www.elsevier.com/locate/geomorph

Geomorphology 59 (2004) 237–246

Evolution of soil properties on stabilized sands in the

Tengger Desert, China

Duan Zhenghua,b,*, Xiao Honglangb, Li Xinrongb, Dong Zhibaob, Wang Gangc

aXinjiang Institute of Ecology and geography, Chinese Academy of Sciences; 40 Beijing South Road, Urumqi, 830011, P.R. of ChinabKey Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute,

Chinese Academy of Sciences; 260 Donggang West Road, Lanzhou, 730000, P.R. of ChinacState Key Laboratory of Arid Agroecology, Lanzhou University, 298 Tianshui Road, Lanzhou, 730000, P.R. of China

Accepted 16 July 2003

Abstract

The spatial and temporal patterns of pedogenesis on stabilized dunes at Shapotou, northwestern China, were studied on the

time sequences of 0, 18, 35 and 43 years. The spatial pattern of soil formation was estimated by measuring the thickness of

accumulated sand fractions on the stabilized dune surface and by analyzing the characteristics and properties of soil. The results

showed that the environment of soil formation and circulation of soil material were influenced in the processes of shifting-sand

fixation, and the mean soil particle size changed from >0.2 to < 0.08 mm in 0–20 cm soil depth with the succession from

cultivated plants to natural vegetation. The capacity of available soil water increased fivefold. Deep infiltration of water in soil

no longer occurred due to the increase in soil water capacity and the change of redistribution of soil water in profiles. Soil

microorganisms evolved from simple to complex. Interaction of these processes obviously brought about accumulation of soil

fertility, evolution of soil profiles and development of the profiles towards aripsamments. The difference of micro-topography is

closely related to redistribution of material and energy in soil formation.

D 2003 Elsevier B.V. All rights reserved.

Keywords: Aeolian sandy soils; Fixation of shifting sand; Soil fertility; Tengger Desert

1. Introduction forming loess or loess-like deposits (Dan and Yaalon,

The deserts of China constitute one of the dustiest

areas on earth (Littmann, 1991; Yang et al., 1994), but

the stabilization of aeolian deposits is limited. The

absence of vegetation results in the deflation and

resuspension of fine particles from desert areas that

eventually accumulate at vegetated desert margins

0169-555X/$ - see front matter D 2003 Elsevier B.V. All rights reserved.

doi:10.1016/j.geomorph.2003.07.019

* Corresponding author.

E-mail address: duanzh@public.lz.gs.cn (D. Zhenghu).

1971). Stabilized in the past by straw checkerboard

barriers, the mobile dunes change into stabilized sand

in the transition zone of arid grassland and soil

nutrient depleted regions in north China (Ling et al.,

1993). Aeolian deposition is determined by a number

of factors, including distance from the sediment

source (Tsoar and Pye, 1986), existing vegetation

cover (Yaalon and Dan, 1974) and topography (Jor-

genson, 1992). Some 60% of China’s deserts are

sandy, much of it in the form of mobile dunes (Chao

and Xing, 1982). Upon stabilization, the enrichment

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246238

of dune surfaces through aeolian deposition of fine

particles becomes an important geomorphological

process (Danin, 1978). For example, in the Shapotou

area, after decades of stabilization, the succession of

cultivated plants on shifting sand gradually evolved

naturally towards a natural vegetation. Vegetation

cover varied between 20% and 40%, and yearly litter

yield reached 43.6 g m� 2 (Shi and Liu, 1995).

