AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA
ISSN Print: 2151-7517, ISSN Online: 2151-7525, doi:10.5251/abjna.2017.8.3.94.117
© 2017, ScienceHuβ, http://www.scihub.org/ABJNA
Attempt to improve crops irrigation using soil, air canopy and plant leaf
temperature
Abdulrahman Abdualla Al-Soqeer*, Ansary E. Moftah and Fathi A. Gomaa
Department of Plant production and Protection, Faculty of Agriculture and Veterinary Medicine, Qassim
University, Saudi Arabia
[email protected]
ABSTRACT
This study was initiated to provide guidance on the irrigation timing and requirements for some
field crops based on the relationship between plant leaf temperature, canopy air temperature and
soil moisture content in an attempt to improve crop irrigation management. Methodology: A field
experiment on alfalfa and wheat crops was conducted in the Research Station, at the Faculty of
Agriculture and Veterinary Medicine, Qassim University, kingdom of Saudi Arabia. Soil analysis,
evapotrasnspiration rate (ET), stomatal conductance, leaf and air temperature and water use
efficiency were determined. Results: Air temperature was always higher than soil temperature for
both crops. The lowest values of soil and air temperature were recorded in January, but
increased successively starting from February to April. While, leaf temperature increased
gradually during the months of active growth (from February to April). Crop irrigation requirements
were nearly equal during the months of December and January, but both were raised during
February and April. Water use efficiency (WUE) of alfalfa ranged between 0.51 Kg/ m3 for first
cut, and 1.29 Kg/m3 for the second cut. This change in WUE was attributed to increasing rate of
evaporation from the bare soil before germination during December, and January months, for that
the first cut has a low water use efficiency. Conclusion: Soil temperature, air temperature and
plant leaf temperature can be used to determine irrigation requirements for many field crops.
Key words: Leaf-air temperature, evapo-transpiration, irrigation-scheduling, field crops.
gave poor indications of the overall status of the field
concerned (Guderle and Hildebrandt, 2015), unless
very large numbers of samples were processed.
However, with the advances in radiometry and
remote sensing, it might be possible to extend such
plant-based methods to the field scale. For example,
direct measurement of leaf temperature, stomata
conductance and transpiration rate, has been related
to crop water stress based on the fact that under
stress-free conditions the water transpired by the
plants used to evaporate and cool the leaves.
Conversely, in a water-deficit situation, little water
was transpired and the leaf temperature increased.
This was also the dominant mechanism when the
canopy was considered as a whole (Tarara and
Perez Peña, 2015). Therefore, plant canopy
temperature, stomata conductance and transpiration
were useful as an irrigation management tool
because they were related to the water status of the
plant and soil, and they can be measured easily. As
plants transpire, the evaporation of water from liquid
to vapor state consumed heat energy, which lowered
INTRODUCTION
Irrigation is a significant mean of raising production in
agricultural crops. It was essential in arid
environments and was often used to increase crop
productivity in semiarid and humid areas. Due to the
increasing demand of water for general purposes, the
supply available for irrigation was decreasing and
irrigation costs were rising. As a result, new
management strategies were proposed based on
controlled deficit irrigation to ensure low water loss
with minimum yield reduction. To achieve this
delicate balance between water use and crop yield,
farm managers needed an operational means to
quantify plant water stress and thus optimized their
irrigation scheduling (An et al., 2016).
Classical methods for monitoring crop water stress
include in situ measurements of soil water content,
plant properties or meteorological variables to
estimate the amount of water lost from the plant–soil
system during a given period. These methods are
time consuming and produce point information that
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Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
the leaf temperature; this and the movement of water
vapor away from the canopy removed heat and
resulted in a cooling effect. When the plant
evapotranspiration (ET) rate was reduced, such as by
soil water depletion, the rate of heat removal was
reduced and the canopy temperature increased. This
process links canopy temperature with crop water
stress and ET. Detection of crop water stress and ET
enable rational irrigation timing and application
amounts, which could increase crop water
productivity, reduced leaching of water and nutrients
below the root zone, and reduced the time required
for irrigation management (Yu et al., 2015).
MATERIALS AND METHODS
Layout of experimental field: The current study was
carried out at the research Station, Faculty of
Agriculture and Veterinary Medicine, Qassim
University, kingdom of Saudi Arabia during 2014 and
2015 growing seasons. The geographical location
E
720 m altitude. The region has an arid hot climate.
Sprinkler irrigation system were designed and built
for the two crops alfalfa and wheat which cultivated in
an area of 40 m2 for each crop. Discharge rate
gauges were fixed at the inlet line of each crop to
calculate the amount of irrigation water. The soil
moisture content and soil temperature were
measured in the top 20 cm from the soil surface,
before and after irrigation, using the HH2 with The
new W.E.T Sensor, type WET-1, from Delta-T. Air
temperature and canopy air temperature were
measured using mercury thermometers which
installed near the soil surface (5 cm) before
germination, and at graduated position according to
the plant height during different stages of plant
growth. Also, in this study the Li-1600 Steady State
Porometer was used to measure leaf temperature,
transpiration rate and stomatal conductance and the
principles necessary for measurement of leaf
transpiration and the calculation of leaf conductance
to water vapor exchange was covered. Three
replicates for all measured parameter were recorded.
All the agronomic practices were applied as
commonly used for growing alfalfa and wheat crops
and carried out according to the recommendation of
the ministry of agriculture.
Since a major role of transpiration was leaf cooling,
canopy temperature and its reduction relative to
ambient air temperature was an indication of how
capable was transpiration in cooling the leaves under
a demanding environmental load. The relationships
between canopy temperature, air temperature and
transpiration was not simple, involving atmospheric
conditions (vapor pressure deficit, air temperature
and wind velocity), soil (mainly available soil
moisture) and plant (canopy size, canopy architecture
and leaf adjustments to water deficit). These
variables are considered when canopy temperature
was used to develop the Crop Water Stress Index
(CWSI) which is gaining use in scheduling irrigation
in crops (An et al., 2016).
Leaf surfaces always emit thermal radiation, thus,
temperature can be measured based on leaf area.
