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Variation in vineyard evapotranspiration in an arid region of northwest China
Agricultural Water Management 97 (2010) 1898–1904
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Variation in vineyard evapotranspiration in an arid region of northwest China Baozhong Zhang a,b , Shaozhong Kang a,∗ , Fusheng Li c , Ling Tong a , Taisheng Du a a
Center for Agricultural Water Research in China, China Agricultural University, East Campus, 100083 Beijing, China Department of Irrigation and Drainage, China Institute of Water Resources and Hydropower Research, 100048 Beijing, China c Agricultural College, Guangxi University, 530005 Nanning, China b
a r t i c l e
i n f o
Article history: Received 8 April 2010 Accepted 16 June 2010 Available online 4 August 2010 Keywords: Bowen ratio-energy balance Evapotranspiration Crop coefficient Latent heat flux Vineyard
a b s t r a c t Grapevines are extensively grown in the arid region of China, but little information is available on the diurnal, seasonal and interannual variability of vineyard evapotranspiration (ET). To address this question, two vineyards in the arid region of northwest China were taken as an example to study the variation of ET using Bowen ratio-energy balance method in 2005–2008. Results indicate that the Bowen ratio method provided accurate estimate of vineyard ET as the instrument was correctly installed. Irrigation and rainfall increased daily ET by 38 and 175%, respectively, but frost decreased it by 32%. Daily ET had a maximum value of 1.6–3.5 mm/d at the berry development stage, and a minimum value of 0.8–1.7 mm/d at the early and later stages. The total ET was 226–399 mm over the growing season. The ratio of transpiration to evapotranspiration was 0.52 and the modified crop coefficient (Kcm ) was 0.71–0.88 (except 2005) over the whole growing stage. Larger interannual difference of ET and Kcm mainly resulted from the difference of irrigation and rainfall between different years. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The arid region of northwest China is one of the least developed regions in China, with a fragile ecological environment. However, the region has abundant sunshine hours and is suitable for grape growing. In recent years, horticulture has been becoming an important industry for the local economy. Meteorologists, hydrologists, agronomists and ecologists require the knowledge of evapotranspiration (ET), which affects gross crop productivity. So understanding vineyard ET has become a research priority in the arid region of northwest China. There are numerous studies on vineyard ET using lysimeter (Evans et al., 1993; Williams et al., 2003a,b; Williams and Ayars, 2005), heat pulse or heat balance (Trambouze et al., 1998; Yunusa et al., 1997a,b), Bowen ratio (Rana and Katerji, 2008; Teixeira et al., 2007; Trambouze et al., 1998; Yunusa et al., 2004) and eddy correlation (Ortega-Farias et al., 2007; Spano et al., 2000), etc. All of these studies found that vineyard ET varies considerably with regional climate, grapevine type, irrigation scheduling, and management method, e.g. trellis system, canopy size, etc. (Teixeira et al., 2007; Williams and Ayars, 2005; Williams and Baeza, 2007; Williams et al., 2003a,b). These investigated vines were mainly irrigated with drip irrigation (Ortega-Farias et al., 2007; Williams et al., 2003a,b; Williams and Ayars, 2005; Yunusa et al., 1997a, 2004), trained on
a T-trellis support (Williams et al., 2003a,b; Yunusa et al., 1997a, 2004) and located in Australia (Yunusa et al., 1997a,b, 2004), California (Williams et al., 2003a,b; Williams and Ayars, 2005) and South America (Ortega-Farias et al., 2007). To our knowledge, there was little information on seasonal and annual variability in the long-term ET and ratio of transpiration to evapotranspiration (T/ET) over the vineyard canopy under furrow-irrigation. Thus, the understanding of the variability of ET over furrow-irrigated vineyard with single vertical trellis systems in the northwest China is required, preferably under several climatic conditions, especially after a frost, and phenological regimes. Therefore, a 4-year experiment using the Bowen ratio-energy method (BREB) over two furrow-irrigated vineyards was conducted under different rainfall and irrigation conditions in the arid region of northwest China. The objectives of this study are to (1) evaluate the applicability of the BREB in estimating ET; (2) investigate diurnal variation of ET under different weather conditions and underlying surface conditions; (3) quantify seasonal and interannual variation of vineyard ET and T/ET; (4) analyze the effect of leaf area index (LAI) on modified crop coefficient (Kcm ); and (5) compare the ET, T/ET and Kcm in different hydrological years and irrigation regimes. 2. Materials and methods 2.1. Experimental site and measurements
∗ Corresponding author. Fax: +86 10 62737611. E-mail address: [email protected] (S. Kang). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.06.010
The experiments were conducted at two vineyards of Shiyanghe Experimental Station for Water-saving in Agriculture and Ecol-
B. Zhang et al. / Agricultural Water Management 97 (2010) 1898–1904
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Table 1 Summary of irrigation regime during the whole growing season in 2005–2008. 2005 year
Irrigation date Irrigation quota (mm)
May 11 15
May 26 15
June 12 20
July 11 20
2006 year
Irrigation date Irrigation quota (mm)
May 5 41.5
May 28 41.5
June 29 41.5
August 9 41.5
2007 year
Irrigation date Irrigation quota (mm)
May 11 70
June 8 70
June 21 70
August 2 70
2008 year
Irrigation date Irrigation quota (mm)
May 18 60
June 24 60
July 18 60
August 16 60
ogy, China Agricultural University, located in Gansu Province of northwest China during 2005–2008. The site has high sunlight hours with a mean annual sunshine duration over 3000 h, mean annual temperature of 8 ◦ C and frost-free days of 150. The active accumulated temperature and effective accumulated temperature (>10 ◦ C) are about 2153 and 1327 ◦ C during the whole growing season, respectively. The region is limited in water resources with a mean precipitation of 131 mm during the whole growing season. Average groundwater table is below 25 m. The vineyard was irrigated using groundwater with salt concentration of 0.61 g/L. In 2005 and 2006, the experiments were carried out in a vineyard (37◦ 52 20 N, 102◦ 50 50 E, altitude 1581 m) and the field was 177.1 m long (south-north direction) and 57.5 m wide (east-west direction). Soil is sandy loam texture, with a mean dry bulk density of 1.71 g/cm3 . The experimental grapevines (Vitis vinifera L. cv Rizamat) were planted in east-west direction in 2000, with row spacing of 2.9 m and plant spacing of 1.8 m. The trellis for grapevine was divided into three layers, with supporting height of 0.5, 1.0 and 1.5 m, respectively. The vineyard was furrow-irrigated with a single furrow between every two rows, and the irrigation regime as listed in Table 1. The cross-section of the furrows was trapezoidal, with dimensions of 80 cm width at the bottom, 125 cm width at the top and 30 cm depth. In 2007 and 2008, the experiment was carried out in a vineyard (37◦ 51 N, 102◦ 51 E, altitude 1585 m) and the field was 1650 m long (south-north direction) and 1400 m wide (east-west direction). Soil is light sandy loam texture and a mean dry bulk density of 1.47 g/cm3 . The experimental