Published in Agron J 99:1391-1396 (2007)
DOI: 10.2134/agronj2006.0232
© 2007 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Agroclimatology
Surface Energy Fluxes and Evapotranspiration of a Mango Orchard Grown in a Semiarid Environment
Vicente de Paulo Rodrigues da Silva*,
Pedro Vieira de Azevedo and
Bernardo Barbosa da Silva
Federal University of Campina Grande, Av. Aprígio Veloso, 882, Bodocongó, Campina Grande, PB, Brazil, CEP: 58109-970
* Corresponding author (vicente{at}dca.ufcg.edu.br)
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ABSTRACT
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Data from field experiments conducted in the semiarid climatic conditions of northeast Brazil were used to investigate the energy flux relations and evapotranspiration (ET) of a mango (Mangifera indica L.) orchard. The Bowen ratio–energy balance method was applied during the 1998–1999 fruiting cycles to estimate the energy balance components of the mango orchard, while the FAO Penman–Monteith approach was used for determining the reference evapotranspiration (ETo). Results indicated that latent heat flux density (
E) could be obtained, with reasonable precision, as a function of measured net radiation flux density (Rn). The percentage of Rn used as E was higher for the fruit growth and fruit maturation phenological stages, and lower for the flowering and fruit fall stages. For both field campaigns, E was found to be the major component of energy balance, comprising >70% of the available energy. Soil heat flux was always the smaller component, comprising <8%. Daily mean value of ET was higher during the 1998 fruiting cycle than that observed in 1999. Inversely, the ET increased approximately 6% from the 1998 to 1999 fruiting cycle. These results may be used for planning and management of irrigation for mangos grown in similar environmental conditions.
Abbreviations: 
, n, and m, van Genuchten soil parameters • ß, Bowen ratio • BREB, Bowen ratio–energy balance method • 
ea, vertical gradient of vapor pressure • , slope of the saturation vapor pressure curve • T, vertical gradient of air temperature • DAF, day after flowering • DOY, day of year • es, saturation vapor pressure at air temperature • ea, actual vapor pressure of the air • ETo, reference evapotranspiration • ET, evapotranspiration • 
m, matric potential • 
, psychometric constant • G, soil heat flux density • H, sensible heat flux density • E, latent heat flux density • Kc, crop coefficient • Rn, net radiation flux density • Rs, global solar radiation • SWC, soil water content • 
r, residual soil water content • s, saturation soil water content • VPD, vapor pressure deficit
Surface Energy Fluxes and Evapotranspiration of a Mango Orchard Grown in a Semiarid Environment
Vicente de Paulo Rodrigues da Silva*,
Pedro Vieira de Azevedo and
Bernardo Barbosa da Silva
Federal University of Campina Grande, Av. Aprígio Veloso, 882, Bodocongó, Campina Grande, PB, Brazil, CEP: 58109-970
* Corresponding author (vicente{at}dca.ufcg.edu.br)
Received for publication August 17, 2006.
Data from field experiments conducted in the semiarid climatic conditions of northeast Brazil were used to investigate the energy flux relations and evapotranspiration (ET) of a mango (Mangifera indica L.) orchard. The Bowen ratio–energy balance method was applied during the 1998–1999 fruiting cycles to estimate the energy balance components of the mango orchard, while the FAO Penman–Monteith approach was used for determining the reference evapotranspiration (ETo). Results indicated that latent heat flux density (E) could be obtained, with reasonable precision, as a function of measured net radiation flux density (Rn). The percentage of Rn used as E was higher for the fruit growth and fruit maturation phenological stages, and lower for the flowering and fruit fall stages. For both field campaigns, E was found to be the major component of energy balance, comprising >70% of the available energy. Soil heat flux was always the smaller component, comprising <8%. Daily mean value of ET was higher during the 1998 fruiting cycle than that observed in 1999. Inversely, the ET increased approximately 6% from the 1998 to 1999 fruiting cycle. These results may be used for planning and management of irrigation for mangos grown in similar environmental conditions.