Furthermore, soils evolved towards aripsamments

and the surface morphology of aeolian-sand soil

profile also changed (Zhen, 1987), sometimes even

towards a macrobiotic crust (Duan et al., 2003). In the

meantime, numerous microbes, mosses and herbs

appeared in the surface soil layer (Shi et al., 1996;

Li et al., 2002). As a result, the structure and function

of desert ecosystem became better (Harper and Mar-

Fig. 1. Geographical situations of the major deserts (sandy lands) and lo

Taklimakan Desert; (3) Kumtag Desert; (4) Qaidam Basin Desert; (5) Bada

Desert; (9) Mu Us Desert; (10) Otindag Desert; (11) Horqin Sandy Land;

ble, 1998). With the development of a surface crust,

substantial changes in soil properties such as erodibil-

ity, texture, structure, nutrient content and moisture

content have occurred when compared with the orig-

inal aeolian sand. The study on the evolution of soil

properties in the processes of shifting-sand fixation is

very significant for the desert rehabilitation and eco-

environmental improvement.

2. Materials and methods

The study area lies at the southern edge of the

Tengger Desert at Shapotou, northwestern China

(105j00VE, 37j40VN) (Fig. 1). Site elevation is

1300–1350 m. Mean annual precipitation is around

cation of the Shapotou in China. (1) Kurban Tunggut Desert; (2)

in Jaran Desert; (6) Tengger Desert; (7) Ulan Buh Desert; (8) Qubqi

(12) Nenjiang Sandy Land; (13) Huang-Huai-Hai Plain Sandy Land.

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246 239

180 mm, falling predominantly during the months

between May and September (Zhao, 1988). Precipi-

tation is highly variable, dependent on the strength

and extent of the summer monsoonal system. Temper-

atures average 24.3 jC in July and � 6.9 jC in

January. Mean annual pan potential evaporation is

2508 mm. The highest wind speed occurs in the late

spring (April–May), with an average wind velocity of

3.5 m s� 1, and the wind direction is predominantly

northwesterly (Li, 1988).

The Shapotou Desert Research Station was estab-

lished in 1956 to investigate methods of stabilizing

shifting dunes, which threatened the Baotou–Lanz-

hou railway line as it crossed the Tengger Desert. The

stabilization method was a combination of wind-

breaks, straw checkerboard barriers and planted xero-

phytic shrubs (Fig. 2). Awillow branch fence was first

constructed at the edge of the stabilized area, greatly

reducing the entry of blowing sand (Lin et al., 1984).

The straw checkerboard barriers were made of wheat

and rice straw embedded in the sand roughly in a

1�1 m grid, with the straw protruding 10–15 cm

above the surface. Xerophytic shrub seedlings, such as

Artemisia ordosica, Krasch., Hedysarum scoparium,

Fisch. and C.A. Mey, Caragana korshinskii, Kom.

Fig. 2. Plan of different-year stabilized site in Shapotou. The characters in

and Calligonum mongolicum, Turc’z were planted

within the checkerboards (Fearnehough et al., 1998).

The stabilized area was further expanded in 1965 and

1981. As a consequence of shifting-sand fixation,

both vegetation and geomorphology displayed appar-

ent change (Fig. 3).

Soil samples were collected from different sites

representing different topographic and time sequen-

ces. The pedons were described according to Guthrie

and Witty (1982) before being sampled. The sand

layer and thickness of surface ‘‘grey sand’’ were

composed of deposited aeolian particles, desert sand

and organic matter and constituted a developing dune

soil (Fearnehough et al., 1998). In order to examine

the effects of time on sand soil development, dunes

stabilized since 1956, 1965 and 1981 and a shifting-

sand site outside the stabilized area were chosen. In

1999, these gave a time sequence covering 43 years.

Based on the genetic horizon of 1.2-m soil layer

(including soil crust), soil samples of the stabilized

dunes of different ages and types were collected for

particle size and physical and chemical analysis (Fig.

4). Soil particle size was determined using the pipette

method (Wang, 1983). The soil chemical properties—

N, P and K content—were determined using routine

brackets indicate the measure of stabilization dunes in every area.

Fig. 3. Changes in landscape ecosystem in the processes of shifting-sand fixation. (A) Shifting dunes; (B) stabilized sand with straw

checkerboards; (C) landscape of initial intruded vegetable; (D) landscape of stabilizing 43 years; (E) lichen and moss of 1956 stabilized sand

area after rain; (F) herbage vegetable of 1956 stabilized sand area in September.

