IJERD – International Journal of Environmental and Rural Development (2015) 6-1

Research articleerd

Non-uniform Distribution of Soil Salinity Along a Transectof an Irrigation Field in an Arid Region
TAKASHI KUME*
Faculty of Agriculture, Ehime University, Matsuyama, Japan
Email: kume@ehime-u.ac.jp

TADAO YAMAMOTO
Research Faculty of Agriculture, Hokkaido University, Sapporo, JapanKATSUYUKI SHIMIZU
Faculty of Agriculture, Tottori University, Tottori, JapanABDISALAM JALALDIN
College of Resources and Environmental Sciences, Xinjiang University,Urumqi, China
Received 5 January 2015

Accepted 31 May 2015(*Corressponding author)

Abstract We assessed soil salinity at field scale and suggested appropriate water and saltmanagement practices for an arid region. Specifically, we focused on non-uniform salinity
distribution along a transect in a research field. We also examined factors affecting thedistribution of salt, including irrigation, drainage and salt movement. The non-uniform
salinity distribution across the field was probably formed by irrigation management anddistance from main drainage channel, while the effect of soil physical properties andgroundwater was limited. The main drainage channel functioned well during the past
irrigation period when abundant Karez water was available for leaching irrigation, and thiscontributed to the present non-uniform salinity distribution. Currently, farmers use less
irrigation water, which does not promote desalinization. Vertical movement of soluble salts
near the soil surface was dominated by irrigation management. Border irrigation promotes
desalinization but drip irrigation enhances salt accumulation, with salinity increasing after
irrigation because of high evaporation rates in the hyperarid climate. Based on these results,
we explained the following points to local farmers in non-technical language: 1) a drainage
channel is important for desalinization but the current channel is no longer sufficient todischarge salt from the field; 2) drip irrigation is effective for deficit irrigation but itenhances salt accumulation; 3) border irrigation has a positive effect on salt leaching fromsurface layers but the leached salt returns to the surface after irrigation ceases; and 4) there
are high salinity layers below 60 cm soil depth, distributed widely across the fields.
Keywords drainage, hyperarid region, irrigation, non-uniform distribution, soil salinity

INTRODUCTION
It is estimated that saline soil covers 3.1% (397 mega hectares) of the total land area of the earth(FAO, 2005), which is 1.2 times larger than the land area of India. The total area of secondary
saline soil induced by anthropogenic activity such as agriculture is approximately 76.6 Mha(Oldeman et al., 1991), almost twice of the land area of Japan. There are no data to suggest that theamount of saline soil is decreasing; on the contrary, Rengasamy (2008) expects that the prevalenceof saline soil will increase because of climate change and increasing human population.
Salinization is one of the biggest problems affecting agricultural activities, especially in arid
regions. Salinity studies have been conducted since the 1950s. Soil electrical conductivity (EC) has
long been used as an index of salinity in the laboratory (US Salinity Laboratory Staff, 1954),
though electromagnetic induction (McNeill, 1980; Rhodes and Corwin, 1981) and satellite remoteⒸ ISERD

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sensing (Metternicht, 2003; Metternicht and Zinck, 2008) are now widely applied to assess theextent and severity of saline areas. Free numerical modeling software (e.g., Šimůnek et al., 2013) isavailable for simulating the movement of water and salt in soil layers.
In irrigated agricultural fields, non-uniform distribution of soil salinity is caused byinappropriate application of water and salt management practices such as irrigation, drainage andsalt leaching (Kume et al., 2004; Nishimura et al., 2012). This leads to loss of irrigation water anddecreasing crop production. Knowledge of the structure of the non-uniform distribution, andavailable technical solutions, is crucial to effective management of water and salt in arid regions.
However, field conditions and irrigation techniques differ from one place to another, and so a sitespecific approach is needed to help farmers to understand their current situation and to suggest
ways of developing saline soil in an appropriate way.
OBJECTIVE
We assessed soil salinity at field scale and suggested appropriate water and salt managementpractices for an arid region. Specifically, we focused on non-uniform salinity distribution along atransect in a research field. We also examined factors affecting the distribution of salt, including
irrigation, drainage and salt movement.
METHODOLOGY
Research Field
The research field is situated in Paran Karez village near the city of Torpan, in the Xinjiang Uygur
Autonomous Region of China (Fig. 1). The average temperature at Torpan is 14.0 qC. Maximum
and minimum temperatures are 40 qC and −14.5 qC, respectively. Annual precipitation is 16.6 mm.
Torpan is classified as a hyperarid region.

