effects of land-cover type and topography on soil organic carbon storage on northern loess plateau,...
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Effects of land-cover type and topography on soilorganic carbon storage on Northern Loess Plateau,ChinaXiangwei Han a b , Atsushi Tsunekawa a , Mitsuru Tsubo a & Shiqing Li ba Arid Land Research Center , Tottori University , Hamasaka 1390, 680-0001, Tottori,Japanb State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau,Institute of Soil and Water Conservation, Chinese Academy of Sciences , Northwest A&FUniversity , Yangling, Shaanxi, 712100, ChinaPublished online: 10 Jul 2009.
To cite this article: Xiangwei Han , Atsushi Tsunekawa , Mitsuru Tsubo & Shiqing Li (2010) Effects of land-cover type andtopography on soil organic carbon storage on Northern Loess Plateau, China, Acta Agriculturae Scandinavica, Section B -Soil & Plant Science, 60:4, 326-334, DOI: 10.1080/09064710902988672
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ORIGINAL ARTICLE
Effects of land-cover type and topography on soil organic carbonstorage on Northern Loess Plateau, China
XIANGWEI HAN1,2, ATSUSHI TSUNEKAWA1, MITSURU TSUBO1 & SHIQING LI2
1Arid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680-0001, Japan, 2State Key Laboratory of Soil
Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences,
Northwest A&F University, Yangling, Shaanxi 712100, China
AbstractChanges in land cover from cropland to conservation can sequester carbon in soil. On the Loess Plateau of China, vast areasof sloping cropland were converted into forest and grassland to control soil erosion. The northern plateau is atopographically heterogeneous, semi-arid region. A good understanding of the change of soil organic carbon (SOC)storage on the plateau in the process of land-cover change is important for assessing environmental changes and planningfuture land cover. We selected four land-cover types (cropland, planted grassland, abandoned orchard, and secondarygrassland), and two vegetation covers (Stipa bungeana and Caragana korshinskii) on shady and sunny slopes, to analyse theeffects of land cover and slope aspect on SOC storage. Soil C in the top 100 cm was significantly (PB0.05) greater inartificial grassland (2.49 kg m�2) and secondary grassland (2.98 kg m�2) than in cropland (1.69 kg m�2). The SOC poolin the surface soil and throughout the 1-m profile followed the order secondary grassland�artificial grassland � abandonedorchards � cropland. Sequestration extended to deep soil (80�100 cm). Slope aspect affected SOC concentration: winderosion of the shady slope marginally reduced surface SOC relative to the sunny slope. In deep soil, responses of SOCconcentration to slope aspect differed between vegetation covers: under C. korshinskii, SOC concentration was significantlygreater on the shady slope (P B 0.05), but no difference was found under S. bungeana.
Keywords: Grain-for-Green Policy, land-cover change, slope aspect, soil erosion, soil organic carbon pool.
Introduction
The Loess Plateau of China is the site of intensive
study because of its serious soil erosion and typical
land-cover changes resulting from the ‘Grain-for-
Green’ Policy (GFGP), which was introduced to
control erosion. The plateau covers 624 000 km2
(Shi & Shao, 2000). It has a long history of agriculture,
and used to be an important grain source. Because of
over-cultivation, it now suffers the most serious soil
erosion in the world (Shi & Shao, 2000): erosion in
most areas measures 5000�10 000 Mg km�2 per year
(Chen et al., 2007b). Soil erosion is extremely serious
on slopes, and long-term erosion has formed gullies all
over the plateau. The ecosystem has deteriorated
seriously too (Wang et al., 2009). To control soil
erosion and improve the vegetation cover, the Chinese
Government initiated GFGP in 1999. Under GFGP,
cropland with a slope greater than 258 is converted
into grassland or forest. About 5 330 000 ha of crop-
land will have been re-greened by 2010 (Peng et al.,
2006).
Land-cover change is recognized widely as a cause
of SOC pool changes (Lal, 2003a; Mensah et al.,
2003; Degryze et al., 2004). The conversion of forest
and grassland into cropland decreases the SOC pool
(Wang et al., 2001; Bonino, 2006; Zhang et al., 2007).
Conversely, the restoration of grassland (Lemaire
et al., 2005; Breuer et al., 2006), scrubland (Gong
et al., 2006), or forest (Bonino, 2006) increases
the SOC pool. The resultant land cover following
restoration is important to the rate of SOC sequestra-
tion. Gong et al. (2006) found significant differences
in soil organic matter (OM) content among waste-
land, cropland, abandoned land, artificial grassland,
shrubland, and woodland. Robles & Burke (1997)
Correspondence: Xiangwei Han, Arid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680-0001, Japan. Tel: �81-857-23-34111.
Fax: �81-857-29-6199. E-mail: [email protected]
Acta Agriculturae Scandinavica Section B � Soil and Plant Science, 2010; 60: 326�334
(Received 13 March 2009; accepted 22 April 2009)
ISSN 0906-4710 print/ISSN 1651-1913 online # 2010 Taylor & Francis
DOI: 10.1080/09064710902988672
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found different responses of soil OM between
legumes and grass.
