Journal of Arid Environments (2002) 51: 35–54doi:10.1006/jare.2001.0928, available online at http://www.idealibrary.com on

Soil water and chemical characteristics of sandy soilsand their significance to land reclamation

Feng Qi%wz*, Endo Kunihikow, Cheng Guodong

%Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences, 730000 Lanzhou, P. R. China

wDepartment of Geosciences System, College of Humanities and Sciences,Nihon University, Japan

(Received 15 May 2000, accepted 24 September 2000)

Long-term observations were made of moisture and chemical contentchanges in sandy soils at ten locations in China, located in five differentclimatic zones: hyperarid, arid, semi-arid, sub-humid and subtropical humid.These sandy soil zones were delineated based on their bioclimaticcharacteristics, aridity, mean soil moisture content and precipitation. Spatialand temporal variations in soil moisture and water balance components of thetop 1 m soil layer were monitored in different sandy soils. The water balanceequation for the top 1 m soil layer was defined as: DS ¼ (P+U)�E in thehyperarid and arid areas, DS ¼ (P+U)�(D+E+TR) in the semi-arid areas,and DS+DV ¼ (P+U)�(D+E+TR) in the semihumid and subtropical humidareas. Sandy soil organic matter content (OMC), CaCO3, and soluble saltscontent were also investigated. Afforestation and a selection of landmanagement techniques are suggested to slow or stop the development andexpansion of sandy lands. In China, four land management regions, definedby the prevailing natural conditions and complexity of reclamation/mitigationtechniques implemented are: Region I: trees and shrubs to fix shifting sands,land can then be used for high-profit agriculture and commercial crops;Region II: some species of shrub plants and grasses to fix shifting sands;Region III: mechanical methods to enhance biological methods to fix shiftingsands; Region IV: improvement of afforestation practices, and stabilization oflow-lying wetland sites, engineering works, and irrigation systems. Theresults of such programs have important implications in terms of theeconomic benefits of irrigated agriculture and environment of sandy lands inChina.

# 2002 Elsevier Science Ltd.

Keywords: sandy soils; moisture characteristics; sand fixation; afforestation;benefits of irrigation

zPresent address: Department of Geosciences System, College of Humanities and Sciences, NihonUniversity, 3-25-40, Sakurajosui Setagaya-ku, 156-8550 Tokyo, Japan.*Corresponding author. Fax: +81-03-5376-9686. E-mail: fengqi@chs.nihon-u.ac.jp

0140-1963/02/010035 + 20 $35.00/0 # 2002 Elsevier Science Ltd.

36 FENG QI ET AL.

Introduction

Aeolian sandy soils develop through wind action on sandy parent materials andgenerally comprise a sandy layer of 1 m or more in thickness, mainly consisting of well-sorted fine sand, of which 0?02–2?0 mm particles make up over 80% (Table 1).Aeolian sandy soils have weakly developed profiles and a loose consistency (Feng et al.,2000). Sandy soils are largely barren ecosystems characterized by frequent drifting ofsand, poor plant substrates, and weak biological activity. Only a small portion of theprecipitation received is stored in the soil, and evaporation in general from the soil farexceeds other losses, such as surface runoff and percolation. Especially in arid areas,land development can be seriously restricted by the moisture characteristics of sandysoil, including the quantity and the physical form the moisture takes, how it moveswithin the soil profile, and its relationship to other natural factors including rainfallevents, vegetation, and temperature. Besides their organic matter changes (OMC),sandy soils’ moisture regimes and balances are important considerations in theirdevelopment and/or reclamation. Sandy soils in China are not only present in aridareas but also in humid and subtropic areas. A number of studies at fixed points(100 m� 100 m) or in small areas (small agricultural watershed) have investigated soilmoisture and organic matter regimes and the laws governing them in sandy soils(Chen, 1962; Liu & Pu, 1986; Feng, 1998). However, few papers report on thedynamics of moisture variation and chemical change, in particular with respect toagricultural development of different soils (Feng & Cheng, 1998). The primaryobjective of this study was to investigate the state of soil moisture and water balance indifferent sandy lands. The soil OMC, CaCO3 content, and soluble salts distributionwere also investigated. Furthermore, the influence of meteorological factors,vegetation and eco-agricultural development issues in different sandy soils regionson the management goals for these lands was analysed. Finally, recommendations ofland reclamation and afforestation for different sandy soils are discussed, based onexisting natural conditions.

Material and methods

Based on their location and suitability of their soil for agricultural or otherdevelopment, sandy lands in China can be divided into sub-humid, semi-arid, andarid zones. Based on regional differences in the distribution of sandy lands, theircharacteristics and water–energy conditions, ten typical sandy land sites were chosen,each associated with a nearby meteorological station (Table 2; Fig. 1). These wererepresentative of roughly 90% of the sandy lands in China. These included (i) thehyperarid edges of Taklimakan Desert (Xiao Tang Station); (ii) the semi-arid HexiCorridor (Linze Station); (iii) the arid Alxa region in the Tengger desert (EjinStation); (iv) the arid Mu Us desert (Shapotou Station); (v) the semi-arid Yanchi zone(Yanchi Station); (vi) the sub-humid alluvium of the Yellow River in ShandongProvince (Yucheng Station); (vii) the sub-humid alluvium of the Yellow River inHenan Province (Xiajin Station); (viii) the sub-humid desertified lands of Hebeiprovince (Daxin Station); (ix) the sub-humid Horqin sandy soils (Naiman Station);and (x) a subtropical humid type of wind-blown sandy soil in Nanchang Province(Xinjian Station). Data were collected from 1991 through 1994. Each year, soilmoisture storage was calculated as the difference between the end of season (October)and beginning of season (May) soil water content. The ‘precipitation lost’ betweentwo measurement days was defined as the difference between the precipitationreceived and the change in soil moisture over a 1?0 m depth. Sources of precipitationlosses are many, including evaporation from the soil, deep percolation, surface runoff

Table 1. Particle size analysis of 1?0 m thick top layer of sandy soils in China

Climatic zones* Sandy soil Station Grain composition (mm) (%)w HClsolutionloss (%)

Coarse sand(2?0–?2)

