Buried straw layer plus plastic mulching reduces soil salinity

1. Buried straw layer plus plastic mulching reduces soil salinity and
increases sunflower yield in saline soils
Yonggan Zhaoa,b
, Yuyi Lia,1
, Jing Wanga
, Huancheng Panga,
*, Yan Lib
a
Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
b
Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
A R T I C L E I N F O
Article history:
Received 28 March 2015
Received in revised form 25 August 2015
Accepted 27 August 2015
Keywords:
Straw layer
Plastic mulch
Soil water
Soil salinity
Sunflower yield
A B S T R A C T
Soil salinization is a major limitation to high crop yield in saline soils of the Hetao Irrigation District of
Inner Mongolia, China. As such, people are forced to use better and more effective approaches to soil
management due to scarcity of freshwater and the adverse effects of climate. A three-year field
experiment was conducted to investigate the effects of buried straw layer and plastic film mulch on soil
moisture, soil salinity and sunflower (Helianthus annuus L.) yield in saline soils. Four field management
practices were designed: bare ground (BG), plastic mulch (PM), buried maize straw layer (12 t ha1
) at a
depth of 40 cm (SL), and combined application of plastic mulch and straw layer burial (PM + SL). Soil
water at the 0–40 cm layer was higher under SL and PM + SL than under BG and PM within 45 days after
sowing (DAS) but the reverse occurred thereafter. Compared to PM and BG, both SL and PM + SL
significantly decreased the salt content of the upper 40 cm depth at sowing. Furthermore, PM + SL
invariably decreased the salt content throughout the growth period of sunflower. In contrast, SL and PM
moderately increased the salt content during the later growth period. Compared with BG, SL significantly
decreased salt accumulation in the off season. Over the three years, the highest seed and biomass yield,
100-seed weight and head diameters of sunflower were obtained from the PM + SL plots. The average
seed yield (3198 kg ha1
) under PM + SL exceeded the yields under BG, PM and SL by 51.9, 5.9 and 35.7%
respectively. Therefore, PM + SL may be an efficient practice for reducing soil salinity and increasing
sunflower yield in the Hetao Irrigation District and other similar ecological areas.
ã 2015 Elsevier B.V. All rights reserved.
1. Introduction
Soil salinization is one of the major causes of declining
agricultural productivity in numerous arid and semiarid regions
throughout the world (Qadir et al., 2000). High salinity has been a
significant threat to the sustainable development of agriculture
(Mondal et al., 2001; Bakker et al., 2010). The Hetao Irrigation
District, located in northwest China, has an irrigated land area of
570,000 ha. Approximately half of the irrigated land in this area has
saline-alkali problem. High evaporation rate, limited rainfall and
shallow groundwater table contribute to the increase in soil
salinity (Lei et al., 2011). It was reported that most of the saline soils
in the area will eventually become totally unproductive and
possibly abandoned if the salinity problem could not be resolved
immediately and effectively (Wu et al., 2008).
As a salt-tolerant crop, sunflower is one of the most important
crops in this region. Nevertheless, its germination, emergence, and
early growth are very sensitive to soil salinity (Katerji et al., 1994,
1996). Salt accumulation in the root zone is the main cause of yield
decline. Irrigation with water from the Yellow River is the most
readily available strategy for reducing salinity in saline fields (Feng
et al., 2005). However, excessive irrigation without appropriate
drainage systems raises the groundwater table. Thus, this
management option can potentially cause salt accumulation in
the root zone, with a negative effect on crop productivity (Sharma
and Minhas, 2005; Qadir et al., 2009). In recent years, the amount
of water for irrigation coming from the Yellow River has reduced
significantly, thus creating a conflict between water shortage and
salinity control in this region (Lei et al., 2011). Therefore, new
techniques should be developed to address these challenges.
Soil and water management approaches should aim to reduce
unproductive water losses associated with evaporation from soil
surfaces, increase soil moisture storage, maintain soil salinity
levels within acceptable crop production limits, enhance soil
organic matter inputs and nutrient availability, and maintain soil
physical properties in the root zone (Bezborodov et al., 2010).
* Corresponding author.
E-mail address: hcpang@caas.ac.cn (H. Pang).