Topography also influences SOC sequestration
(Norton et al., 2003; Rhoton et al., 2006; Wei et al.,
2006), primarily through influencing the production
of biomass (Tatsuhara & Kurashige, 2001), and
secondarily through its effect on soil water and
temperature and thus on decomposition (Fekedulegn
et al., 2003). Tan et al. (2004) found site variables
(soil taxon, texture, drainage class, slope gradient and
elevation) contributed to more than 50% SOC varia-
tion in cropland and grassland. Liu et al. (2007) found
that slope angle and aspect had more important
effects than did land-cover type on soil OM, clay
content, and nutrient concentration.
SOC concentration is greatest in the surface soil
and decreases with depth. The soil depth to which
SOC is influenced by land-cover change varies
among studies: Degryze et al. (2004) reported that
the change of SOC with depth was restricted to the
surface soil (0�7 cm) in forest, yet Omonode & Vyn
(2006) found a considerable amount of SOC seques-
tered in deeper soil (0�100 cm).
Some studies on the plateau have examined the
effects of land-cover change on the SOC pool (Liu,
S.Z. et al., 2005; Peng et al., 2006; Chen et al.,
2007a), but most examined a limited soil depth (e.g.,
40 cm). Plateau-wide studies used a low spatial
resolution to explain micro-topographic effects.
Most site-based studies were carried out in the middle
to southern part of the plateau, which has higher
precipitation and favors forestry. In contrast, the
northern plateau, at its juncture with the Maowusu
Sandy Grassland, is dry, and the typical vegetation is
grass. The region suffers from both wind and water
erosion (Zhang, 1999), and risks becoming desert.
The ecology is very fragile. Thus, land restoration in
this region is urgent. GFGP was well implemented
there, and most of the slopes were converted into
grassland. This presents the opportunity to study
SOC changes as a result of land-cover change.
However, little information is available on the effects
of land-cover change and topography on SOC on the
Northern Loess Plateau. We conducted a study (1) to
evaluate the effect of land-cover conservation on SOC
sequestration, and (2) to reveal the effect of slope on
SOC concentration since the implementation of
GFGP.
Materials and methods
General description of study area
Soil samples were obtained from a small catchm-
ent, the Liudaogou catchment, in Shenmu County,
Shaanxi Province, China (38847? N, 110822? E). The
elevation ranges from 1094 m to 1274 m. The region
has a semi-arid climate with an average annual
precipitation of 437.4 mm (1957�1989; minimum
108.6 mm in 1965; maximum 819.1 mm in 1967)
(Academia Sinica & Ministry of Water Resources,
1993), 77% of which falls during June through
September. The mean annual temperature is 8.4 8C,
and the mean minimum temperature ranges from �9.7 8C in January to 23.7 8C in July. The annual
cumulative temperature above 10 8C is 3228 8C. The
mean frost-free season is 169 days. The average
annual potential evaporation is 785.4 mm, and the
mean desiccation degree is 1.8 (Li et al., 2007). The
catchment lies in a transition region between the
Loess Plateau and the Maowusu Sandy Grassland,
and thus represents an ecotone in which wind and
water erosion are both significant factors (Zheng et al.,
2006).
The natural vegetation of the study site is shrub�grassland. However, because of excessive cutting,
overgrazing, and serious soil erosion, the vegetation
has degraded. Since the GFGP was adopted, more
than half of the sloping croplands in the study area
have been returned to shrubland or grassland. The
main shrubs planted for recovery are Salix psammo-
phila and Artemisia ordosica on sandy soil, and
Caragana korshinskii on loam and clay soils. Some
of the cropland was planted with alfalfa (Medicago
sativa), and some with apricot (Armeniaca vulgaris).
Years later, the alfalfa grassland degraded, and then
underwent natural succession to secondary grassland
dominated by Stipa bungeana. Because of the water
deficit in the region, the apricot trees didn’t grow
well and were later abandoned. At present, the main
land-cover types are cropland, abandoned land,
grassland, and shrubland. Lowland croplands are
occupied by irrigated maize and vegetables. Sloping
croplands are planted to rainfed potato and beans.
Most of the sloping croplands receive manure and
nitrogen fertilizer, but restored croplands have
received nothing.
The loess extends to a depth of more than 30 m (Li
et al., 2007). Erosion by water and wind has
complicated the soils of the study catchment. The
northwest side of the catchment is covered by wind-
accumulated sand. A channel check dam holds
deposited soil. The southeast side is sandy loess.
Our study was conducted on the sandy loess (Table I).
Soil sampling and laboratory analysis
Site for evaluating effects of land-cover type. Soil samples
were collected from four main restored land-cover
types in the study area: artificial grassland with
planted alfalfa (AGL) for about 8 years; secondary
grassland, used to be planted with alfalfa for almost
Soil organic carbon of different land-covers 327
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10 years, then underwent natural succession to S.
bungeana (SGL) more than 7 years ago; and orchards,
planted almond 8 years ago and covered by some
weeds (ABO). To illustrate the change of soil organic
carbon, samples were also collected from cropland
(CRL), which was continuously tilled and planted
with potato or soybeans for more than 25 years;
currently the area is planted with soybeans.
