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ARTICLE IN PRESS Model

GWAT-3297; No. of Pages 12

Agricultural Water Management xxx (2011) xxx– xxx

Contents lists available at ScienceDirect

Agricultural Water Management

j ourna l ho me page: www.elsev ier .com/ locate /agwat

alt distribution and the growth of cotton under different drip irrigation regimesn a saline area

uoshui Wanga,b, Yaohu Kanga,∗, Shuqin Wana, Wei Hua, Shiping Liua, Shuhui Liua

Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11 A Datun Road,nwai, Beijing 100101, ChinaGraduate University of Chinese Academy of Sciences, Beijing 100049, China

r t i c l e i n f o

rticle history:eceived 28 April 2011ccepted 1 August 2011vailable online xxx

eywords:rid regionottonrip irrigation

a b s t r a c t

A 3-year experiment was conducted in an extremely dry and saline wasteland to investigate the effectsof the drip irrigation on salt distributions and the growth of cotton under different irrigation regimes inXinjiang, Northwest China. The experiment included five treatments in which the soil matric potential(SMP) at 20 cm depth was controlled at −5, −10, −15, −20, and −25 kPa after cotton was established. Theresults indicated that a favorable low salinity zone existed in the root zone throughout the growing seasonwhen the SMP threshold was controlled below −25 kPa. When the SMP value decreased, the electricalconductivity of the saturation paste extract (ECe) in the root zone after the growing season decreased aswell. After the 3-year experiment, the seed-cotton yield had reached 84% of the average yield level for

alinityalt toleranceoil matric potential

non-saline soil in the study region and the emergence rate was 78.1% when the SMP target value wascontrolled below −5 kPa. The average pH of the soil decreased slightly after 3 years of cultivation. Thehighest irrigation water use efficiency (IWUE) values were recorded when the SMP was around −20 kPa.After years of reclamation and utilization, the saline soil gradually changed to a moderately saline soil.The SMP of −5 kPa at a depth of 20 cm immediately under a drip emitter can be used as an indicator forcotton drip irrigation scheduling in saline areas in Xinjiang, Northwest China.

© 2011 Elsevier B.V. All rights reserved.

. Introduction

Xinjiang is the largest cotton production province in China, andotton is a leading cash crop in the region (Hou et al., 2009). How-ver, soil salinity impacts about one-third of the total irrigatedropland in Xinjiang (Chen et al., 2010). Specifically, there are still.1 × 107 ha saline wasteland in Xinjiang, of which 7.27 × 106 haverly saline–sodic soils (Xi et al., 2005). Large amounts of salt-ffected soil not only restrict cotton production, but also threatenontinued development of irrigated agriculture in the area. More-ver, the area is characterized by a dry climate, small amountsf precipitation and shallow groundwater table, which tends toncrease the trend of soil salinization.

Many studies have demonstrated that these saline soils, whichave traditionally been classified as unsuitable for crop growth,an be used successfully for crop growth without long-term haz-

Please cite this article in press as: Wang, R., et al., Salt distribution and thearea. Agric. Water Manage. (2011), doi:10.1016/j.agwat.2011.08.005

rdous effects on crops and soils if proper practices such as adoptionf furrow irrigation on salt leaching, selecting appropriately salt-olerant crops, and artificial subsurface drainage (Moreno et al.,

∗ Corresponding author.E-mail address: [email protected] (Y. Kang).

378-3774/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.agwat.2011.08.005

1995; Barrett-Lennard, 2002; Bassil and Kaffka, 2002a,b; Hansonand May, 2004; Hanson et al., 2006; Roberts et al., 2008) are estab-lished.

However, due to the typical inland arid conditions and waterresources shortages in the region, it is not practical to implementthe management strategies mentioned above. Moreover, since soilinfiltration capacity tends to decrease greatly as soils are satu-rated, excess fresh water cannot flush or prevent ponding on salinesodic soil for salt leaching (Wan et al., submitted for publication).Accordingly, a novel method is needed to decrease the trend of soilsalinization and effectively utilize saline wastelands of this area.

Drip irrigation is considered to be the most efficient irriga-tion method because it can distribute water uniformly, control theamount of water applied precisely, reduce evaporation and deeppercolation, and minimize salinity effects (Elfving, 1982; Batcheloret al., 1996; Ayars et al., 1999; Karlberg and Frits, 2004). Tomatoand cotton grow well on saline soil under drip irrigation in the SanJoaquin Valley in the United States and Karnataka India (Rajak et al.,2006; Hanson et al., 2006). As a measure of the holding strength

growth of cotton under different drip irrigation regimes in a saline

of the soil matrix for water, soil matric potential (SMP) is a criti-cal variable influence on crop yield, runoff, erosion and irrigationscheduling (Phene et al., 1989). Many studies have investigated irri-gation scheduling for a wide variety of crops based on SMP (Kang

dx.doi.org/10.1016/j.agwat.2011.08.005

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mailto:[email protected]

dx.doi.org/10.1016/j.agwat.2011.08.005

ARTICLE IN PRESSG Model

AGWAT-3297; No. of Pages 12

2 R. Wang et al. / Agricultural Water Management xxx (2011) xxx– xxx

Table 1Basic properties and ECe of the initial soil profile.

Soil layers Soil mechanical composition (%) Soil texture Soil bulk density (g/cm3) ECe (dS/m) pH

<0.002 mm 0.002–0.05 mm 0.05–2 mm

0–30 1.18 93.48 5.34 Silt 1.33 45.3 7.4230–60 1.03 98.97 0.00 Silt 1.43 28.6 7.6460–90 0.54 95.39 4.07 Silt 1.47 15.4 7.6890–120 0.41 96.02 3.56 Silt 1.56 30.4 7.54

120–180 0.26 96.06 3.68 Silt 1.38 16.4 7.71180–210 0.34 86.28 13.38 Silt 1.36 10.7 7.83210–240 0.65 99.35 0.00 Silt 1.42 15.6 7.97240–270 0.72 93.82 5.46 Silt 1.36 42.7 7.41

eda

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2

2

w3iiaAiwFsjeia

270–300 0.54 95.86 3.60

t al., 2004; Kang and Wan, 2005); however, studies to developrip irrigation schedules for the reclamation of saline soil by SMPre rare.