1
This author contributed equally to this work.
http://dx.doi.org/10.1016/j.still.2015.08.019
0167-1987/ã 2015 Elsevier B.V. All rights reserved.
Soil Tillage Research 155 (2016) 363–370
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2. Mulching of the soil surface using various materials (e.g., crop
residue, plastic film, sand, or gravel) can reduce evaporative water
loss and help to reduce salt accumulation within the shallow soil
depth (Pang et al., 2010; Li et al., 2013). Agele et al. (2010) showed
that plastic film mulching improved soil moisture, increased soil
temperature, root and shoot biomass, and leaf area development of
sunflower. Similarly, Li et al. (2013) demonstrated that plastic
mulching could serve as a water vapor barrier against evaporation
losses, increase soil moisture storage, and enhance biological
activity. In addition, returning crop residues or applying straw
mulches to the soil surface could improve soil quality and
productivity through favorable effects on soil properties (Lal and
Stewart, 1995). The beneficial effects of straw or residue mulch on
soil organic carbon, water retention, and ratio of water-stable
aggregates have been highlighted in previous studies (Havlin et al.,
1990; Duiker and Lal, 1999). In a long-term field study, Mulumba
and Lal (2008) found that placing crop residues on soil surface
shaded the soil, increased available water, and enhanced soil
aggregate stability.
Burying a straw layer in soil also has potential positive effects
on soil water and salt management (Sembiring et al., 1995;
Tumarbay et al., 2006; Wang et al., 2012). Straw layer serves as a
salt accumulation barrier, inhibiting the movement of salts from
the subsoil and/or shallow groundwater to the topsoil (Qiao et al.,
2006a; Chi et al., 1994). In simulation studies, Cao et al. (2012) and
Tumarbay et al. (2006) demonstrated that applying straw layer
limited grounder water evaporation and reduced salt built-up in
the topsoil. During irrigation, a buried straw layer improved the
water storage capacity of the topsoil by retarding the infiltration
rate (Zhang et al., 2010; Wang et al., 2011). Since the straw layer
extends soil water residence time in the layer above, it might
maximize the dissolution of soluble salts in the soil as the water
moves down the profile, thus improving the salt leaching efficiency
(Zhang et al., 2009). Other benefits of straw layer buried deeply in a
saline soil as reported by other researchers include reductions in
soil pH and bulk density and increases in soil organic matter, and
plant earliness (Zhao et al., 2003; Li et al., 2009; Fan et al., 2012;
Wang et al., 2012).
Currently, plastic film mulching has been widely used to
increase sunflower yield in saline soils. However, burying a straw
layer in the soil or combining straw layer burial with plastic film
mulching is rarely performed in salt-affected fields. Also there is
scanty information on the comparative effects of straw layer burial
and plastic film mulching with the same crop in an irrigated saline
soil. Therefore, a three-year field trial was conducted to explore the
effects of burying straw layer and mulching with plastic film on
sunflower production. We hypothesized that the dynamics of soil
moisture and salinity, and their distribution in the soil profile as
well as sunflower yield and yield components would be affected by
burying a straw layer.
2. Materials and methods
2.1. Study area and site characterization
Field experiments were conducted from October 2010 to
September 2013 at the experimental station of the Management
Department of Yichang Irrigation Sub-district (41
040
N, 108
000
E,
1022 m ASL) in Wuyuan County, Inner Mongolia, China.
The study area has a typical arid continental climate that is very
cold in winter with little snowfall and very dry in summer with
little rainfall. The mean annual precipitation in the region is
approximately 170 mm, occurring mainly between July and
August. The mean annual evaporation is approximately
2068 mm, being 11 times the value of annual rainfall. The annual
average temperature is 8.1
C, with monthly averages of 23.76
C in
July to 10.08
C in January (Wu et al., 2008). The groundwater table
at this site varied from 1.2 to 2.6 m, with a salt concentration of 1.5–
1.8 g L1
. The experimental soil was silty loam with a pH of 8.8 and
contained 11.1 g kg1
organic matter, 35.6 mg kg1
available N,
6.4 mg kg1
available P and 161 mg kg1
available K at the 0–10 cm
layer.
