Catena 59 (2005) 267 – 278
www.elsevier.com/locate/catena
Influences of continuous grazing and livestock
exclusion on soil properties in a degraded sandy
grassland, Inner Mongolia, northern China
Su Yong-Zhong*, Li Yu-Lin, Cui Jian-Yuan, Zhao Wen-Zhi
Linze Inland River Basin Comprehensive Research Station, Cold and Arid Regions Environmental and
Engineering Research Institute, Chinese Academy of Sciences, 260 Donggang West Road,
Lanzhou 730000, China
Received 23 January 2004; received in revised form 4 August 2004; accepted 9 September 2004
Abstract
Overgrazing is one of the main causes of desertification in the semiarid Horqin sandy grassland of
northern China. Excluding grazing livestock is considered as an alternative to restore vegetation in
degraded sandy grassland in this region. However, few data are available concerning the impacts of
continuous grazing and livestock exclusion on soil properties. In this paper, characteristics of
vegetation and soil properties under continuous grazing and exclusion of livestock for 5 and 10 years
were examined in representative degraded sandy grassland. Continuous grazing resulted in a
considerable decrease in ground cover, which accelerates soil erosion by wind, leading to a further
coarseness in surface soil, loss of soil organic C and N, and a decrease in soil biological properties.
The grassland under continuous grazing is in the stage of very strong degradation. Excluding
livestock grazing enhances vegetation recovery, litter accumulation, and development of annual and
perennial grasses. Soil organic C and total N concentrations, soil biological properties including
some enzyme activities and basal soil respiration improved following 10-year exclusion of livestock,
suggesting that degradation of the grassland is being reversed. The results suggest that excluding
grazing livestock on the desertified sandy grassland in the erosion-prone Horqin region has a great
potential to restore soil fertility, sequester soil organic carbon and improve biological activity. Soil
restoration is a slow process although the vegetation can recover rapidly after removal of livestock. A
* Corresponding author. Tel.: +86 931 4967222; fax: +86 931 8273894.
E-mail addresses: [email protected], [email protected] (S. Yong-Zhong).
0341-8162/$ - see front matter D 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.catena.2004.09.001
268
S. Yong-Zhong et al. / Catena 59 (2005) 267–278
viable option for sandy grassland management should be to adopt proper exclosure in a rotation
grazing system in the initial stage of grassland degradation.
D 2004 Elsevier B.V. All rights reserved.
Keywords: Sandy grassland; Grazing management; Soil properties; Degradation; Restoration; Northern China
1. Introduction
Among the human activities that degrade grasslands, overgrazing by livestock is
perhaps one of the most significant (Mainguet, 1994). The effects of overgrazing on the
plant community and soils are considered destructive because of the reduction of canopy
cover, the destruction of topsoil structure, and compaction of soil as a result of trampling
(Taylor et al., 1993; Manzano and Návar, 2000). In turn, these processes increase soil
crusting, reduce soil infiltration, and enhance soil erosion susceptibility (Van de Ven et al.,
1989; Hiernaux et al., 1999; Manzano and Návar, 2000).
The Horqin sandy land (commonly called dHorqin sandy grasslandT), located in the
semiarid agro-pastoral transitional zone of northern China (42841V–45815VN, 118835V–
123830VE), is one of the most severe areas of desertification in China (Zhu and Chen,
1994). Overgrazing in this region is very detrimental to soil and vegetation cover and is
often regarded as one of the main causes of desertification (Li et al., 2000).
To control desertification and protect the regional environment, some measurements,
e.g. planting indigenous trees, shrubs and grasses, returning degraded farmland to
grassland and fencing desertified sandy grassland, have been implemented in parts of the
Horqin region in recent decades. Livestock exclusion practices on desertified sandy
grassland were shown to be good alternatives to recover vegetation and attenuate soil loss
by wind erosion in these erodible grasslands (Zhao et al., 1998; Su et al., 2004). In recent
years, intensive studies concerning the effects of grazing management on vegetation
dynamics have been carried out in the Horqin sandy grassland (Zhao et al., 1998, 1999; Li
et al., 2000), but very few have focused on its effect on soil properties. Information on
these aspects is required for a better understanding of the restoration mechanisms and the
biological feedback of desertification, and for appropriate management and conservation
of desertified sandy grassland.
