Experimental Study on Urban Turfgrass Evapotranspiration from Yinchuan City, China

Experimental Study on Urban Turfgrass Evapotranspiration from
Yinchuan City, China
WANG Jing , YANG Jin-zhong
1. National Key Laboratory of Water Resources and Hydropower Engineering Sciences, Wuhan
University, Wuhan 430072, China
[email protected]
Abstract: Based on the experiments, soil water contents of urban turf field and evapotranspiration of
urban turf and highway green belt turf were analyzed with different irrigation methods in Yinchuan city,
China. The results showed that the variation pattern of turf crop coefficient Kc in the three experimental
sites was same as soil water content and turf reference evapotranspiration. The values of Kc changed
obviously in different months. The mean of Kc for urban turf from sprinkler irrigation was lower than
urban turf and highway green belt turf with flood irrigation, while mean of Kc for highway green belt
turf with flood irrigation was highest. Similarly , the evapotranspiration (or water consumption) of urban
turf irrigated with sprinkler method was less and the growth situation was better than urban turf and
highway green belt turf with flood irrigation method. Evapotranspiration for highway green belt turf
with flood irrigation was most and its growth situation was worst among three experimental sites.
Keywords: Evapotranspiration; urban turf; highway green belt turf; crop coefficient
1. Introduction
Turf evapotranspiration(ET) is the sum of evaporation and truf transpiration. Most study of the turf
evapotranspiration focuses on the selection of grasses species to save water. Beard summarized recent
achievements and gave the difference of evapotranspiration of trufgrass species[1]. Kopec et al. also
studied the evapotranspiration of turfgrass species[2、3、4、5]. The effect of external factors on turfgrass
evapotranspiration were studied by maintenance management of water soil content, soil texture and soil
fertility [6. 7. 8. 9. 10. 11]. Han et al. discussed the evapotranspiration of warm-season, cool-season turfgrass
in greenhouse and the results showed that evapotranspiration was higher in cool-season turfgrass than
in warm-season turfgrass under sufficient soil water. In cool-season the difference of turfgrass
evapotranspiration was not obvious. The warm-season turfgrass had higher drought resistance than
cool-season turfgrass when water was unsufficient[12、13]. Zhang et al. and Xu et al. studied the effect of
irrigation condition on the evapotranspiration of cool-season turfgrass and their results indicated that the
ET of three turfgrasses in different water conditions was significantly different and the ET among
different turfgrasses did not show distinct difference in different environments[14、15]. Gao et al. studied
the ET of different turfgrass species. The result showed that ET was higher in cool-season turfgrass than
in warm-season turfgrass under sufficient irrigation. Under the condition of limit irrigation the
difference between six turfgrasses was significant[16. 17]. Although there are a certain improvements on
the analysis of turfgrass evapotranspiration, more work is needed on evaluation of evaportranspiration of
urban turf and highway green belt turf under different irrigation methods in arid regions. This paper is
concentrated on this problem from field measuring in Yinchuan, china.
，
2. Material and Methods
2.1 Experimental Sites
The experiment on urban turf was conducted in region A and B in Ningxia University experimental
station and the experiment on highway green belt turf was carried out in highway green belt of Gao
Tai-si Li jin park in Yinchuan city. Both sites were situated in Yellow River Alluvial Plain, 38°47′ N,
106°27′ E, the temperature difference between day and night is large. The average annual rainfall is
163.9mm and annual evaporation 1669.3mm.
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2.2 Experimental Design
Sprinkler irrigation and flood irrigation are used for urban turf. Flood irrigation is used for highway
green belt turf.
2.2.1Experimental Design of sprinkler irrigation
The experimental site of sprinkler irrigation was in region A. The effective irrigation control area is
S=2*R*R, where R=14m is the design spray range of sprinkler. TDR(Model TRIME-T3) is used for the
measurement of soil water content. The measurement period is from April to October with the time step
of 4 days and the measurement depths are 0 20cm 20 40cm 40 60cm 60 100cm.