grapevines (Vitis vinifera L. cv Merlot) were planted in 1999 in east-west direction, with row spacing of 2.7 m and plant spacing of 1.0 m. The trellis for grapevine was the same as the previous study. The vineyard was furrow-irrigated and the irrigation regime as listed in Table 1. Each vine row had one furrow. The cross-section of furrow was also trapezoidal, with dimensions of 90 cm width at the bottom, 100 cm width at the top and 30 cm depth. The Bowen ratio instrument (Campbell Scientific, USA) was installed in the vineyard row at the center of vineyard. The net radiation (Rn ) was measured by net radiometer (model Q7.1) mounted at 1.0 m above the canopy. The soil heat flux (G) was measured at two points in 2005–2006, one in the ditch and the other in the ridge, and three points in 2007–2008, one in the ditch and two in the ridge, by heat flux plates (model HFP01, Hukseflux, Delft, The Netherlands) inserted at 80 mm below the ground surface. Surface soil heat flux was calculated by correcting the heat flux at 80 mm for heat storage above the transducers, determined by change in soil temperature of the soil volume above the heat flux transducers. Temperature above the soil heat flux plates was measured with thermocouples (model 105T, Campbell Scientific, USA) at depths of 20 and 60 mm in line with every soil heat flux plate. Temperature and humidity were measured using two integrated temperature–humidity probes inside radiation shields (model HMP45C). The heights of the two fixed measurements were 0.5 and 1.9 m above the canopy. All data were collected by a data
September 11 20
September 9 60
logger (model CR23X) every 5 s and 10 min averages were calculated and stored. Heat pulse sap-flow sensors (SF200, Greenspan Technology Pty Ltd., Australia) were used to monitor trunk sap velocity of six vines continuously in 2007–2008. Two probes were inserted in each plant in eastern and western direction. The thermocouple sensors were at depths of 5 mm below the cambium. Sapwood area was determined by extracting an increment borer and measuring the length of the hydroactive xylem. Scaling from the individual vine to the vineyard was facilitated with a detailed survey of average per plant sapwood area within a 50 m × 50 m plot centered on the Bowen ratio instrument. Soil moisture content was measured using portable device (Diviner 2000, Sentek Pty Ltd., Australia). Diviner 2000 consists of a probe and hand-held data logger and utilizes frequency domain reflectometry (FDR) to measure soil water throughout the profile. 96, 36, 15 and 15 PVC access tubes (1.0 m in length and 0.05 m in internal diameter), were evenly installed in the experimental site in 2005–2008. Measurements were made at 0.1 m intervals with maximal soil depth of 1.0 m every third day in 2005 or every day in 2006–2008. The frequency of the soil moisture measurement was increased to hourly intervals after each irrigation and rainfall. The gravimetric sampling technique and steel rings were used to calibrate the Diviner 2000 unit. Leaf area index (LAI) was measured every 3–10 days using AM300 portable leaf area meter (ADC BioScientific Ltd., UK). In each measurement, six plants were sampled, eight leaves per plant and three readings from each leaf. Moreover, the total leaves of the six plants were used to calculate the average LAI. The solar radiation, precipitation, maximum and minimum air temperature, relative humidity and wind speed were measured with an automatic weather station (Weather Hawk, Campbell Scientific, USA) near the experimental vineyard. Moreover, the reference evapotranspiraton (ETo ) was estimated by the FAO–Penman equation (Allen et al., 1998). 2.2. Bowen ratio-energy balance method Latent flux can be estimated from the energy balance equation: Rn = ET + H + G
(1)
where ET is the latent heat flux (W/m2 ), H is the sensible heat flux (W/m2 ), is the heat of water vaporization (J/kg), ET is the evapotranspiration (mm), Rn is the net radiation (W/m2 ), G is the ground heat flux (W/m2 ). The Bowen ratio is defined as follows: ˇ=
H ET
(2)
Using Eqs. (1) and (2), it is possible to calculate the latent and sensible fluxes: Latent flux ET =
Rn − G 1+ˇ
(3)
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Table 2 Summary of meteorological factors during the whole growing season in 2005–2008. Variable 2
Solar radiation Rs (W/m ) Net radiation Rn (W/m2 ) Temperature Ta (◦ C) Rainfall (mm) Number of days data collected
Sensible flux H =
2005
2006
2007
2008
Average
205.2 110.5 18.5 88.0 161
202.3 120.7 18.2 174.0 160
187.5 110.8 17.7 179.0 164
198.3 116.9 19.0 79.0 147
198.3 114.7 18.4 130.0 158
ˇ (Rn − G) 1+ˇ
(4)
The Bowen ratio (ˇ) can be calculated from the following: ˇ=
T ∂T /∂z = e ∂e/∂z
(5)
where T and e are the temperature (◦ C) and vapor pressure (kPa) difference between the two measurement levels, respectively, is the psychrometric constant (kPa/◦ C). In Eq. (5), it is assumed that eddy diffusivities for heat and water vapour were equal and T and e were measured over the same height intervals. Bowen ratio (ˇ) was calculated from the difference in air temperature measured at two heights above the crop canopy and the difference in specific humidity measured at the same two heights. In this study, the set of criteria for selecting between reliable and unreliable values promoted by Perez et al. (1999) was adopted.
In our study, firstly, water did not flood from the ditch because of lower flow rate of furrow in the vineyard. Secondly, the experimental site was flat and the precipitation was not intensive. Furthermore, segregation belt was built between the vineyard and the surrounding area, so the runoff can be negligible. And also the drainage (D) can be neglected because there is a layer of impermeable clay below about 100 cm. Contribution from water table upward (W) was considered to be negligible because the water table was over 25 m deep. The soil water balance Eq. (6) can be simplified: P + I − ET = S
(7)
Evapotranspiration can be calculated from Eq. (7) once precipitation, irrigation, and soil moisture are known.
3. Results and discussion
2.3. Soil water balance
3.1. Meteorological parameters
Soil water balance is an indirect method for estimating ET and it is based on the principle of conservation of mass:
The variation of solar radiation (Rs ) had similar trends in all years, with peak values of about 330 W/m2 in June (Fig. 1). Rn peaked in early-mid July due to stronger solar radiation and lower surface reflectivity of the canopy during the vigorously growing stage. Daily Ta varied from 5.0 to 26.5 ◦ C and VPD from 0.01 to 2.16 kPa. As shown in Table 2, average Rs was 187.5–205.2 W/m2 , Rn 110.5–120.7 W/m2 , Ta 17.7–19.0 ◦ C and total precipitation 88.0–179.0 mm over the growing season.
P + I + W − ET − R − D = S
(6)
where P is the precipitation (mm), I is the irrigation (mm), W is the contribution from water table upward (mm), ET is the actual evapotranspiration (mm), R is the surface runoff (mm), D is the drainage (mm) and S is the change in soil water storage (mm).
Fig. 1. Daily variation of solar radiation (Rs ), net radiation (Rn ), air temperature (Ta ), vapor pressure deficit (VPD) and rainfall over the growing season in 2005–2008.
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Fig. 3. Diurnal variation of evapotranspiration (ET) pre- and post-irrigation measured by Bowen ratio-energy balance method. The irrigation was applied on the night of 1 August 2007 with the amount of 70 mm.
