PIAHSProceedings of the International Association of Hydrological SciencesPIAHSProc. IAHS2199-899XCopernicus PublicationsGöttingen, Germany10.5194/piahs-379-205-2018A new method for indirectly estimating infiltration of paddy fields in situA new method for indirectly estimating infiltration of paddy fields in situXuYunqiangSuBaolinsubl@bnu.edu.cnhttps://orcid.org/0000-0003-3089-2487WangHongqiamba@bnu.edu.cnHeJingyiCollege of Water Sciences, Beijing Normal University, Beijing 100875, ChinaBaolin Su (subl@bnu.edu.cn) and Hongqi Wang (amba@bnu.edu.cn)5June20183792052103January20189April201813April2018This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/This article is available from https://piahs.copernicus.org/articles/379/205/2018/piahs-379-205-2018.htmlThe full text article is available as a PDF file from https://piahs.copernicus.org/articles/379/205/2018/piahs-379-205-2018.pdf
Infiltration is one of the major procedures in water balance
research and pollution load estimation in paddy fields. In this study, a new
method for indirectly estimating infiltration of paddy fields in situ was
proposed and implemented in Taihu Lake basin. Since when there were no
rainfall, irrigation and artificial drainage, the water depth variation
process of a paddy field is only influenced by evapotranspiration and
infiltration (E+F). Firstly, (E+F) was estimated by deciding the steady
decreasing rate of water depth; then the evapotranspiration (ET) of the paddy
field was calculated by using the crop coefficient method with the
recommended FAO-56 Penman-Monteith equation; finally, the infiltration of the
paddy field was obtained by subtracting ET from (E+F). Results show that
the mean infiltration of the studied paddy field during rice jointing-booting
period was 7.41 mm day-1, and the mean vertical infiltration and lateral
seepage of the paddy field were 5.46 and 1.95 mm day-1 respectively.
Introduction
Infiltration is one of the major significant factors controlling water use
efficiency and influencing the transport of water and chemicals in paddy
fields (Wopereis et al., 1994; Aimrun and Amin, 2009; Zhou et al., 2011). It is
also an important component for water balance research and pollution load
calculating (Huang et al., 2014). Infiltration in flooded paddy fields not
only occurs vertically downwards, but also flows into the earthen ridges
surrounding the fields (Chen and Liu, 2002; Huang et al., 2003). It means
infiltration consists of vertical infiltration and lateral seepage. Vertical
infiltration (vertical percolation) is the vertical movement of water beyond
the root zone to the water table. In flooded rice fields, there is a
continuous downward flow of water from the puddled layer to below the plow
pole that basically prevents capillary rise into the root zone (Bouman et
al., 2007). Lateral seepage (lateral flow/seepage) is the lateral movement
of subsurface water of a paddy field. The study revealed the existence of
lateral flow through the ridges to the adjacent lower fields (Janssen and
Lennartz, 2007). With well-maintained ridges, lateral seepage is generally
small (Bouman et al., 2007). But the study showed lateral seepage flow may
occur either underneath well-maintained ridges or through and underneath
ill-maintained ridges (Bouman et al., 1994).
The infiltration of paddy fields can be obtained through field experiments
monitoring with instruments, such as cylinder, infiltrometer and lysimeter.
But it is often prohibitive because of the excessive time and expenditure
involved in the execution (Khepar et al., 2000). There are also some
difficulties for measuring and calculating the infiltration of paddy fields
in situ with multiple runoff outlets. The prediction of infiltration (F) is
complicated. Researchers commonly assume a constant infiltration rate which
is an overgeneralization of a dynamic process in modeling the water balance
of rice fields, through the puddled topsoil. This assumption is at times
misleading because the infiltration rate of rice fields is affected by range
of soil physical and hydraulic properties, such as structure, texture,
conductivity of different layers, and also by the hydrologic environment,
e.g. subsoil moisture content, groundwater table depth and ponded water
depth on the soil surface (Wickham and Singh, 1978; Khepar et al., 2000; Lin et
al., 2014).
Based on synchronous observation of precipitation and water depth, we can
use the method (Huang et al., 2014; Zhou et al., 2016a) to estimate the
evapotranspiration and infiltration (E+F) of paddy fields in situ. When
there were no rainfall, irrigation and artificial drainage, the water depth
variation process of a paddy field is only influenced by (E+F). We can
choose the steady decline processes of water depth to estimate (E+F) by
deciding the steady decreasing rate of water depth. This method can be
applied to general paddy fields in situ with multiple runoff outlets and
dynamic variation of lowest ridge height during growing season.
