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SHORT COMMUNICATION
Soil organic carbon sequestration under different fertilizerregimes in north and northeast China: RothC simulation
J. WANG1, C. LU
1, M. XU1, P. ZHU
2, S. HUANG3, W. ZHANG
1, C. PENG2, X. CHEN
4 & L. WU5
1Ministry of Agriculture Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources and Regional
Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081, China, 2Centre of Agricultural Environment and Resources,
Jilin Academy of Agricultural Sciences, Changchun, 130033, China, 3Institute of Plant Nutrition, Resources and Environment,
Henan Academy of Agricultural Sciences, Zhengzhou, 450002, China, 4College of Resources and Environment, Northwest A&F
University, Yangling, 712100, China, and 5Sustainable Soils and Grassland Systems Department, Rothamsted Research, North
Wyke, Okehampton, Devon EX20 2SB, UK
Abstract
Soil organic carbon (SOC) modelling is a useful approach to assess the impact of nutrient
management on carbon sequestration. RothC was parameterized and evaluated with two long-term
experiments comparing different fertilizer treatments in north (Zhengzhou) and northeast
(Gongzhuling) China. Four nutrient application treatments were used: no fertilizer (Control), mineral
nitrogen–phosphorus–potassium fertilizers (NPK), NPK mineral fertilizer plus manure (NPKM), and
NPK mineral fertilizer plus straw return (NPKS). The comparison between simulated and observed
data showed that the model can adequately simulate SOC contents in the Control, NPK and NPKM
treatments but overestimated in the NPKS treatment at both sites. By changing the value of
decomposable plant material:resistant plant material (DPM:RPM) ratio from the default value to 3.35
for the NPKS treatment at the Zhengzhou site, dynamics of simulated SOC agreed with measured
values. A pseudo-parameter, straw retention factor was introduced to adjust the amount of straw
incorporated into soils. Using the inverse simulation method and the modified value of the ratio, the
best-fitted value was 0.24 for the NPKS treatment at the Gongzhuling site. This result indicated that
retaining straw on the soil surface makes less contribution to carbon sequestration than if it is
incorporated. With this modification for straw, the model produced reasonable predictions for the
two sites. The model was run for another 30 years with the modified parameter values and current
average climatic conditions for different fertilizer treatments at both sites. The results suggested that
the NPK application plus the addition of manure or straw would be better management practices for
carbon sequestration.
Keywords: RothC simulation model, modelling, carbon sequestration, soil organic matter, long-term
experiment
Introduction
Soil organic carbon (SOC) plays an important role in soil
fertility and can contribute to the mitigation of climate change
through the sequestering of carbon (C) in soils. However, the
conversion from natural to agricultural ecosystems and
unsustainable management of agricultural fields have caused a
rapid and significant decline in SOC. It was estimated that the
magnitude of SOC loss from croplands in the Midwestern
United States was between 25 and 40 Mg C ha�1, or about 30–
50% of the antecedent level after about 50 yrs of cultivation
(Lal, 2002). SOC depletion also happened in China, especially
in the black soils in northeast China (Xin et al., 2002) where
the steppe meadow was converted into agricultural land
during the 1950s and has been under cultivation ever since.
Huang (2005) reported that for croplands of the same soil
type, the SOC content in China was less than half of that in
Europe. Of the five major cereal crop regions in China, the
region with the greatest SOC content is in northeast China
(only about 1.0–1.5%) and the region with the second smallest
content is in north China (0.5–0.8%) (Pan & Zhao, 2005). It isCorrespondence: C. Lu. E-mail: calu@caas.ac.cn
Received February 2012; accepted after revision December 2012
182 © 2013 The Authors. Journal compilation © 2013 British Society of Soil Science
Soil Use and Management, June 2013, 29, 182–190 doi: 10.1111/sum.12032
SoilUseandManagement
believed that about 60–70% of SOC lost could be
resequestered by appropriate agricultural management
practices (Lal, 2002). C sequestration in agricultural soils is
recognized as a win–win strategy for food security as well as
CO2 mitigation (Lal, 2002; Smith, 2004) and has been the
focus of research and extension worldwide. However, the
challenge for agronomists is to identify for different regions
the appropriate management practices that can increase and
maintain SOC.