Fig. 2. Comparison of average daily evapotranspiration (ET) estimated by the Bowen ratio-energy balance and soil water balance methods. ( ) Data from 10 May to 6 October 2005; (䊉) data from 19 May to 7 October 2006; ( ) data from19 May to 5 October; ( ) data from 10 May to 20 September. ETBREB , measured evapotranspiration by the Bowen ratio-energy balance method, ETWB , measured evapotranspiration by soil water balance method.
3.2. Comparison of evapotranspiration measured by the Bowen ratio-energy balance (BREB) and soil water balance methods Daily average evapotranspiration (ET) calculated over 7-day periods using the soil water balance method (ETWB ) were compared with the corresponding daily average ET measured by the Bowen ratio method (ETBREB ) during the growing season (Fig. 2). The slope of the regression is 0.98, with R2 of 0.824. The root mean squared error (RMSE) is 0.35 mm/d. The results suggest that the Bowen ratio method is accurate in measuring vineyard ET in the arid regions northwest China. However, these results did not fully mean that the BREB method was going to work properly on a 30-min periods, because the overestimation can be counterbalanced by the underestimation during daytime or the nighttime. Some reports also showed that most of the cases in which the BREB method fails appear in the evening, during the night and in the early morning or under advection condition (Unland et al., 1996; Perez et al., 1999). The errors on 30-min period of BREB will be discussed based on lysimeter and eddy covariance methods in our further study. Although the BREB method may have errors in the estimation of vineyard ET on 30-min intervals, the measured ET by BREB is reliable when adopting the certain criteria for rejecting inaccurate data (Perez et al., 1999). Therefore, the measured ET variation by the BREB method will be used to study vineyard diurnal, seasonal and interannual evapotranspiration later. Many related studies also showed that the BREB method can be used to validate the estimated ET by models (Kato et al., 2004; Rana et al., 1997).
indicated that soil evaporation after furrow-irrigation could be 7–8 mm/d in a vineyard, which was significantly greater than our measurement (1.6 mm/d), such was due to lower proportion of the irrigation furrow width to total vineyard area in this study. Fig. 4 shows the diurnal pattern of ET pre- and post-rainfall (16:00–20:00 h on 30 July, 2006, with the rainfall of 29.0 mm). It shows that the peak value of ET increased dramatically from 0.3 mm/h on 30 July to 0.8 mm/h and its corresponding daily ET increased from 1.6 to 4.4 mm/d, with an increase of 175%. Because of less soil coverage by the canopy in this study, more incident radiation transmitted to the bare soil resulted in greater soil evaporation, thus rainfall increased the ET sharply. Yunusa et al. (2004) indicated that the soil evaporation accounted for 80% of ET when all soil surface was wetted. Brunel et al. (2006) also showed that rainfall increased sparsely vegetated palmyra ET significantly in an arid oasis ecosystem. Thus irrigation and rainfall, i.e. the change of soil water content, are the key factors affecting the evapotranspiration and energy partition.
3.3.2. Effect of frost on evapotranspiration Due to higher difference between day and night temperature in the desert oasis region, frost injury is a regular occurrence during early and late parts of the growing season. Fig. 5 shows diurnal pattern of ET pre- and post-frost (at dawn on 10 September, 2006). Though the Rn , Ta and VPD should be no significant difference, the daily ET decreased from 1.4 mm/d pre-frost to 0.9 mm/d post-frost, a reduction of 32%. Earlier research in Sweden already indicated that freezing damage caused a decrease of 10% ET for a mixed Norway spruce-Scots pine forest (Grelle et al., 1999; Humphreys et al., 2003). It suggested that frost damaged the cell membrane and leaf structure (Li et al., 2003; Qu et al., 2007) which decreased the stomatal opening and subsequently led to the decrease of transpiration and evapotranspiration.
3.3. Evapotranspiration under different weather conditions and underlying surface conditions 3.3.1. Effect of irrigation and rainfall on evapotranspiration For sparsely vegetated surfaces, the soil evaporation contributes to the ET greatly (Spano et al., 2000; Testi et al., 2004). The ET increased dramatically after irrigation at night on 1 August, 2007, and its peak value at midday increased from 0.3 mm/h on 1 August to 0.5 mm/h on 2 August (Fig. 3). Accordingly, the daily ET increased from 2.1 to 2.9 mm/d. The possible reasons were the following: (1) soil evaporation increased with the increase of soil moisture in the furrow after irrigation. (2) Plant transpiration enhanced with the increased soil water content at root-zone. Araujo et al. (1995)
Fig. 4. Diurnal variation of evapotranspiration (ET) pre- and post-rainfall measured by Bowen ratio-energy balance method. The rainfall occurred at 16:00–20:00 h on 30 July, 2006 with the amount of 29 mm.
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Table 3 Transpiration (T), evapotranspiration (ET), ratio of transpiration to evapotranspiration (T/ET) and modified crop coefficient (Kcm ) in different growing stages in 2005–2008. “–” Not measured. Year
Stage
Days
Daily T rate (mm/d)
T total (mm)
Daily ET rate (mm/d)
ET total (mm)
T/ET
Kcm
2005
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
Date 5.7–5.17 5.18–6.20 6.21–7.10 7.11–8.20 8.21–9.10 9.11–10.14 5.7–10.14
11 34 20 41 21 34 161
– – – – – – –
– – – – – – –
1.4 1.3 1.5 1.6 1.5 1.2 1.4
15.5 43.0 29.3 64.8 31.2 41.8 225.6
– – – – – – –
0.28 0.32 0.43 0.47 0.50 0.78 0.44
2006
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
5.1–5.8 5.9–6.10 6.11–7.3 7.4–8.10 8.11–9.2 9.3–10.7 5.1–10.7
8 33 23 38 23 35 160
– – – – – – –
– – – – – – –
1.1 1.9 2.7 2.9 2.6 1.3 2.2
9.0 61.7 61.9 111.5 60.3 44.4 348.8
– – – – – – –
0.26 0.53 0.69 0.89 1.02 0.66 0.71
2007
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
5.1–5.7 5.8–6.7 6.8–7.3 7.4–8.10 8.11–9.15 9.16–10.11 5.1–10.11
7 31 26 38 36 26 164
– – 1.3 1.6 1.3 0.6 1.2
– – 33.2 61.3 45.2 16.6 156.3
1.3 1.9 3.0 3.1 2.4 0.8 2.3
8.8 59.8 78.3 116.3 87.0 21.0 371.1
– – 0.42 0.53 0.52 0.79 0.52
0.47 0.75 0.84 0.89 1.02 0.51 0.83
2008
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
5.4–5.10 5.11–6.10 6.11–6.23 6.24–8.10 8.11–9.15 9.16–9.27 5.4–9.27
7 31 13 48 36 12 147
– 1.0 1.2 1.9 1.5 0.8 1.4
– 30.7 15.8 91.9 54.1 9.5 202.0
1.7 1.9 2.3 3.5 3.1 1.6 2.7
11.7 58.7 30.3 167.5 111.4 19.4 398.9
– 0.52 0.52 0.55 0.49 0.49 0.52
0.40 0.57 0.62 1.09 1.14 1.04 0.88