Evapotranspiration (ET) of paddy fields can be calculated by using the crop
coefficient method with synchronous meteorological data. We could get rice
evapotranspiration (ETc) of paddy fields with multiplying reference
crop evapotranspiration (ET0) which can be determined by the
recommended FAO-56 Penman-Monteith equation, by crop coefficients
(Kc) according to different rice growing stages (Allen et al., 1998). With
the obtained (E+F) and ETc, the infiltration of paddy fields can be
calculated by subtracting ETc from (E+F).
Materials and methodsStudy area
The experimental paddy field (31.47361∘ N, 119.45020∘ E)
located at Liyang, Changzhou, Jiangsu Province is about 900 m2. Deep
water irrigation mode under an intermittent irrigation system is adopted.
Except for drying period, water depth keeps at least 30 mm. The rice is
transplanted in late June, stops irrigation in mid-September, and harvests
in mid-November.
This research area is located at the south bank of the lower reaches of the
Yangtze River and in Taihu Lake basin, where the topography of fields is
almost flat. It belongs to the subtropical humid monsoon climate. The annual
mean temperature is 15.4 ∘C, annual precipitation is 1071.5 mm, annual
sunshine duration is 2047.5 h, and the annual frost-free period is 227.6 days.
Instrument installation and data collection
Data used in this paper includes precipitation and water depth in the
experimental paddy field and fundamental meteorological data of Liyang.
Therein, precipitation and water depth were collected during the rice
growing period in 2014 by using pluviograph and automatic mariograph. The
observation frequency of water depth was 30 min, while that of
precipitation was 10 min. A pluviograph was installed on a fixed tripodal
platform in target plot, and a rain barrel was kept vertically 70 cm high
away from ground. An automatic mariograph was installed near the ridge in
the paddy plot, and the mariograph probe was installed about 2 cm high above
the field bottom to avoid being blocked by mud. The probe installation
height was kept unchanged during the growing period.
The fundamental meteorological data which is on daily scale, was obtained
from Liyang Meteorological Station. The data includes cumulative
precipitation (mm), average relative humidity (%), mean wind speed (m s-1), sunshine duration (h), mean air temperature (∘C), maximum
air temperature (∘C), minimum air temperature (∘C) and net
radiation (MJ m-2 day-1). The mean speed is measured at 2 m
above the ground level.
Data analysis methodsThe method for estimating
(E+F) of paddy fields
The (E+F) of paddy fields is estimated by using the water balance model
(Khepar et al., 2000; Huang et al., 2014). Water balance equation is shown as
follow:
P+Rin-E+F-Rout=ΔH
where P is the daily precipitation (mm), Rin is the irrigation
water inflow (mm), (E+F) is the evapotranspiration and infiltration loss
(mm), Rout is the water outflow (mm), and ΔH
is the depth variation (mm).
Factors influencing water depth include natural factors and artificial
factors. Natural factors mainly include (E+F) and precipitation. Artificial
factors mainly include irrigation and artificial drainage. When there were
no rainfall, irrigation, and artificial drainage, the steady decline of
water depth variation process line is only affected by (E+F) process.
Therefore, the Eq. (1) can be simplified as follow:
-E+F=ΔH
The key procedure for estimating (E+F) based on synchronous observation of
precipitation and water depth is to detect steady decline processes of water
depth which were selected to calibrate (E+F) by deciding the steady
decreasing rate of water depth. The rice growing period includes four
stages, rice regreening, tillering, jointing-booting and maturation. The
(E+F) analysis of this paper is applied to the rice jointing-booting stage
with water kept in the paddy field all the time.
The method for calculating ET of paddy fields
The crop coefficient method with the recommended FAO-56 Penman-Monteith
equation (Allen et al., 1998) is applied to calculate the ET of the paddy
field with synchronous meteorological data. In this paper, single crop
coefficient method was applied. During the research period of rice
jointing-booting stage, water is kept in the paddy field, indicating there
is no water stress. The ETc of the paddy field is calculated as follow:
ETc=Kc×ET0
Where ETc is the daily ET (mm day-1) of paddy field, ET0 is the
reference crop evapotranspiration (mm day-1), and Kc is the rice
coefficient.
