Potential and sustainability for carbon sequestration with improved soil management in agricultural soils of China
Post on 30-Aug-2016
e 12 D
Agriculture, Ecosystems and Environme1. Introduction
Agricultural soils generally have lower organic matter
content than natural lands because of reduced C input (due to
annual harvest and removal of crop residue, etc.), high organic
C decomposition (due to frequent tillage), increased soil
erosion (Paustian et al., 1997; Bowman et al., 1999; Lal,
2002a, 2004) and other factors. Many studies have demon-
strated that improved management practices can increase the
C content of arable soils towards the levels found in natural
lands (Smith et al., 2000a; West and Post, 2002; Lal, 2004).
Increasing agricultural soil stocks has been suggested as an
important measure to sequester CO2 from the atmosphere to
help stabilize atmospheric CO2 concentrations and has been
estimated that 0.40.9 Pg C year1 can be sequestered withinglobal agricultural soils (Paustian et al., 1998). The Kyoto
Protocol under Article 3.4 includes the component of C
uptake by soil management in the framework of controlling
greenhouse gases emissions and hence has generated a broad
interest in studying C sequestration of agricultural soils
through improved managements.
The industrial C emissions of China are about
1 Pg C year1, second only to the United States (Marlandet al., 2005). As a signatory country of the Kyoto Protocol,
although it currently has no obligation to cut carbon dioxide
emissions, China is looking for ways to curb C emission and
to enhance C sequestration. The arable land in China covers* Corresponding author. Tel.: +86 10 6488 9808; fax: +86 10 6488 9399.
E-mail address: email@example.com (H. Yan).
0167-8809/$ see front matter # 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.agee.2006.11.008Arable land soils generally have lower organic carbon (C) levels than soils under native vegetation; increasing the C stocks through
improved management is suggested as an effective means to sequester CO2 from the atmosphere. Chinas arable lands, accounting for 13% of
the worlds total, play an important role in soil C sequestration, but their potential to enhance C sequestration has not yet been quantitatively
assessed. The C sequestration by agricultural soils is affected by many environmental factors (such as climate and soil conditions), biological
processes (crop C fixation, decomposition and transformation), and crop and soil management (e.g. tillage and manure application).
Estimation of the C sequestration potential requires the quantification of the combined effects of these factors and processes. In this study, we
used a coupled remote sensing- and process-based ecosystem model to estimate the potential for C sequestration in agricultural soils of China
and evaluated the sustainability of soil C uptake under different soil management options. The results show that practicing no-tillage on 50%
of the arable lands and returning 50% of the crop residue to soils would lead to an annual soil C sequestration of 32.5 Tg C, which accounts for
about 4% of Chinas current annual C emission. Soil C sequestration with improved soil management is highly time-dependent; the effect
lasted for only 2080 years. Generally, practicing no-tillage causes higher rate and longer sustainability of soil C sequestration than only
increasing crop residue into soils. The potential for soil C sequestration varied greatly among different regions due to the differences in
climate, soil conditions and crop productivity.
# 2006 Elsevier B.V. All rights reserved.
Keywords: Carbon sequestration; Soil management; Process model; Remote sensingAbstractPotential and sustainability for c
soil management in ag
Huimin Yan *, Mingku
Institute of Geographic Sciences and Natural Resource
Received 5 April 2006; received in revised f
Available onlinon sequestration with improved
ultural soils of China
o, Jiyuan Liu, Bo Tao
arch, Chinese Academy of Sciences, 11A Datun Road,
7 October 2006; accepted 7 November 2006
nt 121 (2007) 325335
(Kern and Johnson, 1993; Freibauer et al., 2004; Lal, 2004;
Paustian et al., 1995; Buyanovsky and Wagner, 1998).
s andabout 124 Mha, accounting for about 13% of the worlds
total. Chinas agricultural soils have relatively low C content
level, because of intensive use, long cultivation history and
the use of crop residue as fuels and feed for domestic
animals, hence may have a great potential for C sequestra-
tion through improved land management. It is estimated that
about 90% of C uptake by agricultural systems would be
emitted or returned to the atmosphere (Lin et al., 1997). C.S.
Li et al. (2003) and K.R. Li et al. (2003) estimated that under
conventional soil management Chinas cropland are losing
1.6% of their soil organic carbon (SOC) while U.S.
croplands are only losing 0.1%. However, although there
are many studies describing agricultural SOC stocks (S.Q.
Wang et al., 2005; X.B. Wang et al., 2005; Liu et al., 2006),
SOC loss due to cultivation (Wu et al., 2003; Song et al.,
2005), and the significance of improved soil management on
increasing soil C sequestration (C.S. Li et al., 2003; K.R. Li
et al., 2003; S.Q. Wang et al., 2005; X.B. Wang et al., 2005),
few quantitative studies concerning agricultural soil C
sequestration have been undertaken at the national level in
China. Only Lin et al. (2002) and Lal (2002b) estimated soil
C sequestration potential in China through proposed
cropland management activities by IPCC, using the rates
of C gain for various activities within the corresponding
area. Therefore, there is a significant gap of spatially explicit
quantification on C sequestration potential and its sustain-
ability with improved soil management in the agricultural
soils of China.
Many studies have been conducted in other regions to
assess the potential of agricultural soil sequestration at
national or regional level, and have explored the options to
enhance C sequestration (e.g. Smith et al., 2000a,b;
Vleeshouwers and Verhagen, 2002; Marland et al., 2003;
West and Marland, 2002, 2003; Dendoncker et al., 2004).