2.2.2 Experimental Design of Flood Irrigation
The experiment of urban turf was in region B and the experiment for highway green belt turf was in
Gao Tai-si Li jin park. Both sites are rectangle with irrigation area 10m×11m and 15m×6m, respectively.
TDR, buried in the middle of the regions, is used to measure soil water contents. The monitoring time,
period, depth and lawn maintenance are same as in Region A.
～
、 ～
、 ～
、 ～
2.3 Measurement Methods
Irrigation flux was measured by flowmeter. The relative humanity of the atmosphere was measured
by psychrometer. Windspeed was measured by light three-cup anemorumbometer. Sunshine hours was
measured by FJ-2 sunshine recorder. Maximum and minimum temperature and precipitation was
collected from nearby meteorological station.
3. Analysis of Soil Water Content Changes with Different Irrigation Methods
3.1 Water Content Variation of Urban Turf Field with Sprinkler Irrigation
Soil water content in 0~20cm soil layer is high and changes with time distinctly. Soil water content
in 20~80cm soil layer is lower compared with topsoil and the change of water content is not as large as
top soil, especially in 40~80cm soil layer. Water content for different depth increases from April to
October.(Fig.1). The water content differences may come from the following reasons: 70%~90% of
turfgrass roots are in 0~20cm soil layer, which leads to most of water loss by root uptake; soil texture
is sandy loam in 0~20cm,while other three layers are clay loam; with atmospheric and ground
temperature change, the frequency and duration of irrigation increase, which caused water accumulation
in top soil and kept a dynamic balance of water in 20~80cm soil layers.
①
②
③
3.2 Water Content Variation in Urban Turf Field with Flood Irrigation
It is shown in Fig 2 that the soil water content varied with time greatly in 0~80cm soil layer, and
variations of soil water content in different layers with a same manner. The maximum soil water content
reached 38%, and minimum 13%. The reasons of the water content variation are: irrigation amount of
flood irrigation is larger than sprinkler irrigation each time; soil texture is sandy loam in
0~80cm; irrigation water not only satisfies roots uptake in 0~20cm but also causes leakage to
20~80cm soil layers.
②
③
①
Fig1. Soil water content of urban turf in sprinkler irrigation with time
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Fig. 2 Soil water content of urban turf in flood irrigation
3.3 Water Content Variation in Highway Green Belt Turf Field with Flood Irrigation
Soil water content in 0~20cm soil layer is low and varies greatly. Soil water content in 20~80cm
soil layer keep stable, around 30% to 40% (Fig.3). The water content variations are mainly caused by
the following reasons:
flood irrigation amount is larger each time, and frequency and duration of
frequency are less than sprinkler irrigation; soil texture is sandy in 0~20cm,while other three layers are
loam, which increase roots uptake in 0~20cm and topsoil leakage becomes serious. Other soil layers
keep a dynamic balance of water.
①
②
Fig.3 Soil water content of highway green belt turf in flood irrigation
4. The Evaluation of Turf Reference Evapotranspiration in the Experimental Sites
4.1 Calculation of Reference Crop Evapotranspiration(ET0)
FAO Penman and FAO Penman-Monteith methods are used to calculate reference turf
evapotranspiration ET0. The results are shown in Table.1 and Fig.4.
Method
FAO Penman
FAO Penman-Monteith
Table 1 calculation of ET0
ET0( annual mean mm/y)
ET0 (daily mean mm/d)
2.184
786
4.521
1627
Annual evaporation in Yinchuan (mm/y)
1669
The calculated annual mean ET0 is 786mm and 1627mm from FAO Penman and FAO
Penman-Monteith, respectively. The large difference from the two methods may be caused by the
radiation item of the reference crop evapotranspiration ET. Considering annual evaporation in Yinchuan
1669mm, the ET0 from FAO Penman-Monteith reflectes real actual evapotranspiration of turf. (Tab.1).
