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1. R. Salghi et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 3), January 2014, pp.89-93
RESEARCH ARTICLE
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OPEN ACCESS
Partial Rootzone Drying: Changing Alternation Frequency at
Different Phenological Stages and Impact on Tomato Crop
N. Affi*, A. El Fadl*, M. El Otmani*, M.C. Ben Ismail*, L.M. Idrissi**, R.
Salghi***
* Département d‟horticulture, Institut Agronomique et Vétérinaire Hassan II, IAV-CHA, BP 121 Ait Melloul,
Morocco, Agadir
** Département de biologie, laboratoire de biotechnologies végétales, faculté des sciences, université Ibn Zohr,
BP8106 Agadir, Morocco
*** Département de Génie de l‟Environnement et Biotechnologie, ENSA, Université Ibn Zohr, BP1136 Agadir,
Morocco
ABSTRACT
The goal of the current work was to assess the effect of different alternation frequency applied at different
phenological stages on physiological parameters of a Partial rootzone drying (PRD) irrigated tomato crop. Three
treatments were applied. Besides the control irrigated at 100% of its water requirements, T3 and T4 are both
treatments that received 50% of water requirements and that were irrigated by PRD strategy. Crop cycle was
divided into three stages: S1 lasted from transplanting to 6 th truss flowering, S2: the period separating the 6th
truss flowering and the 2nd truss harvest, S3: lasted for the remaining crop cycle period beginning at 2 nd truss
harvest. While T4 was alternated every 10 days similarly, T3 was alternated every 14 days, 12 days and 10 days
during S1, S2 and S3, respectively. T3 maximum daily shrinkage (MDS) was 70% higher than T4 showing that
the later is more efficient than the former. As far as stomatal conductance (Cs) and leaf water potential (Ψl),
results show that both PRD treatments were affected by stress without noticing any statistical differences in
terms of those parameters. The control presented the highest Cs and Ψl levels during the whole crop cycle and
the lowest water use efficiency (WUE).
Keywords – alternation, Cs, leaf water potential, MDS, PRD
I.
INTRODUCTION
It is all known that water supply is limited in
the world and irrigation of agricultural lands accounts
for over 85% of water usage worldwide [1]. New
water-saving techniques such as the partial root-zone
irrigation (PRI) or partial root-zone drying (PRD)
have been proposed as an agronomic practice for
more efficient use of the limited water resources. The
PRD is a potential water saving irrigation strategy
that utilizes plant-to-shoot chemical signaling
mechanisms to influence shoot physiology. It works
in drip irrigation or furrow irrigated crops where each
side of the row is watered independently. When the
crop is irrigated, soil on only one side of the row
receives water while the other is allowed to dry [2]. at
each irrigation time, only a part of the rhizosphere is
wetted while the other side is kept dry [3].
Earlier results demonstrated that PRD reduced
transpiration, and maintained higher level of
photosynthesis [4]. Regarding the effect of PRD on
plant water relations, it was shown that the PRD
reduces tomato stomatal conductance by 20% and
maintain, therefore, the leaf water potential.
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II.
MATERIALS AND METHODS
2.1 Experiment Location
The experiment was carried out in the
Agronomic and Veterinary Hassan II Institute - the
Horticultural Complex of Agadir in a multi-tunnel
greenhouse and on an area of 1322 m2. The used
tomato cultivar is „Pristyla‟ that was grafted on
„beaufort‟. The crop was planted in 10th October 2012
and was conducted in vertical trellising and on a
single stem. Crop cycle lasted for 9 months.
2.2 Soilless system
Soilless system consists of containers (10 m
length, 25 cm depth and 40 cm width). Each
container is an experimental unit composed of 20
plants. The used substrate is sandy-silty (78% sand,
19% silt and 3% clay). This later was deposed over
two drainage layers: 5 cm coarse gravel layer and 5
cm fine gravel layer. As far as the separation between
root sides for PRD treatments, each container
consists of two juxtaposed substrate filled containers
and plants were planted on the juxtaposition line to
allow root separation.
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2. R. Salghi et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 3), January 2014, pp.89-93
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III.