These characteristics can carry advantages over
sensors that require physical contact with the plant,
which often sample an area of insufficient size to be
representative of the plant–atmosphere energy and
water balance. Therefore, measurement of leaf
temperature was possible using Steady State
Porometer (LI-1600). The concept of using
porometers for farm management, including irrigation
management, was ascribed to Monteith and Szeicz
(1962) and Tanner (1963), the first to report plant
canopy measurements using portable radiometers.
Wiegand et al. (1968) and Bartholic et al. (1972) were
among the first to use airborne thermal scanners to
differentiate crop and soil water status. The objective
of this study was to test if soil, air and leaf
temperature parameters as well as evapotraspiration
rate can be used as indicator for irrigation
management and irrigation requirements of field
crops.
Experimental measurements
Soil and water analysis: Before starting the
experiment, disturbed and undisturbed soil samples,
with three replicates, from 0-20 cm depth were
collected and used to determine some physical and
chemical characteristics of the experimental soil site.
Soil physical analysis: Soil mechanical analysis
was carried out using hydrometer method and calgon
as dispersing agent according to Day (1965). Soil
bulk density determined using undisturbed soil cores
according to Klute (1986). Soil moisture content at
field capacity (FC) and permanent wilting point
(PWP) were determined using pressure membrane
apparatus. A saturated undisturbed and disturbed soil
samples were equilibrated at air pressure of 0.33 and
15 bar, respectively, according to Klute (1986), and
the values of the available water (AW) were
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calculated as the difference between (FC) and
(PWP).
Calculate
the
actual
Evapotranspiration:
ETa (mg cm-2 day-1) = [( Ɵv fc – Ɵv bi) /100]× ds
Soil chemical analysis: Total soluble salts, and soil
reaction (pH) were determined in soil extract (1:2.5),
according to Page (1982).
Eta = actual evapotranspiration (cm)
Chemical analysis of irrigation water: Electrical
conductivity and water reaction (pH) were determined
according to Page (1982).
Ɵv bi = volumetric
irrigation(%)
Ɵv fc = volumetric
capacity(%)
ds
Three vital soil properties: Soil water content
before and after irrigation, Electrical conductivity (EC)
and Temperature were measurements using HH2
with the new W.E.T Sensor, type WET-1, from DeltaT Devices. HH2 can measures water content,
electrical conductivity and soil temperature based on
the theory of applying the frequency of Time Domain
Refract meter (TDR). The HH2 is able to display and
store the 3 outputs produced by the W.E.T Sensor:
water content, electrical conductivity and soil
temperature. The outputs can be stored in the HH2
for subsequent downloading to a PC using HH2 Read
PC software. Air temperature and canopy air
temperature were measured using mercury
thermometers which installed near the soil surface,
and graduated position according the plant height
during different stages of plant growth.
moisture
moisture
content
content
at
field
before
= depth of irrigated soil (cm)
All physical and chemical properties for soil and
irrigation water were determined according to Klute
(1986).
Water use efficiency (WUE): Watts and Goltz
(1985) defined WUE as the total yield in (kg/ht)
divided by total amount of
seasonal actual
evapotranspiration (m3/ht).
Ɵv wp = volumetric moisture content at wilting
pointe(%)
Leaf
temperature,
transpiration and
leaf
conductance: All mentioned parameters were
measured using the Li-1600 Steady State Porometer.
Measurements of transpiration and the calculation of
water vapor conductances of single leaves are nearly
always based on the measurement of vapor added
by transpiration into the air inside a chamber
(cuvette) enclosing the leaf or a leaf surface (Ansley
et al., 1994). In an 'open' system, a flow of air passes
through the chamber and the leaf transpiration rate is
calculated from the difference in water vapor content
of the air entering and leaving the chamber, the flow
rate and the leaf area. A typical 'closed' system would
have the leaf enclosed for a short period of time in a
chamber along with a humidity sensor so that the rate
of transpiration is a function of the rate of increase of
humidity in the chamber. Closed systems, while
useful for photosynthesis measurements, have
limited applicability for determination of transpiration
rates because the increasing air humidity causes a
reduction in the vapor pressure gradient from the leaf
to the air and, consequently, a reduction in the
transpiration rate. This, combined with problems of
water vapor adsorption to the chamber, render them
much less useful and reliable than open systems
even though they require less instrumentation. In an
open system, the leaf transpiration rate is equal to
the additional amount of water vapor leaving the
chamber above that entering. The leaf transpiration
rate E (mg cm-2 S-1) is related to the volume flow rate
by
ds
E = (pc-pa)*F/A
Calculation of the total irrigation water: According
to Borham (2001), the depth of total water irrigation
was calculated by using the following equation
dw (m3 ht-1) = [( Ɵv ai – Ɵv bi) /100]× ds
dw = total depth of irrigation water requirement (cm)
Ɵv ai = volumetric moisture content after irrigation(%)
Ɵv bi = volumetric
irrigation(%)
ds
moisture
content
before
= depth of irrigated soil (cm).
Net irrigation requirement:
dnir (m3 ht-1) = [( Ɵv fc – Ɵv wp) /100]× ds
dnir = net irrigation water requirement (cm)
Ɵv fc = volumetric
capacity(%)
moisture
content
at
field
= depth of irrigated soil (cm)
pc (mg cm-3) is the water vapor density in the cuvette
(chamber), Pa is the water vapor density in the dry air
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stream entering the cuvette (constant = 2%), A (cm2)
is the leaf area, and F (cm2 s-1) is the flow rate of the
dry air into the cuvette that can be expressed as:
reaches a steady state, it calculates and displays the
leaf diffusion conductance (the reciprocal of
resistance). A leaf with a rapidly changing gradient
indicates that the stomata are relatively open. The Li1600 instrument uses the last equation with rb = 0.15
s/cm to calculate stomata resistance. Stomata
conductance is computed as gs (cm/s) = 1/rs, where
rs (s/cm) is computed according to the last equation.