Fine sand(0?20–0?02)

Silt(0?02–0?002)

Clay(o0?002)

Hyperarid Taklimakan Xiaotang 66?9 32?1 0?9 0?0 0?1Arid Alxa Ejin 62?4 33?7 2?5 0?2 1?2

Hexi Corridor Linze 64?3 26?9 4?9 0?1 3?8Mu Us Shapotou 74?9 24?2 0?7 0?2 0?0

Semi-arid Yanchi Yanchi 61?1 22?3 14?8 0?5 1?3Semihumid Alluvium of Yellow

RiverYucheng 52?3 32?5 12?3 2?1 0?8

Xiajin 58?0 31?7 8?4 0?8 1?1Horqin Naiman 61?9 30?0 2?0 3?1 3?0Hebei Daxin 48?4 38?9 12?1 0?2 0?4

Subtropical humid Nanchang Xinjian 47?0 46?6 6?0 0?2 0?2

*Location of sites shown in Fig. 1.wThe classification of soil fractions according to the soil taxonomy of International Soil Science Society (ISSS).

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Table 2. Annual mean meteorological parameters measured for sandy soils in China for the period 1990–1994

Climatic zones* GeographicZones Station

Precipitation(mm)

Evaporation(mm)

Evaporation/precipitation

Air temperature(1C)w

Vegetativecover (%)z

Hyperarid Taklimakan desert Xiaotang 53?7 3180 59?21 11?0 0?5Arid Hexi Corridor Linze 110?4 2341 21?20 7?4 5?1

Alxa Ejin 101?4 3020 29?78 8?9 1?8Mu Us desert Shapotou 178?6 3100 17?35 9?8 1?4

Semi-arid Yanchi Yanchi 286?0 2112 7?38 7?9 8?0Semihumid Horqin Naiman 416?1 1710 4?11 6?1 10?0

Alluvium of Yellow River Yucheng 616?0 2229?0 3?62 13?1 12?0Xiajin 565?5 2203?0 3?86 12?7 10?0

Hebei Daxin 657?0 1758 2?68 10?5 13?0Subtrophical humid Nanchang Xinjian 1500?0 1594 1?06 17?3 14?0

*Location of sites shown in Fig. 1.wMeasured 1?0 m above the surface soil.zIn 10 m�10 m station plot.

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Figure 1. Map of fixed-site soil moisture and chemical observation locations and regions ofsandy soils in China. (I) hyperarid zones, (II) arid zones, (III) semi arid zones, (IV) semi-humidzones, (V) humid zones, (VI) Tibet Plateau, (�1?0) aridity.

SOIL WATER AND CHEMICAL CHARACTERISTICS OF SANDY SOILS 39

and subsurface flow to watercourses and uptake by weeds and natural vegetation, andsnow blowoff. The soil water storage efficiency was calculated as the soil water storagedivided by incident precipitation (Feng et al., 2000).

In situ volumetric soil moisture content, at 0?2 m increments up to a 1?0 m depth,was measured weekly using a neutron scattering probe (Troxler ElectronicLaboratories) calibrated using the oven-drying method of soil moisture measurement.For the 0–0?2 m surface layer of the soil, a special surface probe was available tomeasure the average moisture. The probe was calibrated at the time of tubeinstallation using gravimetric soil moisture content and bulk density measurements(Holmes, 1956). Taking soil moisture determined by the gravimetric method as thenormal value, a mean-square deviation across the different sites of soil moisturedetermined by the neutron scattering probe method in the 0–0?2 m layers of arid areasoils was 2?3–5?6%, and 0?73–1?5% in layers deeper than 0?2 m. In sandy soils ofhumid and subtropical humid zones, the deviation in both shallow and deep layersvaried between 0?5% and 2?2% (Zhang, 1989). In this study, all quantities areexpressed in terms of volume of water per unit land area (equivalent depth units)during the period considered.

Soil moisture characteristic curves were determined on core samples using ceramictension tables and a pressure plate apparatus following the procedure of U.S. SoilConservation Service (1967). The cores were successively equilibrated on ceramictension plates at matric potentials of 0, �1?0, �3?0, �5?0, �10?0, and �34?0 J kg�1.Undisturbed subsamples were then placed in a pressure plate apparatus andequilibrated successively to �66, �100, �300, �500, and �1500 J kg�1 matricpotential. Bulk density was determined using the known core volume and the ovendry weight of the core contents. Soil property measurements were unreplicated at the57 sites in each region, and there was a total of 570 samples for ten regions in the

40 FENG QI ET AL.

1992–1993 sampling. Details of the sampling and analysis procedure are presented inBresler et al. (1969) and Hillel (1974, 1982). Surface soil properties along with fieldcapacity and wilting point values through the profile are summarized in Table 3. On-site automated weather stations provided hourly measurements of air temperature andevaporation, which were averaged on an annual basis for 1991–1994 (Table 2).

The particle size distribution of soil samples (Table 1) was determined by sieving anaqueous suspension after dispersion by treatment with hydrogen peroxide to removeorganic matter, hydrochloric acid to remove carbonate, and mechanical agitation indilute sodium hexametaphosphate solution (Bouyoucos, 1951; Brewer, 1964).Soil loss yields in the sample include all the erosion as well as HCl solution loss (%;Table 1) (Davidson, 1965).

To determine the soil OMC, triplicate samples were obtained at depth intervalsof 0?1 m, from the soil surface to a depth of l?0 m using steel cylinders with individualvolumes of 0?1 m3 (and diameter and height ¼ 50?3 mm). The cylinders were pressedvertically into the soil, then emptied into a 200cm3 metal cup. The cup wasthen sealed with rubberized fabric. The soil samples were brought to the laboratoryand analysed for OMC as soon as possible within 48 h. The OMC was measuredby drying the sample for one day at 1051C and heating the dried sample for 4 hat 6501C. The weight difference between the dried and heated samples divided by thatof the dried sample was taken as the OMC. The mean OMC in the 0–0?2, 0?2–0?4,0?4–0?6, and 0?6–1?0 m layers was calculated from the triplicate samples of thelayer(s).

