NT biomass yields were two
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a 209
Semiarid Mediterranean Clay Soil
Table 7. Wheat yield responses under various crop rotations (Mg·ha–1).
rotation 1994-1995 1995-1996 1996-1997 1997-19981998-19991999-20002000-20012001-2002 2002-2003 Yield
ratio aAverage
CW 0 3.13d 1.98d 0.94e 1.10c 0.29c 0.93d 2.60d 1.82c 1.001.42D
WF 0 3.71b 2.90b 2.05a 3.20b 0.44a 2.24a 3.21c 3.28b 1.842.34A
WBF 0 2.86e 3.22a 1.44c 3.71a 0.31b 2.12b 3.38b 3.65a 1.762.30AB
WMF 0 3.39c 2.64c 1.05d 3.24b 0.26d 1.96c 3.83a 3.19b 1.592.17C
WLF 0 3.76a 2.73c 1.73b 3.16b 0.05e 2.10b 3.41b 3.65a 1.632.29B
Average 0F 3.37A 2.70C 1.44E 2.88BC 0.27F 1.87D 3.29A 3.11AB 2.10
aratio of wheat yields under fallow based rotations to continuous wheat for the average of 1996-2003. CW = Continuous Wheat, WF = Wheat-Fallow, WBF =
Wheat-Barley-Fallow, WMF = Wheat-Maize-Fallow, WLF = Wheat-Lentil-Fallow. In the column (small or italic letters) or row (capital letters), means fol-
lowed by the same letters do not differ by LSD test at p = 0.05.
Table 8. Tillage and residue management sy ste m’s effects on wheat above-ground biomass (Mg·ha–1).
treatment 1994-
1995 1995-1996 1996-1997 1997-
1998 1998-1999 1999-20002000-
2001 2001-20022002-2003 Average Yield
ratio a
NTr 0.15c 11.64b 9.91b 3.01c9.79a 5.07c 3.96b6.02d 6.49b 6.23C
NTp 0.41b 11.20c 10.65a 3.56b9.60a 5.31b 4.80a6.48c 6.74a 6.52B
NTm 0.52a 12.67a 9.59b 4.42a9.62a 5.35a 4.75a6.92a 6.53ab 6.71A
CT 0.19c 9.99d 9.93b 4.68a8.64b 4.27d 2.29c6.80b 6.03c 5.87D
Average 0.32F 11.37A 10.02B 3.92E9.41B 4.99D 3.95E6.55C 6.45C 6.33
NTr/CT 0.79 1.16 0.99 0.64 1.13 1.19 1.73 0.93 1.08 1.07
NTp/CT 2.16 1.12 1.07 0.76 1.11 1.24 2.10 0.95 1.12 1.29
NTm/CT 2.74 1.27 0.97 0.94 1.11 1.25 2.07 1.02 1.08
athe wheat above-ground biomass ratio of NT to CT in averaging over years. NTr = Full removal of flat residues in no-tillage, NTp = Partial removal of flat
residues in no-tillage, NTm = Total maintenance of flat residues in no-tillage, CT = Conventional tillage. In the column (small and italic letters) or row (capital
letters), means followed by the same lette rs do not differ by LSD test at p = 0.05.
times higher than CT in 2000-200 1 where the wh eat was
under severe droughts in mid- and late seasons. However,
in wet years (>400 mm); NT /CT varied from 0.97 to 1.27.
In general, yield advantage of NT over CT increased due
to residue cover level (yield ratio s of 1.07; 1.29 and 1.38
for NTr; NTp and NTm).
3.3.2. Cropping System’s Effects
Rotation effects on above-ground wheat biomass for the
nine years are exhibited in Table 9. Cropping systems
tested in this trial respond consistently among environ-
ments and there was a strong interaction among envi-
ronments or years and cropping system (P < 0.001) (Ta-
bles 4 and 9).
From results presented in Table 9, continuous wheat
(CW) permitted the lowest yearly average biomass yield
among the cropping systems tested in this experiment.
However, especially in 199 5-1996 and 1997-1998 and in
2001-02, CW out yielded WBF and WLF respectively.
