The effect of winter flood irrigation with saline water on groundwater in a typical irrigation area

Abstract

Flood irrigation in the winter has been widely applied in northwest China for several years, but little attention has been paid to the flood irrigation program to date. In order to seek a reasonable irrigation quota, a flood irrigation experiment using two common quotas (1,800 and 1,200 m3ha-1) was conducted in an area irrigated by saline water in the Nanjiang basin with shallow groundwater. Soil electrical conductivity in six treatments irrigated by saline water, with various salinity backgrounds, was investigated using Hydra and DDS-307 before and after flood irrigation. The results indicate that the quota of 12,00 m3ha-1 was small enough to prevent soil salt from leaching out of the root zone. Although the quota of 1,800 m3 ha-1 may guarantee regular plant growth in the following year, it resulted in at least 267.2 g mr2 of salt entering the shallow groundwater. Therefore, flood irrigation had an important and profound effect on plants, soil environment, and shallow groundwater. The quota of flood irrigation in winter should be determined cautiously according to the hydraulic characteristics and salt background of the soil.

Full text

The effect of winter flood irrigation with saline water on
groundwater in a typical irrigation area
Yujiang He, Wenjing Lin and Guiling Wang
ABSTRACT
Flood irrigation in the winter has been widely applied in northwest China for several years,
but little attention has been paid to the flood irrigation program to date. In order to seek a
reasonable irrigation quota, a flood irrigation experiment using two common quotas
(1,800 and 1,200 m
3
ha
1
) was conducted in an area irrigated by saline water in the Nanjiang
basin with shallow groundwater. Soil electrical conductivity in six treatments irrigated by saline
water, with various salinity backgrounds, was investigated using Hydra and DDS-307 before
and after flood irrigation. The results indicate that the quota of 12,00 m
3
ha
1
was small enough
to prevent soil salt from leaching out of the root zone. Although the quota of 1,800 m
3
ha
1
may
guarantee regular plant growth in the following year, it resulted in at least 267.2 g m
2
of salt
entering the shallow groundwater. Therefore, flood irrigation had an important and profound
effect on plants, soil environment, and shallow groundwater. The quota of flood irrigation in
winter should be determined cautiously according to the hydraulic characteristics and salt
background of the soil.
Yujiang He
Wenjing Lin
Guiling Wang (corresponding author)
Institute of Hydrogeology and Environmental
Geology, CAGS,
Zhonghua Street 268,
Shijiazhuang 050061,
Hebei Province,
China
E-mail: guilingw@163.com
Key words |flood irrigation, groundwater, irrigation area, saline water, soil environment
INTRODUCTION
Flood irrigation in the winter is effective for water storage in
soil, the improvement of the soil environment, and the
leaching of soil salt (Yang et al.), especially for some
areas that are irrigated using saline water (Beltran et al.
;Karlberg et al.). Storage irrigation in the
autumn as well as irrigation in the winter and early spring
(Fan ) are conducted to satisfy the water demand of
overwintering crops, to regulate the imbalance of water
resource supply and requirements, to utilize wastewater, to
arrange labor, etc. Each type of the above irrigation methods
occurs frequently in early winter and early spring, and the
irrigation frequency rises daily with increased contradic-
tions between the supply and requirements of water
resources (Li ). Furthermore, irrigation was one of the
critical measures used to promote cotton yield in the Nan-
jiang basin in northwest China (He et al.), which
lacked fresh water in the summer but not during the winter.
However, irrigation in the winter evoked increased
damage, which was evidenced by the groundwater depth
of less than 2 m in about 62% of the cotton irrigation
area in Nanjiang, China. Secondary salinization was
often caused by flood irrigation in areas with lower
groundwater levels (Runyan et al.). In addition, exces-
sive irrigation water induced a rise in the water table and
the subsequent intense phreatic evaporation that led to
the upward movement of salt from groundwater (Sing
et al.) and the accumulation in the ground surface
(Wang et al.).
Flood irrigation will directly cause serious pollution in
shallow groundwater sources in these areas, but little atten-
tion has been focused on this issue to date (Malash et al.
;Roberts et al.). Hence, using a typical experimen-
tal area of the Nanjiang basin as an example (from the inter-
transform of irrigation water, soil water, and groundwater),
356 © IWA Publishing 2015 Water Science & Technology: Water Supply |15.2 |2015
doi: 10.2166/ws.2014.121