The daily precipitation and pan evaporation data during the
sunflower growing seasons are provided in Fig. 1. The total
precipitation during the experimental period was 54.5 mm in 2011
(27 May–24 September), 238.6 mm in 2012 (5 June–3 October), and
64.8 mm in 2013 (2 June–30 September), accounting for 68.7,
64.3 and 59.0% of annual precipitation, respectively. The first and
third seasons were drier than average (145.2 mm) for the
corresponding period of the previous 10 years, whereas the
second season was wetter. There were four heavy rainfall events
(daily precipitation intensity 20 mm) before 60 DAS in the second
season. Although no irrigation was applied during the growing
period of each season, abundant rain water was received in the
trials in the wet year.
Pan evaporation also varied greatly among the three experi-
mental seasons (Fig. 1). The total pan evaporation was 1330.9 mm
in 2011, 1019.1 mm in 2012, and 1238.2 mm in 2013. Daily
fluctuations in pan evaporation were large, ranging from 1 mm
to 26 mm. Generally, the pan evaporation declined during the
experimental period, and a higher evaporation occurred during the
first half of the growing season. Therefore, more water loss to
evaporation occurred in the early experimental period.
2.2. Experimental design and filed management
Experiment was conducted in field micro plots from October
2010 to October 2013. The field with an area of 48 m2
(6 m 8 m)
was divided into three blocks; each block had four treatments,
Fig. 1. Daily precipitation and pan evaporation during the growing period of
sunflower in 2011 (a), 2012 (b) and 2013 (c).
364 Y. Zhao et al. / Soil Tillage Research 155 (2016) 363–370

3. giving a total of 12 plots (2 m 2 m) arranged in a randomized
complete block design. The treatments were: (i) bare ground (BG),
(ii) mulching with plastic film 1–2 days before sowing each year
(PM), (iii) burying a straw layer at a depth of 40 cm at the beginning
of experiment (SL), and (iv) combined use of plastic mulch and
buried straw layer (PM + SL). A sketch of the PM + SL plot is shown
in Fig. 2.
Each plot was insulated by double-plastic sheets buried to a
100 cm depth relative to the soil surface to minimise the effects of
lateral water and salt movement between plots. The upper 40 cm of
soil in the SL and PM + SL plots was removed at intervals of 20 cm
depth and placed in different positions before uniformly placing
the (air-dried) chopped maize straw to a thickness of about 5 cm
(equal to 12 t ha1
). The dug soil was refilled layer-by-layer and
then flattened with a harrow to a bulk density consistent with the
initial value. Plots were flood-irrigated in later October at
approximately 0.6 m3
per plot. To leach soluble salts for sunflower
germination in each growing season, a second irrigation (0.6 m3
plot1
) was applied approximately 10 d before sowing. The straw
layer burying operation was done once at the beginning of the
experiment.
At sowing, the plots were ploughed to a depth of 15–20 cm and
manually harrowed to a physically acceptable mellowness.
Complete fertilizer was applied at 180 kg ha1
N, 120 kg ha1
P2O5 and 75 kg ha1
K.
Sunflower (cv LD 5009) was seeded at a row spacing of 60 cm
and density of 49,000 plants per hectare. Seeding was manually
done on 28 May 2011, 8 June 2012 and 2 June 2013 and the crop was
harvested in September each year. After harvest and removal of
sunflower stalks, flood irrigation was done using the same pre-
sowing water volume per plot. Other management practices were
performed according to local agronomic practices.
2.3. Sampling and measurements
Weather data were obtained from the weather station at the
experimental site. During the sunflower growing seasons, soil
samples were collected to a depth of 40 cm at 20-cm increments at
approximately 15 days intervals. Sampling was delayed 1–2 days
when there was rainfall on sampling day. Soil sampling points
were chosen from one of the two plant rows per plot. Similarly,
yearly soil samples were taken to a depth of 100 cm at 20-cm
increments at sowing and harvesting of sunflower. The samples
were ground fine enough to pass through a 2 mm sieve and
analysed for salt contents. Soil salinity was measured from the
electrical conductivity of 1:5 soil water extract. Salt contents were
then inferred from measured electrical conductivity values on per
cent basis according to Pang et al. (2010).