Saline wastelands have been successfully reclaimed for waxyorn growth in the middle of the Hetao Plain in the Ningxiautonomous Region of China in recent years (Jiao et al., 2008;an et al., 2008; Tan and Kang, 2009; Wan et al., submitted forublication). The primary management strategies employed toccomplish this include applying mulched drip irrigation on salineastelands and irrigation by controlling the SMP at a depth of 20 cm

mmediately under the emitter throughout the growing season. AnMP of −10 kPa at a depth of 20 cm immediately under the dripmitter was found to be useful as an indicator of corn drip irri-ation scheduling for saline soil in Ningxia Plain, China. Tan et al.2008) also indicated that when the soil matric potential at a depthf 20 cm immediately under the emitter is maintained at greaterhan −10 kPa under mulch drip irrigation, the soil salinity and pHalue in the 0–40 cm layer decreased gradually as the planting yearsncreased. Wan et al. (submitted for publication) found that afterears of cultivation and drip leaching, very saline soil graduallyhanged to a moderately saline soil. However, the salt contents,oil texture and climate conditions in Ningxia are quite differentrom those in Xinjiang (Wang et al., 1993), thus further studies areeeded in the Xinjiang area.

The objectives of this study were as follows: (1) to measure theffects of different irrigation regimes under drip irrigation on saltistribution in the soil profile during and between planting years;2) to measure the effects of different SMP threshold on cotton yieldnd water use under mulched-drip irrigation; and (3) to define theasis for irrigation scheduling of drip-irrigation cotton and wateresource planning under saline land conditions in Northwest China.

. Materials and methods

.1. Experimental site

A field experiment was conducted from 2008 to 2010 on salineasteland at Karamay Farm (latitude: 45◦22′N, longitude: 84◦50′E,

50 m a.s.l.), which is located in the middle of the Jungger Basinn Xinjiang Province, northwest China. The study area is character-zed by a typical inland arid climate with annual precipitation ofpproximately 105 mm, most of which falls from June to August.ccording to Wang et al. (1993) and Xi et al. (2005), the saline soil

n the experimental is the typical type of saline soil in Xinjiang,here the main ions are chlorine and sulphate. According to the

AO soil classification, the soil in our experiment field is the desertoil (Gypsisols) which is widespread in the north and south Xin-

Please cite this article in press as: Wang, R., et al., Salt distribution and tharea. Agric. Water Manage. (2011), doi:10.1016/j.agwat.2011.08.005

iang region. The average groundwater table is about 3.0 m and thelectrical conductivity is 52 dS/m while the irrigation water whichs pumped from the reservoir in the west suburbs of Karamay isbout 0.3 dS/m. The typical inland arid climate and special geo-

Silt 1.52 56.4 7.49

graphical conditions make salt accumulation on the surface of thesoil profile likely in this region. The ECe (electrical conductivity ofsaturated-soil extract) of the soil at a depth of 30 cm is 45.3 dS/m(Table 1), which is too high to plant crops. The soil texture, soil bulkdensity, ECe and pH are shown in Table 1.

2.2. Experimental design

2.2.1. Plot layout, irrigation water managementOur research group had reclaimed the saline wasteland success-

fully for corn growth in the middle of the Hetao Plain in the NingxiaAutonomous Region of China in recent years (Jiao et al., 2008; Tanet al., 2008; Tan and Kang, 2009). The primary irrigation strategiesare controlling the SMP at a depth of 20 cm immediately under theemitter throughout the growing season and it was found that theoptimal SMP threshold for corn was −10 kPa. Similarly, in order tofind the optimal SMP threshold for cotton in Xinjiang saline area weset up the five SMP threshold treatments in this study, in which theSMP at a depth of 20 cm immediately under the emitter was con-trolled at levels higher than −5 kPa (S1), −10 kPa (S2), −15 kPa (S3),−20 kPa (S4), and −25 kPa (S5). The five treatments were replicatedthree times in 15 plots and laid out in a completely randomizedblock design. The position and location of the beds was the sameduring all 3 years of the experiments.

Cotton was planted directly on a flat field in 20 rows for eachplot in 2008, while in 2009 and 2010, each of the 15 plots consistedof ten raised (15 cm) beds, with 0.8 m between bed centers (Fig. 1).Each bed was 0.4 m wide and 3.8 m long; therefore, each plot was8.0 m × 3.8 m.

Each treatment had a separate gravity drip irrigation systemconsisting of a tank and 30 drip tubes (ten tubes per plot). The tank(1000 L) was 1 m above the ground. Drip tubes with emitters spaced0.2 m apart were placed at the center of each raised bed. Irrigationwas applied as soon as the potential neared the target value of SMPfor each treatment, except during the seeding stage when morewater was required. One vacuum gauge tensiometer was installed0.2 m directly underneath one emitter located in the center of themiddle bed within the plot for each treatment. The tensiometerswere observed three times a day (at 8:00, 12:00, and 18:00 h).

2.2.2. Plant management and measurementsSeeds of the cotton (Gossypium hirsutum L.) hybrid Xinluzhong

No. 26 were sown on 30 May 2008, 10 May 2009 and 7 May 2010 indouble rows. The rows were 0.3 m apart, and the seeds within a rowwere sown 10 cm apart. Thinning was conducted on the 15th, 20thand 25th day in 2008, 2009 and 2010, respectively. The beds weremulched with white polyethylene sheets after sowing. To ensure

e growth of cotton under different drip irrigation regimes in a saline

that the seedlings survived, approximately 40 mm of water wasapplied after sowing.