Abbreviations: , n, and m, van Genuchten soil parameters • ß, Bowen ratio • BREB, Bowen ratio–energy balance method • ea, vertical gradient of vapor pressure • , slope of the saturation vapor pressure curve • T, vertical gradient of air temperature • DAF, day after flowering • DOY, day of year • es, saturation vapor pressure at air temperature • ea, actual vapor pressure of the air • ETo, reference evapotranspiration • ET, evapotranspiration • m, matric potential • , psychometric constant • G, soil heat flux density • H, sensible heat flux density • E, latent heat flux density • Kc, crop coefficient • Rn, net radiation flux density • Rs, global solar radiation • SWC, soil water content • r, residual soil water content • s, saturation soil water content • VPD, vapor pressure deficit
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INTRODUCTION
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THE MANGO CROP is widely grown in Brazil, with the northeast region being the main area of production providing 53% of national fruit production. The semiarid climate of this region presents very favorable prospects for the growth of many crops. This is mainly due to its energy availability, although there are some water availability restrictions. Mean annual rainfall is less than 400 mm (Silva, 2004). Currently, most tropical fruits like mango, grape vine, pineapple, guava, and coconut are extensively cultivated in this region using irrigation water from the San Francisco River.
Mango fruit is considered an important economic alternative in the Brazilian northeastern region, where large-scale commercial orchards have been established in the middle reaches of the San Francisco River Valley. Several researches (Evans et al., 1993; Sepaskhah and Kashefipour, 1995; Ferreira et al., 1996; Daamem et al., 1999; Azevedo et al., 2003, 2006; Yunusaa et al., 2004) have investigated the water-use and evapotranspiration of most tropical and subtropical fruits. Crop evapotranspiration may be estimated, with reasonable precision, by micrometeorological models, depending on the level of errors associated with variables measurement and instrument sensitivity. The Bowen ratio–energy balance method (BREB) has been often used to estimate evapotranspiration from soil–vegetation systems (Mastrorilli et al., 1998; Todd et al., 2000; Wever et al., 2002; Silberstein et al., 2003). This method has been used mainly because of its relative simplicity and precision for vertical water vapor flux estimation. However, this technique must be used with caution since it does not reproduce the turbulent nature of the evapotranspiration process (Steduto and Hsiao, 1998). Perez et al. (1999) studying errors associated with the BREB method found that on average 40% of the total data, which corresponds to the night-time period and periods during precipitation and irrigation events, must often be rejected. When obtained by the Bowen ratio–energy balance, the water requirements of mango orchards grown in northeast Brazil are not constant throughout their productive cycle (Azevedo et al., 2003). Yunusaa et al. (2004) studied the evapotranspiration components of an irrigated vineyard in inland Australia for warm dry days in mid-February (Period 1) and cool humid days in late March (Period 2) using the energy balance method. It was found that the increase in the partitioning of Rn through E was associated to a reduced vapor pressure deficit of the air. This enhanced dissipation of energy absorbed by the canopy, thus making the vineyard canopy cooler in Period 2 compared with Period 1. Recently, Azevedo et al. (2006) used three water levels to determine evapotranspiration and water-use efficiency in coconut palms grown in a semiarid environment of northeast Brazil. They concluded that evapotranspiration and yield are strongly affected by varying soil water levels.
Many authors have used the least-squares linear regression method to establish a relationship between short wave and net radiation fluxes (Kaminsky and Dubayah, 1997; Silberstein et al., 2001; Alados et al., 2003). These studies have shown a high correlation between latent heat flux and net radiation data. Although this procedure has been applied to many agricultural meteorological studies, for mango crops it is still incipient. Despite the difficulties in obtaining long-wave radiation by simple models, short-wave radiation can be measured by radiometers or estimated, with reasonable precision, by satellite data. On the other hand, estimates of latent heat flux based on net radiation measurements can be extremely useful for crop evapotranspiration studies. Thus, the main objectives of this study were: (i) to evaluate the behavior of the surface energy balance components and relationship between net radiation and latent heat flux for three levels of evaporative atmospheric demand; and (ii) to determine the evapotranspiration of a mango orchard grown in the climatic conditions of the semiarid region of northeast Brazil.