Most of previous studies have used empirical approaches
based on a comparison of measured organic C levels between
arable and natural lands or on observations of the organic C
change with improved management at limited sites (Lal and
Bruce, 1999; Smith et al., 1997, 1998, 2000a,b; West and Post,
2002). However, soil C sequestration is a complex process that
is influenced by many factors, such as organic C inputs from
crop residue or applied organic manure, climatic and soil
conditions, and the original C levels, and thus has high spatio-
temporal heterogeneity. A realistic estimate of the C
sequestration potential at regional or national scales requires
integrating the effects of various factors that affect C inputs to
and loss from soils and accounting the inherent high spatial
heterogeneity and temporal variability. Some studies have
linked site level process-based model with GIS to extrapolate
point measurements to regional scales (Falloon et al., 1998,
2000; Zimmerman et al., 2005). A combination of process-
based mechanistic modeling and satellite remote sensing is an
effective approach to integrate the effects of various factors on
soil C processes and to quantify the high spatial heterogeneity
in the rates of the C sequestration. Remotely sensed surface
H. Yan et al. / Agriculture, Ecosystem326properties combined with biogeochemical models have beenCurrently, no-tillage is practiced on only 5% of the worlds
cropland (1379 Mha globally) (Lal, 2004). The amount of
crop residue produced in the world is a large quantity, about
3.5 Pg year1, but only 5060% of the residue producedmay be returned to the soil (Lal, 1999). In China, only about
25% is returned to the fields (Ministry of Agriculture of
China, 1998). Most crop residue was either used as fuel or
feed for domestic animals in rural areas before 1980s, or
burned on field after 1980s when farmers ceased taking crop
straw as fuel due to improved living conditions. So, the
objectives of this study were to: (1) use a coupled remote
sensing- and process-based ecosystem model of CEVSA
(Cao and Woodward, 1998; Cao et al., 2003) to make a
spatially explicit quantification of the C sequestration
potential of Chinas arable lands; (2) evaluate the effec-
tiveness of different management options based on the
modelled C uptake rate and its sustainability; (3) make a
mechanistic analysis on the regional pattern of C
sequestration potential. The soil management options
considered in the present study are practicing no-tillage
and increasing crop residue input into soils.
2. Materials and methods
Estimation of soil C sequestration requires quantification
of the rates of C inputs and releases under improved soil
management. The source of increment in SOC is the net C
fixed by crops, usually measured as net primary productiv-
ity (NPP), but only a part of the fixed C actually is
incorporated into soils while the other parts are removed for
harvest or for clearing the field. Soils lose C from
heterotrophic respiration (HR), soil erosion by wind and
water. In the present study, only HR is included in
calculating soil C loss. The soil C sequestration was
estimated using a coupled remote sensing- and process-
based model (Fig. 1) that calculates the C inputs from crop
growth and the decomposition of C under differentused to predict C fluxes into and out of ecosystems and to
evaluate potential mechanisms of terrestrial CO2 sequestra-
tion (Nemani et al., 2003; Cao et al., 2004).
Soil C sequestration can be achieved by increasing the net
flux of C from the atmosphere to the terrestrial biosphere by
storing more of the C from net primary production in the
longer-term C pools in the soil or by slowing decomposition.
No-tillage can significantly reduce soil C release by
reducing the turnover of soil aggregates and the exposing
of young and labile organic matter to microbe decomposi-
tion (Paustian et al., 2000). This method has been taken as an
effective and environmentally friendly soil C sequestration
strategy (Lal, 2004). No-tillage and preferential crop
residues management (increasing C input) are two important
and widely recognized measures to enhance C sequestration
Environment 121 (2007) 325335management options.
s and2.1. Crop NPP and C inputs into soils
The rate of C input into agricultural soils was calculated
as the proportion of crop NPP that is returned into soils,
including crop residues and manure application. The NPP in
a given area at the present time was estimated using a remote
sensing-based production efficiency model, GLO-PEM. The
model consists of linked components that describe processes
of canopy radiation absorption, utilization, autotrophic
respiration, and the regulation of these processes by
environmental factors such as temperature, water vapor
pressure deficit, and soil moisture (Prince and Goward,
1995; Cao et al., 2004). It calculates NPP as follows:
H. Yan et al. / Agriculture, Ecosystem
Fig. 1. A schematic representation of the model for estimating soil carbon
sequestration. The meaning of acronyms are as follows: fraction of photo-
synthetically active radiation (FPAR), light use efficiency (LUE), auto-
trophic respiration (Ra), gross primary production (GPP), net primary
production (NPP), soil organic matter (SOM).NPP X
tStNteg Ra (1)
where St is the incident PAR in time t, Nt the fraction of
incident photosynthetically active radiation (PAR) absorbed
by vegetation canopy (FPAR) calculated as a linear function
of NDVI (Prince and Goward, 1995), eg the light useefficiency of the absorbed PAR by vegetation in terms of
gross primary production, and Ra is the autotrophic respira-
tion calculated as a function of standing aboveground bio-
mass, air temperature, and photosynthetic rate.
The NPP of crops consists of the organic C in the
economic products (e.g. grain), roots and straw (stems,
leaves, stalks, etc.), which were calculated using the C
allocation parameters as given in Table 1.
The C in the economic products of crops is usually
removed from crop lands; a part of the C in straw and roots is
removed away for other uses (e.g. fuel and livestock feed) or
is burned for clearing the field, and only the remaining C
enters into soil as the source of C. In addition, organic
manure is also an important C source for agricultural soils,
however, in China most of organic manure originated fromcrop products. At present, according to the national statistic
data, altogether 25% residues are returned into soils with
17% being directly incorporated into soils and 8% as organic
manure input into soils in China (State Environmental
Protection Administration of China, 2000). In the present
study, the rate of C input into the soil was estimated as a part
of NPP based on the C allocation among crop organs and the
survey of actual data inputs, including from the applied
organic manure. C input included all roots and returned
straw, and the proportions of NPP to roots and straws were
calculated by the mean value of different crops listed in
Table 1 because the crop types are unavailable for the
2.2. SOC decomposition
The rate of C release from agricultural soils was
calculated as the rate of heterotrophic respiration using a
process-based ecosystem model, CEVSA (Cao and Wood-
ward, 1998; Cao et al., 2003). In simulating organic carbon
transformation, decomposition and accumulation, CEVSA
divides soil organic matter into surface litter, root litter,
microbes, and slow and passive C pools, each of which has a
specific decay rate (Cao et al., 2003). All SOC transforma-
tions and decomposition in these pools are treated as first-
order rate reactions that are affected by temperature, soil
moisture, nitrogen availability, soil texture, and the lignin/
The original CEVSA did not consider the effects of
tillage on SOC dynamics. In natural lands, soil organic
matter is physically protected in microaggregates to
microbial decomposition. Tillage of arable lands enhances
soil organic matter decomposition by disturbing the physical
protection. It is estimated that the decay rate of SOM in
cultivated soils is several times higher than that of natural
Environment 121 (2007) 325335 327
Carbon allocation to economic products, straw and roots (Li et al., 1994)
Cropa Grain Straw Root
Wheat 0.28 0.42 0.3
Corn 0.3 0.44 0.26
Cotton 0.19 0.48 0.33
Soybeans 0.28 0.44 0.28
a Scientific names: wheat (Triticum aestivum), corn (Zea mays), cotton
(Gossypium hirsutum) and soybeans (Glycine max).lands (Balesdent et al., 2000; Six et al., 1998; Li et al., 1994).