WF rotation was best performi ng in year of severe drough t
(i.e. 1997-1998) as compared to other cropping systems.
WF and WBF surpassed all other rotations in adapting
wheat to produce and accumulate dry matter in 1999-
2000 where GRS was only 152 mm. Biomass yield ad-
vantage for biennial and triennial rotation over CW var-
ied from 48% to 76%.
It is clear from this analysis that farmers could choose
either WF or WBF as appropriate cropping systems.
However, for an intimate integration of grain and live-
stock productions, WBF would a desired and reliable
choice since it is including a dual purpose crop, barley.
Other cropping sequences including forage crops are also
of relevance to dryland farmers if well managed [4].
3.4. Yield-Rainfall Relationships
Table 10 presents the regression coefficients of linear
relations between yields and GSR, vegetative phase
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a
210 Semiarid Mediterranean Clay Soil
Table 9. Rotation effect on above-ground wheat biomassa (Mg·ha–1).
Rotation 1994-1995 1995-1996 1996-1997 1997-19981998-19991999-20002000-20012001-20022002-2003 Biomass
ratio b Average
CW 0.27b 11.38d 7.50e 3.16cb 3.72c 3.24d 1.96e 6.04d 4.04c 1 4.59E
WF 0.35ab 11.74a 10.98b 6.85a 10.56b 6.22a 4.65a 6.54c 6.62b 1.76 7.17A
WBF 0.41a 10.66e 12.00a 2.42c 12.16a 6.07a 4.55b 6.79b 7.52a 1.69 6.95B
WMF 0.25b 11.45c 9.59d 3.85b 10.45b 3.80c 4.06d 7.48a 6.38b 1.48 6.37D
WLF 0.31ab 11.64b 10.03c 3.30b 10.17b 5.62b 4.51c 5.92e 7.68a 1.58 6.57C
Average 0.32F 11.37A 10.02B 3.92E 9.41B 4.99D 3.95E 6.55C 6.45C 6.33
aWheat plants were harvest at heights of 10 - 15 cm. bRatio of wheat biomass yields under fallow based rotations to continuous wheat for the average of
1995-2003. CW = Continuous Wheat, WF = Wheat-Fallow, WBF = Wheat-Barley-Fallow, WMF = Wheat-Maize-Fallow, WLF = Wheat-Lentil-Fallow. In the
column (small or italic letters) or row (capital le tt ers), means followed by the same letters do not differ by LSD test at p = 0.05.
Table 10. Regression coefficients for grain yield and growing season (GSR), vegetative phase (VPR) and reproductive phase
(RPR) rainfall by tillage-residue management and c r opping system.
Cropping system
CW 0.869 0.714 0.779
WF 0.753 0.707 0.451
WBF 0.620 0.574 0.393
WMF 0.643 0.529 0.578
WLF 0.726 0.663 0.482
Tillage and residue management system
NTr 0.507 0.617 0.539
NTp 0.709 0.630 0.516
NTm 0.755 0.675 0.538
CT 0.731 0.649 0.532
NTr = Full removal of flat residues in no-tillage, NTp = Partial removal of flat residues in no-tillage, NTm = Total maintenance of flat residues in no-tillage, CT
= Conventional tillage. CW = Continuous Wheat, WF = Wheat-Fallow, WBF = Wheat-Barley-Fallow, WMF=Wheat-Maize-Fallow, WLF =
rainfall (VPR) and reproductive phase rainfall (PPR) as
explained in Table 5. Wheat yields are more dependent
on GSR and vegetative phase rainfall (VPR) as regres-
sion determinants are higher. CW is more responding to
seasonal variability of rainfall than the other cropping
systems. This confirms the stressed environment charac-
terizing continuous cropping. This result can be ex-
plained by the low yields of this cropping system. In
other terms, water conditions under fallow based rotation
helped wheat to depend less on late rainfall and hence
avoid late or mid-drought [14]. This is mainly due to
available water stored in so il profile fro m previous year’s
rainfall. This explains the stabilising benefit from fallow
in semiarid areas. Especially, from Tables 8 and 10, un-
der wheat—fallow, wheat is better user of rainfall p attern
or distribution and hence avo iding intermittent drought or
water deficit than in other cropping systems.
