21st Century COE Program
Final Report of“Program for Arid Land Science”

Tottori University
2007

Contents

1. OUTLINE .............................................................................................................................. 1
1) 21ST CENTURY COE PROGRAM ............................................................................................... 1
2) PROGRAM FOR ARID LAND SCIENCE ...................................................................................... 1
3) OBJECTIVES ........................................................................................................................... 2
4) OUTLINE OF THE RESEARCH AND EDUCATION ACTIVITIES ..................................................... 2
5) FOCAL POINT.......................................................................................................................... 4

2. RESEARCH ACHIEVEMENTS ........................................................................................... 5
1) ENVIRONMENTAL MONITORING GROUP ................................................................................. 52) ENVIRONMENTAL RESTORATION TECHNOLOGY GROUP ......................................................... 83) PLANT PRODUCTION GROUP ................................................................................................ 134) UTILIZATION OF NATURAL ENERGY GROUP ......................................................................... 16
5) SOCIO-MEDICAL SCIENCE GROUP......................................................................................... 19

3. ORIGINAL PAPERS ............................................................................................................22

1. Outline
1) 21st Century COE Program
In response to a report by Japan's Ministry of Education, Culture, Sports, Science andTechnology (MEXT), entitled "A Policy for the Structural Reform of Universities," this program
was established in 2002 to cultivate a competitive academic environment among Japanese
universities by giving targeted support to the creation of bases for world-class research andeducation (Centers of Excellence: COE). By raising the standards for both education and researchat these centers, the program seeks to elevate Japanese universities to the ranks of the world’s
most prestigious institutions, while fostering the education of talented, creative people who will
be qualified to assume future roles as world leaders.
In fiscal year (FY) 2002, 113 COEs (50 universities) were selected from among 464
applications (163 universities), including the Arid Land Research Center (ALRC).
2) Program for Arid Land Science
The objective of the Program for Arid Land Science is to develop a new arid land science,
which is both innovative and multidisciplinary, that is without parallel in the world, with thegoal of educating young researchers capable of fulfilling the abovementioned objectives of the
program. The program will build upon knowledge and technologies from the field of agriculturethat have been established by Tottori University and will aim to establish overseas research andeducational bases in many of the world's arid regions.
(1) Operating period
FY2002 to FY2006(2) Research field and keywords
Research field: environmental sciences
Keywords: combating desertification, environmental restoration technology,
plant production, utilization of natural energy, socio-medical science(3) Related faculties and centersz Arid Land Research Centerz Bioresources Science, Bioenvironment Science, the United Graduate School of
Agricultural Sciencesz Design and Information Engineering, Engineering of Social Development, Graduate
School of Engineeringz Medicine, Graduate School of Medical Sciences1(4) Organization
Leader: Atsushi Tsunekawa(Shinobu Inanaga from FY2002 to FY2004)
Research groups and researchers:z Environmental Monitoring: Reiji Kimura, Mitsuhiro Inoue, Hiroshi Yasuda, Osamu
Hinokidani, Hisao Anyouji, Hiroshi Nawataz Environmental Restoration Technology: Norikazu Yamanaka, Tahei Yamamoto,Toshimasa Honna, Yoshinobu Kitamura, Atsushi Tsunekawa
z Plant Production: Kiyoshi Tanaka, Shinobu Inanaga, Yukihiro Sugimoto, Satoshi
Yamada, Ping Anz Utilization of Natural Energy: Tsutomu Hayashi, Makio Kamichikaz Socio-medical Science: Youichi Kurozawa, Takayuki Nose
3) Objectives
Nearly half (41%) of the world's land surface is covered by arid lands that are increasingly being
affected by desertification. Since ecosystems do not recognize political boundaries, scientificcooperation among nations is urgently needed if the problem of desertification is to be addressed.
Japan has ratified the United Nations Convention to Combat Desertification (UNCCD), andunder this agreement, provides both technical support and public financial support to meet its
obligations. As a matter of fact, Japan has become the world's largest financial donor, but more
technical support is required. Therefore, the promotion of research that will become the basis forcombating desertification is an urgent priority.
The objectives of this program are to develop a new arid land science that is without parallel in theworld, and to educate young researchers capable of fulfilling the abovementioned objectives. The
program will build upon knowledge and technologies from the field of agriculture that have been
established by Tottori University, and will establish overseas research and educational bases in manyof the world's arid regions.
Further development of the program will be necessary to advance sciences that will further
contribute to combating desertification around the world, educate young researchers in this field, andfulfill Japanese obligations under the UNCCD to provide financial, scientific, and technical support,
and to recruit researchers. The relevant scientific knowledge that is available is insufficient to meet
the UNCCD objectives, and development of the socio-medical field is especially primitive. As such,the program will enhance new development in sciences related to arid lands.
4) Outline of the research and education activities
As shown in Figure 1, the COE for arid land science has been developed with close ties between
2research and education in collaboration with overseas research and educational bases. We have used
this approach to establish the “new arid land science” defined in this project.
development of the “New Arid Land Science”
Integration of the
Healthy life
three themes
Sustainable foodsupplyArid land health care andCreation of a decent
medical services
living environment
２００５

Conducting interface studies,
Integration of the achievements of each group

On-going studies of each group
２００３

Environmental Monitoring

２００２

Environmental Restoration Technology

Plant Production

Socio-medical Sciences

Utilization of Natural Energy

Educations andtraining throughthe research

２００４

Contributions
to the research

２００６Capacity Building for the“New Arid Land Science”

z

Support for
employment inoverseas research
institutionsz

Research guidancezSpecial English
conversation course

Postdoctoral Graduate
Researchers Students

Research & education in cooperation with overseas research and educational bases

Fig. 1. Outline of the research and education activities of the center of excellence forarid land research.
Our research has systematized the achievements of this project and the related findings ofprevious research, leading to a unique framework for the new science. Previous research results andachievements have been summarized in two main categories: technologies for diagnosing
desertification and technologies for combating desertification. Based on this knowledge, effective
technical packages for combating desertification have been developed. These achievements havebeen published as “Dryland Science in the 21st Century: Sustainability of Nature and Society”.
The education component of the program has supported young researchers who will become key
components of future networks by developing their research and English communication skills
through visits of various durations to overseas research and educational bases and by providing
lessons in conversational English. Information on international employment opportunities has beensystematically collected and provided to young researchers to help them find rewarding positions atinternational research institutions that focus on desertification. As a result, the number of young
researchers who have presented their research achievements at conferences and who have publishedjournal articles are now 11 and 6 times previous levels respectively. English communication skills
have also improved dramatically. Moreover, young researchers have conducted their studies from amultidisciplinary (holistic) perspective by engaging in joint research with colleagues from3

other specialties.
5) Focal point
To establish the world’s most advanced center of excellence for arid land science and to promote
its future development, we have gone beyond developing the new arid land science to also focus ondeveloping global research and educational networks. We are proud of the following majorachievements:
To improve our international networks, we played a primary role in establishing the
Global Network of Dryland Research Institutes (GNDRI, initiated by the call of the Desert ResearchInstitute (DRI, http://www.dri.edu/), USA; the Jacob Blaustein Institute for Desert Research (BIDR,
http://cmsprod.bgu.ac.il/Eng/Units/bidr), Israel; and ALRC, Japan), a network of the world’s mostadvanced research institutions in arid land science. We have also decided to participate in Central
and West Asia, in North Africa, and in neighboring dry areas in Western China, South Asia, andSaharan Africa as part of the international CWANA+ partnership that has been organized by
ICARDA (http://www.icarda.org/) and the United Nations University (UNU). ALRC, a core institutein this program, provides National Joint-Use Facilities that are available to a network of joint-use
researchers throughout Japan. ALRC has carried out an average of about 50 joint research projects
every year. With this project, ALRC has come to play a role as a hub institute for domestic andinternational research networks. Overseas research and educational bases have been established,resulting in the promotion of research and education on arid land science in Japan even though there
is no arid land in Japan. Furthermore, increasing publicity for the COE will attract excellent students
from abroad and from Japanese universities who have a strong desire to build a career in arid landscience, and highly motivated young researchers have already begun to gather at this COE andproduce significant research results.
To establish a unique new arid land science that includes a range of disciplines outside thetraditional "hard" sciences (including the arts and social sciences, socio-medical sciences, andnatural energy), we have systematized the findings of previous research, of this project, and ofresearch on appropriate technology. By focusing on sustainable development of the nature–societysystem in arid lands, we have developed a framework for a new arid land science that includes
traditional knowledge and appropriate technologies. The result is a series of textbooks entitled“Dryland Science in the 21st Century: Sustainability of Nature and Society” (Kokon Shoin published
Series 1 in March 2006; Series 3 and 5 were published in FY2007, and Series 2 and 4 will be
published in FY2008.

4

2. Research achievements
Figure 2 illustrates and relationships among the five research groups and their research programs,
which are together establishing a new and more holistic arid land science that will combat
desertification and promote sustainable social and economic development in arid lands.

Socio-medical science
Environmental restoration
technology

Ecosystem

Human

Water
Environmental monitoring

Plant production

HealthAgricultural
Production
EnergySemi-Arid Land

Utilization ofnatural energy

Fig. 2. Research programs and coordination among groups in developing
the new arid land science.
The achievements of the five research groups are summarized in the following sections.

1) Environmental Monitoring group
This group conducted research designed to achieve three main objectives: “Elucidation of theprocess and effects of desertification” (the primary target), “Development of methods to evaluate
desertification at a macro scale (Loess Plateau, China) and at the watershed scale (Liudaogou,
Shenmu, Shaanxi, China)”, and “Development of measures of desertification”. Ecologicalassessments have been conducted and measurement techniques have been developed for soils,
vegetation, meteorology, and water resources.
Development of evaluation methods for desertification(1) Soils - Development of methods to monitor the movements of water and heat(2) Water resources - Development of methods to monitor the hydrology and water balance inwatersheds(3) Vegetation and meteorology - Monitoring of desertification using biomass, soil moisture,and remote-sensing data5

Development of measures of desertification
Proposal of appropriate land-use scenarios based on the water balance of an ecosystem and thewater-use efficiency of its vegetation after evaluation of a watershed's current water balance (Fig. 3).

Subject 1

Ecological research group(1) Evaluation of the present conditionof water balance in the river basin(2) Developing the water balance modeland application

Presentation of the method forrecovering the ecosystem such as theselection of vegetation type forgreening and so on.

Evaluation of change of water balance by the scenario
Presentation of suitable land use scenario
In the future…
Economics
Social anthropology

Formation of comfortable
life environment

Fig. 3. Illustration of a process for developing restoration methods.

(1) A three-layer soil model was developed to quantify the movement of heat between bare soil
surfaces and the atmosphere (Kimura et al. 2004a).
(2) A new sensor was developed to correctly measure moisture and salt contents in soils with ahigh salt concentration as a result of progressive salinization.
(3) The three-layer soil model and meteorological data from 43 observatories in the Loess
Plateau of China were used to estimate the plateau's heat and water balances, to reveal the
spatial distribution of soil moisture, and to provide a basis for discussing the plateau's
physical features. Furthermore, the potential distribution of vegetation was determined by
combining the data on the aridity of all areas in the Loess Plateau (estimated from seasonalchanges in soil moisture), the distribution of soil moisture, and the present vegetation(identified by remote sensing). The results have revealed findings that were not documented
in previous studies, and more correctly indicate the degree of desertification (Kimura et al.
2005).
(4) A model with a 1-km grid for estimating the distribution of monthly precipitation wasdeveloped using synoptic-scale analysis and topographic factorial analysis to permit
statistical analysis of precipitation patterns. This study made it possible to show that6

precipitation was the dominant factor responsible for desertification in the Loess Plateau at
this grid scale (Takayama et al. 2004).
(5) In addition to the method for monitoring water balances in watersheds of the Loess Plateau,
we developed an algorithm (using a numerical simulation model and remote-sensing
technology) to estimate evapotranspiration from each land surface in a watershed. Land use
in the watershed was evaluated using monitored data on water outflow and the newalgorithm. In this study, water-use efficiency (WUE) was defined as protection from erosion
achieved per water consumed. WUE of the vegetation in natural rangeland was better thanthat in other land-use systems. That is, natural rangeland provides the best protection against
soil erosion, consumes less water, and retains relatively more water in the soil. Moreover,the usefulness of natural rangeland was recognized based on interviews with local users of
the land and measurements of soil pH, nitrogen content, and hardness in the Loess Plateau(Kimura et al. 2007a; Kimura 2007b).
(6) The percolation characteristics of a check-dam farm and the responses of a huge watershed
to rainfall were predicted from continuous measurements of soil water content andmonitoring of ground and river water levels, thereby revealing the flow of water from thewatershed to the check-dam farm. A management method for the water resources of a small
watershed in the Loess Plateau was proposed using monitoring data and the water outflow
model.
【Publication list】
z

Anyoji H, Yasuda H, Procedure for Determining the Parameters in Linear and Non-linear
Infiltration Equations. Sand Dune Research, 51: 131-144, 2005.

z

Kato T, Kimura R, Kamichika M, Estimation of evapotranspiration, transpiration ratio andwater-use efficiency from a sparse canopy using a compartment model. Agricultural Water
Management, 65: 173–191, 2004.

z

Kimura R, Kamichika M, Takayama N, Matsuoka N, Zhang X, Heat balance and soil moisturein the Loess Plateau, China. J. Agric. Meteorol, 60(2): 103-113, 2004a.
<<ORIGINAL PAPER>>z

Kimura R, Okada S, Miura H, Kamichika M, Relationships among the leaf area index, moistureavailability, and spectral reflectance in an upland rice field. Agric. Water. Management, 69:
83-100 , 2004b.

z

Kimura R, Liu Y, Takayama N, Zhang X, Kamichika M, Matsuoka N, Heat and water balancesof the bare soil surface and the potential distribution of vegetation in the Loess Plateau, China.
Journal of Arid Environments, 63: 439-457, 2005. <<ORIGINAL PAPER>>

7

z

Kimura R, Fan J, Zhang X, Takayama N, Kamichika M, Matsuoka N, Evapotranspiration overthe grassland field in the Liudaogou basin of the Loess Plateau. Acta Oecologica, 29: 45-53,
2006.

z

Kimura R, Bai L, Fan J, Takayama N, Hinokidani O, Evapo-transpiration estimation over theriver basin of the Loess Plateau of China based on remote sensing. Journal of Arid
Environments, 68: 53-65, 2007a. <<ORIGINAL PAPER>>z

Kimura R, Estimation of moisture availability over the Liudaogou river basin of the Loess
Plateau using new indices with surface temperature. Journal of Arid Environments, 70: 237-252,
2007b. <<ORIGINAL PAPER>>z

Takayama N, Kimura R, Kamichika M, Matsuoka N, Zhang X, Climatic features of rainfall in
the Loess Plateau in China. J. Agric. Meteorol, 60(3): 173-189, 2004. <<ORIGINAL PAPER>>z

Wang K, Zhang R, Yasuda H, Characterizing heterogeneity of soil water flow by dye
infiltration experiments. Journal of Hydrology, 328: 559-571, 2006.

z

Yasuda H, Wang K, Mohamed Abd Elbasit Mohamed Ahmed, Anyoji H, Zhang X, Analyses ofRainfall Time Series in the Loess Plateau of China. Periodical fluctuation and links with sea
surface temperature. Journal of Agricultural Meteorology, 60: 617-620, 2005.

z

Zeggaf TA, Anyoji H, Yasuda H, Performance comparison of transpiration models for maizecrop under different crop canopies. Journal of Arid Land Studies, 15: 325-328, 2006a.

z

Zeggaf TA, Anyoji H, Yasuda H, Fixed and variable light extinction coefficients for estimating
plant transpiration and soil evaporation under irrigated maize. Agricultural Water Management,
84: 186-192, 2006b.

2) Environmental Restoration Technology group
This group conducted research on three main topics: "Establishment of water management
technologies at a regional scale to prevent salinization", "Establishment of restoration technologies
for degraded soils," and "Establishment of restoration technologies for biodiversity and forest
ecosystems".
Establishment of water management technologies at a regional scale to prevent salinization(1) Elucidation of saline movements in the soil in response to irrigation and the effects ofgroundwater level on soil salinization (study area: Luohuiqu irrigation area, Shaanxi, China)
In this study, salinization processes for a benchmark site were categorized, and the causal
factors were elucidated. As remedial measures based on water management to prevent
secondary salinization, researchers proposed the following ideas: (a) appropriate control ofgroundwater levels by improving the efficiency of drainage systems; (b) control of the saline
8soil dumped by excavating new wells in fields; (c) management of the use of groundwaterwith high saline concentrations; (d) appropriate repair, maintenance, and management of thesoil surface drainage system; (e) restoration of salinized farmland by means of “warp soil
dressing (Soil dressing using flood flow)" technologies; and (f) application of biologicaldrainage (i.e., using plant evapotranspiration to lower the water level) technologies along
canals and around farm lots to prevent waterlogging.
(2) Effects of cultivating lowland rice on salinization in low-lying fields and in adjacent uplandfields (study area: Central Asia)
This research investigated the fluctuation of salt concentrations in water in the upper soil
layers during the irrigation period and the mechanisms responsible for upward movement ofaccumulated salts from lower soil layers. Accumulated salts in lower soil layers moved into
upper soil layers by upward flux due to negative hydraulic gradients in the lower soil layers
during the occasional interruption and resumption of irrigation water supply in
the growing season Furthermore, the factors responsible for localized salinization underflooded conditions were also elucidated. By analyzing the causes of secondary salinizationin irrigated farmlands, mitigation measures based on water management technologies were
proposed to prevent salinization of lands (Kitamura et al. 2006).
Establishment of restoration technologies for degraded soils(1) Basic research on the restoration of degraded soils was conducted using the facilities andequipment at ALRC. Elucidation of the mechanisms responsible for the creation of acidic
and saline soils in drylands allowed researchers to investigate the reuse of recycled materials(i.e., the use of organic matter such as crop residues and animal manure) and thedevelopment of restoration methods based on this recycling of organic materials.
(2) The mechanisms responsible for the development of saline soils were investigated using
Tottori sand dune soil, and a method for monitoring desertification was developed (Ould
Ahmed et al. 2007).
(3) New aspects of the multiple effects of organic amendments in drylands, such as increasing
Ca availability to plants were discovered.
(4) The mechanisms responsible for the development of acidic and saline soils and theeffectiveness of amelioration using the application of artificial zeolites, were elucidated.
(Andry et al. 2007; Yamada et al. 2007).
Establishment of restoration technologies for biodiversity and forest ecosystems(1) Afforestation methods suitable for local environments in the Loess Plateau of China werestudied by investigating differences in the water-use characteristics of indigenous and exotic
9

tree species, the structures of several forests, and the associated ecosystem functions.
(2) Comparative studies of the ecophysiological characteristics of exotic black locust (Robinia
pseudoacacia L.) from North America and of an indigenous oak (Quercus liaotungensis)
showed that the indigenous oak had higher drought tolerance than black locust.
(3) Studies of ecosystem functions showed that plantations of black locust developed
more severe micro-environments and were less sustainable than natural forests
in terms of their nutrient cycling. As a result, we proposed the necessity forecosystem restoration using native plant species (Tateno et al. 2007).
【Publication list】
zAbou El-Hassan WH, Kitamura Y, Solomon H, Meleha M, Hasegawa K, Effect of subsurface
drainage on rice cultivation and soil salinity in the Nile Delta. Transactions of The JapaneseSociety of Irrigation, Drainage and Reclamation Engineering, 73(2): 43-52, 2005.

z

Abou El-Hassan WH, Zayed BA, Kitamura Y, Shehata SM, Zahor Ahmad and Faridullah,
Effect of reuse drainage water management on rice growth, yield and water use efficiency undersaline soils of Egypt. Asian Journal of Plant Sciences, 5(2): 287-296, 2006a.

zAbou El-Hassan WH, Kitamura Y,

Gamal FS, Eneji AE, Assessment of surge irrigation

technique under furrow irrigation system in the Nile Delt. International Journal of Agricultural
Research, 1(5): 462-470, 2006b.
z

Abou El-Hassan WH, Kitamura Y, Yang SL, Inosako K, Shimizu K, Nishiyama S, Effect ofdrainage water reuse on rice cultivation in the Nile Delta, Egypt. Journal of Sand Dune
Research, 53(1): 19-32, 2006c.

zAbou El-Hassan WH, Kitamura Y, Inosako K, Shimizu K, Nishiyama S, Effect of water
management and tillage practices on rice yield, water use efficiency and physical properties of
paddy soil in the Nile Delta. Transactions of The Japanese Society of Irrigation, Drainage andReclamation Engineering, 74(4): 39-47, 2006d.

z

Al-Busaidi A, Yamamoto T, Inoue T, Irshad M, Mori Y, Tanaka T, Effects of seawater salinity
on salt accumulation and barley (Hordeum vulgare L.) growth under different meteorologicalconditions. Journal of Food, Agriculture & Environment, 5 (2): 2007.

z

Andry H, Yamamoto T, Rasiah V, Fukada M, Improving the Resistance of an Acid Soil to Water
Erosion Using Artificial Zeolite and Hydrated Lime Amendments. Transactions of the JapaneseSociety of Irrigation, Drainage and Reclamation Engineering, 247: 53-64, 2007a.

z

Andry H, Yamamoto T, Inoue M, Effectiveness of Hydrated Lime and Artificial Zeolite
Amendments and Sedum Plant Cover in Controlling Soil Erosion from an Acid Soil. Australian
Journal of Soil Research, 45: 266-279, 2007b. <<ORIGINAL PAPER>>z

Dehghanisanij H, Agass M, Anyoji H, Yamamoto T, Inoue M, Eneji AE, Improvement of saline
10

water use under drip irrigation system. Agricultural Water Management, 85(3): 233-242, 2006.
z

Du S, Yamanaka N, Yamamoto F, Otsuki K, Wang S, Hou Q, The effect of climate on radial
growth of Quercus liaotungensis forest trees in Loess Plateau, China. Dendrochronologia, 25:
29-36, 2007.

z

Eneji AE, Honna T, Yamamoto S, Saitoh T, Masuda T, Nitrogen Transformation in FourJapanese Soils Following Manure + Urea Amendment. Communications in Soil Science andPlant Analysis, 33(1&2): 53-66, 2002.

z

Eneji AE, Irshad M, Honna T, Yamamoto S, Endo T, Masuda T, Potassium, calcium, andmagnesium mineralization in manure-treated soils. Communications in Soil Science and Plant
Analysis, 34 (11-12): 1669-1679, 2003a.

z

Eneji AE, Honna T, Yamamoto S, Masuda T, Endo T, Irshad M, Changes in humic substancesand phosphorus fractions during composting. Communications in Soil Science and Plant
Analysis, 34 (15-16): 2303-2314, 2003b.

z

Eneji AE, Honna T, Yamamoto S, Masuda T, Influence of composting conditions on plant
nutrient concentrations in manure compost. Journal of Plant Nutrition, 26(8): 1595-1604,
2003c.

z

Eneji AE, Honna T, Yamamoto S, Irshad M, The Relationship Between Total and Available
Heavy Metals in Composted Manure. Journal of Sustainable Agriculture, 23 (1): 125-134 ,2003d.

z

Eneji AE, Yamamoto S, Wen G, Inanaga S, Honna T, A comparative evaluation of wet digestionand dry ashing methods for the determination of some major nutrients in composted manure.
Toxicological & Environmental Chemistry, 87( 2): 147- 158, 2005.

zEndo T, Yamamoto S, Honna T, Enej AE, Sodium-Calcium Exchange Selectivity as Influenced
by Clay Minerals and Composition. Soil Science, 167(2): 117-125, 2002.

z

Hennintsoa A., Yamamoto T, Rasiah V, Fukada M, Improving the resistance of an acid soil towater erosion using artificial zeolite and hydrated lime amendments. Transactions of theJapanese Society of Irrigation, Drainage and Reclamation Engineering, 247: 53-64, 2007.

z

Irshad M, Enej AE, Honna T, Yamamoto S, Endo T, Nitrogen use and relationship between
maize biomass and nutrient content in saline and non-saline soils. Sand Dune Research, 48(2):49-56, 2002a.

z

Irshad M, Yamamoto S, Eneji AE, Honna T, Endo T, Influence of Composted Manure andsalinity on Growth and Nutrient Content of Maize Tissue. Sand Dune Research, 49(1): 1-9,
2002b.

z

Irshad M, Yamamoto S, Eneji AE, Honna T, Endo T, Urea and Manure Effect on Growth andMineral Contents of Maize under Saline Conditions. Journal of Plant Nutrition, 25(1): 189-200,
2002c.
11zIrshad M, Honna T, Eneji AE, Yamamoto S, Wheat Response to Nitrogen Source under Saline
Conditions. Journal of Plant Nutrition, 25(12): 2603-2612, 2002d.

z

Irshad M, Honna T, Yamamoto S, Endo T, Eneji AE, Yamasaki N, The Effect of Salt Types on
Nitrogen Release in Manured Soil. Sand Dune Research, 51(2): 67-74, 2004a.

z

Irshad M, Honna T, Yamamoto S, Kato M, Endo T, Zahoor A, Interaction of Saline Water andNitrogen on the Partitioning and Statistical Correlation of Mineral Elements in Maize Plant.
Acta Agronomica Hungarica, 52 (2): 149 –156, 2004b.

z

Irshad M, Yamamoto S, Honna T, Trace Elements Solubilization in Waste Amended
Saline-Sodic Conditions. J. Food, Agriculture & Environment, 2 (3 & 4): 255-259, 2004c.

z

Irshad M, Honna T, Yamamoto S, Eneji AE, Yamasaki N, Nitrogen Mineralization under Saline
Conditions.Commun. Soil Sci. Plant Anal., 36(11 &12): 1681-1689 ,2005.

z

Ishii Y, Sakamoto K, Yamanaka N, Wang L, Yoshikawa K, Light acclimation of needle pigmentcomposition in Sabina vulgaris seedlings under nurse plant canopy. Journal of Arid
Environments, 67: 403-415, 2006.

z

Kitamura Y, Yano T, Honna T, Yamamoto S, Inosako K, Causes of farmland salinization andremedial measures in the Aral Sea basin - Research on water management to prevent secondary
salinization in rice-based cropping system in arid land. Agricultural Water Management,85(1-2): 1-14, 2006. <<ORIGINAL PAPER>>z

Otsuki K, Yamanaka N, Du S, Yamamoto F, Xue Z, Wang S, Hou Q, Seasonal Changes ofForest Ecosystems in an Artificial Forest of Robinia pseudoacacia in the Loess Plateau in China.
Journal of Agricultural Meteorology, 60( 5): 613-616, 2005.

z

Ould Ahmed BA, Yamamoto T, Inoue M, Anyoji H, Drip irrigation schedules with saline water
for sorghum under greenhouse condition. Transactions of the Japanese Society of Irrigation,
Drainage and Reclamation Engineering, 244: 133-141, 2006.

z

Ould Ahmed BA, Yamamoto T, Rasiah V, Inoue M, Anyoji H, The impact of saline water
irrigation management options in a dune sand on available soil water and its salinity.
Agricultural Water Management, 88: 63-72, 2007a. <<ORIGINAL PAPER>>z

Ould Ahmed BA, Yamamoto T, Inoue M, Interaction of temperature and solar radiation effectsorghum growth under drip irrigated saline water. Asian Journal of Plant Sciences, 6(2):359-363, 2007b.

z

Ravolonantenaina, AH, Rakotondrainibe JH, Yamamoto T, Eneji AE, Yasuda H, Technicalevaluation of the borehole project in Mahajanga region of Madagascar and its effect on ruraldevelopment. Transactions of the Japanese Society of Irrigation, Drainage and Reclamation
Engineering, 244: 215-225, 2006.

z

Solomon H, Kitamura Y, Li Z, Yamamoto S, Yang SL, Li P, Waleed A, Otagaki K,
Classification of salinization processes in Luohui Irrigation Scheme, China -Part of water
12

management research to prevent salinization in semiarid land-. Journal of Arid Land Studies,
15(2): 89-105, 2005.
z

Solomon H, Kitamura Y, Traditional irrigation management in Betmera-Hiwane, Ethiopia: themain peculiarities for the persistence of irrigation practices. Journal of Mountain Science, 3(2):139-146, 2006.

z

Tateno R, Tokuchi N, Yamanaka N, Du S, Otsuki K, Shimamura T, Xue Z, Wang S, Hou, Q,
Comparison of litterfall production and leaf litter decomposition between an exotic black locust
plantation and an indigenous oak forest near Yan'an on the Loess Plateau, China. Forest ecology
and Management, 241: 84-90, 2007. <<ORIGINAL PAPER>>z

Yamada M, Fujiyama H, Endo T, Rikimaru UM, Sasaki Y, Yamamoto S, Honna T, Yamamoto
T, Effect of K-type and Ca-type artificial zeoliotes applied to high sodic soil on the growth ofplants different in salt tolerance. Soil Science and Plant Nutrition, 53: 471-479, 2007.
<<ORIGINAL PAPER>>z

Yamamoto T, DehghaniSanij H, Agassi M, Rehabilitation techniques for degraded, irrigated soil
in arid lands. Journal of International Society for Southeast Asian Agricultural Sciences, 10(1):41-50, 2004.

z

Yang SL, Takeuchi S, Yano T, Kitamura Y, Evapotranspiration from citrus trees growing insandy soil under drip irrigation with saline water. Science in China (Series D), 45(0): 41-46,
2002a.

z

Yang SL, Yano T, Aydin M, Kitamura Y, Takeuchi S, Short term effects of saline irrigation on
evapotranspiration from lysimeter-grown citrus trees. Agricultural Water Management, 56(2):131-141, 2002b.

3) Plant Production group
The plant production group focused its research in three main areas: "Mechanisms for the
improvement of crop drought tolerance", "Cloning of genes related to drought tolerance and their
use to generate drought-tolerant plants", and "Increased crop production by controlling root-parasitic
weeds". They accomplished the following achievements:
Mechanisms for the improvement of crop drought tolerance(1) Silicon application improved the drought tolerance of sorghum in dry soils by enhancing
the water uptake ability of the plants (hydraulic conductivity) and by promoting root
elongation (Hattori et al. 2005).
(2) The drought tolerance of a Sudanese sorghum cultivar was associated with its high ability
to develop its root system (by branching and the growth of lateral roots, and the emergence13

of nodal roots from higher internodes) in dry soils (Tsuji et al. 2005).
(3) Porous glass material (PGM) was able to absorb phosphates in wastewater, and the releaseof phytoavailable phosphates from PGM incorporated in the soil improved the growth oftomato plants (Nakazawa et al. 2006).
(4) Patterns of uptake and distribution of 22Na+ in the leaves of several glycophtyes were
investigated. Pumpkin plants accumulated and concentrated 22Na+ in the proximal part ofthe petiole and transported very few 22Na+ to leaf blade. Introduction of this mechanism
for the regulation of sodium mobility in other species would generate new lines withhigher salinity tolerance (Yamada et al. 2002).
Cloning of genes related to drought tolerance and their use to generate drought-tolerant plants
Three new genes whose expression was induced by drought or salinity stress were isolated
from rice using the cDNA subtraction method (Qi et al. 2004, 2005a, 2005b). The expression ofthese genes was increased not only by drought or salinity but also by submergence, exposure to
ethylene and abscisic acid, and other factors. One of the genes resembles the E. coli
antiporter-regulating protein, and was named OsARP. We generated transgenic tobacco plantsthat overexpressed OsARP and confirmed that the transgenic plants showed higher salinity anddrought tolerance.
Because evidence suggests that reactive oxygen species are prominent causes of plantdamage under salinity and drought stress, we generated four kinds of transgenic tobacco, withenhanced production of superoxide dismutase (Badawi et al. 2004a), ascorbate peroxidase(Badawietal.

2004b),

dehydroascorbate

reductase(Eltayebetal.

2006),

ormonodehydroascorbate reductase (Eltayeb et al. 2007) and confirmed that all the transgenic
plants showed more tolerance to salinity and drought stress.
Increased crop production by controlling root-parasitic weeds
Witchweed (Striga spp.) is a group of obligate root-parasitic weeds that are a scourge of
agriculture and food security in many semiarid areas. One important aspect of the biology ofthese parasites that may permit the development of control methods is their requirement for
signaling molecules that indicate the presence of suitable hosts. These molecules including(including germination stimulants) can induce germination of the seeds of these parasites in theabsence of host roots or at great distances from these roots ("suicidal germination"). We haveisolated two compounds (strigol and its deoxy derivative) from Menispermum dauricum and
Lotus japonicus root cultures, respectively, demonstrating that these germination stimulants areof plant origin. We confirmed the involvement of endogenous ethylene in the germination of
Striga hermonthica. The expression of ACC synthase and ACC oxidase genes in the seeds was
14

found to respond to a germination stimulant and to pretreatment in a moist warm environment,
respectively.

【Publication list】
z

An P, Inanaga S, Li XJ, Eneji AE, Zhu NW, Interactive effects of salinity and air humidity on
two tomato cultivars differing in salt tolerance. Journal of Plant Nutrition, 28: 459-475, 2005.

z

An P, Inanaga S, Zhu NW, Li XJ, Fadul HM, Mars M, Plant species as indicators of the extent
of desertification in four sandy rangelands. African Journal of Ecology, 45: 94-102, 2007.

z

Badawi GH, Yamauchi Y, Shimada E, Sasaki R, Kawano N, Tanana K, Tanaka, K, Enhanced
tolerance to salt stress and water deficits by overexpressing superoxide dismutase in tobacco(Nicotiana tabacum) chloroplasts. Plant Science, 166(4): 919-928, 2004a.

z

Badawi GH, Yamauchi Y, Shimada E, Sasaki R, Kawano N, Kubo A, Tanaka, K, Enhanced
tolerance to salt stress and water deficits by overexpressig ascorbate peroxidase in tobacco(Nicotiana tabacum) chloroplasts. Physiolgia Plantarum, 121: 1-8, 2004b.

z

Eltayeb AE, Kawano N, Badawi GH, Kaminaka H, Sanekata T, Morishima I, Shibahara T,
Inanaga S, Tanaka K, Enhanced tolerance to ozone and drought stresses in transgenic tobacco
overexpressing dehydroascorbate reductase in cytosol.

Physiologia Plantarum, 127: 57-65,

2006.
z

Eltayeb AE, Kawano N, Badawi GH, Kaminaka H, Sanekata T, Morishima, Shibahara T,
Inanaga S , Tanaka K, Overexpression of monodehydroascorbate reductase in transgenic
tobacco confers enhanced tolerance to ozone, salt and polyethylene glycol stresses. Planta,
225(5): 1255-1264, 2007. <<ORIGINAL PAPER>>z

Hattori T, Inanaga S, Araki H, An P, Morita S, Luxov M, Lux A, Application of siliconenhanced drought tolerance in Sorghum bicolor. Physiologia Plantarum, 23(4): 459-466, 2005.
<<ORIGINAL PAPER>>z

Inoue T, Inanaga S, Sugimoto Y, El-Siddig K, Contribution of pre-anthesis assimilates andcurrent photosynthesis to grain yield, and their relationships to drought resistance in wheat
cultivars grown under different soil moisture. Photosynthetica, 42 (1): 99-104, 2004.

z

Nakazawa R, Tomemori H, Hirano A, Mochizuki H, An P, Inanaga S, Effects of application of
porous glass materials treated with phosphate on the growth of tomato plants andphyto-available phosphate in soil. Soil Science and Plant Nutrition, 52(4): 540-544, 2006.
<<ORIGINAL PAPER>>z

Qi Y, Yamauchi Y, Ling J, Kawano N, Li D, Tanaka K, Cloning of a putative
monogalactosyldiacylglycerol synthase gene from rice plants (Oryza sativa L.) and its
expression in response to submergence and other stresses. Planta, 219: 450-458, 2004.
<<ORIGINAL PAPER>>
15z

Qi Y, Yamauchi Y, Ling J, Kawano N, Li D, Tanaka K, The submergence –induced gene OsCTP
in rice (Oryza sativa L.) is similar toEscherichia coli cation transport protein ChaC. Plant

Science, 168(1): 15-22, 2005a.
z

Qi Y, Yamauchi Y, Ling J, Kawano N, Li D, Tanaka K, Identification and cloning of asubmergence induced gene OsGGT (glycogenin glucosyltransferase) from rice (Oryza sativa
L.) by suppression subtractive hybridization. Planta, 221: 437-445, 2005b.

z

Tsuji W, Inanaga S, Araki H, Morita S, An P, Sonobe K, Development and distribution of rootsystem in two grain sorghum cultivars originated from Sudan under drought stress. Plant
Production Science, 8(5): 553-562, 2005. <<ORIGINAL PAPER>>z

Yamada S, Takeoka A, Yamauchi M, 22Na+ and 36Cl- mobility in salinized excised leaves ofseveral crop plants. Soil Sciecne and Plant Nutrition, 48(1): 23-29, 2002.
<<ORIGINAL PAPER>>

4) Utilization of Natural Energy group
The Utilization of Natural Energy group has focused on the development of systems forgenerating electric power and producing water based on natural energy sources such as wind andsolar power. As in the other research groups, the goal is to find ways to combat desertification andsupport greening of the desert. This work focused on two main areas: research on wind turbines
suitable for use in desert environments, and the development of a device for extracting fresh waterfrom moist air.
Development of a wind turbine suitable for desert environments
To develop a wind turbine suitable for desert environments, we developed three windturbines for use in wind tunnel and field experiments: a multi-stage Savonius wind turbine, astraight-bladed vertical-axis wind turbine (VAWT), and a horizontal-axis wind turbine (HAWT).
The three designs were compared in terms of their performance characteristics (e.g., torque).
The torque variation of a three-stage out-phase Savonius rotor decreases to about 1/6 of
one-stage rotor. This small torque variation prevents the vibration that causes problems forone-stage rotors. Also, the three-stage out-phase Savonius rotor begins to rotate at lower windvelocities (the starting performance improved). Increasing the number of guide vanes of a
Savonius rotor improves its starting performance; however, it also decreases the torque at highrotation speeds (Hayashi et al. 2004a, 2005b; Li et al. 2006).
Experimental analysis of the torque variation during one rotation of a straight-bladed VAWT,
whose performance does not depend on wind direction (unlike a Savonius rotor), demonstrated
its effectiveness. To improve the aerodynamic efficiency of this VAWT, we developed
16equipment for measuring the aerodynamic characteristics of straight blades (i.e.,
two-dimensional wings) based on the use of two force sensors. Under the conditions of amoderate Reynolds number (Re = 150 000) that a small wind turbine blade sees, theaerodynamic characteristics (lift, drag, and moment efficiencies) of a two-dimensional wing
moving at pitch frequencies of 0.16, 0.22, and 0.33 Hz, with an angle of attack between 4° and
20°, showed hysteresis. The hysteresis characteristics became unacceptably large as the pitch
frequency increased (Hara et al. 2005b, 2005c).
Wind speed was varied like a sine wave by a special wind tunnel, and the performance of astraight-bladed VAWT was monitored under these conditions. Increasing the number of rotor
blades improved the ability of the VAWT to respond rapidly to variations in wind speed. As aresult of the transient-response characteristics of the VAWT in response to increasing windspeed, the rotor torque first increased, then the rotational speed increased (Kang et al. 2005).
For a wind turbine installed in hilly terrain, as in China's Loess Plateau, the wind is expected
to flow uphill so that it blows upwards against the wind turbine rather than horizontally. To
adapt a VAWT to such conditions, we developed an advanced VAWT with inclined
straight-blades around a vertical axis for use in field tests. The possibility of torque increase by
inclined blades for wind blowing upward or downward was demonstrated in the wind tunnel
test. (Hara et al. 2005a)
Development of a device for extracting fresh water from moist air
To develop a device capable of extracting fresh water from moist air, we used athermoelectric module equipped with Peltier devices to cool the air below its dew point.
Experiments were conducted in a controlled-environment chamber under several
combinations of constant temperature and relative humidity so that we could investigate theeffects of these parameters, as well as of the air flow rate, on the rate of water production.
Water production increased at high relative humidity and with increasing air flow rate.
However, water production began to decrease when the temperature of the cooled air in thedevice approached the dew point as a result of high air flow rates. As the air flow increased,
the water production of heat exchanger with widths of 120 mm became bigger than that of heatexchanger with widths of 80 mm. The maximum water production was achieved when thetemperature of the cooled air in the device fell to 2.5 to 4.8 °C below the dew point (Hayashi etal. 2004a, b, c).
Results of field experiments
As the first step in field experiments to test the ability to produce electric power and fresh
water utilizing natural energy sources, we used experimental results and observed
17meteorological data to simulate the energy and water production rates for the Tottori Sand Dunearea. In this simulation, we assumed that operation of the water extraction device wascontrolled by both the dew point and the battery level. The water production rates were thencalculated using a range of dew points and wind turbine performance levels (Hayashi et al.
2005d).
To validate these results, a field test of the system was carried out in the Tottori Sand Dunearea in August 2005, and photovoltaic modules were used as the power source. This test
demonstrated the system's ability to produce water using Peltier devices. The system produced
a total of 12.7 kg of water in August 2005. The water production during the summer
depended strongly on the operation efficiency of the system, which it was defined as theratio of total hours during which it was able to operate to total hours of a month.
The values of relative humidity and dew point in August were sufficiently high to satisfy thesystem's operational requirements. Since the relative humidity and dew point change gradually,
the operation of the system depends primarily on the battery's voltage. The results also showedthat the optimal period for producing water was from night to early morning. These results
suggested that it will be necessary to increase the system's battery capacity or to change thesystem's controller so that it operates only during the optimal period. Nonetheless, the systemdeveloped during this study proved to be highly durable and reliable, without any equipment
failures during the 2-year field experiment.
Moreover, the novel water-extraction device provided high performance (water production)
and a compact design. (A patent for the device has been filed with the Patent Office of Japan.)【Publication list】
zHara Y, Kang I, Hayashi T, Paraschivoiu I, Measurements of Torque Characteristics of a
Vertical Axis Wind Turbine with Inclined Straight Blades. The EXPO World Conference onWind Energy, Renewable Energy, Fuel Cell (WCWRF 2005), Hamamatsu, Japan, CD-ROM,
2005a.

zHara Y, Kang I, Moriya T, Ariyasu K, Hayashi T, Development of a Measuring System withTwo Force Sensors of Aerodynamic Forces Acting on a Two-Dimensional Wing. The 6th
KSME-JSME Thermal and Fluids Engineering Conference, Jeju, KOREA, CD-ROM, JE.08,
2005b.

zHara Y, Kang I, Moriya T, Hayashi T, Aerodynamic Forces on an Airfoil in Pitching and/or in a
Periodically Varying Wind. Proc. the 30th Annual Congress of the American RomanianAcademy of Arts and Sciences (ARA), Chisinau, Moldova: 559-562, 2005c.
<<ORIGINAL PAPER>>z

Hayashi T, Liu W, Sassa K, Hara Y, Possibility of Using a Mini Doppler Sodar for Wind
18

Characteristics Investigation. Proc. 1st World Wind Energy Conference and Exhibition, Berline,
Germany, CD-ROM, VD1.21, 2002.
z

Hayashi T, Li Y, Hara Y, Suzuki K, Wind Tunnel Tests on a Three-stage Out-phase Savonius
Rotor. Proc. 2004 European Wind Energy Conference & Exhibition, London, UK, CD-ROM,
2004a.

z

Hayashi T, Liu W, Nozima K, Hara Y, Tagawa K, A Study on a Water Maker System Using
Peltier Devices Supplied With Electricity by Wind Power For The Purpose of Use in Arid
Regions. Proceedings The 3rd World Wind Energy Conference & Renewable Energy Exhibition
The 2nd Wind Power Asia, Beijing China, 2004b.

z

Hayashi T, Hara Y, Tagawa K, Liu Y, Tanaka K, Nojima K, Development of Fresh Water
Making Systems Using of Peltier Devices or Moisture Absorbent. The 30th Annual Congress of
the American Romanian Academy of Art and Sciences (ARA), Chisinau, Moldova: 593-596,
2005a.

z

Hayashi T, Li Y, Hara Y, Wind Tunnel Tests on a Different Phase Three-Stage Savonius Rotor.
JSME International Journal, Series B, 48(1): 9-16, 2005b. <<ORIGINAL PAPER>>z

Hayashi T, Liu W, Nojima K, Hara Y, Tagawa K, A Study on a Water Maker System using
Peltier Devices, The 6th KSME-JSME Thermal and Fluids Engineering Conference, Jeju,
KOREA, CD-ROM,JE.08, 2005c. <<ORIGINAL PAPER>>z

Hayashi T, Tanaka K, Hara Y, Liu Y, Nojima K, Tagawa K, A Study on Water Making System
Using Renewable Energy in Tottori Sand Dune. Proc. of the EXPO World Conference on Wind
Energy, Renewable Energy, Fuel Cell (WCWRF 2005), Hamamatsu, Japan, CD-ROM, 2005d.
<<ORIGINAL PAPER>>z

Kang I, Ariyasu K, Hara Y, Hayashi T, Paraschivoiu I, Characteristics of a Straight-Bladed
Vertical Axis Wind Turbine in Periodically Varying Wind. The EXPO World Conference onWind Energy, Renewable Energy, Fuel Cell (WCWRF 2005), Hamamatsu, Japan, CD-ROM,2005. <<ORIGINAL PAPER>>z

Kang I, Hayashi T, Hara Y, Ariyasu K, A Measurement Method by Wind Tunnel Experiment of
the Moment of Inertia of a Vertical Axis Wind Turbine. Renewable Energy 2006, Makuhari
Messe, Chiba, Japan, CD-ROM, P-W-23: 889-892, 2006.

z

Li Y, Hayashi T, Hara Y, Kawamura T, Performance of Different Phase Three-Stage Savonius
Rotor. Renewable Energy 2006, Makuhari Messe, Chiba, Japan, CD-ROM, O-W-4-3: 787-790,
2006.