The objective of this study was to compare the effects of continuous grazing and
exclusion of livestock on soil physical, chemical and biological properties in a desertified
sandy grassland of a wind erosion-prone region.
2. Materials and methods
2.1. Study location and site description
The study was conducted at the Naiman Desertification Research Station (NDSR) of
the Chinese Academy of Sciences, located in the south-central part of the Horqin sandy
land, approximately 10 km northeast of Naiman County, Inner Mongolia, China
S. Yong-Zhong et al. / Catena 59 (2005) 267–278
269
(42858VN, 120843VE, altitude ca. 360 m a.s.l.). The topography of this area is
characterized by sand dunes alternating with gently undulating interdunal lowlands, with
20 to 120 m thickness of sandy deposits. The climate is semiarid, with windy and dry
winters and springs, and warm and comparatively rain-rich summers followed by short and
cool autumns. The 40-year mean annual temperature is 6.5 8C (range from 5.1–7.7 8C)
with the coldest and warmest monthly mean temperatures of 13.1 8C ( 16.6 to 9.7 8C)
in January and 23.7 8C (21.6–25.8 8C) in July, respectively. Mean annual precipitation is
366 mm with 70% occurring between July and September. Mean potential evaporation is
about 1935 mm year 1. Average annual wind velocity varies between 3.4 and 4.1 m s 1
with the frequent occurrence of gales (wind speed N20 m s 1) (Li et al., 2000). The soils
are light yellow and have a loose structure caused by a high proportion of sand (85–95%)
and low organic matter content (0.15–0.5% organic C) (Su and Zhao, 2003), so they are
particularly susceptible to wind erosion. The vegetation in degraded sandy grassland is
generally dominated by psammophytes, including some grasses (e.g. Cleistogenes
squarrosa L (Trin.) Keng, Setaria viridis (L.) Beauv., Phragmites australis Trin. ex
Steudel Nomencl., Digitaria ciliaris (Rotz) Koeler, Leymus chinensis (Trin.) Tzvel.,
Pennisetum centrasiaticum Tzvel.), forbs (Mellissitus ruthenicus (L.) C.W.Chang, Salsola
collina Pall., Corispermum elongatum Bge. ex Maxim., Agriophyllum quarrosum (L.)
Moq., Artemisia scoparia Waldst.et Kit.), shrubs (e.g. Caragana microphylla Lam.,
Lespedeza davurica (Laxm.) Schindl.), and subshrubs (e.g., Artemisia halodendron Turcz
ex Bess., Artemisia frigida Willd.).
The study site is a 50 ha open and flat natural grassland, located about 2 km northeast
of NDRS. It was subjected to continuous livestock grazing by sheep and cattle and had
undergone slight desertification in the early 1990s, but the characteristics of soils and
vegetation cover were relatively homogeneous. In 1992, a restoration project was initiated.
The exclosures were established gradually and grazing by domestic herbivores was
gradually excluded, allowing the natural vegetation to recover. In the initial removal of
livestock, the dominant plant species in the whole area was grasses, accompanied by some
legumes and forbs; shrubs and subshrubs were few. The vegetation cover averaged 54%.
Sand content in the topsoils (0–15 cm) was 90.4% and soil organic C concentration was
2.37 g kg 1 (Xu et al., 1994).
2.2. Sampling design and field investigation
Three sites along a gradient of non-grazed exclusion restoration time were selected
for sampling: (1) 10EX, non-grazed exclusions for 10 years; (2) 5EX, non-grazed
exclusions for 5 years; and (3) CG, the areas outside exclusions with continuous
grazing.