Reference crop evapotranspiration (ET0)
The FAO Penman-Monteith method defines the reference crop as a hypothetical
crop with an assumed height of 0.12 m, with a surface resistance of 70 s m-1, and an albedo of 0.23, closely resembling the evaporation from an
extensive surface of green grass. The reference crop evapotranspiration
(ET0) is defined and calculated using the FAO-56 Penman-Monteith
equation:
ET0=0.408ΔRn-G+γ900T+273u2es-eaΔ+γ1+0.34u2
where ET0 is reference crop evapotranspiration (mm day-1),
Rn is the net radiation at the crop surface
(MJ m-2 day-1), G is the soil heat flux density
(MJ m-2 day-1), T is the mean daily air temperature at 2 m
height (∘C), u2 is the wind speed at 2 m height (m s-1),
es is the saturation vapour pressure (kPa), ea is the
actual vapour pressure (kPa), es-ea is the saturation
vapour pressure deficit (kPa), Δ is the slope vapour pressure curve
(kPa ∘C-1), and γ is the psychrometric constant
(kPa ∘C-1).
Rice coefficient (Kc)
The crop coefficient incorporates crop characteristics and averaged effects
of evaporation from the field of the single crop coefficient method. The
FAO-56 Penman-Monteith equation gives the recommended values of crop
coefficient during different crop growing stages under standard condition.
For rice coefficient (Kc), the recommended value was adjusted to the
non-standard condition value, using the follow equation:
Kc=Kc,mid+0.04u2-2-0.004RHmin-45h30.3
where Kc,mid is the recommended value of the mid-season stage
(including rice jointing-booting stage), RHmin is
the mean value for daily minimum relative humidity (%) during the
mid-season growing stage, and h is the mean maximum plant height (m).
Water depth and precipitation of the paddy field during rice
jointing-booting stage.
Schematics of (E+F), ETc and infiltration of the paddy
field.
A new method for indirectly estimating infiltration of paddy
fields
Since when (E+F) and ETc of the paddy field have been obtained, the
infiltration can be calculated by subtracting ETc from (E+F):
F=E+F-ETc
where F is the infiltration loss (mm).
(E+F) of different paddy fields using the same method.
YearGrowing stageStudy area(E+F)Source(mm day-1)2014rice jointing-bootingLiyang, Jiangsu4–15Zhou et al. (2016b)2013rice jointing-bootingHaidian, Beijing4–12Zhou et al. (2016a)2012rice jointing-bootingHaidian, Beijing8–12Huang (2014), Huang et al. (2014)ResultsEstimated (E+F) of the paddy field
The water depth and precipitation of the paddy field during rice
jointing-booting stage are shown in Fig. 1. The periods described by black
dotted line indicate the steady declines of water depth with no rainfall,
irrigation, and artificial drainage. Those steady decline processes can be
used for estimating (E+F). Meanwhile, the periods described by solid line
indicate the water depth variation mutation periods. In those situation, the
(E+F) should be arbitrarily approximated with the mean value of adjacent
growing period under the same weather condition. In this paper, we just
discussed the estimated (E+F) of water depth during steady decline periods.
Using the proposed method, (E+F) during the rice jointing-booting stage was
calculated. As shown in Fig. 2, the maximum (E+F), minimum (E+F) and mean
(E+F) were 15.63, 3.69 and 10.62 mm day-1 respectively. Compared with the
(E+F) of different paddy fields using the same method, we got the proximate
parameter range of (E+F) (Table 1).
Calculated ETc of the paddy field
According to the related FAO irrigation and drainage papers, rice
coefficient (Kc,mid) is 1.2 and the mean maximum rice height
is 1.0 m (Allen et al., 1998). ETc of the paddy field is shown
in Fig. 2. The maximum ETc, minimum ETc and
mean ETc were 6.23, 1.21 and 3.21 mm day-1 respectively.
Estimated infiltration of the paddy field
In this study, there are 45 days of the rice jointing-booting stage in total
and 27 values of infiltration of the paddy field were obtained. As shown in
Fig. 2, the maximum infiltration, minimum infiltration and mean infiltration
were 12.71, 2.20 and 7.41 mm day-1, respectively.
Vertical infiltration of different paddy fields in Taihu Lake
basin.