RESULTS AND DISCUSSION
3.1 Greenhouse internal climate
According to VPD variation during the crop
cycle, three phases are observed. The first period can
be considered of law evaporative demand since the
VPD didn‟t exceed 1,5kPa. The second period
registered a slight VPD increase that remains,
however, suitable for tomato crop development and
growth . At the end of the crop cycle, VPD values
reached their maxima (4,5 kPa) and the internal
greenhouse climate became too difficult.
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
S2
24/06/13
09/06/13
25/05/13
10/05/13
25/04/13
10/04/13
26/03/13
11/03/13
24/02/13
13/01/13
0.5
29/12/12
2.5 Adopted Treatments
Besides control treatment that received
100% of its daily water requirement, two PRD
treatments were applied:
- T3: that treatment combined PRD and 50% of
crop water requirement supply and was alternated
every 14 days during transplanting – 6th truss
flowering stage, every 12 days during 6th truss
flowering – 2nd truss harvest stage and every 10 days
during 2nd truss harvest – cycle end stage.
- T4: It consists of 50% tomato water requirements
supply and irrigation events alternation every 10 days
similarly during the whole crop cycle.
2.6 Measured Parameters
2.6.1
Greenhouse climate:
Two parameters were automatically and
continuously measured: temperature and greenhouse
air relative humidity (ADCON Model TR1).
Measures were used to determine vapor pressure
deficit using the following formula:
2.6.2
Stomatal Conductance:
Its weekly measurements were performed
using a porometer (Leaf Porometer, SC1, Dacagon,
USA) and occurred between 12:00 and 14:00.
14/12/12
2.4 Experimental Design
A complete randomized design was used.
Three treatments were applied. Each treatment
consisted of 20 plants and was replicated eight times.
Data were analyzed using MINITAB software
version 15.1.1.0. Treatment means were separated by
Tukey‟s test at P ≤ 0.05.
VPD = es - ea
(3)
Where, es is the saturation vapor pressure at a given
air temperature and ea is the actual vapor pressure.
Stem Diameter Micro-Variations: In order to
monitor, continuously and at real time, stem diameter
microvariations, linear variable transducer (LVDT)
sensors (Sifatron Model D.F. 2.5) were used as
indicators of plant water status in tomato. Indices
derived from continuous stem diameter microvariations data have been developed to interpret these
data. Maximum daily shrinkage (MDS) is the studied
parameter and was calculated as the difference
between maximum daily stem diameter (MXSD) and
the minimum daily stem diameter (MNSD).
VPD (kPa)
2.3 Irrigation
The irrigation was performed using double
drip lines irrigation system with 40 cm spaced
emitters that generate a flow of 2l/h/emitter.
Concerning PRD treatments, alternation was allowed
through small valves that are placed in the beginning
of each drip line. Irrigation and fertilization
management were made within a fertigation station
through electro-valves. Daily reference evapotranspiration ETo was calculated using the formula of
[5]. Global radiation was measured by a pyranometer
(kipp and Zonen model splite).
ETo (mm/j) = 0,0016 x Gr (cal/m2/j)
(1)
To avoid water loss, net maximum irrigation
dose was determined referring to granulometric
properties of the substrate using the following
formula
NMD = f x (Hcc – Hpf) x Z x PSH
(2)
Where, f is the allowed water stock decrease (10%),
Hcc and Hpf are, respectively, field capacity and
welting point substrate moistures, Z is the root depth
and PSH is the percentage of the wetted zone.
According to substrate physical properties, calculated
NMD was equal to 0.768 mm. Using irrigation
system rainfall (4mm/h), each irrigation supply must
last 12 mn. As far as irrigation frequencies, they were
variable since they depend on the Etc/NMD ratio.
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S3
Figure 1: Greenhouse internal vapor pressure deficit
variation through the crop cycle.
3.2 Midday stomatal conductance and leaf
water potential responses
The average midday VPD varied between 1
kPa and 5 kPa recording several fluctuations.