Different soil types are usually quite different in soil
organic carbon concentrations. For the purposes of
comparison, we collected samples from sites with
homogeneous soil conditions in early September
2007. Before land restoration, the sample sites were
cultivated in the same way. Five replicated represen-
tative samples were obtained for each land-cover type.
Site for evaluating the effects of slope. We chose a pair of
slopes facing each other, sunny (slope aspect was
1958, with an azimuth of 08 for north) and shady
(slope aspect was 158). On each slope, we collected
soil samples from two belts, one covered by
C. korshinskii and the other by natural grassland
dominated by S. bungeana. The last two land cover
types were sites for evaluating the effects of slope
(Table 1). The length of the shady slope was about
150 m. Along it, we selected seven sites from each
belt. The length of the sunny slope was about 90 m.
We selected six sites from the C. korshinskii belt and
five from the S. bungeana belt. All sites were spaced
about 20 m apart.
Soil sampling and laboratory analysis. At each sam-
pling site, we took three cores to a depth of 100 cm
at 20-cm intervals using a 20-cm by 5-cm soil auger,
and bulked the samples. We selected 20 sites for
comparison of the land-cover effect and 25 sites for
comparison of the topography effect.
We carefully examined the samples, and removed
roots, leaves, and other unwanted material. All
samples were air-dried and ground to pass through
0.25-mm screens before laboratory analysis. After
digestion in glass cuvettes at 185�190 8C (oil-bath),
the SOC was determined by the K2CrO7 titration
method (Nelson & Sommers, 1982). Soil bulk
density was determined using the core samples.
Calculations and statistical analysis
The SOC pool (DSOC, kg C m�2), expressed as
mass per unit area to a fixed depth, was calculated
from SOC concentration (SOC, g kg�1 soil) and
bulk density (r, g cm�3) as shown in Equation (1):
DSOCi�100�SOCi �ri � di (1)
Table
I.S
elec
ted
pro
per
ties
of
the
surf
ace
soils
of
dif
fere
nt
lan
d-c
ove
rty
pes
.
Soil
part
icle
com
posi
tion
(%)
Lan
d-c
over
typ
eT
ota
lN
(gkg�
1)
Inorg
an
icN
(mg
kg�
1)
Ava
ilable
P(m
gkg�
1)
Ava
ilable
K(m
gkg�
1)
B0.0
02
mm
0.0
02�0
.05
mm
0.0
5�2
mm
CR
L0.2
713.8
5.7
115.3
7.6
76.4
13.5
AG
L0.3
69.7
4.8
130.5
9.1
78.1
9.4
AB
O0.3
112.1
3.9
110.9
8.0
70.1
18.9
SG
L0.3
78.2
2.1
105.0
8.3
83.0
5.5
SB
0.3
37.3
5n
a127.5
8.1
74.9
13.3
CK
0.3
88.7
3n
a120.8
8.4
73.5
15.1
na�
not
ava
ilable
.C
RL�
crop
lan
d;
AG
L�
art
ific
ial
gra
ssla
nd
cover
edby
alf
alf
a;
AB
O�
aban
don
edapri
cot
orc
hard
cove
red
wit
hA
rmen
iaca
vulg
ari
s;S
GL�
seco
nd
ary
art
ific
ial
gra
ssla
nd
cover
ed
pre
dom
inan
tly
by
Stipa
bunge
ana;
SB�
natu
ral
gra
ssla
nd
cover
edb
yS
tipa
bunge
ana;
CK�
natu
ral
shru
bla
nd
pla
nte
dw
ith
Cara
gana
kor
shin
skii.
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where d is the soil depth (cm), subscript i is the
position of the soil layer, and 100 is used for unit
conversion.
To analyse the effect of land cover on SOC
sequestration, we compared soil data obtained from
the four land-cover types. We used one-way analysis
of variance (ANOVA) with land-cover type or soil
layer as the main factor to test the significance of
differences between SOC densities in or among soil
layers. When the analysis indicated a significant
difference (PB0.05), we used the least significant
difference (LSD) procedure to compare means. We
also tested the effects of topography of the paired
sunny and shady slopes in the C. korshinskii and
S. bungeana plots on SOC within each soil layer by
ANOVA. Significant differences were determined at
a�0.05. All statistical analyses were done using the
SPSS software (SPSS, 2006; Version 15.0).
Results
Spatial distribution of SOC and soil bulk density
SOC concentration decreased with increasing soil
depth in all four land-cover types and under both
vegetation covers (Table II). The mean concentra-
tions in the surface soil (0�20 cm) were all signifi-
cantly greater than in the deeper layers (PB0.01).
The SOC concentrations at 20�40 cm were all
approximately 30 to 45% less than in the surface
soil. There was no statistical difference among
concentrations in the lower layers, except in SGL
and S. bungeana, where the concentrations at 20�40 cm were significantly higher than those deeper in
the soil (PB0.05, PB0.01). SOC concentrations
within the same soil layer varied widely: the coeffi-
cients of variation (CVs) ranged from 12.2% to
41.3% (Table II). The top three layers, where the
plant roots concentrated, had higher variation. The
highest concentration in the surface soil appeared in
SGL. Caragana korshinskii had the highest concen-
trations of the deepest four layers. Concentrations
were lowest in CRL throughout the profile.
