close

Вход

Забыли?

вход по аккаунту

?

s11104-017-3467-7

код для вставкиСкачать
Plant Soil
https://doi.org/10.1007/s11104-017-3467-7
REGULAR ARTICLE
Effects of irrigation management during the rice growing
season on soil organic carbon pools
Ying Xu & Ming Zhan & Cougui Cao & Junzhu Ge &
Rongzhong Ye & Shaoyang Tian & Mingli Cai
Received: 29 November 2016 / Accepted: 15 October 2017
# Springer International Publishing AG 2017
Abstract
Objectives When addressing water shortage in rice production, we need to consider the influence of water-saving
irrigation methods on soil organic carbon stocks (SOC).
Methods A typical rice?rapeseed rotation was irrigated
using 3 different strategies in rice growing season over a
3 year period: continuous flooding (CF), alternate wetting
and drying irrigation (AWD), and rain-fed with irrigation
only during drought periods (RFL). Soil samples were
Responsible Editor: Ute Skiba
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11104-017-3467-7) contains
supplementary material, which is available to authorized users.
Y. Xu : M. Zhan (*) : C. Cao : S. Tian : M. Cai
MOA Key Laboratory of Crop Ecophysiology and Farming
System in the Middle Reaches of Yangtze River, College of Plant
Science and Technology, Huazhong Agricultural University,
Wuhan 430070, People?s Republic of China
e-mail: zhanming@mail.hzau.edu.cn
Y. Xu
Hubei Key Laboratory of Waterlogging Disaster and Agriculture
Use of Wetland/Engineering Research Center of Ecology and
Agricultural Use of Wetland, Ministry of Education/College of
Agriculture, Yangtze University, Jingzhou 434023, People?s
Republic of China
J. Ge
College of Agronomy and Resources and Environment, Tianjin
Agricultural University, Tianjin 300384, People?s Republic of
China
R. Ye
Department of Land, Air, and Water Resources, University of
California Davis, Davis, CA 95616, USA
separated into fractions of different stability using sequentially fractionation methods.
Results Compared with CF, AWD had no influence on C
concentrations in physicochemically protected particulate
organic matter in microaggregates (iPOM) at the 0?20 cm
soil depth; however, it significantly increased the iPOM
percentage in the bulk soil mass at the 5?10 cm soil
depth. The RFL method lowered C stocks in iPOM at
0?20 cm soil depth, in comparison with CF and AWD,
which was mainly due to its significant reduction in C
concentrations in iPOM and the iPOM proportion in the
bulk soil mass. The different water regimes had no effect
on C stocks protected in silt and clay in microaggregates
and unprotected free light POM. However, when considering the whole soil profile (0?20 cm), RFL significantly
decreased total SOC stock, whereas there was no difference between CF and AWD.
Conclusions A moderate reduction in irrigation water under AWD strategy had little impact on SOC pools, thus, it
could be considered an alternative water regime in balancing
saving water and maintaining SOC stability.
Keywords Water-saving irrigation . Rice paddy fields .
Soil organic carbon . Microaggregates .
Physicochemically protected particulate organic carbon .
Mineral-associated organic carbon
Introduction
Soil organic carbon (SOC) is a crucial component of soil
quality and productivity. It also plays an important role
Plant Soil
in mitigating climate change through its role as the
largest organic C reservoir (Lal 2004). The SOC can
be partitioned into various functional pools with a range
of degradability and turnover rates (Six et al. 1998;
Sollins et al. 1996). Quantifying and characterizing
these pools is essential to identify the distribution, transformation, and storage of SOC and its response to
changing environment and climate (von L黷zow et al.
2007). The SOC is retained and stabilized in soils
through physical protection (especially in
microaggregates) (Six et al. 1998; Tian et al. 2015),
adsorption on clay surface, and other biochemical mechanisms (von L黷zow et al. 2006; O'Brien and Jastrow
2013), all of which cause SOC to become unaccessible
for decomposition. Correspondingly, SOC can be artificially differentiated into various pools (Gulde et al.
2008; Six et al. 1998), and this approach has been used
to access its short- and long-term responses to field
management (DeGryze et al. 2004; Oorts et al. 2007),
with previous attention mainly given to long-term responses (Huang et al. 2010; Yan et al. 2013; Yu et al.
2012). Therefore, sequential density fractionation by
particle size implies the separation of the total organic
matter into pools that are thought to be more functionally homogeneous with respect to physicochemical
properties and turnover rates (DeGryze et al. 2004; Six
et al. 2002). Moreover, this approach allows better estimation of SOC distribution in various pools (Gunina
et al. 2015), and evaluation of SOC stability (Brown
et al. 2014), further providing a considerable insight into
the mechanisms underlying soil organic matter (SOM)
responses to ecosystem management (Grandy and
Robertson 2007).
Paddy fields are widely considered C sinks with a
high potential for C sequestration (Huang et al. 2012);
therefore, the accumulation and stabilization of SOC in
paddy soils is of strong research interest (Shang et al.
2011; Weller et al. 2016). In China, rice is the main
cereal crop, and approximately 70% of water used in
agriculture is consumed by rice production alone
(Zhang 2007). However, water is becoming scarce as a
result of increasing usage by the industrial, domestic,
and municipal sectors (Xiong et al. 2010). Thus, it is
imperative to develop techniques to increase water use
efficiency without causing a reduction in rice yields.
Some water-saving practices have already been
exercised and studied in China, such as intermittent
irrigation, midseason flooding and drainage with intermittent irrigation (Peng et al. 2011; Zou et al. 2007),
alternating wetting and drying irrigation (Xu et al. 2015;
Yao et al. 2012), and rain-fed cultivation of droughtresistance rice varieties (Luo 2010; Xu et al. 2016).
Changing the water regime not only influences rice
yield and water use efficiency, but also alters soil moisture conditions (Sacco et al. 2012; Zhao et al. 2015),
affecting soil redox potentials (Eh) and the various
biogeochemical processes that underlie the transformation and availability of soil nutrients and C turnover
(Miniotti et al. 2016; Tian et al. 2013b). An earlier study
by Yang et al. (2005) who reported that labile organic C
fractions of the organically treated paddy soil under the
water regimes of continuous waterlogging were significantly lower, as compared with alternate wetting and
drying after a 4 year field experiment. However, little
research has been conducted on the impacts of water
management techniques on accumulation and stability
of SOC in paddy soils.
A continuous rice?rapeseed rotation is a major
cropping system in the middle reaches of the Yangtze
River in Central China (Xu et al. 2016), where the
planted rice and rapeseed account for approximately
39 and 48%, respectively, of their total acreages across
China (FAO 2014). Although rainfall is abundant in this
region, drought often occurs in July and August and
therefore water shortage remains a major problem for
rice production because of this uneven distribution of
rainfall though the year. Some water-saving irrigation
techniques include alternate wetting and drying irrigation (AWD) and aerobic rice are exercised by farmers in
this region (Yao et al. 2012). Nevertheless, to our knowledge, no studies have focused on the effects of watersaving irrigation during the rice-growing season on
SOC pools in Central China. Valuable information is
needed to optimize water management oriented to maintain SOC stock for the rice-rapeseed rotation systems in
Central China. We hypothesized that stabilization of
SOC associated with physicochemical protection in soil
aggregates in traditional flooded paddy soil would be
changed by the application of a water-saving irrigation
practice. To test this hypothesis, we applied 3 water
regimes during the rice growing season of a rice?rapeseed rotation system, and included the local popular
water saving irrigation regime (alternate wetting and
drying irrigation, AWD), the combination of rainfed
drought resistant rice varieties with irrigation only during drought periods (RFL), and the traditional flooding
strategy. After the 3rd year?s rice harvest, we quantified
and compared the distribution of SOC in the various
Plant Soil
pools with different stability and their sizes in paddy
soils. This information is required to understand the
SOC dynamics and developing water-saving irrigation
practices which maintain stabilization of SOC in paddy
soil.