Nutrient sources, such as manure, mineral fertilizers and
harvest residues, such as straw, can affect the quantity and
quality of organic materials in soils and hence the amount of
C sequestered. In China, numerous studies based on long-
term field experiments suggested that balanced application of
mineral fertilizers can maintain and even increase SOC
content owing to increased crop production and residue
return (Cai & Qin, 2006; Fan et al., 2008; Ludwig et al.,
2010). Other reports showed that continuous application of
mineral fertilizers alone would not maintain SOC content
(Su et al., 2006; Zhu et al., 2007). However, the combined
application of mineral fertilizers and manure is an optimal
nutrient management practice for C sequestration (Cai &
Qin, 2006; Guo et al., 2007; Fan et al., 2008; Zhang et al.,
2010; Pathak et al., 2011). In addition, the use of straw as
an amendment could potentially increase C sequestration
(Smith et al., 1997a; Jarecki & Lal, 2003; Lou et al., 2011).
Because of the slow transformation rate of organic materials
in soils, monitoring the influence of organic amendments on
SOC change requires information gained from sampling
programmes carried out over many years.
Long-term field experiments are required to monitor SOC
dynamics in response to management practices, but cost
limits the number of climatic conditions and soil types that
can be investigated and the duration of individual studies.
Consequently, process-based models can be a useful tool to
predict SOC changes in response to changes in management
practices and improve our understanding of C turnover
in soils. In the past decades, a series of SOC models or
SOC embedded models have been developed and tested
(Smith et al., 1997b). Several reviews on the models have
been published (Wu & McGechan, 1998; Ma & Shaffer,
2001).
The RothC model can be used to estimate C sequestration
under different fertilizer application programmes and has
been evaluated against results of long-term experiments from
many parts of the world (Smith et al., 1997b; Shirato &
Taniyama, 2003). However, only limited tests have been
carried out in China (Yang et al., 2003; Guo et al., 2007;
Ludwig et al., 2010; Wan et al., 2011), and repara-
meterization would be required for certain management and
environmental conditions (Skjemstad et al., 2004; Shirato
et al., 2005; Kaonga & Coleman, 2008; Liu et al., 2009;
Todorovic et al., 2010). The aims of this study were to: (i)
evaluate the RothC model against data from two long-term
experiments conducted in north and northeast China,
respectively, and (ii) predict the SOC changes under different
farm management practices.
Materials and methods
Site description
Two long-term field experiments with the application of
manure or straw together with mineral fertilizers were selected
for model evaluation and the assessment of C sequestration.
These experiments began in 1990. One was located in
Zhengzhou (ZZ, hereafter), Henan province, northern China.
The other was in Gongzhuling (GZL, hereafter), Jilin
province, northeast China. Soil types, chemical properties of
the initial soils in 1990 and climatic conditions for the
experimental sites are given in Table 1.
Cropping practices
The long-term experiment had a continuous maize mono-
cropping system at GZL, and a maize–wheat double-cropping
system at ZZ. At ZZ, wheat was sown in mid-October and
harvested around the end of May in the following year, and
then maize was planted in early June and harvested in
Table 1 General description and soil properties (0–20 cm) at the
sites
Zhengzhou (ZZ) Gongzhuling (GZL)
Coordinate 34°47′N,
113°41′E
42°57′N,
148°57′E
Climate Warm-temperate,
semi-humid
Mild-temperate,
semi-humid
Mean annual
precipitation (mm)
645 525
Mean annual
temperature (°C)
14.8 4.5
China soil
classification
Fluvo-aquic soil Black soil
FAO soil
classification
Calcaric Cambisol Luvic Phaeozems
Soil texture Light loam Clay loam
Clay content
(<0.002 mm) (%)
13.4 31.0
Silt (0.002–0.05 mm) (%) 60.7 40.1
Sand (0.05–2 mm) (%) 26.5 28.9
Bulk density (g cm�3)a 1.41 1.24
Soil sample depth (cm) 20 20
SOC (g kg�1) 6.7 13.5
Total N (g kg�1) 0.67 1.42
pH (1:2.5 w/v water) 8.3 7.2
aAverage value of all the treatments measured during the
experimental periods.