In the present study, The CEVSA model was modified to
account the effect of tillage by using a parameter that
measures the increases on the decay rates of different C
pools relative to that in soils with no tillage (Leite et al.,
2004) (Table 2).
2.3. Data sources and model running
We use the coupled models of GLO-PEM and CEVSA to
calculate the average values of NPP, rates of SOC
study, we applied the methods of Lobell et al. (2002) at the
county level in China to estimate the cropland NPP of all
counties in 1996. The statistic-based NPP is computed by the
NPP g C m2
i1Yi1 MCi 0:45g C g1=HIi 0:9PNi1 Ai
where Y is the reported yield of crop i, MC is the typical
harvest moisture content (mass water/harvested mass,
g g1), HI is the harvest index (ratio of yield mass to
s anddecomposition, and the rates of soil C sequestration for
1990s. GLO-PEM is a top down model which estimates C
assimilation based on light use efficiency (LUE) and
ecophysiological processes, and its effect was highlighted
by its avoidance of spatial extrapolation or landcover
classification in NPP estimation over large scales (Goetz and
Prince, 1999). The satellite data used in estimating NPP
were obtained from the Pathfinder AVHRR Land (PAL) data
at resolutions of 8 km and 10 days that were derived from
channels 1, 2, 4 and 5 of AVHRR sensors aboard the NOAA-
7, 9, 11, and 14 satellites (Cao et al., 2004). AVHRR/NDVI
at 10 days temporal scale cannot only be used to calculate
crop absorption of photosynthetically active radiation, but
also provides regional applicable information about crop
dynamics and cropping system by describing crop growth
process. In fact, the multi-cropping system, including single-
, double- and triple-cropping systems, have been subsumed
in the calculation. However, with the coarse resolution of
8 km, two or more crop types were comprised in one pixel,
and so AVHRR is incapable to distinguish crop types.
Spatial and temporal heterogeneity in vegetation LUE due to
relative coarse spatial resolutions and complex cropping
system would induce errors. Improvements in the approach
to account for both spatial and temporal heterogeneity when
implementing LUE model at coarse resolution and multiple
cropping systems are important for future development of
the model. Nonetheless, the AVHRR was taken as the most
state-of-the-art, globally or regional applicable and free
available satellite data in the past two decades, which
provide a beneficial trade-off among the spatial resolution,
repeat cycle and data volume for regional to global
The cropland distribution in China was derived from the
National Land Cover Project (NLCD) database based on the
Enhanced Thematic Mapper (ETM+) images acquired in
1999 and 2000 for all of China (Liu et al., 2003, 2005). The
information on soil properties was derived from the 1:
4,000,000 soil map of China. The climate data (temperature,
precipitation, relative humidity, sunshine duration, and wind
speed) used were those interpolated for 0.18 grid based ondata from 730 meteorological stations for each 10 days from
H. Yan et al. / Agriculture, Ecosystem328
Parameters for the tillage effects on the decay rates (Leite et al., 2004)
Carbon pool No tillage Conventional tillage
Active 1 1.8
Slow 1 4
Passive 1 1.81991 to 2000.
After obtaining crop NPP using the remote sensing data
we ran the soil C model driven by the average values of NPP
and climate data during the 1990s with seven soil
management scenarios (including current status scenario,
three realistic scenarios and three ideal scenarios) (Table 3).
Then we calculated the differences in the rates of soil C
change and in the soil C pool at the equilibrium levels underdifferent soil managements, so as to analyze the soil C
potential and the effectiveness in enhancing soil C potential
of the different options.
2.4. NPP validation with statistic data
Model validation over a large-scale is difficult because
field measurements are not available to evaluate remotely
sensed measures. Fortunately, county-level census data
could provide agricultural ecosystems a comprehensive,
independent measure of total plant production throughout
the growing season, and thus C uptake for comparison to the
satellite-derived estimates (Malmstrom et al., 1997). In this
Environment 121 (2007) 325335
Soil management scenarios for soil carbon sequestration estimates
Current soil management 25% crop residue return and
50% CR Increasing crop residue return
to 50% with conventional tillage
50% NT Practicing no tillage in 50% of
arable lands with current crop
50% CR + 50% NT Increasing crop residue return to
50% and practicing no tillage in
50% of arable lands
100% CR Increasing crop residue return to
100% with conventional tillage
100% NT Practicing no tillage in 100% of
arable lands with current crop
100% CR + 100% NT Increasing crop residue return to
100% and practicing no tillage in
100% of arable landsaboveground biomass) and A is the harvested area. In this
study, 10 major crops are considered (N = 10) and it is
assumed that 45% of crop biomass is C and 80% of NPP
is allocated to aboveground parts. Potential variability
within species for each of the factors used to convert yield
to NPP was not considered in this study. Values for MC and
HI were taken and adapted from Zhang and Zhu (1990),
Fang et al. (1996) and Lobell et al. (2002) (Table 4).
counties for subsequent comparisons. According to the
options separately. The upper limit of the C sequestration of
Chinas agricultural soils is estimated to be 6 Pg C with all
crop residue returns to soils and practicing no-tillage on all
of the arable lands.