The d13C and d18O stable isotope composition of CaCO3 (aragonite plus calcite)was measured for the o62?5 mm fraction of 22 samples using a VG PRISM massspectrometer and standard preparation methods (Drimmie et al., 1996). Selective acidextraction provided data for CaCO3 with minimal dolomite interference (Al-Aasm,1990). Replicate analyses were within 70?4%. Aragonite d13C and d18O values werecalculated by correcting for detrital calcite, as outlined in Van Stempvoort et al.(1997). Small isotopic fraction differences between aragonite and magnesium calcite(Romanek et al., 1996; Tarutani et al., 1969) were ignored.

Soil salinity as conductivity was determined from measurements of bulk soilelectrical conductivity using electromagnetic induction (Rhoades & Corwin, 1980;Corwin & Rhoades, 1982, 1984; Dalton et al., 1984). Measurement methods andcalibrations for individual soils are reported and reviewed in detail by Rhoades (1976,1978, 1980, 1984). In situ measurement results are shown in Table 5.

Infiltration rate (%), defined as the ratio of infiltration of rainfall (mm) to totalrainfall (mm) for a rainfall event, was estimated for each rainfall event from 1991 to1994. The method used two points at the same distance from access tubes for neutronprobe measurements, one under natural conditions and another covered by plasticbefore rainfall event. The infiltration rate was calculated as the difference between thesoil moisture contents measured by neutron scattering at the two points, 4 days afterthe rainfall event.

The monthly evaporation rate from bare sandy land was determined using a waterbalance approach (Rockstrom & Valentin, 1997). The water balance of the top 1?0 msoil (all parameters in mm), usually expressed in integral form, was calculated on aunit area basis (Hillel, 1998):

�S þ�V ¼ ðP þ I þ UÞ � ðR þ D þ E þ TRÞ ðEqn 1Þwhere D is the downward drainage out of the top 1?0 m soil layer, E is the evaporationfrom the soil surface, I is the irrigation applied, P is the rainfall, R is the runoff, andrepresents the inflow of water from upstream zones and runoff flow as a result ofrainfall partition due to soil crusting, DS is the change in soil water storage in 0–1?0 msoil layer, TR is the transpiration by plants, U is the upward capillary flow into the top1?0 m soil layer, and DV is the increment of water incorporated in vegetative biomass.

Table 3. Properties of sandy soil (water availability (WA) and water-table (WT) variations) in the top 1?0 m soil profile

Climaticzones* Sandy soil Station

Bulkdensity

(g cm�3)

Porosity(%)

Capillaryheight (m)

Wiltingmoisture(g cm�3)

Fieldcapacity(g cm�3)

Saturated watercontent(g cm�3)

WA(mm)

WT(m)

Hyperarid Taklimakan Xiaotang 1?41 46?0 0?53 0?54 2?23 17?0 9?2 4?5Arid Hexi Corridor Linze 1?60 38?9 0?52 0?74 2?41 22?3 17?0 2?3

Alxa Ejin 1?40 43?7 0?50 0?73 3?55 21?7 15?4 4?0Mu Us Shapotou 1?56 41?5 0?55 0?65 3?30 23?5 19?5 4?0

Semi-arid Yanchi Yanchi 1?45 44?2 0?75 0?52 4?98 28?0 25?1 3?8Semihumid Alluvium Yellow Yucheng 1?53 43?4 0?73 0?85 10?82 29?0 26?1 2?8

Rive Xiajin 1?36 45?1 0?52 1?05 8?72 33?5 22?4 2?1Horqin Naiman 1?70 35?4 0?65 0?57 4?89 19?7 29?8 3?0Hebei Daxing 1?05 44?7 0?60 1?05 7?51 27?3 26?2 2?7

Subtropical humid Nanchang Xinjian 1?48 39?7 0?57 0?61 4?74 27?0 32?9 3?0

*Location of sites shown in Fig. 1.

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42 FENG QI ET AL.

The water balance differed according to the sandy soil studied. Evapo-transpirationrates in the sandy soils are shown in Table 4.

These indices are neither specifically designed to incorporate all properties andprocesses that might contribute to soil moisture (e.g. infiltration and storage invegetation) nor did this study seek to discuss all the above factors at each site. Instead,infiltration and vegetation are used to indicate relative differences between sites on thebasis of a subset of soil properties. A discussion of what the full subset of propertiesincludes and represents is covered elsewhere (Feng et al., 2000). Here we only usesome results to deduce the basic soil moisture conditions, the OMC, soil solutionsalinity, and CaCO3 variation for potential agricultural activities. Sites where theground-water tables were deeper than 3?0 m from the soil surface, and these watershad little effect on the moisture of the top 1?0 m soil layer. The vegetative cover waslow (below 14%) and only discussed for comparative purposes for semi-desert zones.

Results and discussion

Coarse grain sand particles (0?02–2?0 mm) make up 80% or more of the sandy soilsof China (Table 1). Sandy soils have low water content, water-retention capacity(Table 3), and OMC, but high CaCO3 content (Table 5). Below the 1?0 m of topsoil,soil water content is stable, whereas in the 1?0 m of topsoil the water varies rapidlyaccording to soil particle size, meteorological factors, vegetation, and dry soilthickness (Feng, 1999).

Soil water changes

Variation according to climatic zone

According to the content, distribution and dynamics of variation of soil moisture,sandy soils in China can be categorized as: hyperarid, arid, semi-arid, sub-humid, andsubtropical humid. The dry-sand surface profile of some sandy land soils is the resultof surface evaporation, heat conduction, and pore water diffusion, and results inconditions where water movement can be severely limited by their water-repellentnature (Feng, 1994). Rain that falls on the surface of a water-repellent sand does notpenetrate evenly. Trenches dug a few days after a good significant rainfall eventshowed that water moved downward through narrow channels, leaving the interveningsoil quite dry and causing considerable variation in the moisture content of the sand.The channels, tongues or preferential flow paths are due to either a localized lowerwater repellency or to surface ponding, where hydrostatic pressure aids water entry.