5) Socio-medical Science group
There have been many studies of common tropical infectious diseases such as malaria,
19

schistosomiasis, and dengue fever. Such studies have formed the basis for the field of tropical
medicine. However, desertification and drought present a serious threat to the well-being and healthof the populations in arid and semi-arid areas, yet despite the size and global extent of these
populations, there have been few studies of dryland health and medicine. Thus, no specialized areaof health science has been established for these regions. The Socio-medical Science group has thus
set out to develop the field of dryland health and medicine in an attempt to improve the health ofpeople living in these areas. The group's research has focused on two primary areas: "Simple andacceptable methods for assessing the health of people in arid or semi-arid areas", and "Prevention of
diseases specific to arid and semi-arid areas".
Simple and acceptable methods for assessing the health of people in arid or semi-arid areas
Few studies have examined the health or the health-related quality of life (HR-QOL) of
populations in arid and semi-arid areas, and no study has identified the factors that influence
HR-QOL in these areas. To provide a preliminary basis for assessing health in these areas, weinvestigated the HR-QOL of inhabitants of China's Loess Plateau by using a 36-item short-form
health survey instrument (SF-36) to explore the relationships among social factors, lifestyles,
and health conditions and their impacts on HR-QOL (Mu et al. 2007, 2008). This survey was
carried out by means of a questionnaire directed at the heads of households or theirrepresentatives. HR-QOL was assessed using a three-dimensional survey (SF-36) of general
health perceptions, vitality, and general mental health: the potential risk factors capable ofinfluencing HR-QOL were social factors (education, income, medical insurance, and access to
medical care), lifestyles (regular physical exercise, cigarette smoking and alcohol intake), andhealth conditions (chronic diseases and respiratory symptoms). We used partial correlation
coefficients and multiple-regression analysis to explore the factors capable of influencing
HR-QOL. The HR-QOL scores for women were lower than those for men. The partial
correlation coefficients between HR-QOL and chronic diseases, respiratory symptoms, accessto medical care, medical insurance, age, and income were statistically significant.
Prevention of diseases specific to arid and semi-arid areas
Table 1 summarizes the most important diseases specific to arid and semi-arid areas.
Table 1. Specific diseases in arid and semiarid areas• Heat illness• Respiratory diseases due to dust and sandstorm• Infectious diseases
Zoonosis, Malaria• Nutritional disorders
Malnutrition, Deficiency of iodine• Water pollution related diseases• Disorders due to dryness

20

Heat-related illnesses include heat cramps, heat exhaustion, and heat stroke. Heat stroke canbe particularly severe; it is often fatal when core temperatures rise to more than 40.5 °C. In
Saudi Arabia, which has a very hot and dry climate, the number of deaths from heat stroke wasmore than 1000 during the 1985 Haj season. Most deaths were among pilgrims from outside
Saudi Arabia. Our study indicated that rates of sweating were similar under low or highhumidity at the same temperature, even though subjects felt less hot at low humidity. Thisdifference between the perception of heat and the actual state of the victim's body may explain
why many pilgrims from outside Saudi Arabia suffered heat stoke under the region's hot, dry
conditions.
Dust and sandstorms have caused considerable damage to transportation systems, but theirimpact on public health is less well known. Floating dust can cause pneumoconiosis and is apotential allergen. Diagnosis or assessment of occupational pneumoconiosis is based on
exposure to dust, symptoms, lung function tests (spirometry), chest X-rays, and (rarely)
biopsies. However, a simple non-invasive method is needed for monitoring non-occupational
pneumoconiosis in large populations. Urinary protein 1 (uP1) has been found to be a useful new
lung-specific biomarker of several lung diseases. uP1 is a low-molecular-weight protein (16kDa) synthesized by the non-ciliated bronchiolar Clara cells and secreted in large amounts into
the lumen of the lungs. We investigated the relationship between uP1 values and changes inlung function as a result of pneumoconiosis (Kotani et al. 2007). The results suggest thatmeasurement of uP1 may become a useful non-invasive index of the fibrotic changes that occur
in pneumoconiosis.
【Publication list】
z

Kotani K, Kawabata I, Mu H, Kurozawa Y, Itoh Y, Urinary protein 1/Clara cell 16
concentrations and lung functions in male subjects with pneumoconiosis. Ann Clin Biochem,
44: 560-562, 2007. <<ORIGINAL PAPER>>z

Mu H, Kurozawa Y, Kotani K, Liu G, Liu P, Nishino S, Ito TY, Tsunekawa A, Factors
associated with health related quality of life in inhabitants of the Loess Plateau region.
CAS-JSPS China-Japan Joint Open Seminar on Combating Desertification and Development in
Inland China: 68-69, 2007. <<ORIGINAL PAPER>>z

Mu H, Kurozawa Y, Kotani K, Liu G, Liu P, Tsunekawa A, Nishino S, Ito TY, Health-related
quality of life and recognition of desertification among inhabitants of the Loess Plateau regionof China: findings for city and village communities. Journal of Environmental Health, 70:
38-43, 2008. <<ORIGINAL PAPER>>

21

3. Original papers

22

JＨｇ血ＭＥｔｅｏｍＬ（農業気象）６０(2)：103-113,2004

ＦｕｌｌPaper

HeatBalanceandSoilMoiStureintheLoesSPlateau,China

ReijiKIMuRA*'↑,MakioKAMIcHIKA*,NaruTAKAYAMA*，
NobuhiroMATsuoKA*＊andXingchangZHANG**＊(f繍善藷繍鱒鶴蝋蝋磯｡c…）
AbStract

Athree-1ayersoilmodelwasusedfbrclarifyingtheheatbalanceandsoilwatercontentinthe
LoessP1ateau,china,andappliedtoactualbaresoilfields(TottoriSandDuneandShenmuDistrict，
ShaanxiProvince,china)．Thedi丘erencebetweentheobservedandcalculatedevaporationperday

wasapproximately0.18ｍｍ（5Ｗ、~2)ｔｏ0.21ｍｍ(6Ｗ、-2)．Becauscofitsmoderatemixtureof
sand，siltandclay，yellowloessialsoninShenmuaHEctswaterretentivityandrestrictionof
evaporationfromthesoilsurfnce・Theseasonalchangeofheatbalanceandsoilwatercontentwas
examinedusingmeteorologicaldatainYulinnearShenmu、Theannualmeansofsensibleheatand

latentheatiluｘｗｅｒｅ２３Ｗｍ－２ａｎｄｌ９Ｗｍ－ｚ（Ｚ３９ｍｍｐｅｒｙｅａｒ)，respectively・Thesoilwatercontentofthesecondandthirdlayersremainedcomparativelyhighinwinter・
Keywords：Heatbalance,LoessP1ateau,Soilwatercontent．

LImtrOdunctiOm

TheLoessPlateauinChinaislocateｄｍＬｏｎｇｌＯＯ－

ｎ５ｏＥａｎｄＬａｔ､34-40.Ｎ,anditsrangecorresponds

almostexａｃｔｌｙｔｏｔｈｅｍｉｄｄｌｅｒｅａｃｈｅｓｏｆｔｈｅＨｗａｎｇ
Ｈｏ(YellowRiver)．Annualprecipitationisapprox‐
imately400mm（ｍｉｎｉｍｕｍｌ５０ｍｍ,ｍａｘｌｍｕｍ７５０ｍｍ）withva1iabilityintimeandspace（Yangand
Shao,2000)．Accordingtothewaterdeficitindeｘ
ＷＤＩｂｙＷａｎｇａｎｄＴａｋａｈａｓｈｉ（1999）andaridity
indexbyUNEP(1997),theLoessP1ateaubelongsto
thesemi-aridregion、Compoundingtheproblemis
improperlandusesuchastheover-cultivation,overpasturing,andtheover-defbrestation,whichresulted
intheseriousproblemofdesertihcationafterthel7thcentury(Tamura,1990)．Yellowloessialsoilis
transportedintorivers,andcarriedbywindstoothercountries，suchasJapan・AdditionaUy，fbrthe
peoplewhoinhabittheLoessP1ateau，secunng
enoughwaterfbrtheirdailyneedsisdifficult・About
60millionpeopleincludingfarmerslivehereinspite
ofsuchanunstableconditionForseveralyears，
however，ｔｈｅｒｅductionoffarmlandandpromotion↑Correspondingauthor:E-mailrkimura@alrc・tottori-u・acjp
ReceivedonJune30,2003．

AcceptedonJanuaryZ9，２００４

ofgreeninghavebeenrecommendedbytheChinese
government・Theneedfbranincreaseinvegetation
issurelyadmittedinsuchaplace・Itisthoughtthat
inlportantnndingsfbrdealingwithdesertihcation
canbeobtainedbycontinuouslymonitoringsucha
greenlngreglon・

Theamountofexistingvegetationrealisticallyshowstheprogressivedegreeofdesertification，and
themostimportantfactorthatsupportsplantproductionissoilmoisture，ｗｈｉｃｈｉｓｔｈｅｒｅｓｕｌｔｏｆｔｈｅ

ｈｅａｔａｎｄｗａterbalances、Consequently,themonitoringofdescrtificationispossiblebyconsideringthe
relationshipamongthekindofexistingvegetation，
amountofexistingvegetation，andthesoilwatercontent（Shinoda，2002)．Ｔｈａｔｉｓ，theseasonalchangeoftheheatandwaterbalancescanbecomean
importantfactorinsearchingfbrthecurrentstateof
desertification・However，nodetailedstudyonthe
seasonalchangeoftheheatandwaterbalancesfbr
baｒｅｓｏｉｌｓｕｒｆａｃｅｓｉｎｔｈｅｗｈｏｌｅａｒｅａｏｆtheLoess
P1ateauhasbeencarricdout・

Thefbllowingstudywasconductedtoclarifythe
quantitativefbrmulationofheatbalanceandsoil
watercontentfbrbaresoilsurfaceontheLoess

Plateau・First，ｔｈｅsoilmodeldevelopedbyKondo
andXu（1997）wasemployedtocalculateheatbal‐－１０３－

JHgl・jCMbZeoM．（農業気象）６０(2),２００４
anceandsoiIwatercontent・Ｔｈｅｓｏｉｌｍｏｄｅｌｂｙ

ＫｏｎｄｏａｎｄＸＵ（1997)delimitedthesoildepthof70
cmintotenlayersindetaiLInthisstudy，asimple
three-layersoilmodelinwhichthe70cmsoildepth
wasdelimitedtothreelayers（0-2,2-22ａｎｄ22-70ｃｍ)wasappliedinconsiderationofthedepthoftherootzone・Becausethedepthoftherootzoneisdeep
inasemi-aridregionliketheLoessP1ateau，ｔｈｅｎｕｍｂｅｒｏｆｓｕｃｈｔｈｉｃｋｌａｙｅｒｓｃａｎｂeaddedtothis
modelinconsideringthevegetationinthefnture・If
thesoillayersaredelimitedindetail，themodel
calculationisverycomplicatedbecauseofthecomplexityofweightmgfbrthedistributionoftheroot・Themodelwasveriliedbycomparingtheobserved
resultsintheTOttoriSandDuneandtheLoess

P1ateau（ShenmuDistrict，ShaanxiProvince，
china)．Next,thefbaturesofyellowloessialsoilin
Shenmuweredehnedbyconsideringsoilphysics
characteristicsobtainedbyindoorexperimentsand
modelcalculation、Finally,theseasonalvariationof

heatHux（Ｗｍ~2),旧thelatentheatflux（Ｗｍ~z)，
andGthesoilheatllux（Ｗｍ－ｚ)．
ＴｈｅｖａｌｕｅｓｏｆＨａｎｄ１Ｅａｒｅｇｉｖｅｎｂｙ（Kondo，2000）

Ｈ＝cppCHU(ＺＫ－Ｔ)，（２）Ｅ＝ＩＯＣ間叩(ｈ９鬮塾!(迅)－９)，（３）where

β＝，＋CHU(F/､)，（４）

Ｏ≦８＜６８３t．

（６）〃－．ｍ(鶚）（３）
Ｍ･叩柵)沖.．(晉釧も，Inthcabove,cpisthespccificheatofair(Jkg-lK-1)；,0,thedensityofair(kgm-3);ＣＨ,thcbulktrans化r
coeflicientfbrsensibleheat；ＵＺａｎｄ９ｔｈｅｗｉｎｄ

ｓｐｅｅｄ(ｍｓ~'),tempcrature(℃）andspecifichumidity(kgkg-l),respectively,attheobservationheightz(、);９sat(、),thespecifichumidityatsaturationat

heatbalanceandsoilwatercontentwasexamined

temperaturen（Ｋ);ﾉ,thelatentheat（Jkg~'）ofusingmeteorologicaldatainYulinnearShenmu．

evaporationofwater;β,theevaporationefliciency
byKondｏａｎｄＸｕ（1997);ｈ,therelativehumidity

2.Three-LayerSonModel

whenthewatervaporandliquidwaterareinequilib‐

Themodeldividedthesoilmtothreelayers：0-2,

曇=Zｉ

）

watermovementbyliquidandvaporphases，thevolumetricsoilwatercontentinrespectivesoil
layers，andheatbalancewerecalculatedusingthe
initialvalueandboundaryconditions(Fig.１)．The
imtialandboundaryconditionsfbrwaterandthermalregimeswereｔｈｅｓａｍｅａｓｔｈｏｓｅｏｆＫｏｎｄｏａｎｄＸｕ（1997)．Theboundaryconditionsofthegroundsurfaceandthebottom,thatis,（Qliq)z=０，（Qv圏ルー０，(Q1iq)ｂｏｔＩｏｍ,(Qvap)bottom,arerepresentedmFig・LAt
thebottomtheheatexchangewasassumednotto
takeplace，TheinitialconditionsofthevolumetricsoilwatercontentOandthesoiltemperatureTGwill
desclibedinChapters3and5、が2-22ａｎｄ22-70ｃｍ・Thetimeseriesofthevertical

5A,n画

Surface２cｍ
ｇｉｉｏ＋６A,ｎｍ,ｌｉｄ＋Ｑ,a｡

２２ｃｍ

721

､19）

2.1Heatbalanceonsonsurface

8人,ａｎ妬。

Ｂｏｔｔｏｍ７０ｃｍ

Theheatｂａｌａｎｃｅｏｆｔｈｅｓｏｉｌｓｕｒｆａｃｅｃａｎｂｅex-pressedby(Kondo,2000）（１）（１－幼S↓＋“↓＝ｇｏ”＋Ｈ＋IE＋Ｇ
Here,'研q/isthealbedoofsoilsurface,Ｓ↓theglobal

Ｆｉｇ．１．Schematicrepresentationofthethree-layer

solarradiation(Ｗｍ－２),どtheemissivityofthesoil

surface（assumedasunityinthisstudy),Ｌ↓thedownwardlongwaveradiation（Ｗｍ－２)，othe
Stefan-Boltzmanconstant（5.67×10~8Ｗ、~２Ｋ-4)，
nthesonsurfacetemperature（Ｋ),Hthesensible－１０４－

soilmodelinthisstudy・Pmstheprecipitation；
Etheevaporation；、,thesurfacetemperature；
Ｔｂ１，ＴＧ２ａｎｄＴＧ３，thesoiltemperaturein

respectivelayers;０，，０２ａｎｄ仏，thevolumetricsoilwatercontentinrespectivelayers,QIiq,theliquidphaseofthewaterflux;Qvap，thevapor
phasewaterUux．

ＫｉｍｕｒａｅＺａＬ：HeatBalanceintheLoessPlateau

riuminsmallsoilporesbyKondoandＸｕ（1997);E
thedmsiondistanccofwatervapor（、）ｂｙＫｏｎｄｏ
ａｎｄＸｕ（1917);nthecoefIicientofmoleculardih‐

soiltemperatureinindividuallayerscanbeexpressedby（ＫｏｎｄｏａｎｄＸｕ,1997）

器一六会(９噸十仏勵)，

sionofwatervaporinthcair（＝2.54×10~sm2s-l)；
9,theaccelerationofgravity(ｍｓ－２);Ｊ(9),thesoil

ＯＴＧ１ＤＱｈＺＥｓｏｉｌ

ＯＺｃＧｐＧＯｚｃＧｐＧ，（'0）

waterpotentialfbrthevolumetricsoilwatercontent

O(m3m-3)(、);Ｒｗ,thegasconstantofwatervapor(＝461.5,2Ｋ~1s-2)；ＴＧ,thesoiltemperature(℃)；
八,/b,几,and/bthesoilparametersdelinedinEq．
(6)（Tableｌ);andaaothe8atSaturation・
Inthisstudy,GiseXpressedas（Kondo,1994）⑧=-｣WⅦ等乃)ぬ（７）

Ｈｅｒｅ,cGisthespecifichcatofsoil（Jkg-lK-l),,oG
thebulkdensityofson(kgm-3),rthetime(s),andzthedepth(、)．

FukumotoandHirota（1994)notedthatthebulk
transfercoefficientCHcanbeexpressedas
CiIU＝0.0027＋0.0031×0.74Ｕ（８）ThecoefIicientisO74whenthewindspeedat2m
highisconvertedtothatａｔＯ５ｍｈｉｇｈ（roughness
lengthzo＝0.01ｍ)，byassumingthelogarithmic
windproiile・
TRcanbefOundthroughsuccessiveapproximaP
tionsofEq．(1)，withtheHuxesHMEandG
evaluatedfiPomEqs.（２）tｏ(8)．
２．２WaterandheattrmnsfCrwithinthesoil

Thetemporalvariationofsoilwatercontentand

TableLSoilparametersusedinthisstudy・ParametersfbrTottorisandandclaｙｌｏａｍｌｎ

where

QF-jI･等（､）Here,pwisthedcnsityofwater(＝1,OOOkgm-3),Qliq
istheliquidwaterHux(ｋｇｓ－ｌｍ~2),Qvapisthewater
vaporHux（kgm~2s-1),凪｡i,（Ｗｍ－２）isthelatent
heatfluxwithinthesoiMGthethelmalconductivity(Wm-lK-1)，ａｎｄＱｈｉｓｔｈｅｈｅａｔＵｕｘｉｎｓｏｉｌ(Ｗｍ－２)．Whcnz=0.02ｍ,瓜.ilisverysmallcompared
withOQh/ozandnegligibleinthecalculationat
depthsgreaterthanOO2m（ＫｏｎｄｏａｎｄＸｕ,1997)．
Thedennitionofdepthbetweentherespectivelayers，
inwhichheatandwateraretransfErred,isbasedon

astudybyAbramopouloseＭＬ（1988)．Thatis,it
wasdefinedasthedistancebetweenthecentersofthe

eachlayer・スGandcGpGaregivenby(Kondo,1994）
スＧ＝0.251＋0.501/３，（12）
ＣＭＧ＝(l-esat)C圏Ps＋aCwPw，（13）
wherecspsisthethermalcapacityofsoil(Jm-3K-l）
andcwpwisthethermalcapacityofwater（＝4.2×l06

Jm-3K-l)．TheweightingfbrｽGandcGpGbetween

therespectivelayersissetat５０％・ＴｈｅｌｉｑｕｉｄｗａｔｅｒｆｌｕｘＱ１ｉｑｃａｎｂｅｅｘpressedby(ＫｏｎｄｏａｎｄＸｕ,1997）

０噸--M㈲-Ｍ（u）

ＬａｎｚｈｏｕａｒｅｔｈｅｒｅｓｕｌｔｆｒｏｍＫｏｎｄｏａｎｄＸＵ（1997)．
Soil
Place

where
Sand
TottoriＣ１ａｙｌｏａｍＷｍ死hou４

トー4×Ⅲ仰(-``)-1+(二毛m０＜Ｂbat，

（16）

where

８

０

８９３
４３１

９５６

１５２

６１３
９

Ｃ１ａｙ（％）

個四Ｎ４００２０４

１１

１

●●

０００２０４００７３１２

２

●●●

２０４５４

８１

Soiltexture

Sand（％）
Ｓｉｌｔ（％）

ﾊﾟｰﾊ㈱：（'‘）

Loess
Shenmu

３４４
５３０５

●ＣＯ●

５

●■

５４

０００００４１００２０２

６
３８

●

cslos（106Jm-3K-1）

●

ん

９０

ん（103）た（10-4ｍ）●●●/)k(、）

３

６
Ｃ

４３

ａ

４０１

－妙趣（、）

０００８００６０９４０２

aaC(m3m-3）＆(m3m-3）

Rqa[（10〒sms-l）

（９）

and

ｽｰﾊ`㈲~！（Ⅳ）‘＝０，０≧Osat．

（18）

Here,Kisthehydraulicconductivity（ms-1);Ksat，
theKatsaturation;ｑｂａｎｄｃ,thesoilparameters；
andAt,ｔｈｅsoilwaterpotentialatsaturation・Ａｓ‐sumingthatthewaterfluxatthebottom（Zim`ｔｏ､）
occursonlyingravitationalpotentialconditions,ｉｔiｓ－１０５－

JMg血MbZeomL（農業気象）６０(2),２００４
soiltemperatureinindividuallayers、

glvenasQ1iq(Zbottom)＝－P螺K・（19）

３．verificationofThree-LayerSoilModel

Inthisstudy,thehydraulicconductivitiesbetween
thefirstlayerandthesecondlayerKl-2andbetween
thesecondlayerandthethirdlayerKz-3aredefiｎｅｄ

3.1Tottorisandａｓ、

serveddatafromtheTottoriSandDuneattheArid

K1-z＝０．９．Ｋl＋０．１．Ｋ２，０１＜０２，
Kl-2＝０．１．Ｋ!＋０．９．Ｋ２，０１≧02,

（20）
（21）

and

layer・Ｉｆａｗｅｉｇｈｔｉｎｇｏｆ５０％ｉｓｇｉｖｅｎｔｏＫ１,water

expressedby(KondoandXu,1997）

9..=筈(`["差T･)]）(23）

凡=鵲，<`…

（24）

０２４４８７２１６１２０１“ｌ６８屋:tiZJjiiji1iijii;巫］

０２４４８７２‐９６１２０１４４１６８＝-蝋8mA．…;…錫謡髄---:￣澱:Ｈ１磯（｡）

０２４４８７２９６１２０１４４１６８

where

００００

１８６４２００００００

ｒ日道時＆“二。、Here,Rmisthetransportrouteofwatervaporinthesoil(、）（KondoandXu,1997),and9sat(TG)isthesaturatedspeciIichumidityatthetemperatureTG・ＡｓｓｅｅｎｉｎＦｉｇ、１，theliquidwatermovement
betweenthefirstlayerandtheatmosphere，andthewatervaporrnovementatthebottom,arenotconsidered（ＫｏｎｄｏａｎｄＸｕ,1997)．Thedatausedinthis

(8)

釦㈹卯刈川

theheatbalance・ThewatervaporUuxQvapcanbe

０００００

Kz-3haslittleefbctonthecalculatedresultsof（Ｑ」⑩員巨巴圏巳小膚 一。⑫ｌａｙｅｒｉｓｅｑＵａｌｔｏｏｒｌａｒｇｅｒｔｈａｎｔhatinthesecond
layer,theweightingfbrthehydraulicconductivityis
setat90％fbrK2mEq.(21)．TheaverageofK2and
K3isusedfbrK2-3inEq.（22)．Theweightingfbr

加却⑩扣

whcnO,＜０２．Whenthesoilwatercontentinthefiｒｓｔ而三Ｉ３Ｈ１ｉｉＩ鴇Ii1Ii:M8IliA….､(o剛ＪｕｎＢｌ２３４５６７鈩長彦）面聟自四

movementfromthesecondlayerbecomesverylarge

的叩０

Eq.(20)becausethethicknessandsoilwatercontent
ofthefirstlayerarelessthanthoseofthesccond

０５

fbrthehydrauUcconductivityissetat90％fbrK1m

LandReSearchCenter,TottoriUniversity,from31
Mayto7June,2002．Thesoiltextureissand(sand96％,silt１％andclay3％）(Tablcl)．Thcrewasno
rainfallduringthisperiodTheobservationelements
werethesolarradiation（ＥＫＯ;MS801)，reflectedsolarradiation(EKqMS62),downwardlongwave
radiation（ＥＫＯ;MS202)，windspeed（YOUNQ
YG3102)ataheightof2m,precipitation,tempera‐ture,andrelativehumidity(VAISALA;ＨＭＰ４５Ａ)．
ThesedataweresampledeverylOs，thenaveraged
overl-hperiods・Soiltemperaturewasmeasuredat
deｐｔｈｓｏｆ１，４，１０，１８，２６，３４，４２ａｎｄ５０ｃｍｕｓｉｎｇ鈩禧菱ご融旨⑪員四（22）
Here,Ｋ,,K2andK3arethehydraulicconductivities
fbrtherespectivelayers・Equations（20）ｔｏ（２２）weredeterminedbycomparingthecalculatedresults
ofliquidwaterlluxwithvariousweightingsfbrthe
hydraulicconductivity，withthatfromalO-1ayer
modelhaviｎｇａｄｅｔａｉｌｅｄｒａｎｇｅｆｒｏｍＯｔｏ２ｃｍ,Ｚｔｏ６ｃｍ，６ｔｏｌ４ｃｍ，１４ｔｏ２２ｃｍ,Ｚ２ｔｏ３０ｃｍ,…ｕｐｔｏａ
ｄｅｐｔｈｏｆ７０ｃｍ，soastominimizethediHerence
betｗｅｅｎｔｈｅｍ・Inconsideringtheliquidwaterflux
betweenthehrstandthesecondlayer,theweighting
K2-3＝０．５．Ｋ２＋０．５．Ｋ3．

Thecalculatedresultwasverinedusingtheob‐

上蝋81ｉｆ・…乢鰯謡醗・一目一粥I認臨.（｡）0２４４８７２９６１２０１４４１６８Time(hＯ

Fig.２．Diurnaldistributionsofthe（a）observed

modelaresolarradiation，reflectedsolarradiation，

downwardlongwaveradiation，airtemperature，
windspeed,vaporpressure,andprecipitation、Initialconditionsarethevolumetricsoilwatercontentand－１０６－

solarradiation，downwardlongwaveradiation，（b）thecalculatedsensibleheatUux,latentheat

fluxandsoilheatflux，ａｎｄ（c）ａｎｄ（d）the
calculatedandobservedsoiltemperatureandsoil
watercontentinrespectivelayers(0-2,2-22ａｎｄ
22-70ｃｍ)fbrtheTottorisand,fromlJuneto7
June2002（７days)．

ＫｉｍｕｒａｅｒａＬ：HeatBznInnceintheLoessPl2tean

thermocouples・Soilwatercontentwasobservedby
gravimetricsamplingatdepthsofl,４，１０，１８，２６，３４，
４２，５０，５８ａｎｄ６６ｃｍａｔｌ８００ＪＳＴ・

thisstudy，theaccuracyofcalculatedheatenergy，
especiaUyevaporation，ｗａｓcxaminedbycomparmg
theobservedandcalculatedsoilwatercontent,andFigure2illustratesthediurnaldistributionsoftheobservedsolarradiation,downwardlongwaveradiation，soiltemperature，andsoilwatercontentin
individuallayers（0-2,2-22ａｎｄ22-70ｃｍ),asweU

accumulatedevaporation,fbrtheobservationperiod
Accumulatedevaporationfbrtheobservation
periodwascalculatedfromthechangeofsoilwatercontentabovethezero-Uuxplane（ZFP)．Figure3
depictstheverticaldistributionofvolumetricsoil
watercontentandhydraulicpotentialon31Ｍａｙａｎｄ
７June・TheZFPduringthisperiodexistedbｅｔｗｅｅｎ
ｄｅｐｔｈｓｏｆｌＯａｎｄ２０ｃｍ・ＴｈｅＺＦＰｂｅｃａｍｅｄｅｅｐｅｒ
ｗｉｔｈｄｒｙｉｎｇｂｙevaporationAccumulatedevapora‐tionduringthisperiodwasO84mmwhｅｎＺＦＰｗａｓ

asthecalculatedsensibleheatHux，１atentheatflux，

soilheatllux,soiltemperatureandsoilwatercontent
froml-7June,２００２(７daystotal)．Aninitialvalue
ofthesoilwatercontentfbrthecalculationwas

measuredatl800JSTon31May(Fig.３)．Asthere
wasnorainfnUmthisperiod,adrysoilsurfncelayer(characteristicofsandysoil)developedOn31May，

ｌＯｃｍ,ａｎｄ３２ｍｍｗｈｅｎＺＦＰｗａｓ２０ｃｍ、Converse‐

thevolumetricsoilwatercontentiｎｔｈｅｆｉｒｓｔｌａｙｅｒ

1y,accumulatedevaporationpredictedbythesimula-

ｗａｓＯ・ＯＯ４ｍ３ｍ~3,withminimalwaterretentivity・

tionmodelwas2.１ｍｍ、ThediHerencebetweenthe

Figure2ccomparestheobservedvalues（iiUedmarks）withthecalculatedvalues（lines）ofsoil
temperatureintherespectivelayers，Thevaluefbr
thefirstlayerwasobsｅｒｖｅｄａｔａｄｅｐｔｈｏｆｌｃｍ；fOr
thesecondlayer,themeanvalueofobservationsat4，
１０ａｎｄｌ８ｃｍｗｅｒｅｕｓｅｄ；andfbrthethirdlayer,theobservedandcalculatedevaporationperdayｗａｓ

Ｏ１８ｍｍ（sWm-2)．Additionally，thecalculated
valuesofthesoilwatercontentonthelastday（７June)wereconsistentwiththeobservedvalues(Fig.
2.)．Dailyevaporationfbrthisperiodrangedfrom

meanvalueofobservationsat２６，３４，４２ａｎｄ５０ｃｍ

0.1ｔｏＯ３ｍｍ・Thedrysoilsurfacelayerrestrictedevaporationremarkablywel1.

ｗｅｒｅｕｓｅｄＡｔｎｉｇｈｔｏｎ４ｔｏ５June,ｔｈｅｃalculated

3.2YemOwloessialsomintheLoessPlateau

valuesofthefirstlayerwerelowerthantheobserved

Theobservationwasperfbrmedintheexperlmentalstation（LiudaogouBasin）locatedinShenmu

values、Thereasonwhythediffbrencebetweenthem
atnightislargecouldnotbeclarifiedatthepresent
time・Whenviewedoverall,however,thiscalculated
resultwasconsistentwiththeactualsituation．

，Figure2bpresentsthecalculatedresultsofheatbalance,andFig2dcomparestheobserved（filledmarks)andcalculated(lines)sonwatercontentln

District，ShaanxiProvince，china（Fig.４)．In
Shenmu,ｅｒｏｓｉｏｎｂｙｂｏｔｈｗｉｎｄａｎｄｗａｔｅｒａｒｅｓｅvere，
andtheamountofearthandsanddepositedintothe
YellowRiverwasconsideredserious（Academia
SinicaandMinistryofWaterResources,1993)．Ｔｈｅ
stationislocatedat38o47'NlatitudeandllOo21'E

1ongitude，Ｔｈｅｂａｓｉｎａｒｅａｉｓ７ｋｍ２,andthealtitudeis
０l,２２４ｍ、Ｍｏｓｔｏｆｔｈｅｌａｎｄｓｕｒｆａｃｅｉｓｂａｒｅｓｏｉｌand0

shortgrass・Accordingtostatisticsfroml957tol989(33years),theaverageannualtemperaturewas●。

437ｍｍ（ｍｉｎｉｍｕｍｌＯ９ｍｍ，maxlmunl891mm)．
Thesestatistics，thewaterdeficitindexPWZDIby
WangandTakahashi（1999),andtheradiativedry‐
nessindexbyBudyco（1956）indicatethatthisobservatoryisinasemi-aridregion

Ｉ

５６

Ｄ〃

soiIwat…tentO(m]in9jl

●。

00.O5

。

０

斗

（巳。）二］ロの己一己、釦（【■。）二冨冠己一一○ｍ-60●、。。◎。。。

０
２

０
２

-60

8.4℃（thecoldest-9.7℃inJanuary,thewarmest
23､7℃ｉｎJuly),withanaverageannualrainfallof

oＩＩｏｚｌｏ３１ｏ４１ｏ３１ｏ６１ｏ７IMraulicpotentiaI(cmH20）

Fig.３．Verticaldistributionofsoilwatercontent
andhydraulicpotentialon31May（dots）ａｎｄ７
Ｊｕｎｅ（circles)．

Thesoiltextureintheexperimentalstationis

sandyloam（48％sand,３９％ｓｉｌｔａｎｄ１３％clay)．
Thesoilparametersusedinthisstuｄｙａｒｅｓｈｏｗｎｉｎ
Ｔａｂｌｅｌ、TheparametersinEqs.（15)tｏ（18),which
representthewaterretentioncurveandthehydraulicconductivity，ｗｅｒｅdeterminedusingtheresultsob-－１０７－

JZg河c・Ｍｂ/eｏｍＬ（農業気象）６０(2),２００４

l 1ijli hijijijLi1Ii;１

３６Ｎ〆=fj妻:'?=if三iＬ
鞍､〆･･の~へ｜吾｡p/‐1.1-..-..9Fig.４．LocationandvegetativeclassificationoftheLocssP1ateauandexperimentalsiteinShenmu，
ShaanxiProvmce,china・Ｉ：Forest，１１：Forestandtypicalgrass・ＩⅡ：ShortgrasslV：Desertandshortgrass・ThisclassificationwasquotedfToｍＹａｎｇａｎｄＳｈａｏ（2000)．Thechainlineistheborderlineof
theLoessP1ateau．

Ⅵo･･●●･￣｡~･Ｔｏｏ

DC･ＤＣ｡●●｡●●ぜ･・o凪ｃＤＣＱｏ・●…￣

24

４８

16

7２

9６

17

-H(Cal.） ,..…･･･…lE(CaL）汕汕、０畑------0(Cal.）

Ｆ(b）Oｕｕ－

0－』雲'《Ｗ３ｗ(…繩2４》堅いＡｕｇｕｓｔ(0,＝0.0085,82＝0.045,03＝0.09)．

００００００thecalculationwasmeasuｒｅｄａｔｌ５００ＢＳＴｏｎｌ４#1繍臘
纐削(議霞亀圖…lf餅鷲ﾋﾞ鰯…`lt1ilFl穗薗…蕊,欄i露惠Augustl5

4８……･…２２２ｃｍＣａｌ．

△Z22cmObs．

72

9６------22-70ｃｍＣａｌ．
。２２j70cmObS．

;:Ａ型ＡＬＡ響△
4８

7２

9６

●O-2cmObs．▲２２２cmObs．■z2-70cmObs、へ----22-70ｃｍCal．
可一一一一一o-2cmCaL・…．.…･･･２－辺ｃｍＣａＬ,Ｅ０．１５

仮、

ｇｏ.’
山

鳥0.05
芦

＝0
．

丙0２４４８７２１６Time(h、Fig.５．Diurnaldistributionsofthe（a）observed
solarradiation，ａｎｄｄｏｗｎｗａｒｄａｎｄｕｐｗａｒｄ
ｌｏｎｇｗａｖｅｒａdiation，andcalculatedupwardsoilheatHux,sontemperatureandsoilwaterconteｎｔ

ｆｒｏｍｌ５ｔｏｌ８Ａｕｇｕｓｔ２００２（４days)．RainfH11
measuredat6､４ｍｍoccurredintheevenmgofl4
August・Aninitialvalueofthesoilwatercontentfbr

０００００
０８６４Ｚ

22-70ｃｍ),andthecalculatedupwardlongwaveradiation（＝on4),sensibleheatHux,latentheatflux，(日）

O（轍屋震乙面皆目四measuredbyusingthermocouples、Thesedatawere
sampledeverylOs,thenaveragedoverl-hpeliods・
Soilwatercontentwasmeasuredaｔｄｅｐｔｈｓｏｆｌ，４，
１０，１８，２６，３４，４２，５０，５８and66cmbygravimetricsampnngatｌ５００ＢＳＴ，
Figure5depictsthediurnaldistributionsoftheobservedsolarradiatio､,downwardlongwaveradiation，upwardlongwaveradiation，soiltemperature
andsoUwatercontentineachlayer(0-2,2-22ａｎｄｒ屋達Ｃ壷皆⑪ロ四servedbyYangandShao(2000)．Otherparameters
weredeterminedbymdooreXperimentsasdescribedinChapter4
Meteorologicaldataweremeasuredfroml5tol8
August2002（４days)．Solarradiation,reUectedsolarradiation，upwardlongwaveradiation，and
downwardlongwaveradiationweremeasuredwitha
fbur-componentradiometer（EKOmodelMR40)．
Acupanemometer（YOUNG;YG3102）andvcnti‐
latedpsychrometer(VaisalamodelHMP45A)were
establishedat2mabovethegroundSoiltemperaPturesatl，４，１０，１８，２６，３４，４２and50cmwere－SoIarRadiation(Obs.）oUpwHIdLongwavcRadiaXion(Cal.）…………DownwaJdLongwnveRadiaIion(Obs.）-------UpwmdLongwm'cRadiation(Obs.）

longwaveradiation，（b）thecalculatedsensible
heatflux，latentheatHuxandsoilheatHux，ａｎｄ（c）ａｎｄ（｡）thecalculatedandobservedsoil
temperatureandsoilwatercontentinindividual
layers（0-2,2-22ａｎｄ22-70ｃｍ）fbrtheyellow～loessialsoil,ｆｒｏｍｌ５ｔｏｌ８Ａｕｇｕｓｔ２００２．

－１０８－

ＫｉｍｕｒａｅｍＬ：HeatBalanceintheLoessPlatezuuu

Figures5cand5dcomparetheobservedand

dottedlinerepresents-TottoriSandDune，andthe

calculatcdvaluesofthesoiltemperatureandsoil
watercontent・CalculatedvaluescorrespondwelldashedlinerepresentstheclayloaminLanzhou

withobservedones,asinTottoriSandDuneHow-

ＫｏｎｄｏａｎｄＸｕ（1997)．Lanzhouislocatedinthe

ever,thecalculatedvaluesofsoiltemperaturefbrthe

southwesternpartoftheLoessPlateau(Fig.４).The
soilwatercharacteristicscurveofyellowloessialsoil
issimilartothatinLanzhou・AssumingthatthesoH
waterpotentiａｌａｔｔｈｅｗｉｌｔｉｎｇｐｏｉｎｔｉｓｄｅｆｉｎｅｄａｓ-1585ｍ(ｐＦ＝4.2wastheassumedwiltingpointin
thisstudy）（Kawaguchi,1991),thevolumetricsoil
watercontentatthewiltingpointisOO6（Fig.６)．
Hence,ｔｈｅｓｏｉｌｗａｔｅｒｃｏｎｔｅｎｔＯ１ａｎｄＯｚｄｕｒingthis
perioddidnotsupportplantgrowth(Fig.５)．Here，Hrstlayerandtheupwardlongwaveradiationwere
lowerthantheobservationvaluesatnight，asin
TottoriSandDune，

Accumulatedevaporationdulingtheobservation

period（１５tol8August）wascalculatedfromthechangeofsoilwatercontentabovetheZFP，asdescribedinSection3・LTheZFPduringthisperiod
existedｂｅｔｗｅｅｎｄｅｐｔｈｓｏｆ４ａｎｄ８ｃｍ・Accumulated
evaporationduringthｉｓｐｅｒｉｏｄｗａｓＯ２６ｍｍｗｈｅｎ
ＺＦＰｗａｓ４ｃｍ，ａｎｄ0.98ｍｍｗｈｅｎＺＦＰｗａｓ８ｃｍ、Conversely，theaccumulatedevaporationpredicted
bythesimulationmodelwas１．０９ｍｍ、ThediHbrencebetweentheobservedandcalculatedevapora-tionperdaywas0.21ｍｍ（6Ｗ、－２)．Thiscalcula‐tionaccuracywasalmostequaltothaｔ（0.173mm

day-1＝５Ｗ、－２）evaluateｄｂｙｔｈｅｓｏｉｌｍｏｄｅｌｏｆ
ＫｏｎｄｏｅＭＬ（1994)ａｎｄＫｏｎｄｏａｎｄＸｕ（1997)．
４．FeaturesofYenowLoessialSom

Figure6iUustratestherelationshipbetweenthe
volumetricsoilwatercontentandsoilwaterpotentiaLThecirclesrepresentobservedvalues，andthe(19％sand,５５％silt,ａｎｄ２６％clay）（Tableｌ）ｂｙ

8,ａｎｄBzisthevolumetricsoilwatercontentfbrthehrstandsecondlayers,respectively(Fig.１)．
Figure7showstherelationshipbetweenthevolumetricsoilwatercontentandthedifnsiondistanceofwatervaporRThecirclesrepresentvaluesobservedinindoorexperiments，andthesolidlinethe
resultfromEq.(6)．Thedottedlinerepresentsthc
Tottorisand,andthedashedlinerepresentstheclay
loaminLanzhou，ａｓｄｅｔｅｒｍｉｎｅｄｂｙＫｏｎｄｏａｎｄＸｕ(1997)．ThevalueofFdetermincdbyindoorexper‐
imentscanbeestimatedfromEqs.(3)ａｎｄ(4),that
is

F＝ＩＯＤ["9sat(亜)－９］、
Ｅ

（25）

ＣＨＵ．

soUdlmerepresentstheresultfromEq.（16)．Ｔｈｅ
105

104
10〕

｡ぐ三壱=ごくくくP、IＤＵ■●●●￣●●●●●●●の●●●●●①ＣＧ●の●■●■■●■のり●●●●●●●■Ｃｓ●●●●●●●p■●●●●●●●●■●■●●B●Ｃ●●□●●●■●●●●●●●p●●●■●●●●●●●●
1０－２