Fig. 4. Changes in soil profile morphology on stabilized sand dunes. (A) Leeward slope dunes stabilized in 1981; (B) leeward slope dunes

stabilized in 1965; (C) leeward slope dunes stabilized in 1956; (D) windward slope dunes stabilized in 1956; (E) hollow dunes stabilized in

1956.

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246240

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246 241

methods (Nanjing Institute of Soil Sciences, Chinese

Academy of Sciences, 1978). The soil bulk density

was determined using the cutting ring method. The

number of bacteria, fungi and actinomyces was deter-

mined using the flat panel smear methods (Xu and

Zheng, 1986). At the same time, the field survey and

the analyses of crust and dust particle sizes were

conducted. The amount of aeolian deposition was

studied using a transect of dust traps that consisted

of metal cylinders 350 mm high and 250 mm in

diameter, sediment being collected through a funnel

at the base of the cylinder. Measurements of aeolian

deposition have been made at Shapotou since August

1990 (Zhang et al., 1993). Traps were placed away

from shrubby vegetation at different topographic

positions and remained in the field for 3 years from

1994 to 1996. Trapped sediment was dried and

weighed monthly.

In order to examine changes in surface morphology

after sand dunes stabilized, the topography of the

region of the artificial stabilized sand dunes was

measured using a Theodolite and compared to 1964

measured results. Because the existing topography

reduced from northwest to southeast in the stabilized

area, we calculated relative height and undulation

degree at all points using the regional inclination as a

base level. Statistical analysis (ANOVAwith LSD and

regression analysis) was carried out by using SPSS

10.0 for Windows at a pV 0.05 significance level.

Table 1

Influences of different sand-fixing ages and landform positions on soil m

Soil-forming factors

Sand-fixing

age (years)

Landform position Soil depth

(cm)

n < 0.01

(%F

Dust Height 5.2 m 10 24.2

0 Leeward slope 0–20 5 0.2a

18 Leeward slope 0–17 5 3.2b

35 Leeward slope 0–20 5 5.0c

43 Leeward slope 0–20 5 8.0dC

43 Leeward slope 15–20 3 3.5B

43 Leeward slope 40–50 3 1.2A

43 Interdune depression 0–7 5 9.0C

43 Interdune depression 0–4 5 7.2C

Mean content of particle size < 0.01 mm marked (a) are significantly diffe

Mean content of particle size < 0.01 mm in the 43-year stabilized sand ar

from those marked (B) and (C).

3. Results and discussion

3.1. Changes in soil texture

Soil succession was significantly accelerated due to

the improvement of soil-forming environment and the

quickening of mobile aeolian-sand soil towards ari-

psamments in the processes of shifting-sand fixation.

Shifting sand (parent material) in Shapotou region has

a mean particle size of >0.2 mm, of which >0.2 mm

particles occupy 30–40% and >0.02 mm particles

f 95%, while silt-sized particles do not occur, and,

therefore, it has a better water permeability and poor

water retentiveness. During the processes of shifting-

sand fixation, large amounts of silt-sized particles

(0.01–0.05 mm) were deposited on the sand surface

and thereby altered the original soil mechanical com-

position. Generally, >0.2 mm particles in surface layer

reduced by 5% or less, 0.02–0.2 mm fine sand

content decreased by 60–80%, 0.02–0.002 mm silt

content reached 14–20% and < 0.01 mm physical

clay content increased from 1.5% to 2%. Soil hygro-

scopicity and plasticity significantly improved. Mean

particle-size value decreased to 0.08–0.14 mm and

tended to become finer with time. This shows that

shifting sand is no longer the only soil substrate and

that other transported materials, including dustfall,

also play an important role in altering soil texture

(Table 1).

echanical composition (%)

Particle size (mm)

S.E.)