Hyperarid. Mean air temperatures are 311C, varying between 231C and 421C in theTaklimakan Desert (mean 281C) and between 19?31C and 421C in the TenggerDesert. In the Taklimakan and Tengger deserts, relative humidities are only 21–33%and 30–40% and gentle breezes (10 m high) are of 2–3 and 3–4 m s�1 blow,respectively. Along with the high temperatures, these conditions contribute to the highevaporation rates. Soil moisture content in hyperarid soils is low, on an average lessthan 3%. The thickness of the dry soil layer (moisture o1%) generally varies between0 and 0?20 m in hyperarid areas, and sometimes reaches 0?40 m in prolonged rainlessor drought periods (Figs 2 & 3; Zhu, 1989). Precipitation in desert areas occursmainly between June and August, but the wetted surface layer dries up quickly. Amean soil moisture content of 1?2% varies from a depth of 0?10 m in March, to 0?40 min June. Less variation in moisture content occurs between June and August when

Table 4. Mean evapo-transpiration rate (mm) per month (1991–1994) from top 1?0 m soil layer

Climatic zones* Month Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Mean

Hyperarid Xiaotang 0?16 0?14 0?13 0?24 0?58 0?45 1?01 0?35 0?21 0?32 0?25 0?15 0?33Arid Linze 0?15 0?23 0?31 0?34 0?45 0?42 1?22 0?58 0?56 0?55 0?41 0?28 0?45

Ejin 0?15 0?22 0?22 0?48 0?56 0?47 1?01 0?56 0?42 0?41 0?34 0?32 0?43Shapotou 0?27 0?21 0?23 0?34 0?88 0?45 2?01 0?85 0?91 0?53 0?45 0?25 0?62

Semi-arid Yanchi 0?27 0?31 0?32 0?34 0?95 0?49 2?01 1?08 0?81 0?63 0?51 0?25 0?66Semihumid Yucheng 0?53 0?58 1?35 1?79 2?42 2?65 3?21 4?22 2?56 2?78 1?51 1?02 2?05

Xiajin 0?58 0?56 1?45 1?98 2?32 2?56 3?44 4?66 2?10 2?96 1?12 0?88 2?05Naiman 0?47 0?44 0?58 1?31 2?48 3?06 3?54 3?87 3?58 1?56 0?82 0?48 1?85Daxing 0?54 0?51 1?05 1?38 1?89 2?56 3?44 4?03 2?15 2?14 1?18 0?77 1?80

Subtropical humid Xinjian 1?32 1?03 2?02 2?21 3?56 3?59 4?21 5?11 4?23 4?10 3?20 2?15 3?06

*Location of sites shown in Fig. 1.

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Table 5. Organic matter, CaCO3, and salt content in the top 1?0 m soil layer of several sandy lands in China

Geographic zone* Sandy land Station Depth (m) Organic matter (%) CaCO3 content (g kg�1) Salt content ((g kg�1)

Hyperarid Taklimakan Xiaotang 0–0?20 0?31 127?9 4?050?20–0?40 0?16 129?9 3?460?40–0?60 0?12 135?0 4?40

0–1?0 0?13 133?6 4?47

Arid Alxa Ejin 0–0?20 0?38 64?2 0?460?20–0?40 0?24 43?5 0?580?40–0?60 0?15 41?0 0?59

0–1?0 0?17 45?4 0?63Mu Us Sapotou 0–0?20 0?29 50?1 1?61

0?20–0?40 0?15 41?0 1?700?40–0?60 0?24 22?9 1?30

0–1?0 0?15 29?6 1?50Hexi Corridor Linze 0–0?20 0?52 15?3 2?37

0?20–0?40 0?27 14?2 1?650?40–0?60 0?20 10?8 1?47

0–1?0 0?22 16?6 1?46

Semi-arid Yanchi Yanchi 0–0?20 0?11 36?1 1?290?20–0?40 0?06 20?0 1?420?40–0?60 0?04 37?1 1?38

0–1?0 0?05 33?0 1?36

Semihumid Alluvium ofYellow River

Yucheng 0–0?20 1?11 1?2 0?10

0?20–0?40 0?58 1?5 0?060?40–0?60 0?42 0?8 0?41

0–1?0 0?71 0?8 0?16Xiajin 0–0?20 0?64 2?3 0?72

0?20–0?40 0?65 1?2 0?640?40–0?60 0?72 0?7 0?72

0–1?0 0?70 1?1 0?68

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Horqin Naiman 0–0?20 1?56 0?2 0?320?20–0?40 1?00 1?1 0?280?40–0?60 0?55 1?0 0?26

0–1?0 1?04 4?1 0?32Hebei Daxing 0–0?20 0?81 0?1 0?37

0?20–0?40 0?43 1?1 0?380?40–0?60 0?31 0?8 0?37

0–1?0 0?38 4?0 0?39Subtropical humid Aeolian Xinjian 0–0?20 1?20 0?9 0?04

0?20–0?40 1?11 1?2 0?080?40–0?60 1?06 1?5 0?09

0–1?0 1?08 0?9 0?09

*Location of sites shown in Fig. 1.

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46 FENG QI ET AL.

moisture levels are at their lowest. When a rainfall event of over 10 mm occurs, the soilmoisture of the 0–0?2 m profile may take 5–7 days to be restored to March values,whereas the 0?2–0?4 m profile may take up to 6–10 days (Figs 2 & 3). Theprecipitation can thus evaporate within one week in a hyperarid region. Consequently,the water balance equation in the top 1 m soil layer can be simplified from eqn. (1) to

�S ¼ ðU þ PÞ � E ðEqn 2ÞArid. In the arid areas the dry soil layer varies between 0?0 and 0?15 m, and is at

most 0?20 m deep. In these areas, soil moisture content in the 0–0?1 m soil profile isless than 1% before the rainy season in June, and the profile below 0?4 m has a fairlyconstant moisture content of 2–3%. After a rainfall event, the soil moisture contentbelow 0?20 m can increase to 3–4%, at most 4–5%, while the thickness of the dry sandlayer can vary significantly in the range of 0–0?4 m. A rainfall event of 40 mm or moremay increase the soil moisture in the 0–3?0 m soil profile by 3–4%, whereas a 30–40 mm event will affect only the 0–2?0 m soil profile (Fig. 2). Rainfall events of 10 mmor less only wet the surface of the dry sandy layer and can entirely evaporate in a fewdays. There is a significant vertical variation in soil moisture content in the top 0?6 mof soil in arid sandy soils. Due to the low vegetative cover (0–5?0%) in these areas, TR

and DV can be considered negligible. The downward drainage out of the top 1 m soillayer, D, can similarly be omitted from the analysis of the soil profile. Thus, the waterbalance equation reduces to