､
、

、

０

ＯＳ

、
、

Ｌ、

-Loess(Cal.）．
.…………TbttoTi型､。
（KondomdXILl907）

10.1-------1亜n丁hmD（KmdomdXu､1,97）

0-］

102

-~甑
０(m3m3）10.ｕ-----○－----万-一・！
OLocss(Indoorcxperimem）－－－Loess(Cal.）

OLocss(FicldobsJ’00~~~~~~~~~￣~~－－－~－－－~~~~~~~~~－－~~一計------

３

、
、

、‐〆

弓,0’

102

、

（戸巨）母

倉'０２

、

10判

10-5
10

0

Fig.６．Relationshipbetweenthevolumetricsoil
watercontentandsoilwaterpotentiaLThe･………･･･lbttorisand(KolldoandXu,1917）－－－－Lamhou(KondoandXu,1197）

10-Ｊ

lO-z

０(m3m-]）

瞠畿皇10-1

Fig.７．Relationshipbetweenthevolumetricson

circlesrepresentobservedvalues，andthesolid

linerepresentstheresultfromEq．（16）fbr
yellowIoessialsoiLThedottedｌｉｎｅrepresents
theTottorisandvalues，andthedashedline
representsthevaluesｆｂｒｃｌａｙｌｏａｍｉｎＬａｎｚｈｏｕ
ｂｙＫｏｎｄｏａｎｄＸｕ（1997)．
－１０９－

watercontentandthediHilsiondistanceofwater

vaporRThecirclesrepresentvaluesobserved
inindoorexperiments，andthesolidline

representstheresultfromEq．（６）fbryellow
loessialsoiLThedottedlinerepresentsthe

Tottorisandresults，andthedashedline
representstheresultsfbrclayloaminLanzhou

byKonｄｏａｎｄＸｕ（1997)．

､L4g7jCMbZeoM．（農業気象）６０(2),２００４
FcanbeestimatedbysubstitutingtheobservedZH,ｑ，ＥａｎｄＣＨＵｉｎｔｏＥｑ｡（25）（ＫｏｎｄｏａｎｄＸｕ,1997)．
ＡｓｓｅｅｎｉｎＦｉｇ､７，therelationshipbetweenOandF
fOryellowloessialsoilcloselyresemblesthatof
Tottorisand，ｅｘｃｅｐｔｆｂｒｔｈｅｍａｘｉｍｕｍｖａｌｕｅｏｆＲ
Ｒｅｓistancetoevaporationdrasticallymcreasesfbr

O≦0.1（m3m~3).Figure8depictstherelationshipbetweenthevolumetricsoilwatercontentandthe

evaporationefliciencyβderivedusingEq.(4)．βfbr
yellowloessialsoildrasticallydecreasesfOrO≦0.1(m3m-3)．AssumingthatthesoilwaterPotentialat

theheldcapacityisdehnedas－１ｍ（pF＝Zwas

assumedtobetheheldcapacityinthisstudy）(Kawaguchi,1991),Batthefieldcapacity（0f）of

yellowloessialsoilwasO19（ｍ３ｍ－３）（Fig.６)．
Theseresultsmdicatethatcomparativelyhighevap‐orationcontinuesuptotheiieldcapacity,butevapo-

rationdrasticallydecreaseswhenO≦0.1（ｍ３ｍ－３)，
becausetheupwardwatermovementproducedby
capiUaryactionisrestrictedduetothesoiltexture・
Waterpermeabilityofthissoilwascomparatively
highwhencomparedwiththeclayloammLanzhou(seethevalueofKsatmTablel)．Theseproperties
wererenectedinthesimulatedresultoflatentheatfluxIEinFi9.5ｂ・Thelatentheatnuxbecamelarge
thedayafterthel4Augustrainfnll・However，

evaporationwasagainrestrained2dayslater（１６August),asintheresulthrTottoriSandDune・Asmentionedabove，thefbllowingfeaturesof
yellowloessialsoilcanbecomparedtothoseｏｆ
TottorisandandclayloammLanzhou：（１）Thewaterretentivityissuperiortｏｔｈａｔｏｆ

Ｔｏｔｔｏｒｉｓａｎｄ，ａｎｄａｌｍｏｓｔｔｈｅｓａｍｅａｓｔｈａｔｏｆｃｌａｙ
ｌｏaminLanzhou．

（２）Thecomparativelyhighevaporationratecon‐tinuesuptothefieldcapacityOr・However,evaporaP
tionefliciencydrasticallydecreaseswhene＜Bfbecauseofrestrictcdupwardwatermovement，asin
Tottorisand・Conversely,evaporationfromtheclay
loamcontｉｎｕｅｓｓｔｅａｄｉｌｙｆｏｒａｌｏｎｇｔｉｍｅｄｕｅｔｏthe
capiUaryaction、Figure9presentsthesimulated
dailyevaporationusmgthesoilparametersfbrclay
loaminLanzhou、Theevaporationrateishigher
thanthatofyellowloessialsoiLAlthoughLanzhou
andShenmuarelocatedontheLoessP1ateau,theyexhibitquitediferentheatbalancesbecauseofdifbr‐

encesinsoilphysics．
（３）YellowloessialsoUaHectsbothwaterretentiv‐
ityandrestrictionofevaporationｆｒｏｍｔｈｅｓｏｉｌｓｕｒ－
ｆｈｃｅｂｅｃａｕｓｅｏｆｔｈemoderatemixtureofsand，silt
andclay・ThissoilcanbeconsideredsUperiorfrom
theviewpointofwaterretentivityunderthetopsoil
layerd1.5

５．SeasonalChangeofHeatBalance

OLoess(mdoorexperimen0-Locss(Cal.）andSoilWaterContent…………Tbttorisand(KondoandXu,1997）----‐Lamhou(KolldoandXu,1997）

Inthisportionofthestudy,theseasonalchangeof

ｍｉｈ:ﾎﾟ?ご妻~１

QＱ

theheatbalanceandsoilwatercontentwasconsid-

eredusingthesoilparametersestimatedinChapter4

0.5

2.5

一＝三宍式ゴニー･･－■､－－－－－－ジグ

Ｐ

，

５

０(m3m-3）

10-1

２

loessialsoiLThedottedlinerepresentsthe

representsthevaluesfbrclayloammLanzhou
byKondｏａｎｄＸｕ（1997)．

５０

Au9.15Ａｕｇｌ６Ａｕ9.17Aug､1８

linerepresentstheresultfromEq.(4)fbryellow
Tottorisandvalues，andthedashedline

０（ＡｖａｌｕｅｏｆＣＨＵ＝OO2ms-1wasadoptedfbrthe

calculation)．Thecirclesrepresentvalues
observedmindoorexperiments，andthesolid

１

Fig.８．Relationshipbetweenthevolumetricsoil
watercontentandtheevaporationeHiciencyβ５

ゴ１０－２２

１

０

２

○

●

、0．

（－１ン⑩つＥＥ）ＥＣ一］⑩」ｏＱｍシ山‘

０

Fig.９．Calculateddailyevaporationusinｇｔｈｅｓｏｉｌ
ｐａｒａｍｅｔｅｒｓｆｂｒｃｌａｙｌｏａｍｉnLanzhou・Meteo‐
rologicalconditionsusedfbrthecalculationwere－１１０－

thesameasinFig5．

ＫｉｍｕｒａｅｒａＬ：HeatBalanceintheLoessPlatezuu

andmeteorologicaldatainYulinnearShenmu(ｒｅｆｂｒｔｏＦｉｇ４)．BecausetherewasnometcorologicalobservatoryinShenmu，themeteorologicaldataof
Yulin，whichwasthenearestShenmu，wasused

Oneoftheadvantagesofthemodelusedinthisstudy
isthattheheatbalancecanbecalculatedbyusingthe

routinedataofthemeteorologicalobservatory・SoilpropertiｅｓｉｎＹｕｌｉｎａｒｅａｌｍｏｓｔｔｈｅｓａｍｅａｓｔｈｏｓｅｉｎ
Ｓｈｅｎｍｕ(YangandShao,2000)．Thedatausedin
thecalculationaresunshineduration,thedaily-mean
airtemperature，thedailymaximumandminimum
airtemperatures，thedaily-meanwindspeed，thedaily-meanspecifichumidity，andthedaUyamountofprecipitation．DiurnalvariationsofmeteorologicaldatawererequiredfbrthecalculationForthis

meltinginthecalculationofsoiltemperatureHow‐
ever,becausethesoilwatercontentinthisregionis
comparativelysmall，ｔｈｅｅ舵ctoflatentheatonthechangeofsoiltemperatureissmallerthantheeHect
ofheatconductivity、Consequently,theinHuenceof
latentheatwasneglectedinthisstudy、FigurelOshowstheobservedprecipitation，calculateddailymeansensible,latentandsoilheatfluxes,dailymean
soiltemperature，andthesoilwatercontentofrespectivelayersatl200BSTfbrl99g・
Thepeakofsensibleheatfluxappeaｒｅｄｉｎｓｕｍｍｅｒ(70Ｗ、-2)．Theannualmeanofsensibleheatfluｘ
ｗａｓ２３Ｗｍ－２、ＴｈｅvaluesoflatentheatBIuxclosely
correspondedtotherainfnllcvents，ａｎｄｔｈｃｐｅａｋ

ｖａｌｕｅｗａｓｌｌＯＷｍ－２（3.9ｍｍday~')．Theannual

study，thcsevariationswereestimatedbyusinga
methodofKondoandXu（1997)．Asfbrtheinitialmeanoflatentheatfluxwａｓｌ９Ｗｍ－２，andannual

conditionsofOanｄＴＧ,ａｓｓｕｍｅｄｖａｌｕｅｓｏｆＯａｎｄＴＧ

oftheannualrainfnll（283ｍｍ）evaporated・The

ａｒｅｆｉｒｓｔsubstitutedThemodelcalculationsare

valueofsoilheatHuxwaswithin±Ｚ０Ｗｍ－２・

repeatedfbratimescaleofseveralyearsormore
underthesamepatternofweatherconditionsuntilO
andTGineachlayerapproachesasteady-state・

Theseasonalchangeofsontemperaturemthenrst
layerTG1andsecondlayerTG2showedthesimilartendency・FromDecembertoFebruary,theT1G1andＴｈｅｓｅｒｅｓｍｔｓａｒｅｔｈｅｎａｓｓｕｍｅｄａｓｔｈｅｉｎitialcondi-

tionsofOandTG・Whentheseasonalvariationoftheheatbalance，
soiltemperature,ａｎｄsoilwatercontentiscalculated，

anaccurateestimationvaluecannotbederivedby
usingtheboundaryconditiondefinedinChapter2・However,theboundaryconditionbasedontheobservationcannotbesetbecausethereisnoobserva‐

tiondataTherefbre,inthischapter,thegroundsoil
isdividedinto221ayers,thethicknessofeachlayeris
0.02,0.20,0.48,0.48,0.48ｍ,？･･,untiladepthof9､８２
misreached、Theamplitudeoftheseasonalchange

ofsoiltemperaturewas0.2℃inlowerboundary(9.82ｍ)．Moreover,thesoilwatercontentoftheevaporationwas239mm・Therefbre,ｉｎ1999,85％

TG2felltobelowO℃，andthepeakreachedabout-10℃・TakahashieML（2002）observedthedailymeansoiltemperature（depth；10,30,60,ａｎｄｌＯＯｃｍ）inAnsai（ShaanxiProvince,china)aboutｌＯＯ
ｋｍａｗａｙｆｒｏｍＹｕｌｉｎｆｒｏｍｌ９９８ｔｏｌ９99．According
tostatisticsfieoml970tol997，theaverageannual

temperaturewas8.8℃inAnsai(thecoldcst-6.8℃
inJanuary,ｔｈｅｗａｒｍｅｓｔ２２,4℃ｉｎJuly)，withan

averageannualrainfallof423ｍｍ(TakahashieML，
2002)．A1thoughthemeteorologicalconditionswere
alittledi舵rent，thescasonalchangeofTGzandthe
verticalprofileofsoiltemperaturewasagoodlike‐nessoftheobservationresultbyTakahashieraL(2002)．Inthefilture,however,itwillbenecessary

seventhlayerwasalmostconstantthroughoutthe

todoalong-termobservationintheactualneld,ａｎｄ

year・However,thecalculationresultofheatba1ance

toverifythecalculationresulLAccordingtotheobservationresult，itisnecessarytoconsiderthe
e化ctofthermalconductivityandthermalcapacity
fbrthefrozensoUonthesoUtemperature・
Ｔｈｅｓｏｉｌｗatercontentofthefirstlayerwas
sensitivelyreactivetotherainfbLllevent・Adecrease
inthesoilwatercontentofthesecondlayerwas

andsoilwatercontentbyusingtheboundaryconditiondeHnedinthischapterwasnotsodiHferentfrom
theonedeiinedbytheboundaryconditioninChap‐
tｅｒ２becausetheheatbalanceonthegroundsurfnce
ismainlya丑ｅｃｔｅｄｂｙｔｈｅｌａｙｅｒｆｒｏｍｓｕｒｆａｃｅｔｏｌｍ(XuandHaginoya,2001)．ＷｈｅｎＴＧ≦－３℃,theliquidphaseofthewaternuxQＩｉｑｗａｓａｓｓｕｍｅｄａｓｚｅｒｏ（XuandHaginoya,2001)．ＩｎＳｈｅｎｍｕ,itisthoughtthattheairtemperaturefallstobelowO℃，
andthesonfreezesduringwinterperiodTherefbre，itisneccssarytoconsideralatentheatoffreezingor

remarkablefbrtheperiodofsummerwhenitrained
little・However,thesoilwatercontentofthesecond

andthirdlayersremainedcomparativelyhighin
winter・Ｉ、theLoessP1ateau,ａ“farmer,swisdom,,isappliedtocultivationpracticesinordertoeHectively－１１１－

JＨｇ恥MbZeoMb（農業気象）６０(2),２００４
Ｄ

Ｂ・０ＤＢＤＵ■

０■０

Ｂ㈹、０犯加”０

（ＥＥ）産

￣

●

■

■

￣

1,Ｉ ,JＬ

■

￣

，
￣

■

6０

0

□･Ｉ

I， ．，Iﾛ．．＿，

120１８０２４０３００３６０

themodelcalculationwillbedecided,andtheheat←，（ミニ）エbalanceandsoilwatercontentinthewhoIeareaof
theLoessP1ateauwillbeexHmined０（Ｎ‐屋一声）四一

０００００
５０５４

6０

2０

8０

240

300

6．Conclusion

360

Thisstudypresentedathree-1ayersoilmodelbased
onthesoilmodelbyＫｏｎｄｏａｎｄＸｕ（1997）andverifiedthemodelbycomparingthcobservedresults
0

5０

2０

8０

240３００３６０

intheTottoriSandDuneandtheLoessP1ateau(ShenmuDistrict,ShaanxiProvince,Ｃｈｍａ)．The
modeldividedthesoilintothreelayers，with

００００

２２卦

（甲〔二房）◎
（Ｐ）。』

0

6０

2０

8０

240

300

360

０

6０

2０

8０

240

300

３６０

０００
４２

2０

soiltypesintheLoessP1ateauweredividedbythe
particlesizedistribution(YangandShao,2000)．In
thefnture，thesoilparametersofeachsoilusedby

■●●●

□●●●

千尾

Ｉ．
6０１２０

ili=ii:H１ｉｌＨｉｒ

、

￣

0

【

●白
び

ｎ

■■

ｎ

■■

ｎ

■■

上二言一壱』』｜・信－－＝＝ご□Ｇ●■｡●●●●● p●●

■■■■

ｎ
万

■■

、

￣

脈

三頭!ｉ
－
－

肺

３２１０

（【‐Ｅ、皀邑の

０００

１

－０

180２４０３００３`ＯＤａｙ

Fig.１０．Thecalculatedresultsofseasonalchange
fbrYulininl999、Ｆｉｒｓｔｐａｎｅｌｉｓｔｈｅｄａｉｌｙ
ａｍｏｕｎｔｏｆｐｒecipitation，secondpaneltheresultofdailymeansensibleheatflux，thirdpanelthe
latentheatUux，fburthpanelthesoUheatUux，
fifthpanelthesoiltemperature，andbottom
panelthevolumetricsoilwatercontentfbr
respectivｅｌａｙｅｒｓａｔｌ２００ＢＳＴ．
utnizethefbaturesinherenttoyeUowloessialsoU：
thesoilwatermaintainedinthepreviousyearis

thicknessesofO-Z，Ｚ－２２ａｎｄＺ２－７０ｃｍ・Thetime

seriesoftheverticalwatermovementbyliquidand
vaporphases，thevolumetricsonwatercontentin
respectivesoillayers，andtheheatbalancewere
calculatedbyconsidcringtheinitialvalucand
boundaryconditions、Thcrcwasgoodagreementbetweenobservedand
calculatedresultsofevaporationandsoilwatercontent、ThediHerencebetweentheobservedandcalcu-

1atedevaporationperdaywas0.18ｍｍ(5Ｗ、~z)ｔｏ
0.21ｍｍ（6Ｗ、-2)．
ＴｈｅｙellowloessialsoilaHectsbothwaterretentivityandrestrictionofevaporationfromthesoilsurfnce・AlthoughtheyarebothlocatedontheLoess
P1ateau,LanzhouandShenmupresentedquitedifer‐
entheatbalancesThatis，alargediHbrenceis
causedintheclimatedependingonthesoilparticle
sizedistribution・

Theseasonalchangeoftheheatbalanceandsoil
watercontent･wasconsideredusingthemeteorologicaldatainYulmnearShenmu・Theannualmeans

utilizedfbrcultivationthefbllowingyear・However，
consideringthattheheldcapacityｍｔｈｉｓｒｅｇｉｏｎｉｓ

ofsensibleheatanｄｌａｔｅｎｔｈｅａｔＨｕｘｗｅｒｅ２３Ｗｍ~Z

Ｏ１９(ｍﾖm-3),thesoUwaterconditionisverysevere

Eighty-fivepercentoftheannualrainfH11（283ｍｍ）
evaporatedThesoilwatercontentofthefirstlayer
wassensitivelyreactivetorainfallevents、Thesoil

fbrcropproduction・Mostoftherainfnllisconcentratedinthesummerandautumnmonths（Juneto
September)(AcademiaSinicaandMmistryofWater

Resources,1993)．Therefbre,rainfallcanhardlybe

ａｎｄｌ９Ｗｍ－２（Ｚ３９ｍｍｐｅｒｙｅａｒ)，respectively・

watercontentofthesecondandthirdlayers

remainedcomparativelyhighinwinter．

expcctedinthewinterandspring・Thewindspecdis

highinsprmg（AcademiaSinicaandMinistryof
WaterResources，1993)，soitisduringthistime，
whenthesoilsurfacedriesoutremarkably,thatwinderosionisprofnse・Thisstudyexaminedtheseasonalvariationofthe
heatbalanceandsoilwatercontentinShenmuThe

Ａcknowledgements

Theauthorswouldliketoexpresstheirgratitude
toDr・KobayasioftheFacultyofHorticulture，
ChibaUniversity；Ｄｒ・AraiandstudentsoftheArid
LandResearchCenter,TottoriUniversity；ａｎｄＤｒ・ShaoandthemanyresearchersofInstituteofSoil－１１２－

ＫｉｍｕｒａｅｒａＬ：HeatBalanceintheLoessPlate2m

andWaterConservation,ＣＡＳ,china,fbrconsider-ableadviceanddiscussionsonthepresentresearch
ThanksarealsoextendedtoMr､ＹａｏａｎｄＭｒ・Maoftheheatandwaterbalancesfbrnonvegetatedsurfaces､ＪＵ４ｐｐＬＭ醜omL,36,1676-1695．

Kondo，Ｊ､，Ooka，Ｈ､，Matsushima，Ｄ・andSaigusa，Ｎ､，１９９４：Apredictionmodellbrthescasonal

lnstituteofSoilandWaterConservation，ＣＡＳ，

variationofevaporationfTomnon-vegetatedchina,whokindlyassistedwithfieldexpenments．
References

Abramopoulos,Ｒ,Rosenzweig,Ｃ・andChoudhury，
Ｂ・’１９８８：ImprovedgroundhydrologycalculationsfOrglobalclimatemodels（ＧＣＭs):Soilwatermovementandevapotranspiration・Ｊｋｄｊ‐
ｍａｔｅ，1,921-941.

groundsurfaces：（２）Experimentalverihcation・エル"・Sbc.Ｈ)）ｄＭＪﾜﾉﾋz〃此so肌7,386-392（inJapanesewithEnglishsummary)．
Shinoda，Ｍ曇，２００２：Dese7rα"ＣＪＣ！〃are・Seizando，Tokyo,169pp.（ｉｎJapanese)．
Takahashi,Ｈ､,Araki,Ｋ,Nagasawa,Ｔ､,Hongo,Ａ､，
Zhang,ＩａｎｄＬｉ,Ｓ・’２００２：Theevapotranspiration
ontheslopesduringspringintheLoessPlateau，ＡcademiaSinicaandMmistryofWaterResources，1993:川師oirq/YVMhwesZemI7MMeq/ＳｂｊＪα"α

ﾘﾄﾞﾉｍｃ７Ｃｂ"servatjO〃１８．ShaanxiScientificand

TechnologicalPress，Xian，144pp．（inChinesewithEnglishsummary)．
Budyco，Ｍ1.,1956:ＨｅａｒＭｍｚｃｅｑ/Ｔｈｅ比肋忽M6fzce・Gidrometeozidat,Leningrad,Z55pp、

Fukumoto，Ｍ，andHirota，Ｋ・'１９９４：TheeHectof
surfncesoilmoistureonheatbalanceatabaresoil

surfnce・エル"・ＳＤＣ.Ｈ)ﾉdmZルノtzZerReso肌７，３９３－

４０１（inJapanesewithEnglishsummary)．
Kawaguchi,Ｋ,,1991:A"､伽伽crjo"ZopedolQgy・
Yokendo,Tokyo,Z79pp（ｉｎJapanese)．
Kondo,Ｊ・’1994:MbteoMDg)）ｑ/､ｍｅｗα〃ｅｌＭｍ"ｍｅ肱川〃α"ｄＡｅａｔｂａＩα"ｃｅｑ/ＷｚｅＥｍｈ袖zJ肝ノizcaAsakuraShoten，Tokyo，348pp．（inJapa‐
nese)．

Kondo，Ｊ､，２０００:。〃oqphe加scie"Ｃｅ〃ｅａ７肋egmzMszJZ/tzce・UniversityofTokyoPress,Tokyo，
324ppIinJapanese)．

china：ＡｃａｓｅｏｆｓｏｕｔｈｆＨｃｅｄａｎｄｎｏｒｔｈｆｔＬｃed

slopesinAnsaicounty,ShaanxiProvince.』;。g油．
jWeomLHDklm！0,54,37-44(ｉｎJapanese)．
Tamura，Ｓ,，１９９０：Ｂａｓ比ｓ〃dieｓｏ〃ｇ花e"ｍｇｊ〃rｈｅ

ＬｏｅｓｓＰｌａＺｅａｚＪｍＣｈｉ"α・ReportofMonbusho

Grant-in-AidfbrScientiiicResearch（01102023）（ｉｎJapanese)．
UNEP,1997:肌γ〃α山so/・deserr城ａｒｍ"・Amold，London，１８２ｐｐ
Ｗａｎｇ,qandTakahashi,Ｈ・'1999:A1andsurface

waterdcficitmodelfbranaridandsemiaridregion：

ImpactofdesertificationonthewaterdeficitstatusintheLoessP1ateau，china・ＪＣﾉ加皿２，１２，２４４－257．

Ｘｕ,IandHaginoya,Ｓ､,２００１：Anestimationofheat
andwaterbalancesintheTibetanP1atcau、JB

MbreoMbSDc.』ｶﾌﾞ".,79,485-504．
Yang,Ｗ・andShao，Ｍ･’2000:８２"cZ〕ﾉｏ川ｈｅｓｏｊノｗαに（〃rheLoassPm花α".SciencePublisherPress，
Beijmg,305pp.（ｉｎChinese)．

Kondo，Ｊ・ａｎｄＸｕ，Ｊ・'１９９７：Seasonalvariationsin

中国黄土高原における熱収支と土壌水分
木村玲二＊・神近牧男＊・高山成＊・松岡延浩*＊・張興昌…

（二議鑿讓二`;憂所）
要約
中国黄土高原での熱収支と土壌水分特性を明らかにすに近い楡林の１９９９年の気象データを用い，熱収支と土るために，土壌３層モデルを用い，実際の裸地圃場に適壌水分の季節変化について考察した。年平均顕熱フラッ

用した（鳥取砂丘および中国陳西省神木県)。日蒸発量の観測値と計算値の差は０．１８ｍｍ（5Ｗ、-2）から０２１

クスは２３Ｗ、-2,年平均潜熱フラックスはｌ９Ｗｍ－２
Ｑ３９ｍｍｐｅｒｙｅａｒ)であった。冬季の第２層と３層の土ｍｍ（6Ｗ、-2)程度であった。神木地区の黄土は砂，シルト，粘土が適度に混ざり合っていることにより，保水性の効果と蒸発抑制効果の両面を併せ持っていた。神木壌水分は比較的高く維持されていた。

キーワード：黄土高原，土壌水分，熱収支－１１３－

ReturnARTICLE IN PRESS
Journal ofArid
Environments

Journal of Arid Environments 63 (2005) 439–457
www.elsevier.com/locate/jnlabr/yjare

Heat and water balances of the bare soil surface
and the potential distribution of vegetation in the
Loess Plateau, China
R. Kimuraa,, Y. Liub, N. Takayamaa, X. Zhangc,
M. Kamichikaa, N. MatsuokadaArid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680-0001, Japanb
Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku,
Nagoya 464-8601, Japanc
Institute of Soil and Water Conservation, CAS, Yangling, Shaanxi 712100, Chinad
Faculty of Horticulture, Chiba University, Matsudo 271-8510, Japan
Received 13 July 2004; accepted 2 March 2005
Available online 5 May 2005

Abstract
Spatial and temporal changes of heat and water balances are crucial to planting to combat
desertiﬁcation in the Loess Plateau of China. A three-layer soil model and meteorological datafrom 43 observatories were used to estimate the heat and water balances of the bare soil
surface. Results indicate that the annual mean of sensible heat ﬂux ranged from 13 to
36 W m2 and the latent heat ﬂux from 14 W m2 (179 mm yr1) to 40 W m2 (521 mm yr1).
Water retention and restriction of evaporation from the soil surface are affected by the yellow
loessial soil including medium loam, light loam and sandy loam, but not heavy loam. The
distribution of fractional extractable water and the existing vegetation have been compared toreveal the potential vegetation distribution leading to the aridity distribution in the plateau.
r 2005 Elsevier Ltd. All rights reserved.
Keywords: Aridity; Evaporation; Heat ﬂux; Soil water content; Three-layer soil model

Corresponding author. Tel.: +81 857 21 7031; fax: +81 857 29 6199.

E-mail address: rkimura@alrc.tottori-u.ac.jp (R. Kimura).
0140-1963/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jaridenv.2005.03.030

ARTICLE IN PRESS
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R. Kimura et al. / Journal of Arid Environments 63 (2005) 439–457

1. Introduction
The Loess Plateau of China (area: 62.68  104 km2; latitude: 34–401N andlongitude: 100–1151E) is located at an elevation ranging from 1000 to 1500 m above
mean sea level (Yang and Shao, 2000). The annual precipitation varies from 400 to
500 mm; most of which occurs during June–September months. The water deﬁcit
index (WDI) and the aridity index indicate that the plateau is located in a semi-arid
region (UNEP, 1997; Wang and Takahashi, 1999).
Since the 17th century, serious desertiﬁcation has occurred in the Loess Plateau
due to improper land use (like over-cultivation, over-grazing, over-deforestation,etc.) which caused critical soil erosion and water shortages in the lower reaches of the
Yellow River (He et al., 2003). It became a source area of Asian dust in the springwhen the soil surface is signiﬁcantly dry (In and Park, 2002).
It has been suggested that desertiﬁcation can be monitored using the relationships
among the types and amount of existing vegetation and the soil water content(Shinoda, 2002). Soil moisture is the most important factor that supports plant
production. It is necessary to understand the heat and water balances that generate
the soil water dynamics of the local area in order to obtain the beneﬁts from planting
to combat desertiﬁcation. For example, it can help in selecting appropriate drought
resistant vegetation. However, there are presently no comprehensive studies of theheat and water balances in the Loess Plateau area.
We developed a three-layer soil model to study the heat and water balances of thebare soil surface in the Loess Plateau (Kimura et al., 2004a, b). This model cansimulate temporal variations of water movement in liquid and vapor phases, the soil
water content in the respective soil layers, and the heat balance. In this paper, we
extend the study on heat and water balances of the bare soil surface by incorporating
the seasonal changes of the sensible and latent heat ﬂuxes and of the soil watercontent and the physical features of ﬁve typical soils of the plateau. We illustrate thepotential distribution of vegetation by overlapping the existing vegetation
distribution with that of the index (fractional extractable water remaining in theroot zone ye by Black, 1979) derived from the soil water content. Finally, we describe
the aridity distribution in the plateau.

2. The three-layer soil model
The soil model we developed divides the soil into three layers: 0–2, 2–22, and
22–70 cm (refer to Kimura et al., 2004a for details). The soil type was assumed to be
the same from the ground surface to the bottom. Given the initial value andboundary conditions, the model can estimate the time-series changes of water
movement in the liquid and vapor phases, the volumetric soil water content in therespective soil layers, and the heat balance.
The energy balance of the soil surface is expressed by (Kondo and Xu, 1997)
ð1  ref ÞS # þ L# ¼ sT 4s þ H þ lE þ G,

(1)

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R. Kimura et al. / Journal of Arid Environments 63 (2005) 439–457

H ¼ cp rC H UðT s  TÞ,

441

(2)

and
lE ¼ lrC H Ubfhqsat ðT s Þ  qg.

(3)
k

2

Here, ref is the albedo of the soil surface, S is the global solar radiation (W m ),and  is the emissivity of the soil surface (assumed as unity in this study). Lk
represents the downward longwave radiation (W m2), s is the Stefan–Boltzman
constant (5.67  108 W m2 K4), and Ts is the soil surface temperature (K). H
designates the sensible heat ﬂux (W m2), lE is the latent heat ﬂux (W m2), and G is
the soil heat ﬂux (W m2). cp corresponds to the speciﬁc heat of the air (J kg1 K1);
r is the density of the air (kg m3); CH is the bulk transfer coefﬁcient for sensible
heat; and U, T, and q denote the wind speed (m s1), temperature (K) and speciﬁc
humidity (kg kg1) at a given height z (m). qsat(Ts) represents the speciﬁc humidity atsaturation at temperature Ts (K), l is the latent heat (J kg1) of the evaporation ofwater, b corresponds to the evaporation efﬁciency by Kondo and Xu (1997), and h is
the relative humidity when the water vapor and liquid water are in equilibrium in thesmall soil pores (Philip, 1957).
The soil heat ﬂux is given by
Z 0:7dðcG rG T G Þ
dz.
(4)
G¼
dt
0
Here, cG is the speciﬁc heat of the soil (J kg1 K1), rG is the bulk density of thesoil (kg m3), TG is the soil temperature (1C), t is the time (s), and z is the depth (m).
The water and heat transfer within the soil can be expressed as follows (Kondo
and Xu, 1997):
qy
1 q
¼
ðQ þ Qvap Þ,qt
rw qz liq
Qliq ¼ rw Kqc
 rw K,
qz

(5)

(6)

where

K ¼ K sat

y
ysat

c
,

Qliq ðzbottom Þ ¼ rw K,

(7)
(8)



rD d½hqsat ðT G Þ
,
Fn
dz

(9)

qT G
1 qQh lE soil
¼

,
qt
cG r GcG rG qz

(10)

Qvap ¼
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R. Kimura et al. / Journal of Arid Environments 63 (2005) 439–457

442

where
Qh ¼ lG

qT G
.
qz

(11)

Here, y is the volumetric soil water content (m3 m3), rw is the water density( ¼ 1000 kg m3), Qliq signiﬁes the liquid water ﬂux (kg s1 m2), and Qvap represents
the water vapor ﬂux (kg m2 s1). K corresponds to the hydraulic conductivity(m s1), c is the soil water potential (m), Ksat indicates K at saturation, and c
represents the constant which changes with soil type. ysat denotes y at saturation,
Qliq(Zbottom) is the water ﬂux at the bottom (zbottom), and D corresponds to the
coefﬁcient of the molecular diffusion of water vapor in the air( ¼ 2.54  105 m2 s1). Fn is the transport route of water vapor in the soil (m), Qh
represents the heat ﬂux in the soil (W m2), lEsoil is the latent heat ﬂux within the soil
(W m2), and lG is the thermal conductivity of the soil (W m1 K1).
The data used in the calculation included sunshine duration, the daily mean air
temperature, the daily maximum and minimum air temperatures, the daily mean
wind speed, the daily mean speciﬁc humidity, and the daily amount of precipitation.
Diurnal variations of the meteorological data were required for the calculation. We
used the method of Kondo and Xu (1997) to estimate these variations. From thedaily mean air temperature, the daily maximum and minimum air temperatures, thedaily variation of air temperature can be expressed as a trigonometric function
having two temporal harmonics. The daily mean solar radiation ﬂux is obtained
from sunshine duration, and the daily variation of that can be described as the sumof trigonometric functions having four harmonics. The downward longwave
radiation is obtained from solar radiation and vapor pressure. The downward
longwave radiation, wind speed and speciﬁc humidity were assumed as constantduring the day. Rainfall data from the observatories are given as total daily amounts
and the temporal variation of precipitation intensity can be expressed as a functionof precipitation and time.
Ts can be found through successive approximations of Eq. (1) with the ﬂuxes H, lE
and G evaluated from Eqs. (2)–(4). The time step for the model running is 1 h.
The initial and boundary conditions for the water and thermal regimes were thesame as those of Kondo and Xu (1997). The liquid water movement between the ﬁrst
layer and the atmosphere and the water vapor movement at the bottom were notconsidered. No heat exchange was assumed at the bottom. The assumed values forthe initial conditions of y and TG were used at the start. The model ran for several
years under the same pattern of weather conditions until y and TG in each layer
approached a steady state. These results were then used as the initial conditions of yand TG.
It was observed that the model results of the soil water content and evaporationagreed well with those obtained by gravimetric sampling and lysimeter. Also theobserved results of the column experiments revealed that the model simulation
represented the qualitative differences in evaporation due to soil texture in the Loess
Plateau (Yang and Shao, 2000; Kimura et al., 2004a, b).

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443

3. Model parameterization
3.1. Soil types in the Loess Plateau
The typical soil types in the Loess Plateau include heavy loam, medium loam, light
loam, and sandy loam (Yang and Shao, 2000). Sand was also included in this study
since some parts of the Mu-Us desert cover the northwest portion of the plateau.
Table 1 indicates the particle size distribution of each soil type. The soil
characteristics differ depending on the distribution rate of the sand and clay.
Fig. 1a and b depict respectively, the distribution of soil and vegetation types andthe 43 weather stations (Table 2) involved in the plateau (He, 1989; Wang and
Takahashi, 1999; Yang and Shao, 2000).
3.2. Parameterization
This section provides a simple description of the parameterization of soil water
potential C, surface albedo ref, and evaporation efﬁciency b. Refer to Kimura et al.
(2004b) for a more detailed description.
3.2.1. Soil water potential
The soil water potential is given by Kondo and Xu (1997) as
c ¼ 4  104 expðayÞ 

102
1 þ ð102 =X Þ

yoysat ,

(12)

where


b

X ¼ csatyysat

c ¼ 0;

yXysat .

,

(13)

and
(14)

Here, a and b are constants which are speciﬁc to soil type and Csat is the soil water
potential at saturation. Table 3 lists the soil parameters and constants for each soil.
Table 1
Particle size distribution in the Loess Plateau
Soil texture

Heavy loam
Medium loam
Light loam
Sandy loam
Sand (Mu US)

Content (%)
40.05 mm0.01–0.05 mm

o0.01 mm

9
11
21
48
98

42
50
54
39
1

49
39
25
13
1

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R. Kimura et al. / Journal of Arid Environments 63 (2005) 439–457

Fig. 1. Distribution of (a) soil and (b) vegetation in the Loess Plateau.

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445

Table 2
Observatories used in this study
Station number Place name Lat. (degree) Long. (degree) Altitude (m) Rn (W m2) E (mm) ye
52797
52866
52876
52889
52895
52984
52996
53446
53463
53478
53513
53519
53529
53543
53564
53614
53646
53664
53705
53723
53738
53754
53764
53772
53787
53817
53821
53845
53853
53863
53868
53903
53915
53923
53942
53947
53959
53975
56080
56093
57034
57036
57071

Jingtai
XiningMingheLangzhou
Jingyuan
Lingxia
Huajialing
BaotouHuhehaote
Youyu
LingheHuinong
Ertuokeqi
Tongshen
HequYinchuan
YulingXinxianZhongning
Yanchi
Wuqi
ShuideLishi
Taiyuan
Yushe
GuyuanHuanxian
Yanan
XixianJiexiuLingfen
Xiji
Pingliang
Xifenzhen
LuochuanTongchuan
Yuncheng
YangchengHezhuoMinxian
WugongXian
Menjing

37.18
36.72
36.32
36.05
36.57
35.58
35.38
40.67
40.82
40
40.75
39.22
39.1
39.83
39.38
38.48
38.23
38.47
37.48
37.78
36.92
37.5
37.5
37.78
37.07
36
36.58
36.6
36.7
37.03
36.07
35.97
35.55
35.73
35.82
35.08
35.03
35.48
35
34.43
34.25
34.3
34.83

104.05101.75102.85103.88104.68103.18105109.85111.68112.45107.42106.77107.98109.98111.15106.22
109.7
111.13105.67107.4
108.17110.22111.1
112.55112.98106.27107.3
109.5
110.95111.92111.5
105.72106.67107.63109.5
109.07111.02112.4
102.9
104.02108.22108.93112.43

1631
2295
1814
1517
1398
1917
2451
1067
1063
1346
1039
1091
1380
1460
862
1111
1058
1013
1183
1348
1331
930
951
778
1041
1753
1256
959
1053
744
450
1917
1347
1421
1160
979
376
660
2910
2315
448
398
323

42
45
43
41
41
46
59
41
42
43
38
43
45
49
40
42
41
45
47
47
43
45
43
42
49
50
44
45
43
41
38
49
44
48
46
45
55
55
54
52
50
49
59

217
341
298
278
250
334
300
229
313
250
200
179
202
296
278
198
255
287
219
257
292
268
296
259
406
287
303
315
272
291
274
265
277
277
275
288
464
473
393
356
478
459
521

0.48
1.02
0.88
0.81
0.7
1.02
1.01
0.84
1.08
0.99
0.42
0.04
0.68
1.04
1.01
0.49
0.91
0.99
0.72
0.93
1.06
0.96
0.88
0.9
0.74
1.02
1.06
1.12
1
0.92
1.07
0.96
1.03
1.05
1.05
1.06
0.89
0.94
1.03
1.02
0.81
0.82
0.94

R n is the annual means of the net radiation, E the annual total evaporation, and ye the mean value of thefractional extractable water in the rainy season (June to September) in 1998

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446

Table 3
Soil parameters and constants of the respective soil

Heavy loam
Medium loam
Light loam
Sandy loam
Sand

ysat

yf

yw

yM

Csat

a

b

Ksat  105

c

fMax

0.476
0.451
0.435
0.434
0.36

0.31
0.25
0.21
0.19
0.12

0.16
0.10
0.09
0.05
0.035

0.24
0.18
0.15
0.12
0.08

0.04
0.04
0.04
0.04
0.2

35
60
65
110
160

4
5.5
4.5
4
1.5

0.1
0.5
0.9
2.4
9

10
11.2
10
10
8

0.02
0.008
0.008
0.008
0.01

Table 4
Constants for the albedo

Heavy loam
Medium loam
Light loam
Sandy loam
Sand

ymin

ymax

refminrefmax

0.05
0.11
0.11
0.07
0.03

0.2
0.25
0.25
0.21
0.1

0.09
0.16
0.16
0.17
0.16

0.27
0.27
0.27
0.27
0.22

The values of yf and yw in Table 3 are the ﬁeld capacity and wilting point where thepF value (pF ¼ log10 jC  100jðcmÞ) is 2 (C ¼ 1 m) and 4.2 (C ¼ 158 m). The
experimental results by Naruoka and Yamamoto (1992) and Yang and Shao (2000)
were used to determine constants a and b.
3.2.2. Albedo
The relationship between volumetric soil water content y and albedo ref for ﬁve
soil types were observed and reported (Kondo and Xu, 1997; Kimura et al., 2004b).
The albedo of each soil was deﬁned by the following equation in this study.
ref ¼ xy þ w;

ymin pypymax ,

(15)

where
ref min  ref max,
ymax  ymin

(16)

w ¼ ref max  xymin ,(17)

ref ¼ ref max ;yoymin ,(18)

ref ¼ ref min ;y4ymax .

(19)

x¼

and

Here, ymin and ymax are the volumetric soil water content at an inﬂection point ofref. refmin and refmax are the minimum and the maximum values of the albedo. These
constants are included in Table 4.

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447

3.2.3. Evaporation efficiency
Evaporation efﬁciency b is the ratio of bulk transfer coefﬁcient for latent heat tothat for sensible heat, and ranges from 0 to 1.0. b is determined using the diffusion
distance of water vapor F and the coefﬁcient of the molecular diffusion of water
vapor D ( ¼ 2.54  105 m2 s1) (Kondo and Xu, 1997).
b¼

1.
1 þ C H UðF =DÞ

(20)

F indicates the diffusion distance of water vapor from the liquid surface in the soil
where evaporation into the atmosphere occurs (Kondo and Xu, 1997).
Based on the observed data and the experimental results (Kondo and Xu, 1997;
Kimura et al., 2004b), the relationship between the volumetric soil water content y
and F were determined from the following equation.
 
f D
p y
; 0pyoysat .
(21)
F ¼ f A expðf B y3 Þ þ f C cos
2 ysatHere, fA, fB, fC, and fD are the constants which are speciﬁc to soil type.
Kimura et al. (2004b) parameterized the value of F, which varies with soil type, as  1:5
p 0:833y; y=yM X1,(22)
F ¼ 0:00032 cos
2
ysat
"


 #
0:1 y 3F ¼ f Max  exp 9000;
yM

y=yMo1,(23)

withy f þ yw.
(24)2Here, fMax is the maximum value of F, yf is the ﬁeld capacity, and yw is the wilting
point. The values of yM and fMax of each soil are provided in Table 3.
yM ¼

4. Results and discussion
4.1. Heat and water balances
The seasonal variations of the daily amount of precipitation and the daily meansof the sensible and latent heat ﬂuxes for all soil types are presented (Fig. 2). The
sensible and latent heat ﬂuxes were computed using Eqs. (2) and (3). As precipitation
at the Loess Plateau was statistically normal, we used the meteorological data from1998 for the calculation (Takayama et al., 2004).
The sensible heat ﬂux peak appeared in summer (June–July) in all locations. H
generally exhibited a sinusoidal pattern throughout the year in Yuling and
Ertuokeqi, where rainfall is less than in other locations. The latent heat ﬂux

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20
H
lE

10
0
0

Pr (mm)80
Xian(Heavy loam)00

Pr (mm)Tongchuan(Medium loam)
1030 60 90 120 150 180 210 240 270 300 330 360

20

Xian

60
40
20
0

30 60 90 120 150 180 210 240 270 300 330 360

20

100
80
60
40
20
0

0

0
0

Pr (mm)Yanan(Light loam)
10

0

0
0

Pr (mm)Yuling(Sandy loam)
10Ertuokeqi(Sand)
100030 60 90 120 150 180 210 240 270 300 330 360
DOY60

90 120 150 180 210 240 270 300 330 360

20
0

30

60

90 120 150 180 210 240 270 300 330 360

Yuling

60
40
20
0

80

20

30

40

0

30 60 90 120 150 180 210 240 270 300 330 360

90 120 150 180 210 240 270 300 330 360

Yanan

80

20

60

60

0

30 60 90 120 150 180 210 240 270 300 330 360

30

Tongchuan

80

Pr (mm)Energy (MJm-2day-1) Energy (MJm-2day-1) Energy (MJm-2day-1) Energy (MJm-2day-1) Energy (MJm-2day-1)

448

30

60

90 120 150 180 210 240 270 300 330 360

Ertuokeqi

60
40
20
0

0

30

60

90 120 150 180 210 240 270 300 330 360
DOY

Fig. 2. Seasonal changes of the daily amount of precipitation (mm) and the daily means of the sensible
and latent heat ﬂuxes (MJ m2 day1) in 1998.

approximately corresponded to the rainfall events. Especially in Xian, Tongchuan
and Yanan, there were many days when lE was greater than H because of a lot of
precipitation events. Steady evaporation after rainfall continued for a period in theheavy loam of Xian. In contrast, evaporation was restrained several days later in the
sandy loam and sand.
The spatial distributions of sensible and latent heat ﬂux annual means in the Loess
Plateau in 1998 are illustrated (Fig. 3). The contour lines were determined from
calculated results of 43 observatories using the nearest neighbor method. The annual
means of the sensible heat ﬂux ranged from 13 to 36 W m2. The sensible heat ﬂux
became signiﬁcant (36 W m2) around 351N and 1051E because of the relatively highaltitude (2451 m), which restrains evaporation due to the relatively lower
temperature. The sensible heat ﬂux was greater in the desert area near Yinchuan,
while the latent heat ﬂux annual mean ranged from 14 W m2 (179 mm yr1) to
40 W m2 (521 mm yr1). It increased from Xian to Taiyuan in the northeast in
particular. In contrast, the annual mean of the latent heat ﬂux gradually decreased
from Xian to Yinchuan in the northwest.