< 0.02 < 0.05 < 0.10 < 0.20 < 0.50

F 4.1 38.5 60.4 80.6 97.4 100.0

F 0.1 0.3 0.4 0.76 99.3 100.0

F 0.3 4.8 8.5 22.1 95.1 100.0

F 0.7 6.0 11.0 29.9 92.3 100.0

F 1.6 12.5 24.0 53.8 98.2 100.0

F 0.3 4.1 5.0 12.5 91.8 100.0

F 0.2 1.5 1.8 6.5 59.8 100.0

F 1.8 12.0 25.2 53.6 95.0 100.0

F 1.6 10.0 20.0 41.8 95.7 100.0

rent (Student’s t test, pV 0.005) from those marked (b), (c) and (d).

ea marked (A) are significantly different (Student’s t test, pV 0.05)

Table 2

Physical parameters of surface soil layer

Land type Maximum hygroscopic

moisture (%F S.E.)

Wilting coefficient

(%F S.E.)

Capillary water

(%F S.E.)

Porosity

(%F S.E.)

Bulk density

(g/cm3F S.E.)

Specific gravity

(g/cm3F S.E.)

Moving aeolian-sand

soil

0.45aF 0.02 0.61aF 0.09 4.01aF 0.42 40.07aF 3.32 1.62aF 0.02 2.70aF 0.03

Fixed aeolian-sand

soil (1956)

1.62bF 0.05 3.03bF 0.54 19.18bF 1.63 45.10bF 3.84 1.36F 0.02 2.47bF 0.03

icantly different (Student’s t test, pV 0.05) from those marked (b). n= 5.

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246242

3.2. Improvement of soil water-holding capacity

Owing to the changes in material composition and

mechanical composition, the bulk density and specific

gravity of fixed aeolian-sand soil significantly de-

creased, but its porosity and water-holding capacity

are largely enhanced (Table 2). For example, the

change in soil water-holding capacity significantly

affected the redistribution dynamical changes of soil

moisture after 30.5 mm rainfall on 18 August 1998

(Fig. 5), and in the subsequent 3 days, Fig. 2 shows

that owing to the lower water-holding capacity of

shifting sand, the following rainfall water continuous-

ly seeped through the soil and exhibited a roughly

uniform distribution with depth. In contrast, much of

the rainwater was concentrated within 10 cm surface

layer of the 35-year cultivated vegetation area and no

water recharged the soil below 40 cm depth. For the

former, water was present at depth, whereas for the

latter, rainwater only favored the shallow-rooted

Mean physical parameters of surface soil layer marked (a) are signif

Fig. 5. Redistribution processes of soil moisture afte

plants, but surface evaporation loss greatly increased.

From the comparison of four water distribution dia-

grams, it can be seen that for the different years of

fixed aeolian soils, the dividing line of rainwater deep-

layer recharge lies between 10 and 20 years.

In normal years, soil evaporation on bare shifting-

sand surface is 60–70% of annual precipitation, but in

dry years it may account for z 90% (Chen, 1991;

Feng et al., 1995). Annual precipitation could seep

down to z 5 m below the surface of shifting sand to

recharge deep layer of soil moisture, on the average,

accounting for 10% of annual precipitation (Chen,

1991). However, in the cultivated vegetation area,

much of the precipitation is consumed by plant

transpiration in addition to soil surface evaporation.

Root systems of perennial sand-binding shrubs are

mostly distributed in the 1–3-m soil layer (Liu et al.,

1991), while those of annual herbs with the 10-cm soil

layer. Although the evaporation of vegetated soil is

less than that of shifting sand, the transpiration of

r rainfall in different ages of fixed sandy land.

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246 243

plants is large, accounting for 20–40% of annual

precipitation (Chen, 1991; Feng et al., 1995), and

thus affecting deep infiltration of soil moisture.