3.4. Seasonal variation of evapotranspiration, ratio of transpiration to evapotranspiration and crop coefficient 3.4.1. Seasonal variation of evapotranspiration As shown in Table 3, the ET rate increased from 1.1 to 1.7 mm/d at the budbreak stage to 1.6–3.5 mm/d at the berry development stage and then reduced to 0.8–1.6 mm/d at the leaf fall stage. The variation of vineyard ET rate was related to the net radiation, temperature, soil moisture and growing stage. 3.4.2. Variation of ratio of transpiration to evapotranspiration As seen from Table 3, for 2007 and 2008 the maximum transpiration (T) appeared at the berry development stage, being 1.6 and 1.9 mm/d, respectively, and the ratio of transpiration to evapotranspiration (T/ET) was 0.53 and 0.55, respectively. However, at the leaf fall stage in 2007, the T/ET was higher due to lower ET resulted from weaker solar radiation (Fig. 1), while the impact of weaker solar radiation on T is relatively smaller. Table 3 also shows that the difference of the stem sap-flow rate (T) of grapevines between 2007 and 2008 was lower than that of ET. Possible reason is that the grapevines have an ability to maintain relatively stable stem
sap-flow rate to meet the growth demand. T/ET during the whole growing season was 0.52 in 2007 and 2008, which agreed with the result of Yunusa et al. (2004). 3.4.3. Relationship between the modified crop coefficient and leaf area index Fig. 6 shows that the modified crop coefficient (Kcm ) increased rapidly with the increased leaf area index (LAI) in the early stage, and the leaf area is a key factor limiting ET and Kcm in the early season. At the threshold LAI of about 0.7, the increase of Kcm clearly slowed. This is because grapevines tightly wrapped to trellis wires may create compact hedgerows and the canopy area is only about 1/3–1/4 of the total surface area of the vineyard. Therefore, energy intercepted by the canopy did not increase greatly with the increased LAI, so greater leaf area did not affect evapotranspiration significantly. The modified crop coefficient varied over the growing season, which was similar to that of Grimes and Williams (1990) and Williams et al. (2003a,b), but higher than the value for field crops (Evans et al., 1993), which was mainly caused by wider row distance and lower ground cover. The modified crop coefficient was 0.71–0.88 during the whole growing season in 2006–2008 but only 0.44 in 2005 due to less rainfall and irrigation (Table 3). 3.5. Interannual variation of evapotranspiration
Fig. 5. Diurnal variation of evapotranspiration (ET) pre- and post-frost measured by Bowen ratio-energy balance method. The frost occurred at dawn on 10 September, 2006.
The ET was 1.4–2.7 mm/d during the growing season in 2005–2008 (Table 3), which was in agreement with the previous result (2.0–2.5 mm/d) (Yunusa et al., 2004), but slightly lower than the average ET rate on worldwide (about 3 mm/d) (Evans et al., 1993; Heilman et al., 1996; Oliver and Sene, 1992; Rana et al., 2004; Trambouze et al., 1998; Yunusa et al., 1997b, 2004; Williams et al., 2003b). During the whole growing season, the maximum daily ET rate was 4.3 on 12 August 2005, 5.7 on 23 July, 2006, 4.5 on 25 June, 2007 and 5.8 mm on 23 July, 2008, respectively, which was similar
B. Zhang et al. / Agricultural Water Management 97 (2010) 1898–1904
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Fig. 6. Relationship between modified crop coefficient (Kcm ) and leaf area index (LAI) in 2005–2008. Note: low rainfall and irrigation in 2005.
to the previous result (5.1 mm/d) (Heilman et al., 1996). However, Williams et al. (2003b) measured the daily ET over 6 mm from vineyards in California, USA and such high ET rates may result from frequent irrigation. Moreover, the production practices such as pruning level, trellis size, canopy management practices involving leaf removal, irrigation type and frequency, and prevailing climatic conditions had important effects on the vineyard ET (Williams et al., 2003b). The total ET was 225.6–398.9 mm over the whole growing season in the four consecutive years (Table 3). Williams et al. (2003a) reported that the total ET was about 500 mm for furrow-irrigated and drip-irrigated vineyards. Roux (2007) showed that the total ET was 621 mm for wine grape and 519–827 mm for table grape in South Africa due to longer growing period of grapevine (6–8 months). The difference may attribute to the difference of grapevine age, irrigation method and meteorological condition (Williams et al., 2003b).
4. Conclusions Main findings are outlined as follows:
(1) The Bowen ratio method can provide accurate estimates of vineyard evapotranspiration (ET) in the arid regions when appropriately installed. (2) Irrigation and rainfall increased the ET, but frost decreased the ET. Soil moisture is the key factor limiting the ET. (3) The vineyard ET rate reached the peak value at the berry development stage, and then reduced at the leaf fall stage. (4) Leaf area index was the key factor limiting the modified crop coefficients (Kcm ) in the early season, and Kcm was 0.71–0.88 (except 2005) during the whole growing stage. The ratio of transpiration to evapotranspiration was about 0.52.
Acknowledgements We are grateful for the grant support from financial support from the Chinese National Natural Science Fund (50679081, 50809072, 50869001), the National High-Tech 863 Project of China (2006AA100203) and the program supported by the Ministry of Water Resources of China (200801104-2). References Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop EvapotranspirationGuidelines for Computing Crop Water Requirements. Irrigation and Drainage Paper 56. FAO, Rome. Araujo, F., Williams, L.E., Mathews, M.A., 1995. A comparative study of young ‘Thompson Seedless’ grapevines under drip and furrow irrigation I. Root and soil water distribution. Scientia Horticulturae 60, 235–324. Brunel, J.P., Ihab, J., Droubi, A.M., Samaan, S., 2006. Energy budget and actual evapotranspiration of an arid oasis ecosystem: Palmyra (Syria). Agricultural Water Management 84, 213–220. Evans, R.G., Spayd, S.E., Wample, R.L., Kroeger, M.W., Mahan, M.O., 1993. Water use of Vitis vinifera grapes in Washington. Agricultural Water Management 23, 109–124. Grelle, A., Lindroth, A., Mölder, M., 1999. Seasonal variation of boreal forest surface conductance and evaporation. Agricultural and Forest Meteorology 98–99, 563–578. Grimes, D.W., Williams, L.E., 1990. Irrigation effects on plant water relations and productivity of Thompson Seedless grapevines. Crop Science 30 (2), 255–260. Heilman, J.L., McInnes, K.J., Gesch, R.W., Lascano, R.J., Savage, M.J., 1996. Effects of trellising on the energy balance of a vineyard. Agricultural and Forest Meteorology 81, 79–93. Humphreys, E.R., Black, T.A., Ethier, G.J., Drewitt, G.B., Spittlehouse, D.L., Jork, E.M., Nesic, Z., Livingston, N.J., 2003. Annual and seasonal variability of sensible and latent heat fluxes above a coastal Douglas-fir forest, British Columbia Canada. Agricultural and Forest Meteorology 115, 109–125. Kato, T., Kimura, R., Kamichika, M., 2004. Estimation of evapotranspiration, transpiration ratio and water-use efficiency from a sparse canopy using a compartment model. Agricultural Water Management 65, 173–191. Li, X.W., Zhang, S.F., Chen, S.F., 2003. The research results of chilling resistance in plant and its application. Journal of Biology 20 (3), 32–33. Oliver, H.R., Sene, K.J., 1992. Energy and water balances of developing vines. Agricultural and Forest Meteorology 61, 167–185. Ortega-Farias, S., Carrasco, M., Olioso, A., Acevedo, C., Poblete, C., 2007. Latent heat flux over Cabernet Sauvignon vineyard using the Shuttleworth and Wallace model. Irrigation Science 25, 161–170.