Materials and methods
Site descriptions
The study site was located at an experimental farm
(30�?N, 115�?E) of Huazhong Agricultural University in the town of Huaqiao, Hubei Province, China.
This region has a mid-subtropical monsoon climate,
with a total annual precipitation of 1437 mm and mean
temperature of 17.5 癈 across the past 30 years. Records
from the local meteorological station showed that total
annual precipitation was 1477, 849 and 1302 mm in
2012, 2013 and 2014 (the experimental period), respectively. Further information on monthly mean temperature and accumulated precipitation for this period is
shown in Online Resource 1. The field was cultivated
with rapeseed and rice rotations for nearly a decade. The
soil, derived from the alluvial soil of Yangtze River, is a
subtropical sandy loam classified as Gleysol (FAO classification). The main soil properties (0?20 cm soil
depth) at the start of field experiment were as follows:
pH of 7.0 (extracted by H2O; soil: water = 1:2.5); total
SOC of 14.25 g kg?1; total N of 1.56 g kg?1; nitrate
(NO3?) of 8.48 mg kg?1; ammonium (NH4+) of 12.6 mg
kg?1; total phosphorus (P) of 0.52 g kg?1; available P of
9.56 mg kg?1 (extracted by NaHCO3); available potassium (K) of 93.72 mg kg?1 (extracted by
CH3COONH4); and a soil bulk density (BD) of 1.27 g
cm?3.
Experimental design
A rice?rapeseed rotation was practiced during the experimental years from 2012 to 2014. Detailed information of sowing and harvesting dates is shown in Online Resource 2. After the rapeseed harvest on the 18th
of May 2012, the land was ploughed and puddled after
being soaked for 4 days. Then the beds (1.5 m width)
and furrows (0.3 m width and 0.25 m depth) were built
by machine before sowing the rice. The beds and furrows were kept in use for the no-till rice?rapeseed
rotation in the following experimental cropping seasons.
Rice was directly sown on the beds in early June each
year, and the field was flooded with 1?2 cm of water
until the rice reached the 3-leaf stage. Then the 3 selected water management practices were implemented as
follows: (1) continuous flooding (CF): continuously
flooded with 2?5 cm water, and irrigation stopped 10?
15 days before rice harvest (water naturally disappeared); (2) alternate wetting and drying irrigation
(AWD): irrigate the plots to full furrow once no standing
water is visible in the furrow, but the soil is still wet. This
cycle was repeated until irrigation stopped 10?15 days
before harvest; and (3) rain-fed with limited irrigation to
avoid serious drought (RFL): no irrigation was implemented except during fertilizer application and when
serious drought occurred (the soil has dried out and rice
leaves are wilting).
Different irrigation regimes were established in a
randomized design with 3 replications. Each plot was
3.6 � 8.5 m in size, surrounded by ridges (25 cm high).
Strong black plastic film was used to cover the whole
ridge to prevent lateral water movement. The ditches
between the ridges of the plots were 30 cm wide for
isolation. Each plot was irrigated independently by
pumping water. The amount of irrigation for each plot
was recorded by a water meter installed on the pump. A
detailed record of the average irrigation and total water
input (including rainfall) in each rice season is presented
in Online Resource 2. Irrigation water input for AWD
and RFL was 45 and 75% lower than for CF across the
3 years of rice seasons, respectively.
Rice seeds, Hanyou3 (Oryza sativa L. subsp. indica),
a three?line hybrid rice variety that is drought resistant
and is available to farmers for commercial use (Luo
2010), were sown manually on beds at a spacing of
13 � 30 cm, with 3?4 seeds per hill. After the rice was
harvested, the rape cultivar of Huashuang5 (Brassica
napus L.) was manually broadcasted in each plot with
no-till practices, then thinned out to a density of 270,000
seedlings ha?1. The same fertilization rates (210, 150, and
225 kg ha?1 of N, P2O5, and K2O, respectively) were
applied for all treatments during each rice season. During
each rapeseed?growing seasons, compound fertilizer
(N:P2O5:K2O = 15%:15%:15%) of 750 kg ha?1 was
broadcasted as basal fertilizer for each plot. Detailed
fertilization plans for the rice seasons and rapeseed seasons from 2012 to 2014 can be found in Xu et al. (2016).
For all plots, rice straws and rapeseed stalks were cleared
out soon after the harvest, and their stubbles (about 5 cm
above ground) remained in the field.
Plant Soil
Soil sampling
Five soil samples were randomly collected from each
plot with a soil corer (inner diameter 7 cm) at 0?5, 5?10,
and 10?20 cm depth soon after rice harvest in 2014. The
5 soil cores were then bulked, gently homogenized after
the removal of visible plant materials and air-dried. A
subsample was then used for SOC fractionation, while
another was sieved (0.149 mm) and used for the quantification of total SOC. Soils were also simultaneously
collected for the determination of BD as described by
Bao (2000).
Isolation of SOC fractions
The fractionation sequence is shown in Online Resource
3. Aggregates were separated using the dry-sieving
method described by Gartzia-Bengoetxea et al. (2009).
Air-dried soils were placed in the top of a nest of sieves
mounted on Retch AS200 vibratory sieve shaker
(Retsch Technology, D黶seldorf, Germany). Sieves
were shaken (amplitude 1.5 mm) for 2 min to separate
soil into the following aggregate-size classes: >2000 ?m
(large macroaggregates, LM), 2000?250 ?m (small
macroaggregates, SM), 250?53 ?m (microaggregates,
Mi), and <53 ?m (free silt and clay).
The different aggregates were further fractionated
into subfractions using a modified method of Six et al.
(1998), Six et al. (2000) and Yu et al. (2012). Fifty
grams of LM, SM, and Mi samples were placed into
500-ml centrifuge bottles, followed by additions of
150 ml of 1.85 g cm?3 ZnBr solution. The bottles were
inverted 10 times, incubated at room temperature for
20 min, and centrifuged at 2500 rpm for 30 min. The
resulting supernatant was filtered with a 600-mesh
sieve. The extraction procedures were repeated 3 times
to obtain the unprotected free light particulate organic
matter (fPOM) (material <1.85 g cm?3).
After the removal of fPOM, the remains in the centrifuge bottles from LM and SM aggregates were immersed in deionized water on top of a 250-?m sieve and
shaken with 50 glass beads (side to side; 120 rpm) until
the LM and SM were completely disrupted and only
coarse POM (>250 ?m) remained on the sieve. Regulated continuous deionized water flow passed over the
apparatus ensured that microaggregates within macroaggregates (occluded microaggregates, Mi) were not
subjected to further shaking and were minimally broken
up. Subsequently the samples were sieved through a
53-?m sieve to obtain the Mi (250?53 ?m), and the free
silt + clay sized fraction (free-SC; <53 ?m). The released occluded microaggregates from the LM and SM,
and Mi fractions were dispersed in sodium
hexametaphosphate (0.5%, w/v) solution and shaken
for 18 h to completely disperse fractions. Finally, the
samples were sieved through 53-?m sieves to obtain the
intra-microaggregate POM (iPOM; 250?53 ?m), and
silt + clay sized fraction within microaggregates (intraSC; <53 ?m).
All fractions were placed in pre-weighed aluminum
trays, oven dried at 60 癈 until constant weight,
weighed, and ground for further C and N analysis.