Soil bulk densities of the four land-cover types
varied both horizontally and vertically (Table II).
Unlike previous studies (Chen et al., 2007a; Omo-
node & Vyn, 2006), we found no statistical difference
among land-cover types or soil depths. CRL had the
highest mean value (1.42 g cm�3), and ABO the
lowest (1.32 g cm�3). Yet both of these land-cover
types tended to have higher bulk density in the second
layer (20�40 cm) than in the other layers, perhaps as a
result of tillage. The range of bulk density was smaller
than those of SOC concentration.
SOC pools of different land-cover types
Land-cover type and soil depth had significant effects
on SOC pool (Figure 1). SOC densities of SGL were
greatest, and were significantly greater than in CRL
in all but the deepest soil layer (PB0.01), followed by
those in AGL, which were significantly greater in the
0�20- and 60�100-cm layers than in CRL (PB0.05).
SOC pool in ABO was numerically but not statisti-
cally greater. SOC pools were significantly greater in
the 0�20-cm layer than in the deeper layers (PB
0.01). The patterns of SOC pool change down the
soil profile were inconsistent among land-cover
types: in CRL and AGL, SOC pool decreased to
a constant minimum at 20�100 cm, but in ABO and
SGL the SOC pool at 20�40 cm was significantly
higher than in the deeper three layers, which were
statistically indistinguishable.
The mean SOC pool throughout the soil profile
increased in the order CRLBABOBAGLBSGL
(Table III). The surface soil layer made a large
contribution to the C pool (�1/3), but the deeper
soil nevertheless held a considerable amount of
C (�2/3). Significant differences in SOC pool
among land-cover types were found both in surface
and deep soils.
Organic carbon density at different slope aspects
The surface SOC concentration fluctuated widely
along the slope (Figure 2). The lowest SOC con-
centration always appeared in the midslope. It tended
to be higher on the sunny slope at 0, 60, and 100 m,
and higher on the shady slope at 80 m.
Slope aspect had different effects on concentra-
tions between vegetation covers (Figure 3). Concen-
trations in the surface soil under both covers were
slightly higher on the sunny slope than on the shady
slope, but differences were not significant. Concen-
trations in the deeper layers under C. korshinskii were
significantly greater on the shady slope (PB0.05),
but there was no significant difference under
S. bungeana.
Discussion
SOC is balanced by gains and losses of organic C.
The gains are determined mainly by the amount and
types of plant and animal residues, while the losses
are regulated by the oxidation of existing soil OM, by
erosion, and, generally, also by leaching as dissolved
organic carbon, which could be ignored in our study
area owing to the low precipitation. Factors that
regulate both influence the SOC pool.
Soil organic carbon of different land-covers 329
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Our results show that land-cover change had
significant effects on SOC. This is consistent with
results from previous studies under different climate
conditions (Degryze et al., 2004; Breuer et al., 2006;
Omonode & Vyn, 2006; Chen et al., 2007a). Crop-
land has relatively low SOC, because crop residues
are usually removed from the field during harvest,
intensive management breaks down soil aggregates
and increases SOC decomposition, and activities
such as tillage and harvesting destroy the surface-soil
structure, thus exacerbating erosion (Gregorich &
Anderson, 1985; Gregorich et al., 1998). Our results
show that when croplands were abandoned or
converted into grassland, SOC pool to a 1-m depth
increased by 21% and by 47% to 76%, respectively.
This increase could be explained by an increase in
the input of residues, a decrease in decomposition,
or a decrease in soil erosion because of vegetation
protection.
The increments of SOC after restoration appear to
have differed among land-cover types. The greatest
SOC pool was found in SGL, followed by AGL,
ABO, and CRL; this was consistent with previous
results (Peng et al., 2006; Li et al., 2007). Restored
land planted with grass (AGL, SGL) had signifi-
cantly greater SOC than did CRL, but the aban-
doned orchard (ABO) did not have significantly
greater SOC than did CRL. Alfalfa, planted in AGL
and the early SGL, produced as much as 400 t dry
hay ha�1 (Jiang et al., 2007) and considerable root
biomass (Cheng et al., 2007). High productivity
indicates high C gains. Fruit trees in ABO have less
Table II. Soil organic carbon (SOC) concentration and bulk density (r) at different intervals under four land-cover types and two natural
vegetation covers.