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Trambouze, W., Bertuzzi, P., Voltza, M., 1998. Comparison of methods for estimating actual evapotranspiration in a row-cropped vineyard. Agricultural and Forest Meteorology 91, 193–208. Unland, H.E., Houser, P.R., Shuttleworth, W.J., Yang, Z.L., 1996. Surface flux measurement and modeling at a semi-arid Sonoran Desert site. Agricultural and Forest Meteorology 82, 119–153. Williams, L.E., Ayars, J.E., 2005. Grapevine water use and the crop coefficient are linear functions of the shaded area measured beneath the canopy. Agricultural and Forest Meteorology 132, 201–211. Williams, L.E., Baeza, P., 2007. Relationships among ambient temperature and vapor pressure deficit and leaf and stem water potentials of fully irrigated, field-grown grapevines. American Journal of Enology and Viticulture 58 (2), 173–181. Williams, L.E., Phene, C.J., Grimes, D.W., Trout, T.J., 2003a. Water use of young Thompson seedless grapevines in California. Irrigation Science 22, 1–9. Williams, L.E., Phene, C.J., Grimes, D.W., Trout, T.J., 2003b. Water use of mature Thompson seedless grapevines in California. Irrigation Science 22, 11–18. Yunusa, I.A.M., Walker, R.R., Blackmore, D.H., 1997a. Characterisation of water use by Sultana grapevines (Vitis vinifera L.) on their own roots or on Ramsey rootstock drip-irrigated with water of different salinities. Irrigation Science 17, 77–86. Yunusa, I.A.M., Walker, R.R., Guy, J.R., 1997b. Partitioning of seasonal evapotranspiration from a commercial furrow-irrigated Sultana vineyard. Irrigation Science 18, 45–54. Yunusa, I.A.M., Walker, R.R., Lu, P., 2004. Evapotranspiration components from energy balance, sapflow and microlysimetry techniques for an irrigated vineyard in inland Australia. Agricultural and Forest Meteorology 127, 10–93.
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Variation in vineyard evapotranspiration in an arid region of northwest China Baozhong Zhang a,b , Shaozhong Kang a,∗ , Fusheng Li c , Ling Tong a , Taisheng Du a a
Center for Agricultural Water Research in China, China Agricultural University, East Campus, 100083 Beijing, China Department of Irrigation and Drainage, China Institute of Water Resources and Hydropower Research, 100048 Beijing, China c Agricultural College, Guangxi University, 530005 Nanning, China b
a r t i c l e
i n f o
Article history: Received 8 April 2010 Accepted 16 June 2010 Available online 4 August 2010 Keywords: Bowen ratio-energy balance Evapotranspiration Crop coefficient Latent heat flux Vineyard
a b s t r a c t Grapevines are extensively grown in the arid region of China, but little information is available on the diurnal, seasonal and interannual variability of vineyard evapotranspiration (ET). To address this question, two vineyards in the arid region of northwest China were taken as an example to study the variation of ET using Bowen ratio-energy balance method in 2005–2008. Results indicate that the Bowen ratio method provided accurate estimate of vineyard ET as the instrument was correctly installed. Irrigation and rainfall increased daily ET by 38 and 175%, respectively, but frost decreased it by 32%. Daily ET had a maximum value of 1.6–3.5 mm/d at the berry development stage, and a minimum value of 0.8–1.7 mm/d at the early and later stages. The total ET was 226–399 mm over the growing season. The ratio of transpiration to evapotranspiration was 0.52 and the modified crop coefficient (Kcm ) was 0.71–0.88 (except 2005) over the whole growing stage. Larger interannual difference of ET and Kcm mainly resulted from the difference of irrigation and rainfall between different years. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The arid region of northwest China is one of the least developed regions in China, with a fragile ecological environment. However, the region has abundant sunshine hours and is suitable for grape growing. In recent years, horticulture has been becoming an important industry for the local economy. Meteorologists, hydrologists, agronomists and ecologists require the knowledge of evapotranspiration (ET), which affects gross crop productivity. So understanding vineyard ET has become a research priority in the arid region of northwest China. There are numerous studies on vineyard ET using lysimeter (Evans et al., 1993; Williams et al., 2003a,b; Williams and Ayars, 2005), heat pulse or heat balance (Trambouze et al., 1998; Yunusa et al., 1997a,b), Bowen ratio (Rana and Katerji, 2008; Teixeira et al., 2007; Trambouze et al., 1998; Yunusa et al., 2004) and eddy correlation (Ortega-Farias et al., 2007; Spano et al., 2000), etc. All of these studies found that vineyard ET varies considerably with regional climate, grapevine type, irrigation scheduling, and management method, e.g. trellis system, canopy size, etc. (Teixeira et al., 2007; Williams and Ayars, 2005; Williams and Baeza, 2007; Williams et al., 2003a,b). These investigated vines were mainly irrigated with drip irrigation (Ortega-Farias et al., 2007; Williams et al., 2003a,b; Williams and Ayars, 2005; Yunusa et al., 1997a, 2004), trained on
a T-trellis support (Williams et al., 2003a,b; Yunusa et al., 1997a, 2004) and located in Australia (Yunusa et al., 1997a,b, 2004), California (Williams et al., 2003a,b; Williams and Ayars, 2005) and South America (Ortega-Farias et al., 2007). To our knowledge, there was little information on seasonal and annual variability in the long-term ET and ratio of transpiration to evapotranspiration (T/ET) over the vineyard canopy under furrow-irrigation. Thus, the understanding of the variability of ET over furrow-irrigated vineyard with single vertical trellis systems in the northwest China is required, preferably under several climatic conditions, especially after a frost, and phenological regimes. Therefore, a 4-year experiment using the Bowen ratio-energy method (BREB) over two furrow-irrigated vineyards was conducted under different rainfall and irrigation conditions in the arid region of northwest China. The objectives of this study are to (1) evaluate the applicability of the BREB in estimating ET; (2) investigate diurnal variation of ET under different weather conditions and underlying surface conditions; (3) quantify seasonal and interannual variation of vineyard ET and T/ET; (4) analyze the effect of leaf area index (LAI) on modified crop coefficient (Kcm ); and (5) compare the ET, T/ET and Kcm in different hydrological years and irrigation regimes. 2. Materials and methods 2.1. Experimental site and measurements
∗ Corresponding author. Fax: +86 10 62737611. E-mail address: [email protected] (S. Kang). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.06.010
The experiments were conducted at two vineyards of Shiyanghe Experimental Station for Water-saving in Agriculture and Ecol-
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Table 1 Summary of irrigation regime during the whole growing season in 2005–2008. 2005 year
Irrigation date Irrigation quota (mm)
May 11 15
May 26 15
June 12 20
July 11 20
2006 year
Irrigation date Irrigation quota (mm)
May 5 41.5
May 28 41.5
June 29 41.5
August 9 41.5
2007 year
Irrigation date Irrigation quota (mm)
May 11 70
June 8 70
June 21 70
August 2 70
2008 year