At harvest, sunflower heads were manually removed. The head
diameters were determined in five randomly selected plants with a
string and a ruler. The above ground biomass was determined
gravimetrically by oven-drying the samples at 105
C for 30 min,
and then at 65–75
C for 48 h. Fresh seeds were oven-dried at 50
C
for 2 d and weighted to determine the average seed yield and 100-
seed weights (Baydar and Erbas, 2005).
2.4. Calculation of salt accumulation
To determine the effect of straw layer on salt control in the off
season, samples at 20-cm increments up to a depth of 100 cm were
taken after autumn irrigation (22 October 2010, 20 October
2011 and 18 October 2012) and before spring irrigation (9 May
2011, 25 May 2012 and 18 May 2013). Salt accumulation in soil
(SAS) was calculated by subtracting the value of salt in autumn
after irrigation (SSA) from the corresponding value in the next
spring before irrigation (SSS). The amount of salt per area
(Mg ha1
) of each horizon was calculated as the respective soil
salinity (g kg1
) multiplied by the bulk density of the soil and the
layer thickness.
2.5. Statistical analysis
All data within each individual year were analyzed using the
analysis of variance (ANOVA) procedure to test the effects of the
Fig. 2. A sketch of the plot with plastic film mulch and straw layer burial (PM + SL).
Fig. 3. Soil water content in the 0–40 cm soil layer under BG, PM, SL and PM + SL
treatments during the three sunflower growing seasons: 2011 (a), 2012 (b) and 2013
(c). BG: bare ground; PM: plastic mulch; SL: straw layer burial at 40 cm depth;
PM + SL: combined plastic mulch and straw layer burial. Values are means of three
replicates standard deviation.
Y. Zhao et al. / Soil Tillage Research 155 (2016) 363–370 365

4. treatments on the measured parameters. Mean comparisons were
performed using the Fisher’s LSD (the least significant difference)
test at P 0.05. The analysis was conducted using the SPSS
13.0 program.
3. Results
3.1. Soil water
The dynamics of soil water within the 0–40 cm soil layer depth
differed among treatments during the three growing seasons
(Fig. 3). In 2011, both the SL and PM + SL treatments had greater soil
water content than the BG and PM treatments before 49 DAS.
Thereafter, soil water decreased sharply under PM + SL at later
growth stages (Fig. 3a) but only changed slightly in other
treatments. Soils in the PM plots retained more water than BG
during the whole growing period but this was not significant. In
2012, the soil water content fluctuated according to rainfall
(Fig. 3b). For all the plots, soil water dropped rapidly at 47 DAS, but
increased dramatically at 61 DAS and declined again after that. The
PM + SL, SL and PM generally retained more water than BG in the
whole growing season, except for a lower water content under SL
and PM plots at 47 and 76 DAS. Further, the soil water content was
slightly greater after the first two rainfall events under the PM+SL
treatment than under the other treatments. In 2013, the soil water
decreased sharply from 15 to 45 DAS but the SL and PM + SL
treatments retained more soil water than the BG and PM
treatments (Fig. 3c). Thereafter, the soil water was lower under
PM + SL than other treatments. From 45 DAS until harvest, there
was little change in soil water across treatments. Overall, the
mulched treatments had much more water than the un-mulched
treatments. Due to a rainfall event (16.6 mm) at 69 DAS, the soil
moisture in all plots increased at 74 DAS and then gradually
decreased at varying rates with time among the plots.
Soil water content within the entire 100 cm profile at sowing
indicatedthatthetopsoilofthestrawlayerplotsretainedmorewater
than controls (Fig. 4a–c). Compared to no straw layer plots (PM and
BG), the mean soil moisture of the two straw layer plots (PM + SL and
SL) at the upper 20 cm depth increased by 4.3% in 2011, 3.7% in 2012,
and 4.0% in 2013. Also, the subsoil (20–40 cm) water content of the
straw layer plots was higher than control plots. However, soils in the
control plots had more water than the plots with straw layer at
depthsbelow40 cmbutsignificantdifferenceswereobservedonlyin
2011. At harvest, soils in the PM + SL, SL and PM plots had more water
than BG at the upper 40 cm depth (Fig. 4d–f), but no significant
difference was found at the 0–20 cm depth in 2011. In the mulch
plots,therewasnoobviouschangeinsoilwaterbetween PM + SLand
PM at the upper 20 cm depth, whereas the values were lower under
PM + SL than under PM below 20 cm depths. In the non-mulched
plots, SL had more water in the soil profile than BG, especially at the
upper 40 cm depth.