this study examines the basic movement theory of soil water
and salt and estimates the pollution of shallow groundwater
resulting from flood irrigation.
METHODS
Experimental setup
The experiment was conducted at the Bazhou Experimental
Station of Irrigation in the Nanjiang basin. Both surface
water and groundwater were available for irrigation at the
experimental farmland. The surface water (F) was from a
river, with total dissolved solids (TDS) of 0.90–1.01 g L
1
.
The TDS of groundwater at the experimental site was
2.98–3.21 g L
1
with the hydrochemical type of ClSO
4
-Na
(referred to as S). The groundwater table in the area is
located at a depth 1.50–2.00 m below the surface. Further-
more, the soils in the experimental fields were mainly
loamy sand, sandy loam, and sand, which were distributed
at depths of 0–50, 50–120, and 120–160 cm, respectively.
In addition, the field was planted with cotton that exhibited
a low yield for several years.
Treatments
The irrigation programs were as follows: (1) irrigation with
saline groundwater throughout the growth season using
three water quantities: 5,250 m
3
ha
1
(5250S), 4,500 m
3
ha
1
(4500S), and 3,750 m
3
ha
1
(3750S); (2) rotation irrigation
with fresh water and saline water at a total quantity of
3,750 m
3
ha
1
and three ratios, including 80% saline water
and 20% fresh water (80S20F), 67% saline water and 33%
fresh water (67S33F), and 50% saline water and 50% fresh
water (50S50F); (3) flood irrigation with fresh water at a
total quantity of 1,800 and 1,200 m
3
ha
1
for different treat-
ments during the growth season (Figure 1).
Monitoring
Soil water content, electrical conductivity (EC), and temp-
erature were automatically monitored in situ using a
Stevens Hydra Probe Soil Sensor (Stevens, Co. Ltd, Port-
land, Oregon, USA).
Soil sampling and analysis
Soil samples were collected from each plot during the exper-
iment. The EC of the soil was measured by sampling each
treatment before and after irrigation. Soil samples were
drawn from 0 to 100 cm depths at an interval of 10 cm
and from 100 to 160 cm depths at an interval of 20 cm. An
18 g soil subsample was separated from each sample, and
it was subsequently added to 90 mL water. The analytical
methods for the soil saturation extract were the same as
those used for the water sample analyses. EC was tested
using a DDS-307 conductivity meter (Lei Ci, Co. Ltd, Shang-
hai, China).
RESULTS AND DISCUSSION
The processing analysis of winter irrigation
The results indicate that the soil salt content clearly
decreased in 5200S, 4500S, and 80S20F during the irriga-
tion of 1,800 m
3
ha
1
.Figure 2 shows that at a depth of
0–60 cm in the soil profile, the soil salt content returned to
the background value, which is similar to that during
cotton sowing. At a depth of 0–120 cm, the soil salt content
Figure 1 |The flood irrigation design for the different treatments.
357 Y. He et al. |The effect of flood irrigation on groundwater Water Science & Technology: Water Supply |15.2 |2015

decreased, and soil salt leaching was more obvious at
40–80 cm depths. The figure illustrates that the larger the
salt irrigation amount, the greater the salt accumulation in
the soil profile before irrigation in winter. For instance, in
5250S, which has the most serious soil salt accumulation,
the mean EC of the total soil profile (0–160 cm) was
1,855 μscm
1
before irrigation in winter and 785 μscm
1
after irrigation in winter. Therefore, the effect of soil salt
leaching was proven to be successful. The salt was leached
up to a depth of 120 cm, increasing the EC of the soil
below 120 cm.
Compared with the 1,800 m
3
ha
1
program, the soil salt
leaching effects were unsatisfactory under the irrigation pro-
gram of 1,200 m
3
ha
1
(3750S, 3000S, and 50S50F), and the
soil salt was leached below 40–50 cm (Figure 3). For
example, in 3750S, the change of soil EC was greater at a
depth of 0–40 cm, and irrigation in winter had little influ-
ence on soil EC. Evidently, the irrigation program was so
small that the soil salt could not be leached out of the root
zone. The salinification phenomenon is most likely to
occur under strong evaporation. Hence, considering the
normal growth of cotton, the flood irrigation program
should target 1,800 m
3
ha
1
.
The equilibrium analysis of soil salinity
The soil salt balance refers to the income and expenditures
of soil salt during specific periods (equalizing stage) and
spatial ranges (equalizing zone). Figure 4 shows the circu-
lant graphs of soil salt in a field. There was no flow in the
lateral direction, so there was no soil salt exchange. There-
fore, the balanced equation of soil salt is as follows:
ΔS¼Sin Sout ¼(SpþSiþSrþSt)(SdþSc) (1)
where ΔSis the change in soil salt storage in the profile
[ML
3
], S
in
is the inflow water amount [ML
3
], S
out
is the out-
flow water amount [ML
3
], S
p
is the inlet salt amount with
Figure 2 |Variability of EC for different treatments by WI (1,800 m
3
ha

