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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
94
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/ m
3 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.
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
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
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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).
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.
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 m
2 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.
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).
Soil chemical analysis: Total soluble salts, and soil reaction (pH) were determined in soil extract (1:2.5), according to Page (1982).
Chemical analysis of irrigation water: Electrical conductivity and water reaction (pH) were determined according to Page (1982).
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 Delta-T 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.
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 moisture content before irrigation(%)
ds = 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 moisture content at field capacity(%)
Ɵv wp = volumetric moisture content at wilting pointe(%)
ds = depth of irrigated soil (cm)
Calculate the actual Evapotranspiration: ETa (mg cm
-2 day
-1) = [( Ɵv fc – Ɵv bi) /100]× ds
Eta = actual evapotranspiration (cm)
Ɵv fc = volumetric moisture content at field capacity(%)
Ɵv bi = volumetric moisture content before irrigation(%)
ds = 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 (m
3/ht).
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
E = (pc-pa)*F/A
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:
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 (cm
3 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 0
OC.
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)
Combining equations:
rs = (A/F)(pl – pc)/(rs + rb)
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.
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
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 Li-1600 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.
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).
RESULTS
Physical and chemical properties of soil and irrigation water
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.
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Table (1): Chemical and physical analyses of the experimental soil used in the study.
Sample NO.
ECe1:2.5
S/m
pH
1:2.5
Saturation
%
F.C %
0.33 bar
W.P%
15 bar
A.W
%
Sand
%
Silt
%
Clay
%
Texture
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.
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 2.2
OC,
while the mean of air temperature mean was about 3.6
OC 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.
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 2.2
OC. 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 14
OC
and air temp. was about 12.5OC, while at soil
moisture content of 13.1%, temperatures were about 12
OC and 11.7
OC, respectively. In contrast, data in
the figure showed in most cases rather relationship between air and soil temperature.
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 (R
2 = 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 15.24
OC 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 8.7
OC 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 14.9
OC 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 4.1
OC with an average of 2.73
OC 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 12.8
OC 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 (R
2 = 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 19.6
OC; while the monthly average
temperature of soil during the same period was about 17.9
OC. 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 10
OC during the month (between
23.5OC and 13.7
OC), while the canopy air
temperature was fluctuating within about 12OC
(between 26.8OC and 11.6
OC). Comparing the
monthly average of canopy air temperature with that of leaf temperature, the results showed that average temp of canopy air was about 19.6
OC 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 4.8
OC 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 17.6
OC and 27.7
OC 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 (R
2 = 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 23.6
OC.
Moreover, the monthly average temperature of soil was also higher than those recorded in other months, and was about 19.6
OC. Results showed also that the
monthly average temperature of canopy air was 23.62
OC; while the monthly average temperature of
plant leaves was about 25.68OC.
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
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 22.6
OC and 27.3
OC. 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 (R
2 =
0.646).
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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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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
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.
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.
month 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
12.04 14.08 12.11 19.83 1.54 1.13 0.42 ---- ---- 2.04
January 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 ----
Seepage water (in m3/day) = seepage losses (in m/day) X surface area (in m
2)
Table(3): Water use efficiency for Alfalfa crop.
Cuts Sample # Total dry weight (g/ m
2)
Total dry weigh Kg/ht
Total irrigation requirement m
3/ht
Water use efficiency Kg/m
3
1st
cut , March 15
1 456.4 1916.88
3152.52 0.51
2 338.8 1422.96
3 376.8 1582.56
4 355.6 1493.52
AVERAGE 381.9 1603.98
2nd
cut April 15
1 357.6 1501.92
1136.52 1.29
2 264.0 1108.8
3 420.4 1765.68
4 359.6 1510.32
AVERAGE 350.4 1471.68
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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/m
3 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.
Wheat Crop
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 14.2
OC, while
the average temperature of soil was 12.2OC.
However, the mean value of air temperature during this month was about 2.6
OC and the mean value of
soil temperature during same month was about 3.2
OC. The recorded results showed also that the
difference between air temperature and soil temperature ranged from 1.2
OC to 3.3
OC with an
average of 1.97OC during the month.
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.
Date 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
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 3.2
OC. 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 (R
2 = 0.524).
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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).
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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
December (germination stage); they were 9.73OC,
8.65OC, respectively. Results showed that during
January temperature range was increased for air and soil, reaching 9.8
OC, 7.5
OC, respectively, indicating
significant changes in the degrees of air and soil temperature.
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 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.
1/1/2015 9.20 9.80 14.40 22.40 1.60 1.11 0.49 0.60
4/1 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 (10.4
OC) 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.
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001
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).
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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 14.2
OC, 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 7.4
OC,
while the range of canopy air temperature was about 12.7
OC. Comparing canopy air temperature with plant
leaf temperature, data in the same table showed that the mean value of the former (14.2
OC) was lower
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 2.2
OC and 8.4
OC 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 14.0
OC and
22.2OC.
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.
Date Soil temp. cᵒ
Air
temp. c
o
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
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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 fourth-degree, provided with lower significant correlation coefficient (r = 0.38) and low regression coefficient value of (R
2 = 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).
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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 18.3
OC 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 6.9
OC 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 18.3
OC 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 0.1
OC and 5.6
OC with an average of 3.17
OC 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.
Date 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
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 18.9
OC and 26.6
OC during the month. Data
in Fig (17) indicated a moderately positive
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 fourth-degree, and with moderately significant positive correlation coefficient (r = 0.63) and a regression coefficient value of (R
2 = 0.4).
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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)
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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
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.
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.
month 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 ----
Table (9): Plant height (cm), yield components; total irrigation water and WUE of wheat crop.
Sample # Plant hit (cm)
Spikes m-2
Kernels spike
-1
1000-Kernel weight
Grain yield (g/m
2)
Straw yield (g/m
2)
Total Grain yield (Kg/ht)
Total irrigation requirt (m
3/ht)
Water use efficiency (Kg/m
3)
1 66 552 46.0 42.4 656.8 729.8 2758.56
3853.5 0.688
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 (m
3/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/m
3, 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.
DISCUSSION
The present study showed that plant canopy temper-ature, 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).
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 re-duced, 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 wa-ter 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.
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Collected data in this study showed that the monthly averages of the various measurements taken for al-falfa and wheat crops were nearly similar and corre-lated 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 Feb-ruary to April. Similarly, leaf temperature increased with time. However, the difference between leaf tem-perature 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 ac-cordance with those obtained by Yildirim and Demire (2011).
Our results indicated that using transpiration methods with soil and air temperatures were useful methods to improve irrigation management by providing guid-ance, 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 deter-mined 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, includ-ing 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).
Stomatal conductance estimates the rate of gas exchange (i.e., carbon dioxide uptake) and transpiration (i.e., water loss) through the leaf stomata as determined by the degree of stomatal aperture and therefore the physical resistances to the movement of gases between the air and the interior of the leaf (Sack and Buckley, 2016). Hence, it is an effective tool for increasing the water use efficiency (Table 9) for crops. With more open stomata allowing greater conductance, and consequently indicating that photosynthesis and transpiration rates are potentially higher. Results can be used as a proxy for measuring photosynthetic rate. The heritability of stomatal conductance is reasonably high, and gives high correlation with yield; greater leaf conductance
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.
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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