�S ¼ ðP þ UÞ � E ðEqn 3ÞSemi-arid. In semi-arid zones, during the rainy season (between July and

September), soil moisture content of sandy steppe lands is high, on average 3–4%or at most 4–5%. After the rainy season, soil moisture content rapidly decreases to 2–3% but the thickness of the dry sand layer rarely exceeds 0?2 m (Fig. 2). Soil moisturecontent in the 1?0–2?0 m soil profile may increase to 4–5% from July to August due toprecipitation. For a 20–30 mm rainfall event, the variation of moisture content insandy steppe lands is not as great as that observed in the semi-desert areas. Thus, incomparison to semi-desert areas, the elevated soil moisture content lasts longer duringthe rainy season and the soil moisture content in the dry sand layer is relatively highdue to different soil macroporosity. The soil moisture content in the sand layer ofsteppe lands generally varies between 3% and 5% so that rainfall may directly seepinto the deeper sand layers. The soil moisture content below 1?0 m can increase to3–5% depending on the amount of rainfall, and slowly revert to its original pre-rainfallsoil moisture content with increasing rainless days. As surface vegetation cover can

Figure 2. Seasonal variations of water contents in sandy soils of different zones. ( )Xiaotang, ( ) Shapotou, ( ) Ejin, ( ) Yanchi, ( ) Yucheng, ( ) Xiajin, ( )Daxing, ( ) Naiman, ( ) Linze, ( ) Xionjian.

Figure 3. Soil moisture variations with depths in sandy soils of different zones. ( )Xiaotang, ( ) Ejin, ( ) Linze, ( ) Shapotou, ( ) Yanchi, ( ) Yucheng, ( )Xiajin, ( ) Naiman, ( ) Daxing, ( ) Xionjian.

SOIL WATER AND CHEMICAL CHARACTERISTICS OF SANDY SOILS 47

reach 6% in these areas, TR must be considered, and the downward drainage out ofthe top 1 m soil layer was deemed significant by way of an analysis of the soil moistureprofile. Thus, the water balance equation can be represented as

�S ¼ ðP þ UÞ � ðD þ E þ TRÞ ðEqn 4ÞSub-humid. Soil moisture content of the 0?10–0?30 m layer is sensitive to

precipitation events. When a 10–15 mm rainfall event occurs, soil moisture contentincreases immediately by 3–4% to reach 6–9%, but 4–5 rainless days may reduce themoisture of the 0–0?1 m of topsoil to 4–5% (Figs 2 & 3). A 20-mm rainfall canincrease the soil moisture content in the 0?40–1?0 m profile by 3–5% and that below1?0 m by 2–3%. However, 5–6 days after the event, a layer of dry sand may form in40–50 mm profile. In general, the soil moisture content in the 0?6–1?0 m profile variesbetween 5% and 6%, and the moisture content in deeper sand layers below 1?0 mbetween 7% and 11% (Fig. 2). As vegetative cover reaches 3–12% in the area, the TR

is an important factor in the water balance. An analysis of the soil moisture profile thatshowed downward drainage out of the top 1?0m soil layer, D, was also significant.Thus, the resulting water balance equation was

�S þ�V ¼ ðP þ UÞ � ðD þ E þ TRÞ ðEqn 5ÞSubtropical humid. The soil moisture content in aeolian sand subtropical lands is

relatively high. The soil moisture content in the 0–1?0 m sand layer generally varies in3–6%, with an average of 8–9% from May to June, 2–3% from July to August, 4–5%from September to December, and 3–5% from December to March (Fig. 2). In thetwo low-rainfall periods of December–March and early July to mid-August, andespecially in mid-August, the 0–1?6 m soil profile has a low moisture content, rangingfrom 1% to 3% (Fig. 2). It is only in September that it increases to a certain extent. Ananalysis of the soil moisture profile showed that downward drainage out of the top1?0 m soil layer, D, was also significant. Thus, the resulting water balance equationwas

�S þ�V ¼ ðP þ UÞ � ðD þ E þ TRÞ ðEqn 6ÞInter-seasonal variation

As an example of detailed measurements, Figs 2 and 3 show mean soil water contentof the top 1?0 m soil profile (1991–1994) at each of the different sampling sites(points) within each of the ten areas surveyed. The seasonal variation in soil moisture

48 FENG QI ET AL.

content is difficult to distinguish in plots that are so highly localized. However, thesurface of every sandy soil is generally homogeneous over every study area, hence datafrom localized meteorological stations can allow the determination of the general lawscontrolling soil water movements in distinct areas.

The first 10 days of March to the last 10 days of May is the weak water loss stage.During this period sandy soils area are almost continuously covered with dry sand,except for short periods of rainy or snowy days. Although the dry surface can restrictevaporation, soil water loss continues slowly due to the porous properties and rapidheat conduction of sandy soils (Table 4) (Wang, 1990). In this period, rainfall is lighterand even a larger rainfall event (410 mm) can only give limited recharge due to rapidevaporation. The rising air and soil temperatures and resulting evaporation result inrapid water loss (Table 4). Prior to this stage (middle to late February), soils innorthern China begin to thaw. By the first 10 days of March the potential evaporationhas risen sharply due to rapidly rising temperatures, frequent winds, and dry soilsurfaces. However, actual evapo-transpiration rates are low due to the low soilmoisture water. Mean soil moisture content varies 1–2%, 1–3%, 4–5%, and 3–4% inhyperarid, arid, sub-humid and semi-arid areas, respectively (Fig. 2). The soil watercontent during this season is insufficient for non-irrigated agricultural cultivation,although the temperature is high enough for cultivation (5–151C, 3–121C, 0–21C, 2–161C, and 5–251C in hyperarid, arid zones, semi-arid, semihumid and subtropicalzones, respectively). Consequently, recharging is essential.