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MATERIALS AND METHODS
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Experimental Site and Crop Management
Field experiments were performed at the Bebedouro Experimental Station of the Brazilian Organization for Agriculture and Animal Research (Embrapa Semi-Árido) in the semiarid region of the middle reaches of the San Francisco River Valley at Petrolina, PE (Brazil; 09°09' S, 40°22' W; 365.5 m above sea level). The region has a semiarid climate, as described by Azevedo et al. (2003).
Micrometeorological measurements were taken during the 1998 and 1999 fruiting cycles (from June to November) at a 7-yr-old mango orchard, of the variety ‘Tommy Atkins’. The orchard trees had an average height of 5.2 m and were planted in February 1992, the rows were spaced at 8.0 m with 5.0 m between trees. The experimental plot was 90 m long from north to south and 100 m from east to west. This area had a relatively flat topography and was surrounded by other extensive mango fields. During both fruiting cycles the prevailing wind direction was eastern with mean speed of about 2.5 m s–1.
In both experimental periods, the fruiting cycle started at the induction of flowering (application of a 4% solution of potassium and calcium nitrate) and was divided into the following phenological stages, as a function of the day after flowering (DAF): flowering (0 
DAF 20), fruit fall (21 DAF 70), fruit growth (71 DAF 120), and fruit maturation (121 DAF 150). In terms of day of year (DOY), the measurements covered the period from DOY = 161 to DOY = 319, with the phenological stages starting on the following dates: flowering: DOY = 161 (10 June); fruit fall: DOY = 182 (1 July); fruit formation: DOY = 222 (10 August); and fruit maturation: DOY = 272 (29 September). The phenological stages occurred on approximately the same dates in both experimental periods with the same flowering induction date. In both measurement periods, the mango orchard was irrigated daily by a well-designed drip irrigation system, according to a different crop coefficient (Kc) for each year. Crop coefficients of 0.75 and 1.0 were used in the 1998 and 1999 fruiting cycles, respectively, for irrigation scheduling of the mango orchard. Theses Kc values were selected according to the traditional farmer's management practices.
The mango orchard productivity analysis was based on fruit type, according to the following classification: large (>500 g), medium (between 400 and 499 g), and small (<400 g). An analysis of variance was performed to test the difference between the two measurement periods, using Turkey's test at p < 0.05, for the mango productivity parameters (average fruit weight, number of fruits per plant, and yield). Also, the determination coefficients (r2) were evaluated statistically at p < 0.05 level probability according to t tests. Cloudiness affects the order of magnitude of several atmospheric variables such as: solar radiation, air temperature, relative humidity, and energy fluxes. Therefore, three limits of evaporative demand were established as a function of the net radiation (Rn): (i) low (Rn 250 W m–2), (ii) moderate (250 < Rn < 350 W m–2), and (iii) high (Rn 
350 W m–2), corresponding to high, moderate, and low cloudiness conditions, respectively.
Energy Balance
Neglecting the advection effects, energy stored in the canopy, and photosynthetic energy flux, the energy balance was obtained as follows:
 | [1] |
where Rn is the net radiation flux density, E is latent heat flux density, H is sensible heat flux density, and G is soil heat flux density (all in W m–2). Thus, assuming equality between the turbulent exchange coefficients for heat and water vapor, E based on Bowen ratio (ß = H/E 
T/ea) was obtained as (Mastrorilli et al., 1998):
 | [2] |
where is the latent heat of vaporization (2.501 MJ kg–1), is psychometric constant (kPa °C–1), T is above canopy vertical gradient of air temperature (°C), and ea is above canopy gradient of vapor pressure (kPa). Mango evapotranspiration (ET) in mm d–1 was calculated by dividing E by latent heat of vaporization. Following Perez et al. (1999), only daytime periods (Rn > 0) were studied.