Different treatment responses in terms of stomatal
conductance and Ψl during different measurement
points are illustrated by fig. 2B and fig.2A. The
highest stomatal conductance and Ψl levels were
recorded by the control T0 with statistically
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3. R. Salghi et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 3), January 2014, pp.89-93
Leaf water potential (10xMPa)
4/3/13
18/03/2013
25/03/2013
T3
01/04/2013
T4
08/04/2013
15/04/2013
T0
22/04/2013
06/05/2013
14/05/2013
25/05/2013
10/06/2013
17/06/2013
-6
-7
a
-8
a
a
b
ab
b
b b
b
bb bb
a
a
a
a
a
a a
-9
a
-10
-11
A-12
Stomatal Conductance (mmol/m2/s)
11/03/2013
120
ns
ns
* * *
*
* ns
110
a
100
b
ns
ns * *
* *
* *
ns * *
*
a
90
b
80
70
60
b bb b
b
b
* * *
* * *
*
* *
ns *
a
b
b
b
b
*
*
*
b
*
*
a
a
bb
b
b
*
*
*
*
*
*
ns ns *
*
*
a
b
b
b
b
b
b
b
50
B
40
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T3
T4
T0
midday VPD (kPa)
5
4
3
2
1
17/6/13
10/6/13
27/5/13
14/5/13
6/5/13
22/4/13
8/4/13
15/4/13
1/4/13
25/3/13
18/3/13
4/3/13
C
11/3/13
0
S3
Figure 2: Stomatal conductance (B), leaf water
potential (A) and midday VPD variation (C)
Stomatal conductance (mmol/m2/s)
Leaf water potential (10xMPa)
significant differences at 46 % and 84 % of the
measurement points, respectively, showing that the
Ψl is more water stress sensitive compared to the
stomatal conductance. Some research works suggest
that the PRD strategy helps maintain the water status
of tomato plant [3]. However, others researches that
are in accordance with our findings reported the
difference between the PRD treatment Ψl and control
Ψl which records the highest values [6], [7], [8], [9].
These differences are results of phenological stage
effect on tomato crop[8], the soil water status within
the irrigated rootzone side [8], [9] and specie and
variety specificity [6].
During the whole measurement period, there
was no statistically significant difference neither for
stomatal conductance nor Ψl when comparing T3 to
T4. Nevertheless, regression curves (fig.3) show
another difference. In fact, when comparing
regression line slopes, we noticed that T3 regression
line slope is twice that of T4 indicating the ability of
T4 to maintain Ψl despite of stomatal conductance
decrease whereas T3 Ψl was greatly reduced when
same stomatal conductance decline occurs.
According to [10], for tomato crop , a permanent
value of Ψf less than -0.6 MPa indicates that plants
are affected by water stress although midday Ψl
could vary between -0.8 MPa and -1.2MPa without
any effects on plant performance. Thus, PRD
treatments were along the measurement period under
progressive stress without reaching the threshold of
danger.
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-5
-6 45
-7
95
145
T3 y = -0.096x - 2.939
-8
-9
R² = 0.630
T4 y = -0.047x - 6.780
R² = 0.555
-10
-11
T0
y = -0.039x - 3.669
R² = 0.464
-12
Figure 3: leaf water potential and stomatal
conductance correlation
3.3 Maximum daily shrinkage
At the beginning of the measurement period,
which corresponds to S2 and in terms of MDS, T3
and T4 responses were completely different. While
T3 MDS reached an average of 81µm, that of T4
didn‟t exceed 47µm, 40% lower than T3. Besides, the
rates of the average increase over the control were
141 % and 40 % for T3 and T4, respectively. Hence,
MDS results indicate that T3 is 100% more stressed
than T4. Since S2 is a low evaporative demand
period (VPD≤2kPa) and the phenological stage of the
crop is identical (F6 -R2), the explanation of the
previous results exclude any climate or phenological
stage role. Thus, the effect of alternation frequency
adopted during S1 is confirmed. It seems, in fact, that
developing roots were not enough able to search for
water when they were left to dry the soil.