H. Yan et al. / Agriculture, Ecosystems and Environment 121 (2007) 325335 329
Harvest index (HI) and moisture content (MC) of major crops
Cropa MC (%) HI
Rice 14 0.43
Wheat 12.5 0.37
Corn 13 0.44
Sorghum 14.5 0.39
Millet 13 0.38
Soybean 12 0.44
Cotton 8.3 0.4
Rapeseed 13 0.25correlation analysis, the estimates of crop NPP using this
methodology are essentially consistent with NPP derived
from county-level statistics (correlation coefficient
R = 0.68) (Fig. 2). Although the state reported crop yield
and the other agricultural statistics are likely biased due to
underestimation of cropland area, the use of data at the
county level provides a large number of samples for
evaluating remote sensing estimates of NPP.
3.1. The potential for C sequestration
Under the improved land management options, the
agricultural SOC pool of China could be increased by 2.3%To avoid errors in regions with sparse agriculture, we
limited our analyses to those counties where cropland area
accounted for more than 30% of the total county area
according to statistical data. Furthermore, we limited our
selection to those crops growing on more than one million ha
according to 1996 data. This resulted in a total of 1171
Potato 80 0.5
Sugar beets 85 0.4
a Scientific names: rice (Oriza sativa), sorghum (Sorghum bicolor),
millet (Panicum miliaceum), rapeseed (Brassica napus), potato (Solanum
tuberosum) and sugar beets (Beta vulgaris).up to 60.9%. The average rate of C sequestration (during the
period from starting practicing improved management
measures to reaching an equilibrium soil C status) ranges
from 21.5 to 71.7 Tg C year1 (Table 5). The results showthat no-tillage is very effective in enhancing soil C stocks
with high C sequestration potential. Increasing crop residue
Carbon sequestration potential under no-tillage (NT) and crop residues (CR)
potential (Tg C)
Yearly average carbon sequestr
potential (Tg C year1)
50% CR 231.8 23.2
100% CR 1146.2 57.1
50% NT 1247.3 21.5
100% NT 2497.2 43.0
50% NT + 50% CR 2372.0 32.5
100% NT + 100% CR 6024.0 71.7return can only produce a moderate C sequestration potential
and rates. Increasing crop residue return to 50% could
sequester 232 Tg C of soil C, only equivalent to 18% of the
sequestrated C with practicing no-tillage on 50% of the
arable lands. A combination of practicing no-tillage and
increasing crop residue return is the most effective measure
for sequestering C. 50% CR + 50% NT (increasing crop
residue return to soils from 25% to 50% and practicing no-
tillage in one-half of the arable lands, leaving another half
under conventional tillage) can sequester 2372 Tg C, which
almost double the sum of practicing the two management
Fig. 2. Comparison of NPP derived from GLO-PEM model and from
statistics. The production and sown area data were taken from national
natural resource database (http://www.naturalresources.csdb.cn).The rates of agricultural soil C sequestration change
significantly over time (Fig. 3A). The C sequestration rates
are normally high in the early stage of practicing no-tillage
and increasing crop residue return, and then decrease with
consequent increases of soil C pool and finally became zero
Saving of agricultural fossil
fuel-carbon (Tg C year1)Total carbon mitigation
potential (Tg C year1)
58 1.9 23.4
58 3.8 46.8
73 1.9 34.4
84 3.8 75.5
H. Yan et al. / Agriculture, Ecosystems and Environment 121 (2007) 325335330
Fig. 3. Annual soil C stock (A) and C sequestration rates (B) of converting
traditional cropland management to no-tillage (NT), crop residue return
(CR) and combination of NT and CR (NT + CR), and annual fractional
increases of soil carbon sequestration caused by CR, NT and the interaction
term of combining NT and CR (C).
Fig. 4. Maps of carbon sequestration potential for (A) no-tillage (NT)
practiced on all cropland scenario, (B) 100% crop residues returned into soil
scenario (CR), and (C) combination of 100% NT and 100% CR (NT + CR)
scenario (the other four scenarios have similar spatial patterns and different
quantity under same measurements implemented). The number is the codes
for nine agricultural regions of China.
Temperature (T), precipitation (P), net primary production (NPP) and cropland area (A) of nine agricultural regions in China
Names of agricultural regions Codea T (8C) P (mm) NPP (g C m2 year1) A (million ha)
Northeast Region 1 2.2 573.3 425 31.1
Innermongolia and the Great Wall Region 2 4.1 379.2 258 14.8
Huang-Huai-Hai Region 3 13.5 676.4 565 30.4
Loess Plateau Region 4 9.1 479.9 323 16.0
Middle and lower reach of Yangtze River Region 5 16.7 1541.3 761 34.9
Southwest Region 6 14.5 1097.1 581 30.0
South China Region 7 20.1 1579.9 912 11.5
Ganxin Region 8 5.7 150.6 110 8.8
Tibet Region 9 0.9 430.0 127 1.5a Code number of the nine agricultural regions in China.
as soil C reaches a new equilibrium level. However, these
changes differ among different management options. The
rate of C sequestration by increasing crop residue return is
higher than by practicing no-tillage in the first 5 years, but
decreases more sharply and becomes lower (Fig. 3B), while
the rate of C sequestration by combining no-tillage and
increasing crop residue return is higher than the sum of the
two managements practiced separately at any stage.
Thereafter, the C sequestration capacity of practicing no-
tillage lasted longer than increasing crop residue return, and
a combination of practicing no-tillage and increasing crop
residue return lasted longer than any other two measure-
ments practiced separately (Fig. 3A and C). For example, it
would take about 60 years for soil C to reach a new
equilibrium level of practicing no-tillage, but would just take
20 years with increasing crop residue return from 25% to
100%. With a combination of practicing no-tillage and
increasing crop residue return from 25% to 100%, soil C
would take about 85 years to reach a new equilibrium level.