1
).
Figure 3 |Variability of EC for different treatments by WI (1,200 m
3
ha

1
).
358 Y. He et al. |The effect of flood irrigation on groundwater Water Science & Technology: Water Supply |15.2 |2015

precipitation [ML
3
], S
i
is the inlet salt amount with irrigation
[ML
3
], S
r
is the inlet salt amount with the vertical recharge
by phreatic water [ML
3
], S
t
is the inlet salt amount of fertili-
zer application [ML
3
], S
d
is the outlet salt amount from soil
water leakage [ML
3
], and S
c
is the outlet salt amount from
plants [ML
3
].
The salt amount entered into the soil was positive, and
the flow out of the soil was negative. The observed TDS
values of precipitation, irrigation water, fresh water, and
groundwater were 0.07, 3.00, 0.98, and 2.73 g L
1
, respect-
ively. The salt flowing out from soil water infiltration
adopted the average value in the profile at different
times. Therefore, the TDS was 8.53 g L
1
in the bud stage,
9.77 g L
1
in the early blooming period, 9.56 g L
1
in the
later blooming period, and 5.73 g L
1
during irrigation in
the winter. These values were the measured mean values
in the study area.
According to the practical planting pattern in the
experimental areas, the total salt amount in cotton was
267.0 g m
2
(Gong et al. ). In the bud stage, early
blooming period, and later blooming period, the outlet salt
amounts were 30, 60, and 10% of that measured during
the whole year, respectively. The depth of the calculation
was the mean buried depth of the groundwater for each
period. Therefore, in the cotton growth period, the buried
depth of the groundwater was 160 cm, and it was 200 cm
during irrigation in winter. For example, note the values
recorded for 4500S that are shown in Table 1.
Table 1 indicates that 94% of the inlet salt amount was
from precipitation and irrigation, and only a small portion
Figure 4 |The equilibrium diagram of soil salt.
Table 1 |Results of the soil salt balance under the 4500S treatment (g m

2
)
Period
Outlet salt amount by
Subtotal
Inlet salt amount by
Subtotal
Change in soil
salt storage
Soil water
leakage Plant
Precipitation and
irrigation
Fertilizer
application
Vertical recharge by
phreatic water
First–third irrigation
(1–21 days)
14.5 80.0 94.5 246.2 7.5 16.9 270.6 176.1
Fourth–eighth irrigation
(22–52 days)
7.8 160.0 167.8 460.7 7.5 10.4 478.6 310.8
9th–11th irrigation
(53–73 days)
2.9 27.0 29.9 324.1 4.5 22.9 351.5 321.6
Irrigation in winter
(74–155 days)
731.7 0.0 731.7 184.1 0.0 6.3 190.4 –541.3
Sum (1–155 days) 756.9 267.0 1,023.9 1,215.1 19.5 56.5 1,291.1 267.2
359 Y. He et al. |The effect of flood irrigation on groundwater Water Science & Technology: Water Supply |15.2 |2015