In 2008, 2009 and 2010, a basal dose of 450 kg/ha of compoundfertilizer (monoammonium phosphate: 16% N, 35% P2O5, 8% K2O)

dx.doi.org/10.1016/j.agwat.2011.08.005



R. Wang et al. / Agricultural Water Management xxx (2011) xxx– xxx 3

tion o

wiiit

dafitowdi2Shcpwy

Fig. 1. Dimensions of beds and posi

as uniformly applied to the plots at the time of plowing. The dress-ng was supplemented with urea (46% N), and applied by mixingt with irrigation water at a concentration of 30% (w/w). Each timerrigation was conducted, 0.15 L urea solution was added to theank.

Three plants were randomly selected and fixed in each plot toetermine the plant height, leaf area index (LAI) and stem diametert the end of the cotton growing season from 2009 to 2010. Thenal emergence percentage was measured from 2008 to 2010 onhe thinning day for each plot and calculated based on the numberf hills. Since the seeding date was relatively late in 2008 and no bedas raised when seeding, the emergence rate was low and the bollsid not grow well enough for harvest due to the low temperature

n the late growing stages. Accordingly, there were no yield data for008. In 2009 and 2010, harvest was started on 2 October and 30eptember finished on 20 November and 25 November and the totalarvest period lasted 48 days and 56 days, respectively. The seed


otton was picked by hand at 4–7-day intervals and the total weighter plot was checked at each harvest time. In addition, the irrigationater use efficiency (IWUE) was calculated by dividing the total

ield of the seed cotton by the total quantity of the irrigation water.

f the tensiometer and soil samples.

2.2.3. Soil salinity and pHSoil cores were obtained from each plot using an auger (2.0 cm

diameter, 15 cm high) on 12 May (before seeding) and 14 Septem-ber (irrigation ceased) in 2008, on 30 April (before seeding), 14 May(after first irrigation), 28 July (flowering stage), 1 September (bollsstage) and 21 November (after harvest) in 2009, and on 13 Septem-ber (irrigation ceased) in 2010. The samples were obtained from 0,5, 10, 15, 20, 25, 30, 35, and 40 cm from the emitters and all the sam-ple depths were the same, being 0–5, 5–10, 10–20, 20–30, 30–40,40–60, 60–80, 80–100, and 100–120 cm deep (Fig. 1). The threereplicate soil samples were mixed into one sample per treatment.

All soil samples were air-dried and passed through a 1 mmsieve. Soluble salt estimates and soil pH were based on extracts ofsaturated soil. The EC and pH value were determined using a con-ductivity meter (DDS-11A, REX, Shanghai) and a pH meter (PHS-3C,REX, Shanghai). In this study, ECe is the abbreviation of electricalconductivity of saturated-soil extract.


In this experiment, ECe values within the root zone were inte-grated to account for both spatial and temporal variations, and werecalculated in the soil about 40 cm horizontally to the center of raisedbeds at a depth of 0–40 cm. For example, the average root-zone ECe

dx.doi.org/10.1016/j.agwat.2011.08.005




itation

vk3

E

widssw

E

wtt(i

ECe(J)

wm(id

2

vs

3

3

dp

Fig. 2. The reference crop evapotranspiration (ET0) and precip

alue in the soil profile on date i (ECe(i)) was calculated from ECe(j,) and S(j, k) data (j = 0, 5, 10, 15, 20, 25, 30, 35, 40; k = 5, 10, 20, 30,5, 40):

Ce(i) =

∑j = 0, 5, 10, 15, 20, 25, 30, 35, 40k = 5, 10, 20, 30, 40

ECe(i, j, k) × S(j, k)

∑j = 0, 5, 10, 15, 20, 25, 30, 35, 40k = 5, 10, 20, 30, 40

S(j, k)

(1)

here ECe(i, j, k) is the ECe value of the soil sample in soils on the date, in which j is the horizontal distance to drip line and k is theepth to soil surface. S(j, k) is the representative area of the soilample. The soil samples in 2008 and 2010 were obtained beforeowing and after irrigation ceased. The ECe value for 2008 and 2010ere calculated by:

Ce = [ECe(b) + ECe(a)]2

(2)

here ECe(b) and ECe(a) refer to the spatial weighted mean value ofhe soil profile before sowing and after irrigation ceased. In 2009,he samples were obtained on 30 April (before seeding), 14 Mayafter first irrigation), 28 July (flowering stage), 1 September (afterrrigation ceased), and the ECe value for 2009 was calculated by:

Ce = {[(ECe(b) + ECe(f )]/2} × 15 + {[ECe(f ) + ECe(J)]/2} × 73 + {[EN

here ECe(b), ECe(f), ECe(J), ECe(a) refer to the spatial weightedean value of the soil profile on 30 April (before seeding), 14 May

after first irrigation), 28 July (flowering stage), 1 September (afterrrigation ceased), respectively while N is the irrigation period (123ays).

.2.4. Statistical analysisThe treatments were analyzed by single-factor analysis of

ariance (ANOVA). An ̨ = 0.05 level was considered to indicateignificance.

. Results and discussion

.1. Weather


The reference crop evapotranspiration (ET0) and rainfall datauring cotton growing periods in the 3 years of the experiment arerovided in Fig. 2. The total ET0 values during the cotton growing

during the growing period of cotton in 2008, 2009 and 2010.

+ ECe(a)]/2} × 35(3)

periods in the 3 years were 907.1 mm, 818.2 mm and 850.4 mm,respectively. Also it can be seen from the data that the ET0 valueduring the cotton growing periods of the 3 years had similar varia-tion trend, which was climbing up from late April to late June andthen remaining until late July and declining from then on. There-fore, the highest evaporation rate may occur during flowering andbolls stages of cotton.