Organic C and N concentrations of bulk soils and fractions were measured by an elemental analyzer
(VarioMax CNS, Elementar, Germany). Since all samples had little or no carbonate (inorganic C) content, the
measured C concentrations can be considered to represent the organic C concentrations of the analyzed
fractions.
All fPOM, iPOM, intra-SC and free-SC derived from
the fractionation procedure were shown in Online Resource 3. The POM (fPOM and iPOM) and SC (intraand free-SC) fractions originating from the different
aggregate size classes are considered to have the same
functional features in the SOC pool (fPOM represents
the labile SOC pool, while, iPOM, intra-SC and free-SC
were considered as the intermediate and passive SOC
pool, respectively). Therefore, in our study, data from all
fPOM, iPOM, intra-SC and free-SC from LM, SM and
Mi aggregates classes were combined.
Other measurements
At maturity, grain yields of rice and rapeseed were
measured from a 3 m2 area in each plot and the final
rice yield for all treatments was adjusted to a standard
moisture content of 0.14 g H2O g?1 fresh weight (Yao
et al. 2012). Moreover, 6 subsamples of the rice harvest
and a 1 m2 area of rapeseed plants in each plot were
randomly sampled and oven-dried at 85 癈 to a constant
weight to obtain the aboveground biomass. The soil
water content (SWC, m3 m?3) at a 5?cm depth was
monitored (6 points in each plot) using a ProCheck
digital sensor (Decagon Devices, Pullman, WA, USA).
The SWC were measured 11 to 15 times (about 7? to
10?days interval) in the rice growing seasons and 9 to
12 times (about 10? to 15?days interval) in the rapeseed
growing seasons. Soil Eh was measured at a depth of
Plant Soil
10 cm with a portable Eh meter (FJA-5, Nanjing ZhuanDi Instrument & Equipment CO., LTD. Nanjing, China)
3 times at tillering, booting, filling, and mature stages of
rice in 2013, respectively.
Calculations and statistical analysis of the data
Bulk SOC stocks (g C m?2) in the 0?5, 5?10, and 10?
20 cm depths were calculated as follows:
SOC stocks � D BD SOC 10
�
where D is the thickness (cm) of the soil layer, BD is the
bulk density (g cm?3), and SOC is the SOC concentration (g C kg?1 soil) of each soil layer.
Stocks of SOC (g C m?2) in each fraction of the 0?5,
5?10, and 10?20 cm depths were calculated as follows:
Stocks of SOCi � D BD SOC i W i 10
�
where SOCi is the SOC concentration of the ith size
fraction (g C kg?1 fraction), and Wi is the proportion
of the ith size fraction in total fractionated soil mass (%).
The C:N ratios of the bulk soil and each fraction
(fPOM, iPOM, intra-SC and free-SC) were computed
by dividing the SOC stock by the soil organic nitrogen
stock.
Fig. 1 Changes in the soil water content (m3 m?3) under various
water regimes during the cycles of rice?rapeseed rotations from
2012 to 2014 in Huaqiao, China. CF, continuous flooding; AWD,
alternate wetting and drying irrigation; RFL, rain-fed with limited
irrigation to avoid serious drought. n is the soil water content
number of the three water regimes during crop seasons. In box
All data were analyzed as a complete randomized
design using the SAS 9.0 statistical software (SAS Institute, Cary, NC) for analysis of variance with the
generalized linear model procedure. The effect of water
regime on SWC, crop production, BD and Eh were
tested by one?way ANOVA followed by the Student?
Newman?Keuls test, and the data are presented as
means of 3 replications. Water regime and size classes
were considered to be fixed effects, whereas replicates
were considered to be a random effect. When significant, differences among treatments and fractions were
identified at the 0.05 probability level of significance
using the Student?Newman?Keuls test, and the results
are given as the means of 3 replications � standard error.
Results
Soil water content and crop production
The SWC decreased with decreasing irrigation and obvious
differences were found among the CF, AWD and RFL
treatments during the 3 rice growing seasons (Fig. 1). The
average SWC over the whole study period was 0.39 m3 m?3
at CF plots, and was reduced to 0.35 m3 m?3 at the AWD
plots and to 0.24 m3 m?3 at the RFL plots. The RFL
plots, center values are medians, solid lines indicate variability
outside the upper and lower quartiles, and dots denote outliers.
Different lower?case and upper?case letters within the same crop
season colmn indicate significant differences at the 0.05 and 0.01
levels by the Student?Newman?Keuls test, respectively
Plant Soil
treatment effected the SWC in the following rape growing
seasons (Fig. 1), which was significantly lower than those
preceded by the CF and AWD water regimes (P < 0.05).
There was no significant difference in the grain yield
and total biomass among the 3 water regimes of rice in
2012 and 2014 (Fig. 2a, b). In 2013, grain yields and
aboveground biomass production of rice in the RFL
treatment was 6.07 and 12.77 t ha?1, respectively, producing significantly less than CF and AWD treatments
(CF; 7.38 and 15.62 t ha?1, AWD; 7.31 and 15.38 t ha?1,
respectively). However, the plots preceded by the CF
and AWD treatments had lower grain yields of rapeseed
(1.83 and 2.00 t ha?1, respectively) and lower total
biomass of rapeseed (5.93 and 6.59 t ha?1, respectively)
than those preceded by the RFL treatment (2.80 and
8.61 t ha?1, respectively) in 2013. In 2014, although
there was no difference in the grain yield among the 3
water regimes for rapeseed, the total biomass in the plots
preceded by the RFL water regime (10.95 t ha?1) was
significantly higher than those in the plots preceded by
the CF and AWD treatments (7.54 and 6.98 t ha?1,
respectively). It should be noted that the 3 water regimes
during the rice growing season had no effect on annual
yields and aboveground biomass from 2012 to 2013 and
from 2013 to 2014 (Fig. 2).
particulate organic matter in microaggregates (iPOM)
(250?53 ?m), which accounted for 54?73% of the bulk
soil weight, depending on the depth (Fig. 3). Silt and
clay protected in microaggregates (intra-SC) (<53 ?m)
(accounting for 13?18% of the bulk soil mass) had an
almost equal mass percentage to the non-occluded silt
and clay in microaggregates (free-SC) (<53 ?m) (accounting for 9?15% of the bulk soil mass) in the upper
soil layer (< 10 cm soil depth) in all treatment plots.
However, more soil mass was distributed in intra-SC
(accounting for 26?31% of the bulk soil mass) than in
free-SC (accounting for 10?13% of the bulk soil mass)
at 10?20 cm soil depth. In contrast, the unprotected free
light POM (fPOM) fractions (material <1.85 g cm?3)
was the least abundant, contributing 1?4% to the total
(Fig. 3). At >5 cm soil depth, the average weight of
POM was strongly influenced by the water regime. The
AWD treatment decreased the average weight of fPOM
at 5?10 cm soil depth relative to the RFL treatment, and
there were no significant differences between CF and
RFL or between CF and AWD (Fig. 3). The percentage
of iPOM was 1.14 times higher in AWD than in CF at 5?
10 cm soil depth; whereas, at 10?20 cm depth, RFL had
the lowest average weight of iPOM (Fig. 3).
Carbon concentration in bulk soil and fractions
Mass proportions of different fractions in bulk soil
The SOC fractions obtained in the 3 water regimes
mainly consisted of physicochemically protected
Fig. 2 Rice and rapeseed grain
yield (a) and aboveground
biomass (b) at maturity under
different water regimes
throughout the experimental
period of 2012?2014. CF,
continuous flooding; AWD,
alternate wetting and drying
irrigation; RFL, rain-fed with
limited irrigation to avoid serious
drought. The error bars indicate
the standard deviation of 3
replicates. Different lower-case
and upper-case letters for each
item indicate significant
differences at the 0.05 and 0.01
levels by the Student?Newman?