Irrigation date Irrigation quota (mm)
May 18 60
June 24 60
July 18 60
August 16 60
ogy, China Agricultural University, located in Gansu Province of northwest China during 2005–2008. The site has high sunlight hours with a mean annual sunshine duration over 3000 h, mean annual temperature of 8 ◦ C and frost-free days of 150. The active accumulated temperature and effective accumulated temperature (>10 ◦ C) are about 2153 and 1327 ◦ C during the whole growing season, respectively. The region is limited in water resources with a mean precipitation of 131 mm during the whole growing season. Average groundwater table is below 25 m. The vineyard was irrigated using groundwater with salt concentration of 0.61 g/L. In 2005 and 2006, the experiments were carried out in a vineyard (37◦ 52 20 N, 102◦ 50 50 E, altitude 1581 m) and the field was 177.1 m long (south-north direction) and 57.5 m wide (east-west direction). Soil is sandy loam texture, with a mean dry bulk density of 1.71 g/cm3 . The experimental grapevines (Vitis vinifera L. cv Rizamat) were planted in east-west direction in 2000, with row spacing of 2.9 m and plant spacing of 1.8 m. The trellis for grapevine was divided into three layers, with supporting height of 0.5, 1.0 and 1.5 m, respectively. The vineyard was furrow-irrigated with a single furrow between every two rows, and the irrigation regime as listed in Table 1. The cross-section of the furrows was trapezoidal, with dimensions of 80 cm width at the bottom, 125 cm width at the top and 30 cm depth. In 2007 and 2008, the experiment was carried out in a vineyard (37◦ 51 N, 102◦ 51 E, altitude 1585 m) and the field was 1650 m long (south-north direction) and 1400 m wide (east-west direction). Soil is light sandy loam texture and a mean dry bulk density of 1.47 g/cm3 . The experimental grapevines (Vitis vinifera L. cv Merlot) were planted in 1999 in east-west direction, with row spacing of 2.7 m and plant spacing of 1.0 m. The trellis for grapevine was the same as the previous study. The vineyard was furrow-irrigated and the irrigation regime as listed in Table 1. Each vine row had one furrow. The cross-section of furrow was also trapezoidal, with dimensions of 90 cm width at the bottom, 100 cm width at the top and 30 cm depth. The Bowen ratio instrument (Campbell Scientific, USA) was installed in the vineyard row at the center of vineyard. The net radiation (Rn ) was measured by net radiometer (model Q7.1) mounted at 1.0 m above the canopy. The soil heat flux (G) was measured at two points in 2005–2006, one in the ditch and the other in the ridge, and three points in 2007–2008, one in the ditch and two in the ridge, by heat flux plates (model HFP01, Hukseflux, Delft, The Netherlands) inserted at 80 mm below the ground surface. Surface soil heat flux was calculated by correcting the heat flux at 80 mm for heat storage above the transducers, determined by change in soil temperature of the soil volume above the heat flux transducers. Temperature above the soil heat flux plates was measured with thermocouples (model 105T, Campbell Scientific, USA) at depths of 20 and 60 mm in line with every soil heat flux plate. Temperature and humidity were measured using two integrated temperature–humidity probes inside radiation shields (model HMP45C). The heights of the two fixed measurements were 0.5 and 1.9 m above the canopy. All data were collected by a data
September 11 20
September 9 60
logger (model CR23X) every 5 s and 10 min averages were calculated and stored. Heat pulse sap-flow sensors (SF200, Greenspan Technology Pty Ltd., Australia) were used to monitor trunk sap velocity of six vines continuously in 2007–2008. Two probes were inserted in each plant in eastern and western direction. The thermocouple sensors were at depths of 5 mm below the cambium. Sapwood area was determined by extracting an increment borer and measuring the length of the hydroactive xylem. Scaling from the individual vine to the vineyard was facilitated with a detailed survey of average per plant sapwood area within a 50 m × 50 m plot centered on the Bowen ratio instrument. Soil moisture content was measured using portable device (Diviner 2000, Sentek Pty Ltd., Australia). Diviner 2000 consists of a probe and hand-held data logger and utilizes frequency domain reflectometry (FDR) to measure soil water throughout the profile. 96, 36, 15 and 15 PVC access tubes (1.0 m in length and 0.05 m in internal diameter), were evenly installed in the experimental site in 2005–2008. Measurements were made at 0.1 m intervals with maximal soil depth of 1.0 m every third day in 2005 or every day in 2006–2008. The frequency of the soil moisture measurement was increased to hourly intervals after each irrigation and rainfall. The gravimetric sampling technique and steel rings were used to calibrate the Diviner 2000 unit. Leaf area index (LAI) was measured every 3–10 days using AM300 portable leaf area meter (ADC BioScientific Ltd., UK). In each measurement, six plants were sampled, eight leaves per plant and three readings from each leaf. Moreover, the total leaves of the six plants were used to calculate the average LAI. The solar radiation, precipitation, maximum and minimum air temperature, relative humidity and wind speed were measured with an automatic weather station (Weather Hawk, Campbell Scientific, USA) near the experimental vineyard. Moreover, the reference evapotranspiraton (ETo ) was estimated by the FAO–Penman equation (Allen et al., 1998). 2.2. Bowen ratio-energy balance method Latent flux can be estimated from the energy balance equation: Rn = ET + H + G
(1)
where ET is the latent heat flux (W/m2 ), H is the sensible heat flux (W/m2 ), is the heat of water vaporization (J/kg), ET is the evapotranspiration (mm), Rn is the net radiation (W/m2 ), G is the ground heat flux (W/m2 ). The Bowen ratio is defined as follows: ˇ=
H ET
(2)
Using Eqs. (1) and (2), it is possible to calculate the latent and sensible fluxes: Latent flux ET =
Rn − G 1+ˇ
(3)
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B. Zhang et al. / Agricultural Water Management 97 (2010) 1898–1904
Table 2 Summary of meteorological factors during the whole growing season in 2005–2008. Variable 2
Solar radiation Rs (W/m ) Net radiation Rn (W/m2 ) Temperature Ta (◦ C) Rainfall (mm) Number of days data collected
Sensible flux H =
2005
2006
2007
2008
Average
205.2 110.5 18.5 88.0 161
202.3 120.7 18.2 174.0 160
187.5 110.8 17.7 179.0 164
198.3 116.9 19.0 79.0 147
198.3 114.7 18.4 130.0 158
ˇ (Rn − G) 1+ˇ
(4)
The Bowen ratio (ˇ) can be calculated from the following: ˇ=
T ∂T /∂z = e ∂e/∂z
(5)
where T and e are the temperature (◦ C) and vapor pressure (kPa) difference between the two measurement levels, respectively, is the psychrometric constant (kPa/◦ C). In Eq. (5), it is assumed that eddy diffusivities for heat and water vapour were equal and T and e were measured over the same height intervals. Bowen ratio (ˇ) was calculated from the difference in air temperature measured at two heights above the crop canopy and the difference in specific humidity measured at the same two heights. In this study, the set of criteria for selecting between reliable and unreliable values promoted by Perez et al. (1999) was adopted.