Total rainfall during the experimental period was 70.8, 81.2 and114.6 mm, with 7, 6 and 9 effective rainfall (>5 mm) events. Therewere four heavy rainfall events (rainfall intensity >16 mm/h) inearly July 2008, which was twice as many as observed in 2009 and2010 and had an adverse effect on cotton growth. Since the seedingdate was delayed, the seedling establishment stage for cotton wasin early July 2008, and the roots were not yet strong enough to tol-erate the salts leached by sudden rainfall from the soil surface intothe root zone. Furthermore, the sharply decrease in temperatureduring the bolls stage in 2008 caused the bolls to fall off in largenumbers. Due to these factors, there were no yield data for 2008.

3.2. Irrigation

Before cotton emerged, all of the treatment plots were irrigatedwith the same amount of water to ensure uniform germination.

Based on the management strategy described by Jiao et al. (2006)and Wan et al. (submitted for publication), the first depth of waterafter seeding was four times that of the normal depth of 10 mmto enable the seedlings to survive. Irrigation treatments were initi-ated on 15 June 2008 (15 days after seeding), 2 June 2009 (22 daysafter seeding) and 5 June 2010 (25 days after seeding), which corre-sponded to the days the seedlings were thinned each experimentalyear. Subsequently, irrigation was only applied when the soil matricpotential reached the target values for S1, S2, S3, S4 and S5. In Xin-jiang region, the maximum evapotranspiration of cotton was foundto be 10 mm/day and to ensure that the SMP value can be higherthan the target value after irrigation we applied the same amountof irrigation water (9.8 mm) each time during the growing season.


3.3. Soil matric potential

Fig. 3 shows the SMP at a depth of 20 cm immediately under thedrip emitters for the different SMP treatments in 2008, 2009 and

dx.doi.org/10.1016/j.agwat.2011.08.005

Please cite this article in press as: Wang, R., et al., Salt distribution and the growth of cotton under different drip irrigation regimes in a salinearea. Agric. Water Manage. (2011), doi:10.1016/j.agwat.2011.08.005




0

5

10

15

20

25

30

35

40

908479746964573934292419149

Day after sowing

Soil

mat

ric

pote

ntia

l (-k

Pa)

S1 (-5kPa) S2 (-10kPa) S3 (-15kPa)

S4 (-20kPa) S5 (-25kPa) 2008

0

5

10

15

20

25

30

35

40

10196918681766964595447423732272217126

Day after sowing

Soil

mat

ric

pote

ntia

l(-k

Pa)

S1 (-5kPa) S2 (-10kPa) S3 (-15kPa)

S4 (-20kPa) S5 (-25kPa) 2009

0

5

10

15

20

25

30

35

40

1091049994898479746964595449443934292419149

Day after sowing

Soil

mat

ric

pote

ntia

l (-k

Pa)

S1 (-5kPa) S2 (-10kPa) S3 (-15kPa)

S4 (-20kPa) S5 (-25kPa) 2010

Fig. 3. The change in soil water potential at a depth of 20 cm immediately under emitters for different treatments in 2008 and 2009.

dx.doi.org/10.1016/j.agwat.2011.08.005




emit

Soil

dept

h (c

m)

S1 (-5kPa) S2 (-10kPa) S3 (-15kPa) S4 (-20kPa) S5 (-25kPa)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40

Unit: dS/ m 0

8

16

24

32

40

48

lar to

2tiddswtdfipwm

3

3

otc

Distance fro m

Fig. 4. The spatial distribution of ECe in the vertical transect perpendicu

010. The SMP for each treatment was basically maintained at thearget value for most of the growing period. The changes in the SMPn the middle and late growing stage were more intense than thoseuring the early growing stage due to the higher evapotranspirationemand (Fig. 2), which resulted in more water evaporating from theoil. Plants in the S1 plot grew faster, which resulted in the requiredater increasing; As a result, the SMP for S1 decreased rapidly from

he target value and sometimes the SMP value of S1 treatment couldrop below the target value before irrigation but the exceedinggure was quite low (within 5 kPa). Conversely, plants in the S5lot grew under unfavorable soil water conditions; therefore, theater requirement decreased as plant growth was inhibited, whichoderated the change in the SMP.

.4. Soil salinity (ECe)

.4.1. The spatial distribution of ECe


It is generally accepted that, because of the point-source naturef drip irrigation, the salts along with water can be pushed towardhe fringes of the irrigated area, forming a desalinization zone in theenter in close proximity to the dripper (Goldberg et al., 1976; Kang,

Distance fro m emitter (cm)

Soil

Dep

th (c

m)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

(A) S2 (-10kPa)

Soil

Dep

th (c

m)

D

-1

-1

-

-

-

-

-

-

-

-

-

(B)

Fig. 5. The spatial distribution of ECe in the vertical transect perpendicular to t

ter (cm)

the drip tapes for each treatment at the end of the experiment in 2008.

1998; Chen et al., 2009). Thus the salts are prone to accumulation atthe periphery of the wetted bulb, which was revealed in the spatialdistribution of the ECe values.

At the end of the experiment in 2008 (Fig. 4), salt leachingoccurred during the growing season for each treatment as a resultof the frequent irrigation, which resulted in the ECe value increas-ing with depth. The ECe value decreased from 0 to 110 cm for S1(−5 kPa) and S2 (−10 kPa) owing to the more frequent irrigationduring the growing season. When compared to the initial ECe valuein the 0–110 cm soil profile (Table 1), the average value was reducedby 61% and 56% for S1 and S2, respectively. Because of the salt accu-mulation at the periphery of the wetted bulb and the soil texture,the ECe values of the surface layer (0–15 cm) 40 cm from the emitterwere relatively high for all treatments. Although there were smalllow ECe zones within 10 cm of the drip emitter at 0–10 cm for S3–S5,there was no considerable change in ECe value below 30 cm whencompared to the initial ECe values (Table 1) prior to planting. Based


on the spatial distribution of ECe at the end of the experiment in2008 the most effective salt leaching treatments were S1 and S2.