Within each site, three plots with an area of 3050 m were marked as the three field
replicates. Within each plot, nine 11 m quadrates were established uniformly, and soil
and plant samples were collected at peak standing crop in August 2002. The aboveground
plant component was sampled by clipping a 0.5 m2 at each sampling quadrate. Plant
phytomass was partitioned into surface litter, standing dead, and live biomass by plant
species. All plant litter was removed from the soil surface before soil samples (0–15 cm)
were collected using a soil auger. Separate cores (7.5-cm diameter) at 0~15-cm were
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S. Yong-Zhong et al. / Catena 59 (2005) 267–278
collected at each sampling quadrate to assess root biomass and soil litter mass. Duplicate
soil cores were also taken at each sampling quadrate for soil bulk density determination.
In addition, three randomly located 5-point transects in each plot were used to
determine percent bare ground, live vegetation, and dead vegetation. Standing litter and
fallen litter heights of each major plant species or group were measured at 15 randomly
located points in each plot.
Although the lack of true replication of exclosure treatments in this study restricts
inference regarding the impact of sandy grassland management on a large scale in the
Horqin steppe, it does not preclude the general comparison of soil properties under
continuous grazing and non-grazed exclosures.
2.3. Laboratory analyses
Soil samples were hand-sieved through a 2-mm screen. At the time of sieving, roots and
other debris were removed from the soil and discarded. Moisture content of the seived soil
was determined gravimetrically. Particle size distribution was determined by the pipette
method in a sedimentation cylinder, using sodium hexamethaphosphate as the dispersing
agent (ISSCAS, 1978). Soil pH and electrical conductivity (EC) was determined in a 1:1
soil–water slurry and in a 1:5 soil–water aqueous extract (Multiline F/SET-3, Germany).
Part of each sample within each plot was composited for enzyme activity and basal soil
respiration (BSR) determination. Another part of each sample was air-dried and finely
ground to pass 0.1 mm sieve and analyzed for organic C and total N by the Walkley–Black
dichromate oxidation procedure (Nelson and Sommers, 1982) and by the Kjeldahl
procedure (UDK140 Automatic Steam Distilling Uint, Automatic Titroline 96, Italy),
respectively (ISSCAS, 1978).
Soil catalase activity was measured using the 0.1N KMnO4 titration method (Johnson
and Temple, 1964). Urease and alkaline phosphatase activities were measured with the
methods described by Tabatabai and Bremner (1972), and Zhou and Zhang (1980),
respectively. BSR was estimated through CO2–C evolution at 28 8C in samples incubated
for 7 days (Mazzarino et al., 1991). Measurements were made in the lab under
standardized soil moisture conditions at 60% of field capacity.
Soil litter and roots were separated with a hand washing method (Laurenroch and
Whitman, 1971). The separated litter from root cores contained small amounts of root
hairs that could not be distinguished. Each plant component was dried at 50 8C, weighed
and ground. Then, plant samples taken from three adjacent sample quadrates were mixed
thoroughly within each category and analyzed for organic C content with the same method
as soil samples (nine per treatment within each category).
2.4. Data analyses
Because the exclosures were at one location and not replicated, we have followed the
approach of Frank et al. (1995) and considered each of the three plots as a replication of
summary statistics. Values from all sampling quadrates within each plot were averaged.
Then, one-way analysis of variance (ANOVA) procedures were used to detect the
differences between means of parameters examined of the three sites. The least significant
S. Yong-Zhong et al. / Catena 59 (2005) 267–278
271
difference (LSD) was performed to determine the significance of treatment means at
pb0.05.
3. Results
3.1. Ground cover characteristics
Live vegetation and litter were highest in 10EX, intermediate in 5EX and lowest in
CG (Table 1). After 10 years of exclusion of livestock, bare ground decreased by 3.4
times compared to the grazed site. Also, standing and fallen litter heights increased
with increased restoration time. Standing litter was 2.7 to 3.4 times higher in 5EX and
10EX, respectively, than in the grazed site, and fallen litter was 3 to 5.7 times higher.