The main advantages of using the Bowen ratio–energy balance method are (i) it requires no information about the aerodynamic characteristics of the surface of interest and (ii) it can integrate latent heat flux over large areas. On the other hand, the disadvantages of the method include sensitivity to the biases of instruments that measure gradients and energy balance terms, and the possibility of discontinuous data when the Bowen ratio approaches –1 (Todd et al., 2000).
A micrometeorological tower was mounted between two selected mango trees in the center of the experimental plot to provide a mean fetch of 380 m in all directions. The sensors for net radiation (Rn), global solar radiation (Rs), and wind speed were installed at 
1 m above the crop canopy. Net radiation was measured with a net radiometer (NR-LITE; Kipp & Zonen, Delft, the Netherlands), Rg with a radiometer (CM3; Kipp & Zonen), and wind speed with a cup anemometer. Gradients of dry- and wet-bulb air temperatures were obtained from measurements at 0.2 and 1.6 m above the crop canopy using dry- and wet-bulb thermometers. Soil heat flux was measured using three soil heat flux plates (CN3; REBS) buried at 0.02 m soil depth 2.2 m away from the trunk of the plant. All these sensors were previously calibrated and connected to a 21X data logger (Campbell Scientific, Logan, UT).
Data were sampled every 5 s, and 10-min averages were obtained. Daily mean values of wind speed at 2-m height, maximum and minimum air temperature, relative humidity, and sunshine were used to obtain the reference evapotranspiration (ETo) using the FAO-56 Penman–Monteith equation. Measurements of these variables were taken at the Bebedouro Meteorological Station, 300 m from the experimental plot. The leaf area index was measured on three different dates throughout the fruiting cycle using a leaf area meter (LICOR 3000).
Once accurately calibrated, radiometers and heat flux plates provided good measures of Rn and G, respectively. However, the vertical gradients of air temperature and relative humidity may be inconsistent due to instrumental maintenance and calibration. For instance, psychometric calibration problems can introduce greater error in the determination of E and H. Thus, in this paper, missing values for crop evapotranspiration were obtained by regression equations in estimating E as a function of Rn for three levels of evaporative demand (high, moderate, and low).
Soil Water Content
Soil water content was obtained by the expression (van Genuchten, 1980):
 | [3] |
where r and s are residual and saturation soil water contents (cm3 cm–3), respectively, , n, and m are the van Genuchten soil parameters, which were determined from van Genuchten and Nielsen (1985). The matric potential (m) was obtained by tensiometric measurements. Detailed information about the determination of soil water content is reported by Azevedo et al. (2003).
The soil matric potential was monitored using six sets of mercury manometer tensiometers positioned under the canopy of two plants and spaced at 50 cm from the trunk of the plant and 117 cm among sets. The tensiometers' porous cups were installed at soil depths of 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, and 220 cm, and measurements were recorded daily at 0700, 1200, and 1700 h. Three trenches were excavated down to approximately 350 cm for measuring average soil root distribution and the depth of groundwater below the ground surface. The soil root distribution was measured by digital image analysis of the root systems.
Reference Evapotranspiration
Daily reference evapotranspiration (ETo) was obtained using the FAO Penman–Monteith approach. Thus, considering a hypothetical crop height of 0.12 m, a fixed surface resistance of 70 s m–1, and an albedo of 0.23, ETo (mm d–1) is given by the equation (Allen et al., 1998):
 | [4] |
where Rn is the net radiation flux density at the surface (MJ m–2 d–1), G is soil heat flux density from the surface to the soil (MJ m–2 d–1), is slope of the saturation vapor pressure curve (kPa °C–1), is psychometric constant (kPa °C–1), U2 is wind speed measured (m s–1) at 2-m height, T is mean daily air temperature (°C), es is saturation vapor pressure at air temperature (kPa), and ea is actual vapor pressure of the air (kPa). All these variables were calculated according to the methodology recommended by FAO (Allen et al., 1998) and G was assumed to be zero in a 24-h period. Allen et al. (2006) recommended no changes for the FAO-PM ETo method for daily (24-h) time steps.