Owing to the evaporation in late winter and early spring, thesalts in S2 treatment that had been leached to deep soil layers in the

Unit: dS/ m0

8

16

24

32

40

48

istance fro m emitter

0 10 20 30 4010

00

90

80

70

60

50

40

30

20

10

S2 (-10kPa)

(cm)

he drip tapes before seeding (A) and after the first irrigation (B) in 2009.

dx.doi.org/10.1016/j.agwat.2011.08.005




Soil

Dep

th (c

m)

(A) S1 (-5kPa) S2 (-10kPa) S3 (-15kPa) S4 (-20kPa) S5 (-25kPa)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40

Unit: dS/ m 0

8

16

24

32

40

48

Soil

Dep

th (c

m)

(B)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40

Unit: dS/ m 0

8

16

24

32

40

48

Soil

Dep

th (c

m)


(C)

0 10 20 30 40-11 0

-10 0

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 400 10 20 30 40 0 10 20 30 40 0 10 20 30 40

Unit: dS/ m 0

8

16

24

32

40

48

F rip ta2

fataolaw

ig. 6. The spatial distribution of ECe in the vertical transect perpendicular to the d009.

ormer irrigation season had moved up to the surface layer (Fig. 5A),nd the average ECe value in 2009 before seeding (Fig. 5A) withinhe 120 cm soil layer was increased to 28.3 dS/m. After seeding, themount of water applied was 40 mm, and the spatial distribution


f ECe after irrigation is shown in Fig. 5B. After the first irrigation, aow ECe zone was generated within about 15 cm of the drip emitternd 0–15 cm, in which the average ECe value was 11.2 dS/m. Thereere still some salts built up in the furrow surface layer (0–10 cm)

pes for treatment in the flowering stage (A), bolls stage (B) and after harvest (C) in

after the first irrigation, and the highest ECe zone was in the ridgeof the bed and below 50 cm.

It is obvious that after applying water with drip irrigation, saltswere leached to a certain extent during the flowering and bolls


stages in 2009 (Fig. 6A and B). The average ECe value in the soilprofile for S3 (−15 kPa) and S4 (−20 kPa) was lower than that ofS1 (−5 kPa) (Fig. 6A), which occurred because that the soil samplesof the flowering stage in 2009 were obtained on the same date for

dx.doi.org/10.1016/j.agwat.2011.08.005




Soil

Dep

th (c

m)


S1 (-5kPa) S2 (-10kPa) S3 (-15kPa) S4 (-20kPa) S5 (-25kPa)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40

Unit: dS/ m 0

8

16

24

32

40

48

endicu

ttafSuwtbttwAzCah

opsttwitcpuri

bcvwti4

se

decreased, and there was a linear relationship between these fac-tors in 2008, 2009 and 2010. Since the difference in irrigation waterapplied during the growing seasons was small among S3 (−15 kPa)

EC2010 = 0.50SMP + 5.6 R2 = 0.71

EC2008= 0.86SMP + 3.3 R2 = 0.82

EC2009 = 0.59SMP + 4.9 R2 = 0.93

0

5

10

15

20

25

30

Ave

rage

EC

e in

root

zone

(dS/

m)

2008

2009

2010

Fig. 7. The spatial distribution of ECe in the vertical transects perp

he five treatments whereas the irrigation was not synchronous. Onhe date of 28 July (flowering stage), irrigation just occurred in S3nd S4 treatment thus in the figure better salt leaching effect wereound in S3 and S4 treatment. Since the irrigation interval for S3 and4 treatment were longer than that of S1 and S2, the salt would builtp soon after the irrigation. The most obvious effect of salt leachingas observed in S1 (−5 kPa), for which the average ECe values in

he low ECe zone were 6.2 and 4.3 dS/m during the flowering andolls stages, respectively. In the bolls stage, the ECe value of the S1reatment was less than 10 dS/m throughout the soil profile, andhe average ECe value in the 0–110 cm soil profile was 7.9 dS/m,hich was 73% lower than that of the initial soil ECe value in 2008.lthough there were zones of relatively low ECe values within rootones for other treatments after a period of irrigation (Fig. 6B and), no considerable changes were found in the average ECe valuest depths below 40 cm, where the ECe values were still relativelyigh (>20 dS/m).

Irrigation was halted after the bolls stage to allow the bolls topen thus some salts accumulated in the soil profile during thiseriod (Fig. 6C). The ECe values became higher in the 0–110 cmoil profile for S1–S5 treatment after harvest when compared tohose observed during the irrigation period. For the S1 treatment,he average ECe value throughout the soil profile increased by 41%hen compared to that in the bolls stage, and the relevant rate

ncreases were 6%, 25%, 35% and 58% for treatments S2–S4, respec-ively. Despite some salt buildup in the soil profile after irrigationeased, the average ECe values in the root zone and the entire soilrofile for S1 were 5.9 dS/m and 11.2 dS/m, respectively. These val-es were still lower than those of the other treatments, and wereeduced by 87% and 63%, respectively, when compared with thenitial soil ECe values.

Investigation of the salt content of the entire soil profile in theolls stage in 2009 (Fig. 6B) and 2010 (Fig. 7) revealed that the saltoncentration became lower in the same stage in 2010. The ECe

alue in the entire profile decreased by 1.5% for the S1 treatmenthile it decreased by 4.3%, 11%, 44.9% and 11.9% for S2–S5, respec-

ively. However when compared with the initial soil ECe values thencreasing rate from S1 to S5 treatment were 73.8%, 40.1%, 19.7%,


9.3%, and 21.0%.After 3 years of cultivation, the average ECe value of the entire

oil profile for the −5 kPa treatment was 7.8 dS/m at the end of thexperiment (Fig. 7), and the saline–sodic soil has been turned into

lar to the drip tapes for each treatment in the bolls stage in 2010.

a moderately saline soil, which was similar to the results of a studyconducted in Ningxia by Wan et al. (submitted for publication). Itis a relative low-lying place around the experiment field where it isdifficult to drain off water by surface drainage system. Our strategyis to leach the salt into the underground water after several years ofirrigation and the salt would be drained off through undergroundwater.