From Ta ble 10, the relation between yield and rainfall
parameters is positively correlated to residue level under
NT, mainly for GSR and VPR. CT is f ound intermediate
between NTm and NTp in responding to rainfall parame-
ters in a semiarid area. This can explain that residue
management is equivalent to water management in dry
areas under NT.
3.5. Stability Analysis of Grain Yields
Soil management systems have substantial impacts on
ecosystem processes that contribute to annual crop yield
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a 211
Semiarid Mediterranean Clay Soil
variability. Understanding and capitalizing on wheat
yield time-variability or stability has become one of the
most intriguing problems in current NT production re-
search in Morocco. An ideal agricultural technology or
system is one that achieves the highest yield across
multi-environments. Wheat yields under no-tillage were
shown to increase with respect to other traditional or
convention al tillage systems. Slopes with b < 1.0 indicate
better adaptation to poor environments, while genotypes
with “b >1.0” are best used in superior environments as
suggested by [35] .
Stability analysis provides useful parameter estimates
when numbers of treatments and environments consid-
ered in the analysis are sufficiently large [36], which is
the case in this study. The regression of treatment aver-
age yield on the environmental index resulted in regres-
sion coefficients shown in Table 11.
The yield potential of the No-tillage systems was gen-
erally superior to conventional tillage systems, but there
was no yield stability sacrificed to achieve the greater
yield potential. Table 11 gives the regression coefficient
(b) values of the tillage-residue management and crop-
ping systems developed from linear regression analysis.
Tillage-residue management treatments have “b” val-
ued ranging from 0. 90 to 1.05, while for the cropping
systems, “b” varied from 0.69 to 1.09. The No-tillage
treatments have a slope close to unity which shows an
average response to environmental conditions, as meas-
ured by the environment mean. In Figure 1, WF, WBF an d
WMF are showing identical linear trends in terms of
Table 11. Stability parameters for tillage—residue management and cropping systems based on grain yield data (1994-2003).
Slope b t-stat R-Square CV %
Tillage—Residue Management
NTr 1.006 90.18 0.988 63.84
NTp 1.050 44.00 0.987 61.63
NTm 1.042 27.74 0.968 60.81
CT 0.900 18.94 0.911 62.84
Cropping systems
CW 0.686 10.75 0.790 73.19
WF 1.084 30.63 0.967 56.11
WBF 1.085 19.55 0.926 61.82
WMF 1.048 35.54 0.971 65.70
WLF 1.095 42.11 0.986 63.39
CV = Coefficient of Variation; NTr = Full removal of flat residues in no-tillage, NTp = Partial removal of flat residues in no-tillage, NTm = Total maintenance of
flat residues in no-tillage, CT = Conventional tillage. CW = Continuous Wheat, WF = Wheat-Fallow, WBF = Wheat-Barley-Fallow, WMF =
Wheat-Maize-Fallow, WLF = Wheat-Lentil- Fallow.
Figure 1. Yield stability regression plots for cropping systems.
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a
212 Semiarid Mediterranean Clay Soil
grain yield and environment relationships. WLF is an
intermediate situation. Continuous wheat system is more
practical in low rainfall areas and harsh environments as
explained by low b. As shown in Figure 2, all 3 variants
of NT exhibited a higher linear tendency between yield
and environment as compared to CT.
One measure of yield variability is the coefficient of
variation of yield (Table 11). It is shown that NTr and
CT among tillage treatments and CW and WMF among
cropping sequences are having grain yield highly vari-
able than the other treatments. This maintains the con-
clusion that NT associated with residue cover and con-
servation cropping system (WF) are most likely to adapt
to conditions of Moroccan semiarid areas.
Following the method of [35], the environmental mean
of each tillage or cropping system was placed on the x
axis and the regression coefficient (yield stability) was
placed on the y axis to determine the relationship among
yield and yield stability (Figure 3). This figure shows
that the stability coefficient “b” increases with improve-
ment in environments.