SOC (g kg�1)
Land-cover type Depth (cm) Number of samples Mean SD CV (%) r (g cm�3)
CRL 0�20 5 2.05** 0.66 32.4 1.35
20�40 5 1.22 0.33 26.7 1.51
40�60 5 1.06 0.33 31.6 1.45
60�80 5 0.82 0.12 15.0 1.38
80�100 5 0.85 0.22 26.0 1.39
AGL 0�20 5 3.38** 0.73 21.7 1.35
20�40 5 1.82 0.52 28.8 1.24
40�60 5 1.44 0.60 41.3 1.40
60�80 5 1.24 0.39 31.5 1.37
80�100 5 1.36 0.30 22.4 1.42
ABO 0�20 5 2.78** 0.52 18.8 1.33
20�40 5 1.52 0.53 34.5 1.43
40�60 5 1.35 0.50 37.4 1.26
60�80 5 1.04 0.18 17.4 1.28
80�100 5 1.06 0.19 18.4 1.30
SGL 0�20 5 3.83** 0.64 16.7 1.42
20�40 5 2.24* 0.80 35.5 1.41
40�60 5 1.73 0.28 16.3 1.46
60�80 5 1.43 0.27 18.8 1.42
80�100 5 1.42 0.29 20.5 1.30
SB 0�20 12 3.15** 0.59 18.7 na
20�40 12 1.90** 0.45 24.0 na
40�60 12 1.41 0.35 24.7 na
60�80 12 1.29 0.29 22.8 na
80�100 12 1.22 0.25 20.5 na
CK 0�20 13 3.32** 0.90 27.2 na
20�40 13 2.32 0.35 15.3 na
40�60 13 2.16 0.26 12.2 na
60�80 13 1.95 0.34 17.2 na
80�100 13 1.97 0.51 26.1 na
*,**Difference significant at PB0.05 or PB0.01 [one-way analysis of variance (ANOVA) and least significant difference (LSD)]; SD�standard deviation. na�not available. CRL�cropland; AGL�artificial grassland covered by alfalfa; ABO�abandoned apricot orchard
covered with Armeniaca vulgaris; SGL�secondary artificial grassland covered predominantly by Stipa bungeana; SB�natural grassland
covered by Stipa bungeana; CK�natural shrubland planted with Caragana korshinskii. The values for SB and CK are the average of the
sunny and shady slopes.
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residual input than do grass, but they take up more
soil water and restrict weed growth, thus limiting C
gains. The difference in SOC between AGL and
SGL implies an effect of restoration time (Li et al.,
2007). Jiang et al. (2006) reported that SOC under
alfalfa increased over 20 years and then decreased as
a result of reduced production because of depletion
of soil water by old alfalfa stands. The age of
grasslands in our study was within the increasing
period, and the alfalfa was replaced by secondary
grasses, which need less water, thereby maintaining
high production. The levels of SOC increment were
somewhat different from those in other studies
(Gong et al., 2006; Omonode & Vyn, 2006; Chen
et al., 2007a; Li et al., 2007). This difference can be
explained by differences in soil, climate, and time of
restoration. The greater SOC in AGL and SGL than
in ABO indicates that restoration to grassland helped
to sequester C. Restoration time is also an important
factor influencing C-sequestration rate.
The highest SOC concentration and C sequestra-
tion were found in the surface soil. SOC at 0�20 cm
accounted for more than 30% (Table III) of the SOC
to 1 m. This is consistent with results in the
literature (Mensah et al., 2003; Degryze et al.,
2004; Chen et al., 2007a). We found C sequestration
to a depth of 100 cm in AGL and SGL. This result
disagrees with some studies (Mensah et al., 2003;
Degryze et al., 2004; Chen et al., 2007a), but
supports the findings by Lemaire et al. (2005) that
grassland soils can store significant amounts of SOC
at greater depths. Omonode & Vyn (2006) similarly
found 71% of SOC sequestered in the 20�100-cm
layer, comparable to our two-thirds. The SOC
Soil depth (cm)80-10060-8040-6020-400-20
SO
C in
eac
h so
il la
yer
( kg
Cm
-2)
1.20
1.00
0.80
0.60
0.40
0.20
0.00
SGL
AGL
ABO
CRL
Land-cover type
a
ab
bc
c
a
ab ab
b
aab
abb
aab
bcc
aab
abb
A
A
A
A
BB
B B
BB
BB
B
B
BC
BC
C
C
C
C
Figure 1. Soil organic carbon (SOC) pool in each soil layer. Error bars represent standard error. Within a land-use type, bars with a
different uppercase letter differ significantly among soil layers [PB0.05; one-way analysis of variance (ANOVA) and least significant
difference test (LSD)]. Within a soil layer, bars with a different lowercase letter differ significantly among land-cover types. CRL�cropland;
AGL�artificial grassland covered by alfalfa; ABO�abandoned apricot orchard covered with Armeniaca vulgaris; SGL�secondary artificial
grassland covered predominantly by Stipa bungeana; SB�natural grassland covered by Stipa bungeana; CK�natural shrubland planted to
Caragana korshinskii.
Table III. SOC pools (kg C m�2) in four land cover types measured at 0�100 cm (DSOC100), 0�20 cm (DSOC20), and 20�80 cm (DSOC80)
DSOC100
DSOC20 DSOC80
Land cover type Mean (kg C m�2) Mean (kg C m�2) DSOC20/DSOC100 (%) Mean (kg C m�2) DSOC80/DSOC100 (%)
CRL 1.69 a 0.56a 33.1 1.14a 67.4
AGL 2.49bc 0.91bc 36.5 1.58a 63.4
ABO 2.05ab 0.74ab 36.1 1.31ab 63.9
SGL 2.98 c 1.08 c 36.2 1.90 b 63.7
DSOC20/DSOC100�DSOC at 0�20 cm/DSOC at 0�100 cm. DSOC80/DSOC100�DSOC at 20�80 cm/DSOC at 0�100 cm. Values labeled with the
same letter do not differ significantly (p�0.05, LSD). CRL�cropland; AGL�artificial grassland covered by alfalfa; ABO�abandoned
apricot orchard covered with Armeniaca vulgaris; SGL�secondary artificial grassland covered predominantly by Stipa bungeana.