© 2013 The Authors. Journal compilation © 2013 British Society of Soil Science, Soil Use and Management, 29, 182–190
Soil C sequestration under long-term fertilizer applications 183
mid-September. Wheat was irrigated 2 or 3 times (ca. 75 mm
each) depending on the amount of precipitation, and maize
was irrigated once at sowing with 75 mm of water. At GZL,
maize was sown in late April and harvested in late September.
At both sites, hand weeding was carried out to control weeds.
Fungicide and pesticides were applied during the growth
season when needed. Grain and straw were air-dried and
weighted separately for yield and aboveground biomass
calculation.
Experimental design
The experiments were in a randomized block design without
replication (plot size 400 m2). Four common treatments for
both sites were selected from the entire experiments: (i)
Control – no fertilizer application; (ii) NPK – mineral
nitrogen (N), phosphorus (P) and potassium fertilizers (K);
(iii) NPKM – mineral NPK fertilizers in combination with
manure; and (iv) NPKS – mineral NPK in combination with
straw.
Nutrient management is shown in Table 2. At each site,
total amount of N applied (i.e. mineral plus organic) was the
same for all treatments except the Control, while the amount
for each crop was determined by local practices, cultivar,
climate and soil conditions. For the NPKM treatment, 70%
of N applied to wheat at ZZ and maize at GZL was from
manure. For the NPKS treatment, the amount of mineral N
added was reduced as straw was returned. The amount of
mineral P and K added was not reduced for the NPKS and
NPKM treatments partially due to difficulty in quantifying
how much P and K from the organic amendments was
available to the crops (Duan et al., 2011). Mineral N, P and
K fertilizers used were urea, calcium superphosphate and
potassium sulphate, respectively. P and K fertilizers were
applied at sowing at both sites. At ZZ, 70% of mineral N
was applied at sowing, and the remaining as top-dressing at
the stem elongation stage. At GZL, one-third of mineral N
was applied at sowing and the rest as top-dressing at the
jointing stage.
On average, 25 Mg ha�1 yr�1 horse or cow manure (fresh
mass, equalled 2.04 Mg C ha�1 yr�1) and 23 Mg ha�1 yr�1
composted farmyard manure (fresh mass, equalled 2.45 Mg
C ha�1 yr�1) were applied once a year as basal fertilizer for
NPKM at ZZ and GZL, respectively. 6 and 7.5 Mg
ha�1 yr�1 of maize straw (dry matter, including 14% water
content), which equalled 2.27 and 2.86 Mg C ha�1 yr�1,
were retained for NPKS at ZZ and GZL, respectively. Straw
was incorporated into soils before wheat was sown at ZZ,
and broadcast in the furrows in mid-July after top-dressing
at GZL. Manure was applied in the same way as straw at
ZZ, but was incorporated into the soils after the harvest of
maize at GZL. Details of complete experimental design at
the two sites have been described elsewhere (Wang et al.,
2010; Zhang et al., 2010; Zhao et al., 2010). Soil samples
from the plough layer (0–20 cm) for soil nutrients and
carbon content were collected annually from each treatment
after maize was harvested.