In our study, firstly, water did not flood from the ditch because of lower flow rate of furrow in the vineyard. Secondly, the experimental site was flat and the precipitation was not intensive. Furthermore, segregation belt was built between the vineyard and the surrounding area, so the runoff can be negligible. And also the drainage (D) can be neglected because there is a layer of impermeable clay below about 100 cm. Contribution from water table upward (W) was considered to be negligible because the water table was over 25 m deep. The soil water balance Eq. (6) can be simplified: P + I − ET = S
(7)
Evapotranspiration can be calculated from Eq. (7) once precipitation, irrigation, and soil moisture are known.
3. Results and discussion
2.3. Soil water balance
3.1. Meteorological parameters
Soil water balance is an indirect method for estimating ET and it is based on the principle of conservation of mass:
The variation of solar radiation (Rs ) had similar trends in all years, with peak values of about 330 W/m2 in June (Fig. 1). Rn peaked in early-mid July due to stronger solar radiation and lower surface reflectivity of the canopy during the vigorously growing stage. Daily Ta varied from 5.0 to 26.5 ◦ C and VPD from 0.01 to 2.16 kPa. As shown in Table 2, average Rs was 187.5–205.2 W/m2 , Rn 110.5–120.7 W/m2 , Ta 17.7–19.0 ◦ C and total precipitation 88.0–179.0 mm over the growing season.
P + I + W − ET − R − D = S
(6)
where P is the precipitation (mm), I is the irrigation (mm), W is the contribution from water table upward (mm), ET is the actual evapotranspiration (mm), R is the surface runoff (mm), D is the drainage (mm) and S is the change in soil water storage (mm).
Fig. 1. Daily variation of solar radiation (Rs ), net radiation (Rn ), air temperature (Ta ), vapor pressure deficit (VPD) and rainfall over the growing season in 2005–2008.
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Fig. 3. Diurnal variation of evapotranspiration (ET) pre- and post-irrigation measured by Bowen ratio-energy balance method. The irrigation was applied on the night of 1 August 2007 with the amount of 70 mm.
Fig. 2. Comparison of average daily evapotranspiration (ET) estimated by the Bowen ratio-energy balance and soil water balance methods. ( ) Data from 10 May to 6 October 2005; (䊉) data from 19 May to 7 October 2006; ( ) data from19 May to 5 October; ( ) data from 10 May to 20 September. ETBREB , measured evapotranspiration by the Bowen ratio-energy balance method, ETWB , measured evapotranspiration by soil water balance method.
3.2. Comparison of evapotranspiration measured by the Bowen ratio-energy balance (BREB) and soil water balance methods Daily average evapotranspiration (ET) calculated over 7-day periods using the soil water balance method (ETWB ) were compared with the corresponding daily average ET measured by the Bowen ratio method (ETBREB ) during the growing season (Fig. 2). The slope of the regression is 0.98, with R2 of 0.824. The root mean squared error (RMSE) is 0.35 mm/d. The results suggest that the Bowen ratio method is accurate in measuring vineyard ET in the arid regions northwest China. However, these results did not fully mean that the BREB method was going to work properly on a 30-min periods, because the overestimation can be counterbalanced by the underestimation during daytime or the nighttime. Some reports also showed that most of the cases in which the BREB method fails appear in the evening, during the night and in the early morning or under advection condition (Unland et al., 1996; Perez et al., 1999). The errors on 30-min period of BREB will be discussed based on lysimeter and eddy covariance methods in our further study. Although the BREB method may have errors in the estimation of vineyard ET on 30-min intervals, the measured ET by BREB is reliable when adopting the certain criteria for rejecting inaccurate data (Perez et al., 1999). Therefore, the measured ET variation by the BREB method will be used to study vineyard diurnal, seasonal and interannual evapotranspiration later. Many related studies also showed that the BREB method can be used to validate the estimated ET by models (Kato et al., 2004; Rana et al., 1997).
indicated that soil evaporation after furrow-irrigation could be 7–8 mm/d in a vineyard, which was significantly greater than our measurement (1.6 mm/d), such was due to lower proportion of the irrigation furrow width to total vineyard area in this study. Fig. 4 shows the diurnal pattern of ET pre- and post-rainfall (16:00–20:00 h on 30 July, 2006, with the rainfall of 29.0 mm). It shows that the peak value of ET increased dramatically from 0.3 mm/h on 30 July to 0.8 mm/h and its corresponding daily ET increased from 1.6 to 4.4 mm/d, with an increase of 175%. Because of less soil coverage by the canopy in this study, more incident radiation transmitted to the bare soil resulted in greater soil evaporation, thus rainfall increased the ET sharply. Yunusa et al. (2004) indicated that the soil evaporation accounted for 80% of ET when all soil surface was wetted. Brunel et al. (2006) also showed that rainfall increased sparsely vegetated palmyra ET significantly in an arid oasis ecosystem. Thus irrigation and rainfall, i.e. the change of soil water content, are the key factors affecting the evapotranspiration and energy partition.
3.3.2. Effect of frost on evapotranspiration Due to higher difference between day and night temperature in the desert oasis region, frost injury is a regular occurrence during early and late parts of the growing season. Fig. 5 shows diurnal pattern of ET pre- and post-frost (at dawn on 10 September, 2006). Though the Rn , Ta and VPD should be no significant difference, the daily ET decreased from 1.4 mm/d pre-frost to 0.9 mm/d post-frost, a reduction of 32%. Earlier research in Sweden already indicated that freezing damage caused a decrease of 10% ET for a mixed Norway spruce-Scots pine forest (Grelle et al., 1999; Humphreys et al., 2003). It suggested that frost damaged the cell membrane and leaf structure (Li et al., 2003; Qu et al., 2007) which decreased the stomatal opening and subsequently led to the decrease of transpiration and evapotranspiration.
3.3. Evapotranspiration under different weather conditions and underlying surface conditions 3.3.1. Effect of irrigation and rainfall on evapotranspiration For sparsely vegetated surfaces, the soil evaporation contributes to the ET greatly (Spano et al., 2000; Testi et al., 2004). The ET increased dramatically after irrigation at night on 1 August, 2007, and its peak value at midday increased from 0.3 mm/h on 1 August to 0.5 mm/h on 2 August (Fig. 3). Accordingly, the daily ET increased from 2.1 to 2.9 mm/d. The possible reasons were the following: (1) soil evaporation increased with the increase of soil moisture in the furrow after irrigation. (2) Plant transpiration enhanced with the increased soil water content at root-zone. Araujo et al. (1995)
Fig. 4. Diurnal variation of evapotranspiration (ET) pre- and post-rainfall measured by Bowen ratio-energy balance method. The rainfall occurred at 16:00–20:00 h on 30 July, 2006 with the amount of 29 mm.