Fig. 4. Distribution of soil water in the soil profiles at sunflower sowing and harvest
under BG, PM, SL and PM+SL treatments in 2011, 2012 and 2013. BG: bare ground;
PM: plastic mulch; SL: straw layer burial at 40 cm depth; PM + SL: combined plastic
mulch and straw layer burial. Values are means of three replicates standard
deviation.
Fig. 5. Salt content in the 0–40 cm soil layer under BG, PM, SL and PM + SL
treatments during the three sunflower growing seasons: 2011 (a), 2012 (b) and 2013
(c). BG: bare ground; PM: plastic mulch; SL: straw layer burial at 40 cm depth;
PM + SL: combined plastic mulch and straw layer burial. Values are means of three
replicates standard deviation.
366 Y. Zhao et al. / Soil Tillage Research 155 (2016) 363–370

5. 3.2. Soil salt
The variations in salt content within the 0–40 cm soil layer
among treatments are shown in Fig. 5. In 2011, the changes in the
salt content were small before 82 DAS, ranging from 2.5 to
4.4 g kg1
(Fig. 5a). Thereafter, the salt content increased rapidly up
to harvest, especially under BG and SL. Shortly after sowing, soils in
the PM + SL plots had the lowest salt content, being 18.9–48.1% less
than BG, 13.9–38.3% less than PM, and 19.9–49.9% less than SL
treatments, respectively; these differences were significant. The
salt content under PM was lower than BG, but differences were
significant only at 66 and 96 DAS. Also SL had 9.6–17.6% more salts
than BG before 33 DAS but increased it after that. In 2012, the
treatment effects on salt content were not as large as in 2011
(Fig. 5b) and temporal variations within the growing season were
negligible. The fluctuations in salt content leveled off mainly
because the site received an excessive rainfall during the growing
season. In 2013, the salt content in all plots increased from 30 DAS
to a peak at 62 DAS, and then decreased until 90 DAS (Fig. 5c). Like
the previous seasons, the salt content under PM + SL was lower by
21.0–42.5, 6.0–39.3, and 8.4–32.7% compared to the BG, PM and SL
treatments. In the corresponding straw burial plots, SL had a lower
salt content before 44 DAS when compared to the no straw layer
plots.
The salt profile (0–100 cm) showed that the contents in the
upper 40 cm depths were significantly lower under straw layer
plots than under no straw layer controls at sowing (Fig. 6a–c).
Particularly in 2012, the plots with straw layer (SL and PM + SL) had
lower salt contents down to 80 cm depth because of extra
rainwater (11.6 mm) received 5 days before sowing. Compared
with BG and PM, the salt content of the 0–20 cm and 20–40 cm soil
layers under PM + SL and SL decreased on average by 23.0 and 13.9%
in 2011, 26.2 and 21.5% in 2012, and 9.6 and 28.7% in 2013. After
sunflower harvest, the salt content in the topsoil (0–20 cm) layer
increased relative to the content at sowing (Fig. 6d–f), especially in
the non-mulch plots. Compared to BG, the topsoil salinity of PM
and PM + SL decreased by 35.8, 14.0 and 51.3% in 2011; 39.6 and
42.2% in 2012, and 34.2 and 31.4% in 2013. Also the salt content
under SL was lower than under BG. At depths below 20 cm, there
were no significant differences in soil salinity between BG and SL,
but the salinity was significantly higher under PM and PM + SL than
under BG and SL. Between the two mulch treatments, PM + SL had a
lower salt content than PM in the entire 100 cm soil profile.