3.3. Spatial pattern
Fig. 4 shows the spatial pattern of C sequestration
potential of arable lands in China under no-tillage and crop
residues management scenarios. Although the value of soil C
sequestration rates under different measures are remarkable
different, its spatial variability is similar. The C sequestra-
tion potential is higher in Southeast and lower in Northwest
China. Such regional variation is generally related to the
pattern of crop productivity and hence the amount of crop
residue returns to the soils (Fig. 5). Among the nine
agricultural regions in China (Table 6 and Fig. 3), NPP
varied from 110 g C m2 year1 in Ganxin Region to912 g C m2 year1 in the South China Region. Due to
H. Yan et al. / Agriculture, Ecosystems and Environment 121 (2007) 325335 331
Fig. 5. Map of carbon input with 100% crop residues return.Fig. 6. Carbon sequestration potential under 100% crop residue returned
scenario (A) and no-tillage implemented on all cropland scenario (B) in nine
agricultural regions of China that are lined up according the average C input
in each region, (the former six regions (8, 9, 2, 4, 1, 3) are located in the
north of China, and the latter three (6, 5, 7) are in the South of China). The
dotted line are trendline of Carbon Sequestration Potential with increasing C
input in the two parts of China, indicating there are regional differentiation
on C sequestration capacity between North and South China.Fig. 7. Carbon sequestration efficiency (ratio of C input to C emission)
under 100% crop residue returned scenario (A) and no-tillage implemented
on all cropland scenario (B) in nine agricultural regions of China. The nine
regions are lined up according the average C input in each region same asFig. 6.
the difference in crop productivity, soil C input would
change from 55 to 456 g C m2 year1 when a half of cropresidue would be returned to soil. Because soil C
sequestration rates are linearly correlated with C inputs
(Fig. 6), high crop productivity and hence more crop residue
return can cause more soil C sequestration.
The regional pattern of soil C sequestration is
controlled by climate conditions that affect SOC decom-
position. The warm and moist climate in southern China
can cause higher decomposition rates. Provided that the
same amount of crop residue is input into the soil, there
would be more C sequestered into the soil in northern
China (upper dot-line in Fig. 6) than in southern China
(lower dot-line in Fig. 6). Therefore, although having
equivalent C input levels, the Huang-Huai-Hai Plain
Region sequesters more SOC than the warmer and moister
southwest Region (Fig. 7). For the regions where both
temperature and moisture control organic matter decom-
position (such as Tibet) had the highest C sequestration
efficiency (ratio of C uptake to C input) (Figs. 7 and 8). In
the arid and semi-arid regions (2, 4, 8) of Northwest
China, the C sequestration efficiency is higher than the
humid region (1, 3, 6, 5, 7) located in East and South of
China (Fig. 7).
H. Yan et al. / Agriculture, Ecosystems and332Fig. 8. Maps of C sequestration efficiency of soil (ratio of C input to Cemission) (A: CR; B: NT).4. Discussion and conclusions
Chinas arable lands have a large potential for C
sequestration. Theoretically, the upper-limit of the agricul-
tural soil C sequestration potential with all crop residue
return and practicing no-tillage in all cropland would be
6.0 Pg C, close to the cumulative historic SOC loss of about
7.1 Pg C from the cultivated soils in China (Wu et al., 2003).
The realistic soil management option, 50% crop residue
return and practicing no-tillage in 50% of cropland, having a
C sink capacity of 2.4 Pg C (equivalent to 35% of the
historic SOC loss), would lead to annual soil C uptake of
32.5 Tg, 60% more than the current C uptake by all forests
(Fang et al., 2001). Practicing no-tillage can also reduce C
release with a decrease of energy use at the rate of
23.8 kg C ha1 year1(Smith et al., 1998). The annual fossilfuel saving C in China would be 1.9 and 3.8 Tg C year1 for50% no-tillage and 100% no-tillage, respectively. Conse-
quently, the total C mitigation potential is 75.5 Tg C year1
in the case that all crop residues is returned into soils
together with practicing no-tillage in all of the arable lands
(Table 5). The enhanced C uptake and reduced C release
from practicing 50% no-tillage and 50% crop residue return
is estimated to be 34.4 Tg C year1, equivalent to 4.5% ofthe Chinas total C emission in 2000 (Marland et al., 2005).
The no-tillage together with increasing crop residue
return (NT + CR) strategy is the most effective measure for
C sequestration through the combination of increasing SOC
input and decreasing SOC decomposition. The relationship
between effects of no-tillage and crop residue return is not
linear and non-additive but interacts with each other and
therefore intensifies soil C sequestration capacity. This
results in not only more C sequestration than the sum of
practicing the two management options separately, but also a
longer duration of C sequestration (Table 3). Accordingly, C
sequestration through the combination of practicing no-
tillage and increasing crop residue return could be attributed
to three terms: crop residue return (black area in Fig. 3C),
no-tillage (dark grey area in Fig. 3C) and the interaction
between crop residue return and no-tillage (light grey area in
Fig. 3C). At the preliminary stage of practicing no-tillage
together with increasing crop residue return, the contribu-
tions of crop residue or no-tillage predominate over the
interaction term; but with the attaining of new equilibrium
state by practicing two managements separately, the
interaction term begins to play a significant role, yielding
almost one third of sequestered C could benefit when a new
balance is attained (Fig. 3C). Relative to increasing crop
residue return, no-tillage soils have higher potential for C
sequestration by virtue of the resulted long sustainability of
C uptake. Although no-tillage has a high C sequestration
capacity, the average C sequestration rate is limited by low C
input, especially in the northwest of China where crop NPP
are generally low (Fig. 4A).
Soil C accumulation is far from linear (Smith et al., 1997;
Environment 121 (2007) 325335Freibauer et al., 2004), and this study shows that the rates of
s andC sequestration are highly time-dependent, they decrease
with time and finally approach zero as soil organic C pool
reaches a new equilibrium level. Our results also show that
the rates of C uptake resulting from practicing no-tillage
are smaller than the rates from increasing crop residue
return in the early stage, but become higher after several
years and last for longer. Some studies that used constant
rates and duration of C uptake to estimate the C
sequestration of agricultural soils can only give a reason-
able result within restricted areas and periods, because the
C sequestration rate and its sustainability are changed with
the crop NPP, climate and soil conditions (Smith et al.,
1998; Dendoncker et al., 2004). Our estimated C
sequestration rates decrease with time, which are in
agreement with the studies of Marland et al. (2003) and
West and Post (2002), but the C sequestration rate does not
coincide with experiments-based result at the initial years.
The possible reasons here are that our estimates had
assumed that NT was practiced at a presumed equilibrium
state with lower SOC level after centuries of cultivation.