3.3. Variations of soil micro-flora

Microorganism numbers in fixed aeolian-sand soil

in the Shapotou Region are a few tens of times higher

than that in unvegetated shifting sand (Table 3), due to

high organic matter content and high soil fertility in

the surface layer of fixed aeolian-sand soil. Fungi and

bacteria in fixed aeolian-sand soil are mostly concen-

trated in the surface layers and decrease rapidly with

depth. The total number of bacteria in shifting sand

often exceeds that in fixed aeolian-sand soil, but their

distribution increases with depth. This is because

surface layer of shifting sand is very dry and therefore

unfavorable to microorganism survival. The number

of microorganisms as an indicator of soil fertility can

reflect the increase in soil fertility from shifting sand

to aeolian-sand soil fixed by cultivated vegetation.

3.4. Nutrient accumulation

The increase in water-holding capacity and plant

biomass in surface layers of fixed aeolian-sand soil

greatly speeds up the accumulation and mineralization

of organic matter. Furthermore, the fixed surface is

favorable as a trap for airborne nutrients (for example,

dustfall and rainfall) and to avoid soil nutrient loss.

The changes in soil-forming condition thereby enable

the shifting-sand ecosystem of lower biological activ-

ity to develop towards a soil ecosystem of higher

biological activity.

From shifting sand to fixed aeolian-sand soil,

higher plants developed as soil organic matter signif-

Table 3

Microorganism numbers under different soil conditions (100 individuals/k

Soil type (g/kg) Soil depth (cm) Bacteria Fungi

Fixed aeolian-sand 0–1 6196aF 282 10.2aFsoil (1965) (1) 1–6 2537bF 96 5.4bF

6–16 63cF 21 1.5cFMoving aeolian-sand 0–1 23aF 2 0.4aF

soil (2) 1–6 95bF 7 0.6bF6–16 261cF 16 0.5abF

Mean microorganism numbers and soil organic matter under different dep

from those marked (b) and (c). n= 3. All mean microorganism numbers a

significantly different (Student’s t test, pV 0.05) from those marked (2). n

icantly increased. The organic matter content in the

surface soil layer on the leeward slope of the sandy

land fixed for 39 years was 10 times that of shifting

sand (Table 4). Owing to the influence of micro-

topographical conditions, the accumulated amount of

organic matter in interdune depressions is highest:

The same trend has been observed for N, P and K, and

especially obvious is the available K accumulation.

The nutrient content in the aeolian sand fixed by

natural vegetation in the control plot is roughly the

same as that in the sandy land fixed by cultivated

vegetation for several decades. However, the soil-

layer thickness in the cultivated vegetation plot is

shallow, and its nutrient content at depth is less than

that of the sand land fixed by natural vegetation.

3.5. Evolution of soil profile morphology

Although the mobile aeolian-sand soil at the study

area exhibits some fertility features, it is essentially

devoid of higher plants and the biological processes in

areas of wind activity are quite weak. Except for the

difference in dark and light color caused by soil

moisture content and the weak stratified structure

formed in the wind deposition processes, the whole

soil profile is composed of loose yellow-brownish fine

sand, suggesting that it is still in initial pedogenesis.

The profile of aeolian-sand soil in the cultivated

vegetation area can be divided into a crust, a transi-

tional layer and the original shifting-sand layer. The

crust is light gray in color (10YR 6/3–6/4) and mainly

composed of silt and fine sand (Duan et al., 2003). It

has weak stratified structure formed by blowing sand,

dustfall and litter after the sandy land was fixed by

vegetation. In addition, it also exhibits an obvious

monsoon rhythm in features. Under the influences of

g soilF S.E.)

Actinomyces Total number Soil organic carbon

0.7 20.1aF 1.3 6226aF 288 11.73aF 0.96

0.3 22.8aF 1.5 2565bF 99 4.77bF 0.34

0.1 6.7bF 0.5 71cF 22 1.13cF 0.08

0.06 50.4aF 4.6 74aF 7 0.70aF 0.05

0.05 214.8bF 15.4 311bF 22 0.72aF 0.06

0.05 40.2cF 3.8 302bF 20 0.66bF 0.05

th marked (a) are significantly different (Student’s t test, pV 0.05)

nd soil organic matter under fixed aeolian-sand soil marked (1) are

= 3.