Soil organic carbon of different land-covers 331
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concentration in deep soil was significantly lower in
cropland than in grassland. Crops did not grow well
in CRL, the roots were shallow, and crop residues
are always removed in the study area. Because of the
limited precipitation, little SOC can leach down.
This led to a low SOC level in deep soil. In contrast,
in AGL and SGL, roots of alfalfa could reach deeper
than 500 cm (Cheng et al., 2007), and the above-
and below-ground biomass was eventually trans-
formed into SOC.
The pattern of SOC distribution along the slope is
a result of severe soil erosion. Erosion by water and
re-deposition change the SOC distribution (Gregor-
ich & Anderson, 1985; Gregorich et al., 1998; Lal,
2003b; Liu, S.Z. et al., 2005), resulting in an increase
in SOC from the top to the bottom (Norton et al.,
2003). However, wind erosion removes surface soil
particles from exposed areas and deposits them in
protected areas, regardless of gradient position,
fuzzing up the trend of SOC distribution (Gregorich
et al., 1998). The effect of erosion on SOC is affected
by slope angle (Gregorich et al., 1998). Our shady
slope had a greater angle, so erosion and accumula-
tion would be more serious there (Rhoton et al.,
2006), perhaps explaining the increasing trend.
Slope aspect is another factor associated with SOC
quantity. Usually, soil on shady slopes contains more
SOC than does soil on sunny slopes on the Loess
Plateau (Lian et al., 2006). Our result under C.
korshinskii in deep soil is consistent with this conclu-
sion. The reason is that a shady slope usually has
a lower temperature and a higher water content
(Brubaker et al., 1993; Zhang et al., 2007). For a
plant such as C. korshinskii with a deep root system,
high water content favors fine root growth in deep
soil in our dry study area (Cheng et al., 2007),
resulting in more OM below the ground. A high
water content and low temperature also restrain soil
OM decomposition, decreasing SOC loss (Fissore
et al., 2008). In contrast, for a plant with shallow
roots (Li et al., 2005), namely S. bungeana, no
difference was found. The trend in the surface soil
was different from that in the deep soil: SOC
concentration was numerically (although not signifi-
cantly) greater on the sunny slope, perhaps on
account of wind erosion. The northwest wind pre-
vails in the catchment (Zhang, 1999; Kimura et al.,
2006), thus targeting the shady slope at our study
site, and removes surface particles, especially plant
residues and fine particles, reducing SOC on the
shady slope.
The SOC level in the study area is very low. The
average SOC pool to 1 m was 2.31 kg C m�2, which
was less than one-fourth of the average SOC pool in
China (9.1 kg C m�2, Wang et al., 2000; 10.53 kg C
m�2, Xie et al., 2004; 9.6 kg C m�2, Yu et al., 2007).
The mean 0�20-cm surface SOC pool (0.83 kg C
m�2) was much lower than that of the Loess Plateau
(2.46 kg C m�2, Xu et al., 2003). The low SOC level
is attributable to the low plant production due to
water deficit, low temperatures, and serious water
and wind erosion.
Acknowledgements
This research was supported by the Japanese Society
for Promotion of Science (JSPS) Core University
Programme and the Global Centre of Excellence
(COE) Programme of the Ministry of Education,
Culture, Sports, Science and Technology of Japan.
The authors thank Prof. Ming’an Shao and Dr Jun
Fan of the Institute of Soil and Water Conservation,
Chinese Academy of Sciences, for their support.
References
Academia Sinica and Ministry of Water Resources (1993). Memoir
of Northwest Institute of Soil and Water Conservation 18.
Shaanxi Scientific and Technology Press, Xi’an (in Chinese).
Bonino, E.E. (2006). Changes in carbon pools associated with a
land-use gradient in the Dry Chaco, Argentina. Forest Ecology
and Management, 223, 183�189.
Figure 3. Profile distribution of SOC concentration under C.
korshinskii and S. bungeana.
1.0
2.0
3.0
4.0
5.0
6.0
0 20 40 60 80 100 120 140
Distance from summit (m)
SO
C c
once
ntra
tion
(gC
kg-1
) SB-ShadySB-Sunny
CK-ShadyCK-Sunny
Figure 2. Spatial distribution of surface (0�20 cm) SOC concen-
tration on sunny and shady slopes. SB-Shady (Sunny) � Stipa
bungeana on shady (sunny) slope; CK-Shady (Sunny) �Caragana
korshinskii on shady (sunny) slope.
332 X. Han et al.
Dow
nloa
ded
by [
Mos
kow
Sta
te U
niv
Bib
liote
] at
11:
01 0
9 O
ctob
er 2
013
Breuer, L., Huisman, J.A., Keller, T., & Frede, H.G. (2006).
Impact of a conversion from cropland to grassland on C and
N storage and related soil properties: analysis of a 60-year
chronosequence. Geoderma, 133, 6�18.