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Fig.4
ET0 of turf from two methods on
4.2 The Calculation of Turf Evapotransprition ET
Turf evapotranspiration ET can be evaluated by water balance in the experimental sites, The
equation includs irrigation, effective rainfall, groundwater recharge at any time and so on. The water
balance equation can be written as:
Wt - W0 = Wr + P0 + K + M - ET
(1)
Where P0 is the effective rainfall, M irrigation, ET evapotranspiration, K groundwater recharge, W0 the
soil water storage at the beginning; Wt the soil water storage at time t, Wr additional water which is
caused by scheduling wetting zone. All items in equation (1) are estimated in time interval t (days).
The effective rainfall P0 is 66.4mm. Because the groundwater table is deep in the study site and soil
water content is not in excess of field capacity, the groundwater recharge and deep percolation are
neglected. Other terms in (1) are measured in the experiment and the calculated turf evapotransprition
ET for three study sites are shown in Tab.2.

4.3 Calculation of Turfgrass Crop Coefficients (Kc)
Turfgrass crop coefficient (Kc) is used with ET0 to estimate turfgrass crop evapotranspiration rates.
Kc reflectes the effect of turfgrass biological characteristic, yield level, soil tillage on turfgrass water
requirement. Kc can be calculated by
Kc=ET/ET0
(2)
Where Kc is the turfgrass crop coefficient (dimensionless), ET the turfgrass crop evapotranspiration
(mm/d), and ET0 the turfgrass reference crop evapotranspiration (mm/day).
The Kc evaluated from the experiments for urban turfgrass and highway green belt turfgrass in
different times are shown in Tab.3 and Fig.5.
Table2 monthly turf evapotranspritation ET for experimental sites (mm)
Apr
May
June
July
Aug
month
Urban turf’s ET in sprinkler irrigation
2.040
3.159
3.810
4.214
3.687
Urban turf’s ET in flood irrigation
2.233
3.104
2.896
4.205
4.114
Highway green belt turf’s ET in flood irrigation 2.955
3.312
4.421
3.987
4.105
Sep
2.448
2.465
2.916
Oct
1.974
2.248
2.222
Table 3 Kc for urban turf and highway green belt turf
month
Apr
May
June
July
Kc
Kc for urban turf in sprinkler irrigation
0.51
0.68
0.67
0.91
Kc for urban turf in flood irrigaiton
0.55
0.66
0.51
0.91
Kc for highway greenbelt turf in flood irrigation 0.73
0.71
0.78
0.86
Sep
0.65
0.65
0.77
Oct
0.70
0.80
0.79
ET
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Aug
0.80
0.89
0.89
Fig. 5 The calculated Kc between urban turf and highway green belt turf
Kc increases from April to July and reaches its maximum in July, and then decreases from July until
October. The values of Kc are large in June, July and August. The value of Kc is higher in October than
September because the average temperature in October is lower than September while irrigation amount
in October is equal to in September. As matter of fact, it suggestes that the irrigation amount should be
less in October than in September without turfgrass growing. Keeping other conditions unchanged in
water balance equation, it shows that turf evapotranspriation ET varies a little in September and in
October. At the meantime, turf reference evapotranspriation ET0 in October is lower than in September,
while turf crop coefficient in October higher than in September. (Tab.3 Fig.5)
5. Conclusions
The variation pattern of turf crop coefficient Kc in the three experimental sites is same as that of soil
water content and turf reference evapotranspiration. The values of Kc change obviously in different
months. The mean of Kc for urban turf from sprinkler irrigation is lower than other two situations, while
mean of Kc for highway green belt turf with flood irrigation is highest. Similarly, the
evapotranspiration(or water consumption)is less and the growth situation is better for the turfgrass with
sprinkler irrigation than others. It suggests that sprinkler irrigation is a recommended irrigation method
in the study area.
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*Ningxia Natural Science Foundation (NA003-200-2005)
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