Keuls test, respectively. ns = no
significant difference in the
annual rice?rapeseed rotation
Table 1 shows the SOC concentrations of bulk soil and
various fractions. Total SOC concentration (g C kg?1
soil) at >5 cm soil depth decreased significantly under
Plant Soil
Fig. 3 Mean weight percentage of total unprotected free light
(material <1.85 g cm?3) particulate organic matter (fPOM), total
physicochemically protected (250?53 ?m) particulate organic
matter in microaggregates (iPOM), total (<53 ?m) silt and clay
protected in microaggregates (intra-SC), and total (<53 ?m) silt
and clay non-occluded in microaggregates (free-SC) in the 0?5, 5?
10 and 10?20 cm soil layers under different water regimes. CF,
continuous flooding; AWD, alternate wetting and drying irrigation;
RFL, rain-fed with limited irrigation to avoid serious drought.
Presented values are means (n = 3) and error bars denote the
standard errors. Within the same soil depth and the same fraction,
lowercase letters indicate significant differences among treatments
(P < 0.05) according to the Student?Newman?Keuls test
the RFL treatment, compared with that in the CF and
AWD treatments (P = 0.009 and 0.005, respectively;
Table 1). There was no significant difference in total
SOC concentration between the CF and AWD treatments. In general, fPOM consistently represented the
highest concentrations of SOC across fractions, water
treatment, and soil depth, ranging from 73 to 105 g C
kg?1. At 5?10 cm soil depth, concentrations of SOC in
fPOM in AWD plots were significantly higher than
those in CF and RFL plots (P = 0.006); however, there
was no significant difference among the 3 treatments at
other soil depths. There was no significant difference in
C concentration in the iPOM fraction between the AWD
and CF treatments. At 10?20 cm depth, the SOC concentration of iPOM under the RFL treatment decreased
significantly (P = 0.001 and 0.008, respectively) compared with that in the CF and AWD treatments, while
water management had no significant effects on the
iPOM concentration at 0?10 cm soil depth (Table 1).
Water management appeared to have no effects on the C
concentration of the intra-SC at all soil depths (Table 1).
In contrast, the C concentration of free-SC was 11 and
13% higher in the AWD and RFL treatments, respectively, compared with the CF treatment at the soil surface (0?5 cm) (Table 1).
Bulk SOC stock and SOC stocks within fractions
Water management affected the bulk SOC stock; however, the significance of this response was dependent on
soil depth (Table 2). In the 10?20 cm soil layer, the RFL
treatment decreased the bulk SOC stock, when compared with the CF and AWD treatments (P = 0.008), and
there were no significant differences between CF and
AWD treatments (Table 2). However, when the whole
soil profile (0?20 cm) was considered, no differences in
bulk SOC stock were observed between CF and AWD
or between CF and RFL (Table 2). Furthermore, no
differences were observed in the SOC stocks among
the 3 water regimes at <10 cm soil depth (Table 2).
The effects of water management on the SOC stock
of various fractions in soils are presented in Table 2. As
expected, the highest amount of SOC is stored in the
iPOM fraction in all 3 water managements at all investigated soil depths (0?5, 5?10, and 10?20 cm), and this
fraction contained between 35 and 52% of the total SOC
stored in the entire soil profile (0?20 cm). In contrast,
the free-SC fraction had relatively low C stocks, contributing only 6 to 13% of the bulk SOC. The SOC
stocks of the fPOM fraction contributed between 10
and 22% of the total SOC stocks, whereas the intra-SC
Plant Soil
Table 1 Organic carbon concentration in bulk soil (g C kg?1 soil) and fractions (g C kg?1 fraction) under the different water regimes at
different soil depths determined after the 3rd year rice harvest of established rice?rapeseed rotations
Soil depth (cm)
Bulk SOC
fPOM
iPOM
Intra-SC
Free-SC
Water regime
CF
AWD
RFL
0?5
17.19 � 0.14
16.77 � 0.62
16.51 � 0.50
5?10
13.54 � 0.13 a
13.00 � 0.15 a
12.41 � 0.21 b
10?20
10.68 � 0.38 a
9.84 � 0.46 a
7.74 � 0.32 b
0?20
13.80 � 0.09 a
13.20 � 0.10 a
12.22 � 0.28 b
0?5
102.85 � 2.10
104.97 � 4.96
96.70 � 4.52
5?10
87.24 � 2.89 b
102.54 � 3.67 a
79.84 � 2.94 b
10?20
89.75 � 2.75
83.95 � 3.95
73.04 � 4.71
0?5
13.14 � 0.22
12.68 � 0.20
12.42 � 0.30
5?10
10.83 � 0.36
10.77 � 0.34
11.04 � 0.28
10?20
8.52 � 0.14 a
7.94 � 0.18 a
6.73 � 0.17 b
0?5
13.93 � 0.55
14.32 � 0.31
14.74 � 0.09
5?10
11.58 � 0.16
12.73 � 0.23
12.31 � 0.44
10?20
12.39 � 0.49
11.52 � 0.51
11.20 � 0.24
0?5
12.79 � 0.15 b
14.19 � 0.31 a
14.48 � 0.18 a
5?10
12.25 � 0.33
12.70 � 0.10
13.29 � 0.31
10?20
10.63 � 0.26
10.25 � 0.67
10.11 � 0.08
fPOM total unprotected free light particulate organic matter (material <1.85 g cm?3 ), iPOM total physico-chemically protected particulate
organic matter in microaggregates (250?53 ?m), intra-SC total silt and clay protected in microaggregates (<53 ?m); and free-SC total silt and
clay non-occluded in microaggregates (<53 ?m). CF continuous flooding, AWD alternate wetting and drying irrigation, RFL rain-fed with
limited irrigation to avoid serious drought. Values represent mean � standard error (n = 3). Different lowercase letters within the same row
indicate significant differences (P < 0.05) among water regimes, according to the Student?Newman?Keuls test
fraction had a relative proportion of 10 to 33% of the
total SOC stocks at all investigated soil layers.
Overall, we found no statistically significant differences in the SOC stock of fPOM and intra-SC fractions
among the 3 water regimes at all soil depths (Table 2).
However, the AWD water regime soils revealed significantly higher SOC stocks (P = 0.007) in the iPOM
fraction than the CF and RFL treatment soils, while no
differences were detected between the CF and RFL
water regimes at 5?10 cm soil depth (Table 2). Moreover, the C stock of iPOM under the CF and AWD
treatments was significantly higher than that of the
RFL treatment in the subsurface soil layer (10?20 cm)
(P = 0.003; Table 2) and the whole soil profile
(P = 0.004; Table 2). The relatively low C stock of the
iPOM fraction in the RFL treatment soils in the 10?
20 cm soil layer was related to the significantly lower
(P = 0.018) masses of iPOM as well as the lower
(P = 0.001) C concentration of iPOM fraction compared
with those in the CF and AWD treatments (Fig. 3 and
Table 1). Notably, in the surface soil layer (0?5 cm),
compared with the CF treatment, the water-saving irrigation techniques (AWD and RFL treatments) significantly increased the C stock of the free-SC fraction
(P = 0.017; Table 2).
Carbon to nitrogen ratios and soil bulk density
Clear differences in C/N ratios of various fractions were
observed. For all water regimes and depths, the fPOM
had the largest C/N ratios (Fig. 4a?d), whereas at the
10?20 cm and the 0?20 cm soil depth, only the C/N
ratios of iPOM differed among water managements, and
C/N ratios decreased significantly in the order:
CF > AWD > RFL (Fig. 4c, d).