3.3. Salt accumulation during the off season
The effect of straw layer burial on salt accumulation in soil (SAS)
during the off seasons is shown in Table 1. For each soil layer, the
salinity was significantly lower under SL than under BG. Conse-
quently, the SL treatment decreased the SAS during the non-growing
seasons, particularly in the 0–40 cm soil layer. In 2010–2011 for
example, the SAS in the 0–40, 40–100 and 0–100 cm soil layer under
SL was 94.4, 54.1 and 87.2% lower than that under BG. Significant
differences in the SAS between SL and BG were observed only in the
0–40 cmsoillayerduringthe2011–2012season.ComparedtoBG,the
SAS in the 0–40 and 0–100 cm layer under SL decreased by 21.3 and
10.3%; in contrast, the value under SL increased moderately in the
40–100 cm soil layer. There was also a positive effect of straw layer
burial in reducing SAS during 2012–2013, but no significant
Fig. 6. Salt distribution in the soil profiles at sunflower sowing and harvest under
BG, PM, SL and PM + SL treatments in 2011, 2012 and 2013. BG: bare ground; PM:
plastic mulch; SL: straw layer burial at 40 cm depth; PM + SL: combined plastic
mulch and straw layer burial. Values are means of three replicates standard
deviation.
Table 1
Salt accumulation (Mg ha1
) in the soil layers of 0–40, 40–100 and 0–100 cm under BG and SL treatments in the off season.
Depth
(cm)
Treatment 2010–2011 2011–2012 2012–2013
SSA SSS SAS SSA SSS SAS SSA SSS SAS
0–40 BG 19.6 a 29.6 a 10.0 a 22.1 a 28.8 a 6.7 a 18.9 a 22.0 a 3.0 a
SL 16.2 b 16.8 b 0.6 b 14.0 b 19.3 b 5.3 b 17.7 b 18.4 b 0.7 b
40–100 BG 9.7 a 11.8 a 2.2 a 9.5 a 9.8 a 0.2 a 8.0 a 10.6 a 2.6 a
SL 8.2 b 9.2 b 1.0 b 7.5 b 8.5 b 0.9 a 7.1 a 9.1 b 2.0 a
0–100 BG 29.2 a 41.4 a 12.2 a 31.6 a 38.6 a 6.9 a 26.9 a 32.6 a 5.6 a
SL 24.5 b 26.0 b 1.6 b 21.6 b 27.8 b 6.2 a 24.8 b 27.6 b 2.7 b
BG: bare ground; SL: burying of a straw layer at a depth of 40 cm.
SAS = SSS – SSA; SSA = salt content in autumn after irrigation, SSS = salt content in spring (following year) before irrigation, and SAS = salt accumulated in the off season. Means
within the same column followed by the same letter do not differ significantly (LSD, P 0.05).
Y. Zhao et al. / Soil Tillage Research 155 (2016) 363–370 367

6. difference occurredinthe 40–100 cmlayer. Alsosaltaccumulationin
the 0–40, 40–100 and 0–100 cm soil layer in the SL plots reduced by
77.2, 21.0 and 51.3% relative to the BG plots.
3.4. Sunflower yields
The effect of straw layer and plastic mulching on sunflower
yields and yield components is shown in Table 2. Compared to BG,
the seed yield of sunflower under PM, SL and PM + SL increased
25.7, 12.1 and 31.0% in 2011, 26.0, 12.19 and 31.9% in 2012, and 72.8,
11.6 and 85.9% in 2013. In addition, the biomass (above ground)
yield under PM, SL and PM + SL increased by 47.9, 12.9 and 58.8% in
2011;17.7, 4.9 and 24.9% in 2012, and 49.6, 11.6 and 60.6% in
2013 relative to BG. In general, the straw burial treatments
performed better than the respective no straw layer treatments.
Over the three years, the highest seed yield (3198 kg ha1
) and
biomass yield (13,730 kg ha1
) were obtained from PM + SL, which
were 51.9, 5.9 and 35.7%, and 39.0, 9.7 and 48.8% higher than yields
from BG, PM and SL, respectively. The higher seed yield under
PM + SL were attributed to larger yield components (Table 2). In
each season, there were no significant differences in the sunflower
yields and yield components between PM and PM + SL. The yields,
100-seed weight and head diameters were significantly lower
under SL than PM. However, when combined with plastic film
mulching, it had a large positive effect on plant growth.