Table 4

Variations of soil nutrients in the process of shifting-sand fixation

Sand-fixing age (a) Dune position Sampling Organic Total nutrient content (g/kg) Available nutrient content (mg/kg)

depth (cm) carbon (g/kg)N P K N P K

0 (Shifting sand) Composite sample 0–5 0.86 0.06 0.06 7.75 7.05 1.34 48

40–50 0.82 0.06 0.04 6.34 – 0.22 54

14 Leeward slope 0–17 2.48 0.20 0.10 10.46 34.11 1.70 104

30 Leeward slope 0–20 4.33 0.16 0.14 10.46 14.58 1.99 75

39 Leeward slope 0–2 8.14 0.31 0.17 10.46 25.40 4.53 100

15–20 5.59 0.08 0.08 10.46 18.50 0.84 104

40–50 0.45 0.05 0.05 9.46 3.45 1.20 42

Interdune depression 0–7 11.07 0.32 0.17 10.46 34.97 5.40 79

Windward slope 0–5 9.20 0.26 0.15 10.46 29.48 3.34 112

26 Windward slope 0–5 5.36 0.23 0.13 8.47 3.29 2.44 70

Sand land fixed by Windward slope 0–5 5.57 0.33 0.17 8.34 23.50 5.29 95

natural vegetation 20–54 1.97 0.08 0.12 9.17 8.10 2.18 –

54–76 1.39 0.05 0.14 8.80 11.60 1.93 –

76–100 0.87 0.02 0.11 9.17 9.30 1.33 –

Table 5

Mean value contrast of topographical changes of 385 measuring

points in the sandy land fixed by cultivated vegetation (unit: m)

Observed year Relative

height

Undulation

degree

Vertical

range

1964 5.97 1.50 10.31

1984 4.93 1.36 5.99

Annual mean

decrease

0.05 0.01 0.22

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246244

landform and sand flow, annual deposited thickness in

the area varies between 1 and 10 mm. The crusts

around shrubs and herbs are covered by 2–8 mm of

litter with lichen and mosses. Beneath it is an organic-

matter-stained layer, 5–10 cm in thickness. It has a

compact and lumpy structure and contains large

amounts of plant roots and undecomposed litter.

The transitional layer below the soil crust is virtu-

ally the sand layer formed before being fixed, yellow-

ish-brown in color (10YR 5/4–5/6), 15–20 cm thick

and contains some roots. Owing to the prolonged

migration of humus, fine soil particles and mineral

elements during pedogenesis, this layer has a higher

fertility than shifting sand (Table 4). It also has a

certain consistence and weak block structure. Soils on

the leeward slope have a thicker crust, but roots are

few due to deficient moisture. Soil crusts in the

interdune depressions are thin, although the depres-

sions have been fixed by vegetation for 20–30 years.

Because heavy-rain-induced runoff often flows to the

interdune depression, the dense root layer is much

thicker than the soil crust. The shifting sand at the

bottom still retains its original deposition condition,

belonging to loose and structureless aeolian sand.

With the increase in crust thickness, soil water con-

dition becomes worse, hence, only a few fine root

system and coarse shrub root exist in this layer.

During the sand fixation processes by cultivated

vegetation, the differentiation of soil body is signifi-

cantly reinforced, although its evolution processes are

similar to those under natural vegetation condition,

because of greater plant density, the differentiation

rate of the former is much faster than the latter.

Fine soil layers deposited at different landform

positions can be classified into three configurations:

First, a fine soil layer developed on the leeward slope

of sand dunes has the greatest depth and it thickens at

an annual rate of 5–8 mm. During the initial sand

fixation stage, comparatively large amounts of aeolian

sand join the formation of soil profile. Some 20 years

later, the shifting sand has been largely fixed except at

its margin, and annual deposition is reduced to 2–5

mm. Fine sand transported by winds in windy season

and silt transported by weak wind formed interbeds or

crossbeds, with a total thickness >20 cm. Due to

limited precipitation in the region, there is white

crystal or powdery gypsum layer and calcareous

deposits formed at 10–15 cm depth. Second, the

windward slope of sand dune is eroded, so has the

least accumulated sand and dustfall. Although there is

Table 6

Mean dust deposition rate of different topographic positions (kg/ha2)

Position January February March April May June July August September October November December Annual mean

Dune crest 55 208 272 314 884 423 525 433 107 56 136 88 3500

Interdune

depression

106 417 635 773 2004 961 626 588 235 132 268 172 6938

Height between dune crest and interdune depression is 8.2 m. Level distance between dust traps is 25 m.