After the 3rd rice harvest, the CF treatment had lower
soil BD compared with the water-saving irrigation treatments (AWD and RFL) in the 0?10 cm soil depth, while
no differences were observed between the AWD and
RFL treatments (Fig. 5). BD did not significantly differ
among the CF, AWD, and RFL treatments in the 10?
20 cm soil layer (Fig. 5).
Plant Soil
Table 2 Organic C stock (g C m?2) of bulk soil and fractions under the different water regimes at different soil depths determined after the
3rd year rice harvest of established rice?rapeseed rotations
Soil depth (cm)
Bulk SOC
fPOM
iPOM
Intra-SC
Free-SC
Water regime
CF
AWD
RFL
0?5
886 � 43
1028 � 56
1018 � 41
5?10
782 � 39
839 � 33
822 � 14
10?20
1457 � 46 a
1389 � 59 a
1125 � 45 b
0?20
3124 � 41 ab
3257 � 38 a
2965 � 83 b
0?5
184 � 13
222 � 4
198 � 21
5?10
125 � 1
121 � 5
140 � 17
10?20
153 � 19
142 � 26
116 � 22
0?20
462 � 31
485 � 27
454 � 47
0?5
422 � 21
468 � 16
403 � 16
5?10
346 � 11 b
433 � 16 a
379 � 9 b
10?20
635 � 23 a
585 � 36 a
394 � 31 b
0?20
1403 � 50 a
1486 � 27 a
1176 � 43 b
0?5
100 � 3
99 � 10
100 � 11
5?10
108 � 19
106 � 11
90 � 5
10?20
383 � 13
369 � 21
369 � 12
0?20
591 � 8
574 � 21
560 � 2
0?5
53 � 10 b
94 � 2 a
87 � 7 a
5?10
91 � 12
71 � 6
92 � 3
10?20
129 � 11
116 � 18
143 � 16
0?20
273 � 31
281 � 23
322 � 11
?3
fPOM total unprotected free light particulate organic matter (material <1.85 g cm ), iPOM total physico-chemically protected particulate
organic matter in microaggregates (250?53 ?m), intra-SC total silt and clay protected in microaggregates (<53 ?m), and free-SC total silt and
clay non-occluded in microaggregates (<53 ?m). CF continuous flooding, AWD alternate wetting and drying irrigation, RFL rain-fed with
limited irrigation to avoid serious drought. Values represent mean � standard error (n = 3). Different lowercase letters within the same row
indicate significant differences (P < 0.05) among water regimes, according to the Student?Newman?Keuls test
Discussion
Changes in SOC stocks
The SOC stock in paddy fields is the net result of
organic matter input and output from decomposition
processes (Castellano et al. 2012; Gulde et al. 2008;
Stewart et al. 2007). It is commonly accepted that
waterlogging associated with rice residue input enhances accumulation of SOC in paddy fields (Lal
2002; Tanji et al. 2003). Therefore, water management
in paddy fields concurrently affects the 2 opposite processes, and are thus likely to have a noteworthy influence on SOC in paddy fields. We observed an apparent
depletion in C concentration and stock in bulk soil under
the RFL treatment, while no significant changes were
found under the AWD treatment relative to the CF
treatment (Tables 1 and 2). Assuming that crop productivity could qualitatively represent C inputs (e.g.,
rhizodeposition, roots, and stubbles) (Huang et al.
2014; K鰃el-Knabner et al. 2010), there were no significant differences in year-round crop yields and aboveground biomass among the 3 water regimes in rice?
rapeseed rotation systems (Fig. 2a, b), indicating comparable annual organic matter inputs among the different
treatments. Since the inputs were same, faster mineralization rates of SOM in the RFL plots as a result of the
more aerobic soil conditions could explain the depletion
in total SOC stock observed under the RFL irrigation
strategy. Flooding a field for subsequent rice cultivation
cuts off the oxygen supply from the atmosphere, reduces
soil Eh, and slows fermentation of organic matter by
switching the microbial activities from aerobic to facultative and anaerobic conditions (K鰃el-Knabner et al.
Plant Soil
Fig. 4 Carbon to nitrogen ratios of bulk soil and fractions in the
0?5 cm (a), 5?10 cm (b), 10?20 cm (c) and 0?20 cm (d) soil layers
under different water regimes. fPOM, total unprotected free light
particulate organic matter (material <1.85 g cm?3); iPOM, total
physicochemically protected particulate organic matter in
microaggregates (250?53 ?m); intra-SC, total silt and clay
protected in microaggregates (<53 ?m); and free-SC, total silt
and clay non-occluded in microaggregates (<53 ?m). CF, continuous flooding; AWD, alternate wetting and drying irrigation; RFL,
rain-fed with limited irrigation to avoid serious drought. Presented
values are means (n = 3) and error bars denote the standard errors.
Within the same soil depth and the same fraction, lowercase letters
indicate significant differences among treatments (P < 0.05) according to the Student?Newman?Keuls test. Within a treatment
and the same soil depth, bars with a different uppercase letter differ
significantly among the fractions (P < 0.05) according to the
Student?Newman?Keuls test
2010). Soil Eh is used as an index for the oxidation?
reduction conditions in paddy soil, under fluctuating
redox conditions, aerobic heterotrophic respiration is
considered to be responsible for most soil carbon dioxide (CO2) emissions (Deangelis et al. 2010). Considerable increases in soil Eh values were measured in the
RFL plots in the different growth periods in 2013
(Fig. 6). Moreover, our previous report showed an apparent increase in annual CO2 emissions in RFL plots
relative to the CF and AWD treatments (Xu et al. 2016).
In addition, it is puzzling that an increase in soil Eh
under the AWD treatment did not lower SOC stock in
Fig. 5 Soil bulk density (g cm?3) under the different water regimes at different soil depths determined after the 3rd year rice
harvest of established rice?rapeseed rotations. CF, continuous
flooding; AWD, alternate wetting and drying irrigation; RFL,
rain-fed with limited irrigation to avoid serious drought. Presented
values are means (n = 3) and error bars denote the standard errors.
Bars with a different lowercase letter differ significantly among
treatments (P < 0.05) according to the Student?Newman?Keuls
test
Fig. 6 Soil redox potential (mV) during rice growth period under
different water regime practices in 2013. CF, continuous flooding;
AWD, alternate wetting and drying irrigation; RFL, rain-fed with
limited irrigation to avoid serious drought. The error bars indicate
standard errors of 3 replicates. Different lower-case and upper-case
letters for each growth stage indicate significant differences at the
0.05 and 0.01 levels based on the Student?Newman?Keuls test
among treatments, respectively
Plant Soil
comparison with the CF treatment (Fig. 6 and Table 2).
This raises the question of why the stabilization mechanism of SOM was not affected under the AWD treatment when the amount of irrigation water was reduced
(Online Resource 2). Previous studies have shown that
in many aerobic soils SOC occluded in microaggregates
and trapping by silt and clay is considered an important
protection mechanism for SOM accumulation (Six et al.
1998; Tian et al. 2015). Hence, we assume that different
irrigation regimes might have different influences on
SOC stabilization in paddy fields in terms of physicochemical protection by aggregations.
Impact of water managements on SOC fractions stock
Few studies have investigated the mechanisms responsible for the accumulation of SOM in paddy soils such
as occlusion in aggregates and formation of organomineral associations (Kimura et al. 2004). The density
fractionation method has been used to further reveal and
evaluate accumulation and stabilization of SOC under
different field management practices (DeGryze et al.
2004; Oorts et al. 2007; Yu et al. 2012). This method
can separate SOM into active, intermediate and passive
OM pools, with the increasing stability of OM from
fPOM (unprotected free light OM) to iPOM (physicochemically protected OM in microaggregates) and finally to mineral-associated SOM (von L黷zow et al. 2007).