Brubaker, S.C., Jones, A.J., Lewis, D.T., & Frank, K. (1993). Soil
properties associated with landscape position. Soil Science
Society of America Journal, 57, 235�239.
Chen, L.D., Gong, J., Fu, B.J., Huang, Z.L., Huang, Y.L., & Gui,
L.D. (2007a). Effect of land cover conversion on soil organic
carbon sequestration in the loess hilly area, Loess Plateau of
China. Ecological Research, 22, 641�648.
Chen, L.D., Wei, W., Fu, B.J., & Lu, Y.H. (2007b). Soil and water
conservation on the Loess Plateau in China: review and
perspective. Progress in Physical Geography, 31, 389�403.
Cheng, X.R., Huang, M.B., & Shao, M.A. (2007). Vertical
distribution of representative plantation’s fine root in wind-
water erosion crisscross region, Shenmu. Acta Botanica
Boreali-Occidentalis Sinica, 27, 0321�0327 (in Chinese).
Degryze, S., Six, J., Paustian, K., Morris, S.J., Paul, E.A., &
Merckx, R. (2004). Soil organic carbon pool changes
following land-use conversions. Global Change Biology, 10,
1120�1132.
Fekedulegn, D., Hicks Jr, R.R., & Colbert, J.J. (2003). Influence
of topography aspect, precipitation and drought on radial
growth of four major tree species in an Appalachian
watershed. Forest Ecology and Management, 177, 409�425.
Fissore, C., Giardina, C.P., Kolka, R.K., Trettin, C.C., King,
G.M., Jurgensen, M.F., Barton, C.D., & McDowell, S.S.
(2008). Temperature and vegetation effects on soil organic
carbon quality along a forested mean annual temperature
gradient in North America. Global Change Biology, 14, 193�205.
Gong, J., Chen, L., Fu, B., Huang, Z., & Peng, H. (2006). Effect
of land cover on soil nutrients in the loess hilly area of the
Loess Plateau, China. Land Degradation & Development, 17,
453�465.
Gregorich, E.G., & Anderson, D.W. (1985). Effects of cultivation
and erosion on soils of four toposequences in the Canadian
prairies. Geoderma, 36, 343�354.
Gregorich, E.G., Greer, K.J., Anderson, D.W., & Liang, B.C.
(1998). Carbon distribution and losses: erosion and deposi-
tion effects. Soil & Tillage Research, 47, 291�302.
Jiang, H.M., Jiang, J.P., Jia, Y., Li, F.M., & Xu, J.Z. (2006). Soil
carbon pool and effects of soil fertility in seeded alfalfa fields
on the semi-arid Loess Plateau in China. Soil Biology &
Biochemistry, 38, 2350�2358.
Jiang, J.P., Xiong, Y.C., Jia, Y., Li, F.M., Xu, J.Z., & Jiang, H.M.
(2007). Soil quality dynamics under successional alfalfa field
in the semi-arid Loess Plateau of northwestern China. Arid
Land Research and Management, 21, 287�303.
Kimura, R., Fan, J., Zhang, X.C., Takayama, N., Kamichika, M.,
& Matsuoka, N. (2006). Evapotranspiration over the grass-
land field in the Liudaogou Basin of the Loess Plateau,
China. Acta Oecologica, 29, 45�53.
Lal, R. (2003a). Global potential of soil carbon sequestration to
mitigate the greenhouse effect. Critical Reviews in Plant
Sciences, 22, 151�184.
Lal, R. (2003b). Soil erosion and global carbon budget. Environ-
ment International, 29, 437�450.
Lemaire, G., Wilkins, R., & Hodgson, J. (2005). Challenges for
grassland science: managing research priorities. Agriculture
Ecosystems & Environment, 108, 99�108.
Li, P., Li, Z.M., & Tan, T.Z. (2005). Dynamic distribution
characters of herbaceous vegetation root system in aban-
doned grasslands of Loess Plateau, China. Journal of
Application Ecology, 16, 849�853 (in Chinese).
Li, Y.Y., Shao, M.A., Zheng, J.Y., & Li, Q.F. (2007). Impact of
grassland recovery and reconstruction on soil organic carbon
in the northern Loess Plateau. Acta Ecologia Sinica, 27,
2279�2287 (in Chinese).
Lian, G., Guo, X.D., Fu, B.J., & Hu, C.X. (2006). Spatial
variability and prediction of soil organic matter at county
scale on the loess plateau. Progress in Geography, 25, 112�123
(in Chinese).
Liu, S.L., Guo, X.D., Fu, B.J., Lian, G., & Wang, J. (2007). The
effect of environmental variables on soil characteristics at
different scales in the transition zone of the Loess Plateau in
China. Soil Use and Management, 23, 92�99.
Liu, S.Z., Guo, S.L., Wang, X.L., & Xue, B.M. (2005). Effect of
vegetation on soil organic carbon of slope land in gully region
of Loess Plateau. Journal of Natural Resources, 20, 529�536
(in Chinese).
Mensah, F., Schoenau, J.J., & Malhi, S.S. (2003). Soil carbon
changes under cultivated and excavated land converted to
grasses in east-central Saskatchewan. Biogeochemistry, 63,
85�92.