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RESULTS AND DISCUSSION
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During both observational periods, the groundwater table remained at 250 cm below the soil surface, while the major root concentration occurred in the soil layer between 140 and 200 cm. For each phenological stage, mean and standard deviation of the climatic variables for the 1998 and 1999 mango orchard fruiting cycles are shown in Table 1
. The 1999 fruiting cycle had mean values lower than those observed in 1998. This behavior also occurred for all stages of development of the fruiting cycle, except the flowering stage, when mean values of air temperature and sunshine were higher in 1999 than in 1998. Also, the cumulated rainfall was slightly higher in 1999 than in 1998, but still measured much less than the long-term normal value. The Kc values used for scheduling irrigation resulted in an applied irrigation water volume of 948.6 and 1143.7 mm in the 1998 and 1999 fruiting cycles, respectively. The leaf area index was measured only for the 1999 fruiting cycle with values being 12.9, 15.0, and 14.1 m2 m–2 for flowering, fruit growth, and fruit maturation phenological stages, respectively.
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Table 1. Average climate variables (± SD) throughout the 1998–1999 fruiting cycles of the mango orchard and long-term normal (1970–2004).
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Energy Balance Components
During the 1998 fruiting cycle, the mean percentages of net radiation (Rn) consumed as latent heat flux (E) and soil heat flux (G) were lower than those obtained for the 1999 fruiting cycle (Table 2
). This result indicated that the 1998 fruiting cycle had a greater evaporative demand. For both years, E was found to be the major component of the energy balance, comprising more than 70% of the available energy; while G was always the minor component, comprising less than 8%.
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Table 2. Mean values of energy used as latent heat flux (E/Rn) and soil heat flux (G/Rn), vapor pressure deficit (VPD) and soil water content (SWC) during the 1998–1999 fruiting cycles of the mango orchard.
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Relationship between Net Radiation and Latent Heat Flux
The high values of the determination coefficient (r2) indicated how good the relationships are between E and Rn (Table 3
). These results may be used for improving current management practices in mango orchards. Hölscher et al. (1997) obtained missing data of E as a function of the average evaporative ratio (E/Rn) for the 4-mo period before the occurrence of instrument technical problems. Zhang and Lemeur (1995) observed that E strongly responds to the magnitude of incident solar radiation. Also, considering that E follows the daytime course of the solar radiation, Sugita and Brutsaert (1991) obtained the E in terms of its similarity with others components of the energy balance. The percentage of Rn consumed as E was higher for periods with low evaporative demand (Table 3). For three evaporative demands the percentage of Rn used as E was higher than 77% while that used as G was <3%.
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Table 3. Equations for the estimation of the latent heat flux for low, moderate and high levels of available energy and energy consumed ratio as latent heat flux (E/Rn) and soil heat flux (G/Rn).
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Evapotranspiration
The time-course of air temperature (mean, maximum, and minimum), crop evapotranspiration (ET), reference evapotranspiration (ETo), and rainfall or irrigation in 1998 and 1999 are given in Fig. 1
. In general, these variables presented higher values in 1998 compared with those of 1999. The higher values of ETo observed in 1998 are associated with an increase in vapor pressure deficit caused by the higher evaporative demand recorded in that year (Table 4
). However, the cumulative ETo values for the flowering and fruit fall stages were lower in 1998. This was due to the higher air temperatures and amount of sunshine as well as the lower values of relative humidity, during these phenological stages in 1999. The daily mean values of ET for the experimental periods of 1998 and 1999 were 4.5 ± 0.4 and 4.3 ± 0.6 mm, respectively. The values of ETo were 5.3 ± 1.03 and 4.9 ± 1.01 mm, respectively. The maximum values of daily ETo for both 1998 and 1999 fruiting cycles occurred during the same time period, around 113 to 118 days after flowering. Maximum ET values for the mango orchard were 5.2 and 5.5 mm d–1 during the growth stage in 1998 and 1999, respectively, which are associated with maximum leaf area index. The cumulative value of ET was higher in the 1999 experimental period than the 1998 experimental period due to the changes in environmental conditions (mainly the decrease of vapor pressure deficit). Yunusaa et al. (2004) found that ET from the vineyard showed a strong response to temporal fluctuations in ETo and rainfall during the entire study period.