The rainy season occurs from late March to late July in southern China and fromthe middle of June to late August in the sub-humid and arid areas. During this periodof higher rainfall, an individual event may exceed 10 mm in hyperarid, 20 mm in arid,and 25 mm in sub-humid areas. Owing to rapid infiltration and the lower water-holding capacity of sandy soils, rainfall can largely recharge the soil water reserve andground-water. Hence, in the plot of water dynamics (Fig. 3) high soil water contentsfrom the top to the bottom of the soil profile prevail throughout the rainy season. Thewater content of the soil profile is generally 1–3% for the hyperarid, 2–4% for aridzone, and 2–6% for the sub-humid areas (Fig. 3), resulting in evapo-transpirationrates that are also high (Table 4). The quantity of recharge water entering sandy soilsand ground-water is related to the original soil water content, the evapo-transpirationrates, and the amount and intensity of precipitation.

From September to late November both the air temperature and groundtemperature gradually decrease and autumn droughts may occur, with a maximumrainless period of 20–25 days. In dry years the quantity of recharge water going intosandy soil and ground-water is small, and the water loss is dominated by evapo-transpiration through plants (Table 4). However, water in the soil profile is about 1–3% greater than in spring (Fig. 3). During September to late November, the rate ofwater loss decreases because of declining air temperatures, vegetative cover andconsequently evapo-transpiration rates (Table 4). When continuous rainless daysexceed ten, water content of sandy soils no longer supports the normal growth ofcrops, so recharging irrigation water is essential at this stage.

From December to mid-February (October to January in southern China) airtemperatures drop below 01C, and the 0–0?2 m sand profile begins to freeze. Soilwater in sandy soil moves upward in gaseous form during sublimation and the wettedsandy surface soil is in an alternating freezing–thawing state due to fluctuating airtemperatures. In winter, water in the dry surface sand profile is continuously lost dueto enhanced transpiration owing to dry winds.

Thus, in China’s sandy lands, air temperature and precipitation play primary rolesin the seasonal variations of soil moisture content. In the rainy season (July–September) rainfall offers recharge water to the soil layers, hence the soil moisturecontents increase markedly. Air temperature variations lead to the loss of poremoisture in surface sand layers and the formation of a dry sand layer through the

SOIL WATER AND CHEMICAL CHARACTERISTICS OF SANDY SOILS 49

raising of ground temperatures and enhancement of evaporation (Shapotou DesertScientific Research Station, Lanzhou Institute of Desert Research, 1991). Increases inair temperatures result in increased water vapor pressures and decreased relativehumidity levels, which in turn increase soil water evaporated from the surface layer(Feng, 1998). Wind also has an obvious effect on the moisture content of sandy soil.Hot and dry winds promote soil water evaporation and result in a larger airtemperature gradient, thus enhancing evaporation from the soil. Also, wind erosionexposes the underlying sand layer and accelerates their moisture loss.

Changes in soil chemical matter

Organic matter changes (OMC)

Along with the deflation and loss of fine materials on the surface, the loss of organicmatter as soil undergoes desertification also has significant effects on nutrients andmicroelement levels in the soil. Changes in organic matter are very significant incomparing sandy soils amongst themselves. The OMC of the soils of the main sandysoil regions studied, at soil depths of 0–0?2, 0?2–0?4, 0?4–0?6, and 0?6–1?0 m arepresented in Table 5. The OMC of the 0?2 m of topsoil ranged from 0?11% to 1?56%in the study areas. Due to the low vegetative cover and meager precipitation, the OMCis greatest at the soil surface and decreases with depth in hyperarid regions. The OMCin the top 1 m soil layer of the hyperarid regions (0?13%) was the lowest of the sandysoils studied. The mean soil OMC of the top 1?0 m soil layers were 0?18%, 0?05%,0?71%, and 1?08% in arid, semi-arid, semihumid, and subtropical regions,respectively; however, in the 0?2–0?4 m soil layer, the average OMC were 0?16%,0?22%, 0?60%, and 0?67%, with an overall mean of 0?45%. The mean OMC wereroughly the same for the 0–0?2 m and 0?2–0?4 m layers for hyperarid and arid areas,given their low vegetative cover and little precipitation, whereas these layers differed inOMC in the sub-humid and subtropical regions. The OMC in these lands declines inthe order: subtropical regions 4 semihumid regions 4 arid regions 4 hyperaridregions and semi-arid regions. In general, the more seriously degraded lands storedless organic matter, particularly from the depth of 0?4 to 1?0 m, and also showed theleast variation in OMC over time.

Compared to other soil types in China, the OMC of sandy soils was lower. TheOMC of the top 1.0 m soil layer of the Calcic Phaeozems of north-western China,Chernozems of eastern Inner Mongolia, Kastanozems of Hebei Province, andYermosols of the Tengger Desert were 6?46%, 4?59%, 2?5–4?5%, and 0?6%,respectively, but the OMC were only 2?78%, 0?73%, 2?14%, and 0?12% for thesandy soils of these regions. Due to sandy soil’s frequent erosion by wind and lowvegetative cover, the organic matter content of sandy soil is lowest amongst Chinesesoils (Feng et al., 2001). As expected, the variations in organic matter storage withregard to the climatic conditions of the regions in this study agree with the report ofXiu et al. (1996) that in sandy soils, the distribution of organic matter storage parallelsthat of water–energy and vegetative cover index. This confirms that the sandy soils ofsubtropical and sub-humid regions store larger amounts of organic matter, and showgreater potential for agriculture activities or afforestation.

Change in salt and CaCO3 contents

The mean solution salt content of the top 0?2 m of sandy soil was 4?05 g kg�1inhyperarid areas, 1?48 g kg�1 in arid areas, 1?29 g kg�1 in semi-arid areas, 0?38 g kg�1 insemihumid areas, and 0?04 g kg�1 in subtropical areas (Table 5). Thus, the soluble saltcontent of sandy soils was greatest in hyperarid areas, and progressively less in arid

50 FENG QI ET AL.

areas, other semihumid desertified lands, and semi-arid areas. The total salt content inthe top 0?2 m of sandy soil was between 0?46 and 5?22 g kg�1 in hyperarid areas,between 0?91 and 1?7 g kg�1 in arid areas, and between 1?29 and 1?42 g kg�1 in semi-arid areas (Guo, 1987). From Table 5, we can get the results, which suggest that thesalt content tends to increase with depth, due to the mean infiltration of rainfall.