The beginning of the period S2 corresponds
to the alternation frequency decreasing by two days
for each treatment except T4. The least MDS values
were recorded for T4 reminding, in one hand, the
benefit of alternation frequency maintenance at
different crop cycle periods and, in the other hand,
previous adopted frequencies during S1. The same
explanation was found by [11] who found that the
application of regulated deficit irrigation with
varying doses depending on the phenological stages
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4. 140
T4
B
T0
120
MDS (µm)
100
80
3
C
2
1.5
1
0.5
14/12/12
17/12/12
20/12/12
23/12/12
26/12/12
29/12/12
1/1/13
4/1/13
10/1/13
13/1/13
16/1/13
19/1/13
18/2/13
21/2/13
25/2/13
28/2/13
3/3/13
26/5/13
29/5/13
1/6/13
4/6/13
8/6/13
11/6/13
14/6/13
17/6/13
25/6/13
28/6/13
0
S2
S3
Figure 4: MDS (A and B) and VPD (C) variation
3.4 Water use efficiency
As showed by the fig.5 below, the control
performed the lowest WUE comparing to PRD
treatments. In fact, T3 and T4 were, respectively,
132% and 168% more efficient than T0. This result
confirms previous findings since higher WUE means
less water loss allowed by stomatal conductance
decrease and leads to MDS reduction as found for
T4.
50
60
a
b
40
30
c
20
10
0
40
T0
20
T3
T4
Figure 5: obtained Water use efficiency
140
T3
A
28 juin 2013
25 juin 2013
19 juin 2013
16 juin 2013
7 juin 2013
13 juin 2013
4 juin 2013
10 juin 2013
1 juin 2013
29 mai 2013
26 mai 2013
3 mars 2013
28 févr. 2013
25 févr. 2013
19 févr. 2013
20 janv. 2013
17 janv. 2013
4 janv. 2013
14 janv. 2013
1 janv. 2013
11 janv. 2013
29 déc. 2012
26 déc. 2012
23 déc. 2012
20 déc. 2012
17 déc. 2012
14 déc. 2012
0
IV.
T0
100
80
60
40
V.
20
0
14 déc. 2012
17 déc. 2012
20 déc. 2012
23 déc. 2012
26 déc. 2012
29 déc. 2012
1 janv. 2013
S2
4 janv. 2013
11 janv. 2013 14 janv. 2013 17 janv. 2013 20 janv. 2013
19 févr. 2013
25 févr. 2013
28 févr. 2013
CONCLUSION
Applying fixed alternation intervals during
the crop cycle seems to be better than varying them at
different phenological stages. Besides, at the
beginning of the crop cycle, long lasting alternation
interval should be avoided.
120
MDS (µm)
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2.5
Water use efficiency
(kg/m3)
leads to a lower performance in citrus plants while
providing the same dose (50%) identically along the
cycle improves both agronomic and physiological
performances.
As far as the stage S3, during the period
ranging from 01/14/2013 to 24/05/2013, which is
considered the beginning of S3, the averages
recorded MDS were 90µm and 53μm for T3 and T4,
respectively. Compared to the control, the fore
mentioned treatments increase rate were 126 % and
33%. Hence, T3 treatment remains the most stressed
despite frequency alternation decrease. This response
confirms the role of alternation frequency previously
applied. T3 MDS results leads to conclude that long
alternation frequency should be avoided at the
beginning of tomato crop subject to PRD strategy.
Referring to the greenhouse internal climate data,
during the same period (Fig.4C), the values of the
VPD are similar to those of S1 showing that the
studied crop was not affected by the internal climate
[12]. In fact, during vegetative stage, root system
wouldn‟t be enough developed and would be unable
to meet plant water needs during prolonged
dehydration period. Identically, [13] concluded that
applied to 100% water requirement irrigated tomato,
the appropriate PRD introduction period is
recommended between fruit set and harvest.
Vapor pressure deficit (kPa)
R. Salghi et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 3), January 2014, pp.89-93
3 mars 2013
26 mai 2013
29 mai 2013
S3
1 juin 2013
4 juin 2013
7 juin 2013
10 juin 2013
13 juin 2013
16 juin 2013
19 juin 2013
25 juin 2013
28 juin 2013
ACKNOWLEDGEMENTS
This work was carried out within the
SIRRIMED « Sustainable use of irrigation water in
the Mediterranean Region» project which was funded
by the European Union within the 7th Framework
Program for Research and Development.
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