Difference in plant community composition was also observed between the treatments
(Table 2). Dominant plant species in CG site were some forbs including A. scoparia
and S. collina. In 5 EX site, major species were annual grasses including A. scoparia,
S. collina, and S. viridis, and legume (Lespedeza dahurica). In 10EX, some annual
and perennial grasses (S. viridis, Cleistgenes mutica and P. australis) and forbs
including A. scoparia, S. collina and Chenopodium glaucum were most dominant
species.
3.2. Above- and belowground biomass and carbon content
Exclusion of livestock on degraded sandy grassland resulted in a significant increase in
the amount of total organic material including above- and below-ground biomass (Fig. 1).
Compared with grazed site, total biomass in 10EX site (920 g m 2) and 5EX site (361 g
m 2) increased by 2.9 and 1.6 times, respectively.
Carbon content in plant components showed the same trend as their biomass among
treatments (Fig. 1). Total C storage of plant components in 10EX was on average 317 g
m 2, with an average of 133g m 2 aboveground C storage and an average of 184 g m 2
belowground C storage, being a 2.4 and 3.3 times increase compared to those in 5 EX
(total: 134 g m 2; above: 78 g m 2; below: 56 g m 2) and in grazed site (total: 98 g m 2;
above:43 g m 2; below:55 g m 2), respectively.
Table 1
Ground cover characteristics at the three study sites
Site
Percent ground cover (%)
Height (cm) of litter
Bare ground
Live vegetation
Litter
Standing litter
Fallen litter
10EX
5EX
CG
LSD0.05
19.2F14.7c
37.0F20.6b
65.4F6.8a
21.30
40.8F13.5a
28.6F10.9b
24.3F7.4b
10.27
40.4F14.4a
34.5F15.9a
10.3F3.8b
13.27
44.8F20.6a
29.9F8.4b
13.2F7.5c
12.83
1.7F0.8a
0.9F0.7b
0.3F0.1c
1.22
a–c, Within ground cover and litter category, meansFS.D. with the same letters are not significantly different
( pb0.05). n=45.
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Table 2
Plant species composition at the three study sites
Species name
Aneurolepidium dasystachys
Aristida adscensionis
Artemisia scoparia
Bassia dasyphylla
Chenopodium glaucum
Chloris virgata
Cleistogenes squarrosa
Corispermum elongatum
Cynanchum thesioides
Eragrostis pilosa
Euphorbia humifusa
Lespedeza davurica
Melissitus ruthenicus
Panicum paludosum
Pennisetum centrasiaticum
Phragmites australis
Potentilla bifurca
Salsola collina
Setaria viridis
Total number of species recorded
Coverage (%)
Above-ground biomass (g m 2)
Life
form
PG
AG
AF
AF
AF
AG
PG
AF
PF
AG
AF
PL
PL
AG
PG
PG
PF
AF
AG
Treatment
10EX
5EX
CG
N
H (cm)
p%
N
H (cm)
p%
N
H (cm)
p%
0
0.3
0.6
2
54
15.3
5.4
0
0.3
11.2
0
0.8
0.3
13.1
40.7
6
1.6
69
29
16
40.8
75
0
8
20
7
32
9
14
0
15
6
0
9
10
40
15
70
20
18
16
0
5
5
10
70
20
40
0
5
30
0
5
5
25
20
70
5
50
80
11.8
56
42
0
0
2.1
2.8
3.5
0
0
0
15.4
0
0
0
0
2.5
70
10.7
10
28.6
59.3
25
8
26
0
0
10
23
10
0
0
0
10
0
0
0
0
20
11
8
10
60
100
0
0
5
30
10
0
0
0
80
0
0
0
0
5
100
50
0
51
59
3
0
2.1
2.4
2
0
3.3
0.6
3.8
0
0
1.3
0
0
27
0.6
12
24.3
13.6
0
10
28
2
0
3
7.8
8
0
5
2
4
0
0
12
0
0
7.1
4
0
10
100
5
0
10
20
5
0
5
5
50
0
0
5
0
0
50
5
N, mean number of individuals per quadrate; H, mean height (cm) of individuals; p%, frequency; AF, annual
forbs; AG, annual grass; PG, perennial grass; PF, perennial forbs; PL, perennial legume.