RothC model
In RothC, including version 26.3 as used, SOC is divided into
four active pools and a small amount of inert organic matter
pool (IOM) (Coleman & Jenkinson, 1999). The four active
compartments are decomposable plant material (DPM),
resistant plant material (RPM), microbial biomass (BIO) and
humified organic matter (HUM). Each compartment
decomposes according to first-order kinetics at a rate chara-
cteristic of that material. The IOM compartment is resistant
to decomposition. Decomposition rates for the active pools
depend on air temperature, soil moisture and vegetation
Table 2 Annual application rate of N, P and K (kg ha�1) for each crop, the source and carbon input by organic amendments
Treatments
Zhengzhou (ZZ) Gongzhuling (GZL)
Maizea Wheat Maize
Mineral
N-P-K
Mineral
N-P-K
Organic amendments
Mineral
N-P-K
Organic amendments
Source N-P-K
Average C
input/Mg C ha�1 Source N-P-K
Average C
input/Mg C ha�1
Control 0 0 – – – 0 – – –
NPK 188-41-78 165-36-68 – – – 165-36-68 – – –
NPKM 188-41-78 50-36-68 HM, CMb 115-66-92c 2.04 50-36-68 FYMb 115-39-77c 2.45
NPKS 188-41-78 121-36-68 Maize straw 42-8-86c 2.27 112-36-68 Maize straw 53-6-58c 2.86
aN, P and K to maize in 1991 and 1992 were 165, 36 and 68 kg ha�1 yr�1, respectively. bThe manure types were horse manure from 1990 to
1998 and cattle manure from 1999 to 2008 at the Zhengzhou site. Manure was not applied in 2007. HM, horse manure; CM, cattle manure;
FYM, farmyard manure mixed with crop residue and soil. cThe nutrient amount added by straw and manure based on Zhao et al. (2010).
© 2013 The Authors. Journal compilation © 2013 British Society of Soil Science, Soil Use and Management, 29, 182–190
184 J. Wang et al.
coverage. Clay content is also used to calculate maximum
moisture deficit in the topsoil (0–20 cm) and affects the
partitioning of C between that lost in gaseous emissions from
the soil and that transferred to BIO + HUM.
Carbon input to soils and driving variables
Grain yield and straw dry matter (DM) for both crops were
measured in all treatments at ZZ, while only grain yield and
limited straw DM were available at GZL. Therefore, straw
DM from maize at GZL was calculated through a mean of
the harvest index from all the treatments measured in 2003,
2006 and 2007. The value was 0.45 � 0.03. The belowground
C input by roots was estimated with a root: aboveground DM
ratio and the proportion of roots in the top 20 cm of the soil.
The values of the two parameters used for maize were 0.35
and 0.86 (Li et al., 1994; Yang et al., 2000), and 0.43 and 0.75
for wheat (Ma, 1987; Li et al., 1994), respectively. Wheat at
ZZ was harvested by combined harvester leaving a stubble
height about 20 cm. By considering the differences of plant
height at harvest between the treatments, C input by wheat
stubble was about 26% of straw for the mineral fertilizer
treatments but 35% for the Control treatment at ZZ. Maize
at both sites was harvested by hand, and stubble was about
3% of straw for all the treatments. The contribution of weeds
to C input was ignored as they were removed manually. For
all the treatments, organic C contents for wheat and maize
were taken as national averaged values, that is, 39.9% and
44.4% (oven-dried basis), respectively (NCATS, 1994).
Monthly average air temperatures and amount of
precipitation between 1989 and 2008 were obtained from the
nearest meteorological stations at both sites. Monthly
evapotranspiration was calculated by the Penman–Monteith
equation (Allen et al., 1998) and then divided by 0.75 to
obtain monthly open-pan evaporation required by the model
(Coleman & Jenkinson, 1999).
In the model, the quality of plant materials added to soils
is distinguished by a DPM: RPM ratio. The larger the ratio,
the faster it decomposes. The ratio was set to 1.44. Manure
was split into DPM (49%), RPM (49%) and HUM (2%),
according to the model defaults. Because no measured data
were available, the IOM in the topsoil was set to 1.39 and
2.68 Mg ha�1 for ZZ and GZL, respectively, based on the
equation set by Falloon et al. (1998). It was assumed that
SOC content was in dynamic equilibrium at the start of the
experiments.