Moreover, the assimilated C and climate conditions remain
constant in this study. In reality, when the management is
changed from CT (conventional tillage) to NT, there is a
possibility that agricultural yields will also change, and the
effect of decreased or increased yield is most apparent in
the early years (Marland et al., 2003). In this study we
examine soil C uptake capability under present conditions
and do not consider any C loss or sequestration from crop
yield by land use or climate changes. Thomson et al.
(2006) showed that NT increased C sequestration rates by
2080 g C m2 year1 on the Huang-Hai Plain of Chinausing a different model. This is comparable to our
estimates in this region (with an average C sequestration
rate of 25 g C m2 year1 under NT and46 g C m2 year1 under NT together with 100% cropresidues returned during the first 20 years). Our results are
also consistent with the estimates of West and Post (2002),
who used a global database of long-term agricultural
experiments. They showed that change from CT to NT can
sequester 57 14 g C m2 year1.The variations in crop productivity, residue return, and
climate and soil conditions affect the regional pattern of soil
C sequestration (Paustian et al., 1995, 1998; Freibauer et al.,
2004). The crop NPP in China is generally higher in the
southeast and lower in the northwest, in agreement with our
estimated rates of agricultural C sequestration. Among the
nine agricultural regions in China, the annual average
temperature varies from 0.9 8C to the highest of 20.1 8C,and the annual precipitation from 150 mm to the maximum
of 1580 mm (Table 6). The difference in climate conditions
can explain the regional heterogeneity in our estimated C
sequestration rates for China (Huang et al., 2002). Generally,
warm and moist climate causes higher SOC decomposition
rate, while in the regions where organic matter decomposi-
tion is limited by low temperature, more C can be
H. Yan et al. / Agriculture, Ecosystemsequestered into the soil.Regional quantification of soil C mitigation potential and
sustainability is helpful for developing climate policies and
land management strategies. Soil C sink is not infinite but
will get to a saturation status after decades with the
implementation of land management (Watson et al., 2000).
The time taken for sink saturation to occur is highly variable
dependent on soil type, temperature and soil moisture. In this
study, we used a coupled remote sensing- and process-based
ecosystem model to estimate the potential and sustainability
for C sequestration of agricultural soils of China. This
coupled model integrates the effects of various factors
(climate, management, soil properties, etc.) on soil C
processes, with which C sequestration potential in China is
estimated with spatially explicit data on 0.18 0.18 grids,and the temporal profiles of C sequestration from measures
practiced to a new C equilibrium status reached are
described. The results obtained in this study are the greatest
potential to accumulate C from the beginning of the
implementation of measures until the time at which soil C
reaches a new equilibrium through taking account of the C
input, land management, climate, soil type, and many other
factors. The model input data are mainly based on remote
sensing measurements, which provide the most suitable data
for large scale research, and are the best available data of
cropland extent, climate and soil in China. The estimates of
crop NPP using this methodology agree well with county-
level crop statistics data. In reality, nevertheless, converting
100% of arable agriculture to no-till farming or incorporat-
ing 100% crop residues into soils is not achievable. Our aims
of taking into account the three scenarios (including 100%
NT, 100% CR, 100% NT + 100% CR) were to establish the
potential for C sequestration that could be obtained under
optimum conditions and to recognize the effects of C
sequestration with time and space under different measures.
Although the three realistic scenarios (including 50% NT,
50% CR and 50% NT + 50% CR) may be possible in terms
of soil and climate suitability, the application of no-tillage or
crop residue return can be constrained by the economic
conditions and the availability of technical equipment. Lal
(2004) showed that potential soil C sink capacity of
managed ecosystems equals approximately the cumulative
historic C loss, whereas the attainable soil C sink capacity is
only 5066% of the potential capacity. The physical,
technical and economic feasibility of no-tillage agricultural
and crop residues management are not taken into account in
this study, so the C sequestration potentials may be
overestimated. Incorporating the above-mentioned limita-
tions into our modeling will be an important step forward to
improve regional C sequestration potential estimates and
regional variability assessment. Besides, incorporating the
role of erosion into the model and using finer resolution
satellite data with the ability for determination of the spatial
distribution of crop types also are significant to narrow the
uncertainties of model results. Nevertheless, the results
presented here provided us with the basic information that
Environment 121 (2007) 325335 333there is a large C uptake potential in agricultural soils of
Academy of Sciences Hundred Talents Project (Mingkui
Soc. Am. J. 63, 186191.
H. Yan et al. / Agriculture, Ecosystems and Environment 121 (2007) 325335334Buyanovsky, G.A., Wagner, G.H., 1998. Carbon cycling in cultivated land
and its global significance. Global Change Biol. 4, 131141.
Cao, M.K., Woodward, F.I., 1998. Net primary and ecosystem production
and carbon stocks of terrestrial ecosystems and their response to
climatic change. Global Change Biol. 4, 185198.
Cao, M.K., Prince, S.D., Li, K.R., Tao, B., Small, J., Shao, X., 2003.
Response of terrestrial carbon uptake to climate interannual variability
in China. Global Change Biol. 9, 536546.
Cao, M.K., Prince, S.D., Small, J., Goetz, S., 2004. Satellite remotely sensed
interannual variability in terrestrial net primary productivity from 1980
to 2000. Ecosystems 7, 233242.
Dendoncker, N., Wesemael, B.V., Rounsevell, M.D.A., Roelandt, C., Let-
tens, S., 2004. Belgiums CO2 mitigation potential under improved
cropland management. Agric. Ecosyst. Environ. 103, 101116.
Falloon, P., Smith, P., Smith, J.U., Szabo, J., Coleman, K., Marshall, S.,
1998. Regional estimates of carbon sequestration potential: linking the
Rothamsted carbon model to GIS databases. Biol. Fertil. Soils 27, 236
Falloon, P., Smith, P., Coleman, K., Marshall, S., 2000. How important is
inert organic matter for predictive soil carbon modelling using theCao) and the Project of National Science Foundation of
China (30590384). We thank Dr. Changhui Peng, Dr. Heqing
Huang and two anonymous reviewers for their very helpful
comments during the finalization of this manuscript.