3.3. Soil physical properties
The particle size distribution showed more silt and clay and less sand in the top 15 cm
of soils under the non-grazed sites compared with soils under the continuously grazed site
(Table 3). In comparison with the original soil at the initiation of livestock exclusion in
Fig. 1. Biomass and carbon content in plant component on grazed and grazing exclusion sites. Within category,
the same letters bars are not significantly different ( pb0.05). Vertical bars show S.D. n=9.
S. Yong-Zhong et al. / Catena 59 (2005) 267–278
273
Table 3
Particle size distribution and bulk density of soils (0–15 cm) under different treatments
Treatment
Particle size distribution (%)
Sand (2–0.05 mm)
Silt (0.05–0.002 mm)
Clay (b0.002 mm)
Bulk density,
g cm 3
Before exclusion (1992)
10EX
5EX
CG
LSD0.05
90.4
89.7F2.8b
91.6F3.2ab
94.8F3.8a
3.11
6.6
7.4F2.4a
5.7F1.1b
3.2F1.2c
2.58
3.0
2.9F1.3a
2.7F0.9a
2.0F0.7a
NS
1.34F0.10c
1.44F0.09b
1.58F0.05a
0.06
Within columns, meansFS.D. with the same letters are not significantly different ( pb0.05). n=3.
1992 (Xu et al., 1994), sand content in the CG soil has increased by 4.4%, whereas it
slightly decreased following livestock exclusion.
Soil bulk density was highest in CG site and lowest in 10EX. There was a significant
difference between the treatments (Table 3).
3.4. Soil chemical properties
Soil pH was significantly higher in the continuously grazed soils compared to the EX
soils, but it was not significantly different between the 5EX and the 10EX. Electrical
conductivity was statistically and numerically similar under the three treatments (Table 4).
Soil organic C concentration in the 0–15 cm depth was highest in 10EX site and
lowest in CG site (Table 4). A significant difference for organic C concentration was
observed between 10EX site and CG site ( p=0.01). However, there were no statistically
significant differences between 10EX and 5EX ( p=0.072) and between 5EX and CG
( p=0.114). In the CG site and 5EX site, the spatial variability of soil organic C was
higher than that in the 10EX site. When C concentration was multiplied by bulk density
and expressed on an areal basis, C storage in the 0~15 cm depth exhibited a similar
pattern to that of C concentration, but the differences were narrowed and not significant
( F=0.986, p=0.377).
Total N concentration showed a similar pattern to that of organic C concentration, with
the highest value in 10EX, but no statistically significant difference was found between the
three treatments ( F=0.602, p=0.537). Furthermore, total N storage in the 0–15 cm soil
depth was slightly higher in the CG site than in 10EX and 5EX sites ( F=0.692, p=0.503)
(Table 4).
Table 4
Soil chemical properties (0–15 cm) under different treatments
Treatment PH
10EX
5EX
CG
LSD0.05
7.77F0.09b
7.82F0.16b
8.04F0.21a
0.16
EC,
As cm
Organic C
1
46F15a
51F12a
49F11a
NS
g kg
1
2.79F0.55a
2.42F1.01ab
2.10F0.71b
0.43
Total N
gm
2
559.3F115.6a
519.1F211.4a
498.3F172.6a
NS
g kg
1
0.269F0.047a
0.251F0.10a
0.248F0.086a
NS
C/N ratio
gm
2
54.0F10.1a 10.36F1.01a
53.9F21.6a 9.57F0.98b
58.8F21.1a 8.62F1.22c
NS
1.11
Within columns, meansFS.D. with the same letters are not significantly different ( pb0.05). n=3.