Statistical analysis
The ANOVA and least significant difference (LSD) methods
were applied to compare mean C input in the considered
treatments over the entire experimental period using SPSS
16.0. Model performance was evaluated by the root-mean-
square error (RMSE) and relative error (E), which indicates
the bias in the total difference between simulations and
measurements (Smith et al., 1997b):
RMSE ¼ 100O
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiXni¼1
ðPi � OiÞ2=ns
: ð1Þ
E ¼ 100n
Xni¼1
ðOi � PiÞ=Oi: ð2Þ
where Oi is observed value, Pi is predicted value, O is the
mean of the observed data, and n is the number of paired
values.
Results and discussion
C inputs under long-term fertilizer application
Average annual C input (Mg C ha�1 yr�1) from the crops
(including roots and stubble) under the Control treatment
showed a range from 0.94 at GZL to 1.50 at ZZ (Figure 1).
Application of mineral fertilizer (the NPK treatment)
significantly increased crop biomass (Wang et al., 2010;
Zhang et al., 2010), hence annual C input from the crops, at
both sites (2.45–3.72 Mg C ha�1 yr�1). It has been shown that
the incorporation of straw (the NPKS treatment) and manure
(the NPKM treatment) did not benefit crop biomass
immediately compared with the NPK treatment (Wang et al.,
2010; Zhang et al., 2010). Therefore, annual C input by the
crops showed no significant differences between the NPK,
NPKM and NPKS treatments. As expected, total annual C
input was significant larger in the treatments with straw
returned or manure applied than that in the NPK treatment.
The input under the NPKS and NPKM treatments was
1.50–1.66 times of that under the NPK treatment at ZZ and
2.01–2.16 times at GZL.
Model evaluation and modification
The simulated and measured SOC agreed well, and the
values of RMSE were less than 10% in the Control, NPK
and NPKM treatments at both sites (Figure 2a–c and e–g).
The result is consistent with the reported simulations in
China for similar treatments (Yang et al., 2003; Guo et al.,
2007). However, the SOC content was overestimated
compared with measured data in the NPKS treatment
(Figure 2 d and h). The worst simulation result occurred for
treatment NPKS at GZL.
Overestimation of the SOC content for treatments
involving the incorporation of straw or its retention after
harvest has been reported by Ludwig et al. (2005), Shirato
et al. (2005), Liu et al. (2009) and Heitkamp et al. (2012).
© 2013 The Authors. Journal compilation © 2013 British Society of Soil Science, Soil Use and Management, 29, 182–190
Soil C sequestration under long-term fertilizer applications 185
(a) ZZ
CK NPK NPKM NPKSAnn
ual c
arbo
n in
put (
Mg
C/h
a/yr
)
0
2
4
6
8
10
A
BC
a
b b b
C
(b) GZL
CK NPK NPKM NPKS Ann
ual c
arbo
n in
put (
Mg
C/h
a/yr
)
0
2
4
6
8
10
Crop-COrganic amendment C
a
b b bA
B
C C Figure 1 Average annual carbon input from
crops (including roots and stubble) and
organic amendments in the treatments
between 1990 and 2008. Different small letters
(annual C input from crops) and capital
letters (total annual C input) show significant
difference at 0.05 level of Fisher’s LSD for
each site.
(f) GZL: NPK
SO
C (
Mg/
ha)
10
20
30
40
50
60
(e) GZL: Control
10
20
30
40
50
60
(h) GZL: NPKS
1990 1995 2000 2005 2010 10
20
30
40
50
60
(g) GZL: NPKM
10
20
30
40
50
60
(b) ZZ: NPK
SO
C (
Mg/
ha)
10
20
30
40
50
60
(a) ZZ: Control
10
20
30
40
50
60
(d) ZZ: NPKS
Year1990 1995 2000 2005 2010
10
20
30
40
50
60
(c) ZZ: NPKM
10
20
30
40
50
60
RMSE = 4.7%E = 0.8%
RMSE = 8.2%E = –0.2%
RMSE = 6.7%E = –3.2%
RMSE = 13.2%E = –10.4%
RMSE = 8.1%E = 2.5%
RMSE = 7.9%E = –0.6%
RMSE = 7.8%E = –2.0%
RMSE = 24.7%E = –22.5% Figure 2 Comparison between simulated and
observed SOC contents in the topsoil
(0–20 cm) of different treatments at ZZ (a–d)
and GZL (e–h) (● Observed,— Simulated).