4. Discussion
From this long-term study, it can be concluded that pro-
duction of winter wheat under No-tillage can have agro-
nomic benefits over conventional tillage systems, al-
though in some years it can result in lower yields. The
important finding from this study is that No-tillage h as to
be adopted as a system, combining both direct seeding
and retention of crop residues. It was concluded that No-
till with stubble retained treatment was the best option in
terms of higher and more efficient use of water
Figure 2. Yield stability regression plots for tillage-residue management systems.
Figure 3. Stability regression coefficients plotted against the average environmental means of tillage-residue management and
ropping systems. Stability regression coefficients were positively associated with yield. c
Copyright © 2011 SciRes. AJPS
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a 213
Semiarid Mediterranean Clay Soil
resources. Basically, NTp could be adopted in mixed
crop-livestock systems of semiarid areas for the purpose
of guarantying grain and feed.
Due to high grain and biomass production under NT,
our results demonstrate also, the effectiveness of No-tillage
with mulching in increasing rainfall use compared to the
conventional tillage system and complete stubble re-
moval under No-tillage in the semi-arid area of the
Chaouia region. This is explained by wheat yield—rain-
fall relationships. In fact, residue retention under NT may
have helped managing rainfall and carrying over soil
moisture during the growth and development of wheat
[37]. These possible good relations at the soil-residue
interface vis-à-vis rainfall distribution are the main rea-
sons for NT durability [13,38,39]. However, [13,40,41]
reported that the major limitation to NT adoption by
smallholder farmers is crop residue tradeoffs as soil
amendments and livestock bedding, feed, and/or other
off-field purposes and its low availability in dry areas
and droughty years.
From this study, it can be concluded th at either wheat-
fallow or wheat-barley-fallow can be promoted in semi-
arid areas but without an y involvement of tillage syste ms.
However, in semiarid Spain, authors found that wheat-
fallow is having low efficiency in increasing wheat
yields [37,38].
In this experiment, continuous wheat was found not
durable vis-à-vis changing climate. The instability and
low yields of continuous cereal have been reported by
other authors from semiarid Mediterranean areas [42].
From the stability analysis, NT is adapting to most
weather conditions occurred during the course of the
experiment. In other words, this analysis indicated that
yields in the No-tillage system were less influenced by
adverse growing conditions than conventional tillage
system, particularly under low rainfall. It is then, to the
decision of farmers, to manage the cropping system ac-
cording to technical and economical considerations:
In harsh and economically constrained environments,
continuous wheat can be used but is still risky. How-
ever, NT is an optio n f or reducing suc h ri sk [43].
In area of low rainfall (less than 300 mm), wheat-
fallow is a requirement for stable grain production
under NT [14]. However, this is not in agreement
with other authors from dry areas in Spain [44] and
US Great Plains [45].
In areas of favorable rainfall and weather conditions,
either lentil or barley could be used without additional
reliance on row crop drills as for corn [15]. Better
water supply for plants due to residue retention under
NT could result in higher yield [46].
In mixed farming, farmers may choose to include
barley or other forage crops in the three year rotation
to compensate for residue availability [47,48].
Considering the advantages of NT wheat production
systems to the region, such as earlier planting, reduced
erosion and improved soil conservation and fertility, ag-
ronomic changes that bring about optimal yields under
NT would be desirable. An in-depth understanding of the
physiological factors, that in some years, limit yield un-
der NT production systems may be useful in designing
genetic [49] or agronomic measures [50] necessary to
optimize yield under NT.
For a thorough understanding on impact of each deci-
sion, modeling is needed. Process-oriented crop growth
models simulate the effects of genetics, management,
weather and stresses on plant growth and yield [51].
In semiarid Mediterranean region, soil quality evalua-
tion under conservation and conventional tillage systems
should be prioritized [52] and carbon and nitrogen dy-
namics modeled under these contrasting systems [53].
These models will be the research focus in near future
and for estimating environmental consequences of shift-
ing to No-tillage technologies and conservation cropping
sequences in both dry [54] and irrigated systems [55].
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Special thanks to all postgraduate and graduate students
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