F = [(Tc/273.15) + 1)](101.3/P)*M
Tc (OC) is the cuvette temperature, P (KPa) is the
barometric pressure at the measurement site, and M
(cm3 s-1) is the standard volumetric flow rate of dry air
into the cuvette as measured by the Li-1600 and
equal to 101.3 KPa and 0OC.
Combining equations:
Data analysis: To compare effects of temperature,
evapotraspiration and stomatal conductance on
irrigation water requirements of alfalfa and wheat
crops, combined analyses of variance (ANOVA)
across plots were carried out using CoStat software
computer program, using ANOVA and Least
Significant Difference (LSD) test at p<0.05to compare
treatments. Microsoft excel was used for graphing
and scatter plot (CIMMYT, 1988).
rs = (A/F)(pl – pc)/(rs + rb)
RESULTS
Leaf conductance to water vapor loss is derived from
the transpiration rate. Conductance is usually
presented rather than their inverse, a resistance,
since conductance is a proportional to the flux and
they express the regulatory control exerted by the
stomata on transpiration rates. If transpiration rates
representative of leaves in their natural environment
are needed then it is necessary to determine leaf
temperatures as well as the vapor pressure of the
atmosphere and then recalculate a transpiration rate
using the stomata conductance determined in the
chamber and a boundary layer conductance. Since
stomata respond to the micro environmental
conditions, an important condition for the
recalculation of natural transpiration rates is that the
chamber conditions be sufficiently close to natural
conditions that the stomata conductance does not
change when the leaf is enclosed or that the
measurement be completed before the stomata have
time to respond.
Physical and chemical properties of soil and
irrigation water
Thus, leaf transpiration can expressed in terms of the
vapor density gradient between leaf and air divided
by the sum of stomata plus boundary layer diffusive
resistances:
E = (pl - pc)/(rs + rb)
a- Soil: The results recorded in Table (1)
explained some physical and chemical
properties of the soil used in the
experimental units that were assigned for the
cultivation of alfalfa and wheat. The results
showed that soil was sandy loam with
moderate clay content (around 15.6%). This
relatively high content of clay seemed to
improve the amount of soil water content at
field capacity of 0.33% (saturation% mean
was about 53%), wilting point (was about
6.17 bar), and available water (about
11.21%). Moreover, the chemical analysis
showed that electrical conductivity (ECe) was
about 0.37 ds/m, and the pH was about 8.25
which refer to slightly alkaline soil. In
addition, field capacity measurements (FC at
33%) recorded relatively high values that
ranged between 17.28 – 18.37 bars (Table
1). All these values of soil physical and
chemical characteristics indicated the
suitability of the soil for cultivating alfalfa and
wheat crops.
Steady State Li-1600, an effectively open chamber is
clamped to the leaf surface and water vapor released
through the stomata sets up a RH gradient along the
chamber. The instrument monitors RH at two points
along the flux path and, once the flux gradient
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Table (1): Chemical and physical analyses of the experimental soil used in the study.
Sample
NO.
ECe1:2.5
pH
Saturation
S/m
1:2.5
%
F.C
%
0.33
bar
W.P%
A.W
Sand
Silt
Clay
Texture
15
bar
%
%
%
%
class
1
0.40
8.26
51.47
17.28
6.14
11.14
78.33
5.01
16.66
Sandy
loam
2
0.40
8.23
56.86
18.37
5.95
11.26
80.00
5.00
15.00
Sandy
loam
3
0.30
8.28
50.52
17.65
6.41
11.24
76.66
6.68
15.00
Sandy
loam
mean
0.37
8.25
52.95
17.77
6.17
11.21
78.33
5.56
15.55
Sandy
loam
ECe = Siemens/meter (S/m); F.C = Field capacity; W.P = Welting point; A.W = Available water.
Irrigation water quality: Analysis of the water used
for irrigation of the studied crops showed that the
electrical conductivity of the water was about 1.38
ds/m which indicate the presence of some salts
though in low concentration, thus it was classified
according
to
Ayers
and
Westcott
(1985)
classification, as slightly saline water. The analysis of
irrigation water showed also that the pH of the water
was around 7.18, which was about neutral and again,
it is good for irrigation of many crop species.
This narrow change in soil moisture content values
before irrigation has not converted into significant
changes in soil temperature, where the soil
temperature range did not exceed 2.2OC. The results
showed also that there was no clear relationship
between soil or air temperature and soil moisture
content before irrigation. In this regard at soil
moisture content of 11.2%, soil temp was about 14OC
and air temp. was about 12.5OC, while at soil
moisture content of 13.1%, temperatures were about
12OC and 11.7OC, respectively. In contrast, data in
the figure showed in most cases rather relationship
between air and soil temperature.
Alfalfa Crop
December (Germination stage): This stage referred
to the situation in which seeds started to germinate
and there were many bare areas in the experimental
plots without vegetative cover. The results illustrated
in Fig (1) showed that air temperature was always
higher than soil temperature during the month of
Dec., however, soil temperature was more stable
than the air temperature and did not exceed 2.2OC,
while the mean of air temperature mean was about
3.6OC during the month. Data in the figure showed
also that the changes in soil moisture content values
before irrigation during the month did not exceed
1.9%, ranging between 11.2% and 13.1% by volume.
Based on the above data concerning the correlation
between soil temp, air temp and soil moisture
content, data recorded in Fig (2) illustrated the
relationship, based on the best fit equation between
the differences in air or soil temperature and total
amounts of irrigation water. In this regard the
statistical analysis showed a multiple relationship,
with second-degree, with highly significant correlation
coefficient (r = 0.83) and a regression coefficient
value of (R2 = 0.695).
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Fig. 1: The relation between soil moisture content before irrigation and soil or air temperature during
germination stage of alfalfa plants (December).
Fig. 2: The relation between the differences in soil or air temperature and total irrigation water of alfalfa
plants during germination stage of alfalfa plants (December).