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449

Fig. 3. Spatial distribution of the annual means of the sensible and latent heat ﬂuxes (W m2) in the Loess
Plateau in 1998.

Fig. 4 depicts the spatial distribution of annual precipitation Pr and the drainage
PrE in the Loess Plateau in 1998. Pr ranged from 174 to 784 mm yr1, and PrE
from 0 to 346 mm yr1.
4.2. Soil water dynamics
Fig. 5 presents the seasonal variations of soil water in the respective layers. There
were some days when y1 in Xian and Tongchuan was close to the saturated soil watercontent ysat , due to the low inﬁltration rate (refer to saturated hydraulic conductivity

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R. Kimura et al. / Journal of Arid Environments 63 (2005) 439–457

Fig. 4. Spatial distribution of annual rainfall Pr (mm) and the drainage Pr–E (mm) in the Loess Plateau in
1998.

Ksat in Table 3). The decrease of soil water content in the ﬁrst layer after a rainfall
was slower in Xian, Tongchuan, and Yanan than at Yuling and Ertuokeqi since
water supplied to the ﬁrst layer lasted longer. However, the soil water content in theﬁrst layer after a rainfall in Yuling and Ertuokeqi decreased remarkably due to therupture of capillary continuity (Kimura et al., 2004a).
We next examined the soil water content in the second and third layers (y2 and y3 ).
The relatively steady evaporation in the heavy loam of Xian continued due tocapillary action, so the decrease in soil water content of the second and third layers
was greater than that at the other four locations. The soil water content of themedium loam, light loam, sandy loam, and sand remained relatively high in the

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θ (m3m-3)

θ 1(0 to 2 cm)

θ (m3m-3)

θ 3(22 to 70 cm)

Xian(Heavy loam)

0.4

0.2

0

0

30

60

90

120 150 180 210 240 270 300 330 360

Tongchuan(Mediumloam)

0.4

0.2

0

θ (m3m-3)

θ 2(2 to 22 cm)

451

0

0.3

30

60

90

120 150 180 210 240 270 300 330 360

Yanan(Light loam)

0.2
0.1
0

θ (m3m-3)

0
0.4

30

60

90

120 150 180 210 240 270 300 330 360

Yuling(Sandy loam)

0.2

0

0

30

60

90

120 150 180 210 240 270 300 330 360

θ (m3m-3)0.2
Ertuokeqi(Sand)

0.15
0.1
0.05
0

0

30

60

90

120 150 180 210 240 270 300 330 360

DOY
Fig. 5. Seasonal variations of the soil water content in the respective soil layers.

winter, when it rained little. The results of Kimura et al. (2004b) indicate that yellow
loessial soil, except for the heavy loam, affects both water retentivity and restrictionof evaporation from the soil surface due to the moderate mixture of sand, silt, andARTICLE IN PRESS
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452

clay. These soil types are superior to heavy loam from the standpoint of water
retention in the lower layer. ‘‘Farmer’s wisdom’’ is applied to cultivation practices inthe Loess Plateau to effectively utilize the features inherent in yellow loessial soil; soil
water maintained from the previous year is utilized for cultivation in the following
year.
4.3. Fractional extractable water
The extractable water in soil is ecologically signiﬁcant for the vegetation. Black(1979) expressed this critical aspect using the fractional extractable water remaining
in the root zone ye , as given byye ¼

y  yw.
y f  yw

(25)

Kimura and Kondo (1999) examined the relationship between ye and the leaf
transfer coefﬁcient in ﬁve soil types and two vegetation types (grass and sorghum).
Their result indicated that the leaf transfer coefﬁcient drastically decreases whenye o0:3. Black (1979) also suggested that the ratio of actual evapo-transpiration toequilibrium evapo-transpiration in Douglas ﬁr trees begins to decrease when ye o0:4.
Fig. 6 illustrates the seasonal change of ye in the respective areas. ye in Eq. (25) is theFig. 6. Seasonal changes of the fractional extractable water ye in Xian, Tongchuan, Yanan, Yuling, andErtuokeqi.

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453

mean value of the second and third layers. It must be noted that soil water changes
due to root water uptake were not considered. The rainy season in the plateau isfrom June to September, and the peak of ye appeared in this season. The annual
rainfall in Ertuokeqi is comparatively small (272 mm yr1), so ye is less than 0.5
except in the rainy season. ye was smaller in Xian than at the other locations(Tongchuan, Yanan, and Yuling) throughout the year despite the signiﬁcant amountof rainfall (601 mm yr1) since water loss by evaporation for heavy loam is greaterthan for other soils. In contrast, ye remained substantial in Tongchuan(Pr ¼ 634 mm yr1), Yanan (568 mm yr1), and Yuling (353 mm yr1), even in
winter, when it rains little. ye has occasionally exceeded 1.0 in the rainy season, andthe forest has been found around Tongchuan and Yanan. The annual precipitationin Yuling is less than that in Xian; however, the water retention of sandy loam issuperior to that of heavy loam due to its physical characteristics.
Variations between the annual rainfall and the mean value of ye (June–September)are presented (Fig. 7). The result in the drought year of 1999 is also provided for
Xian, Tongchuan, Yanan, Yuling, and Ertuokeqi. The dispersion between ye and theannual precipitation became small when Pr4300 mm, except for heavy loam. The
soil water content was close to the ﬁeld capacity when Pr4400 mm. However,the precipitation intensity controls ye when Pro300 mm. ye will differ, even withthe same amount of precipitation. These tendencies can be observed from symbols aand b for light loam and c and d for sandy loam in Fig. 7. Concentrated rainfall
tends to keep the ye high; 70 mm of rainfall per day occurred (symbol a). Most
rainfall evaporates and the soil water retentivity becomes low after a uniform rain
(symbol b).

1.2
Heavy loam
Medium loam

1

Light loam
Sandy loam

θe

0.8

c

Sand
Xian (1999)

0.6

y=0.6246*ln.x-3.1944
a

0.4

d

Yanan (1999)
Yuling (1999)
Ertuokeqi (1999)

y=(7.36*10-9*x3)+(-1.36*10-5*x2)+0.0085*x-0.729

0.2

b
0

Tongchuan (1999)

0

100

200

300

400

500

600

700

800

900

Pr (mmy-1)
Fig. 7. Relationship between ye and the annual rainfall.

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454

4.4. Classification of aridity
The degree of aridity is important in arid land studies. The representative arid
indices include the radiative dryness index (Budyco, 1956) and Ep/Pr (e.g., Penman,
1948; UNEP, 1997), where Ep is the potential evaporation and Pr is theprecipitation. They are based on the concept of heat and water balances and arelimited in classifying the degree of aridity. It is more realistic to monitor the seasonalvariation of the soil water content to determine the aridity. We used ye as the aridity
index. The dispersion between ye and the annual precipitation became small when
Pr4300 mm, except for the heavy loam, as seen in Fig. 7. However, the precipitation
intensity strongly inﬂuenced ye when Pro300 mm. A linear relation was found forthe heavy loam. While ye changes substantially with the precipitation intensity when
Pro300 mm, the relationship between the annual rainfall and ye can be represented
as below (solid line in Fig. 7).
ye ¼ 0:6246 lnðPrÞ  3:1944; Heavy loam; 567oPro784,(26)

ye ¼ ð7:36  109 Pr3 Þ þ ð1:36  105 Pr2 Þ þ 0:0085Pr  0:729,
Except for heavy loam;

180oPro634,

ð27Þ

These relationships were gleaned from data from 1998. However, there are large
inter-annual variations in the annual precipitation in semi-arid regions, such as theLoess Plateau. The mean value of the annual precipitation from 1980 to 2000 was
thus applied to the above equations to calculate ye . Fig. 8 depicts the spatial
distribution of ye estimated from the above equations. The classiﬁcation of the arid

ForestShrub
0.4 grass
TypicalShort grass
Others40

Latitude (deg)

39
38

0.4
0.6

0.6

1

1

0.8

37
0.8
36

1
1

0.8

1

35
102

103

104

105

106 107 108 109
Longitude (deg)

110

111

112

Fig. 8. Spatial distribution of ye using the mean value of the annual rainfall from 1980 to 2000 andEqs. (26) and (27), and comparison between the distribution of ye and the existing vegetation.

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455

Table 5
Ratio for respective vegetation with different distribution patterns of ye
Vegetation type

Forest (%)

Shrub (%)

Typical grass (%)

Short grass (%)

ye o0:4
0.4–0.6
0.6–0.8
0.8–1.0
ye 41:0

0
0
3
22
75

0
0
5
51
44

3
2
12
68
15

17
31
32
20
0

zones by UNEP (1997) could not detect these tendencies since the evaporation
intensity is related to the soil’s physical properties as well as climatic conditions.
A steady value of ye should not appear where Pro300 mm, i.e., when ye o0:8, as
described in Section 4.3. The growth of vegetation is unstable in such places. Table 5
includes the ratio for each vegetation with different distribution patterns of ye . These
were detected by overlapping the distribution of the existing vegetation (Fig. 1b) withthe distribution of ye (see Fig. 8). A large fraction of forest (97%) exists where
ye 40:8. In particular, 75% of the forest is present where ye 41:0. The remaining 3%
is present where the effect of orographic precipitation is strong.
Ninety-ﬁve percent of the shrub growth was found where ye 40:8. The remaining
5% could be found where the effect of orographic precipitation is strong, as with theforest.
Eighty-three percent of typical grass is present where ye 40:8. Forest and shrubs
would certainly have originally existed in such a place. The land use in this area
includes plant ﬁelds on terraces, a gully erosion ﬁeld, and a pasture ﬁeld.
Eighty percent of the short grass can be found where ye o0:8. The remaining 20%(0:8oye o1:0) is in the Mu-Us desert, which lies to the west of Yuling. This area isthe typical grassland where Mongolians engaged in stock-farming in ancient times.
Desertiﬁcation has progressed rapidly since the 1950s due to human activities (Inner
Mongolian Research Group, 1992; Xue, 1996; Bo and Long, 2002). While shrub andtypical grass could potentially grow in this region, desertiﬁcation continues due toimproper land use, such as over-grazing (Bo and Long, 2002). Wang and Takahashi(1999) analysed the impact of desertiﬁcation and suggested that this region should be
carefully conserved or protected. Numerical experiments indicate that desertiﬁcationin the Inner Mongolian grassland inﬂuences the regional climate, leading to reduced
evaporation, reduced rainfall, and increased surface temperature (Xue, 1996).
Based on these results, the aridity was classiﬁed asye X1:0;
0:8pye o1:0;

Forest area;
Shrub and typical grass area;

ye o0:8;

Short grass area:

The biomass is affected by the precipitation intensity in areas where ye o0:8.
Miyazaki et al. (2003) while reporting the heat balance, leaf area index, and biomassin central Mongolia (annual precipitation: 200 mm) observed that rainfall intensity

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R. Kimura et al. / Journal of Arid Environments 63 (2005) 439–457

at the beginning of summer (June to July) greatly inﬂuences vegetation activity.
Thus, maintaining sufﬁcient soil water content in the growth period (June to July)will greatly affect subsequent vegetation activity.
It is very difﬁcult to classify the aridity in the Loess Plateau, where ye o0:8, since
ye varies greatly with the rainfall intensity. Classiﬁcation based on the annual
precipitation is also difﬁcult for areas where ye o0:8. An evaluation method thatcombines the seasonal changes of ye with the biomass change monitored by remotesensing would be more effective for examining the aridity in such areas.

5. Conclusions
We studied the heat and water balances of bare soil and examined the physicalfeatures of ﬁve soil types in the Loess Plateau. We also explored the potential
distribution of vegetation and determined the aridity in the plateau.
We estimated the seasonal changes of the sensible and latent heat ﬂuxes using
meteorological data from 1998. The annual means of the sensible heat ﬂux ranged
from 13 to 36 W m2, while the latent heat ﬂux was from 14 W m2 (179 mm yr1) to
40 W m2 (521 mm yr1).
The relationship between the annual precipitation and annual evaporation
indicated that evaporation depended greatly both on the rainfall amount and on
the soil type and precipitation intensity. The results also indicated that both water
retention and restriction of evaporation from the soil surface were affected by yellow
loessial soil that included medium loam, light loam, and sandy loam, but not heavyloam.
The dispersion between the fractional extractable water ye and the annual
precipitation became small when Pr4300 mm, except for the heavy loam. The soil
water content was close to the ﬁeld capacity when Pr4400 mm. However,precipitation intensity inﬂuences ye when Pro300 mm, even with the same amountof precipitation. A linear relation was found between ye and Pr for the heavy loam.
We also explored the potential distribution of vegetation in the Loess Plateau bycomparing the distribution of ye and the present vegetation. A large fraction of forest(97%) existed where ye 40:8. Ninety-ﬁve percent of the shrub growth was foundwhere ye 40:8. Eighty-three percent of the typical grass was growing where ye 40:8.
Forest and shrubs are expected to grow in such areas. Vegetation growth is expected
to be unstable due to the dependence of ye on rainfall intensity in areas where
ye o0:8, where 80% of the short grass could be found.

Acknowledgements
The authors would like to express their gratitude to Dr. Shao and many
researchers of the Institute of Soil and Water Conservation, CAS, China, andstudents of the Arid Land Research Center, Tottori University, for their advice
and discussions regarding the present research. Thanks are also extended to Mr. Yao

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457

and Mr. Ma of the Institute of Soil and Water Conservation, CAS, China, whokindly assisted with the ﬁeld experiments. This research was supported by the 21stCentury COE Program of the Ministry of Education, Culture, Sports, Science andTechnology.
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Journal ofArid
Environments

Journal of Arid Environments 68 (2007) 53–65
www.elsevier.com/locate/jnlabr/yjare

Evapo-transpiration estimation over theriver basin of the Loess Plateau of China
based on remote sensing
R. Kimuraa,, L. Baib, J. Fanc, N. Takayamaa, O. HinokidanidaArid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680-0001, Japanb
Faculty of Horticulture, Chiba University, Matsudo 271-8510, Japanc
Institute of Soil and Water Conservation, CAS, Yangling, Shaanxi 712100, Chinad
Faculty of Engineering, Tottori University, Koyama, Tottori 680-8552, Japan

Received 12 October 2005; received in revised form 22 March 2006; accepted 23 March 2006
Available online 11 May 2006

Abstract
In northeastern Loess Plateau of China, wind and/or water erosion are severe, and the amount ofearth and sand pouring into the Yellow River is large. It is necessary to establish a land-use systemthat guarantees the water cycle in the river basin to prevent soil erosion and utilize land resources
continuously. We targeted the water balance, especially regarding evapo-transpiration (ET), over theriver basin in the northeastern Loess Plateau. For ET estimation, an algorithm referring to the
SEBAL method (a remote sensing surface energy balance algorithm for land) based on remotesensing was outlined and validated with the observation result over natural grassland. ET by land-use
difference and the spatial distribution of ET over the river basin were examined using the algorithm.
r 2006 Elsevier Ltd. All rights reserved.
Keywords: Evapo-transpiration; Grassland; Landsat 5; Remote-sensing; SEBAL

1. Introduction
Two-ﬁfths of the land area in China is threatened by wind or water soil erosion. Fivebillion tons of sediment are transported into the sea annually (Coen, 2003). In particular,
the earth and sand ﬂowing out from the Loess Plateau to the Yellow River has reached 1.6
Corresponding author. Tel.: +81 857 21 7031; fax: +81 857 29 6199.

E-mail address: rkimura@alrc.tottori-u.ac.jp (R. Kimura).
0140-1963/$ - see front matter r 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jaridenv.2006.03.029

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billion tons year1 in the downstream areas. The riverbed has increased by 10 cm every
year; in 1972, for the ﬁrst time in Chinese history, the Yellow River ran dry before reaching
the sea (He et al., 2003). Increased sediment loads have led to ﬂooding risks and threatened
the lives of many people. Asian dust caused by wind erosion in the spring, when the soil
surface is very dry, is also a serious environmental problem in China and in theneighboring areas of Mongolia, Korea, and Japan (In and Park, 2002).
In the northeastern Loess Plateau, erosion by both wind and water are severe, and theamount of sediment ﬂowing into the Yellow River is particularly large. To prevent soil
erosion and utilize land resources continuously, it is necessary to establish a land-use
system that guarantees the water cycle in the river basin. Recently, positive results wereobtained in the EROCHINA project entitled ‘‘A participatory approach for soil and water
conservation planning, integrating soil erosion modeling and land evaluation, to improve
the sustainability of land use on the Loess Plateau in Northern China’’ from the viewpointof the soil’s physical and chemical properties, runoff discharge, and soil erosion (e.g. Chenet al., 2003; Coen, 2003; Elsen et al., 2003; Messing et al., 2003; Stolte et al., 2003a b;).
However, no comprehensive studies of water balance have been conducted, especiallyregarding evapo-transpiration (ET) over the river basin of the Loess Plateau.
This study was conducted to clarify the quantitative formulation of ET over the river
basin using remote-sensing techniques. First, we outlined the algorithm for ET estimationreferring to the concept of Bastiaanssen et al. (1998a) and Tasumi (2003), and validated theestimation result with the observation ET over the grassland (Kimura et al., 2005a). Next,
ET was estimated by land-use differences using the algorithm, and the spatial distributionof ET over the river basin was examined.
2. Observation site and experimental method
The observation data was taken at an experimental station of the Liudaogou Basinlocated in Shenmu District, Shaanxi Province, China (381470 latitude and 1101210 longitude;
Fig. 1) from 5 June to 31 August 2004 (Kimura et al., 2005a). The basin area is 7 km2, andthe altitude is 1224 m. According to statistics from 1957 to 1989, the average annual
temperature was 8.4 1C (the coldest 9.7 1C in January and the warmest 23.7 1C in July),
with an average annual rainfall of 437 mm (minimum 109 mm, maximum 891 mm)(Academia Sinica and Ministry of Water Resources, 1993).
The soil texture at the experimental station was sandy loam (48% sand, 39% silt, and
13% clay). The station was covered by the dominant grass species, Stipa bungeana. Trin.
Plant height was 10–15 cm, and the leaf area index (LAI) was 0.7–1.0 during this period.
The root zone was within 34 cm. Fig. 1 depicts the land-use type in the Liudaogou Basin.
On the hillside, rain-fed cultivation (e.g. millet, soybean, mugwort, and potato) has been
conducted. Irrigated farmlands lie in the lowland areas (e.g. maize). On steep slopes withan inclination over 251, the planting of grass and/or shrub has been recommended by the
Chinese government since 1999. In 1993, most of the area was farmland, while grasslandand shrub sharply increased in 2004. Compared to 1993, shrub increased by 6% andgrassland increased by 22% in 2004. The percentage of farmland decreased from 73% to43% (Kimura et al., 2005a).
Meteorological data included air temperature (Valsala; HMP45A; instrumental height
150 cm), humidity (Vaisala; HMP45A; 150 cm), wind speed (Young; 03001; 220 cm),
precipitation (Davis Inst. Corp.; Rain Collector II), solar radiation, reﬂected solar

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Fig. 1. Location and vegetative classiﬁcation of the Loess Plateau and land-use classiﬁcation in the Liudaogou
Basin: I. Forest. II. Forest and typical grass. III. Short grass. IV. Desert and short grass. The dashed and dottedline is the borderline of the Loess Plateau. The bold line is the watershed divide of the Liudaogou Basin.

radiation, upward long-wave radiation, downward long-wave radiation (Kipp & Zonen;
CNR-1; 175 cm), soil water content at ten depths (Delta-T; ML2X; 6, 10, 18, 26, 34, 42, 50,
58, 66 and 100 cm), and soil temperatures at eight depths (Thermocouple; 1, 4, 10, 18, 26,
34, 42 and 50 cm). Meteorological data were sampled every minute with a datalogger(Cambell Scientiﬁc; CR10X), and averages were computed every hour. The soil watercontent was sampled at 1200 and 2400 BST.
We used the zero ﬂux plane (ZFP) method for observing ET over the grassland (Aryaet al., 1975; Scott, 1993). The ZFP separates the region of the soil where the water ﬂow(hydraulic gradient) is upward from that where the water ﬂow is downward. Accumulated
ET for the observation period can be calculated from the change of soil water content
above the ZFP (Kimura et al., 2005a). ET could not be observed during and following therainfall events, since the ZFP was near the surface. Accordingly, we interpolated for thedata deﬁcit period by using the Penman–Monteith equation and surface resistance, whichwere represented as a function of soil water content. The root mean squared error between
the observed and the calculated values of ET was 0.55 mm day1. This error was close to
the observational error, and the total simulated ET agreed with the observation during thegrowing period (Kimura et al., 2005a).
When applying ET estimation for the small river basin, a higher spatial resolution
satellite image (e.g. LANDSAT TM/ETM+and ASTER) is preferred. In this study,
LANDSAT5 TM images were used. Only three images could be obtained during theobservation period (on 16 June, 2 July, and 3 August 2004).

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3. Algorithm for ET estimation
The heat balance of the surface can be expressed by the following equations:
Rn ¼ H þ lE þ G,

(1)

Rn ¼ ð1  ref ÞS# þ L#  L" .

(2)
2

2

Here, Rn is the net radiation (W m ), H the sensible heat ﬂux (W m ), lE the latent
heat ﬂux (W m2), G the soil heat ﬂux (W m2), ref the surface albedo, Sk the global solar
radiation (W m2), Lk the downward long-wave radiation (W m2), and Lm the upward
long-wave radiation (W m2).
The values of H are given using the bulk equation by
H ¼ cp rC H UðT s  TÞ.

(3)
1

1

3

Here, cp is the speciﬁc heat of air (J kg K ), r the density of air (kg m ), CH the bulk
transfer coefﬁcient for sensible heat, U the wind speed (m s1), Ts the surface temperature(1C or K), and T the temperature (1C or K).
We referred to the SEBAL algorithm for estimating the sensible heat ﬂux H(Bastiaanssen et al., 1998a; Tasumi, 2003). SEBAL assumes that temperature difference
Ts–T (dT in the following) in Eq. (3) is linearly proportional to the surface temperature Ts.
dT can be developed using two extreme pixels, termed cold pixel and hot pixel. The cold
pixel was selected from the deep water surface, and it was assumed that H ¼ 0 (i.e.
dT ¼ 0). In the hot pixel, ET from a very dry bare soil surface was assumed to be zero.
Accordingly, sensible heat ﬂux was calculated as follows:
H ¼ Rn  G,


Ts
G¼
ð0:0038ref þ 0:0074ref 2 Þð1  0:98NDVI4 Þ Rn .
ref

(4)
(5)

Here, NDVI is the normalized differential vegetation index. Eq. (5) was cited from
Bastiaanssen (2000). Surface albedo ref and NDVI could be estimated from the reﬂectanceof each band (Bands 1, 2, 3, 4, 5, and 7 of LANDSAT5 TM), and the upward long-wave
radiation and Ts could be calculated from Band 6 (Bastiaanssen, 2000; Tasumi, 2003).
Thermal correction was not applied to Ts. Tasumi (2003) suggested that the error in Ts
estimation is absorbed at dT estimation when uncorrected Ts is used, and therefore a bias
does not appear in the ﬁnal ET estimation. For Sk and Lk, we used the observation data ofthe meteorological station. dT in the hot pixel was calculated by substituting CHU and H
into Eq. (3). CHU can be expressed using the atmospheric stability function (Dyer andHicks, 1970; Kondo et al., 1978) as shown below:
CHU ¼

u ¼

ku
,
ln ðz  d=zT Þ þ cH

kU
,ln ðz  d=z0 Þ þ cM

cM ¼ lnðx20 þ 1Þðx0 þ 1Þ2
þ 2ðtan1 x  tan1 x0 Þ : unstable;ðx2 þ 1Þðx þ 1Þ2

(6)

(7)

(8)

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cM ¼ 2:333 lncH ¼ 2 ln

1 þ 3z þ 10z3
: stable;1 þ 3z0 þ 10z30

yT þ 1: unstable;
yþ1

cH ¼ 400 ln

1 þ 0:0175z þ 0:005z2: stable;1 þ 0:0175zT þ 0:005z2T

57

(9)

(10)

(11)

x ¼ ð1  16zÞ1=4 ,(12)x0 ¼ ð1  16z0 Þ1=4 ,(13)

0:4gðz  dÞH,
cp rTu3(14)

0:4gz0 H,
cp rTu3

(15)

yT ¼ ð1  16zT Þ1=2 ,(16)y ¼ ð1  16zÞ1=2 ,(17)

0:4gzT H.
cp rTu3

(18)

z¼

z0 ¼

zT ¼

Here, k is the von Karman’s constant ( ¼ 0.4), u the friction velocity (m s1), z theobservational height of wind speed (m), d the zero plane displacement (m), zT theroughness length for sensible heat (m), CH the stability correction factor for sensible heat,z0 the roughness length for momentum (m), CM the stability correction factor for
momentum, and g the acceleration ( ¼ 9.8 m s2). The value of U at the weather station
was converted into the wind speed at 100 m considering the atmospheric stability (Eq. (7)),
assuming that friction velocity u was constant with height over the weather station. In
SEBAL, wind speed at 100 m above the land surface is assumed to be uniform over thesatellite image (Bastiaanssen, 2000).
d, z0, and zT were determined by the following equations (Allen et al., 1998):
2
H c,
3

(19)

z0 ¼ 0:123H c ,(20)zT ¼ 0:1z0 ,

(21)

d¼

where Hc is the plant height (m), calculated asH c ¼ 0:601LAI;(22)

LAI ¼  ln ½ð0:66  SAVIÞ=1:08=2:02,(23)

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58

where SAVI is the soil-adjusted vegetation index (Huete, 1988). These two equations were
derived from ﬁeld observation using the spectral irradiance instrument (Analytical Spectral
Device Inc., FieldSpec FR). Fig. 2 indicates the relationship among LAI, SAVI, and Hc. The
dotted line is the result of an equation by Bastiaanssen (1998). While the relationship was slightly
different from the observation, the sensitivity of ET estimation to these differences was small. To
ﬁnd the dT of the hot pixel, the loop of Eqs. (6)–(18) was repeated until convergence in CHU was
met. The sand dune area, located in the south-western part of the basin, was selected as the hot
pixel. The value of d and z0 were then assumed as zero and 0.01 m (Oke, 1978).

Observation

3

Fitting
Bastiaanssen(1998)

LAI

Maize

2

MilletShrub

SoybeanMugwort1
MilletSand dune

Italian millet
Potatoy=-ln((0.66-x)/1.08)/2.02

0
0

0.2

0.4
SAVI

0.6

0.8

3

Maize

Hc (m)

2

Shrub

1

Italian millet

MilletMilletSoybeanSand dune

y=0.601*x

PotatoMugwortNatural grass

0
0

1

2

3

LAI
Fig. 2. Relationships among leaf area index (LAI), soil-adjusted vegetation index (SAVI), and plant height (Hc).

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The sensible heat ﬂux H and CHU for the target pixel can also be calculated using theabove procedure and dT function. Latent heat ﬂux lE for the target pixel can be calculated
as the residual of Eq. (1). In the SEBAL, 24-h ET was estimated assuming a constantevaporative fraction during a day (Bastiaanssen, 2000), while Tasumi (2003) adopted
another fraction using the alfalfa reference ET. In this study, we used the fraction using areference crop ET (ET0) by Allen et al. (1998) as
ETF ¼

ETinst,ET0instET0inst ¼

0:408DðRn  GÞ þ gð37=TÞUfes  ea g,
D þ gð1 þ 0:34UÞ

(24)

(25)

where ETF is the fraction at the satellite image time, ETinst is estimated ET for the target
pixel at the satellite image time (mm h1), ET0inst is reference crop ET at the selected
weather station at the satellite image time (mm h1), D is the slope of the saturation vapor
pressure curve at air temperature T (K), g is the psychrometric constant (kPa 1C1), es is
the saturation vapor pressure at air temperature (kPa), and ea is the actual vapor pressure(kPa). Assuming that the ETF was equal to the 24-h ETF, the 24-h ET was estimated withthe equation below:
ETð24Þ ¼ ETF ET0ð24Þ ,ET0ð24Þ ¼

0:408DðRn  GÞ þ gð900=TÞUfes  ea g.
D þ gð1 þ 0:34UÞ

(26)
(27)

Here, ET(24) is the 24-h ET, and ET0(24) is the 24-h ET0 at the selected weather station.
4. Results and discussion
4.1. Validation of ET estimation
Fig. 3 depicts the seasonal variations of daily precipitation, 24-h ET, 24-h ET0, and ETF
over the grassland. Total precipitation was 338 mm during this period. ET0 was at its
maximum at 7 mm day1 in July, gradually decreasing thereafter. ET was approximately
1 mm day1, except for a comparatively large value after the rainfall events. This value wassomewhat small compared to that with crops. On many days, ETF was under 0.5. Zhao etal. (2004) estimated the seasonal change of ET from an alfalfa ﬁeld in Dingxi County ofGansu province on the Loess Plateau. Daily ET ranged from 2 to 3 mm day1 in thesummer season. The ET from the grassland was small compared with that from alfalfa.
Chikaarashi et al. (1979) reported that ET over grassland (mixed planting of Digitaria
adscendes HENR., Setaria vividis P. BEAUR. var. minor OHWI, Cuperus microiria STEUD.,
and Justica procumbens L. var. leucantha HONDA) growing in Japan was 1.6 times greaterthan evaporation from the soil surface during the growing period (1.24 times for a decade).
Kimura et al. (2005a) conﬁrmed that ET from grassland was about 1.5 times greater thanevaporation from the soil surface during the growing period, and annual ET was 1.24 times
that of annual evaporation. These results coincided with the ﬁndings of Chikaarashi et al.
(1979).

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60

Pr (mmday-1)

60
40
20
0
160

180

220

200

240

ET, ET0 (mmday-1)

DOY
10
8

ET(Obs.)ET0ET(Cal.)

6
4
2
0
180

160

200
DOY

220

240

1.5

ETF

Observation

Calculation

1
0.5
0
160

180

220

200

240

DOY
Fig. 3. Seasonal distributions of daily precipitation (Pr), daily evapo-transpiration (ET), daily reference evapotranspiration (ET0), and the fraction using a reference crop evapo-transpiration (ETF). The symbols represent thecalculated results using the algorithm. DOY refers to day of year.

Table 1
Estimated soil-adjusted vegetation index (SAVI), leaf area index (LAI), plant height (Hc), surface albedo (ref),normalized differential vegetation index (NDVI), and observed surface albedo over the grassland

16 June (DOY ¼ 168)
2 July (DOY ¼ 184)
3 August (DOY ¼ 216)

SAVI

LAI

Hc

ref

NDVI

ref (obs.)

0.13
0.11
0.18

0.35
0.33
0.40

0.20
0.20
0.24

0.19
0.20
0.19

0.14
0.16
0.25

0.16
0.20
0.17

DOY refers to day of year.

Table 1 presents the estimated result of SAVI, LAI, Hc, ref, NDVI, and observed ref ofgrassland. During this period, observed LAI ranged from 0.7 to 1.0. While the estimation
was slightly smaller than that of the observation, the effect of this difference on the ET
estimation was small in the algorithm. The estimated ref almost coincided with theobservation.

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Table 2Comparison of the observed and calculated values of the evapo-transpiration (mm day1)

16 June (DOY ¼ 168)
2 July (DOY ¼ 184)
3 August (DOY ¼ 216)

ET (obs.)

ET (ETF)

ET (EF)

1.4
1.7
3.1

1.2
1.9
3.0

1.2
1.9
3.3

ET (ETF) denotes the result using the reference crop evapo-transpiration (Eq. (24)), and ET (EF) the result using
the evaporative fraction by Bastiaanssen (2000) (Eq. (28)).

Fig. 3 illustrates the estimation result of 24-h ET and ETF over grassland. Table 2 also
reveals the estimation result for three days. Here, ET estimation using the evaporative
fraction by Bastiaanssen (2000) is also presented. The evaporative fraction is
EF ¼

ETinst,ðRn  GÞinst

(28)

where (RnG)inst is the observed value at the selected weather station at the satellite image
time. The root mean squared error between the observed ET and the estimated ET was
0.17 mm day1 using Eq. (24), whereas it was 0.20 mm day1 using Eq. (28). The result
using Eq. (24) was a little better than that of Eq. (28). According to the sensitivity analysis,
an error of 0.41 mm day1 existed in estimating ET with an observational error of 710%
in net radiation, 0.2 1C in air temperature, 0.5 m s1 in wind speed, and 72% in humidity.
The estimated error was within the meteorological observation error.
4.2. Estimating evapotranspiration over the Liudaogou Basin
Fig. 4 presents the spatial distribution of ET over the Liudaogou Basin on 2 July 2004
using the algorithm. ET was distributed from 0 to 5.5 mm day1. ET from lowland areas
beside the river channel was large, while that from the rain-fed farmland and the bare land
was small. Table 3 compares ET by land-use types for 3 days. ET from the farmland withirrigation was the largest, compared with that from other land cover. ET from rain-fed
farmland almost coincided with that of grassland. The farm production in this area is low,owing to the shortage of soil water, carbon, and nitrogen content in the soil (Bai et al.,2004). ET from shrubs was large, compared with that from grassland. Chikaarashi et al.
(1979) reported that ET over shrub (Amorpha fruticosa L.) growing in Japan was 1.8 times
greater than that from the grassland during the growing period. As Tables 3 and 4
demonstrate, ET from the shrub-land was 1.4 times that of grassland; thus, this result wascomparatively close to the ﬁndings of Chikaarashi et al. (1979). In this basin, Caragana
korshinskii (shrub type) has been artiﬁcially seeded to prevent soil erosion. However, it wasconsidered that the grassland was more appropriate from the point of water-use efﬁciency(WUE). Here, WUE was deﬁned as protection from erosion achieved per water consumed(Kimura et al., 2005a). According to ﬁeld experiment results in the river basin on the Loess
Plateau, 6750 kg ha1 soil was lost from the bare soil surface by soil erosion, and3750 kg ha1 soil was lost from farmland; in contrast, 93 kg ha1 was lost from natural
grassland and 60 kg ha1 from the forest (Smil, 1996). Comparing the amount of loss fromthe grassland with that from the forest does not reveal much difference between them: soARTICLE IN PRESS
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62

0
0.50
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5

Fig. 4. Spatial distribution of daily evapotranspiration over the Liudaogou Basin on 2 July 2004. The bold line is
the watershed divide of the basin.

Table 3Comparison of the evapo-transpiration by land-use difference for 3 days (mm day1)

Farmland (irrigation)
Farmland (rain-fed)
Shrub
Grassland

16 June (DOY ¼ 168)

2 July (DOY ¼ 184)

3 August (DOY ¼ 216)

Average

2.3
1.2
1.2
1.2

2.9
1.3
2.9
1.9

4.0
3.0
4.0
3.0

3.1
1.8
2.7
2.0

Table 4Comparison of evapo-transpiration by land-use difference during the observation period (mm)Total PrET0

ET (grassland)

ET (shrub)

ET (farmland with irrigation)

ET (rain-fed farmland)

338

346

127

171

197

114

WUE is comparatively high in the grassland. According to Kimura et al. (2005b), thearidity index in this area has potential for supporting grassland. To prevent further soil
erosion, it is very important to cover the bare land surface with such natural grassland.
Since 1984, alfalfa has been artiﬁcially seeded, but Stipa bungeana is the dominant species
in this basin (Bai et al., 2004).
Table 4 depicts ET by land-use difference during the observation period. ET ofgrassland is presented in Fig. 3. As for other land-use ET, we ﬁrst calculated from Table 3
how many times as large as the ET from grassland are the ET from farmland with

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irrigation, the ET from rain-fed farmland, and the ET from shrub. Next, we estimated theland-use ET by multiplying those values by ET from grassland in Table 4. We investigated
the surface runoff in the small basin of the Liudaogou (1 km2). When considering the land
use in this small basin, the amount of ET was 132 mm during the observation period in
Table 4. The residual 206 mm corresponded to runoff and inﬁltration. According to theobservation, the amount of surface runoff was 88 mm, so 26% of the rainfall was
distributed in the surface runoff. The sum of rain-fed farmland and shrub area accounted
for 66% of this small basin (shrub was 23%, and rain-fed farmland was 43%). It wasconsidered that turning these land covers into grassland was important for preventing soil
erosion and for water storage in the ground, considering the high WUE of grassland.
Hereafter, we will observe the other water balance components and evaluate water balance
in detail.
In SEBAL, seasonal ET estimation employs an assumption similar to that made for 24-h
ET estimation; namely, 24-h ETF for an image date can be applied to ETF for a certain
time period. Such an assumption was used in Table 4. However, this assumption does not
apply in the case of a long period between satellite images. If we can estimate seasonal ET
using the most recent satellite images possible, the accuracy of the amount of ET over theriver basin will improve during the target period.
5. Conclusions
An algorithm for estimating the ET referring to the SEBAL method was introduced andvalidated with observation over grassland. In this algorithm, the following calculation was
adopted:(1) d, z0, and zT were estimated using the simple equations by Allen et al. (1998). The
equations for LAI and Hc were derived from ﬁeld observation. LAI estimation using
the empirical equations by Bastiaanssen (1998) was slightly different from theobservation, but the effect of this difference on the ET estimation was small.
(2) For estimating the 24-h ET, we utilized the fraction using the ET0 by Allen et al.
(1998). The result was slightly better than that of the evaporative fraction (Eq. (28)).
(3) Thermal correction was not applied to the surface-temperature estimation. While someerror may occur in the Rn calculation due to the error in Lm, much of this error impact
is calibrated into the dT function at the cold and hot pixels. For general operational
purposes, uncorrected surface temperature is recommended (Tasumi, 2003).
The SEBAL method has been veriﬁed in many places, such as Turkey, China, and Egypt(e.g. Bastiaanssen et al., 1998b; Bastiaanssen, 2000; Chemin et al., 2004). However, few
references have been made to the natural grassland in semi-arid regions. Applicability tosuch natural vegetation was conﬁrmed in this study.
Acknowledgments
The authors would like to express their gratitude to Dr. Mingan Shao and their manycolleagues in China. This research was supported by the JSPS Core University Program
and the 21st Century COE Program of the Ministry of Education, Culture, Sports, Scienceand Technology.

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Kimura, R., Liu, Y., Takayama, N., Zhang, X., Kamichika, M., Matsuoka, N., 2005b. Heat and water balancesof the bare soil surface and the potential distribution of vegetation in the Loess Plateau, China. Journal of
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Journal of Arid Environments 70 (2007) 237–252

Journal ofArid
Environmentswww.elsevier.com/locate/jaridenv

Estimation of moisture availability over the
Liudaogou river basin of the Loess Plateau using new
indices with surface temperature
R. Kimura
Arid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680-0001, Japan
Received 6 June 2006; received in revised form 1 November 2006; accepted 15 December 2006
Available online 20 February 2007

Abstract
This study presents developments of indices for surface moisture condition estimations aiming at amore mechanistic approach compared to previous indices. Moisture availability (ma), calculated as
the ratio of actual evapotranspiration (ET) to reference evapotranspiration (ET0), and soil watercontent were estimated over a river basin on the Loess Plateau of China using two newly developed
indices. A modiﬁed temperature–vegetation dryness index (MTVDI) was calculated from satellitederived surface temperature, and aerodynamic minimum and maximum surface temperatures
estimated from meteorological data. MTVDI corresponded well to seasonal variations of ma over an
area of varied land use, and especially well in areas of grassland. A wet-edge index was derived fromthe relationship between MTVDI and the normalized differential vegetation index (NDVI), theMTVDI–NDVI triangle space, which is achieved by plotting MTVDI as a function of NDVI.
The wet-edge index showed the relationship to ma of various land surfaces and soil water contents in
the river basin. However, we concluded that a wider range of vegetation cover and soil moisture
content were needed to calculate a meaningful wet-edge index. These two indices have advantages
that can estimate surface moisture condition qualitatively. They can be used as aridity and/or
drought indices.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: Evapotranspiration; Reference evapotranspiration; Remote sensing; Surface temperature; Vegetationindex

Tel.: +81 857 21 7031; fax: +81 857 29 6199.