© 2013 The Authors. Journal compilation © 2013 British Society of Soil Science, Soil Use and Management, 29, 182–190
186 J. Wang et al.
For example, Ludwig et al. (2005) stated that the simulation
with the default settings and with aboveground residues
incorporated into the soil overestimated the changes in
maize-derived SOC by 1.6-fold after 24 yrs of continuous
maize cropping in a silt-loam soil. Therefore, it could be
deduced that the overestimation of SOC may be attributed
mainly to the C turnover rate for straw being too small,
thereby causing an apparent accumulation of SOC in the
soils.
At ZZ, an overestimation of SOC (E = �10.4%) for the
NPKS treatment could be due to an inappropriate setting of
DPM:RPM. The default value is suitable when root biomass
is the main source of C input to the soil (Figure 2 a, b, e
and f). However, the value should be greater when a large
amount of straw is incorporated into the soil, as straw C has
a shorter residence time than does root C (Rasse et al.,
2005). To improve simulation accuracy for the treatment at
ZZ, a modification of the ratio was made. Following
Ayanaba & Jenkinson (1990), the ratio was set to 3.35,
which improved the prediction of SOC changes (Figure 3).
An independent data set collected at Quzhou site, Hebei
province, northern China, was used to further evaluate the
model (Figure 4).
The model with the modified value of the ratio accurately
predicted SOC dynamics in the topsoil (0–20 cm) under
conventional tillage with straw incorporation. However,
others have reported that there is only a slight improvement
in the simulations with a similar modification to the ratio
value (Ludwig et al., 2005; Shirato et al., 2005). The
discrepancies between the modelling performances highlighted
that further improvement of the model would be needed to
simulate C dynamics in the soil with straw added.
The model was run for treatment NPKS at GZL with the
modified value of the ratio. The simulation was improved
but still overestimated the SOC content (E = �14.5%,
Figure 6), suggesting that simulation of SOC with straw
retention could not be improved, simply by changing the
DPM:RPM ratio. A more accurate estimation of the amount
of surface-retained straw that is incorporated into the soil
also needs to be considered in the simulation. Following the
method proposed by Liu et al. (2009), an extra parameter,
straw retention factor (fs), was introduced to adjust the
amount of straw incorporated into the soil. By using an
inverse simulation technique, the fitted value of the factor
can be determined by taking RMSE as a criterion. To do so,
the value of fs was varied from 0.00 to 1.00 with an
increment of 0.01. The model was repeatedly run for the
whole experimental period with different values of fs. When
the DPM:RPM ratio was set to 3.35, fs was 0.24 while
RMSE was a minimum (Figure 5). With the modifications in
both parameters, simulation for treatment NPKS at GZL
agreed well with the observations (RMSE = 5.6%, Figure 6).
Year
1990 1995 2000 2005 2010
SO
C (
Mg/
ha)
10
15
20
25
30
35
Observed Original, DPM:RPM = 1.44 Modified, DPM:RPM = 3.35
Figure 3 Comparison between simulated and observed SOC
contents in the topsoil (0–20 cm) for treatment NPKS at the ZZ site.
SOC changes were simulated with different DPM:RPM ratios (solid
line for 1.44 and solid line with open cycle for 3.35).