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January (Seedling stage): This stage referred to the
situation in which seeds were germinated and
seedlings were produced but did not fully cover the
experimental area. Data reported in Fig (3) showed a
very good correlation between soil and air
temperatures; on contrary, changes in thermal
degrees of air and soil did not have a steady
relationship or similar direction with soil moisture
content before irrigation in many cases. For instance,
at soil moisture of 11.4% air temp and soil temp
were 9.8 and 7.2, respectively; while at soil moisture
content of 12.9%, the temperatures recorded 6.8 and
4.4, respectively, and at soil moisture of 14.1% these
temperatures were 6.1 and 5.2, respectively; which
indicated negative correlation between soil moisture
content and air or soil temperatures. Therefore, data
recorded in Fig (4) showed a strong inverse
relationship with correlation coefficient (r = - 0.78)
between the difference in thermal degrees of air or
soil and total irrigation water requirements during the
month of January at seedling stage of alfalfa plants.
These obtained results might indicate that the smaller
the differences between air and soil temperature the
greater
the
amount
of
irrigation
water.
Fig. 3: The relation between soil moisture content before irrigation and soil or air temperature during
seedling stage of alfalfa plants (January).
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Fig. 4: The relation between the differences in soil or air temperature and total irrigation water of alfalfa
plants during seedling stage of alfalfa plants (January).
February (Juvenile stage): This stage referred to
the early vegetative stage of plants a situation in
which plants grown active and covered all the
experimental area with their vegetative systems.
Results concerning the relationship between the
three factors that affected the growth of alfalfa plants
namely: canopy air temp, soil temp and soil moisture
content are shown in Fig. (5). Data indicated that
always canopy air temperature was higher than soil
temperature, the monthly average (during February)
of air temperature was 15.24OC while the monthly
average of soil temperature was 12.97OC; however,
soil temperature was relatively more stable than that
of canopy air temperature. In this regard, at soil
moisture of 6.2% soil temperature recorded about
8.7OC during the month, while canopy air
temperature was about 11.1OC. While, at soil
moisture content of 13.9% the monthly average of air
temperature was 14.9OC while the leaf temperature
was about 19.7OC. Data reported in the same figure
demonstrated also that, the difference between
canopy air temperature and leaf temperature ranged
from 1.7 to 4.1OC with an average of 2.73OC during
the month of February, during which the change in
moisture content values before irrigation ranged
between 6.2% and 14.2% by volume. This high
change in moisture content values before irrigation
has converted into visible changes in leaf
temperature, which ranged between 12.8OC and
22.4OC.
Data recorded in both figures (Fig. 5 and Fig. 6)
showed obviously that there was no clear relationship
between soil or canopy air temperature and soil
moisture content before irrigation. In this regard, data
in Fig (6) illustrated the relationship of the difference
between the canopy air, leaf temperature and total
volume of irrigation water requirements. The
statistical analysis found multiple relationship with the
fourth-degree regression factor, and with low moderate significant correlation coefficient (r = 0.596)
and a regression coefficient value of (R2 = 0.355).
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Fig. 5: The relation between soil moisture content before irrigation and soil or canopy air temperature
during juvenile stage of alfalfa plants (February).
Fig. 6: The relation between the differences of leaf or canopy air temperature and total irrigation
requirements of alfalfa plants during juvenile stage of alfalfa plants (February).
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March (Juvenile stage): The results recorded in Fig
(7) indicated that canopy air temperature was slightly
higher than soil temperature, particularly when the
soil moisture content was in the rage of 11.6% to
12%. Otherwise, values of air temperatures were
very close to those of soil temperatures which were
slightly higher as compared with air temperatures. In
this regard, the fluctuating values of air temperature,
during the month, were reflected in the determination
of the monthly average temperature of canopy air
which was about 19.6OC; while the monthly average
temperature of soil during the same period was about
17.9OC. It was obvious also that soil temperature was
more stable than that of canopy air temperature,
where the temperature fluctuating range of the soil
did not exceed 10OC during the month (between
23.5OC and 13.7OC), while the canopy air
temperature was fluctuating within about 12OC
(between 26.8OC and 11.6OC). Comparing the
monthly average of canopy air temperature with that
of leaf temperature, the results showed that average
temp of canopy air was about 19.6OC while the
average leaf temperature was about 21.5OC.
The collected data demonstrated also that the
differences between canopy air temperature and leaf
temperature ranged from 0.6 to 4.8OC with an
average of 1.83OC during the juvenile stage of plants
(at March). Moreover, the change in moisture content
values before irrigation during same period of plant
growth did not exceed 8%, but it was fluctuating
within the range of 5.3% to 13.3% by volume. The
change in moisture content values before irrigation
during at this time of growth was converted into
visible changes in leaf temperature, where the leaf
temperature was fluctuating in the range between
17.6OC and 27.7OC during same period of plant
development. On the other side, data in Figure (7)
indicated that there was no consistent relationship
between soil or canopy air temperature and soil
moisture content before irrigation. Thus, Figure (8)
showed the relationship of the differences between
canopy air temp, leaf temp and irrigation water
requirements. The plot indicated in Fig (8) showed
multiple relationship with third-degree, and with highly
significant correlation coefficient (r = 0.81) and a
regression coefficient value of (R2 = 0.66).
Fig. 7: The relation between soil moisture content before irrigation and soil or canopy air temperature
during juvenile stage of alfalfa plants (March).
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Fig. 8: The relation between the differences of leaf or canopy air temperature and total irrigation
requirements of alfalfa plants during juvenile stage of alfalfa plants (March).
April (late vegetative stage): This stage referred to
the beginning of the mature stage of plants in this
stage plants became fully grown and produced all
their vegetative systems that covered all the soil of
the experimental units. Data reported in Fig (9)
indicated that during this stage of plant growth,
canopy air temperature was, in most cases, higher
than soil temperature either at low or high soil
moisture content. The monthly average of canopy air
temperature during this month showed higher values
than those of other months, recorded about 23.6OC.
Moreover, the monthly average temperature of soil
was also higher than those recorded in other months,
and was about 19.6OC. Results showed also that the
monthly average temperature of canopy air was
23.62OC; while the monthly average temperature of
plant leaves was about 25.68OC.
soil moisture content ranged between 5.6% and
12.5% by volume. Again, this grate change in
moisture content values before irrigation during this
month was converted to observable changes in plant
leaf temperature. In this concern, leaf temperature
was higher than that recorded in other growth periods
and ranged between 22.6OC and 27.3OC. The
obtained data showed also that there was no reliable
relationship between soil or canopy air temperature
and soil moisture content measured before irrigation.