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Table 3 Transpiration (T), evapotranspiration (ET), ratio of transpiration to evapotranspiration (T/ET) and modified crop coefficient (Kcm ) in different growing stages in 2005–2008. “–” Not measured. Year
Stage
Days
Daily T rate (mm/d)
T total (mm)
Daily ET rate (mm/d)
ET total (mm)
T/ET
Kcm
2005
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
Date 5.7–5.17 5.18–6.20 6.21–7.10 7.11–8.20 8.21–9.10 9.11–10.14 5.7–10.14
11 34 20 41 21 34 161
– – – – – – –
– – – – – – –
1.4 1.3 1.5 1.6 1.5 1.2 1.4
15.5 43.0 29.3 64.8 31.2 41.8 225.6
– – – – – – –
0.28 0.32 0.43 0.47 0.50 0.78 0.44
2006
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
5.1–5.8 5.9–6.10 6.11–7.3 7.4–8.10 8.11–9.2 9.3–10.7 5.1–10.7
8 33 23 38 23 35 160
– – – – – – –
– – – – – – –
1.1 1.9 2.7 2.9 2.6 1.3 2.2
9.0 61.7 61.9 111.5 60.3 44.4 348.8
– – – – – – –
0.26 0.53 0.69 0.89 1.02 0.66 0.71
2007
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
5.1–5.7 5.8–6.7 6.8–7.3 7.4–8.10 8.11–9.15 9.16–10.11 5.1–10.11
7 31 26 38 36 26 164
– – 1.3 1.6 1.3 0.6 1.2
– – 33.2 61.3 45.2 16.6 156.3
1.3 1.9 3.0 3.1 2.4 0.8 2.3
8.8 59.8 78.3 116.3 87.0 21.0 371.1
– – 0.42 0.53 0.52 0.79 0.52
0.47 0.75 0.84 0.89 1.02 0.51 0.83
2008
Budbreak Rapid shoot growth Anthesis Berry development Fruit maturity Leaf fall Whole season
5.4–5.10 5.11–6.10 6.11–6.23 6.24–8.10 8.11–9.15 9.16–9.27 5.4–9.27
7 31 13 48 36 12 147
– 1.0 1.2 1.9 1.5 0.8 1.4
– 30.7 15.8 91.9 54.1 9.5 202.0
1.7 1.9 2.3 3.5 3.1 1.6 2.7
11.7 58.7 30.3 167.5 111.4 19.4 398.9
– 0.52 0.52 0.55 0.49 0.49 0.52
0.40 0.57 0.62 1.09 1.14 1.04 0.88
3.4. Seasonal variation of evapotranspiration, ratio of transpiration to evapotranspiration and crop coefficient 3.4.1. Seasonal variation of evapotranspiration As shown in Table 3, the ET rate increased from 1.1 to 1.7 mm/d at the budbreak stage to 1.6–3.5 mm/d at the berry development stage and then reduced to 0.8–1.6 mm/d at the leaf fall stage. The variation of vineyard ET rate was related to the net radiation, temperature, soil moisture and growing stage. 3.4.2. Variation of ratio of transpiration to evapotranspiration As seen from Table 3, for 2007 and 2008 the maximum transpiration (T) appeared at the berry development stage, being 1.6 and 1.9 mm/d, respectively, and the ratio of transpiration to evapotranspiration (T/ET) was 0.53 and 0.55, respectively. However, at the leaf fall stage in 2007, the T/ET was higher due to lower ET resulted from weaker solar radiation (Fig. 1), while the impact of weaker solar radiation on T is relatively smaller. Table 3 also shows that the difference of the stem sap-flow rate (T) of grapevines between 2007 and 2008 was lower than that of ET. Possible reason is that the grapevines have an ability to maintain relatively stable stem
sap-flow rate to meet the growth demand. T/ET during the whole growing season was 0.52 in 2007 and 2008, which agreed with the result of Yunusa et al. (2004). 3.4.3. Relationship between the modified crop coefficient and leaf area index Fig. 6 shows that the modified crop coefficient (Kcm ) increased rapidly with the increased leaf area index (LAI) in the early stage, and the leaf area is a key factor limiting ET and Kcm in the early season. At the threshold LAI of about 0.7, the increase of Kcm clearly slowed. This is because grapevines tightly wrapped to trellis wires may create compact hedgerows and the canopy area is only about 1/3–1/4 of the total surface area of the vineyard. Therefore, energy intercepted by the canopy did not increase greatly with the increased LAI, so greater leaf area did not affect evapotranspiration significantly. The modified crop coefficient varied over the growing season, which was similar to that of Grimes and Williams (1990) and Williams et al. (2003a,b), but higher than the value for field crops (Evans et al., 1993), which was mainly caused by wider row distance and lower ground cover. The modified crop coefficient was 0.71–0.88 during the whole growing season in 2006–2008 but only 0.44 in 2005 due to less rainfall and irrigation (Table 3). 3.5. Interannual variation of evapotranspiration
Fig. 5. Diurnal variation of evapotranspiration (ET) pre- and post-frost measured by Bowen ratio-energy balance method. The frost occurred at dawn on 10 September, 2006.
The ET was 1.4–2.7 mm/d during the growing season in 2005–2008 (Table 3), which was in agreement with the previous result (2.0–2.5 mm/d) (Yunusa et al., 2004), but slightly lower than the average ET rate on worldwide (about 3 mm/d) (Evans et al., 1993; Heilman et al., 1996; Oliver and Sene, 1992; Rana et al., 2004; Trambouze et al., 1998; Yunusa et al., 1997b, 2004; Williams et al., 2003b). During the whole growing season, the maximum daily ET rate was 4.3 on 12 August 2005, 5.7 on 23 July, 2006, 4.5 on 25 June, 2007 and 5.8 mm on 23 July, 2008, respectively, which was similar
B. Zhang et al. / Agricultural Water Management 97 (2010) 1898–1904
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Fig. 6. Relationship between modified crop coefficient (Kcm ) and leaf area index (LAI) in 2005–2008. Note: low rainfall and irrigation in 2005.
to the previous result (5.1 mm/d) (Heilman et al., 1996). However, Williams et al. (2003b) measured the daily ET over 6 mm from vineyards in California, USA and such high ET rates may result from frequent irrigation. Moreover, the production practices such as pruning level, trellis size, canopy management practices involving leaf removal, irrigation type and frequency, and prevailing climatic conditions had important effects on the vineyard ET (Williams et al., 2003b). The total ET was 225.6–398.9 mm over the whole growing season in the four consecutive years (Table 3). Williams et al. (2003a) reported that the total ET was about 500 mm for furrow-irrigated and drip-irrigated vineyards. Roux (2007) showed that the total ET was 621 mm for wine grape and 519–827 mm for table grape in South Africa due to longer growing period of grapevine (6–8 months). The difference may attribute to the difference of grapevine age, irrigation method and meteorological condition (Williams et al., 2003b).
4. Conclusions Main findings are outlined as follows:
(1) The Bowen ratio method can provide accurate estimates of vineyard evapotranspiration (ET) in the arid regions when appropriately installed. (2) Irrigation and rainfall increased the ET, but frost decreased the ET. Soil moisture is the key factor limiting the ET. (3) The vineyard ET rate reached the peak value at the berry development stage, and then reduced at the leaf fall stage. (4) Leaf area index was the key factor limiting the modified crop coefficients (Kcm ) in the early season, and Kcm was 0.71–0.88 (except 2005) during the whole growing stage. The ratio of transpiration to evapotranspiration was about 0.52.
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