Fig. 1 Location of Torpan in the Xinjiang Uygur
Autonomous Region, ChinaⒸ ISERD

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Fig. 2 Map of investigation area, showing
transect x-x’, soil profile samplingpoints (A-D), and reference soil
sampling points (E-H)

IJERD – International Journal of Environmental and Rural Development (2015) 6-1

The village of Paran Karez has been developed using water from Paran Karez over the last
300 years. The term Karez means a horizontal series of vertically dug wells that are then linked byunderground water canals. Unfortunately, Paran Karez dried up in 2010. Farmers irrigated theirfields with Paran Karez groundwater 20 years ago and now they pump up groundwater from wells
for irrigation. The main crops grown are cotton, maize, wheat and cumin. The most common
irrigation methods are basin irrigation and border irrigation; drip irrigation has been introduced insome areas beginning in 2013.
Materials and Methods
We defined a transect, x-x’, in the irrigated field (Fig. 2) to reveal horizontal soil salinity
distribution and took soil samples at 10 meter intervals in June 2013, October 2013, May 2014 andNovember 2014. Soil samples were taken from 0–5 cm and 5–15 cm below the soil surface. Soilelectrical conductivity was measured in a soil-water extract (soil:water = 1:5, EC1:5). To examine
the topography of the transect, we conducted a level survey at 50 meter intervals in May 2014. To
examine the vertical profiles of soil salinity and soil physical properties, we also took soil samples
at four points, A, B, C and D on the transect at six soil depths from each profile wall: 0–5, 5–15,15–30, 30–60, 60–90 and 90–120 cm below the soil surface. The same sampling and measurement
regime was used at four reference points, E, F, G and H, some distance away from the transect.
RESULTS AND DISCUSSION
Soil Physical Properties
Soil physical properties affect water and salt movement in soils. Therefore, soil physical properties
were examined to understand non-uniform distributions of soil salinity in irrigated fields. The soil
texture was classified as International Society of Soil Science at the four points along the transect(A to D) was silty loam (SL) as shown in Table 1. The soil was mainly composed of silt and it
contained less than 10% clay. The same silty loam texture was seen at the reference points (E to H).
Soil bulk density showed that the soils were somewhat compacted, and soil permeability wasreduced, ranging from 10−5 to 10−6 cm/s−1. Particle density ranged from 2.64 to 2.76 g/cm−3,indicating low organic matter content. From these results, we expect that the differences of soil
physical properties were not so large that it did not affect non-uniform distribution of the soil EC.
Table 1 Average values of physical properties of soil from 0-1.2 m soil depth at points A-D
along the transect x-x’
PointSoil textureABCDSLSLSLSLSoil bulk density(g/cm3)
1.27
1.31
1.35
1.27

Particle density(g/cm3)
2.64
2.76
2.74
2.76

Soil permeability(cm/s)
1.8×10−5
1.8×10−6
1.8×10−6
3.6×10−6

Effect of Irrigation Methods on Surface Soil Salinity
Irrigation practices affect water and salt movement, especially salt leaching at the soil surface. As
shown in Table 2, the average value of EC1:5 for all data including non-irrigated fields, and EC1:5
excluding non-irrigated fields ranged from 4.8 to 7.6 dS/m and from 2.2 to 3.5 dS/m, respectively.
The highest EC1:5 values were observed in non-irrigated fields 280-300 m away from the main
drainage channel along the transect (Fig. 2), whereas the lowest EC1:5 values were obtained near themain drainage channel. EC1:5 was high in the non-irrigated fields because of the lack of saltleaching without irrigation, and salt accumulation from the vicinity by lateral water flow. It is clearthat irrigation and drainage management affects surface soil salinity.
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Changes in average EC1:5 during the research period (Table 2) can be interpreted in the light ofirrigation management practices and salt movement. First, border irrigation leached surface salt tothe deeper soil layers (June 2013), and the leached salt was returned to the soil surface byevaporation (October 2013). Second, drip irrigation induced intense capillary rise and promoted
salt movement from deeper layers to the surface (May 2014) (Zhang et al., 2014). Finally, salt
continuously rose to the soil surface by evaporation and showed the highest EC1:5 at the end of theresearch period (November 2014). This shows that border irrigation promotes leaching of salt todeeper soil layers, while drip irrigation enhances salt mobility from deeper soil layers to the surface.
Table 2 Descriptive statistics for EC1:5 at four measurement times
Data used forstatistical analysis

Sampling date(Month/Year)

Irrigation

N=31 (0-300 m)(Including datafrom salt
accumulate fields,
280-300 m fromdrainage channel)

06/2013
10/201305/2014

Border irrigation
Drip irrigation

11/201406/2013
10/201305/2014
11 2014

N=28 (0-270 m)(Irrigated fieldsonly)