Therefore, the relationship of the differences between
canopy air temperature, leaf
temperature and
irrigation water requirements of alfalfa plants during
this stage of growth were plotted in (Fig. 10). In this
regard, a multiple relationship with third-degree was
found with highly significant correlation coefficient (r =
0.80) and a regression coefficient value of (R2 =
0.646).
Results showed that the change in moisture content
values before irrigation during this stage of growth did
not exceed 6.9% through the month of April, at which
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Fig. 9: The relation between soil moisture content before irrigation and soil or canopy air temperature
during late vegetative stage of alfalfa plants (April).
Fig. 10: The relation between the differences of leaf or canopy air temperature and total irrigation
requirements of alfalfa plants during late vegetative stage of alfalfa plants (April).
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month of February to April. Data showed also that
irrigation needs were nearly equal during December
and January, and then tended to rise gradually during
the month of February and April. In addition,
temperature of plant leaves increased gradually
during the months of plant growth, it was from
February to April. However, the difference between
leaf temperature and canopy air temperature did not
take in most cases a consistent direction.
Monthly averages of different measurements for
alfalfa crop: Data recorded in Table (2) showed the
monthly averages of the various measurements
taken for alfalfa crop. According to the data in the
table it could be deduced that the monthly averages
of soil temperatures were always lower than those of
air or canopy air temperatures. Moreover, the lowest
values of soil, and air temperature were recorded in
January and then increased successively from the
Table (2): Monthly changes in soil temperature, air temperature and moisture content before and after irrigation,
amount of irrigation, actual irrigation water lost and differences between soil and air temperatures of alfalfa plants.
Soil
temp
. cᵒ
Air
Decembe
r
12.04
January
month
Moisture
content
before
irrigatio
n
Moisture
content
after
irrigatio
n
total
irrigation
requiremen
t (cm)
Actual
irrigation
requiremen
t (cm)
Water
lost by
evap.
And
seepag
e
Leaf
temp
.
Diff.
betwee
n
leaf
and air
temp
Diff.
betwee
n
soil
and air
temp.
14.08
12.11
19.83
1.54
1.13
0.42
----
----
2.04
7.17
9.36
13.02
20.72
1.54
0.95
0.59
----
----
2.18
February
12.97
15.24
10.07
22.60
2.32
1.35
0.97
17.88
2.73
----
Mars
17.87
19.62
10.57
22.02
2.29
1.43
0.85
21.45
1.83
----
April
19.62
23.62
9.56
21.68
2.43
1.64
0.79
25.68
2.06
----
temp
.c
3
2
Seepage water (in m /day) = seepage losses (in m/day) X surface area (in m )
Table(3): Water use efficiency for Alfalfa crop.
Cuts
1st cut , March
15
2nd cut
15
April
Sample #
Total
dry
weight (g/ m2)
Total dry weigh
Kg/ht
1
456.4
1916.88
2
338.8
1422.96
3
376.8
1582.56
4
355.6
1493.52
AVERAGE
381.9
1603.98
1
357.6
1501.92
2
264.0
1108.8
3
420.4
1765.68
4
359.6
1510.32
AVERAGE
350.4
1471.68
015
Total
irrigation
requirement m3/ht
Water
use
efficiency Kg/m3
3152.52
0.51
1136.52
1.29
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
Water use efficiency (WUE): water use efficiency is
typically defined as the ratio of biomass produced to
the rate of transpiration. Data in Table (3) indicated
that WUE of alfalfa ranged between 0.51 Kg/ m3 for
first cut, and 1.29 Kg/m3 for the second cut, this
difference may be attributed to the increase in the
rate of evaporation from the bare soil before and
during germination in the month of December and
January. Therefore, the first cut has a low water use
efficiency than the other cuts. Otherwise, WUE
increased through the following stages of plant
growth.
December (Germination stage): Data registered in
Table (4) indicated that values of air temperature
during this month were higher than those of soil
temperature during same time. Besides, the monthly
average of air temperature was about 14.2OC, while
the average temperature of soil was 12.2OC.
However, the mean value of air temperature during
this month was about 2.6OC and the mean value of
soil temperature during same month was about
3.2OC. The recorded results showed also that the
difference between air temperature and soil
temperature ranged from 1.2OC to 3.3OC with an
average of 1.97OC during the month.
Wheat Crop
Table (4): Daily changes in soil temperature, air temperature, moisture content before and after
irrigation, amount of irrigation, actual irrigation water lost and differences between soil and air
temperatures of Wheat plants during month of December.
Soil
temp.
cᵒ
Air
temp.
c
Moisture
content
before
irrigation
Moisture
content
after
irrigation
total irrigation
requirement
(cm)
Actual
irrigation
requirement
(cm)
Water
lost
by
evap.
And
seepage
Diff.
between
soil and
air temp.
12/12/2014
14.20
15.50
17.10
24.50
1.48
0.57
0.91
1.30
15/12
12.70
14.50
15.60
19.80
0.84
0.80
0.04
1.80
18/12
11.20
14.50
14.60
23.40
1.76
1.07
0.69
3.30
21/12
12.00
14.10
12.20
21.50
1.86
1.55
0.31
2.10
23/12
12.80
14.00
13.00
19.85
1.37
1.32
0.05
1.20
25/12
12.00
15.00
13.60
21.80
1.64
1.27
0.37
3.00
28/12
11.00
12.90
13.10
19.90
1.36
1.30
0.06
1.90
30/12
11.80
13.00
15.30
21.30
1.20
0.93
0.27
1.20
Mean
12.21
14.19
14.31
21.51
1.44
1.10
0.34
1.97
LSD5%
0.45
2.20
2.15
3.70
0.42
0.98
0.27
1.10
Date
Data plotted in Figure (11) illustrated that the change
in moisture content values before irrigation during the
month did not exceed 4.9%, ranging between 12.2%
and 17.1% by volume. In contrast to that for alfalfa,
this limited change in the soil moisture content values
before irrigation has not translated into visible
changes in soil temperature. In this regard, the range
of soil temperature did not exceed 3.2OC. Data
showed also that there was no consistent relationship
between soil or air temperature and moisture content
before irrigation. Statistical analysis results recorded
in Fig (12) confirmed the relationship of the
differences between air temperature, soil temperature
and total irrigation water requirements of wheat
plants at the month of December (seedling stage).