E-mail address: rkimura@alrc.tottori-u.ac.jp.
0140-1963/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jaridenv.2006.12.021

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1. Introduction
Many studies of the degree of aridity in arid or semi-arid regions are based on climatic
data. Aridity indices used include the radiative dryness index deﬁned by Budyco (1956) andthe Ep/Pr ratio (e.g., Penman, 1948; Thornthwaite and Wilm, 1944; UNEP, 1997), where
Ep is potential evaporation and Pr is precipitation. Wang and Takahashi (1999) pointed
out that these indices were developed from semi-empirical relationships between observed
evapotranspiration (ET) and climatic factors, and do not capture physical processes in thesoil–vegetation–atmosphere continuum (SVAC). However, these convenient indices arestill used in the classiﬁcation of aridity (Millennium Ecosystem Assessment, 2005; UNEP,
1997).
Many studies of land-surface aridity have used satellite data. The most often usedindices are the normalized differential vegetation index (NDVI; Rouse et al., 1974), thesoil-adjusted vegetation index (SAVI; Huete, 1988), and the modiﬁed SAVI (MSAVI; Qi
et al., 1994), all of which use remotely sensed data of visible and near-infrared wavelengths.
These methods have been used to estimate changes in vegetation, surface soil moisture, and
ET. Recently, the potential for the combined use of microwave and optical data as an aid
for crop management has been explored (Moran et al., 1997), and an algorithm combining
satellite data with meteorological data (e.g., SEBAL, a remote-sensing surface energybalance algorithm for land; Bastiaanssen et al., 1998) was developed and used to estimate
water balance at river-basin scale (Bastiaanssen, 2000; Kimura et al., 2007).
Of the many indices that use remotely sensed data, the relationship between surface
temperature (Ts) and vegetation indices (e.g., NDVI) has, in particular, been used toinvestigate the vegetation and moisture conditions of land surfaces (e.g., Luquet et al.,
2004; Moran et al., 1994; Nemani et al., 1993; Sandholt et al., 2002; Vidal and DevauxRos, 1995). These approaches can be grouped into three broad categories:(1) The Ts–NDVI relationship (e.g., Goward et al., 1985; Nemani and Running, 1989)
typically shows a strong negative relationship between surface temperature and thespectral vegetation index. The slope of the Ts–NDVI curve provides information on
moisture conditions, such as stomatal resistance and ET at the intrinsic surface (e.g.,
deciduous forest).
(2) The Ts–NDVI method was later extended to develop a soil-canopy water deﬁcit index(WDI) using information in the Ts–NDVI space (Moran et al., 1994); the WDI was
originally derived from the concept of crop water stress index (CWSI) introduced byJackson et al. (1981). This approach uses a ‘‘vegetation index–temperature (VIT)
trapezoid’’, and is based on the hypothesis that a trapezoidal shape will result from aplot of the difference between observed surface temperature and air temperature(TsTa) vs. vegetation index at the intrinsic surface (e.g., an alfalfa crop) if there is
sufﬁcient variation of fractional vegetation cover and surface water conditions. For
this approach, a range of vegetation cover and soil water content investigated is a
critical factor in determining the shape of the trapezoid, and thus demonstrating therelationship.
(3) Following Moran et al. (1994), Sandholt et al. (2002) developed a simpliﬁed land
surface dryness index (TVDI). In this approach, a scatterplot of remotely sensed
surface temperature and NDVI was assumed to take a triangular shape, and the TVDI
could be estimated from the dry and wet edges of the triangle (Fig. 1). The TVDI

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239

No evaporation
Dry Edge (Ts=a+b NDVI=Tsmax)

Ts

B
No transpirationC•Max
evaporation

Max transpirationA
Wet Edge
NDVI

Fig. 1. Ts–NDVI triangle space (after Sandholt et al., 2002). TVDI of point C can be estimated as AC/AB.

approach was applied by Sandholt et al. (2002) in northern Senegal to a 140  140 km
area of mixed land cover (which included dry grasslands, areas of shrubs, andcultivated areas) and related to soil moisture status.
The TVDI approach has an advantage over other indices (such as the Ts–NDVI
curve and the VIT trapezoid) in that it can be applied to mixed land surfaces, and derives
surface moisture status from satellite information only. However, since the determinationof the maximum and minimum surface temperature in the TVDI equation is comparatively
empirical, the TVDI approach has some limitations when applied on a small scale.
We developed a MTVDI and wet-edge index, a conceptually new index incorporating thegeneral principles of Jackson et al. (1981), Moran et al. (1994) and Sandholt et al. (2002), andwhich combines the use of meteorological data and remotely sensed satellite data. We applied
MTVDI and wet-edge index to the Liudaogou River basin on the Loess Plateau of China,
and validated our results using moisture availability (ma ¼ ET/ET0, where ET0 is thereference ET deﬁned by Allen et al., 1998) for different land surfaces and soil water contents.
2. Indices2.1. Temperature– vegetation dryness index
Fig. 1 illustrates the Ts–NDVI triangle space (Sandholt et al. 2002). A negative
relationship between Ts and NDVI is shown by the dry edge (the hypotenuse of thetriangle), which represents the upper limit of Ts. The left side of the triangle represents thebare soil relationship in the range from dry to wet. The wet edge was assumed to be ahorizontal line, as opposed to a sloping wet edge as in the trapezoid approach (Moranet al., 1994).
TVDI is deﬁned as
TVDI ¼T s  T s min,a þ b  NDVI  T s min(1)

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240

where Ts is the observed surface temperature (1C or K), T s min (the wet edge) is theminimum surface temperature within the triangle, and a and b are coefﬁcients deﬁning thedry edge, calculated as a linear ﬁt to data. The value of a +b  NDVI (the dry edge) can be
represented by T s max , where T s max is the maximum surface temperature for a particularvalue of NDVI. T s min and T s max are estimated as the mean minimum and maximum
surface temperatures over small intervals of NDVI. TVDI at point C (Fig. 1) can be
estimated as AC/AB.
Sandholt et al. (2002) suggested that the spatial variation of TVDI reﬂected variations ofsurface moisture on a ﬁne scale. Although this method offers useful information about
surface moisture, it has some limitations.

 In order to deﬁne the dry and wet edges, a large study area is needed so that surface
moisture status can be obtained for a wide range of vegetated surfaces. This is difﬁcult
to achieve in the small river basins typical of arid or semi-arid regions.
 Calculation of the dry and wet edges is comparatively empirical, because the size of thearea studied determines the shape of the triangle.
2.2. A new MTVDI
We deﬁned the MTVDI as follows (Fig. 2):
MTVDI ¼T s  T s min,
T s max  T s min(2)

where Ts is the observed surface temperature at a given pixel of remotely sensed data (1C orK), and T s min and T s max are minimum and maximum surface temperatures for thereference crop (Allen et al., 1998) simulated using energy balance equations andmeteorological data. The effects of varieties of physiological activities on Ts can beseparated from the effects of meteorological varieties by normalization.
The basic equation for the heat balance of a land surface isR#  G ¼ sT 4s þ H þ lE,

(3)

where
R# ¼ ð1  refÞS# þ L# ,
k

(4)
2

2

and R is the total incident radiation (W m ), G is the soil heat ﬂux (W m ), s is the
Stefan–Boltzmann constant (5.67  108 W m2 K4), H is the sensible heat ﬂux (W m2),
NDVI

Wet-edge index

Satellite Image
Landsat5
Ts
Tsmax

MTVDI

Meteorological
data
Tsmin
Fig. 2. Flowchart of the method for estimating the MTVDI and the wet-edge index.

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241

lE is the latent heat ﬂux (W m2), ref is the surface albedo, Sk is the global solar radiation(W m2), and Lk is the downward long-wave radiation (W m2).
The ﬂuxes H and lE can be expressed by the bulk transfer equations:
H ¼ cp rC H UðT s  TÞ(5)

lE ¼ lrC H Ub qsat ðT s Þ  q ,

(6)

and

where cp and r are the speciﬁc heat (J kg1 K1) and density (kg m3) of the air, CH is thebulk transfer coefﬁcient, U is the wind speed (m s1), T is the air temperature (1C), l is thelatent heat of vaporization (J kg1), b is the evapotranspiration efﬁciency (which has avalue of one at sufﬁcient wet condition and a value of zero at the sufﬁcient dry condition(ETE0)), qsat(Ts) is the speciﬁc humidity at saturation at Ts (kg kg1), and q is the speciﬁc
humidity (kg kg1). Substitution of Eqs. (5) and (6) into Eq. (3) yields the following
equation for Ts:R#  G  sT 4s  cp rC H UðT s  TÞ  lrC H Ub qsat ðT s Þ  q ¼ 0.
(7)In Eq. (7), it is assumed that the canopy and ground can be regarded as a single planesurface.
Allen et al. (1998) recommended the use of a reference ET (ET0) value to estimate actual
ET. ET0 can be derived from the original Penman–Monteith equation and a hypotheticalreference crop with an assumed crop height of 0.12 m, a ﬁxed surface resistance of 70 s m1,
and a surface albedo of 0.23. The aerodynamic resistance (ra) of a reference crop surface
can be deﬁned (Allen et al., 1998) and converted into CHU as follows:
ra ¼

208
1
.
¼
U
CHU

(8)

The soil heat ﬂux (G) as expressed by Allen et al. (1998), is:
G ¼ 0:1  Rn ,(9)

Rn ¼ ð1  refÞS # þ L#  sT 4s ,

(10)

2

where Rn is the net radiation (W m ). In this study, T s max and T s min in Eq. (2) are deﬁned
as Ts for a reference crop when b ¼ 0 and 1, respectively.
According to Jackson et al. (1981) and Moran et al. (1994), both the CWSI and the WDI
are related to the actual and potential ET rates of a surface, that is,lE
T s  T s max¼ 1  CWSI ¼,
T s min  T s max
lE p

(11)

ðT s  T a Þ  ðT s  T a ÞdrylE
¼ 1  WDI ¼,
ðT s  T a Þwet  ðT s  T a Þdry
lE p

(12)

where lE is the actual ET, lEp is the potential ET, Ta is the air temperature (1C or K), andthe wet and dry indices correspond to the left and right limits of the trapezoid. The
MTVDI concept is similar to those for CWSI and WDI (Eqs. (11) and (12)).
The wet edge index is derived from the MTVDI–NDVI triangle space (Fig. 2). The wetedge is estimated as the mean minimum MTVDI value over small intervals of NDVI.

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3. Errors and assumptions in the estimation of MTVDI
There may be some errors in the estimation of MTVDI from satellite data andmeteorological data: No atmospheric correction or surface emissivity correction was applied in the Ts
estimation. However, surface emissivity was given as 0.98 for respective land surfaces inthe estimation. It should be noted that surface emissivity is different from each land
surface. Generally, it is difﬁcult to get a meteorological data for atmospheric corrections
in arid or semi-arid regions. Atmospheric corrections and uncertainties in surface
emissivity associated with satellite-borne surface radiometric temperatures lead to
uncertainties of 1–3 1C in Ts (Campbell and Norman, 1998).
 It is assumed that the radiometric surface temperature (Ts of Eq. (2)) and aerodynamic
surface temperature (T s min and T s max of Eq. (2)) are the same in this study. However,they are not exactly the same according to Campbell and Norman (1998).
 According to the sensitivity analysis, there was an error of 0.41 mm d1in the estimationof ET. The error of 0.41 mm d1 corresponds to the energy level of 12 W m2 and an
aerodynamic surface temperature of 2 1C.
 The estimated error for radiometric surface temperature is almost the same as that for
aerodynamic surface temperature. It is assumed that these errors will be negated bynormalization in the calculation of MTVDI.
 The value of Ts can be affected by shade arising from orographic effects. Estimates ofT s min and T s max in Eq. (2) must take the effect of shade into account. Because most of
the slopes in our study area face either east or west, with an inclination of less than 251,
we assumed that shade had no effect on our MTVDI estimation. (In such a condition,
solar radiation in the slopes is almost same as that in the ﬂat surface (Tsuboi, 1990)).

4. Test site and analysis methods
4.1. Site description and experimental method
The study area was the Liudaogou River Basin located in Shenmu District, Shaanxi
Province, China (381470 N 1101210 E) (Fig. 3). The basin size is approximately 3  4 km.
According to statistics from 1957 to 1989, the average annual temperature is 8.4 1C (thecoldest 9.7 1C in January, the warmest 23.7 1C in July), with an average annual rainfall of
437 mm (minimum 109 mm, maximum 891 mm) (Academia Sinica and Ministry of Water
Resources, 1993). In this basin, both wind erosion and water erosion are severe, and theamount of earth and sand deposited in the Yellow River is considered to be a serious
problem (Academia Sinica and Ministry of Water Resources, 1993). Heavy rainfall in thesummer is the main cause of soil erosion in Shenmu. The aridity index used by UNEP
(1997) indicates that this district lies in a semi-arid region. According to the potential
distribution of vegetation determined by Kimura et al. (2005), the original vegetation typein this district would have been grassland.
Fig. 3 shows land use in the Liudaogou Basin. Production levels from rain-fed
cultivation on hillsides (e.g., millet, soybean, mugwort, and potato) are very low, owing toa shortage of soil water and the low carbon and nitrogen content in the soil. Soil water

5.49kmFig. 3. Location of the Loess Plateau and land-use classiﬁcation in the Liudaogou Basin. The bold line shows the boundary of the watershed.

OthersRain-fed cultivation (lowland)

Grass land

Shrub

Bareland (including sand dune)

Rain-fed cultivation (hillside)

6.15kmR. Kimura / Journal of Arid Environments 70 (2007) 237–252

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content is comparatively high in lowland areas, where maize is cultivated. Natural andintroduced grasses and shrubs grow on the steep slopes. The soil texture at theexperimental site is sandy loam (48% sand, 39% silt, and 13% clay). The site is covered by
the locally dominant grass species, Stipa bungeana Trin. Grass height at the time of ourstudy was 10–15 cm, and the leaf area index (LAI) was 0.7–1.0 during the growing season.
The root zone extended to a depth of 34 cm. Some seasonal variations of ET and surface
resistance are described by Kimura et al. (2006).
Meteorological data was recorded from June 2004 to September 2005 and included airtemperature (Vaisala; HMP45A; instrument height 150 cm); humidity (Vaisala; HMP45A;
150 cm); wind speed (Young; 03001; 220 cm); precipitation (Davis Inst. Corporation; Rain
Collector II); solar radiation, comprising reﬂected solar radiation, upward long-wave
radiation, and downward long-wave radiation (Kipp and Zonen; CNR-1; 175 cm); soil
water content at 10 depths (Delta-T; ML2X; 6, 10, 18, 26, 34, 42, 50, 58, 66 and 100 cm);and soil temperatures at eight depths (Thermocouple; 1, 4, 10, 18, 26, 34, 42 and 50 cm).
The meteorological sensors were sampled with a datalogger and multiplexor (Campbell
Scientiﬁc; CR10X and AM16/32) at 1-min intervals, and averages were computed hourly.
The soil water content was sampled daily at 1200 and 2400 BST. Soil-moisture sensors
were set horizontally, except for one that was installed vertically from the soil surface to adepth of 6 cm to provide an average soil moisture to that depth.
LANDSAT5 TM images were used to determine NDVI and Ts. The resolutions ofbands 1–5, and 7 are 30 m, and that of band 6 is 120 m. Seven images were obtained within
the meteorological observation period. Acquisition dates of the images are shown in Fig. 5.
4.2. Observed ET and estimation of ET and ET0
Observed ET and estimation of ET and ET0 were used in the calculation of ma that wasa validation data for indices (Eqs. (13) and (15)).
The zero ﬂux plane (ZFP) method was used to determine ET over the grassland (Arya etal., 1975; Scott, 1993). The ZFP method separates the region of the soil where water ﬂow(hydraulic gradient) is upward from that where water ﬂow is downward. Cumulative ET
for the observation period can be calculated from the change of soil water content above
the ZFP. We could not observe ET during and following rainfall events, because the ZFP
was then too near the surface. We, therefore, used the Penman–Monteith equation andsurface resistance (which is a function of soil water content) to interpolate and ﬁll thesegaps in the data. The root mean square error between the observed and the calculated
values of ET was 0.55 mm d1. This error was close to the observational error, and thetotal simulated ET agreed with that observed during the growing period (Kimura et al.,2006).
ET was not observed in cultivated areas (hillside and lowland) or shrub land. We used
the SEBAL algorithm (Bastiaanssen et al., 1998) to estimate ET in these areas. SEBAL
uses spectral radiances recorded by satellite sensors and meteorological data to determine
the heat balance components at land surfaces. Instantaneous ET is estimated as a residualof the heat balance. Daily ET can be computed from the evaporative fraction. SEBAL has
been veriﬁed in many places, including Turkey, China, and Egypt. Kimura et al. (2007)
applied SEBAL in natural grasslands in the Liudaogou Basin and found that the root
mean square error between the observed and estimated ET was 0.17 mm d1. The
estimated error was within the meteorological observational error.

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245This study used a reference crop ET (ET0) deﬁned by Allen et al. (1998) to examine themoisture availability (ma) over the several types of land surface. For areas other thangrassland, the following equations were used to estimate ma:ma ¼

ETinst,ET0 inst

ET0 inst ¼

0:408DðRn  GÞ þ gð37=TÞUðes  ea Þ,D þ gð1 þ 0:34UÞ

(13)

(14)

where ETinst is estimated ET using SEBAL for the target pixel at the time of capture of thesatellite image (mm h1), ET0 inst is reference crop ET at the selected weather station at thetime of capture of the satellite image (mm h1), D is the slope of the saturation vapor
pressure curve at air temperature (kPa 1C1), g represents the psychrometric constant(kPa 1C1), T and U are the air temperature (K) and wind speed (m s1) at 2 m height, es is
the saturation vapor pressure at air temperature (kPa), and ea is the actual vapor pressure(kPa).
In grassland areas, the following equations were used to estimate ma:
ma ¼

ETð24Þ
,ET0 ð24Þ

ET0 ð24Þ ¼

0:408DðRn  GÞ þ gð900=TÞUðes  ea Þ,D þ gð1 þ 0:34UÞ

(15)

(16)

where ET(24) is the 24-h observed ET using the ZFP method, and ET0 ð24Þ is the 24-h ET0 at
the selected weather station. According to Allen (2000), ma in Eq. (13) can be assumed tobe the same as that in Eq. (15); that is, ma is presumed to be constant during a single day.
5. Results and discussion
5.1. Application of MTVDI
The relationship of TVDI and MTVDI to ma (ET/ET0) over the Liudaogou Basin on 2
July 2004 was shown in Fig. 4. Although both indices show a good correspondence tomoisture availability, the coefﬁcient of determination (R2) for MTVDI and ma was higher
than that for TVDI. Same tendencies were recognized in all acquisition dates of the images.
A plot of MTVDI as a function of NDVI, also showing the wet edge, for each
LANDSAT TM image is shown in Fig. 5. The wet edge differs for each image; thesigniﬁcance of this is discussed in Section 5.2.
When there are varied land uses and conditions of variable surface moisture are
introduced, the triangle shapes in the MTVDI–NDVI space of Fig. 5 can be regarded as
equivalent to those of Sandholt et al. (2002), except for the dry winter season (23November 2004 in Fig. 5). However, the triangle may not be determined correctly fromsatellite data if the area of interest does not include a full range of land-surface conditions.
Therefore, calculation of the dry and wet edges in the TVDI equation was empirical.
However, the MTVDI equation was not affected by the triangle shape.
Fig. 6 presents the relationship between ma and MTVDI for all the land surfaces in the
study area together, and for grassland alone, using the seven LANDSAT TM images. With

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R. Kimura / Journal of Arid Environments 70 (2007) 237–252

Fig. 4. Relationship of TVDI and MTVDI to moisture availability (ma).

the exception of grassland areas, ET was estimated using the SEBAL algorithm, which hassome limitations: In the dry winter season, most of the vegetation in the basin died, so transpiration
would have been minimal. The algorithm does not allow for this.

 Two pixels within the area of interest are used to ﬁx boundary conditions for the energybalance in the SEBAL calculation. These are known as the ‘‘hot pixel’’ and the ‘‘cold

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247

Fig. 5. MTVDI–NDVI space for the 7 LANDSAT TM images used in this study. The wet edge is shown as astraight line, and was calculated as the mean minimum MTVDI over the NDVI intervals (Sandholt et al. 2002).

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pixel’’. The hot pixel is selected as a dry, bare area where ET is assumed to be zero. In
this study, an area of sand dunes near the basin boundary was used as the hot pixel.
This approach cannot be applied immediately after rainfall, because of the resulting
evaporation in the ‘‘hot pixel’’.
For this latter reason, fewer estimations of ET were possible in the cultivated areas andshrub lands (Fig. 6a). The MTVDI corresponded well to the seasonal variation of mafor the various land surfaces, especially for the grassland, and the coefﬁcient ofdetermination (R2) for MTVDI and ma (R2 ¼ 0.8746; Fig. 6b) was higher than that for
mixed land uses.
Grassland
Rainfed cultivation (lowland)
Rainfed cultivation (hillside)
Shrub landay=-1.0995x+0.827
R2=0.8454

ma

1

0.5

0
0

0.5
MTVDI

1

b
y=-0.8672x+0.7409

ma

1

R2=0.8746

0.5

0
0

0.5
MTVDI

1

Fig. 6. Relationship between moisture availability (ma) and MTVDI: (a) for different land surfaces and (b) for
grassland alone.

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249

5.2. Wet-edge index
The relationship between the wet edge and ma for the different land surfaces is shown in
Fig. 7. We found that ma tended to decrease with increases in the wet edge. Fig. 8 shows therelationships between ma and the fractional extractable water remaining in the root zone(ye), which can be represented by the equation:y  yw,(17)
ye ¼
y f  yw

Grassland1

Rainfed cultivation (lowland)
Rainfed cultivation (hillside)ma

Shrub land

0.5

0
-0.2

0

0.2
Wet edge

0.4

0.6

Fig. 7. Relationship between moisture availability (ma) and the wet-edge value for different land surfaces.

Grassland1

Rainfed cultivation (lowland)
Rainfed cultivation (hillside)ma

Shrub land

0.5

0

0

0.5
θe

1

Fig. 8. Relationship between moisture availability (ma) and the fractional extractable water remaining in the rootzone (ye) for different land surfaces.

ARTICLE IN PRESS
250

R. Kimura / Journal of Arid Environments 70 (2007) 237–252

1

ƒÆ
e

y=-0.6967x+0.6094
R2=0.8216

0.5

0
0

0.5
Wet edge

Fig. 9. Relationship between the fractional extractable water remaining in the root zone (ye) and the wet-edgevalue.

where y is the average volumetric soil water content in the root zone (m3 m3) (to a depthof 34 cm), yf is the ﬁeld capacity (0.19 m3 m3), and yw is the wilting point (0.05 m3 m3) ofvolumetric soil water content. Although the value of ye was observed in the grassland, ma
tended to increase with increases in ye. We assumed that ye in the grassland was
representative of the soil water content throughout the basin. However, ye should actually
be observed for each of the land surfaces.
Fig. 9 shows the relationship between the wet edge and ye. A good correspondence isevident (R2 ¼ 0.8216). These results suggest it might be possible to use the wet edge as anindex to approximate the surface moisture status over the entire river basin. However, thewet edge is greatly affected by variability in land-surface conditions; that is, the types anddistribution of vegetation cover and variability of soil moisture content. The size of thestudy area will be important when using the wet-edge index.
6. Conclusions
Two new indices (MTVDI and the wet-edge index) for estimating ma and soil watercontent were introduced and compared with observations over the Liudaogou Basin of the
Loess Plateau of China. MTVDI was determined from satellite-derived surface
temperature and aerodynamic minimum and maximum surface temperatures frommeteorological data. MTVDI was demonstrated to have a relationship to the seasonalchange of ma for mixed land surfaces, and especially for grassland areas (R2 ¼ 0.8746). The
wet-edge index was estimated from the MTVDI–NDVI triangle space. Wet-edge values
reﬂected the seasonal variation of ma in land surfaces of variable cover and for variations
in soil water content in grassland areas (R2 ¼ 0.8216). These indices have advantages thatcan estimate surface moisture condition such as ma qualitatively. They should be used as
the aridity and/or drought indices. It should be noted that such indices do not adequate toARTICLE IN PRESS
R. Kimura / Journal of Arid Environments 70 (2007) 237–252

251

the quantitative estimation for ma and/or ET. Additional work in other river basins isrequired to further test these indices.
There are some limitations to the use of MTVDI and the wet-edge index.
(1) These indices were signiﬁcantly affected by meteorological conditions when calculating
the aerodynamic surface temperature, so they are limited to small-scale uses. For
applying to large-scale uses, a detailed grid of meteorological data is needed.
(2) For estimating the wet edge, a range of vegetation cover and soil water content isneeded. The use of this index will be difﬁcult in areas where vegetation cover does not
greatly vary, and where there is limited water. Consequently, the wet-edge index iscomparatively empirical, as were past indices such as TVDI.
If in the future a detailed grid of meteorological data can be applied, these indices will be
useful tools for water management and for the detection of water stress of vegetation atriver-basin scale. However, any stress factors such as nutrient limitations, disease, insect
predation could reduce ma. Additional work is required to separate such stresses fromwater limitations.
Acknowledgements
The author expresses his gratitude to Dr. J. Fan and his many colleagues in China. This
research was supported by the JSPS Core University Program and the 21st Century COE
Program of the Ministry of Education, Culture, Sports, Science and Technology.
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ReturnJＨｇ血ＭｾreoMb（農業気象）６０(3)：173-189,2004

FUllPaper

ClimaticFeatureso症RainfmintlleLoeSsPIateauinChina

NaruTAKAYAMA*,ReijiKIMuRA*,MakioKAMIcHIKA*，
NobuhiroMATsuoKA*＊andXingchangZHANG**＊｜皇鱗議!i蝋lilillI醐蝋i

Yangling,Shaanxi，７１２１００China
Wehaveresearchedenvironmentalmonitoringtosupportanti-desertiiicationactivitiesmthe
LoessP1ateaulnthisthesis,thespatialdistribution,thevariance(stability)andthetrendofannual
precipitationwerestudiedlnaddition,thestabilityofprecipitationinthesummerrainyseasonwas

estimatedfromtheviewpointofseasonalfbaturesofprecipitation，ThesamplingdistributionofthemeanoftheannualprecipitationwasresampledbytheBootstrapmethodateachobservationpomt，
andthemeanoftheannualprecipitationwasestimatedbyintervalestimationThetimeseriestrend
oftheannualprecipitationwasanalyzedbyusingtheintervalestimationmeaｎｏｆｔｈｅａｎｎｕal
precipitation，Thestabilityofprecipitationinthesummerrainyseasonwasanalyzedfromthe
relationshipbetweentheprecipitationratioandtheprecipitationstabilityindexfbrtheperiodofhve
days・ＩｔｓｅｅｍｓｔｈａｔｔｈｅｍｅａｎｏｆａｎｎｕａｌｐｒｅｃipitationwasthelowestintheTengeriDesertandthe
WulanbuDesert・ButtheregionontheQuiUanmountainrangeatthewestsideofthosedesertsnear
Menyuanhadmuchprecipitation・Therainfallincreasedinlow-1atituderegions・Thevariationof
annualprecipitationwasthelargestinthenorthemMaowUsuDesert，thenortheasternWulanbu
Desert,ａｎｄaroundWugonglncontrast,thevariationsofannualprecipitationweresmallaround
Menyuan・WecouldnotseeatrendfbrannualprecipitationinthewholeoftheLoessP1ateaufrom
l980to2000・However,itseemsthatthereweresignificanttrendsatafewobservationpoints、We

proposedtherainyseasonstabilityindex(RSS，)}basedontherelationshipbetweentheprecipitation■

ratioPRPW)andtheprecipitationstabilitymdexESI(jbj)．Theanalysisofthefbatureofprecipitation
byusingRSS9)clarifiedthattherainyseasonisnotequallystablebetweentheeastsｉｄｅａndthewest
sideoftheLoessP1ateau,eveniftheannualprecipitationisａｔｔｈｅｓａｍｅｌｅｖｅＬ
Ｋｅｙｗｏｒｄｓ：Thefbaturesofprecipitation,Precipitationratio,Precipitationstabilityindex，TheLoessP1ateau,Rainyseasonstabilityindex．

1oesssoilisveryhighlyerodible,sosteepguUiesare

１．Introdulction

fbrmedintheLoessP1ateau、About１．６biUiontons

ＴｈｅＬｏｅｓｓＰ１ａｔｅａｕｉｎＣｈｉｎａｉｓａｓｅｍｉ－aridarea

locatedE100otoll5ｏａｎｄＮ３４ｏｔｏ４０ｏ・Theland-

scapeoftheLoessP1ateauisrepresentedbystairtypeheldinwhichevenmountaintopsarecultivated，
anderosionvalleys(gulnes)．Thisregionisthefront
lineofdesertiiicationinChina・About７０％ofthe

annualprecipitationisconcentratedinthesummer(chinaMeteorologicalAdministration，1994）ａｎｄPresentedattheAnnualMeetingofChugoku-Shikoku
BranchonNovember12,2003．
RcceivedonOctober20,2003．

AcceptedonApril30,2004.

ofsoilperyearHowoutfromtheYellowRiver(Niu
andLiu，1989）ａｎｄabout９０％ofthatoriginates
fromtheLoessP1ateau(NagasawaetaL，1993)．
ＴｈｅcurrentdesertificationofChina，asrepresentedbytheLoessP1ateau,istheresultofthefbrmofagricultureineachera,thescaleofeconomic
activity，andthenaturalrecoverabilitydeterminedbyprecipitationandtheecosystem・Desertiiication
hasthusrepeatedlyadvancedandretreatedｆｏｌｌｏｗ‐
ingacomplexpattern（ZhuetaZ，1989;Zhu,1990；
Yoshino,1997)．However,theChinesegovernment
istryingtopreventsoilerosionbyrestoringvegeta-－１７３－

JMg伽MbteoM．（農業気象）６０(3),２００４
tion、Therefbre,Ｃｕltivationonsteephillsandpastur‐inghavebeenfOrbiddenorrestricted

ltisextremelyimportanttostudytheclimaticfeatures，especiallyrainfall，inordertoprevent
desertificationbysuitableaDrbrestation・Wehave
doneresearchonenvironmentalmonitoringnecessarytosupportanti-desertificationactivitiesinthe
LoessP1ateaufrom2001incooperationwithInstituteofSoilandWaterConservation，theChinese

AcademyofScience・Inthisthesis,thespatialdistribution,thevariability（stability）andthetrendof
annualprecipitationwerestudied・Thestabilityof
precipitationmthｅｓｕｍｍｅｒｒａｍｙｓｅａｓｏｎａｔｅａｃｈｐｏｉｎｔｗａsestimatedfromtheviewpointofseasonalfeatureofprecipitation・
TheMann-Kendalltest(Kendall,1938),akindof
non-parametrictestmethod，isoftenusedfbrtrend
analysisofprecipitation(MolnarandRamirez,2001；
LazaroeML，2001）becauseofthedifYicuItyofcollectinglong-termdatatodefinetheprobability
densityfUnctionofprecipitation・However,accordingtodistributionofprecipitationoverapproximatelylOOyearｓａｔｓｉｘｏｆｐｏｉｎｔｓｉｎＪａｐａｎ（LiueML
1999)，thedistributionofannualprecipitation
becameasymmetricalwhenthedatawastotaledovershortterms・Inthisstudy，theLoessPIateauis
locatedinthesummerrainzoneinwhichcloud-burstshappensuddenly，sotheprobabilitydistribu-

甲UＤｍＰＩＭ

tionofprecipitationmaybeasymmetric・Moreover，
itisdiHiculttoexaminetheprobabiIitydistribution
ofprecipitationbasedonmanyobservationpoints
andlongperiodsofdatacollection・

Inthisstudy,theintervalestimationofthepopulationmeanofannualprecipitationwasperfbrmed
TheBootstrapmethod（Efron，1982）wasusedto
resamplethesampledistributionofthemeanof
annualprecipitationfbrtheintervalestimation・The
spatialdistributionandtimeseriestrendofannual
precipitationwereanalyzedusingtheestimatedｉｎ‐
tervalmeanofannualprecipitationasthestandard
valuelnaddition，theprecipitationratiointhe

periｏｄ(pRPM}andtheprecipitationstabilityindex(ERI(1,j)}weredefinedtoanalyzefeatureofseasonalrainfH1LThevariability(stability)ofprecipitationin
thesummerralnyseasonwasanalyzedfromthe
relationshipbetweenERP((,ｊ）ａｎｄESI(`,ｊ）ａｔｅａｃｈpoint．
2．Methods

2.1Studyarea

ThestudyareaextendsfromN33o35′toN41o34′

ａｎｄｆｒｏｍＥ９８ｏ１３′ｔｏＥ１１８ｏ９'．Thisareaisinland
andincludestheLoessP1ateau，Thelocationoftheobservationpointsandgeographica1featuresare
showninFi9.1．Thenameofeachobservationpoint
iｓｓｈｏｗｎｉｎＦｉｇ､Zandthecoordinatesofeachpoint

包りＨ【DUmUrUⅢ

Ｄ・Ｍ１

De3erq蕊溌:麺謹
孚罰ﾐﾖb農骸竃琴＝昌診

Ｆｉｇ．１．TopographicfeaturesintheLoessPlateau,ａｎｄlocationofeachobservationpoint、－１７４－

ＴａｋａｙａｍａｅｔａＬＲａｉｎｆｎＵｉｎｔｈｅＬｏessPIateau

TableLObservationpoint，ｓｎａｍｅｓ，pointcode，１atitude，longitudeandtheintervalmeanofannual

precipitationwith９５％ofconfidenceleveL

ObservationpointsCode

Taiyuan

Yushe

GuyuanPmInnxizm
Yanan
XixianJiexiuLingfenxiji
Pmgliang

XifmzEhen

LuochuanTongchuan
Yunchcng
Yangcheng
Maduo
Henan

Maqu
Ruoergal
HezhuoMinxian

Wugong
Ｘｉａｎ

ＬｕＩＲｈｉＭｅｎｊｍｇ１０２．８５

１０３．８８

１０４．６８９９．９８
１０３．１８
１０５．００１０８．５２
１０９.８５
１１１．６８
１１２．４５
１０７．４２
１０６．７７

１０７.９８

１０９．９８１１１．１５
１０６．２２
１０９．７０１１１．１３
１０５．６７
１０７．４０１０８．１７
１１０．２２１１１．１０１１２．５５

１１２．９８
１０６．２７１０７．３０１０９.５０１１０．９５

１１１．９２

１１１．５０１０５．７２
１０６.67107.63109.50109.07111.０２
１１２．４０９８．２２

１０１．６０１０２．０８

１０２．９７
１０２.９０１０４０２
１０８．２２

１０８．９３

１１１.0３
１１２．４３－１７５－●●●●●■●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●

Lishi

１０１．７５

８６３０５２５２１８４４２８５８４７７２４１２０５５２７５３１２１１１５０２１０３４６３５１６６６７８２９

Shuide100.６２

Ｐｕ0)（ｍ、）Ⅲ刑朋伽棚剛測川Ⅷ川柳川剛側柳川川別ⅢⅢⅢ川伽川耶帆側柳州伽俶棚州川柳柵棚切邪価伽伽側抑川皿棚測剛棚川畑価

Wuqi

104.05●●●の●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●◇●●

YanChi101.62

月0)（ｍ、）
１７４６３６１３０６９１５７３８０１６．９０４３５９１９１９９０３７０５６３１６８９８３１４１３４５１４３４

Zhongnlng

102.6795％intervalestimationoftheannualprecipitation
３５９１７８９７２８７３５３５５８１５３７０１５５１２７９１３８３６６８９０９２７６５３００９５７５６７８

XinXianLongitude

５９５９４０７０３５１７６５６２３２．２３５３３６４０８０７６９５６３８１６３６３３７３０２５１９１００８３
１４１２３３２２３４４１２３３１１２３３１３４１２４３４３４３３４４３４３４４５５４５３５５６４５５５５５Yuling●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●

YinchuHn

２８８７２２５７８８８７７２０５２０３８８３７８８２００８７０８００３７７５３２８３８２３０８０３５０５３
９３１２７３０５５５３５６８０７２１８３４２４４７９５５７００５６７００９５７８００４９７０５０４２３０８

lYuhehaote

Youyu
Lmghe
Huinong
Ertuokeqi
TongshenHequ７７７６６６６６５５５１００００９９９９８８８７７６７７７７６６６６７６５５５５５５５４４４３５４４４４４Baotou３３３３３３３３３３３４４４４４３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３３

Menyuan
Jingtai
Qiapuqia
XiningMingheLangzhouJmgyuanXinghai
Lingxia
Huajialing
Wulatehouqi

ｌ２３４５６７８９ｍｕｎ⑬Ⅱ週肥灯肥旧加Ⅲｎ羽刈羽妬刀泌汐刈弧ｎ羽糾萌茄刀犯羽判孤姐佃“伯柘仰州⑭別別皿兒

Wuwei

Position（degree）
T2titudeJMg血MbZeoM．（農業気象）６０(3),２００４
ａｒｅｓｈｏｗｎｉｎＴａｂｌｅｌ・Therearevariousdescriptions
oftheextentoftheLoessPlateau・Inthisthesis,theeastemborderoftheLoessP1ateauistheTaihang
Mountains，thewestemborderisRiyueMountain，

thesouthernborderistheGuanzhangBasininclud‐
ingXian(51),andthenorthemborderisthedesert
area，TheLoessP1ateauwasfbrmedbyparticles
transportedandaccumulatedbywindfromthe
desertzone(NaruseandOno,1997).Theseparticles
arecarriedbythenorthwestwindfromSiberianhigh(ＬｉｕｅＭＬ，1992)．TheTibetanP1ateauandthe
glacicroftheKonlunMountainsalsosupplyloess(SmalleyandKrinsley,1978;Fang,1995)．
Ｘｉａｎ（51)，locatedinthesoutheastpartofthestudyarea，ｉｓａｔｔｈｅｓｏｕｔｈｅｒｎｅｎｄｏｆｔｈｅＬｏｅｓｓ

Thequotientofannualprecipitationandobservationdayswascalculatedasthemeanofprecipitation
ofａｄａｙｆｂｒｅｖｅｒｙｙｅａｒｆｒｏｍｌ９６１ｔｏ２０００because
thedatamcludesfniledobservations・Themeanof

precipitationofadayatobservationpoint/fbreach
yearyisdesignatedasX(yJ)．ThemedianofdistributionofXW)isdesignatedasXmed・Ｗｈｅｎｔｈｅｎｕｍｂｅｒ
ｏｆｄａｔａｆｂｒｗｈｉｃｈＸ(Ｍ＞ＸｍｅｄｉｓＲ，Ｒｃａｎｂｅ
ａｐｐｒｏｘｉｍａｔｅｄｂｙｔｈｅｎｏｒｍａｌｄistributionwitha
meanE(R）andvariancePtzr(R）ifthenumberof
dataNexceeds25andthepopulationofX()ﾙﾉ）ishomogeneous．

Ｅ(R)=半（１）Ｍ､=牒言（２）Ｐ１atcauThesouthernsideoftheLoessP1ateauisa

plainwherewheatismoreactivelycultivated(ShaanxiMeasurementCommittee’1999)．Because
Xian(51)isintheplainzone,theobservationpoints
locatedinthesouthernportionoftheloesszonein
thestudyareaareTongcheng（19）andYangcheng(43)．VegetationbecomessparserandsparseraswegonorthfromXian(51）intheprovlnceofShaanxi、
AduneappearsintheMaowusuDesertnearYuiling(22),andWulatehouqi（12)innorthernmostpartof
thestudyareaislocatedinthedesertareacalledthelnnerMongoUanP1ateau(Liu,1998)．Amountainousregionof4,Ｏ００ｔｏ５,OOOmaltitudeisfbundinthe
southwestofWuwei(1),locatedonthewesternedge
oftheTengeriDesert、TheTaihangMountains(2,OOOto3,OOOmclass)arefbundalongtheeasternedgeinthestudyarea、ItseastsideistheNorth
ChinaP1amthatincludesBeijmg,anditswestsideis

Theteststatisticis

R-E(R）

ｚ＝ｲ元7715（３）

ThenuUhypothesisisrejectediflZ|≦2.58,whenthelevelofsignificanceisdeiinedasα＝0.01．The
Thomtestconfirmedthehomogeneityoftheprecip
itationdatafbralltheobservationpoints、
2.3Intervalestimationofmeanvalueofannual

precipitation

First,``theaverageannualprecipitation,,isde6ned
ateachobservationpoint・Thetrendofannual

theLoessPlateau、

precipitationwasexaminedbycomparing“theaverageannualprecipitation,,ａｎｄ“theannualprecipitationofeachycar.，,However,thereweremanyfniled
observationsduringl961tol979，sotheannual
precipitationcouldnotbecalculatedatmostobservationpomts・Thefmedobservationsarenotinter‐
polatedfrompresumedvalues・Onlymeasurements

2.2Rainfmdataandtestofhomogeneity

froml980to2000withfewfniledobservationsare

Theprecipitationdatausedinthisstudyisdaily
precipitationacquiredatthemeteorologicalobserva‐
tionstations（53points）locatedaroundtheYelIow
Riverfroｍｌ９６１ｔｏ２０００、Itisnecessarytonotethehomogeneityofmeasurementswhenwetreatlongtermmeteorologicaldata、Buildingsaroundthe
observationpointandachangeinthemeasunngusedmethodwillhavedegradedthehomogeneiｔｙｏｆｔｈｅｄａｔａ（Jones，1995)．ＴｈｅＴｈｏｍｔｅｓｔｗａｓｕｓｅｄｔｏ

ｃｈｅＣｋｔｈｅｈｏmogeneityofprecipitationdata、Ｔｈｅ
Ｔｈｏｍｔｅｓｔｉｓｕｓｅｄｔｏｃｈｅｃｋｔｈｅｈｏｍogeneityof
long-termmeteorologiｃａｌｄａｔａａｓｒｅｃｏｍｍｅｎｄｅｄｂｙ
ＷＭＯ,althoughitisanon-parametrictest(Peinado‐
Serna,1985)．

ThearithmeticmeanofannualprecipitationofZ1
yearsmaybeconsidｅｒｅｄａｓ“theavcrageannual
precipitation.，,However,inHuencescausedbyperiodicorabmptclimatechanges，adistributionof
atmosphericpressureeachyear,andtheweatherare
includedinannualprecipitation・Whenthedistribu‐
tionofannualprecipitationof21yearsisasymmet-

ric,thepointpredictionofthearithmetｉｃｍｅａｎｗｉＵ
ｂｅｎｏｔａｂｌｅｔｏｒｅｐｒｅsenｔ“theaverageannualprecip‐
itation.，,Inthisstudy,theintervalestimationofthe
populationmeanofannualprecipitationwascalcu-

1atedwithaconiidencecoefIicientof９５％・Itisthoughtthatthepopulationmeanofannualprecipi‐－１７６－

Takayamaeraﾉ.：RaiMallintheLoessPlateau

tationisintheestimatedsectionattheprobabilityof

2.4Analysisofchangeofannualprecipitation

９５％・Thclowerandupperboundsofthisestimated

The９５％confidenceintervalofthemeanof

sectionweredeiinedasPlf(7)ａｎｄＰＭ(j)（ｍ、),respec‐tively9Detailsofthepopulationtypeandvariancearenotknown,sotheparametricestimationmethod
cannotbeappliedTheintervalestimationofthe
populationmeanwasestimatedusingtheBootstrap
resamplemethod（Efron,1982)．Theintervalesti‐
mationofthepopulationmeancanbeestimatedwithoutassumingthenormautyofthepopulationby
usingthismethod・Thefbllowingwerethusemployed、
1）Theannualprecipitationinyear`γ，atobserva‐
tionpointγ，（ＰＷ)：ｍ、）ｗａｓｎｕｍｂｅｒｅｄａｓ
Ｐ(1980,ｊ)→0,Ｐ(1981,ｊ)→11..,Ｐ(zooo,ｊ)→20.
2）Twenty-onerandomnumbersfiPomOtｏ２０ｗｅｒｅ
ｍａｄｅ，ａｎｄｔｈｅｖａｌｕｅｏｆＰＷ）correspondingto
eachrandomnumberwaschosenasthesample

annualprecipitation(PlfO)≦POﾙﾉ)≦EC)）ateachob-distlPibution、

3）Thearithmeticmeanofannualprecipitation（Ｍ)wascalculatedfromthesampledistribution
choseninstep2)．

servationpointisdefinedastheaverageannualpre‐
cipitation・Yearswithlessprecipitationthanthe
confidenceinterval(ＰＷ)＜2,0)）aredefinedasyears
withonlyalittleprecipitation，Yearswithmore

precipitationthantheconfidenceinterval（ＰＭ＞RUG)）aredefinedasyearswithmuchprecipitation、Yearswithmuchprecipitationandyearswithonlya
littleprecipitationwereexaminedtodeterminethe
diDrerencescomparedwiththeaverageannualprecip‐
itationTheannualprecipitationdeviationindex
andtheannualprecipitationvariationindexare
dehnedinthefbllowingequations．
(Yearswithonlyalittleprecipitation）（４）
ＰＤＩｑｊ)＝Ｐ()ﾙﾉ)－町9）(Yearswithmuchprecipitation）