YearStudy areaCropVertical infiltrationSource(mm day-1)2007–2009Taihu Lake basinirrigated rice2Zhao et al. (2012)2008Danyang, Jiangsuirrigated rice6.0Cheng et al. (2009)–Danyang, Jiangsuirrigated rice6.4Li et al. (2010)2010Taihu Lake basinirrigated rice1Lin et al. (2012)2010Taihu Lake basinirrigated rice2–3Lin et al. (2011)2010Suzhou, Jiangsuirrigated rice4.23Yin (2012)2011Suzhou, Jiangsuirrigated rice4.02Yin (2012)Discussions
In practices, vertical infiltration and lateral seepage are not easily
separated because transition flows can neither be classified as vertical
percolation nor lateral seepage (Wickham and Singh, 1978). Typical combined
values for vertical infiltration and lateral seepage vary from
1–5 mm day-1 in heavy clay soils to
25–30 mm day-1 in sandy and sandy loam soils (Bouman and
Tuong, 2001). The preferred rate of infiltration is
5–15 mm day-1 in irrigated temperate rice lands where
infiltration may be needed to leach organic toxins that can persist from year
to year (Wopereis et al., 1994). The vertical infiltration and lateral
seepage rates of paddy fields vary from 1 to 6 mm day-1, with the mean
value of 3 mm day-1 in Tuanlin, Hubei province, and 3.8 mm day-1
in Jinhua, Zhejiang province (Cabangon et al., 2004). The research observed
the vertical infiltration through the plough pan and the lateral seepage on
sloping land formed into terraces and showed that the higher the position on
sloping land was, the greater the potential of water losses was because of
higher vertical infiltration and lateral seepage (Tsubo et al., 2005). The
study carried out in Taiwan indicates the vertical infiltration and lateral
seepage rates of the flat paddy field through the bottom of the ridge were
4.0 and 3.3 mm day-1 respectively with the plow sole underneath, and
8.5 and 4.5 mm day-1 respectively without the plow sole underneath
(Huang et al., 2003). Therefore, in the experimental paddy field with a plow
sole in this study, the infiltration range of
2.20–12.71 mm day-1 is moderate and credible, which
demonstrates the new method for indirectly estimating infiltration of paddy
fields in situ is relatively reliable.
The physical and hydraulic characteristics of the plow sole and the
underlying subsoil determine the magnitude and constancy of vertical
infiltration rate (Bouman et al., 1994). For many studies, there were usually
assumed or measured values in vertical infiltration rates. According to the
Jiangsu province actual observed statistic data, the vertical infiltration
rate of single crop rice region with clay soil, loam soil and sandy loam
soil are 1.2–4, 2.1–5.3 and 5.5–9.8 mm day-1 respectively (Wu, 2015). In the Taihu Lake basin, with
approximate soil texture of loam soil, the vertical infiltration of
different paddy fields is shown in Table 2, which illustrates the
approximate vertical infiltration range of Jiangsu province.
The estimated infiltration values of the paddy filed were analyzed using
SPSS 20.0, and the box and whisker plot were shown in Fig. 3. The first
quartile (25th percentile) infiltration values of the paddy filed was 5.46 mm day-1. Then the mean vertical infiltration of the paddy field was
assumed to be 5.46 mm day-1, according to the previous analysis of
vertical infiltration in Jiangsu province and Taihu Lake basin. Subtracting
the mean vertical infiltration from mean infiltration of 7.41 mm day-1,
the mean lateral seepage of the paddy field turned out to be 1.95 mm day-1. The mean lateral infiltration accounted for 26.4 % of the
infiltration, indicating the lateral seepage was also an important component
of infiltration in paddy fields in situ with multiple runoff outlets. The
lateral seepage should also be paid more attention in future paddy field
research.
The box and whisker plot of infiltration of the paddy field.
Conclusions
A new method for indirectly estimating infiltration of the paddy field was
put forward. The (E+F) of the paddy field were estimated by deciding the
steady decreasing rate of water depth, when there were steady decline
processes of water depth. The ET of the paddy field was calculated by using
single crop coefficient method with the recommended FAO-56 Penman-Monteith
equation. Therefore, the infiltration was calculated by subtracting
calculated ET from estimated (E+F). The mean infiltration of the paddy field
during rice jointing-booting period was 7.41 mm day-1. By analyzing the
infiltration values obtained in this study and the reference vertical
infiltration in Jiangsu province and Taihu Lake basin, the mean vertical
infiltration and lateral seepage of the paddy field in situ turned out to be
5.46 and 1.95 mm day-1 respectively.
The underlying research data belongs to the project which is not publicly accessible.
The authors declare that they have no conflict of
interest.
This article is part of the special issue “Innovative water
resources management –understanding and balancing interactions between
humankind and nature”. It is a result of the 8th International Water
Resources Management Conference of ICWRS, Beijing, China, 13–15 June
2018.
Acknowledgements
This work is supported by Major Project on Science & Technology of Water
Body Pollution Control & Treatment (2017ZX07301-003).
Edited by: Dingzhi Peng
Reviewed by: two anonymous referees
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