Balesdent, J., Chenu, C., Balabane, M., 2000. Relationship of soil organic
matter dynamics to physical protection and tillage. Soil Till. Res. 53,
Bowman, R.A., Vigil, M.F., Nielsen, D.C., Anderson, R.L., 1999. Soil
organic matter changes in intensively cropped dryland systems. Soil Sci.China, and the mitigation potential is noteworthy in C
mitigation options. These results are also useful to make
climate policy and land management strategies by virtue of
the spatial variability and temporal sustainability of C
uptake potential under different soil management measures.
However, we should note that soils have a finite capacity to
store C, and gains in soil C can be reversed if proper
management is not maintained; on the other hand, many C
sequestration measures have not only positive effects but
also potential negative effects to the environment and farm
profitability. Typically, practicing NT would increase
pesticide usage, promote N2O emission, increase the need
for high initial equipment costs and raise the risk of fungal
attack in wetter areas (Freibauer et al., 2004). Therefore,
managements and policies to sequester C in soils need to
have a discreet and comprehensive consideration.
This study was supported by Chinese Academy of
Sciences International Partnership Project Human Activ-
ities and Ecosystem Changes(CXTD-Z2005-1), National
Key Basic Research Project (G2002CB412507), ChineseRothamsted carbon model? Soil Biol. Biochem. 32, 433436.Fang, J.Y., Liu, G.H., Xu, S.L., 1996. Carbon stocks of terrestrial ecosystem
in China. In: Wang, G.C., Wen, P.Y. (Eds.), Greenhouse Gas Consistence
and Emission Monitoring and Related Process. China Environmental
Science Press, Beijing, China, pp. 109128.
Fang, J.Y., Chen, A., Peng, C.H., Zhao, S.Q., Ci, L.J., 2001. Changes in
forest biomass carbon storage in China between 1949 and 1998. Science
Freibauer, A., Rounsevell, M.D.A., Smith, P., Verhagen, J., 2004. Carbon
sequestration in the agricultural soils of Europe. Geoderma 122, 123.
Goetz, S.J., Prince, S.D., 1999. Modeling terrestrial carbon exchange and
storage: evidence and implication of functional convergence in light-use
efficiency. Adv. Ecol. Res. 28, 5792.
Huang, Y., Liu, S.L., Shen, Q.R., Zong, L.G., 2002. Influence of environ-
mental factors on the decomposition of organic carbon in agricultural
soils. Chin. J. Appl. Ecol. 13, 709714 (in Chinese).
Kern, J.S., Johnson, M.G., 1993. Conservation tillage impacts on national
soil and atmospheric carbon levels. Soil Sci. Soc. Am. J. 57, 200210.
Lal, R., 1999. Soil management and restoration for C sequestration to
mitigate the accelerated greenhouse effect. Prog. Environ. Sci. 1, 307
Lal, R., Bruce, J.P., 1999. The potential of world cropland soils to sequester
C and mitigate the greenhouse effect. Environ. Sci. Policy 2, 177185.
Lal, R., 2002a. Soil carbon dynamics in cropland and rangeland. Environ.
Pollut. 116, 353362.
Lal, R., 2002b. Soil C sequestration in China through agricultural intensi-
fication and restoration of degraded and desertified ecosystems. Land
Degrad. Dev. 13, 469478.
Lal, R., 2004. Soil carbon sequestration impacts on global climate change
and food security. Science 304, 16231627.
Leite, L.F.C., Mendonca, E.S., Machado, P.L.O.A., Filho, E.I.F., Neves,
J.C.L., 2004. Simulating trends in soil organic carbon of an Acrisol
under no-tillage and disc-plow systems using the Century model.
Geoderma 120, 283295.
Li, C., Frolking, S., Harriss, R.C., 1994. Modeling carbon biogeochemistry
in agricultural soils. Global Biogeochem. Cycles 8, 237254.
Li, C.S., Zhuang, Y., Frolking, S., Galloway, J., Harriss, R., Moore, B.,
Schimel, D., Wang, X.K., 2003. Modeling soil organic carbon change in
croplands of China. Ecol. Appl. 13, 327336.
Li, K.R., Wang, S.Q., Cao, M.K., 2003. Vegetation and soil carbon storage
in China. Sci. China Ser. D 33, 7280.
Lin, E.D., Liu, Y.F., Li, Y.E., 1997. Agricultural C cycle and greenhouse gas
emission in China. Nutr. Cycl. Agroecosyst. 49, 295299.
Lin, E.D., Li, Y.E., Guo, L.P., 2002. Carbon emissions and sinks in agro-
ecosystems of China. Sci. China Ser. C 45, 3039.
Liu, J.Y., Liu, M., Zhuang, D., Zhang, Z., Deng, X., 2003. Study on spatial
patterns of land use change in China during 19952000. Sci. China Ser.
D 46, 373384.
Liu, J.Y., Tian, H.Q., Liu, M., Zhuang, D., Melillo, J.M., Zhang, Z., 2005.
Chinas changing landscape during the 1990s: large-scale land trans-
formation estimated with satellite data. Geophys. Res. Lett. 32, L02405,
Liu, D.W., Wang, Z.M., Zhang, B., Song, K.S., Li, X.Y., Li, J.P., Li, F.,
Duan, H.T., 2006. Spatial distribution of soil organic carbon and
analysis of related factors in croplands of the black soil region, North-
east China. Agric. Ecosyst. Environ. 113, 7381.
Lobell, D.B., Hicke, J.A., Asner, G.P., Field, C.B., Tucker, C.J., Los, S.O.,
2002. Satellite estimates of productivity and light use efficiency in the
United States agriculture, 19821998. Global Change Biol. 8, 722735.
Malmstrom, C.M., Thompson, M.V., Juday, G.P., Los, S.O., Field, C.B.,
1997. Interannual variation in global scale net primary production:
testing model estimates. Global Biogeochem. Cycles 11, 367392.
Marland, G., Boden, T.A., Andres, R.J., 2005. Global, Regional, and
National Fossil Fuel CO2 Emissions (http://cdiac.esd.ornl.gov/trends/
Marland, G., West, T.O., Schlamadinger, B., Canella, L., 2003. Managing
soil organic carbon in agriculture: the net effect on greenhouse gasemissions. Tellus 55B, 613621.