This relation clearly indicated a multiple relationship
with fourth-degree, and with relatively highly
significant correlation coefficient (r = 0.72) and a
regression coefficient value of (R2 = 0.524).
016
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
Fig. 11: The relation between soil moisture content before irrigation and soil or canopy air temperature
during germination stage of wheat plants (December).
Fig. 12: The relation between the differences in soil or air temperature and total irrigation requirements
of wheat plants during germination stage (December).
017
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
December (germination stage); they were 9.73OC,
8.65OC, respectively. Results showed that during
January temperature range was increased for air and
soil, reaching 9.8OC, 7.5OC, respectively, indicating
significant changes in the degrees of air and soil
temperature.
January (Seedling stage): Results obtained in table
(5) and illustrated in Figure (13) referred to significant
changes occurred in air and soil temperatures
comparing with those recorded above, during
germination stage (in the month of December). In
addition, the monthly average of air and soil
temperatures was lower than those reported during
Table (5): Daily changes in soil temperature, air temperature, moisture content before and after irrigation, amount of irrigation,
actual irrigation, water lost and differences between soil and air temperatures of Wheat plants during month of January.
Date
Soil
cᵒ
1/1/2015
9.20
4/1
temp.
Air
temp. c
Moisture
content
before
irrigation
Moisture
content
after
irrigation
total
irrigation
requiremen
t (cm)
Actual
irrigation
requiremen
t (cm)
Water lost
by
evap.
And
seepage
Diff.
between
soil and air
temp.
9.80
14.40
22.40
1.60
1.11
0.49
0.60
10.90
11.00
11.90
22.60
2.14
1.61
0.53
0.10
6/1
10.70
12.00
14.20
22.00
1.56
1.15
0.41
0.30
8/1
10.70
10.90
11.90
22.10
2.04
1.61
0.43
0.20
11/1
4.90
5.70
12.50
21.80
1.86
1.49
0.37
0.80
13/1
6.00
6.30
15.10
22.70
1.52
0.97
0.55
0.30
15/1
12.40
15.30
16.50
20.40
0.78
0.69
0.09
2.90
18/1
10.40
11.00
13.00
20.20
1.44
1.39
0.05
0.60
20/1
4.90
10.40
14.80
20.60
1.16
1.03
0.13
5.50
22/1
5.30
5.50
14.50
20.30
1.16
1.09
0.07
0.20
25/1
8.00
9.40
12.50
20.60
1.62
1.49
0.13
1.40
27/1
8.50
8.60
12.00
20.30
1.66
1.59
0.07
0.10
29/1
10.50
10.60
11.80
20.00
1.64
1.63
0.01
0.10
Mean
8.65
9.73
13.47
21.23
1.55
1.30
0.26
1.00
LSD 5%
2.50
2.80
1.70
1.20
0.36
0.52
0.24
2.40
Data plotted in Fig (13) illustrated clearly that both air
temperature and soil temperature showed similar
trend in most cases of soil moisture content. The only
deviation was at soil moisture of 14.8% at which air
temperature (10.4OC) was significantly higher than
soil temperature (4.9OC). Therefore, changes in
temperature degrees of air and soil temperature
showed a steady relationship and direction at most
values of soil moisture content before irrigation. Data
in Fig (14) showed the strong relationship between
the differences in air and soil temperature with the
irrigation water requirements of wheat plants during
the month of January with relatively high correlation
coefficient (r = 0.71) which indicated that the higher
the amount of irrigation water the smaller the values
of difference between air and soil temperatures.
018
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
Fig. 13: The relation between soil moisture content before irrigation and soil or air temperature during
seedling stage of wheat plants (December).
Fig. 14: The relation between the differences in soil or air temperature and total irrigation requirements
of wheat plants during seedling stage (January).
001
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
than that of the later (18.8OC). Moreover, the
recorded results showed also that the difference
between canopy air temperature and leaf
temperature ranged between 2.2OC and 8.4OC with
an average of 4.6OC during this month and growth
stage. Statistical analysis of collected data showed
that the change in moisture content values before
irrigation during juvenile stage of wheat (February)
did not exceed 12.1%, ranging between 5.8% and
12.1% by volume. This observed change in moisture
content values before irrigation was translated into
detectable changes in leaf temperature, since leaf
temperature values fluctuated between 14.0OC and
22.2OC.
February (Juvenile stage): During this stage of
growth collected data showed that values of canopy
air temperature were very close to those of soil
temperatures during the month of February (Table 6).
In this concern, the monthly mean value of canopy air
temperature was about 14.2OC, and the monthly
mean value of soil temperature was about 14.1OC.
However, soil temperature was more stable than that
of canopy air temperature, therefore, the range of soil
temperature during the month did not exceed 7.4OC,
while the range of canopy air temperature was about
12.7OC. Comparing canopy air temperature with plant
leaf temperature, data in the same table showed that
the mean value of the former (14.2OC) was lower
Table (6): Daily changes in soil temperature, air temperature, moisture content before and after irrigation, amount of irrigation,
actual irrigation, water lost and differences between soil and air temperatures of Wheat plants during month of February.
Soil
temp.
cᵒ
Air
temp.
o
c
Moisture
content
before
irrigation
Moisture
content
after
irrigation
total irrigation
requirement
(cm)
Actual
irrigation
requirement
(cm)
Water lost
by evap.
And
seepage
Leaf
temp.