Overall, these results indicate that when the SMP at a depth of20 cm immediately under the emitter is controlled to be higher than−5 kPa during the growing season, the effect of salt leaching can beoptimized in Xinjiang, China. These findings are concordant withthose of Jiao et al. (2008) and Wan et al. (submitted for publication).

3.4.2. The relationship between the average ECe values in the rootzone after the growing season and SMP

According to cotton root distribution under drip irrigation(Hanson et al., 2006; Hu et al., 2009), we consider the root zoneof cotton plant in this study being within 40 cm of the emitter anda depth of 40 cm. As shown in Fig. 8, the average ECe value in the rootzone after the growing season increased as the control target of SMP


302520151050

Soil matric potential (-kPa)

Fig. 8. The relationship between the average ECe values in the root zone after thegrowing season and SMP.

dx.doi.org/10.1016/j.agwat.2011.08.005




Table 2Irrigation and amount of applied water for each treatment during the cotton growing period in 2008, 2009 and 2010.

Years Treatments Seasonal waterdepth (mm)

Fresh water forseedlings (mm)

During treatment Seasonal water depthvs. control (%)

Irrigation times Water depth (mm)

2008 S1 (−5 kPa) 705.6 40.0 68 665.6 100S2 (−10 kPa) 499.8 40.0 47 459.8 69S3 (−15 kPa) 333.2 40.0 30 293.2 44S4 (−20 kPa) 313.6 40.0 28 273.6 41S5 (−25 kPa) 294.0 40.0 26 254 38

2009 S1 (−5 kPa) 676.2 40.0 65 636.2 100S2 (−10 kPa) 499.8 40.0 47 459.8 72S3 (−15 kPa) 411.6 40.0 38 371.6 58S4 (−20 kPa) 401.8 40.0 37 361.8 57S5 (−25 kPa) 284.2 40.0 25 244.2 38

2010 S1 (−5 kPa) 667.2 40.0 65 627.2 100S2 (−10 kPa) 581.0 40.0 56 541.0 86S3 (−15 kPa) 402.6 40.0 38 362.6 58S4 (−20 kPa) 314.4 40.0 28 274.4 44

tigts2rtwwimlttsfst

3

aiaartca70pgctiaaa

ow

S5 (−25 kPa) 275.2 40.0

o S5 (−25 kPa) in 2008 (Table 2), there was no considerable changen the root-zone ECe value after the growing season, when the tar-et SMP decreased from −15 kPa to −25 kPa. However, in 2009,he root-zone ECe values after the growing season increased con-tantly as the target SMP decreased, and were lower than those in008. This might have been because the frequent irrigation in 2008esulted in the salts being leached to a certain layer. As a result, afterhe irrigation was stopped and the mulch was removed during lateinter and early spring, the salts accumulated in deep soil layersere transferred to shallow soil layers. This would have resulted

n the salt concentration in the soil at the beginning of the experi-ent in 2009 being higher than that at the end of 2008 (Fig. 5A), but

ower than that of the initial salt concentration in 2008. Similarly,he overall root-zone ECe value at the end of 2009 was lower thanhat of 2008. Due to the salt leaching during the three growing sea-ons, the root-zone salt concentration in 2010 was relatively lowor all treatments; thus, the slope of the linear equation in 2010 ismaller than those in 2008 and 2009, which is in agreement withhe results of Wan et al. (submitted for publication).

.5. The spatial distribution of pH at the end of the experiment

As is shown in Fig. 9, the pH of the soil profile increased for the S1nd S2 treatments, whereas it decreased for S3–S5 after irrigationn 2008 (Fig. 9A). When compared with the initial pH (Table 1), theverage pH of the whole soil profile increased by 4% and 6% for S1nd S2 and decreased slightly by 5%, 4% and 0.7% for S3, S4 and S5,espectively. Additionally, there was less considerable difference inhe spatial distribution of pH in the soil profile for 2009 (Fig. 9B)omparing with those in the distribution of ECe among treatments,s indicated by the average pH values of the soil being 7.8, 7.6, 7.9,.7 and 7.6, which were decreased by 2.4%, 0.8%, 3.7%, 1.7% and.8% compared to the initial pH value, respectively (Table 1). TheH value in the soil profile decreased in 2010 (Fig. 9C) after therowing season at a rate of 5.8%, 7.8%, 6.5%, 6.6% and 8.3%, whenompared to the previous year. According to the characteristic ofhe ion movement in this kind of saline soil (Dou et al., 2011), theons that are easily to leached are chlorine and sodium. This can playn important role on the changes in pH. In addition, fertilization canlso change the distribution of ions in the soil, which may have been


nother reason that influenced the pH value in the soil.The results mentioned above indicate that different SMP thresh-

lds play an important role in the salt concentration in the soil,hereas there was less obvious change in the average pH value in

24 235.2 38

the soil, which is similar to the results of a study conducted by Douet al. (2011) in Ningxia saline–sodic soil.