Ministry of Agriculture Division of Energy Project Expert Team, 1998.
Assessment of Biomass Resources Availability in China. China Envir-
onmental Science Press, Beijing, China (in Chinese).
Nemani, R.R., Keeling, C.D., Hashimoto, H., Jolly, W.M., Piper, S.C.,
Tucker, C.J., Myneni, R.B., Running, S.W., 2003. Climate-driven
increases in global terrestrial net primary production from 1982 to
1999. Science 300, 15601563.
Paustian, K., Robertson, G.P., Elliott, E.T., 1995. Management impacts on
carbon storage and gas fluxes (CO2, CH4) in mid-latitude cropland and
grassland ecosystems. In: Lal, R., Kimble, J., Levine, E., Stewart, B.A.
(Eds.), Soil Management and Greenhouse Effect. Advances in Soil
Science. CRC Press, Boca Raton, FL, USA, pp. 6984.
Paustian, K., Cole, C.V., Sauerbeck, D., Sampson, N., 1998. CO2 mitigation
by agriculture: an overview. Clim. Change 40, 135162.
Paustian, K., Elliott, E.T., Six, J., Hunt, H.W., 2000. Management options
for reducing CO2 emissions from agricultural soils. Biogeochemistry
Paustian, K., Collins, H.P., Paul, E.A., 1997. Management controls on soil
carbon. In: Paul, E.A., Paustian, K., Elliott, E.T., Cole, C.V. (Eds.), Soil
Organic Matter in Temperate Agroecosystems: Long-term Experiments
in North America. CRC Press, Boca Raton, FL, USA, pp. 1549.
Prince, S.D., Goward, S.N., 1995. Global primary production: a remote
sensing approach. J. Biogeogr. 22, 815835.
Six, J., Elliott, E.T., Paustian, K., Doran, J.W., 1998. Aggregation and soil
organic matter accumulation in cultivated and native grassland soils.
Soil Sci. Soc. Am. J. 62, 13671377.
Song, G.H., Li, L.Q., Pan, G.X., Zhang, Q., 2005. Topsoil organic carbon
storage of China and its loss by cultivation. Biogeochemistry 74, 4762.
State Environmental Protection Administration, 2000. Report on the state of
the environment in China (http://www.zhb.gov.cn/english/SOE/soe-
Thomson, A.M., Izaurralde, R.C., Rosenberg, N.J., He, X., 2006. Climate
change impacts on agriculture and soil carbon sequestration potential
in the Huang-Hai Plain of China. Agric. Ecosyst. Environ. 114, 195
Vleeshouwers, L.M., Verhagen, A., 2002. Carbon emission and sequestra-
tion by agricultural land use: a model study for Europe. Global Change
Biol. 8, 519530.
Wang, S.Q., Yu, G.R., Zhao, Q.J., Niu, D., Chen, Q.M., Wu, Z.F., 2005.
Spatial characteristics of soil organic carbon storage in Chinas crop-
lands. Pedosphere 15, 417423.
Wang, X.B., Cai, D.X., Hoogmoed, W.B., Oenema, O., Perdok, U.D., 2005.
Scenario analysis of tillage, residue and fertilization management
effects on soil organic carbon dynamics. Pedosphere 15, 473483.
Watson, R.T., Noble, I.R., Bolin, B., Ravindranath, N.H., Verardo, D.J.,
Dokken, D.J. (Eds.), 2000. Land Use, Land Use Change, and Forestry.
Cambridge University Press, Cambridge, UK.
West, T.O., Post, W.M., 2002. Soil organic carbon sequestration rates by
tillage and crop rotation: a global data analysis. Soil Sci. Soc. Am. J. 66,
West, T., Marland, G., 2002. A synthesis of carbon sequestration, carbon
emissions, and net carbon flux in agriculture: comparing tillage prac-
H. Yan et al. / Agriculture, Ecosystems and Environment 121 (2007) 325335 335Smith, P., Powlson, D.S., Glendining, M.J., Smith, J.U., 1997. Potential for
carbon sequestration in European soils: preliminary estimates for five
scenarios using results from long-term experiments. Global Change
Biol. 3, 6779.
Smith, P., Powlson, D.S., Glendining, M.J., Smith, J.U., 1998. Preliminary
estimates of the potential for carbon mitigation in European soils
through no-till farming. Global Change Biol. 4, 679685.
Smith, P., Powlson, D.S., Smith, J.U., Falloon, P., Coleman, K., 2000a.
Meeting Europes climate change commitments: quantitative estimates
of the potential for carbon mitigation by agriculture. Global Change
Biol. 6, 525539.
Smith, P., Milne, R., Powlson, D.S., Smith, J.U., Falloon, P.D., Coleman, K.,
2000b. Revised estimates of the carbon mitigation potential of UK
agricultural land. Soil Use Manage. 16, 293295.tices in the United States. Agric. Ecosyst. Environ. 91, 217232.
West, T.O., Marland, G., 2003. Net carbon flux from agriculture: carbon
emissions, carbon sequestration, crop yield, and land-use change.
Biogeochemistry 63, 7382.
Wu, H.B., Guo, Z.T., Peng, C.H., 2003. Land use induced changes of
organic carbon storage in soils of China. Global Change Biol. 9, 305
Zhang, F.C., Zhu, Z.H., 1990. Harvest index for various crops in China. Sci.
Agric. Sin. 23, 8387 (in Chinese).
Zimmerman, P.R., Price, M., Capehart, W.J., Updegraff, K., Kozak, P.,
Vierling, L.A., Baker, E., Kopp, F., Duke, G., Das, C., 2005. C-Lock
(patent pending): a system for estimating and certifying carbon emission
reduction credits for the sequestration of soil carbon on agricultural
land. Mitig. Adapt. Strat. Global Change 10, 307331.
Potential and sustainability for carbon sequestration with improved soil management in agricultural soils of ChinaIntroductionMaterials and methodsCrop NPP and C inputs into soilsSOC decompositionData sources and model runningNPP validation with statistic data
ResultsThe potential for C sequestrationSustainabilitySpatial pattern
Discussion and conclusionsAcknowledgementsReferences