4. Discussion
Crop growth usually suffers pressures from both drought and
salinity in saline soils. Therefore, to increase yield, it is not only
important to manage the salt level but also to increase soil water
storage. Burying a straw layer in the soil has a significant effect on
soil water distribution. In silty loam soils, the ratio of water
infiltration after irrigation was lower in the straw burial plots than
in the control plots based on our field observation. Similarly, Qiao
et al. (2006a) and Cao et al. (2012) showed that burying a straw
layer in a sandy loam soil retarded the ratio of water infiltration
due to over-burden weight-compaction effect. Consequently, the
buried straw extended water residence time in the soil layer above,
and thus retained more water in the topsoil layers at sowing
(Fig. 5a–c). This was similar to the reports of Zhang et al. (2010) and
Wang et al. (2011) that straw burial increased the water content of
the topsoil by 0.5–3.1%. Our recent soil column study with soils
from this experimental site (Zhao et al., 2013) further confirmed
that the straw layer burial increased the water content of the
topsoil by 4.85%.
During the sunflower growing season, however, the straw
burial plots had significantly lower water contents than the no
straw layer control plots in the later growth period, especially in
2011. There were possibly three reasons for the water depletion.
Firstly, in the straw burial plots, water recharge from deep soil
profile might be less than that in the plots without straw layer
since the soil capillarity was impaired by the straw layers. Thus,
there was no other source of soil water unless from rainfall or
irrigation. Secondly, the lower salinity and higher moisture in the
straw burial plots enhanced sunflower growth, and thus led to a
higher evapotranspiration and consumption of soil water by the
crop. Thirdly, the soil water was possibly lost from the un-mulched
part of soil surface under high evaporation. Nevertheless, there was
a consistently higher soil water in the straw burial plots in 2012
(Fig. 4b), indicating that the buried straw layers can conserve more
rainwater and thus help retain soil water after rainfall events.
Reducing salt in the root zone is very critical to profitable crop
yield in saline soils. The current study showed that the salt content
in the upper 40 cm depth was significantly reduced with straw
layer burial at sowing (Fig. 6a–c). This could be explained by the
high water contents observed in the topsoil layers, which
enhanced the salt leaching efficiency. Zhang et al. (2009) reported
that the application of 5% (mass fraction) wheat straw into the soil
increased the efficiency of salt leaching from 3% to 25%. Feng et al.
(2000) also demonstrated that high soil water helped to promote
ion exchange and absorption, and increased the total dissolved
salts. At sowing, the lower salt content in the upper soil layer under
straw burial treatments implies that the plants would have less salt
stress at emergence and early growth period.
In this experiment, the lowest salt content in the 0–40 soil layer
was always from the PM + SL plots (Fig. 5) throughout the growing
season, particularly in the first year. This was mainly because the
buried straw layer interrupted the continuity of capillary
movement of salt from deep soil layers and served as a barrier
against salt accumulation. Based on soil column studies, Chi et al.
(1994) and Tumarbay et al. (2006) reported that straw layer burial
could inhibit the movement of salts from the subsoil to the topsoil.
More recent studies conducted in saline fields also showed the
beneficial effects of buried straw layers on controlling salt built-up
in the root zone (Li et al., 2012; Wang et al., 2012; Fan et al., 2012).
Thus, the straw layer supported a desalinated layer which is
beneficial to plants. At the early growth period, the SL treatment
also decreased the salt when compared with BG. After that,
however, reductions in salt accumulation under SL were not
significant. This can be explained by the massive water evaporation
losses from the naked surface soil which led to a rapid salt
Table 2
Sunflower seed and biomass (above ground) yields and yield components as affected by straw layer and plastic mulch.
Year Treatment Yields Yield components
Seed (kg ha1
) Biomass (kg ha1
) 100-seed weight (g) Head diameter (cm)
2011 BG 1692 c 5351 d 15.7 b 9.2 c
PM 2127 a 7916 b 16.8 a 12.7 ab
SL 1897 b 6043 c 16.4 a 11.4 b
PM+SL 2217 a 8497 a 16.8 a 13.7 a
2012 BG 2256 c 8919 d 13.1 a 15.7 b
PM 2843 a 10500 b 13.5 a 16.2 ab
SL 2531 b 9358 c 13.2 a 15.9 b
PM+SL 2976 a 11138 a 13.6 a 16.9 a
2013 BG 2367 b 13419 b 13.4 b 15.6 b
PM 4089 a 20071 a 16.1 a 17.2 a
SL 2642 b 14979 b 13.6 b 15.7 b
PM+SL 4400 a 21554 a 16.4 a 17.4 a
BG: bare ground; PM: plastic mulch; SL: burying of a straw layer at a depth of 40 cm; PM + SL: combined plastic mulch and straw layer burial.