EDI(〕ﾙﾉ)＝Ｐ()ﾙﾉ)－巴Uo）(Otheryears）

ＰＤＩｗ)＝Ｏ

5）TheresampleddistributionofM1,..,Ｍiooooisa

nearlynormaldistribution,soPb9)andEJO)ｏｆＭｈ
ｗｅｒｅｏｂｔａｉｎｅｄｆｒｏｍｔｈｅ２・ｓａｎｄ９７．５percentiles
ofthisdistribution,respectively、
6）Ｂ０)ａｎｄＢＯ)ofeachobservationpointwases‐
timatedbythesameprocedures・Becausetherewerenodatafbr2001atTongcheng(19),theintervalestimationwasdonebyusingthe
precipitationdatafbrthe20yearsfroml980tol999，
Tongcheng(19)wasanimportantobservationpomt
locatedinthesouthendoftheloesszone,sothedata
fbrTongchengwasusedintheanalysis・Toexamine
theinHuencesoffaUedobservationin2000，ｔｈｅｄｉｆferencewasexaminedbetweenthesamplcdistributionofl980-2000andl980-1999fbrthepopulationmeanofannualprecipitationataUotherobscrvationpoints．Eachsampledistributionwas
resampledbyusingtheBootstrapmethodtotestthe
significanceofdi雌renceofthepopulationmean、As
aresult,onlytwoobservationpomts,atXinghai(9)andJingtai(3),ｈａｄａdiHerenceofpopulationmean
witha９５％levelofconlidence・However,thedi舵r‐encesinannualprecipitationwereｏｎｌｙ３ｔｏ５ｍｍ,so
wejudgedthatthereislittleproblemwiththe
Tongchengdata．

（６）〃M=芸;芸等:i子（７）4）ThearithmeticmeansofM2,..,MIoooowerecalcu‐

１atedbyrepeatmgprocedures2）ａｎｄ３)．

（５）

where,ｐＤＩＷ）（ｍ、）istheannualprecipitation
deviationindex,ＰＣＰ｡,ｊ）istheannualprecipitation
variationmdex,andthesubscriptsyandノreferto
yearandeachobservationpoint，scode,respectively・
ＰＤＩ(yJ)representsthediferencebetweenannualprecipitationandtheaverageannualprecipitation、Ｔｈe

normalizedPDI()しｊ)dividedbythemeanofPb9)ａｎｄＢＯ)ｉｓＰＣＫｊﾙﾉ)．PCJ'６%ｊ)isuscdtoexaminethetime
seriestrendofannualprCcipitationbetweenthe
points・ThenormalizedindexPCW'Ｗ)issimilarto
thatusedbyLiuandYin(2001)fbrspatialexamlna‐
tionofthetimechangeofraininsummermtheEast
TibetPlateau、

2.5AnalySisofpatternofSeasonalramfall

Theseasonalrainfallpatternismorelmportant
whenconsideringthewaterproblemmtheLoess
Plateau,althoughprecipitationisalsoimportant・In
thisstudy,ｗｅｒｅsearchedtheexpectationofseasonal
precipitationateachobservationpointandconsidercdthepatternofseasonalrainML
Oneyearisdividedinto73hve-dayperiodThemeanprecipitationP(】Ｗ)mtheperiodofratpointノ
froml980to2000wascalculatedasEｎＭ,andthe
standarddeviationwascalculatedasRd(,,〃The
coefYicientofvariationE3I(Mwascalculatedfrom－１７７－

JMg加MeZeoMb（農業気象）６０(3),２００４
P､(1,ｊ)ａｎｄＲｕｆ(Lかateachobservationpoint・
TheregionswherethemeansofannualprecipitationweretheleastweretheTengeridesertareathat

川仰=鶚（８）

HSI(『.ｊ)isdeiinedastheprecipitationstabUityindex，Theprecipitationstabilityindexisacoefficientof
variationofP(yﾚﾑﾉ)fbr20or21yearsateachobservationpoint・ESI(『,ｊ）meansthattherewasstable
rainfallif凪3J(ﾑﾉ)wassmaller・
Next，theprecipitationratiointheperioｄｗａｓ
ｄefinedasinthenextequation・

肌PM=鶚×､｡E105o30',andtheWulanbudesertthatextendsfrom
N39o30'ｔｏＮ４０ｏＯ′andE106o0'ｔｏＥ１０７ｏＯ'・Therewasmoreprecipitationinthesouthernareathaninthenorther、area・But,thereglonontheQuilian
mountainrangeatthewestsideofthosedesertsnear

Menyuan（２）（Ｎ37.30',Ｅ101.20'）ｈａｄｍｕｃｈｐｒｅ‐
cipitationThisspatialdistributionofannualprecip‐（９）

ｉｔａｔｉｏｎｗａｓｓｉｍｉｌａｒｔｏｔｈａｔｏｆｔｈｅＣｈinesecUmate

ＰＲＰＷ)istheprecipitationratiointhepeｒｉｏｄｏｆｔ(％)．Phm9)isthemeanoftheannualprecipitation
duringl980to2000atpoint八ｍｍ)．Theexpecta‐
tionandstabilityofseasonalrainfallateachobserva‐
tionpointwereestimatedfromtherelationbetween
PRPGbj）ａｎｄESI(ﾑﾉ)．
３．ResultsandDiscussion

3.1Spatialdistributionofanmualprecipitation
Themeanofthesampledistributionofannual

precipitationcalculatedbytheBootstrapresample
methodisshowninFi9.2．Thisvalueisahnostequal
tothemeanof21-yearannualprecipitationateachobservationpoint・Tablelpresentstheestimatedintervalmeanofannualprecipitation(Pb(7)andB9)｝

朋炉、【､｡【ⅢextendsfromN37o30′ｔｏＮ４０｡Ｏ′andE103oO′to

resourcemap（ChmaMeteorologicalAdministra‐tion’1994)．Moreover,ＬｉｕａｎｄＹｉｎ(2001）ｓｈｏｗｅｄ
ｔｈｅｒｅｉｓ３００ｍｍｔｏ３５０ｍｍｏｆｐｒｅcipitationaround
Menyuan(2)fromJunetoAugust,byusmgdetailed
surfaceobservationdataovertheEasternTibetan

P1atcaLMenyuan（２）islocatedintheQuilian
mountainrａｎｇｅｏｎｔｈｅｅａｓｔｅｄｇｅｏｆｔｈｅＴｉｂｅｔａn
P1ateauWuwei（１）isoneoftheleastprecipitation
regionsmthisstudyarea；thoughlocatedontheeast
sideofMenyuan(2),itislocatedonthewestedgeof
theTengeriDesert・Thereisalnountainousdistrictof4,000-5,000-meterheightbetweentwoobserva‐
tionpoints，ａｎｄitissuggestedthatthemfluenceof
topographicfeaturesfbrtheprevailingwinddominatestheprecipitationofthetwoobservationpoints．

ＤｐＵＩ

刑皿

Fig.２．SpatialdistributionofthemeanofannualprecipitationintheLoessPlateau（ｍ、)．
－１７８－

ＴａｋａｙａｍａｅｍＬ：RainfnllintheLoessPlateau

Actually，ｗｅｃａｎｓｅｅｔｈａｔｔｈｅｗｅｓｔｐｒｅｖａｉｌｉｎｇｗind
dominatesfromtheNorthAtlantictoEastAsia

along35oN，ｂｙｕｓｉｎｇｔｈｅｍｅａｎｌ９６１－１９９０ｓｕｍmer
600-hPawindhelds(LiuandYin,2001)．Menyuan(2)isundertheinHuenceofthiswestprevailing
windHowever，aroundMenyuan(2)，theeast
prevailingwinddominatedwhenthesummerprecipitationwaslessthaninanormalyear・Ｔｈａｔｉｓ，theorographicprecipitationoftheQuilianmountain
rangemightbeanimportantfactorofthefeatureof
spatialdistributionofprecipitationaroundMenyuan(2)．
３．２Trendofannualprecipitation
Eachobservationpointfbreachyearwasclassified
asayearwithonlyalittleprecipitation,ayearwith
muchprecipitation,ortheaverageannualprecipita‐
ｔｉｏｎｂｙｔｈｅmethoddetailedinparagraph２．４based
onRf0）ａｎｄ児`O)．PDIOLj）fbreachyearateachobservationpoｉｎｔｆｒｏｍｌ９８０ｔｏ２０００ａｒｅｓｈｏｗｎｉｎ

ＴａｂｌｅｚＩｎＴａｂｌｅ２,thepositivevaluesmdicateyears
withmuchprecipitation，negativevaluesindicate
yearswithonlyalittleprecipitation,－indicatethe
averagcannualprecipitation，ａｎｄａｎ“×，,indicatesnodata・First,weanalyzedthetendencyofannualprecip‐
itationinthewholestudyarea、Eachyearfroml980
toZOOOwasclassifiedbasedonthreeindexes，thenumberofobservationpointsclassifiedasyearswith
muchprecipitation,yearswithonlyalittleprecipita‐tion,ａｎｄｔｈｅｍｅａｎｏｆＥＤＩ(y・かＴｈｅｍｅａｎｏｆＰＤＩ(y,ｊ）
representsthetendencyofannualprecipitationover
thewholeofthestudyarea･Theothertwoindexes
representwhethertendencyofprecipitationfbrｅａｃｈｙｅａｒｉｓｏｖｅｒａｌａｒｇｅａｒｅａｏｒｏｖｅｒalocalarea、Ｔｈｅ
ｍｅａｎｏｆＥＤＩ｡ｊ）ateachobservationpoint，thenumberofpointswithmuchprecipitation（positive
points)，thenumberofpointswithonlyalittle
prccipitation（negativepoints)，andthediHbrence
betweenthemareｓｈｏｗｎｉｎＴａｂｌｅ３･However,thefiscalyearwaspermUtedinascendingorderbasedon
themeanofEDIO,ﾉ)．WeseefromTable3thatineightyearswhenprecipitationwastheleast（1997,
1986,1991,1999,1980,2000,1982,1987),themeanof座ＤＪαｊ）andthediDrerencebetweennegativeand
positivcvaluesweremuchlowerthaninotheryears・
Wetherefbreconsideredthattheprecipitationwas(1995,1993,1981,1994,1996,1989,1998),andwas
morethanstandardamounts（heavyprecipitation

years）ｉｎｓｉｘｙｅａｒｓ（1984,1992,1990,1988,1985,
1983)．
WeseefromTable3thattherehavebeennoyears
withmuchprecipitationsince1992．Thismeansthat

therainfallinthewholestudyareamaybedecreasingToexaminethis，weinvestigatedtheannual
variatiｏｎｉｎｔｈｅｍｅａｎｏｆＰＣｙＷ）atallobservation

points（PCP'0)}．Figure3(a）depictstheannual

variationofPCy(，)．ThetimeseriestrendofPC凡）
wasexaminedbylinearregression，althoughmost
observationpointsdidnothavedecreasingorlncrcasingtrendsofPCFCLj)withina95％confidence
level、However，ＰＣｙｍ）includedatimesenes
trendswitha95％coniidencelevelatLangzhou(7)，Henan（45）andWugong（50)，ａｎｄｗｉｔｈａ９９％
confidencelevelatYanan（33)．TheannualvariationsofPCyMatYanan,WugongandLangzhou
areshowninFigｓ３(b),（c）ａｎｄ(d)．Itseemsthat
thercwereadecreasingtrendsofrainfallatYanan(33),Wugong（50）ａｎｄＨｅｎａｎ(45)．Ontheother
hand,itseemsthattherewasanincreasmgtrendof
rainfnllatLangzhou(7)．Significanceoftrendwas
judgedbyanalysisofvarianceatthesefburpoints・
However,thecorrelationislowandtheinc1inationis

alsosmallinLangzhou(7)ａｎｄＨｅｎａｎ(45)．
3.3ReIationshipbetweentrendofannualprecipitationamdspatialdistributionofrainfm
lnthischapter，wediscusswhetherthetendency
ofannualprecipitationinfluencesthespatialdistributionofprecipitation・First，thespatialdistributionsofPCyW)ml997
andl986areshowninFigs4(a）ａｎｄ（b)．The
spatialdistributionofPCy(y,ﾉ）diHbredgreatly
thoughbothl997andl986wereyearswithonlya
littleprecipitation・ＰＣｙＷ)hadanegativedeviation
throughouttheentirestudyarea,anditwasespecial‐lylargearoundLinghe（16),locatedinthenorthern
MaowusuDesertandmthenortheasternWulanbu

Desertinl986・Incontrast，thedistlibutionof

PCPW）inl997hadapositivedeviationaround
Linghc,WulanbuDesertandBaotou（13),althoughthenegativedeviationwaslargerthaninl986inthe
southernpartofthestudyarea・Thespatialdistribu-

tionsofPCy(y,ﾉ)werealsoexaminedfbr2000,1999,

lessthanstandardamountsintheseeightyears(low1991,1987,1982,ａｎｄ1980,whichwereconsidered

precipitationyears)．Moreover,weassumedthatthe

lowprecipitationyears・However,ｗｅｃｏｕｌｄｎｏｔｆｉｎｄ
ａｔｙｐｉｃａｌｔｙｐｅｏｆｒａinfallspatialdistributioninlow

precipitationwasofstandardamountsin7years－１７９－

JMgl9jCMbZeomL（農業気象）６０(3),２００４
Table２．Theannualprecipitationdeviationindex（RDIW)｝
ObservationpointsCode

Yinchuan

ShmideLishi

Taiyuan

XifEmhen
Luochnmn

Tongchuan
Yuncheng
Yangcheng
Maduo

Henan

Maqu
Ruoergal
Wez2huo
Minxian

Wugong
Xian

IuIShiMenjing

Numberofnegativepoints
Numberofpositivepoints
Meanof脛、I()ﾙﾉ）

６８．５－４２．７

４２．７

－７２．５

７．２

－８８．６

－２５．６

４７．５

－４．２

－８．７

－９０．１

－３８．９

－５１．３

－１６．３

２３．９

－９．６

－３９．４

－8９．９

－７８．５

－４５．６

２６．５

５６．８

－２．４

－７１．９

－５１．８

－７０．４

２．８

１５７．６

－２１８

－７６．０

２１．０

－９３．７

７７．９

４６．１
－８．５

－７０．０

－５０．５

６０．０
￣

2３．３

５１．８
－２９．８

７１．５

８５．６１４４．０－４５．０－２９．８１５．１

－６８．２
5３．４

－１８．４

４５．３

１４
－９．７

－７４．９

－３３．４

６６．８

１０．１

－７．５

－２９．８

－５８．１

１０６．８

３２．７

－１１．４

２４．１
－５０．６

－６４．５

－８３．５

－１００．６

－７４．２
４．５

１２

－４６．８

－３８．２

－２９．４

３５．５

－１２３．０

２５．６

－０．２

１４．５

７０．４－４．５

－５４．１
209.9
６５．３

－１０６．９９１．１－１１２．０

６６．０

－４４．４

９．０

－３．０

－５．５１．８

１８．０

－２．１

８９．３

２７．１－８１．６

１２０．２－１２．８１８８．６

１０３．５

１１．３１１４．２

９３．５－９．１

－４８．７

６．６

１５６．９－５７．４－１３１．１－１３．３

６５．０－２９．６

３７．６
－２．２

1１．４

１２．１
９７．１

１１９．２

８１．０－１２２．２

２９．０

６８．６－１４３．４－１７．８

５１．８-72.9

－５３．０

１１．４

７５．７－５５．５

－７４．３

１５７．０
１７９．４
４５．５

９３．９－６０．２

１５１．１－１０９．９

１８．９

１８９．１
６９．９

３０．３

２４．７－８８．４

－３８．８

２４．０

１００．２－２１．１

－１６．８

１６．２

－－１１４．７

９．７－－１０８．３５３．６

８．７－１３６．０

１１５．３－－１３２．１

２４．１

２５．８－１７２．９

１３３．８－－１１３．１

４７．７

－６．７

９４．５

４４．４－１４．５
２９．２

１４８．７
１２８．４

１１．１

-３７．７
－

－３２．７

１４．０

－２６．７

１７２．３

3.0－３４．１

－１２４９

１０５．５

１７．４－３２．５－７５．８－３６．１６７．７

１１４．７

１１３．１

３１２．５

２９８．０

－－１０３．１

１０６．３－７．８２８３．４

４５．２－１５．２－１０３．６

９．５２０８．７

１７７．４－－１５４．３

１６０．１
８０．２
８２．７

－９８．４
－２４．２

５４．６

５．９
－２．４

－１１．４

２０．１

１４．２

－２０．０

３．５
1.6

－１３．５

４１．４

８．７

３．９

－３７．４

３８．８－６．０

－１７．６

６９．２
－１２１．４１７．７

８３．５
－１７．１

１１６．５－３３．３

41.5５６８－１９．９２１．６
１０３．１

4６．５
９６．１

－１３．５

3７．５-34.3

－５．６
－１５．７

－３４．２

－７６．６

２４７．１－７９．８

３８．９－１０７．８

９７．４
－３２．２

－１８．２

４．４

－４６．７

－２１．４

－４５９

－７０．１

６．４

４．１

０５

－４．７

２０．６

￣

－７２．９

３６．１

6８．６

３７．２

２０．０

３．０

－５７．４

５６．０

－２８．５

－２７．３

－５８．８

２９．７

－３２．１

－３３０

－８６．９

6９．９

－２２．３

－

3０．０

－７０．６

－７７．６

－２６．４－８．７

２３．２－１２４．９●●●●●●●●●●●

Lingfeｎｘｉｊｉ
Ｐｍｇliang－１０．４

６１８０９８０２１０８

Jiexiu１４．５

肥泌四ｎ７Ｎ叫印別ｎ個
１１１２１

Xixian

－１８．２

１

Y2nan

４６．０

１９８２４２円uanxizm

７．７

００７１６０

Guyuan

－６４．６

１刊司一冊

Yushc

－２０．７

４８０３０６

Wuqi

－１９．７

｜’

Y2nchi

４３．３

３１８１２

Xinxi2m

Zlhongnlng

５７．８

－２０．９

４６９８８０

Yuling１６．５－１５．０－４．８

９４１９８２５

Youyu
LingheHuinong
Ertuokeqi
Tongshen
Hequ

－３６．１

７２．０

一一一一一一一IIuhehaote

－３６－５

－５０．７

３１２９２５５Baotou－２４０

５９７６４４４

Menyuan
Jingtai
Qiapuqia
XiningMingheLangzhou
Jingyuan
Xinghai
Lingxia
Huajialing
Wulatehouqi

１２３４５６７８９，，，Ｂ叫喧肥Ⅳ旧四刈別迦羽別西妬刀朋ｎ列、犯羽料お茄刀犯羽判刎似佃糾妬妬幻組⑭卯則皿兒

Wuwei

Annualprecipitationdeviationl980(－）１９８１１９８２(－）1983(＋）1984(＋）1985(＋）1986(－）1987(－）1988(＋）

－４９．３
－１１．１
５１．５

１２０．９

３８．５
1４．８

－３４．６
７．９

－７４．９

１２１．０

８８．０

３２

1３

３３

５

1０

３

４１

２７

７

５

２７

８

２９

３２

３６

２

５

３４

７５．５

４４．３

５７．２

－６２．２

－３４．９

３３．１－１２０．６

－４２．０

２０．２

－３５．８

－１８０－

５５．７

ＴａｋａｙａｍａｅｒａＬ：RainMIintheLoessPlateau

fbreachyearateachobservationpoｉｎｔｆｒｏｍｌ９８０ｔｏ２０００．
index(P､ルノ):ｍ、）

19891990(＋）1991(－）1992(＋）１９９３１９９４１９９５19961997(－）19981999(－）2000(－）
－５１．５

1６９．１

6４．５

Ｚ３．２４０．３

－６４．２

3７．８

－５０．５

６．２

８．５

５８．３

－３２．２

－１６．１－９１．７

０．５

８．７１４８－９９

9８．３

－３６．７

－１３．６

８．３

５５．５

－１．６

－４７．０－２４．４

７９．９

－１４．２

－１０４．１

２４．７

２．２

１７．６

Ｌ６

－１００．２

９４．５

９０．４

－４７．６
９．４

４４．７４５．３

－４３．７

－３．６

３６．４

－１７．１

－４．２

－７８．９
－３．６

－１５．０

105.8

－８３．５

４３．６

－７．０

５０．６

－３１．７

７９．２

４９
５１．２

５．１
20.0

－６２．７－

４５．７５２．５－１．９－３１．０－１９．６
７６．６－

－３０．２

１８．５１１７．９－５８．４

７１．８３１．７０．０

２１．５

７０．２

－１０７．３

１９．３

－８．０

１８．３

－３６．１

１３０．４

－５３．５－

４．６７１３４１．７８．６－４６．７－７６．４－

－６７．８

－５５．０

１３６．８

－５１．０

－１４４．６－１０６．４－１０８．９３９．２

６１．７－１１．６

１１１．５

－４６．２

１１０．２

－９４．６

８８．３２２．７－７６．１３４．３

８９．７

－３３．６

３５．７－３．８－０．６１３．６

３７．０

－２８．７

１２８．０

－5７９
－１５．８

－４３．５

－３．７－１７．９
－１４．４

－５７．０

－７９．１

１２３．９

－３４．８

１７２．４

９．９
６．８

－５３．７

3.9

３．３

－６６．８

－６８．１－２０．２－８９．２－９３．４－５３．６－１６１．６－１３２．１－７．０－３１６

６．７１７．２－１４４．７１４．４－８９．９－４７．７－

－６５．１

３３．７

１．５３６．１－８１．１７８．９－７８．８－９１．６３．７－１１９．４－１２３．６－３３．０

－８１９

－４８．７

－１２３．０－２０．５

－９７．８

２．２

３６９－４６３７５．８－１１６．９５０．９

－７４．９

－１２．３

－１４．６

3０．４

１２．８－１４．８－１０１．５－137.1－１５７．７３０．７

０．７－２０．５１３５．２－１０１．６－

191.0

－２５．０

６６．７

８．１

－６８．３

－８７．３

－２．７

－３．９

６０．２－１９０．９－１２９．７－

－１０．０

６６．３

－－２０２．３１１０．３－１４１．５－３６．７－１３．９３０．３－１９１．５８５．４－２０．４－４１．１１８１．６－１９６．３８３．５

－４８．７

１５．２

３７．２

－７７．９

６４．８－２０．４

１７．２

－８３．６

－－１０１．７

－１８．０

０．３

－５５．１
５８．１
－９８．７

－５３．５

－４１．１

－５６．３

－１５６．６

４２．１

１７．９

－２８．０

１１０．９

－１１．５

－２６．９

１５．６
８０４９５

－２６３

１１．９

－５．６

－９６．５

－２．９

ｌｌｌｌｌ

３５．９

１９．８

×

－４９．２

－７７．０

蒟舛叫町刀

６１．６－２９．８

－９．３

１１１１Ｚ

－７３．９

－６６．５
－３３．３

3６．０

2２．１

－３．９

－１３１．３－－１２１．３－３７．１－１０５．３－－１３５．８

－９５．５
－９．６

－２．５

２７．７１９０．５

166.8

６０．０

７７．６

－８５．１

２１．２

－３６．１

１３８．３

５９．６

133.0４．１

４２．８-103.0

４１．５
－３．６

－１８．１５２．２

３６－８

－７５．１

－３０．２１２．１

８６．９４３．０

－１６．１
－１．２

－６０．２

１４７９

－６６．５

－８．６

－８３．８－

３３．４

１５．４－２５．１

－１７．５

－１２．０

－６３．０

１５．４１０．８

－４７．６

ｌｌｌｌ

－１６．３

－２０．３

－２３．２

－１３．９－

６６０５
２９Ｚ６●●●●●●●●●－１０．７

４７８２４７０３０

124.5

０７１２２７６５８
７２０６０６８６
１１１２

－１１．４

７７．７

１１１．０

－３６．９

－４１．１
－２９．８

－２０．７

６４．０

－１０４．３
－９７．４

－１８．０

６４．８

６８．５

4０．１

－１１．４

12.7－

－５１．２

￣

－１７．１

１５３．２

5５．９

３６．４

１７．４

－８４．７

－２８．４－３５．９－４４．５

４２．８６９９－７．１

１５９

－４．３

１２．５

－９６．２－

７５．２

１９．３

1１．４

－６．０

４１．７

９７．９

４２．２
5６．７

1８．５
95.0

5９．８

１８．０

７．３

－０．２

１０４．０

－４２．８

－５６．５
－１５．８
－８６．０

６．７

－４７．９

８４．７

－６４．６

－１１９．７１２．０

９６．５－１４８．０

－６．７

1０

８

３３

４

２０

５

１６

1２

４０

６

３０

１６

２６

１

２７

１２

２２

１７

２１

５

２２

８

４

３８．７

５０４

－５４３

４９２

－１５．１

－４３．７

－３８．６

－６５．７

－１９４．２

－７８．２
－４８．１

２６．１

９３．６
￣

8０．１

－２０．８

－１８１－

３３．２

－７６．４

120.6-147.3－
１２６．３-１０．７１３６．１

４０．０

３１

JMg血MbteomL（農業気象）６０(3),２００４
Table３．ＴｈｅｍｅａｎｏｆＰＤＩＯ,ｊ）ateachobservationpoint，thenumberofpointswith
muchprecipitation（Positivepoints)，ｔｈｅｎｕｍｂｅｒｏｆｐｏｉｎｔｓｗｉｔｈｏｎｌｙａｌｉｔｔle
precipitation(Negativepoints）andthevalueofNegativesubtractedfromPositive．
TendencyofrainfaUYearNcgativepointsPositivepomtsPositive-NegativeMeanof艮､I()ﾙﾉ）

1989
1998

1988
1985
1983

２７６４６９1990

３２２３３２

years

1992

０４８７３５Heavy
precipitation

１

1984

precipitationyeaIs
Figures5(a)ａｎｄ(b)presentthespatialdistribu‐

tionofPC7OIjj)inl985andl983・Forheavyprecipitationyears，reglonsofbothpositivedeviationｓｏｆ
ＰＣＪ'Mandnegativedeviationsexisted，andthe
diHerencewaslargerandmoreregionalthaninlow
precipitationyears．Ｍoreover，areaswithpositive
dcviationofPCγ()ﾙﾉ)weredistributedregionallyand
wereremarkable，soweconsideredthattherewere

someareaswithregionalintensiverainfaUinthecase
ofheavyprecipitationyears・
Figure6illustratesthespatialdistributionofthe
standarddeviatiｏｎｏｆＰＣｙ(yJ)anddepictsthedegree

ofvariationofannualprecipitationfroml980to

－４２．０

－３８．６

－３５．８
－３４．９

４０．０

、乃肥刀羽別

1996

－４３．７

１

years

1994

－６２．２
－５４．３

－２０．８

4４．３

’１１

Averageprecipitation

1981

－７６．４

１８４７９６６1993

６０３５２０６

1995’一一一一一一一

198７

５９２２７７５２

1982

３３３２２２２２

2000

７２７２１６２
１１２２２１２

1980

５２１８５４８５

years

1999

１２１１１

Low

precipitation

1991

０１３０２１３７
４４３３３３３２

1997

1986

－１５．１
２０．２

２６．１
３３．２

３８．７

４９．２

５０．４

５５．７
５７．２
７５．５

3.4SeasonalrainfallpatternintheLoessPIateau

Figure7presentstherelationshipbetweenERP(“）
andESIMatMenyuan（２）andLinghe（16)．
ＰＲＰ(“)indicatestheratioofprecipitationtoannual
precipitationintheperiodofLE3IW)indicatesthe
degreeofvariationofprecipitationfromtheannual
precipitationintheperiOdofLExplanatorynotesin
Fi９．７showedchangesfbrfiveperiods．’、winter，
therewasonlyalittlerainfallandtherainfallwas
unstable・However，stablerainfalloccurredfrom

spriｎｇｔｏｓｕｍｍｅｒ・RainfaUdecreasedandwasbecomingunstablefromautumntowinteragain・We
canrecognizefromFig､７thatthereis1ittleprecipi‐
tationandthefbrmofrainfnllisunstable,fromlate

2000Thevariationofannualprecipitationwasthe
largestfromthenorthernMaowusuDesert，thenortheasternWulanbuDesert,andaroundWugong

autumntoearlyspnngERP(【,ﾉ）increasedand
B3I(ﾑﾉ)decreasedfromspringtosummer,soitindi-(5DAnnualprecipitationexhibitcdbothadecreas‐

is，therelationshipbetweenPRPQj）ａｎｄESI(&ﾉ）mgtrendandremarkablevariationatWugong，InshowstypicalfbaturesofrainfallintheLoessP1ateau・so,thevariability(stability)ofprecipitationin
thesummerrainyseasonwasanalyzedfromthe
relationshipbetweenPRP(,,ﾉ）ａｎｄＥＳＩｑｊ）ateachcontrast，ｔｈｅｖｉｃｉｍｔｙｏｆＮ３７ｏ３０′Ｅ101.20′that
centersonMenyuan（２）andtheirsouthmountains
areaexhibitedsmallvariationsinannualprecipita-tion．

catesthetransitiontothestablerainfallseason，Ｔｈａｔobservationpoint・Toperfbrmthisanalysis，therelationshipbetweenPRP(1,ﾉ）ａｎｄRSI([.ｊ）ｗａｓ－１８２－

TakayamaetaLRainf1allintheLoessPlateau

ｍＬ

０．３０

当皀ｑ１ｏ

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▽

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ハ

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1９８２１９８４１９８６１９８８１９９０

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０４０
０３０

Year

鬘陞,。

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△

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Wugong(50）Ｆ0.51＊

▽

△

隻：

０２０

19921994199619982000

０

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1９８０

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０４０

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０５０

(b）

Yanan(33）r=0.61幹△△lヤャ､LLくい▽℃<1

1982198419861988199019921994199６１９９８２０００

Ｙｅａｒ

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LBngzhou(7)Ｆ0.46＊

仁〕

フ

(ア

－Ｏ４０
'９８０１９８２１９８４１９８６１９８８１９９０１９９２１９９４１９９６１９９８２０００１９８０１９８２１９８４１９８６１９８８１９９０１９９２１９９４１９９６１９９８２０００

Ｙｅａｒ

Ｙｅａｒ

Fig.３．（a)Timescriesofthemeanofcoe価cientofvariationofannualprecipitation（PC恥)}．（b),（c)，（d）TimesericsofthecoeHicientofvariationoftheannualprecipitation（PCγＷ)）atobservation

stations．（b）Ｙanan（33)，（c）Wugong（50）ａｎｄ（d）Langzhou(7)．Subscriptsyandノre化rtoyear
andeachobservationpoint,scode,respectively．

approximatedbyEq.（10)ateachobservationpoint・
Theseapproximatedlinesweredefinedasthelineof

onthewestsideoftwodeserts,andwassmallinits

featureswith９５％confidencelevelapproximationat

southernmountainrange，too・Thistendencywas
simUartothespatialdistributionofthevariationof
annualprecipitationindicatedinFi９６．
Ｐｈ‘O）ａｎｄＲ脳O）arenegativelycorrelatedinFi９．
１０．ItfbllowsfromFig，１０thattherainyseasonof
thereglonwhereannualprecipitationisalittleisalso
unstable・Wecouldclassifyallobservationpointsto
８groups，basedontheirgeographicalpositionand
thefEatureofrainfall；theresultsareshowninFigs・
ｇａｎｄｌＯ・Followingthisclassification，itbecame
clearthattherainyseasonisnotequallystableinthe

all53observationpoints・

eastandinthewestsidesoftheLoessPlateauevenif

rainM1feature、

ESI(Ｌｊ)=α(D1nlRP(４Ｊ)+RSS(7)（10）
Theconstantoftheequationwasdefinedasthe

rainyseasonstabnityindexatobservationpointノ(RSSの}・Figure8illustratesthelinesofrainfall

featuresatHuinong（17),Ruoergai(47)ａｎｄＹａｎａｎ(33)．RSS<i)becomessmallerifthesummerrainyseasonisstable,soitclariiiesthefeaturesofrainfall
ateachstation、WecouldobtainlinesofrainMl

Figure9showsthespatialdistributionofRSSO)mannualprecipitationisａｔｔｈｅｓａｍｅｌｅve１．

theLoessP1ateau,ａｎｄFiglOshowstherelationshipbetweenthemeanofannualprecipitation(PmO)）and
RSS9)．RSS①wasthelargestaroundtheTengeri
DesertandtheWulanbuDesert・Incontrast,ＲＳＳ9）
wassmallovertheQuiUanmountainrangelocated

４．ConcluSion

lnthisthesis，weresearchedthefeaturesofrain-

fall,toperfblmtheenvironmentalmonitoringnecessarytosupportanti-desertihcationactivitiesinthe－１８３－

JMgrjCMereomL（農業気象）６０(3),２００４

Ⅲ】⑨【､、、【】『ＪＵＵ【､。【I【□ＵＤｍｏ【U【億豊謬べ量二亀鑿ジ

剥孵EBI

dｕｕＨ

Fig.４．SpatialdistributionofPCy(】ﾙﾉ)ｉｎthecaseoflowprecipitationyears．（a）1997,（b）1986.

Desert(N38oto41o,E104otolO7｡)．Themean

LoessPlateau・First,thespatialdistribution,stabilityandtrendofthcannualprecipitationwerestudiedNext，theseasonalpatternofrainfallandthe

annualprccipitationincreasedinlow-1atitude

stabilityofrainfallinthesummerrainyseasonwere
studiedAsaresult,thefbllowingconclusionswere

onthewestsideoftwodeserts（aroundN37o30′
andE101o20'),hadmuchprecipitation．

obtained．

・Ｉｔｓｅｅｍｓｔｈａｔｔｈｅｍｅａｎａｎnualprecipitationisthe
lowestintheTengeriDesertandtheWulanbu

reglons,But,theQuilianmountainrange,1Ｏcated.Wecouldnotseeincreasingordecreasingtrends
inannualprecipitatiｏｎｉｎｔｈｅｗｈｏｌｅｏｆｔｈｅＬｏｅｓｓ
Ｐｌａｔｅａｕｆｒｏｍｌ９８０ｔｏ２０００ｉｎｔｈｉｓａｎａｌｙｓｉｓＨｏｗ‐－１８４－

9■､■-￣

Takayamae2aにRainfnllintheLoessPlateau■【MDpHMａ【】、'１，【

ｸﾞＵＩ】【冊電壱§鐙諺】■【､【０口【l【⑬【】【Fig.５．SpatialdistributionofPCyMinthecaseofheavyprecipitationyears．（a）1983,（b）1985.

ever,itseemsthattherewasasignilicanttrendin
annualprecipitationatafEwobservationpoints．

QuilianmountainrangeatwestoftheTengen

・Thevariationofannualprecipitationwasthe･WeproposedtheralnyseasonstabUityindex

Desert（Ｎ37.30',Ｅ101.20')．

largestfromthenorthernMaowusuDesert,north-（RSS⑪）basedontherelationshipbetweenthe

easternWulanbuDesert，andaroundWugong（50)．Incontrast,thevariationsofannualprecip‐

precipitationratiointheperiodPRPq,ｊ）andthe
precipitationstabilityindexE31(,,〃Itclarihedthattherainyseasonisnotequallystablefbrthe

itationweresmallaroundMenyuanlocatedonthe－１８５－

JMg加.MbZeomL（農業気象）６０(3),２００４】■Ｏ【ｙＤＵ■【】、,

DIDロ【lｌＤｏ

Fig.６．SpatialdistributionofthestandarddeviationofPCJ'Ｗ)froml980to2000

誉

RRHD(ｉＯＵｎ前。(16）蕊,沁三:…｡：ｓ〉国匹

0.0051.Ｏ１ＳＺＯＺ５３０３Ｓ４Ｄ４Ｓ５･Ｏ５ｓ５ｂＯ６５７ｎ７Ｓ８０｡

０５０５０５０５０５

1/1-3/16
3/17-5/25
5/26-8/３
８/4-10/12
10/13-12/3１

５４４３３２２１１０;鞠榊Ｍ､､,蝿.×．

●。×。◆、魑如麺却酋、酉、暉叩１ｍ鱈如率汕蛮却垣、暇皿

毒Menyuan(2)

ESC

墨｡：

Iiiiji言､三二二-二。

聯;鬘？;`塗i雲《;;異迭宮二｡x高言一０0.0051.01コユＯ２５３０３５４．０４５５０５５６．０６５７.Ｏ７ＳａＯ

２

３４

５６７

RRlKj)(%）

ＲＲ）7上り（%）
Fig.７．Relationshipbetweentheprecipitaｔｉｏｎ

ｒａｔｉｏｉｎｔｈｃｐｅｒｉｏｄｏｆＺ（HRP(【､ﾉ)）ａｎｄthe
precipitationstabilityindex（ESIM｝at

Fig.８．LinesofrainfnllfbaturesatHuinong（17)，
Ruoergai(47)ａｎｄＹａｎａｎ(33)．

Menyuan(2)andLinghe（16)．

－１８６－Takayamaetα此RainfnllintheLoessPIateau

uXU・【ⅢﾜuBlD・ｍＨ§鑑夢蚕箪戸宰票７

Fig.９．Spatialdistributionoftherainyseasonstabilityindex（RSSO)）intheLoessP1ateau．

。。

念啄堕匡

５４３２１０９８７６５４３２１０

ｚ２２２２２ｔｌｌｌ１１１ｌ１１

ｅａｓｔｓｉｄｅａｎｄｔｈｅｗｅｓｔｓｉｄｅｏｆｔｈｅＬｏｅssPlateau
Deveniftheannualprecipitationisatthesamelevel．
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MapsPublishingCompany,Beijing,pplO5-202（中国気象局，1994:中国気候資源地図集．中国地図

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出版社，北京，pplO5-ZO2)．

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MeanoftheannuaIprecipitation(m､）Ｆｉｇ．１０．Relationshipbetweenthemeanofannual

precipitation（E"(7)）andtheramyseason

stabilitymdex（RSS(7)}・ＴｈｅeXplanatorynotes
fbrthegroupcolrespondtotheexplanatory
notesinFig.９．

Efron，Ｂ､，1982:Z7iemckk"娘Ｚｈｅ６ＭＭＺｐα"αorhe77eSZzmpJi"ｇｐ！α"s・SocietyfbrlndustrialandAppliedMathematics,Philadelphia,９２ｐｐ
Ｆａｎｇ,ＸＭ.，１９９５：Theoriginandprovenanceofthe
Malanloessalongtheeasternmarginofthe
Qinghai-Xizang（Tibetan）P1ateauanditsadjacentarea・Ｓｂｉｄｉｉ"ａ（B）,25,426-432．

Jones,Ｐ.，１９９５：Theinstrumentalrecord：itsaccura-

cyanduseinattemptstoidentifythe`CO2signaL，Ｉｎｄ"α枕ｊＳｑ/･c伽ａＺｅＩｍａＭｊ奴app/ｉＭｍｑ/・
伽rimＣａ/花c伽qzJes（eds・byVonStorch,Ｈ・and
Navarra,Ａ､).Springer，Berlin,pp54-75・
Kendal1,Ｍ.０．，１９３８：Anewmeasureofrankcorrelation・Bjomer〃k230,81-93…

Lazaro,Ｒ,，Rodrigo,Ｆ､Ｓ､，Gutierrez,Ｌ､，Donnngo，
Ｆ・andPuigdefabregas,Ｊ・'２００１：Analysisofa30-

yearrainM1record（1967-1997）insemi-aridSE
SpainfOrimplicationsonvegetation・エ且γjﾋﾌﾞＥ"Ｗ‐'ｗ2.,48,373-395．

Liu,Ｇ､,Ishikawa,Ｓ､,Nagasawa,Ｓ・andMaruyama，
Ｔ・’１９９９：Studyonprobabilitydensityfimction
fOrmaximumamountofrainfalliｎａｙｅａｒ・エル"．
－１８７－

mdg血MbZeo肌（農業気象）６０(3),２００４
SDC.Ｈ)）｡、ﾉＷ'tz〃比so肌12,502-510．
Liu，Ｍ(ed.)，1998:ＭＺ肌、ノgeQg〃ん〕ＭｎＣ/ij"α・ChmaAtlasPublishingCompany,Beijing,Z52pp
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Niu,ＬａｎｄLiu,Ｈ､(eds.),1989:他szJJrq/30Ｊﾉeα'、〃ｉｍｇｑ"o〃/)℃ｍｔｈｅＩＭＯＷＲｊＶｅ汎Ｌα"djl叩mve‐
ｍｅ"rj〃Ｃｈｊ"α・TheJapaneselnstituteoflrrigation

andDrainage，Tokyo，７，１１１pp．（牛立峰・劉出版社，北京，Z52Pp.)．

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monsoonAsiaduringthelastglacialageandroleofHimalayambetanHighland,viewedfi･omloessandeoliandust・JGeOgmPhy,106,205-217.