The soluble salt content of the top 0?2 m of sandy soils varied according to thesite. For semi-arid areas, the soluble salt content of this layer was 0?02 g kg�1 inshifting sandy land, 0?03 g kg�1 in semi-fixed sandy lands, and 0?3 g kg�1 in fixedsandy land. In arid areas the soluble salt contents were 0?07 g kg�1 in shifting sandlands, 0?09 g kg�1 in semi-fixed sandy land, and 0?09 g kg�1 in fixed sandy land. Inhyperarid areas, the soluble salt contents were 0?96 g kg�1 in shifting sand land,0?32 g kg�1 in semi-fixed sandy land, and 0?41 g kg�1 in fixed sandy land.

Guo (1987) reported that the Na++K+ and Ca2++Mg2+ content of sandy rankedfrom greatest to least in the order hyperarid areas, arid areas, semihumid areas, andhumid areas. The HCO3

�:Cl� content of sandy soils in different regions ranked fromgreatest to least in the order arid areas, semi-arid areas, and hyperarid areas (Zhao,1995). However, the Cl�:SO4

2� ranked from greatest to least in the order hyperaridareas, semi-arid areas, and arid areas. Thus, in general, soluble salt content, Na++K+

content, and Cl�+SO42� content are greatest in hyperarid areas and least in semi-arid

areas, which is in accord with the moisture, temperatures, and salt ion solubilityprevalent in the sandy soils of China (Guo, 1987).

The CaCO3 content of some sandy soils in China is shown in Table 5. MostChinese sandy soils are calcic soil (i.e. CaCO3 content over 1?0 g kg�1), including allof those in the study areas. However, in the same region, the CaCO3 content can differsignificantly between different sandy lands types. For example, near the Sapotoustation, the CaCO3 content of the top 1?0 m soil layer was below 1?0 g kg�1 in shiftingsand dunes, 1?0–1?5 g kg�1 in semi-fixed sandy soil, and 2?30–3?4 g kg�1 in fixed sandysoil. The CaCO3 content, particularly that of the top 0?4 m, frequently changes due toerosion (Chen & Li, 1987).

Afforestation and land reclamation

As a result of low soil water and organic matter contents in China’s hyperarid and aridsandy soils, their vegetative cover consists primarily of shallow-rooted annuals and isless than 5?1%. Native vegetation growing on sandy soils are xerophilous plants andshrubs or ephemeral plants. The main vegetation, though sparsely distributed in sandylands, is the China cypress (Glyptostrobus pensilis), in subtropical humid zones,Lespedeza bicolor Turcz. is most common; Tamarix ramosissima and Artemisia santolinain semihumid zones; Salix psammophila in semi-arid zones; and Orinus kokonorica andEphedra distachya in arid and hyperarid zones. The extent of the vegetative cover theyprovide is shown in Table 2. However, natural vegetation is of little practical use inland reclamation. In semi-arid areas, from early May onwards the vegetation begins toinfluence soil moisture, decreasing the mean soil moisture in the 0?0–1?6 m sand layerby 1?0–2?0% and the effective water by 0?5–1?5% in semi-arid areas (Table 6). Inareas where plants have been growing at the site for 10–15 years, the soil moisturetends to be near the wilting point, even after rainfall events of 100 mm or more. Thesoil moisture in the top 0?0–1?6 m sand layer cannot be raised to a level of 3.0-4.0%.In such a soil the infiltration depth only varies between 0?6 and 1?0 m, and the soilmoisture in the sand layer below 1?0 m remains below 2?0%. Consequently, anyartificially implanted vegetation gradually changes from deep-rooted and perennialplants to shallow-rooted and annual plants and mosses within 10 or more years.Where vegetative cover is greater than 50% in semi-arid regions, the soil moisture of

Table 6. Water storage changes in semi-arid areas in the year 1994 (mm)

Dates(month/day)

Depth(cm)

Baresandyland

Artemisia Artemisiaordosica

Salixflavida

Caraganakorshinskii

Hedysarumscoparium

5/12 0–40 5?89 6?43 6?66 6?45 4?59 5?1640–100 17?30 13?49 12?21 12?67 13?48 11?920–100 25?12 21?98 24?44 25?19 23?41 27?81

7/12 0–40 4?34 1?74 1?97 2?48 1?52 0?0540–100 12?24 11?63 8?83 12?03 5?18 6?450–100 25?22 27?46 16?53 22?95 23?19 12?54

10/2 0–40 15?40 19?88 20?46 14?29 14?66 14?2640–100 28?61 32?08 29?79 27?87 31?43 40?620–100 43?81 81?22 57?45 58?46 39?31 43?26

SOIL WATER AND CHEMICAL CHARACTERISTICS OF SANDY SOILS 51

the top 0?2 m layer is between 1?0% and 0?5%, lower than 1?2–2?0% found for baresandy soil. Below 0?2 m from the surface, the soil moisture is 2–3% lower than that ofbare sand soil (Table 6). In sub-humid and subtropical zones, the soil moisture invegetated sandy soils decreases by 3–4% and 2–3%, respectively, in the presence ofvegetation. The degree of influence vegetation has on soil moisture depends on theplant species, density, and root system depth. Due to the low soil moisture of sandysoils, the natural vegetation growing on them is made up of xerophilous plants andshrubs or ephemeral plants. In a drought season, the dense root system can lead to soilwater being seriously depleted, thus forming a dry subsurface sand layer, which cannegatively impact on the establishment of further plant species (Xing & Li, 1987).