Previous studies have shown that the carbon fraction in
iPOM is slower than in the fPOM fraction and therefore
recommended as an early indicator for SOC stock
changes under different soil management systems
(DeGryze et al. 2004; Nascente et al. 2013; Yang et al.
2005). Soil organic carbon associated with silt and clay
particles show significantly longer turnover times, and it
has been suggested that the preferential storage in fine
fractions results in a long-term C storage (Pinheiro et al.
2015; Six et al. 2002). However, only a few studies have
evaluated SOC stabilization in paddy fields under watersaving irrigation by monitoring different OM pools with
varied stability. Prior studies have shown that the largest
proportion of soil and C mass were in the silt and clay
fractions (Huang et al. 2010; Yan et al. 2012; Yan et al.
2013). However, we found that a large portion of SOC
(54?73% of total SOC stock) is occluded in the iPOM
fraction (Fig. 3 and Table 2). This is similar to a recent
study by Dou et al. (2016) who reported that the iPOM
accounted for 65?87% of the SOC in afforested soils.
Thus, changes in iPOM pool size can affect SOC stock
to a large extent (Christensen 2001; Oorts et al. 2007).
Our study showed that different irrigation strategies
affect the distribution of SOC in various pools and their
sizes, but this effect depends on the fraction and the soil
depth (Fig. 3 and Tables 1 and 2).
In the present study the AWD irrigation strategy
during the rice-growing season, characterized by the
frequent dry-wet cycles, led to an increased C stock in
the iPOM at 5?10 cm after the 3rd year rice harvest of
established rice?rapeseed rotations (Table 2). Previous
studies have shown that an alternate wetting and drying
water regime stimulates the formation of
microaggregates under paddy conditions (Yang et al.
2005; Zhang and He 2004). The proportion of iPOM
in the soil mass at 5?10 cm, isolated from
microaggregates by fractionation, was higher under the
periodic wet?dry cycles of AWD treatment than under
the CF treatment (Fig. 3). Furthermore, BD is an important characteristic that affects key soil functions such as
water?holding capacity, infiltrability, aeration, and soil
moisture was reported to have a negative correlation
with soil BD (Mora and L醶aro 2014). In our study,
the average SWC at CF plots were significantly higher
than those of AWD and RFL plots across the 3 years rice
growing seasons (P < 0.05) (Fig. 1), and the soil BD was
higher in the AWD treatment than in the CF treatment at
5?10 cm soil depth after 3 years of irrigation practice
(Fig. 5), which produced the higher C stock of iPOM,
although C concentrations in iPOM were not affected in
the AWD plots (Table 1). In contrast, the rain-fed RFL
treatment created the aerobic conditions favorable for
SOM decomposition. This increased the turnover of the
macroaggregates and limited the incorporation of POM
into newly formed microaggregates within macroaggregates (Huang et al. 2014). This may have lead to the
lower C concentration and stock of iPOM in soils under
the RFL treatment (Tables 1 and 2). In addition, the C:N
ratios of the iPOM fraction in the 10?20 cm soil layer
and the whole soil profile differed among water managements (Fig. 4c, d), reflecting the various levels of
organic matter quality and also their different biodegradability (Gunina et al. 2015). The C:N ratios significantly
decreased in the order: CF > AWD > RFL (Fig. 4c, d).
Baisden et al. (2002) showed that lower C:N ratios
during the stabilization of C in mineral-associated
SOM indicated a higher degree of decomposition. In
our previous publication, relative to the RFL treatment,
soil CO2 emissions were significantly lower for the CF
and AWD plots during the rice growing season (Xu et al.
Plant Soil
2016). This might indicate that this fraction had been
processed by microorganisms active in the RFL plots
and thus that part of the C was lost as CO2 (Gunina et al.
2015; Sollins et al. 2009). It is notable that the highly
p r ot e c t e d s i l t an d c l a y tr a p pe d f r a ct i o n i n
microaggregate (intra-SC) was relatively consistent
across the different treatments and soil depths (Fig. 3
and Tables 1 and 2), which is consistent with the concept
that intra-SC is relatively stable over a short term period
(Fern醤dez et al. 2014; Huang et al. 2010). However,
although intra-SC only contributed approximately 20%
to the total SOC stock at the whole soil profile, previous
studies demonstrate that it has a higher Beffective soil C
stabilization capacity^ than the free-SC fraction Plaza
et al. 2013; Stewart et al. 2007). However, long-term
experiments are needed to examine the effects of watersaving irrigation on the intra-SC fraction. Accordingly,
we may conclude that decreases in the SOC sequestration in the RFL irrigation strategy are primarily due to
decreases in the C concentration and thus the C stock of
iPOM.
The status of intermediate (iPOM) and passive OM
pools (intra-SC) can reflect the physicochemical protection of SOC (Cotrufo et al. 2013; Gunina and Kuzyakov
2014; Helfrich et al. 2008). Our study has shown that
water-saving irrigation had some influence on the relatively stable SOC pools (iPOM) rather than passive
SOC pools over the short-term; however, the extent of
change depended on the amount of irrigation water and
method. A severe reduction in irrigation water under
RFL irrigation strategy not only decreased the C concentration of iPOM in bulk soil, but also reduced its
proportion in soil mass at 10?20 cm soil depth. This
might indicate that both mineralization of SOC and
fraction transfer were simultaneously affected, ultimately resulting in the depletion in SOC under the RFL
irrigation practice. A moderate reduction in irrigation
water under the AWD irrigation strategy had a less
drastic effect, accompanied by the potential to enhance
the proportion of iPOM in the soil mass, thus it could be
considered an alternative water regime balancing watersaving and maintaining SOC stability.
Notably, obvious change in C stock of iPOM, and
related soil BD, C:N ratios, were found in subsoil layers
(5-20 cm) in the present study. It also has been found
that subsoil C may easily respond to land-use and/or
management change (Wright et al. 2007; Follett et al.
2009). In subsoil horizons, environmental conditions
may be different from those in topsoil horizons, and
OM storage may be driven by specific processes (von
L黷zow et al. 2006). For example, Fierer et al. (2003)
observed that mineralisation of subsoil C may be much
more sensitive to temperature change than those of
topsoil C. In our study, the relatively labile SOC fractions in subsoil might be more sensitive to air permeability due to soil moisture variation under water-saving
irrigation, meanwhile, were influenced by the organic C
input related to root litter and exudates along root channels and/or through bioturbation (Rumpel and K鰃elKnabner 2010). Although, aboveground biomass was
similar among the three irrigation strategies (Fig. 2), rice
root distribution along soil profile might be different.
Rice root length under aerobic culture conditions was
found in a 72?85% reduction by Kato and Okami
(2011). Similar phenomenon might happen under RFL
treatment, which could reduce the C input by root to the
subsoil. Thus, faster mineralization by aeration and lower C input in subsoil might be the excuse in significant
reduction in SOC fractions under RFL treatment. However, further studies are needed to understand the interactions among rice root growth indicators such as distribution and rhizodeposition, soil properties, and SOC
pools under water-saving irrigation in paddy fields.
Furthermore, exploration of the transformation between
different SOC fractions using 13C/14C labeling is necessary to evaluate accumulation and stabilization of SOC
over short-term and long-term periods (Tian et al.
2013a).