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Peinado-Serna，Ａ・'１９８５：Leccm"ｅｓｃｌｅｃ"'”αZolOga、
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Ｃｈｊ"αPResozl"esarms・XianAtlasPubUshingCom‐ｐany,Xian,157pp.(映西省計測委員会,1999:映西省資源地図集．西安地図出版社，西安，157Pp.)．

Smalley，１.IandKIinsley，，.Ｈ､，１９７８：Loessdepositsassociateddesert８．ｃｔz蛇"ｑ5,53-66．
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toryofChina.』:Chjlz・GeOglYIp奴１(1),61-70．
Zhu，Ｚ，Lin，Ｓ、ａｎｄＤｉ，Ｘ，1989:Z7Deoryq／
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ＴａｋａｙａｍａｅｍＬ：RainMIintheLoessPIateau

中国黄土高原における降水の気候学的特徴
高山成鑪・木村玲二＊・神近牧男＊・松岡延浩*＊・張興昌…

（三議讓蝋嘉所）
約

要
黄土高原における砂漠化対処に必要な環境モニタリン域であった。また，Maowusu（毛烏素）砂漠北部とグを目的として，降水の特性について検討した。まず黄Wulanbu砂漠北東の地域,Wugong(武功)周辺の地域
は，年降水量の変動が最も大きいが，Quilian山脈周辺

土高原における年降水量について，空間分布，安定性(ばらつき)，トレンドを調べた。次に降水の季節パターの多降水地域やその南方の山岳地域などは年降水の変動ンに着目し，夏季を中心とした雨季において，降水がどが小さかった。年降水量のトレンドについては黄土高原の程度安定して出現するかについて検討した。

全域を平均した場合，有意なトレンドは見出せなかっ

はじめに１９８０年から2000年までの５３地点の日降た。しかし，個別の観測点について見た場合には，数箇

水量データを基に，Bootstrap法より年平均降水量の区所の観測点で増加または減少のトレンドを有する可能性

間推定を行った。さらにこの区間推定値を基準として年降水の時系列トレンドを調べた。次に１年を５日間単位が示唆された。

本研究では期間降水比（ERP(ｍｊ)）と降水安定度(ESI(")）との関係から雨季安定度（RSS(/)）を提示し，の期間に分け，各期間の期間降水比(ERP(`ｊ)）と降水安定度（別I(")｝との関係より，各地点における降水の季

夏季を中心とした雨季における降水の安定度（変動度）

節パターンについて検討した。

を評価した。その結果，黄土高原においては同程度の年

年降水量の平均はTengeri（騰格里）沙漠，Wulanbu

降水量の地域であっても，東側地域が西側地域よりも雨(ウランブ)砂漠の周辺(Ｎ38～41.,Ｅ104～107｡）で最季に出現する降水が不安定であることが明らかとなっも少なく，低緯度になるほど降水量は増加した。しかし，た。

2つの砂漠の西側に位置するQuilian（チーリエン）山キーワード：雨季安定度,降水安定度,期間降水比,黄土脈周辺の地域（Ｎ37゜30'，Ｅ101.20'）は多降水な地

高原，降水特性－１８９－ReturnReturnagricultural water management 85 (2006) 1–14

available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/agwat

Causes of farmland salinization and remedial measures in
the Aral Sea basin—Research on water management toprevent secondary salinization in rice-based cropping
system in arid land
Yoshinobu Kitamura a,b,*, Tomohisa Yano c, Toshimasa Honna a,
Sadahiro Yamamoto a,b, Koji Inosako a,baFaculty of Agriculture, Tottori University, Koyamacho-Minami 4-101, Tottori 680-8553, Japan
Japan Science and Technology Agency (JST), 4-1-8, Honcho, Kawaguchi-shi, Saitama 332-0012, JapancTottori University, Hamasaka 1390, Tottori 680-0001, Japanb

article info

abstract

Article history:In the Lower Syr Darya region of the Aral Sea basin, secondary salinization of irrigated lands

Accepted 11 March 2006

has been a crucial problem. To clarify the mechanism of secondary salinization, studies on

Published on line 21 April 2006

water and salt behavior were conducted in an irrigation block where a rice-based cropping
system has been practiced. Results of on-site studies are summarized as follows: (1) since

Keywords:

the performance of land-leveling for rice cultivation was extremely poor, the water level was

Secondary salinization

maintained high enough to submerge the highest portion of each plot, and this causes

Water management

wastage of irrigation water and salt accumulation. (2) A large portion of water introduced toWater and salt balance

rice plots tends to be released into field drains. (3) Due to excessive irrigation of rice plots

Central Asiawith slightly saline river water, dissolved salts were mainly deposited in upland plots in the

Arid land

block and its periphery. Changes in salt accumulation rates were dependent upon the scale

Rice-based crop rotation systemof annual changes in the farmland areas that were converted from the upland condition tosubmerged condition in a process of crop rotation. (4) A remarkable finding was obtained on
salt behavior in saturated shallow soil layers of rice plots. An initial decrease in soil watersalinity in the shallow layer is due to the leaching effects of infiltration during the initialstage, and the subsequent gradual increase is more likely a consequence of mixing with thesaline water that remains in the finer soil pores combined with the concentration effects ofcrop water uptake, and the upward flow from the lower layers due to occasional interruption
and resumption of irrigation water supply. (5) Because seepage water from rice plots flows
underneath the field drain, the rise of the groundwater table and salt accumulation wereaccelerated in the adjacent upland plots. Thus, mixed cropping with rice and upland crops
based on a crop rotation system in an irrigation block accelerates waterlogging and salt
accumulation in upland plots. Based on these results, several remedial measures wererecommended to overcome problems on secondary salinization as follows: (1) avoid mixed
cropping with rice and upland crops, and unify either upland crops or rice in an irrigation
block to control groundwater table; (2) decrease conveyance and field application losses
through improved canal construction and management performance, introduction of canallining, and improved land-leveling performance; (3) maintain and operate drainage canals* Corresponding author. Tel.: +81 857 31 5394; fax: +81 857 31 5394.
E-mail address: ykita@muses.tottori-u.ac.jp (Y. Kitamura).
0378-3774/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.agwat.2006.03.007

2agricultural water management 85 (2006) 1–14

to enhance function, particularly installation of subsurface tile drainage for enhancing
subsurface drainage function and management of drainage outfall for minimizing environmental degradation caused by saline drainage water in the downstream area; (4) develop
a design and management technique of evaporation pond for better effluent management
and reuse of drainage water at the outfall of each irrigation block; (5) reduce the watersupplied for rice and its use for other crops, or returning the saved water to the river fordownstream users including returning to the environment; (6) conclude international water
and/or drainage rights agreements among riparian countries and enactment of a basin-wide
management regulation to control water withdrawal and drainage.
# 2006 Elsevier B.V. All rights reserved.

1.

Introduction

The lower river basin of the Syr Darya, which rises in the Tien
Shan Range, meanders mainly in lowland deserts that receivea low precipitation of 100–200 mm year1 and finally flows into
the Aral Sea. Water withdrawals for irrigated lands along theriver have been conducted since the 1960s. Irrigated agriculture of rice-based cropping system in the Kzyl-Orda region of
the Lower Syr Darya is important to both the national andregional economy. Since rice is a high water-consuming crop,water withdrawals have sharply increased with an increase in
the area planted with rice. The sizable discharge of drainage
from irrigated lands has also sharply increased the river watersalinity level. Under these conditions, the salinity of the lower
reaches of the Syr Darya has increased from 0.4–0.6 g L1 to
1.3–2.0 g L1 in the last three decades (Dmitriev, 1995).
Also, due to excessive and inefficient water use, secondary
salinization (irrigation-induced salinization) of lands exists in
irrigated areas in the region. The estimated average water
distribution and delivery efficiency for the Lower Syr Darya
basin is 0.64, and the estimated irrigation application
efficiency is 0.60 (EC, 1995). Thus, the overall irrigation
efficiency is extremely low (0.38); approximately 62% of thewithdrawn water is estimated to be lost before it reaches thefield and becomes available for use in crop production. Thesewater losses raise the level of the groundwater table and cause
waterlogging and land salinization. Salt accumulation in
farmlands results in an increase in abandoned lands andenvironmental degradation in the region.
A large part of these problems is attributable to the poor
water management of canals and fields under large-scalecanal irrigation systems. Thus, proper water management isessential for preventing secondary salinization and sustainable agriculture in the region. In this study, based on theanalysis on water and salt behavior in an irrigation block
located in the Kzyl-Orda region of the Lower Syr Darya, we
attempted to identify the causes of secondary salinization andsuggest remedial measures to overcome the problems fromthe viewpoint of water management.

2.

Materials and methods

2.1.

Outline of study area

Shamenov kolkhoz (originally a collective farm during theex-USSR era, was privatized after independence, and here-

inafter called kolkhoz) located in the Kzyl-Orda state of
Kazakhstan, which is a rice bowl in the Lower Syr Darya
basin, was selected as the study area (Fig. 1). Although thekolkhoz has a gross area of 19,000 ha, only 1900 ha or 10% of
the area was sporadically reclaimed for agricultural purposes. Land reclamation was conducted mainly in wateraccessible areas with comparatively low and flat topography.
The areas with poor water accessibility due to undulating
topography were left as wastelands. Of the 1900 ha ofreclaimed and later cultivated areas in the kolkhoz, an areaof 600 ha has been abandoned due to severe salt accumulation. The phenomenon of salt accumulation showed atendency to concentrate in small localized spots within
irrigated blocks. When the soil salinity reached a certain
level in some of the areas of limited crop production, they
were abandoned. This situation is commonly observed inmany kolkhozes in the state.
The study area has a continental climate. Average annual
precipitation is 120 mm, which is partial to spring and fall.
Average annual potential evapotranspiration is 2000 mm.
Despite the high latitude (458N), the summer is extremely hotwith an average temperature of 27 8C and a maximum
temperature in excess of 40 8C. Winter is extremely cold withan average temperature of 5 8C and a minimum temperature below 25 8C. For the normal growth of rice, thecropping season must be set from late April to early
September. Since there is no effective rainfall during therice cropping season, irrigation is a prerequisite for growing
rice.
For the study on water and salt balance, Yeltai block(Fig. 2) was selected as the study area. Irrigation water for theblock is transported through the Yeltai Canal, which isdiverted from the main canal (Communism Canal) in the
kolkhoz. The Yeltai Canal separates into two branch canals—
the Northern Branch Canal for the Northern Sub-block andSouthern Branch Canal for the Southern Sub-block. Surface
and subsurface drainage water from farmlands is collectedby the main drain (Yeltai drain) and drained off to thetributary of the Syr Darya river. Out of the block area of
827 ha, an area of 716 ha was cultivated. The remaining
111 ha, including roads, canals, and drains, was not allottedfor cultivation either because it was designated inappropriate for the purpose at the time of development (101 ha) or
because it was abandoned later (10 ha). This block ischaracterized as well-consolidated, i.e., irrigation canaland drainage systems are set independently, and every
individual plot has access to a field canal and a field drain,agricultural water management 85 (2006) 1–14

3

Fig. 1 – Location and plan of the studied kolkhoz in the Lower Syr Darya basin.

through its inlet and outlet, respectively. The size of theseplots varied from 1.5 to 3.5 ha with approximately 2.5 ha on
average. The spacing of field canals is approximately 400 m.
Field drains run in between field canals at intervals of
approximately 400 m. The soil texture of the drain-bed wasclassified as clay.
Based on the soil analysis performed in a rice plot of the
Yeltai block in the 1997 crop season, the soil texture of the plot
was classified as clay loam at depths of less than 70 cm, loam
at depths from 70 to 140 cm, and again clay loam from 140 to
200 cm (Hillel, 1998). The soil of the plot was classified assaline soil, because the electric conductivity (EC) of thesaturated soil extract (ECe) was approximately 10 dS m1, andthe pH was between 7 and 8. The groundwater depth wasapproximately 250 cm in the plot during the non-irrigation
period.

2.1.1.

Water quality in the study area

Characteristics of water quality for surface water and groundwater in the Lower Syr Darya basin in and around the
Shamenov kolkhoz are summarized in Table 1 (Kitamura et al.,2000b). EC was measured using an EC meter; pH was measured
using a pH meter, cations and anions were measured byatomic absorption spectrophotometry and ion chromatography, respectively.

2.1.1.1. Surface water. Judging from the EC and total dissolved
solids (TDS), the irrigation water appeared suitable for direct

4

agricultural water management 85 (2006) 1–14

Fig. 2 – Cropping pattern in Yeltai irrigation block.

use. Only magnesium (Mg2+) and the ratio of Mg2+ to calcium(Ca2+), i.e., Mg2+/Ca2+, exceeded the usual range for irrigationwater. Therefore, the water has a tendency to affect crop
growth mainly by reducing calcium uptake and causing
calcium deficiency (Gupta, 1990). Drainage water falls in therange designated for severe restriction for irrigation purposes(Ayers and Westcot, 1985). In fact, considerable drainage water
is finally drained off to the river, and it causes adverse effects
on water quality in the lower reaches, including the Aral Sea.
However, a series of recent researches (Maas and Grattan,
1999; Kaffka, 2001; Kaffka et al., 2002; Oster and Grattan, 2002)
suggests the possibility of effective reuse of saline drainage
water for salt-tolerant crops and reducing salt loads in return
flows (Oster and Wichelns, 2003).

Based on the water quality data for surface water in andaround the kolkhoz, distinct linear relationships with andwithout a constant term were obtained between EC (dS m1)
and TDS (mg L1) as follows:
TDS ¼ 753:5EC ðr2 ¼ 0:981Þ

(1a)

TDS ¼ 816:0EC  169:97 ðr2 ¼ 0:987Þ;(1b)where r2 is the square of correlation coefficient.

2.1.1.2. Groundwater. As compared with the surface water,
the quality of groundwater was more saline. Groundwater inabandoned farmlands was extremely unusable. As indicated

Table 1 – Characteristics of water quality related to salinity in the Lower Syr Darya basin (Kitamura et al., 2000b)
Parameter(units)Water quality in and around Shamenov kolkhoz
Surface waterRiver and irrigation
canal water

Ponded waterin rice fields

Drainage
water

Cultivated andabandoned fields

1.31–2.88
955–2151
4.6–9.3
5.6–11.3
5.9–17.0––
4.5–12.2
11.2–22.4
0.1–0.3
7.6–8.14
2.46–6.08
1.05–1.44

1.84–3.06
1384–2337
6.2–9.1
7.3–12.7
7.7–15.1––
6.0–13.1
14.0–24.9
0.2–0.3
7.75–7.94
2.70–5.36
1.10–1.72

2.63–4.40
2053–4143
8.4–19.2
11.6–18.3
13.1–20.9––
12.6–25.1
23.7–43.7
0.2–0.5
7.62–8.10
4.13–5.04
0.95–1.63

4.13–73.00
2765–86360
20.3–29.1
20.8–437.0
17.3–982.6––
26.0–795.9
13.6–633.5
0.6–3.2
7.42–8.14
3.68–129.36
0.90–15.90

EC (dS m1)
TDS (mg L1)
Ca2+ (meq L1)
Mg2+ (meq L1)
Na+ (meq L1)
CO32 (meq L1)
HCO3 (meq L1)
Cl (meq L1)
SO42 (meq L1)
K+ (meq L1)
pH
SAR
Mg2+/Ca2+aGroundwater

Ayers and Westcot (1985).

Usual range for
irrigation (FAOa)

0–3
0–2000
0–20
0–5
0–40
0–0.1
0–10
0–30
0–20
0–2
6.0–8.5
0–15
0–1

agricultural water management 85 (2006) 1–14

5

in Table 1, the groundwater in this area is almost within therange designated for severe restriction, and thus, it cannot
potentially be used for irrigation purposes without creating
significant problems. Recent achievements, however, clearly
indicate that saline-sodic waters (4 < EC [dS m1] < 20 or 30;
10 < SAR < 40) can be used to irrigate appropriately tolerant
crops to salinity provided that the root zone salinity is controlled
and adequate soil permeability to both water and air can be
maintained (Kaffka et al., 2002; Oster and Grattan, 2002).

Thus, by measuring Wi at the head of the Yeltai Canal and Wd
at the end of the main drain and a drain outfall, Wc + Wet + Wp
is calculated and is regarded as the total amount of water
consumed in the area.

2.1.2.

DSa ¼ Wr Sr þ Wi Si þ Wg1 Sg1  Wd Sd  Wg2 Sg2  Ps ;Cropping schedule

In the Kzyl-Orda region, an eight-year crop rotation system
has been popularly practiced for some decades (Konokhova,
1985). The rice-based eight-year rotation system has beenpracticed in the study area (Yeltai block). Under this system,
two cropping methods are applicable: one is practiced byintroducing only one scheduled cropping pattern in a whole
block every year (mono cropping), and the other is practiced byintentionally introducing eight patterns (mixed cropping). In
the Yeltai block, the latter method was practiced, i.e., the blockis divided into eight rotation blocks and a scheduled cropping
pattern is allotted in each rotation block. The order andfrequency of crops is: first and second years, rice; third year,
cultivated fallow; fourth and fifth years, rice; sixth year, wheat
cover cropped with alfalfa; and seventh and eighth years,
alfalfa. Under this rotation program, approximately half theirrigated area is allotted for rice cropping and the remainder ismaintained under upland conditions for fodder crops or
fallow. In most rice producing areas in Kazakhstan, this
cropping pattern has been the basis for the design andconstruction of new rice land development.

2.2.

Water balance in the study block

In order to clarify the water balance in the Yeltai block,measurement of flow discharge was conducted using acurrent meter (Model CM-1BN, produced by Toho Dentan
Co., Ltd., Japan) both at the head of the Yeltai Canal and theends of the main drain in two irrigation seasons (Fig. 2).
The water balance in an irrigated area for a certain period isexpressed by the following equation:
D ¼ Wr þ Wi  Wc þ Wg1  Wg2  Wd  Wet¼ Wr þ Wi  Wc  Wp  Wd  Wet ;(2)

where D is the changes in total existing water in the area, W
amount of water (in terms of depth of water spread uniformly
over the soil surface), and Wp is the amount of water outflow
from the area by percolated water originating from irrigationwater, i.e., deep percolation (Wp ¼ Wg2  Wg1 ).Subscript r represents the rain water, i irrigation water, c canal loss, d surface
drainage water, g1 groundwater inflow, g2 groundwater outflow,
p percolated water, and et is the evapotranspiration (ET).
Since there is no effective rainfall during the irrigationseason in the study area, Wr in a normal year can bedisregarded.
When considering the entire cropping season, D can be
regarded as zero and Eq. (2) can be simplified as follows:Wi  Wd ¼ Wc þ Wet þ Wp :

(3)

2.3.

Salt balance in the study block

The salt balance in an irrigated area for a certain period isexpressed by the following equation:(4)

where DSa is the changes in salt amount in the area, W amountof water (in terms of depth of water spread uniformly over thesoil surface), S salt concentration, Ps amount of salt removed
by harvesting plant, and WpSp is the amount of salt outflow
from the area by percolated water originating from irrigationwater
Wp Sp ¼ Wg2 Sg2  Wg1 Sg1 ;by regarding Wr and Ps as zero, DSa can be simplified as follows:DSa ¼ Wi Si  Wd Sd  Wp Sp :(5)

Thus, using observed Wi, Si, Wd, and Sd, the sum of DSa and
WpSp can be calculated as DSa + WpSp = WiSi  WdSd, whichis the change in the amount of salt in the area, includingchanges in groundwater salt in and around the area causedby irrigation and drainage practice. Using the relationshipbetween TDS and EC for surface water, i.e., Eq. (1a) or (1b), Si
and Sd can be estimated from the observed EC values
by using an EC meter (Model CM-21P, supplied by DKKTOA Corporation, Japan) at the head of the Yeltai Canaland ends of the main drain, respectively (Kitamura et al.,2000b).

2.4.

Conveyance losses in a distribution canal

For the measurement of conveyance losses from the existing
canal, a 2-km section with no surface lateral inflow andoutflow was selected in the Northern Branch Canal of theblock (Fig. 2). The study was performed using an inflow–
outflow method, which is based on the direct measurement ofdischarge by using the current meter alternately at the
upstream and downstream ends of the section when canalflow was in a steady state (Kraatz, 1977). Prior to and after thedischarge measurement, the height of the water at both theends was repeatedly checked by reading the graduated gauges
installed to identify the flow condition of the canal section.
The following equation (Kitamura, 1990) was applied for
calculating conveyance losses per unit length:
(
Ln ¼

1:0 



Qout
Qin

1=L )
 100;(6)

where Ln represents conveyance loss rate (% km1), Qin inflow
into the canal section (m3 s1), Qout outflow from the canalsection (m3 s1), and L represents length of the canal section
(km).

6

2.5.

agricultural water management 85 (2006) 1–14

Land leveling and water management in rice plots

In order to assess the land leveling performance for ricecultivation, a grid survey of leveling was performed in twoplots prior to the commencement of irrigation. These plots,with respective areas of 2.4 and 1.8 ha enclosed by solid levees(with a sufficiently high freeboard that could hold water up to adepth of 30 cm), are typical of the block. Ponding depth was
manually monitored with a graduated gauge installed during
the irrigation period in order to obtain a correlation with landleveling performance.

2.6.
Impact of crop rotation system and drainage system
on water and salt behavior in an irrigation block
The aim was to determine the impact of a rotation thatcombined rice and upland crop farming on water and saltbehavior in and around an irrigation block. During 1998, we
measured the groundwater table, hydraulic head of soil water
under submerged condition, and EC in a selected detailedstudy area that consisted of a rice plot (2.4 ha, 136 m  177 m)
and its adjacent fallow plot (2.1 ha, 119 m  177 m) along witha field drain between them (Fig. 3). Based on the crop rotation
system, alfalfa was grown on the rice plot and rice was grownon the fallow plot during the previous year.
Water was released from the main canal to the Yeltai canalstarting on May 3, 1998, and irrigation of the rice plot started
on May 9, 1998. Subsequently, the occasional interruption andresumption of water application was repeated three times
during the first 51 days. The plot was then continuously
irrigated during the last 53 days. On August 16, the amount ofwater application was reduced, because the rice was beginning to ripen. Water application was stopped on August 20. On
August 23, the only surface water present in the rice plot was
located in depressions. Rice was harvested with a combine
harvester on September 13.
Hydraulic head was measured at the ponded water surface
and at depths of 0.6, 1.15, 1.8, and 3.0 m in the rice plot. EC of

ponded water and soil water was also measured at each pointand depth in the rice plot. The water table and EC in the fielddrain and the adjacent fallow plot were also recorded.
Measurement of the groundwater table was performed
through 50-mm diameter PVC pipe installed in the fallow
plot. The bottom 1-m section of the pipe was perforated. The
perforated portion was covered with a non-cotton cloth andenveloped in a gravel filter. The bottom of the pipe was set at
depth of 1.95 m below soil surface in the fallow plot.
Measurement of the hydraulic head and soil water EC was
performed through piezometers installed at depths of 0.6, 1.15,
1.8, and 3.0 m. A piezometer was installed using a nonperforated pipe at each depth. The holes were bored manuallyby 100-mm auger to respective depths, and 50-mm diameter
PVC pipes were inserted. Sand was placed around the bottom
ends, and clayey soil was tamped in above the sand filters. The
spaces surrounding the pipes were then filled with clayey soil,
tamped down firmly with a metal rod, and sealed at the soil
surface with clayey soil. The EC meter was equipped with aprobe that was either lowered into each piezometer or it wasused to test water samples pumped from each piezometer. A
staff gauge was installed in the field drain for measuring thewater level.

3.

Results and discussion

3.1.
Causes of secondary salinization related to water
management
Based on the on-site studies in the study area, causes ofsecondary salinization were linked to the soil and water
management and have been summarized as follows:

3.1.1. Seepage and operational losses from the canal system
3.1.1.1. Heavy seepage losses from the canal system. Based on
the field measurement of inflow and outflow in a 2-km sectionin the Northern Branch Canal of the Yeltai block (Fig. 2), theFig. 3 – Cross-section of the detailed study area and the position of piezometers and an observation well with hydraulicprofile as on July 24, 1998 (Kitamura et al., 2000b).

7

agricultural water management 85 (2006) 1–14

Table 2 – Components of water consumption for rice in the study block
Year

Rice plots
irrigated(ha)

Period ofwaterbalance(days)

Withdrawal
at canal
head (1)(mm (m3 s1))

Canallosses (2)= (1)  0.277(mm)

Field intake(3) = (1) (2) (mm(mm d1))

Field
consumption(4) (mm(mm d1))

Drained (5)(mm(mm d1))

1997
1998

384
537

128
123

6136 (2.32)
3990 (2.23)

1700
1105

4436 (34.7)
2885 (23.5)

1259 (9.8)
1123 (9.1)

3177 (24.8)
1762 (14.3)

Note: (4) = (3)  (5).

equation Qout = 0.8875Qin (r2 = 0.7739) was obtained. Substituting Qout/Qin = 0.8875 and L = 2 in Eq. (6), the conveyance losses
in a distribution canal (Ln) were estimated to be approximately
5.8% km1 (Kitamura et al., 2000a). Such heavy conveyancelosses from earth-made canals cause waterlogging and salt
accumulation in the adjacent area.

3.1.1.2. Heavy operational losses due to insufficient function
and poor management of canal system. The result of the waterbalance study carried out in the Yeltai block (716 ha) issummarized in Table 2 (Kitamura et al., 2000a). In Table 2,
the total losses of the distribution system, i.e., the conveyancelosses from the head of the Yeltai Canal to the turnouts of the
field canals (length: 17.6 km), were estimated at 27.7% based on
the observed conveyance losses of 5.8% km1. During theirrigation season each year, the observed water profile in theirrigation canal of the Yeltai block was almost the upper criticallevel whenever water was distributed to the rice plots. Therefore, it is most probable that the amount supplied at the head of
the canal was equal to the conveyance capacity regardless ofcrop water requirement in the command area as shown in
Table 2. This is due to several reasons: (1) to secure a hydraulichead required for gravity irrigation under inefficient function
and poor management of the canal system in the extremely flat
topography; (2) to maintain deep water in rice plots; (3) tosupplement canal losses; (4) insufficient efforts by farmers forsaving water attributed to extremely low water charge, i.e.,
approximately US$ 0.704 per 1000 m3 (Kitamura et al., 2000a).
Thus, the smaller the rice-cropped area in the block, the larger
the water delivered to the block (in mm) per unit area of ricecropped. The total water discharged at the canal head was
3990 mm in 1998, whereas it was estimated to be as high as
6136 mm in 1997. Generally, due to the abovementioned causes,
the water delivered to rice plots is exceedingly high.
This situation exacerbated unnecessary water supply andunexpected water behavior causing waterlogging and salt
accumulation in and around the area.

3.1.2.

always maintained a higher head than the water level of the
field drain and showed a sensitive reaction to the ponding
water level and hydraulic head in the shallow soil layer in therice plot (Figs. 3 and 4). In Fig. 4, the groundwater table data at
the observation well was available only after May 16, 1998,
because of the limited depth of the well (1.95 m in depth),
namely the groundwater table at the observation well was
deeper than 1.95 m below the soil surface before May 16, 1998.
The significant drops of hydraulic head of soil in the rice plot
and water table of the fallow plot after August 16, 1998 were
due to the termination of water deliveries to the rice plot in
preparation for harvesting. Based on the much deeper
groundwater tables (more than 2.0 m below soil surface)observed at several points nearer to the irrigation canals in
the fallow plot during the irrigation period, we deny thepossibility of the existence of hydraulic linkage between theobservation well and irrigation canals. We infer that seepage
water from the rice plot flows through the permeable soil
strata that is hydraulically linked to the fallow plot underneath the field drain bed, which raises the groundwater table,
and leads to salt accumulation in the fallow plot. The limited
subsurface water flow from the paddy plot to the field drain isprobably due to a combination of low hydraulic gradientsalong the water flow path from the field to the drain, madelower because of the thick sediment located along the bottomof the drain, and to the well–compacted soil of banks used as
farm roads for vehicles and heavy machinery which reduces
the saturated hydraulic conductivity of the soil along thelower portions of the drain banks. Consequently, ricecultivation does not result in adequate salt removal byleaching.

3.1.3. Imbalance of water and salts in an irrigation block
3.1.3.1. Imbalance between inflow of salts into irrigated area
and outflow of salts from the area. Based on our salt balance
study carried out in the Yeltai block, a considerable amount of

Insufficiency of drainage system

Field drains failed not only to sever the hydraulic continuity
between rice plots and upland plots, such as fallow and alfalfa
plots, but are not effective in removing salts from rice plots todrains due to a lack of subsurface drainage. Because of theseepage flow beneath the field drain from the rice plot, the risein the groundwater table and salt accumulation are accelerated in the adjacent fallow plot (Kitamura et al., 2000b).
This is suggested based on the observed fluctuations ofhydraulic conditions among the rice plot, fallow plot, and fielddrain as shown in Fig. 3. Depending on the fluctuations ofhydraulic conditions, the groundwater level in a fallow plot

Fig. 4 – Change in hydraulic head in a rice plot and its
adjacent fallow plot (Kitamura et al., 2000b).

8agricultural water management 85 (2006) 1–14

Fig. 5 – Water and salt balance diagram in the study block.

dissolved salts remained in and around the block (Kitamura
et al., 2000b). This situation brings about a steady increase inaccumulated salts in and around the block every irrigationseason. The result of water and salt balance in the Yeltai blockis roughly summarized in Fig. 5. Only salt inflow and outflow
was obtained by direct measurements, and the other elementsof salt movement were calculated based on the respective
elements of water movements, taking into account theirrespective EC values. As almost all the branch canals run along
the periphery of the block, we assumed that the amount of salt
transports attributable to canal seepage can be divided into
two equal halves, i.e., one half of the amount was moved anddeposited in an area outside the boundary of the block, and theother half was deposited into fields along the canal. We
estimated the amount of dissolved salt from the canal basedon the average increase rate of EC along the canal as describedlater. Percolation and transpiration were considered to be theonly contributors to the salt accumulation in and around riceplots; evaporation from the water surface was not regarded asa contributor. To calculate the amount of salt accumulated in
the root zone due to water uptake by rice plants, we used theroughly estimated value of 460 mm for transpiration during
the growing season (Rockstöm, 2003). The amount of waterdrained from alfalfa plots was estimated based on theassumption that about 25% of the applied water seeps infield drains after each irrigation event. The salinity of thedrainage water from alfalfa plots was regarded to be of thesame level as that of the soil water of shallow layer (at a depthof 0.6 m) observed at the beginning of the irrigation season(approximately 18.00 dS m1, as shown in Fig. 6). The salt

outflow from alfalfa plots was estimated by multiplying theassumed amount of drainage water from the plots with theassumed salinity content of the drainage water. The EC valuesof respective elements of water movements are applied asshown in Table 3. Based on the values of the respective
elements of salt and water movements estimated, we
calculated salt accumulation in alfalfa plots, salt outflow
from rice plots, and finally obtained the amount of dissolved
salt from rice plots that is required for maintaining a saltbalance in rice plots. The salt balance was also simplified asshown in Table 4. The increase in accumulated salt in andaround the block during each irrigation season, i.e.,(DSa + WpSp) in Eq. (5) that is equal to column (7) of Table 4or (1)  (6) = (3) + (5)  (2)  (4) in Fig. 5 (salt-inflow to theblock–salt-outflow from the block), was 4417 Mg (6.2 Mg ha1,

Fig. 6 – Change in EC of groundwater in rice plot (Kitamura
et al., 2000b).

9agricultural water management 85 (2006) 1–14

Table 3 – Applied EC values of respective elements of water movements
Elements of water movement

Inflow to the block
Canal loss
Field intake
Intake for rice plots
Intake for alfalfa plots
Accumulated salt in rice plots
Accumulated salt in alfalfa plots
Drainage water from the block
Drainage water from alfalfa plots

Remarks

Applied EC values(dS m1)
1997

1998

1.82
1.82
1.89
1.89
1.89
1.89
1.89
3.12
18.00

1.53
1.53
1.59
1.59
1.59
1.59
1.59
3.43
18.00

Average of observed EC at the head of the Yeltai Canal
Average of observed EC at the head of the Yeltai Canal
Calculated EC (ECx) using ECx = ECU(1 + 0.0046x)
Calculated EC (ECx) using ECx = ECU(1 + 0.0046x)
Calculated EC (ECx) using ECx = ECU(1 + 0.0046x)
Calculated EC (ECx) using ECx = ECU(1 + 0.0046x)
Calculated EC (ECx) using ECx = ECU(1 + 0.0046x)
Average of observed EC at the end of the main drain
Applied the EC value of the soil water of shallow
layer observed at the beginning of the irrigation season

Table 4 – Salt balance in the study block (716 ha)
YearSalt inflow
to theblock (1)(Mg)

Dissolved
salt from
canal (2)(Mg)

Accumulated
salt inadjacent
area (3) (Mg)

Dissolved
salt fromfields(4) (Mg)

Accumulated
salt in fields(5) (Mg)

Drainedsalt fromthe block (6)(Mg)

Increase inaccumulated
salt in theblock (7) (Mg)

1997
1998

33508
24923

945
703

4643
3452

4483
7109

5202
4769

29091
24514

4417
409

Note: (7) = (1)  (6) = (3) + (5)  (2)  (4).

48.2 kg ha1 d1) in 1997 and 409 Mg (0.6 Mg ha1,
4.6 kg ha1 d1) in 1998, respectively. The reasons for thelarge difference in the salt accumulation rate between two
seasons are: (1) the water quality of the source was slightly
better in 1998 than that in 1997 (Fig. 7), (2) less irrigation water
was applied in 1998 than in 1997 (Table 2), and (3) higher
salinity of drainage water, i.e., a higher amount of dissolved
salt from the block, was observed in 1998 than that in 1997
(Fig. 7). The first two reasons are of minor significance,
whereas the third reason is the main contributing factor. The
third reason was due to the significant increase in the area of
farmlands converted from upland condition to submerged
condition in 1998 as compared with that in 1997. Due to theannual crop rotation in the study block, the area of farmlands
under rice cultivation that was newly converted from thoseunder upland condition in the previous year was 297 ha in
1998, whereas in 1997, only 31 ha were converted from uplandcondition.

3.1.3.2. Over irrigation of rice-planted plots. A large amount ofwater is irrigated to rice-planted plots during the irrigationseason. In the Yeltai block, the water delivered to field canals
for rice plots was 4436 mm in 1997 and 2885 mm in 1998 asshown in Table 2 (Kitamura et al., 2000a). These excessive
amounts result from several reasons, including the preventionof an increase in salinity of ponded water in rice plots. Thissituation brings about waterlogging and salt accumulation in
the adjacent upland areas.
Field consumption, i.e., (4) = (3)(5) in Table 2, is the sum ofET and deep percolation in rice plots. Thus, the daily field
consumption is estimated to be approximately 9.5 (9.1–
9.8) mm d1. ET in rice plots was not observed throughout
the season, however, assuming that ET is approximately 6–
7 mm d1, the downward percolation flow is obtained ataround 2.5–3.5 mm d1.
The amount of drained water from the block widelydiffered each year. The difference in the amounts of water
intake by rice plots between two different years is almost
equivalent to the drained amount. In other words, theremainder after subtracting the amount of water used in arice plot (9.5 mm d1) from the amount of water supplied
through an inlet to each plot consists of surface and subsurface drainage. Based on the on-site situation, it can beunderstood that surface drainage occupies an overwhelmingly
large portion of the total drained amount. This is the major
reason behind the drainage water salinity being far lower than
the soil water salinity in the adjacent rice plot (Fig. 6).

3.1.3.3. Introduction of saline river water with TDS more than
1000 mg L1 for irrigation. The salinity of river water varies

Fig. 7 – Variation in EC value of canal water (Yeltai block).

from 1.31 to 2.88 dS m1 (average 1.78 dS m1) in EC and from
955 to 2151 mg L1 (average: 1285 mg L1) in TDS during
irrigation periods as shown in Table 1 (Kitamura et al.,2000b). The application of saline water to irrigation aggravates
salt accumulation in and around the irrigated area.

10

agricultural water management 85 (2006) 1–14

3.1.3.4. Dissolution of accumulated salts from canal systems.
The salts accumulated along canal systems dissolve in
irrigation water resulting in an increase in salinity. Basedon the observation of the canal water salinity (EC) in the Aitek
Canal, which is the headrace canal used to convey river water
to the kolkhoz, the relationship between EC at the head (ECU)
and that at the end located 50 km downstream of the head(ECD) can be expressed as ECD = 1.23ECU (r2 = 0.675). Thus, theEC of canal water increases 1.23 times while it flows a distanceof 50 km, or the relationship can be expressed as ECx = ECU(1 + 0.0046x), where ECx is the EC at a point located x km
downstream of the head. As mentioned above, this relationship was applied to obtain a rough estimate of the amount ofdissolved salt from canal system as shown in Fig. 5. Thus, thedissolution of accumulated salts from canal systems is also
one of the causes for secondary salinization in irrigated areas.

3.1.4. Causes attributed to water and land management in an
irrigation block
3.1.4.1. Compounded factors to increase soil salinity in theshallow soil layers in rice plots. The observed results of the EC ofsoil water and hydraulic head in the rice plot are shown in
Figs. 6 and 4, respectively. Fig. 8 shows the change in hydraulicgradient at each layer between the observed depths. Figs. 4 and8 suggest that water moved from the soil surface to the deeper
layers under submerged condition. However, water moved
upward in some layers, particularly the 0.6–1.15 m layer, under
the non-submerged condition before irrigation was restarted
after an interruption. The high EC value of soil water at 1.80 m
is attributed to the existence of a heavily salt-accumulated
layer at a depth of approximately 1.80 m (Fig. 6). The salinity ofsoil water at a depth of 3 m was a constant value of 9–10 dS m1
without any significant variation throughout the period. Thissuggests that the soil layer at a depth of approximately 3 m wasin a primary groundwater flow pathway throughout a year.
In the experimental rice plot in the Yeltai block, soil watersalinity at a depth of 0.6 m in the rice plot displayed a very
interesting variation throughout the irrigated period as shownin Fig. 6. At the beginning of the irrigation period, the soil watersalinity at 0.6 m had high EC (approximately 18 dS m1), whichthen decreased sharply to the same level as that of the ponded
water (approximately 2.5 dS m1). However, the EC increased
gradually and leveled off after it reached a certain salinity level(15–16 dS m1). The behavior of soil water salinity at shallow
depths can be explained as follows.
The initial high EC resulted from the upward flow of saline
water from the lower layer of 0.6–1.15 m due to large negative

Fig. 8 – Change in hydraulic gradient at each soil layer.

hydraulic gradients (13.8  102) at the beginning of theirrigation season (Fig. 8). The next sudden decrease in soil
water salinity in the shallow layer is due to leaching effects ofdownward infiltration during the initial stage. The subsequentgradual increase in soil water salinity in the shallow layer ismore likely a consequence of mixing of the downward flowing
water with the saline water that remains in the finer soil porescombined with the concentrating effects of crop water uptake
and occasional upward flow from the lower layer of 0.6–1.15 m
due to negative hydraulic gradients (Fig. 8). The mixing process
is accelerated by the occurrence of large negative hydraulicgradients by the fluctuation of the water table due to theoccasional interruption and resumption of irrigation watersupply during the season. The incidence of high EC values inthe shallow layer rises with the occurrence of large negative
hydraulic gradients as shown in Fig. 8.
Salt-accumulated spots were often seen in rice plots after
ponded water had been drained off for harvesting. Such spots
are often formed above permeable layers. In those spots, themagnitude of occasional upward water flow is much stronger
than that in the other area. This accelerates the convection ofsalt from deeper layers, and thus, the soil water salinity
remains high in shallow layers. The spots above permeable
layers obstruct the normal growth of rice and cause a marked
decrease in yield because of the high content of dissolved salts
in shallow layers.

3.1.4.2. Application of an eight-year crop rotation system in an
irrigation block. The operation of a crop rotation system
involves mixed cropping with rice and upland crops within an
irrigation block and promotes seepage flow along with salt
transport from rice plots to adjacent upland plots (Kitamura
et al., 2000b). As mentioned in Section 3.1.2, there is apossibility that this system has induced waterlogging and salt
accumulation in upland areas adjacent to rice plots in andaround the irrigation block. In this kolkhoz, some blocks inwhich this system had been practiced for several decades
consist of abandoned farmlands in almost half the original
gross area due to salt accumulation. Even in the newly
developed blocks having limited abandoned farmlands, it isanticipated that the salt accumulation will be accelerated, andconcurrently, abandoned farmlands will increase if the eightyear rotation system continues to be practiced.

3.1.4.3. Poor land leveling and careless field water management. It was revealed that the performance of land leveling wasextremely low in rice plots. For example, the undulation varied
from 15.4 to +14.9 cm with a standard deviation (S.D.) of 6.5 cm
in a 2.4 ha plot and from 17.9 to +16.6 cm with a S.D. of 6.85 cm
in another 1.8 ha plot (Kitamura et al., 2000a). Under such field
conditions, it is very likely that a high ponding depth ismaintained so as to ensure that the highest portion in each plot
remains wet. This deep-water management accelerates waterlogging and salt accumulation in the adjacent upland areas.
Fig. 9 shows the pattern of ponding depth in a 2.4 ha plot
during the irrigation period. As shown in Fig. 9, the plot was
supplied with water until the highest portion was saturated,and subsequently, water intake was discontinued to allow thecomplete absorption of the irrigated water by the soil. This
intermittent process was repeated three times during the firstagricultural water management 85 (2006) 1–14

Fig. 9 – Change in ponding depth in a rice plot (Yeltai block).

two months. The plot was then continuously irrigated during
the latter two months.
The first irrigation was performed after sowing in saturated
soil and maintaining a ponding depth at approximately 20 cm
for 10 days. This is required to meet the greatest water demandrate among several irrigation events. Based on the analysis of
the volumetric composition of vapor phases in the soil layers
above the groundwater table conducted immediately before
the first irrigation, the water requirement for saturating soil
was estimated to be approximately 100 mm. When ponded
water was absorbed into the soil, the seed started togerminate. The second irrigation was started when ponded
water disappeared from the lowest portion and was suspended when the highest portion was submerged. The third
irrigation was also performed in the same manner. During thefourth irrigation, the ponding depth was maintained at
approximately 20–25 cm, i.e., 5–10 cm at the highest portionand 35–40 cm at the lowest portion, from early July to lateAugust. The commencement of the fourth continuous irrigation coincided with the end of the tillering stage and the
beginning of the panicle formation stage. This irrigation was
continued until the crop was ready or nearly ripe for harvest.
Based on the existing field water management, we confirmed that a large quantity of water was introduced to a riceplot despite the region’s water scarcity. Maintenance of a highponded water level was mainly attributed to the poor performance in land leveling rather than reasons such as preventionof rice plants from lodging and regulation of soil temperatures.

3.2.

Remedial measures to prevent secondary salinization

Solving the abovementioned causes directly becomes remedial measures to prevent secondary salinization. Since, inmany cases, these causes interact with each other and are
attributable to the restriction of the natural environment,
comprehensive measures should be undertaken.

3.2.1. Measures for alleviation of canal losses andwaterlogging
The problem of heavy seepage from canals is attributable tonot only the leaky characteristic of non-lined canals but also

11

their long conveyance distance. In general, irrigation systems
have long canals due to the flat topography in the region. It is
inevitable to increase the canal length in order to introduce
and convey water from a river to an irrigated area by gravity.
Moreover, the marked characteristic of the Syr Darya river isthat it is liable to meander on account of a remarkably gentle
bed slope and a high coefficient of river regime (the ratio of
maximum to minimum stream flow) in the lower reaches. The
distribution of oxbow (crescent-shaped) lakes along the river isalso an evidence of this characteristic. Therefore, the points ofdiversion (withdrawal) should be decided as the place where
the river has a steady flow and solid banks, although theconveyance distance becomes longer. Alternative measuresrequire investment, and economical evaluation is needed
based on investment efficiency; these measures include an
improvement in structures and are as follows.
(1) Introduce pumping irrigation instead of gravity irrigation,and select a site for withdrawal at a point closer to the area
to be irrigated to shorten the conveyance distance as far as
possible.
(2) In case gravity irrigation is applied, head works should beconstructed to secure sustainable diversion at a pointcloser to the command area.
(3) Provide lining to earth-made canals or introduce pipeline
system for pumping irrigation.
(4) In case lining is economically difficult, it is recommended
to introduce special methods in canal construction tocontrol canal seepage such as a crushing and compaction
method.
(5) Conduct the operation and maintenance of the canalsystem in a conscientious manner so as to preserve its
original conveyance capacity; if this is not done, the waterlevel would exceed the permissible water level for
conveying required discharge, and this would cause
waterlogging in the adjacent area. Thus, special attention
should be paid to keep the canal free from silting, weeds,
aquatic weeds, and trash. In the Yeltai block, canal system
was always affected by clogging due to floating debris,
mainly twigs of thorny shrubs that were used for fences;concurrently, this increased the roughness coefficient andreduced the conveyance capacity of the canal.
(6) Bio-drainage is listed as a possible measure to be
introduced along canals and around farm lots for preventing waterlogging and salinization. This method
involves growing certain types of plants that habitually
draw their main water supply directly from the canalseepage water or the capillary fringe immediately above it(Heuperman, 1999; Bhutta and Chaudhry, 2000) andmaintaining the groundwater table at a safe level thatprevents waterlogging, which depends on the soil texture
at least 2 m from the soil surface (Vlek et al., 2002). Thismethod is also effective for the improvement of theenvironment in the region. The growing of poplars (Populusspp.) and tamarisks (Tamarix gallica) is applicable to themethod (Bhutta and Chaudhry, 2000; IPTRID, 2002).
However, salt-tolerant trees such as tamarix could concentrate the salt in the root zone to high levels because
trees usually exclude sodium and chloride ions from thetranspiration stream. The salt accumulation processes in12agricultural water management 85 (2006) 1–14

the root zone and the water table underlying the trees will
have to be managed to achieve long-term sustainability.
This often involves some form of physical drainage input
to remove salts from the root zone (IPTRID, 2002).

3.2.2. Improvement in hydraulic structures of the canalsystemSince the problem of operational losses caused by inefficienthydraulic function of canal system is closely related to themeasures mentioned in Section 3.2.1, remedial measures
should be planned comprehensively in consideration of thehydraulic function. One difficulty is that gates are either aged
and damaged or not installed at points where hydrauliccontrol and regulation are vital. In fact, the stoppage of canalflow is very difficult in the kolkhoz. When it is necessary tostop the canal flow, a bulldozer has to be used to dump earthand sand into the canal to bank up the flow. This operation
accelerates siltation in the canal system and causes canallosses.
Due to the absence of proper gate structures to control
water level in the canal system, an extra water supply besides
the field irrigation requirement is needed to maintain therequired hydraulic gradient for irrigating fields by gravity. Thisis one of the main causes of the lowered irrigation efficiency inthe area. This problem can be greatly improved by installationof sturdy gates for water level regulation and their correct
operation. Thorough understanding and strengthening ofsystematized organization of the farmers are prerequisites
for the appropriate operation and maintenance of the system.