3.6. Cotton growth and yield

3.6.1. Vegetative growth characteristicsThe final emergence percentage on the thinning day in 2008,

2009 and 2010 is shown in Table 3. Germination, emergence andearly seedling growth are considered to be more sensitive to salin-ity than later stages of cotton growth (Dong et al., 2009), whichwas confirmed by the finding in the present study that the emer-gence rates of the five treatments were relatively low (below 35%)in 2008 due to the high salt concentration in the initial soil. Thesefindings indicate that there were significant differences among thefive treatments in 2008, which may have been caused by the orig-inal differences in the salt content for each plot field. Conversely,in 2009, despite the significant difference in the emergence rateamong the five treatments, the emergence rate could be dividedinto two clusters based on SMP. Specifically, the S1 and S2 treat-ment fell into one group and the emergence rate of those groupswere relatively higher than those of the other group. The reasonsfor these findings were likely because more salt leached out of theroot zone during cotton growing season in 2008 for treatment S1and S2, which reduced the impact of salinity on the emergence rate.There was no considerable difference in emergence rate observedamong the five treatments in 2010, for which the emergence rateswere much higher than in the former 2 years. These findings indi-cated that after 2 years of irrigation, the salt content within the rootzone could be leached to a certain level under which the emergencerate of cotton could be above 67%.

The cotton plant height, LAI and stem diameter at the end ofthe growing season was monitored in 2009 and 2010 (Table 3).In general, the plant height, LAI and stem diameter increased asthe SMP value increased. When compared with the other threetreatments, plants in the −5 kPa and −10 kPa treatments reachedrelatively higher plant height, LAI and stem diameter. As manystudies have noted (Bassil and Kaffka, 2002a,b; Kang et al., 2004;Chen et al., 2009), salt stress reduces the growth of plants; thus, theplant height, LAI and stem diameter of the −25 kPa treatment werethe smallest.


3.6.2. Seed-cotton yield and IWUEBecause of the low emergence rate, the delayed seeding date and

the abrupt decrease in temperature at the bolls stage in 2008, there

dx.doi.org/10.1016/j.agwat.2011.08.005




Soil

Dep

th (c

m)

(A)S1 (-5kPa) S2 (-10kPa) S3 (-15kPa) S4 (-20kPa) S5 (-25kPa)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40

6.7

7.1

7.5

7.9

8.3

8.7So

il D

epth

(cm

)

(B)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40

6.7

7.1

7.5

7.9

8.3

8.7

(C)


Soil

Dep

th (c

m)

0 10 20 30 40-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 10 20 30 40 0 10 20 30 40 0 10 20 30 40 0 10 20 30 40

6.7

7.1

7.5

7.9

8.3

8.7

F rip tap(

wttctiam

ig. 9. The spatial distribution of pH in the vertical transect perpendicular to the dC).

as no yield gained. As shown in Table 4, the yield for S1 (−5 kPa)reatment was 67% of the average yield level for non-saline soil inhis region in 2009 and this level increased to 84% in 2010. Statisti-al analysis showed that maintaining different SMP values during


he growing season had a significant effect on seed-cotton yieldn both 2009 and 2010. Moreover, the seed-cotton yield increaseds the SMP control target increased (Fig. 10), which is in agree-ent with the results of a study conducted by Jiao et al. (2006)

es for each treatment at the end of the experiment in 2008 (A), 2009 (B) and 2010

and Wan et al. (submitted for publication) in Ningxia, NorthwestChina. Although many studies have shown that an SMP between−10 kPa and −30 kPa is generally considered optimal for the cropgrowth (Kang and Wan, 2005) in non-saline soil, the highest yield


was observed under the SMP target value of −5 kPa in saline soilin this study. This was likely because salts move along with water;thus, relatively higher SMP (S1) kept the cotton plant away fromsalinity stress during the growing season, especially in the boll

dx.doi.org/10.1016/j.agwat.2011.08.005




Table 3Cotton vegetative growth characteristics for different SMP thresholds from 2008 to 2010.

Years Treatments Emergence rate (%) Plant height (cm) LAI Stem diameter (cm)

2008 S1 (−5 kPa) 30.5ab – – –S2 (−10 kPa) 34.5b – – –S3 (−15 kPa) 28.5ab – – –S4 (−20 kPa) 34.6b – – –S5 (−25 kPa) 21.3a – – –

2009 S1 (−5 kPa) 49.7b 63.1c 6.7c 1.20b

S2 (−10 kPa) 43.9b 61.5c 6.0bc 1.19b

S3 (−15 kPa) 27.6a 40.1a 4.2ab 1.06ab

S4 (−20 kPa) 27.6a 48.7b 3.6a 1.05ab

S5 (−25 kPa) 22.4a 37.0a 2.4a 0.97a

2010 S1 (−5 kPa) 78.1a 51.0b 5.6c 1.04a

S2 (−10 kPa) 76.4a 57.8c 3.9b 1.21a

S3 (−15 kPa) 72.1a 37.3a 2.8ab 0.93a

S4 (−20 kPa) 71.4a 52.6b 4.2bc 1.14a

S5 (−25 kPa) 67.6a

Values in a row followed by the same letter are not significantly different at p ≤ 0.05.

Table 4Cotton yield and IWUE for different SMP control targets in 2009 and 2010.

Years SMP (−kPa) Yield (Mg/ha) IWUE (kg/ha/mm)

2009 5 2.87b 4.25a

10 2.19ab 4.39a

15 1.87ab 4.55a

20 2.15ab 5.34a

25 1.24a 4.38a

2010 5 3.60a 5.73a

10 2.42b 5.49a

15 2.24ab 6.19ab

20 2.32b 8.46c

c bc

V

dn

twitcstrit

F2

25 1.76 7.48

alues in a row followed by the same letter are not significantly different at p ≤ 0.05.

evelopment stage, whereas relatively lower SMP (S2–S5) couldot prevent cotton plants from suffering from salinity stress.

Irrigation water use efficiency is computed by dividing the cot-on yield by the total irrigation water. As shown in Table 4, thereas no significant difference among the five treatments for IWUE

n 2009. However, a significant difference existed in 2010 andhe highest IWUE was obtained when the SMP target value wasontrolled above −20 kPa. The best fit regression equation was pre-ented in Fig. 10. The relationship between the IWUE and SMPhreshold showed a similar pattern in 2009 and 2010, with a loga-


ithmic increase in IWUE being observed in response to a decreasen SMP threshold (Fig. 10). Moreover, because of the increased yield,he IWUE for all five treatments was higher in 2010 than in 2009.