Conclusions
After the 3rd year rice harvest of established rice?rapeseed rotations in Central China, SOC pools with different stability, separated by fractionation sequence, were
affected depending on the irrigation strategy. Overall, C
stocks in iPOM, the main part of the soil C pool with
intermediate turnover rate, have changed, whereas C
stocks in intra-SC and fPOM were not significantly
influenced by water-saving irrigation strategies. The
AWD strategy maintained the C concentration of iPOM,
and increased the iPOM percentage in soil mass to some
extent. Thus, AWD has potential to stabilize C stocks in
iPOM and the total SOC. Shifts in SOC stocks towards
iPOM under the frequent wetting and drying cycles of
the AWD irrigation strategy appeared to be beneficial
for soil C sequestration. However, a further reduction in
irrigation water provided by the RFL treatment, C
Plant Soil
concentrations in iPOM and its proportion to soil mass
at 10?20 cm depth decreased, and a loss in total SOC
was observed. Elucidating the mechanisms of C sequestration and stability under different water-saving regimes, especially transformation among the different
physiochemically protected SOC pools, still requires
further research. Based on our short-term observation,
we suggest that moderate water-saving irrigation, like
the AWD method, may be an option to balance saving
water and maintaining SOC stability in paddy fields.
Acknowledgments This study was financially supported by the
National Natural Science Foundation of China (Project Nos.
41101280 and 31571622), and the Special Fund for Agroscientific Research in the Public Interest of China (Project No.
201503122). The authors would like to thank Mr. Liesheng Zheng
and Mrs. Haixia Li for their help in laboratory assistance and Mr.
Zhongbin Zhai for his help in managing the experiment fields.
Compliance with ethical standards
Conflict of interest The authors declare that there is no conflict
of interests regarding the publication of this article.
References
Baisden WT, Amundson R, Cook AC, Brenner DL (2002)
Turnover and storage of C and N in five density fractions
from California annual grassland surface soils. Glob
Biogeochem Cycles 16:64?1?64?16
Bao SD (2000) Analytical method for soil and agricultural chemistry. Chinese Agriculture Press, Beijing (in Chinese)
Brown KH, Bach EM, Drijber RA, Hofmockel KS, Jeske ES,
Sawyer JE, Castellano MJ (2014) A long-term nitrogen fertilizer gradient has little effect on soil organic matter in a
high-intensity maize production system. Glob Chang Biol
20:1339?1350
Castellano MJ, Kaye JP, Lin H, Schmidt JP (2012) Linking carbon
saturation concepts to nitrogen saturation and retention.
Ecosystems 15:175?187
Christensen BT (2001) Physical fractionation of soil and structural
and functional complexity in organic matter turnover. Eur J
Soil Sci 52:345?353
Cotrufo MF, Wallenstein MD, Boot CM, Denef K, Paul E (2013)
The microbial efficiency-matrix stabilization (MEMS)
framework integrates plant litter decomposition with soil
organic matter stabilization: do labile plant inputs form stable
soil organic matter? Glob Chang Biol 19:988?995
Deangelis KM, Silver WL, Thompson AW, Firestone MK (2010)
Microbial communities acclimate to recurring changes in soil
redox potential status. Environ Microbiol 12:3137?3149
DeGryze S, Six J, Paustian K, Morris SJ, Paul EA, Merckx R
(2004) Soil organic carbon pool changes following land-use
conversions. Glob Chang Biol 10:1120?1132
Dou XL, Xu X, Shu X, Zhang QF, Cheng XL (2016) Shifts in soil
organic carbon and nitrogen dynamics for afforestation in
central China. Ecol Eng 87:263?270
FAO (2014) FAO statistical databases. FAO, Rome http://faostat.
fao.org
Fern醤dez JM, L髉ez-de-S� EG, Polo A, Plaza C (2014) Shortterm stabilization of organic matter in physically, chemically,
and biochemically protected pools in soils amended with
municipal wastes. Clean: Soil, Air, Water 42:487?493
Fierer N, Allen AS, Schimel JP, Holden PA (2003) Controls on
microbial CO2 production: a comparison of surface and
subsurface soil horizons. Glob Chang Biol 9:1322?1332
Follett RF, Kimble JM, Pruessner EG, Samson-Liebig S, Waltman
S (2009) Soil organic carbon stocks with depth and land use
at various U.S. sites. Soil carbon sequestration and the greenhouse effect, 2nd edn. SSSA special Publication 57,
Madison, pp 29?46
Gartzia-Bengoetxea N, Gonz醠ez-Arias A, Merino A, de Arano
IM (2009) Soil organic matter in soil physical fractions in
adjacent semi-natural and cultivated stands in temperate
Atlantic forests. Soil Biol Biochem 41:1674?1683
Grandy AS, Robertson GP (2007) Land-use intensity effects on
soil organic carbon accumulation rates and mechanisms.
Ecosystems 10:59?74
Gulde S, Chung H, Amelung W, Chang C, Six J (2008) Soil
carbon saturation controls labile and stable carbon pool dynamics. Soil Sci Soc Am J 72:605?612
Gunina A, Kuzyakov Y (2014) Pathways of litter C by formation
of aggregates and SOM density fractions: implications from
13
C natural abundance. Soil Biol Biochem 71:95?104
Gunina A, Ryzhova I, Dorodnikov M, Kuzyakov Y (2015) Effect
of plant communities on aggregate composition and organic
matter stabilisation in young soils. Plant Soil 387:265?275
Helfrich M, Ludwig B, Potthoff M, Flessa H (2008) Effect of litter
quality and soil fungi on macroaggregate dynamics and
associated partitioning of litter carbon and nitrogen. Soil
Biol Biochem 40:1823?1835
Huang S, Peng XX, Huang QR, Zhang WJ (2010) Soil aggregation and organic carbon fractions affected by long-term fertilization in a red soil of subtropical China. Geoderma 154:
364?369
Huang S, Sun YN, Zhang WJ (2012) Changes in soil organic
carbon stocks as affected by cropping systems and cropping
duration in China?s paddy fields: a meta-analysis. Clim
Chang 112:847?858
Huang S, Pan XH, Guo J, Qian CR, Zhang WJ (2014) Differences
in soil organic carbon stocks and fraction distributions between rice paddies and upland cropping systems in China. J
Soils Sediments 14:89?98
Kato Y, Okami M (2011) Root morphology, hydraulic conductivity and plant water relations of high-yielding rice grown
under aerobic conditions. Ann Bot 108:575?583
Kimura M, Murase J, Lu Y (2004) Carbon cycling in rice
field ecosystems in the context of input, decomposition
and translocation of organic materials and the fates of
their end products (CO2, and CH4). Soil Biol Biochem
36:1399?1416
Plant Soil
K鰃el-Knabner I, Amelung W, Cao Z, Fiedler S, Frenzel P, Jahn
R, Kalbitz K, K鰈bl A, Schloter M (2010) Biogeochemistry
of paddy soils. Geoderma 157:1?14
Lal R (2002) Soil carbon sequestration in China through agricultural intensification, and restoration of degraded and
desertified ecosystems. Land Degrad Dev 13:469?478
Lal R (2004) Soil carbon sequestration impacts on global climate
change and food security. Science 304:1623?1627
Luo LJ (2010) Breeding for water-saving and drought-resistance
rice (WDR) in China. J Exp Bot 61:3509?3517
Miniotti EF, Romani M, Said-Pullicino D et al (2016) Agroenvironmental sustainability of different water management
practices in temperate rice agro-ecosystems. Agric Ecosyst
Environ 222:235?248
Mora J, L醶aro R (2014) Seasonal changes in bulk density under
semiarid patchy vegetation: the soil beats. Geoderma 235:
30?38
Nascente AS, Li YC, Crusciol CAC (2013) Cover crops and no-till
effects on physical fractions of soil organic matter. Soil
Tillage Res 130:52?57
O'Brien SL, Jastrow JD (2013) Physical and chemical protection
in hierarchical soil aggregates regulates soil carbon and nitrogen recovery in restored perennial grasslands. Soil Biol
Biochem 61:1?13
Oorts K, Bossuyt H, Labreuche J, Merckx R, Nicolardot B (2007)
Carbon and nitrogen stocks in relation to organic matter
fractions, aggregation and pore size distribution in notillage and conventional tillage in northern France. Eur J
Soil Sci 58:248?259
Peng SZ, Hou HJ, JZ X, Mao Z, Abudu S, Luo YF (2011) Nitrous
oxide emissions from paddy fields under different water
managements in southeast China. Paddy Water Environ 9:
403?411
Pinheiro EFM, Campos DVB, Balieiro FC, Anjos LHC, Pereira
MG (2015) Tillage systems effects on soil carbon stock and
physical fractions of soil organic matter. Agric Syst 132:35?