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Fig. 1. Seasonal time-course for (a) air temperature, (b) crop evapotranspiration (ET) and reference evapotranspiration (ETo), and (c) rainfall or irrigation in 1998 and 1999.
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Table 4. Cumulative reference evapotranspiration (ETo) and crop evapotranspiration (ET) for the 1998 and 1999 fruiting cycles as a function of Day After Flowering (DAF).
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Vapor Pressure Deficit
The 1998 fruiting cycle did not show a clear trend in vapor pressure deficit (VPD), even though maximum and minimum values occurred at the beginning and ending of this experimental period, respectively. Otherwise, the mean values of VPD increased throughout the 1999 fruiting cycle (Table 2). This behavior was caused by an increase in net radiation (Rn) throughout the observational period (June–November). For the 2 yr observed, an increasing behavior was seen in pan evaporation and air temperature throughout the fruiting cycles. This period of the year is typically very dry all over the Brazilian northeast region, particularly in the middle reaches of the San Francisco River Valley. An increasing trend in VPD was also observed by Almeida and Landsberg (2003) on the eastern coast of northeast Brazil for the same period of the year.
Soil Water Status
The volume of irrigated water applied was 20.1% higher in 1999 and caused a 25% increase in soil water content (SWC). The 1998 and 1999 fruiting cycles had relatively uniform SWC with mean values of 0.20 and 0.25 cm3 cm–3, respectively. Mean values of SWC were higher in 1999 as a result of the application of a higher volume of irrigation water during that experimental period (Table 2). Thus, the total volume of water applied to the irrigated plot plus the cumulated rainfall had a significant influence on the estimated SWC for both experimental periods. Rainfall had much less effect than irrigation on SWC in both experimental periods, once the cumulated rainfall was approximately 50 mm. In both experimental periods, the maximum value of the SWC occurred during the middle of the fruiting cycle.
Mango Orchard Yield
Table 5
shows the productivity parameters for each observational year. In 1998, the values of average fruit weight per plant were lower than those observed in 1999 for all fruit type ranges (large, medium, and small). Although the number of fruits per plant was lower in 1998 for medium and small fruit types, it was higher for large fruit type. This resulted in a 68.7% decrease in mango yield from 1998 to 1999 for large fruit type. Also, an increase in the number of medium and small fruit types per plant resulted in an increase in mango yield. These results suggest that the high VPD and low SWC values observed the 1998 experimental period caused a decrease in the productivity parameters. The mango yield in 1998 was lower than both the 1999 yield and the national average (47,648 kg ha–1). The analysis of variance showed that all productivity parameters showed significant difference by Turkey's test at a 5% significance level between the two experimental periods for all fruit ranges, as well as total mango yield.
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CONCLUSIONS
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The results for the mango orchard fruiting cycle indicate that the latent heat flux can be obtained, with reasonable precision, as a function of the net radiation under three general conditions of evaporative demand. This relationship is better for low than for moderate and high energy availability. These results may be used for precise planning and efficient management practices for mango orchards in northeast Brazil. Latent heat flux was the major component of the energy balance equation, comprising >74.0% of the available energy. Soil heat flux was always the smaller component, comprising <6.0%. In both years, maximum value of mango orchard daily evapotranspiration was observed under the most intense canopy development, which is associated with maximum leaf area index at the fruit growth stage. Average reference evapotranspiration (ETo) observed during the 1998 and 1999 fruiting cycles were 5.3 and 4.9 mm d–1, respectively. The higher values of ETo observed in 1998 are associated with the higher evaporative demand recorded in that year.
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ACKNOWLEDGMENTS
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The authors would like to thank the National Council of Scientific and Technological Research (CNPq) for supporting this study and the Brazilian Organization for Agriculture and Animal Research (Embrapa) for allowing them to use its physical facilities of laboratories and filed experimental stations.
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TOP
ABSTRACT
INTRODUCTION