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S. Yong-Zhong et al. / Catena 59 (2005) 267–278
Table 5
Soil enzyme activities and basal soil respiration (BSR) (0–15 cm)
Treatments
Catalase activity
0.1 NKMnO4, ml
g 1ds* 20 min 1
Urease activity
NH3–N, Ag g 1
ds 24 h 1
Alkaline phosphatase
phenol, Ag g 1
ds 24 h 1
BSR, Ag (CO2–C)
g 1soil day 1
10EX
5EX
CG
LSD0.05
1.56F0.41a
1.54F0.32a
1.39F0.35b
0.136
11.3F2.5a
8.7F2.4b
6.1F1.4c
2.33
8.9F2.3a
6.4F1.9b
6.3F1.4b
1.74
3.8F0.8a
2.7F1.2b
2.4F0.5b
0.66
Within columns, meansFS.D. with the same letters are not significantly different ( pb0.05). n=3.
* Dry soil.
The C/N ratio showed a significant difference between the treatments ( F=19.55,
pb0.0001) with a wider average value in the 10EX soils and a narrower value in the CG
soils (Table 4).
3.5. Soil enzyme activities and basal soil respiration
The three enzymes assayed had very low activity but showed significant differences
among the treatments (Table 5). Catalase, urease and alkaline phosphatase activities were
significantly higher in the 10EX soils than in the CG soils. Also, significant differences in
catalase and urease activities were found between the 5EX and the CG, however, alkaline
phosphatase activity was similar (Table 5).
There was a significant difference in BSR among the treatments. The greatest difference
was in the 10EX and the lowest in the CG (Table 5). A positive relationship (r=0.847,
pb0.004) was observed between BSR and organic C.
4. Discussion
4.1. The effects of continuous grazing
Continuous grazing in the erosion-prone sandy grassland is very detrimental to
vegetation and soils. The results indicate that continuous grazing resulted in less
vegetation cover and litter accumulation, soil coarseness, and very low organic C and N
concentrations and microbial activities. Due to continuous grazing and frequent trampling
by sheep and cattle, the ground surface at the CG site became bare and exposed to wind
erosion under strong winds. Accelerated wind erosion due to the decreased vegetation
cover and litter accumulation resulted in soil coarsening and loss of soil organic matter.
The results indicate that sand content increased by 4.4% as compared with that in the
original soil 10 years ago. Loss of fine fractions in soils will have major influences on such
properties as water-holding capacity, soil consistence, and organic C and nutrient presence
and availability (Hennessy et al., 1986). These changes will, in turn, influence the kind and
amount of vegetation the area will support. Our results indicate that A. scoparia became
the dominant species at the CG site and the fraction of annual and perennial grasses in the
S. Yong-Zhong et al. / Catena 59 (2005) 267–278
275
community was less than that in the 10EX site. The palatability of A. scoparia was low for
sheep (Zhang et al., 1998) and its appearance often indicates severe degradation of the
grassland (Zhao et al., 1999).
4.2. Implications for exclusion of livestock
The adoption of livestock exclusion practices had a profound impact on vegetation
recovery, and, in turn, on litter accumulation and improvement of soil fertility. The
results indicate that excluding livestock on degraded sandy grassland resulted in a
significant increase in ground cover due to vegetation recovery and litter accumulation
compared with continuous grazing. This was of practical significance in the erosionprone Horqin sandy grassland. The increased ground cover following exclusion of
livestock effectively protected soil from loss by wind erosion. The elimination of soil
trampling by livestock, as well as the high organic matter content and the presence of
extensive shallow root systems in the EX areas contributed to a significant decrease in
bulk density.
Soil organic C and total N concentrations following 10 years of livestock
exclusion showed a significant and slight increase, respectively, compared to the
adjacent continuous grazing site. The result was in agreement with that of Bauer et
al. (1987) who reported that grazed grasslands contained less organic C and more N
than adjacent ungrazed grasslands. The difference in C/N ratio between treatments
indicates that the impacts of continuous grazing and livestock exclusion practices on
organic C exceed that of total N. The increase in organic C and total N
concentrations resulted mostly from the increase in organic matter returned to the
soil and reduced wind erosion due to vegetation recovery and litter accumulation.