Means within the same column followed by the same letter do not differ significantly (LSD, P 0.05).
368 Y. Zhao et al. / Soil Tillage Research 155 (2016) 363–370

7. accumulation in the topsoil. Therefore, surface mulch is necessary
to enhance the effects of straw layer burial.
In terms of salt control, there was a significant difference in
straw burial effects between the growth and fallow periods. This
might be attributed, in part, to the fact that the higher soil water
and lower salt content under SL stimulated plant growth, and then
increased salt accumulation in the root zone following an
increased water uptake by plants (Bresler et al., 1982). Neverthe-
less, the difference in salt control between the straw burial and no
straw layer control treatments decreased with time. This was
because the beneficial effectiveness of straw layer decreased with
its natural decay since there was no straw burial in the following
year. Further studies are needed to investigate the effective life
span of the buried straw layer.
The benefits of plastic mulch in reducing water loss by
evaporation, decreasing salt accumulation, conserving soil mois-
ture, promoting crop growth and increasing crop water use
efficiency have been widely reported (Xie et al., 2005; Deng et al.,
2006; Mahajan et al., 2007; Chakraborty et al., 2008; Liu et al.,
2009). Lower evaporative water loss contributed to the lower salt
concentration in the topsoil. In our experiments, the plastic mulch
plots had much lower salt content in the 0–40 cm soil layer than
the no-mulch control (Fig. 5). Compared to the treatment with
straw layer burial only (SL), plastic mulch (PM) had lower salt
content in the middle and later period of sunflower growing
season. However, both PM and SL had much higher salt than
PM + SL. These results indicate that the individual use of plastic
mulch performed better than the individual use of straw layer
burial for reducing salt accumulation in the root zone, but the
effectiveness was greater when both treatments were combined.
In the PM + SL plots, a higher soil water and lower salt content
promoted sunflower growth, as indicated by the consistently
higher seed and biomass yield relative to other treatments
(Table 2). Even in 2011 when there was water depletion in the
later growth period under the PM + SL plots which may have had
minor negative effects on plants growth, it still produced the most
yields. This increase in yields could be attributed to the beneficial
effects of mulching with plastic film on soil water and thermal
status, which thus might have shortened the duration of growth
stages. Although the salt content was higher under SL than under
BG in some days during the growing period, sunflower yield and its
components under SL were higher than under BG. This was likely
because of more water storage and lower salt content during the
early growth period due to the straw layer (Qiao et al., 2006b),
which benefited stand establishment and plant growth. The SL
produced significantly lower yield than PM mainly due to elevated
salt content and low soil water during the middle and later growth
periods. However, the integration of straw layer with plastic mulch
was more beneficial to sunflower in saline fields than the single use
of straw layer or plastic mulch.
5. Conclusions
Controlling slat accumulation in the root zone is critical to
increasing crop yields in saline soils. Burying a straw layer in the
soil can reduce the salt content in the topsoil and alter salt
distribution in the profile at sowing. However, its effectiveness was
less than plastic mulch during the sunflower growing period.
Combined plastic mulch with straw layer burial created the lowest
salt content in the 0–40 cm soil depth and the highest sunflower
yields; also, adding a straw layer increased the soil water holding
capacity. Therefore, combining plastic mulching with straw layer
burial can be an effective field management practice for growing
sunflowers in saline soils of the Hetao Irrigation Distract of Inner
Mongolia, China.
Acknowledgements
The authors are thankful to Prof. Tusheng Ren of China
Agricultural University for the critical review and corrections to
the paper. This research was funded by the National Natural
Science Foundation of China (Grant No.: 31471455 and 31000692),
the Institute of Agricultural Resources and Regional Planning,
Chinese Academy of Agricultural Sciences (Grant No.: 2015-25),
and the Special Fund for Agro-scientific Research in the Public
Interest (Grant No.: 200903001).
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