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246 245

bedding formed by blown sand and dust, it is domi-

nated by silt with an indistinct sequences. Annual

deposition thickness varies between 0.5 and 0.8 mm.

The thickness of fine soil layer in the sandy land fixed

during the 1950s to the 1960s is 2–5 cm. Third, the

interdune depression is covered by silt deposits with-

out bedding. The annual deposition varies between

1.0 and 1.5 mm, and, locally, the thickness of fine soil

layer reaches 5–8 cm and contains a certain amount

of organic matter.

3.6. Microtopographical influences

Differences in surface morphology often govern

the redistribution of materials, and thereby affect soil

development. During the fixation processes of shifting

sand, the area’s relief evolved towards uniformed

direction (Table 5). Mass balance obviously appears

as a negative value for the positive landforms, such as

the dune crest, and a positive value for the negative

landforms, including interdune depression, with lee-

ward slope having the largest mass accumulation.

Owing to the changes in climate, landform and

biological condition, each year, f 40 mg/m2 of dust-

fall in the vegetated area joins the soil-forming pro-

cesses as a parent material.

Furthermore, landform plays a very important role

in the redistribution of materials, hence, the windward

slope differs from leeward slope by two times or more

in deposition rate (Table 6). In the initial stage of

shifting-sand fixation, dust plays an important role in

binding soil particles and stabilizing the sand surface,

dust improves the conservation capacity of soil

nutrients and moisture, thus providing an important

condition for vegetation succession. In the latter stage,

the infiltration rate of water in the sandy land fixed by

cultivated vegetation for less than 30 years greatly

decreases and heavy rain may cause surface runoff,

which carries fine soil particles from slopes to inter-

dune depressions. It is this difference in mass balance

that leads to the difference in soil-profile development

and morphology and even causes obvious differenti-

ation of soil physiochemical properties, particle size

and nutrient accumulation.

4. Conclusions

In the succession from cultivated vegetation to

natural vegetation in the experiment plot of shifting-

sand fixation in the past few decades in the Shapotou

Region, significant changes took place in soil fertility

due to changes in soil-forming environments and

material cycles. Firstly, shifting sand is no longer

the only source of soil substrate. Fine particles such as

dustfall exert significant effects on soil texture, modal

particle size reduced from >0.2 to < 0.08 mm and

tended to become finer with time. Secondly, soil

water-holding capacity improved and nearly increased

fivefold. In the process of water redistribution in soil

body, deep infiltration usually no longer occurred.

Thirdly, the number of microorganisms in relation to

the content and distribution of organic matter shows

that the evolution of soil fertility and microbes is an

interactive process. Fourthly, after 39 years of fixa-

tion, the organic matter content in the sandy land

increased tenfold compared to shifting sand and other

nutrients also significantly increased, this is because

the process of nutrient loss, as occurs under shifting-

sand condition, virtually stopped. Fifthly, soil profiles

display obvious differentiation, organic layer and

illuvial horizons have preliminarily formed and its

configuration tends to evolve towards aripsamments.

Acknowledgements

This study was supported by the National Natural

Science Foundation of China (90202015), the Gong-

guan Project of National (2002BA517A11) and the

D. Zhenghu et al. / Geomorphology 59 (2004) 237–246246

Innovation Project of Chinese Academy of Sciences

(KZCX3-SW-324). The authors thank Dr. Ian Living-

stone, Dr. Mike Fullen and Dr. Richard Harper for

their critical review of the manuscript.

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