39
Plaza C, Courtier-Murias D, Fern醤dez JM, Polo A, Simpson AJ
(2013) Physical, chemical, and biochemical mechanisms of
soil organic matter stabilization under conservation tillage
systems: a central role for microbes and microbial byproducts in C sequestration. Soil Biol Biochem 57:124?134
Rumpel C, K鰃el-Knabner I (2010) Deep soil organic matter?a
key but poorly understood component of terrestrial C cycle.
Plant Soil 338(1?2):143?158
Sacco D, Cremon C, Zavattaro L, Grignani C (2012) Seasonal
variation of soil physical properties under different water
managements in irrigated rice. Soil Tillage Res 118:22?31
Shang Q, Yang X, Gao C, Wu P, Liu J, Xu Y, Shen Q, Zou J, Guo S
(2011) Net annual global warming potential and greenhouse
gas intensity in Chinese double rice-cropping systems: a 3year field measurement in long-term fertilizer experiments.
Glob Chang Biol 17:2196?2210
Six J, Elliott ET, Paustian K, Doran J (1998) Aggregation and soil
organic matter accumulation in cultivated and native grassland soils. Soil Sci Soc Am J 62:1367?1377
Six J, Elliott ET, Paustian K (2000) Soil macroaggregate turnover
and microaggregate formation: a mechanism for C sequestration under no-tillage agriculture. Soil Biol Biochem 32:
2099?2103
Six J, Conant RT, Paul EA, Paustian K (2002) Stabilization mechanisms of soil organic matter: implications for C-saturation of
soils. Plant Soil 241:155?176
Sollins P, Homann P, Caldwell BA (1996) Stabilization and destabilization of soil organic matter: mechanisms and controls.
Geoderma 74:65?105
Sollins P, Kramer MG, Swanston C, Lajtha K, Filley T,
Aufdenkamp AK, Wagai R, Bowden RD (2009) Sequential
density fractionation across soils of contrasting mineralogy:
evidence for both microbial-and mineral-controlled soil organic matter stabilization. Biogeochemistry 96:209?231
Stewart CE, Paustian K, Conant RT, Plante AF, Six J (2007) Soil
carbon saturation: concept, evidence and evaluation.
Biogeochemistry 86:19?31
Tanji KK, Gao S, Scardaci SC, Chow AT (2003) Characterizing
redox status of paddy soils with incorporated rice straw.
Geoderma 114:333?353
Tian J, Dippold M, Pausch J, Blagodatskaya E, Fan M, Li X,
Kuzyakov Y (2013a) Microbial response to rhizodeposition
depending on water regimes in paddy soils. Soil Biol
Biochem 65:195?203
Tian J, Pausch J, Fan M, Li X, Tang Q, Kuzyakov Y (2013b)
Allocation and dynamics of assimilated carbon in rice-soil
system depending on water management. Plant Soil 363:
273?285
Tian K, Zhao Y, Xu X, Hai N, Huang B, Deng W (2015) Effects of
long-term fertilization and residue management on soil organic carbon changes in paddy soils of China: a meta-analysis. Agric Ecosyst Environ 204:40?50
von L黷zow M, K鰃el-Knabner I, Ekschmitt K, Matzner E,
Guggenberger G, Marschner B, Flessa H (2006)
Stabilization of organic matter in temperate soils: mechanisms and their relevance under diferent soil conditions - a
review. Eur J Soil Sci 57:426?445
von L黷zow M, K鰃el-Knabner I, Ekschmitt K, Flessa H,
Guggenberger G, Matzner E, Marschner B (2007) SOM
fractionation methods: relevance to functional pools and to
stabilization mechanisms. Soil Biol Biochem 39:2183?2207
Weller S, Janz B, J鰎g L, Kraus D, Racela HS, Wassmann R,
Butterbach-Bahl K, Kiese R (2016) Greenhouse gas emissions and global warming potential of traditional and diversified tropical rice rotation systems. Glob Chang Biol 22:
432?448
Wright AL, Dou F, Hons FM (2007) Crop species and tillage
effects on carbon sequestration in subsurface soil. Soil Sci
172:124?131
Xiong W, Holman I, Lin E, Conway D, Jiang J, Xu Y, Li Y (2010)
Climate change, water availability and future cereal production in China. Agric Ecosyst Environ 135:58?69
Xu Y, Ge JZ, Tian SY, Li SY, Nguy-Robertson AL, Zhan M, Cao
CG (2015) Effects of water-saving irrigation practices and
drought resistant rice variety on greenhouse gas emissions
from a no-till paddy in the central lowlands of China. Sci
Total Environ 505:1043?1052
Xu Y, Zhan M, Cao CG, Tian SY, Ge JZ, Li SY, Wang MY, Yuan
GY (2016) Improved water management to reduce greenhouse gas emissions in no-till rapeseed?rice rotations in
Central China. Agric Ecosyst Environ 221:87?98
Yan Y, Tian J, Fan M, Zhang F, Li X, Christie P, Chen H, Lee J,
Kuzyakov Y, Six J (2012) Soil organic carbon and total
Plant Soil
nitrogen in intensively managed arable soils. Agric Ecosyst
Environ 150:102?110
Yan X, Zhou H, Zhu QH, Wang XF, Zhang YZ, Yu XC, Peng X
(2013) Carbon sequestration efficiency in paddy soil and
upland soil under long-term fertilization in southern China.
Soil Tillage Res 130:42?51
Yang C, Yang L, Zhu O (2005) Organic carbon and its fractions in
paddy soil as affected by different nutrient and water regimes.
Geoderma 124:133?142
Yao FX, Huang JL, Cui KH, Nie LX, Xiang J, Liu XJ, Wu W,
Chen MX, Peng SB (2012) Agronomic performance of highyielding rice variety grown under alternate wetting and drying irrigation. Field Crop Res 126:16?22
Yu HY, Ding WX, Luo JF, Geng RL, Cai ZC (2012) Long-term
application of organic manure and mineral fertilizers on
aggregation and aggregate-associated carbon in a sandy loam
soil. Soil Tillage Res 124:170?177
Zhang QF (2007) Strategies for developing green super rice. Proc
Natl Acad Sci U S A 104:16402?16409
Zhang M, He Z (2004) Long-term changes in organic carbon and
nutrients of an Ultisol under rice cropping in southeast China.
Geoderma 118:167?179
Zhao Y, De Maio M, Vidotto F, Sacco D (2015) Influence of wetdry cycles on the temporal infiltration dynamic in temperate
rice paddies. Soil Tillage Res 154:14?21
Zou JW, Huang Y, Zheng XH, Wang YS (2007) Quantifying direct
N2O emissions in paddy fields during rice growing season in
mainland China: dependence on water regime. Atmos
Environ 41:8030?8042
Документ
Категория
Без категории
Просмотров
5
Размер файла
987 Кб
Теги
017, s11104, 3467
1/--страниц
Пожаловаться на содержимое документа