The available moisture storage in the top 1 m of a sandy soil profile tends to increasefrom hyperarid area to sub-humid areas (Figs 2 & 3). The limiting factor forafforestation is not only the soil moisture but also the lower fertility and coarsertexture of sandy soils (Feng et al., 1999). In semi-arid areas, shifting sands can be fixedthrough biological methods, but more drought-resistant plant species, such asHedysarum scoparium, Caragana korshinskii, Artemisia sphaerocephala, and Psammochloamongolica are required, given the high CaCO3 content, and low soil moisture andorganic matter. In the areas where the sandy soil has an even higher soluble saltcontent, some salt-resistant plant species such as Elaeagnus angustifolia, Populuseuphratica, Populus simonii, Salix matsudana, and Tamarisk spp. can be selected. Onlow-salinity sandy soils Ulmus pumila can be selected as a sand-fixing plant species.Practices in Yanchi zone have shown that Salix psammophila, Artemisia spp., andPopulus simonii are suitable species for the sandy soils in semi-arid areas. In these areasboth seedlings and long cuttings are used to establish vegetation on sandy soils giventhe thicker dry sand soil profile in the area. Owing to adverse soil moisture conditionsin hyperarid and arid areas, shifting sands should first be fixed with sand fences andthen planted with drought-resistant plants such as Hedysarum scoparium, Artemisiasphaerocephala, and Calligonum mongolicum. Three years after establishing strawcheckerboard sand barriers along both sides of the oil-transporting highway in theTaklimakan Desert, some ephemeral annual plants began to survive.

Sandy soils in the sub-humid areas were more easily improved given their betterinitial moisture conditions and higher clay and organic matter content. Through sandfencing to restore vegetation, afforestation, and the establishment of water-diversioncanals, highly profitable farmlands and fruit tree belts have been generated. Afterfertilizer application and mixing the sandy soil with finer-textured soil, the sandy soilin humid areas can be used to plant high-value forages such as sweet clover, alfalfa,

52 FENG QI ET AL.

milk vetch, and sand-fixing trees such as Pinus sylvestris, Pinus tabulaeformis, Salixflavida, and Populus nigra (Feng et al., 1999). Newly reclaimed sandy soils are mostsuitable for planting watermelon, Spanish gourd, potato, sweet potato, sugar beet,peanut, tuber crops, wheat and corn, and are expected to produce a better yield thanthat of degraded sandy soils. Planting leguminous crops on sandy soils contributes tothe enhancement of soil fertility due to nitrogen fixation, while planting sorghum,millet (Panicum miliaceum L.), and rape can enhance ground coverage in spring andthus prevent soil erosion. For instance, three years after reclamation the sunflower(Helianthus annuus L.) and millet (Panicum miliaceum L.) planted on irrigated sandysoil in a sub-humid zone gave yields of 1500–4500 and 2300–3800 kg ha�1,respectively. The yield will reach the yield of 3200–5000 kg ha�1 in non-sandy soilsin the study area. The organic matter increased by three to four-fold and clay contentby 1?83-fold (Feng et al., 1999).

Sandy soils in subtropical zones exhibited better initial moisture and site conditions.There, efforts should be made to select Masson pine to replace China cypress(Glyptostrobus pensilis) and Lespedeza bicolor to establish a sand-fixation system underirrigation. Livestock can be raised and manure applied to improve soil structure. Fruittrees can then be planted and commercial crops produced. Five years of experimentsat the Xinjiang Experiment Station showed that watermelon yield on improved sandysoil could reach as high as 0?10–0?15 Mg ha�1, strawberry yield 0?40 kg ha�1, andrapeseed yield 0?67 kg ha�1. The yield was equal to the yield of non-sandy soils inthese areas (Feng et al., 1999).

To develop agricultural production on sandy soils in sub-humid and subtropiczones, the establishment of a stable agroecosystem is essential, including farmland,protective forests as windbreaks or against erosion, irrigation and drainage systems,deflation tillage systems as well as cultivation and fertilization systems.

Conclusions

In conclusion, sandy soils in China can be divided into four sand stabilization and landreclamation regions based on the amount of soil moisture variability, organic matter,CaCO3, and soluble salt content.

Region IFsubtropical humid areas and semihumid areas cover the region. Sandysoils have a mean moisture content of 3?5% or more, annual precipitation exceeds400 mm, average organic matter content is 0?38–1?08%, CaCO3 content is 0?8–4?1 g kg�1, and total salt content is 0?09–0?68 g kg�1 in the top 1?0 m soil layer. Somekinds of trees and shrubs can be used to fix shifting sands and land can then be usedfor high-profit agriculture and commercial crops. The water balance equation for thetop 1?0 m soil layer is given as DS+DV ¼ (P+U)�(D+E+TR).

Region IIFthe sandy soils have a mean water content ranging from 2?0% to 3?5%,annual precipitation between 250 and 400 mm, organic matter content between0?05% and 0?11%, CaCO3 content between 20?0 and 37?1 g kg�1 and total saltcontent between 1?29 and 1?42 g kg�1. Again, some shrubs and grasses can be used tocontrol erosion. In Region II, covered mainly by semi-arid areas, the water balanceequation for the top 1?0 m soil layer is given as DS ¼ (P+U)�(D+E+TR).

Region IIIFthe mean water content of sandy soil ranges from 2?0% to 2?5%, andannual precipitation varies between 100 and 250 mm. However, the organic mattercontent is lower than 0?17%, CaCO3 content ranges from 16?6 to 45?4 g kg�1, andtotal salt content from 0?63 to 1?46 g kg�1. Mechanical methods should be used toenhance biological methods such as growing grass to stabilize shifting sand. Greaterattention should be paid to the design of better afforestation and major engineeringworks for sand control. In Region III, covered by arid areas, the water balanceequation for the top 1 m soil layer is given as DS ¼ (P+U)�E.

SOIL WATER AND CHEMICAL CHARACTERISTICS OF SANDY SOILS 53

Region IVFthe sandy soil has a mean water content of less than 1?5%, annualprecipitation is less than 100mm, the organic matter content is less than 0.13%,CaCO3 content exceeds 127?0 g kg�1, and total salt content exceeds 3?46 g kg�1. Theonly methods that can be adopted to fix shifting sands are interdune land irrigationand mechanical techniques. In Region IV, covered by hyperarid areas, the waterbalance equation of the top 1 m soil layer is given as DS ¼ (U+P)�E.

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