Nelson, D.W., & Sommers, L.E. (1982). Total carbon, organic
carbon and organic matter, In: A.L. Page, R.H. Miller, &
D.R. Keeney (Eds.),Methods of Soil Analysis, Part 2 (pp. 534�580). 2nd Edn. Agronomy Monograph, vol. 9. ASA and
SSSA, Madison, WI.
Norton, J.B., Sandor, J.A., & White, C.S. (2003). Hillslope soils
and organic matter dynamics within a native American
agroecosystem on the Colorado Plateau. Soil Science Society
of America Journal, 62, 225�234.
Omonode, R.A., & Vyn, T.J. (2006). Vertical distribution of soil
organic carbon and nitrogen under warm-season native
grasses relative to croplands in west-central Indiana, USA.
Agriculture Ecosystems & Environment, 117, 159�170.
Peng, W.Y., Zhang, K.L., & Yang, Q.K. (2006). Forecast of
impact of the returning farms to forests on soil organic
carbon of Loess Plateau. Areal Research and Development, 25,
94�99 (in Chinese).
Rhoton, F.E., Emmerich, W.E., Goodrich, D.C., Miller, S.N., &
McChesney, D.S. (2006). Soil geomorphological character-
istics of a semiarid watershed: influence on carbon distribu-
tion and transport. Soil Science Society of America Journal, 70,
1532�1540.
Robles, M.G., & Burke, I. (1997). Legume, gurass, and con-
servation reserve program effects on soil organic matter
recovery. Ecological Application, 7, 345�357.
Shi, H., & Shao, M.A. (2000). Soil and water loss from the Loess
Plateau in China. Journal of Arid Environments, 45, 9�20.
SPSS Institute Inc. (2006). SPSS 15.0 for Windows. System
Users Guide, SPSS Inc., Chicago, USA.
Tan, Z.X., Lal, R., Smeck, N.E., & Calhoun, F.G. (2004).
Relationships between surface soil organic carbon pool and
site variables. Geoderma, 121, 187�195.
Tatsuhara, S., & Kurashige, H. (2001). Estimating foliage biomass
in a natural deciduous broad-leaved forest area in a
mountainous district. Forest Ecology & Management, 152,
141�148.
Wang, J., Fu, B.J., Qiu, Y., & Chen, L.D. (2001). Soil nutrients in
relation to land cover and landscape position in the semi-arid
small catchment on the Loess Plateau in China. Journal of
Arid Environments, 48, 537�550.
Wang, S.Q., Zhou, C.H., Li, K.R., Zhu, S.L., & Huang, F.H.
(2000). Analysis on spatial distribution characteristics of soil
organic carbon reservoir in China. Acta Geographica Sinica,
55, 533�544 (in Chinese).
Wang, Y.Q., Zhang, X.C., & Huang, C.Q. (2009). Spatial
variability of soil total nitrogen and soil total phosphorus
Soil organic carbon of different land-covers 333
Dow
nloa
ded
by [
Mos
kow
Sta
te U
niv
Bib
liote
] at
11:
01 0
9 O
ctob
er 2
013
under different land uses in a small watershed on the Loess
Plateau, China. Geoderma, 150, 141�149.
Wei, J.B., Xiao, D.N., Zhang, X.Y., Li, X.Z., & Li, X.Y. (2006).
Spatial variability of soil organic carbon in relation to
environmental factors of a typical small watershed in the
black soil region, northeast China. Environmental Monitoring
and Assessment, 121, 597�613.
Xie, X.L., Sun, B., Zhou, H.Z., & Li, A.B. (2004). Soil organic
carbon storage in China. Pedosphere, 14, 491�500.
Xu, X.L., Zhang, K.L., Xu, X.L., & Peng, W.Y. (2003). Spatial
distribution and estimating of soil organic carbon on loess
plateau. Journal of Soil and Water Conservation, 17, 13�15 (in
Chinese).
Yu, D.S., Shi, X.Z., Wang, H.J., Sun, W.X., Chen, J.M., Liu,
Q.H., & Zhao, Y.C. (2007). Regional patterns of soil organic
carbon stocks in China. Journal of Environment Management,
85, 680�689.
Zhang, J.B., Song, C.C., & Wang, S.M. (2007). Dynamics of soil
organic carbon and its fractions after abandonment of
cultivated wetlands in northeast China. Soil & Tillage
Research, 96, 350�360.
Zhang, P.C. (1999). Spatial and temporal variability of erosion by
water and wind in water-wind erosion crisscross region:
taking Liudaogou watershed in Jin�Shaan�Meng contiguous
areas as an example. Journal of Soil Erosion and Soil and Water
Conservation, 5, 93�96.
Zheng, J.Y., Wang, L.M., Shao, M.A., Wang, Q.J., & Li, S.Q.
(2006). Gully impact on soil moisture in the gully bank.
Pedosphere, 16, 339�344.
334 X. Han et al.
Dow
nloa
ded
by [
Mos
kow
Sta
te U
niv
Bib
liote
] at
11:
01 0
9 O
ctob
er 2
013