Also, changes in species composition could also have affected organic matter and
nutrient contents. Exclusion of livestock enhanced the growth and development of
annual and perennial grasses which have dense fibrous rooting systems conducive to
soil organic matter formation and accumulation (Reeder and Schuman, 2002).
However, no significant difference for organic C and total N concentration was
observed between 5EX and CG. This was because the sandy grassland was in the
stage of severe degradation prior to initiating 5EX in 1997 (Xu et al., 1994). The
degradation caused by grazing in the initial stage was relatively easier to be
reversed, but the reversion of severe degradation was a slow process (Xu et al.,
1994).
From analysis of plant–soil system C storage, vegetation recovery and litter
accumulation following exclusion of livestock contributed significantly to C
sequestration. However, in terms of the distribution of C in the plant–soil system,
65%, 79%, and 83% of plant–soil C was in the soil at the 0–15 cm depth in the
10EX, in the 5EX and in the CG site, respectively. This suggests that although inputs
of litter C increased after exclusion of livestock, recycling of aboveground plant C to
the soil was restricted when grazing was excluded and C was immobilized in plant
litter accumulating on the soil surface. A build-up of litter on the surface seemed to
affect plant residue and litter decomposition rates and thus C and nutrient cycling
(Reeder and Schuman, 2002).
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The EX soil had significantly lower pH than that of the CG soil. The difference was
probably related to plant coverage, root systems and SOC content, because extensive
secretion of organic acids from the roots and amounts of CO2 released from roots and
microorganisms could lead to the decrease in pH (Zhou et al., 1992). The EC of the soils
were representative of non-saline soils in this region.
Vegetation recovery and litter accumulation following exclusion of livestock gave rise
to a positive effect on soil biological properties. The low enzyme activity and BSR
measured in this study indicated the very low microbial activity in these degraded sandy
soils. Low microbial activity was unfavorable to the decomposition of the plant residue
deposited on the soil surface and thus limited the release of nutrients from litters
(Frankenberger and Dick, 1983). However, the greater enzyme activities and BSR in the
surface soil of 10EX compared to the CG indicated that biological activity was improved
to a certain degree after exclusion of livestock. This was attributed to increased organic
matter and improved soil environment.
5. Conclusions
The semiarid Horqin sandy grassland is ecologically very fragile. Continuous grazing
gives rise to a considerable decrease in ground cover, which accelerates soil erosion by
wind, resulting in a further coarseness in surface soil, loss of soil organic C and N, and
depletion in soil biological properties. Variations in these parameters indicate the
grassland is in the stage of very strong degradation. Excluding livestock grazing
enhances vegetation recovery, litter accumulation, and development of annual and
perennial grasses. Soil organic C and total N concentrations, soil biological properties
including some enzyme activity and basal respiration improved following 10-year
exclusion of livestock. This indicates that the grassland is recovering. The results also
suggest that soil restoration on degraded sandy grassland is a slow process, although the
vegetation can recover rapidly after removal of livestock disturbance. From a
perspective of ecological restoration and land use as well as C and nutrients recycling
which affects ecosystem function, a viable option for sandy grassland management
should be to adopt proper fencing in a rotation grazing system in the initial stage of
grassland degradation.
Changes in ground cover characteristics, soil particle size distribution, bulk density, soil
organic C and total N concentrations were good indicators of grazing management on
soils. However, direct measures of its impact on wind erosion would be required in this
erosion-prone area.
Acknowledgements
We acknowledge the financial support of the National Natural Science Foundation of
China (40471083), one of the China National Key Projects for Basic Scientific Research:
bThe bio-process of desertification and the mechanism of recovering and reconstructing of
vegetationQ (G2000048704) and the Innovation Foundation (No. 2004110, 2003112) from
S. Yong-Zhong et al. / Catena 59 (2005) 267–278
277
the Cold and Arid Regions Environmental and Engineering Research Institute, CAS.
Authors express our sincere thanks to the reviewers and issue editor of the journal for their
valuable comments, suggestions, and revisions on this manuscript.
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