Soil EC1:5 (dS/m)
Max

Min

4.8
5.8
7.6

47.8
59.6
84.5

0.5
0.2
1.5

Standard
deviation
9.3
11.5
15.0

-

6.9

41.2

0.4

9.4

Border irrigation
Drip irrigation
-2.2
2.7
3.4
3.5

5.4
6.3
8.5
8.9

0.5
0.2
1.5
0.4

1.1
1.6
1.71.9Mean

Relationship Between Soil Salinity and Distance from Main Drainage Channel
The salt distribution before agricultural development of the research field was not known. However,conventional desalinization using techniques such as leaching irrigation has been employed sincethe 1970s, so it is unsurprising that soil salinity increases with increasing distance from the main
drainage channel (Fig. 3). The only exception was seen in May 2014. Regression analysis showed apositive correlation between EC1:5 and distance from main drainage channel (Fig. 3). The highest
coefficient of determination (R2), 0.71, was obtained in October 2013 and the lowest, 0.22, wasseen in May 2014. Similar results were obtained across the irrigated field, from 0 to 270 m from thedrainage channel along the transect x-x’. This relationship was not seen in May 2014 and the R2
value at that time was just 0.02 (data not shown). Conventional desalinization management withabundant Karez water in the past promoted leaching and salt drainage from soil layers. This isconsistent with the EC1:5 data from May 2014, which showed that drip irrigation temporarily
caused a uniform salinity distribution through intense capillary rise in the irrigated field.
The topographic level survey showed that the elevation became higher with increasing
distance from the main drainage channel (Fig. 3). Non-irrigated salt accumulated fields, whichwere located 280–300 m away from the drainage channel, were higher than the irrigated fields.
This implies that salt accumulated fields have not been received enough leaching water because of
their higher elevation, and that dissolved salt moved from nearby fields. The same results wereseen by Kume et al., (2004) and Nishimura et al., (2012).
Distribution of Salinity Profile
Desalinization practice involves a series of leaching and draining salt from soil layers to thedrainage channel. We assessed the salinity profile in the root zone and below to develop an
effective desalinization strategy. Results showed two types of salinity profile as shown in Fig. 4. At
point A, which was the nearest point to the drainage channel, soil salinity was observed to increase
with depth. In contrast, at points B, C and D, salinity decreased with depth below the soil surface.
Salinity of soil from 0 to 40 cm deep increased with distance from the drainage channel, this trend
was similar to the results shown in Fig. 3.
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Fig. 3 Changes in spatial distribution of EC1:5 along the transect x-x’ at four measurement
times and relative height of the transect
High salinity layers (2.0–2.5 dS/m) were found at around 60 cm soil depth at points A, B andC (and also at E, F, G and H, reference points (data not shown)). This indicates that high salinity
layers below 60 cm soil depth are widely distributed across the fields. Based on our field survey, it
was confirmed that groundwater depth was at least 4.0 m below the soil surface, so the effect ofgroundwater on the salinity profile was negligible during the observation period.

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Fig. 4 EC1:5 of soil vertical profiles at points A to D along the transect and distributionof crops cultivated in June 2013
Structure of Non-Uniform Salinity Distribution of the Field
The non-uniform salinity distribution across the field was probably formed by irrigation
management and distance from main drainage channel, while the effect of soil physical properties
and groundwater was quite limited. The main drainage channel functioned well during the past
irrigation period when abundant Karez water was available for leaching irrigation, and thiscontributed to the present non-uniform salinity distribution. Currently, farmers use less irrigationwater, which does not promote desalinization. Vertical movement of soluble salts near the soil
surface was dominated by irrigation management. Border irrigation promotes desalinization but
drip irrigation enhances salt accumulation, with salinity increasing after irrigation because of highevaporation rates in the hyperarid climate.
CONCLUSION
In this study, we identified the primary factors affecting structure of non-uniform salinity
distribution in terms of irrigation and drainage management. Based on these results, we will explain
the following points to local farmers in non-technical language: 1) a drainage channel is importantfor desalinization but the current channel is no longer sufficient to discharge salt from the field; 2)drip irrigation is effective for deficit irrigation but it enhances salt accumulation; 3) borderirrigation has a positive effect on salt leaching from surface layers but the leached salt returns to thesurface after irrigation ceases; and 4) there are high salinity layers below 60 cm soil depth,
distributed widely across the fields.
Two-dimensional profiles of salt and water distribution and their movement within andbetween soil layers are required to manage agricultural activity in the research area. We plan tosimulate salt and water balance using a numerical model assuming installation of various types ofdrainage channels and adoption of different irrigation managements to develop a practical strategy
for irrigation and drainage management for local farmers to employ in the research field.
ACKNOWLEDGEMENTS
This work was supported by JSPS KAKENHI Grant Numbers 24405039 and 25450363.

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