Diff.
between
leaf
and
air canopy
temp
1/2/2015
13.70
13.00
10.80
21.10
2.06
1.83
0.23
20.63
7.63
3/2
14.80
17.30
11.60
20.70
1.82
1.67
0.15
21.07
3.77
5/2
12.80
13.30
11.90
22.50
2.12
1.61
0.51
17.60
4.30
8/2
15.90
20.00
12.10
25.50
2.68
1.57
1.11
22.20
2.20
10/2
16.00
19.00
12.10
20.40
1.66
1.57
0.09
22.10
3.10
12/2
16.50
15.00
10.80
22.50
2.34
1.83
0.51
18.90
3.90
15/2
12.80
12.70
10.30
21.30
2.20
1.93
0.27
16.50
3.80
17/2
15.00
16.30
8.00
22.10
2.82
2.39
0.43
19.20
2.90
19/2
16.30
15.70
7.30
23.30
3.20
2.53
0.67
19.80
4.10
22/2
12.20
7.70
5.80
20.40
2.92
2.83
0.09
16.10
8.40
24/2
9.10
7.30
9.60
21.80
2.44
2.07
0.37
14.00
6.70
26/2
14.30
13.50
7.60
24.70
3.42
2.47
0.95
17.30
3.80
Mean
14.11
14.23
9.83
22.19
2.47
2.03
0.45
18.78
4.55
LSD5%
1.40
2.70
3.30
3.10
0.76
0.26
0.22
2.20
3.25
Date
000
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
Data plotted in Fig (15) illustrated that there was no
steady relationship between soil or canopy air
temperature and soil moisture content before
irrigation. However, the change in soil temperature,
as affected by soil moisture content, showed the
same trend of that change recorded in air
temperature with highly positive correlation. As for
the interaction between air and leaf temperatures
with moisture content, data plotted in Fig (16)
demonstrated the relationship of the difference
between canopy air temperature and plant leaf
temperature with irrigation water requirements for
wheat plants during the month. The statistical
analysis found multiple relationship with fourthdegree, provided with lower significant correlation
coefficient (r = 0.38) and low regression coefficient
value of (R2 = 0.150).
Fig. 15: The relation between soil moisture content before irrigation and soil or air temperature during
juvenile stage of wheat plants (February).
Fig. 16: The relation between the differences in leaf or air temperature and irrigation requirements of
wheat plants during juvenile stage (January).
001
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
March (Late vegetative): The results stated in Table
(7) showed that values of canopy air temperature
were nearly close to those of soil temperature. The
monthly average temperatures of the air and soil
during this growth stage were about 18.3OC and
17.59OC, respectively. Soil temperature showed more
stability than the canopy air temperature. Concerning
this finding, the range of soil temperature during this
month was about 6.9OC or less, while the range of
canopy air temperature was about 11.0OC.
In addition, data in Table (7) indicated that the
monthly average of canopy air temperature was
18.3OC while the monthly average of plant leaf
temperature was about 21.5OC. The results
demonstrate also that the difference between canopy
air temperature and leaf temperature ranged between
0.1OC and 5.6OC with an average of 3.17OC during
this month of growth.
Table (7): Daily changes in soil temperature, air temperature, moisture content before and after irrigation, amount of irrigation,
actual irrigation, water lost and differences between soil and air temperatures of Wheat plants during month of March.
Soil
temp.
cᵒ
Air
temp.
c
Moisture
content
before
irrigation
Moisture
content
after
irrigation
total irrigation
requirement
(cm)
Actual
irrigation
requirement
(cm)
Water lost
by
evap.
And
seepage
Leaf
temp.
Diff.
between
leaf and
air temp
1/3/2015
14.30
19.00
6.70
22.60
3.18
2.65
0.53
19.10
0.10
3/3
15.80
16.50
11.20
21.50
2.06
1.75
0.31
20.40
3.90
5/3
14.50
14.50
8.00
21.40
2.68
2.39
0.29
18.90
4.40
8/3
15.30
15.00
8.60
22.40
2.76
2.27
0.49
20.60
5.60
10/3
17.00
16.50
9.30
22.70
2.68
2.13
0.55
21.80
5.30
12/3
16.10
19.00
7.40
21.80
2.88
2.51
0.37
20.90
1.90
15/3
20.90
20.50
6.70
20.40
2.74
2.65
0.09
21.80
1.30
17/3
20.20
19.00
5.60
22.40
3.36
2.87
0.49
22.10
3.10
19/3
19.80
19.50
9.00
24.00
3.00
2.19
0.81
23.50
4.00
23/3
21.20
16.50
9.30
20.10
2.16
2.13
0.03
20.70
4.20
29/3
18.40
25.50
6.10
20.50
2.88
2.77
0.11
26.60
1.10
Mean
17.59
18.32
8.66
21.80
2.76
2.39
0.37
21.49
3.17
LSD5%
3.90
3.00
3.60
2.90
0.75
0.42
0.58
2.56
1.85
Date
relationship between soil or canopy air temperature
and soil moisture content before irrigation. Thus data
designed in Fig (18) showed the relationship of the
difference between canopy air temperature and plant
leaf canopy temperature with total irrigation water
requirements of wheat crop. The analysis reported
the presence of a multiple relationship with fourthdegree, and with moderately significant positive
correlation coefficient (r = 0.63) and a regression
coefficient value of (R2 = 0.4).
Data plotted in Fig (17) showed that changes in
moisture content values before irrigation during this
month did not exceed 11.2%, and was ranging
between 5.6% and 11.2% by volume. Surly, these
changes in moisture content values before irrigation
were translated into perceptible changes in plant leaf
temperature, thus, plant leaf temperatures ranged
between 18.9OC and 26.6OC during the month. Data
in Fig (17) indicated a moderately positive
002
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
Fig. 17: The relation between soil moisture content before irrigation and soil or air temperature during
juvenile stage of wheat plants (March).
Fig. 18: The relation between the differences in leaf or canopy air temperature and irrigation
requirements of wheat plants during juvenile stage (March)
003
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
close to each other during the months of December
and January, but they increased gradually during the
month of February and March. At same period, plant
leaf temperature gradually increased. The differences
between plant leaf temperature and the canopy air
temperature were higher during February than March
than other months.