of the salt came from the vertical recharge by groundwater.
For instance, the outlet salt from soil water leakage and
cotton were 74 and 26%, respectively. Therefore, it is clear
that light saline water irrigation was the main component
that introduced salt into the soil. In the first–third and the
fourth–eighth periods, irrigation with fresh water was car-
ried out, and it resulted in a soil salt accumulation amount
that was lower than that in the 9th–11th period. In the afore-
mentioned periods, the outlet soil salt amount by soil water
leakage was very small. The difference in the soil salt storage
in the soil profile was 541.3 g m
2
. Furthermore, the soil salt
in the soil profile increased by 267.2 g m
2
, and the salt
accumulation was concentrated below 80 cm during the
period of study. The results indicate that the soil salt was
mainly present at depths of 80–140 cm due to irrigation in
the winter. Therefore, the soil salt was removed by irrigation
and migrated into the groundwater, which eventually led to
shallow groundwater pollution.
Three major environmental problems must be con-
sidered regarding flood irrigation in the winter. The first is
the balance between soil moisture conservation and the
deep seepage of soil water. Irrigation in winter was con-
ducted to store soil water for sowing and for seedlings of
spring wheat the following year. Combined with the removal
of soil salt, irrigation also influenced the agricultural indus-
try and the status of the soil environment the following
year in the irrigated region (Wang et al.). After decreas-
ing the deep seepage of soil water, it was feasible to choose
the 50 mm depth for the winter irrigation quota (Shang et al.
). The ice was pure without salt, so when the soil water
transformed into ice, the salt would precipitate and form
high-concentration areas. The biological tissues in the
high-concentration areas intensely lost moisture. When the
frozen soil melted in spring, the soil strength may have
been lost entirely. Therefore, irrigation influenced the stab-
ility of the soil foundation. Moreover, the melted water
seeping to the surface formed spring floods, affected spring
plowing, and led to soil nutrient loss.
The second problem is the contamination of shallow
groundwater caused by desalinization from flood irrigation.
This is particularly important for areas with shallow ground
water in that flood irrigation in the winter may make the
groundwater severely contaminated. For example, the
flood irrigation practices in Punjab (India) that are used to
grow paddy crops could induce geochemical conditions
that are favorable for the mobilization of arsenic from sur-
face soils, which could eventually elevate arsenic
concentrations in the underlying shallow aquifer (Hundal
et al.).
The third problem is the drainage salinity effect. For the
areas in which the groundwater was shallow with high sal-
inity, the soil salt moved with the groundwater, combined
at the surface, and ultimately exacerbated the process of
soil salinization. Wang et al.()suggested that winter
flood irrigation should use 1,575 m
3
ha
1
of fresh water
every 2 years in areas that were irrigated by saline water in
Nanjiang basin. Moreover, Zhang et al.()proposed
that soil salt accumulates above the relatively impermeable
layer, which is opposite when compared to the flood irriga-
tion situation in the same area.
Therefore, the irrigation quota should be designed
according to the type of irrigation, soil texture, and climatic
conditions. This quota has great significance in terms of the
comprehensive evaluation of surface water and groundwater
resources, the efficient use of water and heat resources in
soil, the reasonable determination of technical parameters
associated with agricultural irrigation, soil protection, soil
salinization prevention, etc.
CONCLUSIONS
The results showed that compared with the 1,800 m
3
ha
1
quota, the soil salt leaching effects were unsatisfactory
under the 1,200 m
3
ha
1
quota, which leached soil salt at
just 40–50 cm. Obviously, the 1,200 m
3
ha
1
quota was so
small that the soil salt could not be leached out of the root
zone. Moreover, the results would affect the normal
growth of cotton in the following year. Therefore, the
1,800 m
3
ha
1
irrigation quota should be chosen in most
of the local fields for improving the soil environment and
the crop production. However, especially the soil water
leakage resulted in a large amount of soil salt (267.2 g m
2
under 4500S) entering the shallow groundwater. To prevent
pollution of the groundwater, the flood irrigation quota in
the winter should be further designed in a rational way
according to the hydraulic characteristics and salt back-
ground of the soil in the local field.
360 Y. He et al. |The effect of flood irrigation on groundwater Water Science & Technology: Water Supply |15.2 |2015

ACKNOWLEDGEMENTS
This study was funded by the National Natural Science
Foundation of China (41302186). We gratefully acknowledge
the Bazhou Experimental Station of Irrigation, Xinjiang,
and China University of Geosciences and Prof. Menggui Jin,
Prof. Bingguo Wang, and others for their fruitful cooperation
on experiments in both the field and laboratory.
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