Year1983 1988 1993 1998 2003
SO
C (
Mg/
ha)
5
10
15
20
25
N1P2S0
N2P2S2
Simulated
Original, DPM:RPM = 1.44 Modified, DPM:RPM = 3.35
Figure 4 Simulated and observed SOC contents in the topsoil (0–
20 cm) for two treatments (N1P2S0 and N2P2S2) with conventional
tillage at Quzhou site, Hebei province, northern China. N1P2S0:
112 kg (urea-N) ha�1 yr�1, 150 kg (P2O5) ha�1 yr�1 and no straw
application; N2P2S2: 187 kg (urea-N) ha�1 yr�1, 150 kg (P2O5)
ha�1 yr�1 and 4.5 Mg straw (DM) ha�1 yr�1. Observed data were
extracted from the literature (Niu et al., 2003; Ludwig et al., 2010).
Straw retention factor (fs)0.0 .2 .4 .6 .8 1.0
RM
SE
(%
)
0
5
10
15
20
Figure 5 Changes in root-mean-square error (RMSE) with the straw
retention factor (fs) that varies from 0.00 to 1.00 with an increment
of 0.01. The lowest RMSE is obtained at fs = 0.24.
© 2013 The Authors. Journal compilation © 2013 British Society of Soil Science, Soil Use and Management, 29, 182–190
Soil C sequestration under long-term fertilizer applications 187
This result indicated that a large fraction of surface-retained
straw may be lost through wind erosion before entering the
soil because of strong winds and dry soils in spring (Yang
et al., 2006).
SOC prediction under current nutrient managements
We used the reparameterized RothC-26.3 model to predict
the impact of current nutrient managements on SOC
dynamics for 30 yrs from 2009 for both sites. Because of the
difficulty of downscaling projected climatic data to the site
level, average climate data between 1990 and 2008 were used
as the driving variables in the simulations, and average
annual C input between 2004 and 2008 was assumed as
annual C input for the prediction.
The rate of C sequestration at GZL was less than that at
ZZ for the corresponding treatments (Table 3). This can be
explained by differences in initial SOC content and cropping
intensity, which affect the amount of crop residue retention.
The Control treatment (No fertilizer application) resulted in
steadily declining SOC contents at both sites, whereas the
application of mineral fertilizers can maintain SOC content
at GZL and significantly increase SOC content at ZZ. The
application of organic materials in combination with mineral
fertilizers was a more effective way for C sequestration than
using mineral fertilizers alone.
Conclusions
This study tested the suitability of the RothC-26.3 model to
simulate SOC dynamics in north and northeast China
compared with data sets from long-term experimental and
specifically estimated soil C sequestration in response to
different strategies in straw and manure applications.
RothC-26.3 adequately simulated SOC content in the
treatments where roots and manure were the main C input
sources (Control, NPK, NPKM), but overestimated the SOC
content when crop straw was retained (NPKS). By
modifying the default setting for DPM:RPM to 3.35 for
treatment NPKS, the simulated SOC contents agreed well
with the observed values at the ZZ site. Inverse simulation
showed that only 24% of surface-retained straw was
effectively returned to the soil. These results indicated that
RothC-26.3 can be used to simulate SOC dynamics under
different fertilizer regimes in north and northeast China, but
modifications are needed when large quantities of straw are
retained. The application of mineral NPK can maintain and
increase SOC content, but crop straw amendment and
manure application are effective ways to enhance soil C
sequestration in the regions.
Acknowledgements
We acknowledge all colleagues for their unremitting efforts at
the long-term experiments. Dr Wendy Wang, University of
Maryland, made contribution to simulation design. The
research was funded by the Beijing Science Foundation
(6102023), the National Science Foundation of China (4117
1239, 40901141) and the National Basic Research Program
(2011CB100501).
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Table 3 Simulated C sequestration rate (Mg C ha�1 yr�1) in the
topsoil (0–20 cm) under different fertilizer regimes at the two
experimental sites for different periods
Treatments 1990–2008 Next 30 years
ZZ
Control �0.16 �0.07
NPK 0.29 0.19
NPKM 0.55 0.35
NPKS 0.47 0.33
GZL
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NPKS 0.08 0.10
Year1990 1995 2000 2005 2010
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