Monthly averages of different measurements for
Wheat crop: Data recorded in Table (8) illustrated
clearly that the monthly averages temperature of soil
was always slightly lower than that of canopy air. The
lowest values of soil, and air temperatures were
recorded during January and then successively
increased at the beginning of February through
March. Values of irrigation requirements were nearly
Table(8): Monthly changes in soil temperature, air temperature and moisture content before and after irrigation, amount of
irrigation, actual irrigation water lost and differences between soil and air temperatures of Wheat plants.
Soil
temp.
cᵒ
Air
temp.
c
Moisture
content
before
irrigation
Moisture
content
after
irrigation
total irrigation
requirement
(cm)
Actual
irrigation
requirement
(cm)
Water lost
by evap.
And
seepage
Leaf
temp.
Diff.
between
leaf and
air temp
Diff.
between
soil and
air temp.
December
12.21
14.19
14.31
21.51
1.44
1.10
0.34
----
----
1.97
January
8.65
9.73
13.47
21.23
1.55
1.30
0.26
----
----
1.00
February
14.11
14.23
9.83
22.19
2.47
2.03
0.45
18.78
4.55
----
Mean
17.59
18.32
8.66
21.80
2.76
2.39
0.37
21.49
3.17
----
Total irrigation
requirt (m3/ht)
Water
efficiency
(Kg/m3)
3853.5
0.688
month
Table (9): Plant height (cm), yield components; total irrigation water and WUE of wheat crop.
Total Grain yield
(Kg/ht)
Sample #
Plant hit
(cm)
Spikes m-2
Kernels
spike-1
1000Kernel
weight
Grain yield
(g/m2)
Straw yield
(g/m2)
1
66
552
46.0
42.4
656.8
729.8
2758.56
2
71
480
47.6
43.0
571.1
634.6
2398.62
3
69
564
46.3
42.2
671.1
745.6
2818.62
4
65
528
50.3
42.0
628.2
698.0
2638.44
Mean
67.8
531
47.6
42.4
631.8
702.0
2653.56
Water use efficiency (WUE): WUE was defined as
the total yield in (kg/hec) divided by total amount of
seasonal actual evapotranspiration (m3/hec); or as
the ratio of biomass produced to the rate of
transpiration. Data presented in Table (9) explained
the agronomic characters of wheat crop, accordingly,
it could be concluded that water use efficiency of
wheat was about 0.688 Kg/m3, this relatively low
efficiency could be attributed to increasing rate of
evaporation from the bare soil during germination and
seedling stages at the month of December and
January.
use
As plants transpire, the evaporation of water from
liquid to vapor state consumes heat energy, which
lowers the leaf temperature (Schuster et al., 2016);
this and the movement of water vapor away from the
canopy removes heat and results in a cooling effect.
In this respect Longobardi et al. (2016) reported that
when the plant evapotranspiration (ET) rate is reduced, such as by soil water depletion, the rate of
heat removal is reduced and the canopy temperature
increases. This process links canopy temperature
with crop water stress and ET. Detection of crop water stress and ET enable rational irrigation timing and
application amounts, which can increase crop water
productivity, reduce leaching of water and nutrients
below the root zone, and reduce the time required for
irrigation management (Al-Bakri et al., 2016). The
concept of using soil and air temperatures for farm
management, including irrigation management was
reported by Liaoa et al. (2016) who found that both
temperatures gave good indication on the state of
water in potato plants.
DISCUSSION
The present study showed that plant canopy temperature, stomatal conductance and transpiration rate
were useful parameters for irrigation management
because they were related to the water status of the
plant and soil, and they can be easily measured by
diffusion porometer instrument (Colaizzi et al., 2012).
004
Agric. Biol. J. N. Am., 2017, 8(3):94-117‫ح‬
Collected data in this study showed that the monthly
averages of the various measurements taken for alfalfa and wheat crops were nearly similar and correlated with soil and air temperature during the growth
period. Data showed that the monthly averages of
soil temperatures were always lower than those of air
or canopy air temperatures. The lowest values of soil
and air temperatures were recorded in January and
then increased successively from the month of February to April. Similarly, leaf temperature increased
with time. However, the difference between leaf temperature and canopy air temperature did not take in
most cases a consistent direction. The irrigation
needs were nearly equal during germination and
seedling stages, but tended to increase as the time
passed until maturity stage. These results are in accordance with those obtained by Yildirim and Demire
(2011).
under warmer temperatures has been associated
with cooler canopy temperatures (Kulasek et al.,
2016). In this regard, transpiration, leaf diffusive
conductance, and atmospheric conditions were found
to take major part in calculating water requirements
and demand (Angelocci et al., 2004). In addition,
Canopy temperature variability was taken as an
indicator of crop water stress severity in many field
crops (Gonza´ lez-Dugo et al., 2005; Caputa, 2016).
CONCLUSION: Soil moisture, leaf temperature, leaf
vapor diffusive conductance, and transpiration rate
measurements in an irrigated wheat and alfalfa were
found to have an important effect on irrigation
frequency and amount of irrigated water. Based on
this study, atmospheric conditions and stomatal
conductance have a significant impact on crop water
status. Results of the study may be taken in
consideration to improve crops irrigation using soil,
canopy and plant leaf temperature.
Our results indicated that using transpiration methods
with soil and air temperatures were useful methods to
improve irrigation management by providing guidance, including irrigation timing and amount of water
to be added to the crop. With these parameters the
amount of irrigation could be preset because if the
crop is water stressed, then the root zone soil will be
depleted enough to accept that much water (Wang et
al., 2016). However, the exact amount of irrigation
that the soil will accept depends partly on soil water
depletion in the root zone either in wheat or alfalfa
crop used in this study. Soil water depletion is determined most directly by in-situ measurement of the
soil water profile. Nonetheless, real-time feedback on
a spatial basis of plant and soil water status, including transpiration and stomatal conductance, was
more effective in order to set irrigation schedules,
detect unexpected conditions such as water stress
and drought conditions (O'Shaughnessy et al., 2011).
ACKNOWLEDGMENT:
The
authors
greatly
acknowledge the Agricultural Research Center in
Qassim University for financial support. The authors
also sincerely acknowledge the research staffs who
were directly or indirectly involved for the execution of
the experiment.
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