I = 0.345 Ln(SMP) + 3.70 R = 0.25

I = 1.51 Ln(SMP) + 2.80 R = 0.58

Y = -0.06 6SMP + 3.06 R = 0.79

Y = -0.075SMP + 3.60 R

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25 30

Soil matric potential (-kPa)

Seed

cot

ton

yeild

(10

kg/h

a)

0

1

2

3

4

5

6

7

8

9

IWU

E (k

g/ha

/mm

)

Yield-20 09

Yield-20 10

IWUE-2009

IWUE-2010

ig. 10. The relationship between seed-cotton yield, IWUE and SMP threshold in009 and 2010.

37.8a 1.9a 0.87a

If the price of water and energy are taken into account, S4(−20 kPa) may be the most advantageous treatment. However, ourstudy was to reclaim the saline wasteland where some salt sensitivecrops can also be planted after years of reclamation. In this sense,S1 treatment was more effective in salt leaching than the S4 treat-ment, which can also be seen from the two treatments’ increasingrate of yield. For S1 treatment the increasing rate was 25.4% whilefor S4 it is 7.9%. Therefore, S1 treatment is the most advantageoustreatment in the long run although it may take more water andenergy in the first few years.

3.6.3. Relationship between yield and root-zone soil salinity (ECe)The relative yield (Yr) responses to the ECe values in the root

zone are presented in Fig. 10. Yr decreased 2.8% for every 1 dS/mincrease in ECe.

According to Maas and Hoffman (1977), crop salt tolerance canbe expressed by the following equation:

Yr = 100 − Yd(ECe − ECt) (4)

where Yr is the relative crop yield (actual yield at the given salin-ity level divided by yield with no salinity effect), ECe representsthe average root zone salinity (electrical conductivity of the satu-rated paste extract, dS/m), ECt is the threshold salinity level (themaximum allowable salinity that does not reduce yield measur-ably below that of a nonsaline condition, dS/m), and Yd is the yielddecrease per unit of salinity increase beyond the threshold.

To compare the results with those of other studies, the equationsin Fig. 11 were expressed as the Maas–Hoffman equation form:

Yr = 100 − 2.8 × (ECe − 4.3) R2 = 0.93 (5)

Computation of Eq. (5) revealed that Yr decreased by 2.8% for eachunit of ECe increase in the root zone above 4.3 dS/m. Maas and Hoff-man reported that cotton can tolerate an ECe (EC of the saturatedsoil extract) of about 7.7 dS/m and that yield decreased by 5.2% foreach unit of ECe increase above the threshold value. However, inthis experiment, the threshold was 4.3 dS/m, which is lower thanthat reported by Maas and Hoffman. This may have been due tothe extremely arid climate and low frequency and amount of pre-cipitation in the Xinjiang region, which increased the rates of soilevaporation and plant transpiration. Although the soil was coveredwith a plastic sheet to reduce soil evaporation, damage occurred


to the sheets due to strong wind and radiation. Thus some waterevaporated from the soil. Additionally, the high evaporative capac-ity in the atmosphere in this region can also accelerate the moistureconsumption rate in the soil by means of crop evapotranspiration.

dx.doi.org/10.1016/j.agwat.2011.08.005

ARTICLE ING Model


12 R. Wang et al. / Agricultural Water Ma

Yr = 10 0-2.8(ECe-4.3)

R2 = 0.93

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30

Rel

ativ

e se

ed-c

otto

n yi

eld

(%)

F

4

ittwracaasoyalaw8yciN

ot

A

mNCNNt

R

A

Wan, S.Q., Jiao, Y.P., Kang, Y.H. Drip irrigation for waxy corn (Zea mays L. var. ceratina

Average root zone ECe (dS/m)

ig. 11. Relative seed-cotton yield response to average ECe in the root zone.

. Conclusions

From the 3-year field experiment conducted in the saline soiln the arid area of Xinjiang, it can be concluded that different SMPhresholds ranging from −5 to −25 kPa had significant effects onhe spatial distribution of salt in the soil, the salt concentrationithin the root zone, and the cotton growth and yield, but had a

elatively small impact on the spatial distribution of pH in the soilnd IWUE of cotton. A low salinity zone in the root zone emergedonsistently throughout the entire growing season when the SMPt 20 cm immediately under the emitters was kept above −25 kPand the average ECe value in the root zone at the end of the growingeason decreased as the SMP increased. Conversely, the total yieldf seed cotton increased as the SMP threshold increased, and theield decreased 66 kg/ha for every 1 kPa decrease in SMP in 2009nd 75 kg/ha in 2010. The most effective SMP control target for salteaching and yield was the S1 (−5 kPa) treatment, for which theverage ECe value in the 0–110 cm soil profile decreased by 73%hen compared with the initial ECe value and the yield reached

4% of the average yield for non-saline soil in this region after the 3-ear experiment. Accordingly, an SMP higher than −5 kPa at 20 cman be used as an indicator for cotton drip irrigation schedulingn the first 3 years of reclamation of saline wastelands in Xinjiang,orthwest China.

It should be noted that the conclusions of this study were basedn 3 years of data. To assess the sustainability of saline land utiliza-ion in Northwest China, many further studies should be conducted.

cknowledgements

This study was supported by the Action Plan for the Develop-ent of Western China of the Chinese Academy of Sciences (Granto. KZCX2-XB2-13), the Knowledge Innovation Program of thehinese Academy of Sciences (Grant No. KSCX2-YW-N-080), theational Science Foundation for Young Scientists of China (Granto. 51009126), and the Project for 100 Outstanding Young Scien-

ists supported by Chinese Academy of Sciences.

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