3.2.3.

Improvement in drainage management

Poor physical function and deteriorated management ofdrainage system lead to destruction of the water and saltbalance, and thus, these accelerate salt accumulation in an
irrigated area. The basic concept to prevent secondary
salinization is to maintain the overall salt balance in an
irrigated area by draining off the excessive salt, which isequivalent to the amount of salt inflow introduced to the areawith irrigation water. For this purpose, proper management isrequired for the improvement and maintenance of thefunction of a drainage system. Judging from the low salinity
level of drainage water (EC: 2.6–4.4 dS m1) as compared withthat of soil water (EC: 10–25 dS m1) in the adjacent rice plot in
the Yeltai block (Kitamura et al., 2000b), it is obvious that
subsurface drainage is not correctly functioning in the system.
Since the drainage and salinity control of an irrigated area by
only an open drain system poses limitations, installation of
subsurface tile drainage is recommended for supplementing
the open drain system to enhance the drainage efficiency(IPTRID, 2001). A tile drain system can effectively remove
accumulated salts from the root zone; however, its introduction appears quite difficult from the viewpoint of the region’s
economical situation. In case tile drainage system is installed
in an area with high salt accumulation, the danger ofdeterioration of the water quality of the downstream reaches
is a possibility due to the outflow of huge amount ofaccumulated salts from the area; hence, adequate attention
should be paid in this regard. Drainage measures should be
decided after due consideration of the effects on theenvironment of the downstream area. The management ofdrainage outfall of each irrigated area, in particular, appears to
be a key issue for minimization of environmental degradation
caused by saline drainage water in the downstream area
(Rhoades, 1989; Oster and Wichelns, 2003).
In the future, each irrigated area should be well equippedwith a special pond at the end of the drainage system tocontrol the quantity and quality of drainage water to bedrained off to the downstream. It is desirable to develop adesign and management technique of evaporation pond forbetter effluent management at the outfall of each irrigation
block. Existing oxbow lakes are available for the ponds, andthe plan should be based on thoughtful consideration of thenatural ecosystem. Prior to this, a certain agreement on
allowable water quality of drainage from each irrigated area
should be concluded among riparian countries. If the management of drainage outfall is combined with the reuse ofdrainage water for irrigation of salt tolerant crops (forages),
the salinity of the drainage water would increase further andits volume would decrease, which can facilitate its final
disposal in evaporation ponds (Kaffka, 2001; Kaffka et al., 2002;
Oster and Grattan, 2002).

3.2.4. Improvement in field management including soil andwater management
Since several of the abovementioned causes of secondary
salinization are related to each other, the measures againstthem should be conjunctively investigated. To improve theseissues, the following measures are proposed:(1) The eight-year crop rotation system, which has beenpracticed popularly in the region, should be modified to a
new system in which wet rice plots and dry upland plots
within the same irrigation block are not combined. In otherwords, the new system is still a rotational system, but itshould unify each irrigation block either an uplandcondition or a rice plot condition.
(2) The land leveling should be performed as precisely as
possible. Generally, the ponding depth of a rice plot ismaintained deep in the region, and this results in an
increase in irrigation water losses. The deep ponding
management may be necessitated in case of rice cultivation not only to protect rice plants from lodging and cold
temperature damage but also to submerge the higher
portion created by the poor land leveling. Thus, precise
land leveling will increase the possibility of decreasing the
ponding depth and improving the efficiency of water use.
Furthermore, this allows canal water level to be relatively
low so that canal losses can also be reduced.
(3) In order to prevent a gradual increase in salinity of ponded
water and soil water in shallow layers caused by theoccasional convection of salt from deeper layers, acontinuous supply of fresh water, which allows the ponded
water to spill over from the outlet to the field drain, wascarried out by the farmers. Thus, this inevitably results inexcessive water supply. Therefore, it is fundamentally
undesirable to carry out rice cultivation in such areas withsaline soils. However, rice cultivation has played an
important role in the regional economy, and farmers havebeen cultivating rice for a long period of time; hence, it isunrealistic to deny and stop its cultivation. It is essential toagricultural water management 85 (2006) 1–14

strengthen water saving management based on a fullcognizance of the dependence of the regional economy onrice cultivation. Since only limited references are available
on the speed of salt movement in saturated soils at the field
scale (Grünberger et al., 2003; Kirk et al., 2003), further
experiments are required to clarify the impact of upward
transport of salts on the salinization in submerged riceplots. For example, percolation control methods, such as
puddling and subsoil compaction (Yamazaki, 1976; Sharma
and Bhagat, 1993), can be considered as measures toprevent the upward flux of dissolved salts. Some advanced
study is required to quantitatively clarify the effects ofsuch methods on the salt flux by convection, dispersion,and diffusion in each soil texture.
(4) In salt-accumulated spots consisting of permeable soil
layers in rice plots, some measures such as replacing or
mixing the existing soils with impermeable soils are
required to reduce the upward movement of salts, which
result in occasional interruption and resumption ofirrigation water supply.
(5) It is necessary to correct farmers’ attitude on the value ofwater. The present water charge is considerably cheap anddoes not encourage water conservation by farmers(Anderson, 1997). Therefore, the water charge should be
revised to an appropriate level to encourage water
conservation by farmers.

3.2.5. Conclusion of international treaty on water withdrawal
and drainage
Among the proposed measures, this issue is the mostimportant and urgent matter. The introduction of a large
amount of saline river water with TDS greater than
1000 mg L1 into an irrigated area is equivalent to the massive
input of salts in an agricultural land, and it directly causes salt
accumulation in the area. The salinity of river water increases
toward the downstream area of the Syr Darya river. This is dueto the repeated use of river water from the upstream reaches
to the downstream reaches. Introduction of greater amountsof river water into irrigated lands and draining off saline waterin the upper reaches of the river results in increased watersalinity in the downstream reaches. Therefore, it is necessary
for riparian countries and irrigation communities to consult
and conclude agreements, including detailed regulations onwater withdrawal from the river, and removal of drainage
water and salt loads to the river with each other. Based on theagreement, proper basin-wide water resources management
should be carried out.

4.

Conclusions

The results of a series of on-site experiments conducted onwater and salt behavior in an irrigated kolkhoz where a ricebased cropping system has been practiced in the Lower Syr
Darya river basin of Kazakhstan are as follows. The causes ofsecondary salinization in irrigated areas are: (1) heavy seepage
losses from canal systems, (2) heavy operational losses due toinsufficient function and poor management of canal systems,(3) insufficient function and poor management of drainage
systems, (4) imbalance between inflow of water and salt into13

irrigated area and outflow of those from the area, (5) overirrigation of rice-planted plots, (6) application of an eight-year
crop rotation system in an irrigation block, (7) poor landleveling and careless field water management, (8) introductionof saline river-water with TDS greater than 1000 mg L1 forirrigation, and (9) dissolution of accumulated salts from canalsystems.
In order to overcome the above problems, the following
remedial measures are recommended: (1) avoid mixed croppingwith rice and upland crops and unify either upland crops or ricein an irrigation block to control groundwater table; (2) decrease
conveyance and field application losses through improved
canal construction and management performance, introduction of canal lining, and improved land-leveling performance;(3) maintain and operate drainage canals to enhance function,in particular, install subsurface tile drainage for enhancing
subsurface drainage function and management of drainage
outfall for minimizing environmental degradation caused bysaline drainage water in the downstream area; (4) develop adesign and management technique of evaporation pond forbetter effluent management and reuse of drainage water at theoutfall of each irrigation block; (5) reduce the applied water torice and use it for other crops, or return the saved water to theriver for downstream users including returning to the environment; (6) conclude international water and/or drainage rights
agreements among riparian countries and enact a basin-wide
management regulation to control water withdrawal anddrainage.

Acknowledgments
This research was partly conducted under the 21st Century
COE Program (Program for Arid Land Science) funded by theJapanese Ministry of Education, Culture, Sports, Science andTechnology, and the Core Research for Evolutional Scienceand Technology (CREST) (Research on Sustainable Water
Policy Scenarios for River Basin with Rapidly Increasing
Population) sponsored by the Japan Science and Technology
Agency (JST). Thanks to referees and colleagues whose
comments and questions helped us improve the paper.

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Returnagricultural water management 88 (2007) 63–72

available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/agwat

The impact of saline water irrigation management options
in a dune sand on available soil water and its salinity
B.A. Ould Ahmed a,*, T. Yamamoto a, V. Rasiah a,b, M. Inoue a, H. Anyoji aab

Tottori University, Arid Land Research Center, 1390 Hamasaka, Tottori 680-0001, Japan
Department of Natural Resources & Mines, 28 Peters Street, Mareeba, Qld 4880, Australia

article info

abstract

Article history:In this study the effect of two levels of irrigation input, each at two frequencies, were

Accepted 2 October 2006

assessed on sorghum (Sorghum bicolor (L.) Moench) grain yield as impacted by available soil

Published on line 9 November 2006

water after irrigation and the electrical conductivity of soil water (ECsw) in a dune sand, in agreenhouse experiment. Saline water (7.32 dS m1) at input amounts equivalent to 50% or

Keywords:

100% of pan evaporation was applied daily or every second day. Using time domain

Saline water irrigationreflectometry technique, soil water content and ECsw were monitored simultaneously just

Available soil water

before and 1–2 h after irrigation. The cumulative recharge by irrigation in the top 25 cm ofSoil water salinity

the profile ranged from 309 to 662 mm and it depended on irrigation input amounts, which

Sorghumranged from 382 to 765 mm, and frequency. The potential cumulative evapotranspiration

Sustainability(ETc) was 578 mm. The daily recharge matched against the corresponding ETc indicated thatgrain yield might have been impacted by water stress in the 50% irrigation input, regardlessof the frequency, but not in the 100% input treatment. The daily ECsw in the root-zone
matched against the FAO threshold (13.6 dS m1) indicated the possibility of salinity stressduring the late maturity stage in the 50% input treatment, regardless of the irrigation
frequency, but no stress in the 100% input treatment. Though there was no water or salinity
stress in the every second day irrigated 100% input treatment, the significant relative yield
reduction, compared with the daily 100% input, is attributed to inherent limited available
soil water capacity and rapid percolation losses between irrigations in this sand. The results
indicate daily irrigation at 100% input is the most appropriate saline water irrigation
management option for this dune sand.
# 2006 Elsevier B.V. All rights reserved.

1.

Introduction

Dwindling supplies of quality water for irrigation andincreasing demand from other users are forcing farmers to
use saline irrigation waters (Rhoades, 1987; Rhoades et al.,
1992; Shani and Dudley, 2001). Several workers (Shani andDudley, 2001; Gideon et al., 2002; Katerji et al., 2003) haveindicated that when saline waters are used for irrigation due
attention should be given to minimize root-zone salinity.
Others have indicated the need for selection and use of

appropriate irrigation systems and practices that will supply
just sufficient quantity of water to the root-zone to meet theevaporative demand and minimize salt accumulation in the
root-zone (Fisher, 1980; Munns, 2002). The third approach is toselect crops/varieties that can tolerate water and salinity
stress to a given degree (DeMalach and Pasternak, 1993;
Mastrorilli et al., 1995; Claudivan et al., 2005).
In the Mauritanian semi-arid regions, irrigated riceproduction, even using quality water (0.10–0.25 dS m1), has
led to rising groundwater levels and increases in soil water* Corresponding author. Tel.: +81 857 21 7213; fax: +81 857 29 6199.
E-mail addresses: ahmed@alrc.tottori-u.ac.jp, a_bouya@yahoo.com (B.A. Ould Ahmed).
0378-3774/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.agwat.2006.10.001

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agricultural water management 88 (2007) 63–72

salinity (2.20 dS m1) in the root-zone (Josserand and Silva,
2002; van Asten et al., 2003). In this country sorghum, which
occupies 60% of the total area under grain production, is adryland crop grown mostly in the arid to semi-arid regions.
Sorghum is widely used for human consumption and as feed
and fodder (Ministère du développement rural, 1998). Josserand and Silva (2002) reported that sorghum in Mauritania
accounts for 25% of the total grain production. Farmers
frequently face crop failure due to drought, but supplementaryor full irrigation for this crop has never been tried out. Thismay be partially due to insufficient water resources other thangroundwater, which is primarily used for human and livestock
consumption. The wells are usually 5–20 m deep and the dryout during consecutive dry years. The groundwater tends tobecome saline after years of water extraction. Under suchcircumstances, people abandon saline wells and move to newwells. This suggests that even if supplementary irrigation is
introduced for sorghum, the potential for irrigation induced
salinity risk is high and the sustainability of the already fragile
soil resources may be at risk.
Data from vegetable producing semi-arid regions of
Mauritania indicate that salinity is already an issue in the
groundwater irrigated projects (SONADER, 1998; Josserandand Silva, 2002). Irrigation is usually gravity fed and the water
application efficiency is very low. The needs for introductionof new irrigation systems and improvements in existing
practices, at least in the intensive vegetable producing
regions, have been identified. The drip irrigation is the mostefficient system in delivering just the required amount ofwater directly in the crop root-zone (Shalhevet, 1991). The useof such system is particularly important where limited water
resources, including saline groundwater, are used for irrigation. However, the coast of installation and maintenance andthe technical skills required for its operation are high for acountry like Mauritania. Nevertheless, for future planningpurposes at least some limited background information
about appropriate management practices is required forsaline water irrigation in drip systems (Ayers and Westcot,
1985; Pasternak and DeMalach, 1987; Gideon et al., 1995) tosustain productivity and soil resource utilization in thiscountry. Thus, a greenhouse experiment was conducted,
mimicking Mauritanian conditions, to assess the effect of
two water input amounts, each at two frequencies, onsorghum grain yield as impacted by available soil water andits ECsw in a dune using saline irrigation water in drip
irrigation system (DIS).

A randomized complete block design with three replicates
was used in this study. The treatments consisted of two
irrigation input amounts, 50% (EP0.5) and 100% (EP1.0) of openpan evaporation, which was measured in the greenhouse.
These amounts were applied at two frequencies (daily andevery second day). In the every second irrigated treatment, theinput on a particular day is equal to the amount applied on theprevious day plus the amount due on that particular day of thedaily irrigated treatment. This implies the total irrigation input
during the growing season in the daily and every second day
irrigated treatment are approximately equal for a given input
treatment. Sorghum was sown, along lateral lines just by theemitters, on 1 April 2004 at 12 plants per block and harvested
on 15 July 2004. Fertilizer was applied, at 180 kg h1 N,
45 kg h1 P, 80 kg h1 K, just before seeding and incorporated
into the soil.
The experimental area was irrigated using DIS and eachtreatment plot (1.2 m  1.2 m) was fed by three laterals thatbranched off from the sub-main pipe. There were 4 emitters,
spaced 30 cm apart, on each one of the 120 cm long laterals.
The discharge rate from the emitters was 2 L h1, which wasmaintained by an operating pressure of 0.1 MPa. Saline water(EC = 7.32 dS m1) irrigation commenced 2 weeks after sowing
and continued until 15 July 2004. However, crop establishment
was achieved using 65 mm of quality water (EC = 0.11 dS m1),
i.e. during the first 2 weeks. The total saline water irrigation
input in the EP1.0 was around 765 mm for daily and every
second day frequency and that for EP0.5 it was around
380 mm. A water-tank was used to prepare saline water,
covered to minimize evaporation and cleaned once in every 5
days. The salinity of the irrigation water used in this study was
based on invoking two assumptions. First, the average salinityof groundwater in Mauritania is 8.0 dS m1 and secondly the
FAO has determined that when saline waters of 6.8 dS m1
were used for irrigating sorghum this could lead to 50% yield
reduction. Therefore we decided to use an average between 8.0
and 6.8 dS m1. At harvest the grain yield was measured afteroven drying at 70 8C for 48 h.
A control using quality irrigation water and the associatedirrigation option treatments were not included in thisexperiment due to inadequate greenhouse space. However,during the subsequent year a control using quality irrigationwater (EC = 0.11 dS m1) at EP1.0 on daily basis was included in
an experiment in the same greenhouse and the grain yieldfrom this control is included as the background in this paper.

2.2.

2.

Materials and methods

2.1.

Experiment

The experiment was conducted in a greenhouse located at theArid Land Research Center, Tottori University in Tottori, Japan.
The textural composition of the soil is 95% sand, 1.3% silt, and3.7% clay and is usually referred to as dune sand. The water
holding capacity of this soil sand is 0.05 cm3 cm3(0.027 cm3 cm3 is wilting point and 0.08 cm3 cm3 is field
capacity, and these correspond to matric potentials of 1.6
and 0.0055 MPa), respectively.

Weather condition

Humidity and temperature were measured every 15 min using(HOBO H8 PRO SERIES LOGGER). The air temperature (maximum, minimum and daily mean) during the growing season
increased from April until July and decreased thereafter. The
mean monthly temperatures were 20 8C for April, 24 8C for
May, 25 8C for June, and 30.1 8C for July. During the growing
season the lowest daily mean temperature was 11 8C in April
and the highest was 48 8C in July. The mean monthly humidity
ranged from 56% to 69%. The lowest diurnal variation in
humidity was 33% in June and the highest was 97% in April.
The weather data were used to compute daily crop evapotranspiration (ETc).

agricultural water management 88 (2007) 63–72

2.3.

Crop evapotranspiration computation

compute soil solution ECsw. The general form of the equationis

Evaporation from open-pans were measured from three smallpans (Esp), 0.2 m internal diameter, located in the greenhouseand was converted to class A evaporation (EP) using Agodzo
et al.’s (1997) equation:
EP ¼ aEbsp(1)

ECsw ¼

where a and b are fitting parameters and a = 0.58 and b = 1.3.
The EP in Eq. (1) was converted to potential evapotranspiration (ETo) using Doorenbos and Pruitt (1977) equation,(2)

The Kpan in Eq. (2) is 0.8 and this value was obtained
following Agodzo et al. (1997) rationale for greenhousecondition using Doorenbos and Pruitt (1977) procedure.
The ETo from Eq. (2) was converted to crop evapotranspiration (ETc) using Doorenbos and Pruitt (1977) equation,
ETc ¼ Kc ETo

(3)

2.4.
Soil water content, bulk electrical conductivity andirrigation
Simultaneous volumetric soil water content (uv) and soil waterelectrical conductivity (ECsw) distributions in the root-zone
were monitored using time domain reflectometry (TDR)
method (Topp et al., 1980; Dehghanisanij et al., 2004; Inoue,
2006). The TDR sensors were installed vertically at two depths(10 and 25 cm) along the dripper lines and near to the emitters.
The TDR sensor installation depths were based on Yamamoto
and Cho (1978) findings who reported the most effective rootwater uptake zone in this dune sand under drip irrigation is
the top 25 cm. Depending on the irrigation frequency, the TDR
readings were taken just before and 1–2 h after every
irrigation. The difference (Duv) between uv before and after
irrigation, at a given depth for a treatment, is considered as the
net recharge. Thus, the Duv from a given depth segment
multiplied by that depth is equal to the amount of water
replenished after irrigation. We consider that most of therecharge was used by the crop between two consecutive
irrigations.

2.5.
TDR calibration for the determination of soil watersalinity, ECsw
There are few published reports on how TDR can be used tomonitor ECsw. Dehghanisanij et al. (2004) and Inoue (2006)
developed functional relationships involving TDR dielectric
constant (Kd), uv, and the TDR conductivity reading (ECa) to(4)

EC a  0:00425u  0:00631
7:05u4  2:17u3 þ 0:56u2 þ 0:0727u  0:0004(5)

The estimates obtained using Eq. (5) were compared withexperimentally determined electrical conductivity (ECexp) of
soil solution (Inoue, 2006; Dehghanisanij et al., 2004). In thiscalibration, irrigation waters of different salinity in different
amounts were added to known soil mass in beakers and the
TDR was used to record uv and ECa. These values were usedin Eq. (5) to compute ECsw. When ECsw obtained using Eq. (5)was compared with ECexp and this indicated there was a
relative error of 16%, which we considered as unsatisfactory.
Therefore, we developed our own predictive equation for
ECsw,
ECsw ¼

where Kc is crop factor and we used the Allen et al. (1998)
published Kc values for the early (ES), mid (MS) and late (LS)growth stages of sorghum and they are 0.7, 1.1 and 0.55,
respectively. For simulating the semi-arid Mauritania growing
condition, we assumed that the ES is approximately the first 35
days after seeding, MS from day 35 to 75, and LS from day 75 to106.

EC a  Bðuv ÞAðuv Þ

The uv in Eq. (4) was computed using Kd of TDR readings.
The equation proposed by Inoue (2006) for ECsw computation is
ECsw ¼

ETo ¼ Kpan EP65

EC a  0:016uv  0:009
4:286uv2  0:6491uv þ 0:0416(6)

The estimates for A and B, in Eq. (4), were obtained from
regression analysis of experimental data collected in thisstudy using Inoue (2006) procedure. The estimates obtainedusing Eq. (6) produced a relative error of 2.7%, thus the ECsw
values reported in this manuscript are all computed using
Eq. (6).

2.6.

Statistical analysis

The mean, simple correlation, and stepwise multiple regression analyses were performed on the data using the SAS/Statg(1991) software package.

3.

Results and discussion

3.1.

Soil water content (uv)

The volumetric soil water content (uv) data shown in Fig. 1
indicate that uv varied temporally depending on the time of
measurement (before and after irrigation on a given day), thecrop age, irrigation input and frequency and the profile
segment. The mean values indicate the average uv after
irrigation > before irrigation (obvious), EP1.0 > EP0.5, anddaily irrigation > every second day, and 10–25 cm
segment > 0–10 cm segment (Table 1). The data indicate
the temporal dynamics in uv depended primarily on irrigation input and frequency. The data also indicate the profile
was recharged by irrigation to 25 cm depth, and the recharge
in general was higher in 10–25 cm segment than in 0–10 cm(not shown). Previous studies (Yamamoto and Cho, 1978)
from the same greenhouse for sorghum indicated that the
major root-water uptake took place from the top 25 cm of soil
profile, therefore hereafter we will place our emphasis onchanges in uv and profile recharge that occurred in the in top
25 cm depth.

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agricultural water management 88 (2007) 63–72

Fig. 1 – The temporal dynamics of soil water content just before and 1–2 h after irrigation, in the different irrigation
treatments.

3.2.

Available soil water and productivity

In this section we converted the changes (Duv) in uv that
occurred between before and after irrigation in the top 25 cmof the profile to millimetre of water and compare it withirrigation input and sorghum potential crop evapotranspiration, ETc (Fig. 2). The recharge in the 0–25 cm segment of thedaily irrigated EP0.5 was approximately equal to theirrigation input, indicating the applied water was in the
top 25 cm of the profile after 1–2 h of irrigation. The ETc
throughout the growing season was usually higher than therecharge in the 0–25 cm, suggesting the irrigation input was
not sufficient to meet the ETc, and consequently a sustainable productivity issue (Agodzo et al., 1997). In the daily

Table 1 – The ranges (minimum and maximum) and average water content during the growing season under different
irrigation input and schedules
Time

Irrigated daily
At 50% of pan evaporation

At 100% of pan evaporation

Range

Mean

Recharge

Range

Mean

Recharge

Soil water (cm cm )In 0–10 cm soil layer
Before irrigation
After irrigation

0.016–0.037
0.021–0.055

0.024  0.003
0.034  0.005

0.010

0.020–0.040
0.022–0.061

0.028  0.007
0.041  0.004

0.013

In 10–25 cm soil layer
Before irrigation
After irrigation

0.015–0.052
0.036–0.074

0.032  0.007
0.052  0.009

0.020

0.017–0.057
0.032–0.078

0.033  0.007
0.059  0.008

0.025

Irrigated every second day
In 0–10 cm soil layer
Before irrigation
After irrigation

0.016–0.033
0.020–0.047

0.020  0.004
0.030  0.003

0.010

0.005–0.047
0.018–0.076

0.024  0.003
0.038  0.007

0.014

In 10–25 cm soil layer
Before irrigation
After irrigation

0.017–0.036
0.022–0.065

0.029  0.008
0.041  0.005

0.012

0.020–0.044
0.026–0.063

0.030  0.005
0.047  0.007

0.017

3

3

Recharge is the difference between the mean of after and before irrigation soil water content.

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agricultural water management 88 (2007) 63–72

Fig. 2 – The profile recharge (the difference between after and before irrigation soil water content multiplied by 250 mm), theirrigation input, and potential evapotranspiration (ETc).

irrigated EP1.0, the recharge through irrigation input and theETc were approximately equal to or overlapped with eachother, indicating that irrigation input recharged the depleted
profile and it was sufficient to meet ETc, provided therecharge was not lost through percolation to depth > 25 cm.
In the every second day irrigated treatment, the trends
observed for ETc at EP0.5 and EP1.0 input are qualitatively
similar to that observed in the daily irrigated treatments(Fig. 2c and d). The irrigation recharge in 0–25 cm of the every
second day irrigated practice was less than the irrigation
input, regardless of the irrigation input. The difference
between irrigation input and recharge (Table 2) is larger inthe EP1.0 input treatment (229 mm) than EP0.5 input (73 mm).
A comparison of the difference between irrigation input andrecharge in the EP1.0 of daily and every second day irrigatedschedule indicates the difference is larger (299 mm) in the

Table 2 – The cumulative profile recharge and percolation losses under different irrigation input and frequency treatments
Irrigation and soil water

Irrigation input
Profile (25 cm) recharge
Percolation to depth > 25 cm

Irrigated daily

Irrigated every second day

50% of pan
evaporation(EP0.5) (mm ofwater during thegrowing season)

100% of pan
evaporation(EP1.0) (mm ofwater during thegrowing season)

50% of pan
evaporation(EP0.5) (mm ofwater during thegrowing season)

100% of pan
evaporation(EP1.0) (mm ofwater during thegrowing season)383
379
4 (1%)

765
662
103 (14%)382
309
73 (19%)765536
229 (30%)

Functional relationship between cumulative recharge (CR) or percolation below (PR) 25 cm depth and total irrigation input (II), irrigation
frequency (IF) and the interaction involving (II and IF). CR = 88.91 + 0.92II0.17II  IF (R2 = 0.99; P < 0.01), PR = 88.91 + 0.08II + 0.17II  IF
(R2 = 0.99, P < 0.02). The numbers within parenthesis in the percolation losses row are percolation losses in percent to depths > 25 cm.

68

agricultural water management 88 (2007) 63–72

latter than the former (103 mm). The aforementioned recharge
versus input differences suggests that percolation losses todepths > 25 cm, during 1–2 h after irrigation, and it increased
with increasing irrigation input and with increasing intervals.
Assuming that soil evaporation losses during 1–2 h after
irrigation are similar in different input treatments, it seems
that approximately 41% of the total growing season input inthe every second day irrigated EP1.0 percolated todepths > 25 cm compared with 16% in the daily irrigatedEP1.0, 24% in every second day irrigated EP0.5, and <1% in daily
irrigated EP0.5. It seems relatively drier profile conditions in
the every second day irrigated treatment favored more rapid
percolation losses than the daily irrigated treatment. Thissuggests frequent irrigation is preferable over less frequent to
reduce percolation losses below the active root-zone in thisdune sand.
Thus, it seems the daily irrigated EP1.0 is the optimum
irrigation management practice for this dune sand in relation
to profile recharge and leaching of salts below the active rootzone.
The cumulative potential ETc (578 mm) during the growing
season was met satisfactorily by the cumulative profile
recharge (662 mm) in the daily irrigated EP1.0 treatment. In
the every second day irrigated EP1.0 treatment there was a
deficit of 42 mm compared with approximately 200 mm deficit
in the daily irrigated EP0.5 and 270 mm in the every second
irrigated EP0.5 treatments. Thus, it seems the available soil
water deficit induced stress was probably highest in the every
second day irrigated EP0.5 treatment, followed by daily

irrigated EP0.5 and every second day irrigated EP1.0 treatments. The results indicate that for meeting the seasonalpotential ETc, form irrigation profile recharge, and for
optimum drainage below the crop root-zone in this dune
sand, the daily irrigated EP1.0 management practice is the best
irrigation management option.
The cumulative profile recharge (PR), computed for eachtreatment, matched against the corresponding irrigation input
indicates percolation losses of approximately 1% in the daily
irrigated EP0.5 and 14% in EP1.0 to depths > 25 cm and 19% in
EP0.5 and 30% in EP1.0 of the every second day irrigatedtreatments. The PR increased with increasing irrigation input(II) but at a given II it decreased with decreasing frequency(Table 2). This suggests that more percolation todepths > 25 cm in the every second day irrigated treatment
than the daily irrigated.
Though leaching fractions were not intentionally
included in the irrigation input treatments, substantial
percolation losses (PL) occurred, particularly in the every
second day irrigated treatment including the EP0.5 input
treatment, which we believe was the most stringent input
treatment. There are at least two aspects that need attention
with regard to the PL. First, the PL seems to increase withincreasing input (II) and with decreasing irrigation frequency(IF) and this is supported by the multiple regression equation
provided in Table 2. The interaction involving II and IF
indicates that when the IF increased to every second day the
PL also increased. We however, intuitively, anticipated the
PL to be smaller in the every second day irrigated (lessFig. 3 – The temporal dynamics in electrical conductivity of soil water, monitored just before and 1–2 h after irrigationcompared with FAO threshold value of 13.6 dS mS1 for sorghum.

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agricultural water management 88 (2007) 63–72

Table 3 – The average electrical conductivity of the soil water (ECsw) under different irrigation treatments in different
segments of the dune sand profile and the yield
Average ECsw (dS m1)

Irrigation treatment
Relative yield (%)

0–10 cm

10–25 cm

0–25 cm

0–10 cm

10–25 cm

0–25 cm

39
29
75
55

15.88  1.78
18.12  3.41
8.72  1.02
9.39  1.82

14.13  0.28
15.97  1.13
8.04  0.47
8.58  0.43

14.94  1.16
17.34  2.28
8.44  0.68
9.38  0.60

26.52
15.43
–
–

115.12
29.96
–
–

45.52
18.98
–
–

50% input daily
50% input every second day
100% input daily
100% input every second day

frequent) treatment than the daily treatment. Contrary tothis expectation an opposite trend was observed and we
speculate this was due to increases in percolation in thissandy soil with increasing in soil dryness. Secondly, thewater retention ability of this soil is so poor that irrigation
input in the every second day irrigated treatment equivalent
to twice as that in the daily irrigated led to increased
percolation, and consequently it might have resulted inhigher crop water stress in the former than the latter
treatment.

3.3.
Electrical conductivity of soil water (ECsw) andirrigation
3.3.1.

Temporal dynamics of ECsw

The data for the electrical conductivity of soil water (ECsw)
shown in Fig. 3 indicates that regardless of the irrigation input
or frequency the mean ECsw in the top 25 cm soil layer
increased with time. The differences between the before andafter irrigation curves indicate the ECsw decreased rapidly
after irrigation, increased until the next cycle of irrigation andthe trend was consistent throughout the growing season. The
trends were qualitatively similar across treatments, but themagnitudes varied with irrigation input and frequency.
Approximately 60 days after seeding, the ECsw increased
rapidly between irrigation events particularly in the EP0.5
input practice and more specifically during late maturity stage,
regardless of irrigation frequency. The ECsw dynamics,
particularly the values before irrigation, indicate the crop
was subjected to salinity stress as the ECsw values duringcertain growth stage exceeded the threshold level (Tanji andKielen, 2002).

3.3.2.

Slope ‘B’ in Eq. (7)Seasonal mean ECsw and threshold salinity (ECt)

Shalhevet (1994) proposed the use of growing season average
ECsw to assess salinity stress on crop yield against the Tanji
and Kielen (2002) proposed threshold (ECt) values. The FAO
proposed threshold ECt are based on soil saturation paste

extract procedure and these values can be converted to ECsw
by multiplying the extract values by 2 (Maas and Hoffman,
1977; Letey et al., 1985; Letey and Dinar, 1986; Oster, 1994;
Shalhevet, 1994). The proposed paste extracted threshold
ECt for 0% sorghum yield reduction due to salinity is
6.8 dS m1. We therefore selected the ECt as 13.6 dS m1(i.e. ECt  2 = ECsw) to assess the possibility of salinity stressin the temporal data (Fig. 3). The data indicate that there
should have been no salinity stress in the EP1.0 input
treatment regardless of the irrigation frequency. On theother hand under EP0.5 treatment the ECsw exceeded thethreshold value at late stage of crop growth under both
frequencies of irrigation, implying that the crop might have
faced some salinity stress. However, as this occurred during
the late maturity stage its impact on grain yield may bequestionable.
Another approach is to assess growing season mean ECsw
in the root-zone against the ECt (Letey et al., 1985; Oster, 1994;
Shalhevet, 1994). The growing season mean ECsw in the top
25 cm of the daily irrigated EP1.0 treatment was 3.4 dS m1
compared with 7.1 dS m1 for EP0.5. The ECsw in the every
second day irrigated EP1.0 was 5.1 and 5.9 dS m1 in EP0.5. The
average ECsw values suggest the crop was not subjected tosalinity stress, regardless of the irrigation management
practices. According to other workers (Shalhevet, 1994) themean ECsw for a given growth stage can also be used as a guideto assess salinity impact during that growth stage or during agiven period. Thus, we computed the mean ECsw during theperiod when ECsw exceeded ECt (Table 3). The mean ECsw
during late maturity stage in the EP0.5 irrigation input was
higher than the threshold ECt value, regardless of irrigation
frequency, suggesting potential salinity stress-induced grain
yield reductions in these treatments. The mean ECsw in EP1.0
during the period when ECsw for EP0.5 exceeded ECt is higher
than the corresponding seasonal mean (see above) but lessthan ECt, indicating no possibility for any salinity induced
yield reduction in EP1.0 even during the late maturity stage(Table 4).

Table 4 – Sorghum grain yield as affected by different irrigation input and frequencies
Grain yield

Irrigation treatment
Irrigated daily at

Yield (kg m2)
Control yield in 2005

Irrigated every second day at

50% of pan
evaporation (EP0.5)

100% of pan
evaporation (EP1.0)

50% of pan
evaporation (EP0.5)

100% of pan
evaporation (EP1.0)

0.128  0.011–

0.226  0.035
0.315  0.031

0.090  0.012–

0.170  0.026–

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agricultural water management 88 (2007) 63–72

Table 5 – Simple linear correlation between sorghum
relative grain yield (%) and cumulative recharge (mm) inthe top 25 cm during the growing season or the meanelectrical conductivity (ECsw) of soil water or meanelectrical conductivity during the period when it was
greater than threshold salinity, or total irrigation input(mm), or irrigation frequency (where daily irrigation = 1
and every second day irrigation = 2)
Intercept

Slope

R2

P

Cumulative recharge
Growing season mean ECsw

9.99
94.39

0.13
7.07

0.99
0.97

0.004
0.03

Late season mean ECsw
Irrigation frequency (IF)Total irrigation input (II)

104.8
ns
2.98

4.42

0.95

0.05

0.081

0.79

0.10

Independent variable2

R = coefficient of determination, p = probability at which therelationship is significant.

3.4.
Sorghum grain yield, profile recharge, the mean ECsw,
as affected by irrigation input and frequency
3.4.1. Discriminating the impact of soil moisture stress versus
salinity stress on grain yield
The cumulative profile recharge (PR) that occurred during thegrowing season, the growing season mean electrical conductivity (ECsw-gm), the late season mean conductivity (ECswls), total irrigation input (II), and irrigation frequency (IF) were
each individually correlated with relative grain yield (Table 5).
The PR, ECsw-gm and ECsw-ls were each significantly correlated with grain yield (Table 5). The stronger significant
relationship between relative yield (RY) and PR as compared to
RY and II indicates that the available soil water, throughirrigation recharge, played a major role rather than II per se indetermining grain yield. This is basic to all the grain yieldmodels available in literature, particularly those developed by
Letey et al. (1985) for irrigated conditions and more specificallywhen saline water was used for irrigation. We mentioned
elsewhere in the text the low water holding capacity of the soil
contributed to high percolation losses. Thus, the yield
reduction under less frequent irrigation, but under similar
total irrigation input as in more frequent irrigation, is
attributed to accelerated percolation losses and low water
holding capacity in this soil. Though percolation losses below
root-zone, based on the amount of irrigation input, cannot be
predicted our results indicate that in sandy soils less frequentirrigation at high input may lead to larger losses and this
aspect needs to be considered in deciding irrigation management options with regard to input and frequency of application. For sandy soils similar to the one tested in this study
frequent irrigations in small amounts, may be even twice in aday, seem to be more appropriate than once everyday.
We mentioned elsewhere in the text the impact of salinity on
grain yield is questionable. To resolve this contradiction we
conducted a stepwise multiple regression analysis with relative
grain yield (Yr) as a function of PR, ECsw-gm, and ECsw-ls, theanalysis indicated that Yr was mainly affected by PR. However,when we included in ECsw-ls, which was marginally significant
in the stepwise procedure the analysis produced a nonsignificant positive coefficient for ECsw-ls, which is physically
impossible. Thus the stepwise analysis conclusively indicatedthat grain yield depended only on PR, which depended both
irrigation input (II) and irrigation frequency (IF) and described by
the equation provided in Table 2.

Fig. 4 – The mean electrical conductivity in different segments of the profile under different irrigation treatments comparedwith FAO threshold value of 13.6 dS mS1 for sorghum.

agricultural water management 88 (2007) 63–72

The simple linear correlation indicated that grain yield was
impacted by the growing season mean ECsw (Table 5). Earlier,based on the threshold salinity (ECt) concept we indicated theimpact of salinity stress on grain yield was marginal (Figs. 3
and 4). Thus, further clarification is needed in the impact ofsalinity stress on grain yield.

3.4.2.
yield

Production functions for assessing salinity stress on

Letey et al. (1985) proposed a model to predict salinity
associated grain yield reductions. The model was based on
three functional relationships, of which only one, yield versus
growing season average ECsw, can be directly applied in thisstudy and this relationship is significant (Table 5). The othertwo functional relationships, yield versus cumulative ETc, andaverage ECsw versus leaching fraction (LF), cannot be tested
due to unavailability of data. Therefore, we cannot use theyield model of Letey et al. (1985) in this study. Other secondaryfunctional relationship proposed by these workers, yieldversus total irrigation input, though proposed for non-saline
water irrigation, was tested and produced a relationshipsignificant only at P < 0.10 (Table 5), suggesting insufficient
data and/or application frequency masking irrigation input
impact. As mentioned elsewhere because the percolation
losses in the dune sand was high, we tested the significance ofyield versus the cumulative profile recharge (PR), a surrogate
for irrigation input, and found the relationship produced thehighest R2 value compared with the other functional relations
tested (Table 5).
To further explore salinity-induced grain yield reduction
we adapted Maas and Hoffman (1977), M–H (1977) relationshipbetween relative yield (Yr) and average root-zone salinity. The
average root-zone salinity in the original M–H formulation isbased on the electrical conductivites of extracts obtained fromsaturated-soil pastes, which we replaced with the TDR
monitored average electrical conductivity of soil water (ECsw)
and adapted equation isY r ¼ 100  BðECsw  ECt Þ

for ECsw > ECt(7)

By definition, Eq. (7) is applicable only when ECsw > ECt,
therefore it can be applied only to late maturity stages of EP0.5
input treatments. The B in Eq. (7) is slope of the yield salinity
curve and other terms have already been defined. By
rearranging the terms in Eq. (7) for B, we computed B for
EP0.5 treatment (Table 3). The computed B values may not bedirectly comparable to those reported in the literature,
because ECsw in Eq. (7) is soil water salinity value whereas
in the original M–H formulation it is paste extract values.
The higher B values are indicative of more salinity stressand less Yr and vice versa (Shalhevet, 1994). The B values(Table 3) indicate the impact of salinity on grain yield washigher in the daily irrigated EP0.5 than every second day
irrigated EP0.5, but mean ECsw for late maturity stage (Table 5)
indicates the stress should have been larger in the every
second day irrigated EP0.5 than the daily irrigated EP0.5. We
are unable to provide any reason for this contradiction.
However, in general, the production functions reported inliterature were developed and tested using data from repeatedapplication of saline water for several seasons or years (Leteyet al., 1985).

71

The data sets gathered and tested to explore production
functional relationships in our study appear to be rather small,as this greenhouse experiment was conducted for only one
season.
It should be noted the salinity stress (Figs. 3 and 4) that wasobserved during the late maturity stage, in both the daily andevery second day irrigated EP0.5, corresponded with decreasesin ETc (Fig. 2), which probably was met by profile recharge andtherefore no water stress should have occurred during thisperiod. This suggests the late maturity stage salinity stressmight have contributed towards the reduction in Yr in theEP0.5 treatments.
The data for every second day irrigated EP1.0 (Fig. 2d)suggest there was no water stress, because irrigation in
general exceeded ETc. The average ECsw indicate there was no
salinity stress in this treatment, the question now arises as towhat caused the reduction in Yr in every second day irrigatedEP1.0. We propose at least two reasons. First, we have alreadyshown the profile recharge was less than the input andsubstantial percolation losses (Table 2) occurred within 1–2 hafter irrigation, thereby reducing the available soil water tocover the 2 consecutive days, particularly during the second
day after irrigation. To resolve this issue one should have thewater content data on the second day after irrigation and thatat depths >25 cm unfortunately, we did not collect this data.
Second, the water holding capacity of this dune sand is verylow (0.05 cm3 cm3) and the water content in the 0–25 cm
segment during the second day was probably insufficient tomeet crop ETc.
Because the experiment was conducted only for one
growing season, it is not known whether repeated irrigation
for several years may lead to gradual build up of salinity in thisdune sand. Further studies are required and are in progress. In
this regard leaching studies involving quality water, if
available, or with saline water to leach out major proportionof the accumulated salt is suggested. The leaching may be
carried out before seeding or after crop harvest. Either of theleaching practice may help to keep the soil resource sustainable even under saline water irrigation.
The marginal to no significant impact of salinity on grain
yield is attributed to few unresolved issues. These are based on
the observation that in general the average ECsw in the soil
profile is less than the salinity of irrigated water (ECi). The
discrepancy could be attributed to several reasons (i) underestimation by TDR; (ii) the rapid percolation carrying the salt
below the monitored depth, through high conductivity ofsand; (iii) salt accumulation on the surface (visual observation). Though, we suspect there was general under predictionof ECsw by TDR, nevertheless the technology is sound forroutine monitoring, but needs further fine tuning with regard
to calibration, particularly for sandy soils with very low water
holding capacity.

4.

Conclusions

The grain yield of sorghum, grown on dune sand and irrigatedwith 7.32 dS m1 saline water, indicated no water or salinity
stress when the crop was irrigated daily at 100% of open-pan
evaporation. On the other hand the crop was subjected to both

72

agricultural water management 88 (2007) 63–72

water and salinity stresses in the 50% open-pan input,
regardless of whether the crop was irrigated daily or every
second day. The unintended percolation below the root-zone
was very high, particularly when dune sand was irrigated lessfrequently and at high input levels. The salinity stress in the
50% irrigation input appeared only during late maturity stage.
The substantial yield reduction in the 100% open-pan input
irrigated every second day, compared with the corresponding
daily irrigation, is attributed to low water holding capacity andrapid percolation losses in this dune sand. Irrigation schedules
based on open-pan measurement is relatively low-techcompared with that based on sophisticated profile water
depletion or crop evapotranspiration (ETc) computations.
Therefore, we recommend the use of this approach forirrigation scheduling in situations where sophistication islimited. In general, we conclude that saline waters of salinity
similar to that used in this study can be used for irrigatingsorghum grown in sandy soils of semi-arid regions, e.g.
Mauritania, at input levels at least equal to the open-pan
evaporation and irrigated daily to reduce or minimize waterand salinity stresses. For such an irrigation management
option in sandy soils we recommend the use of drip irrigation
system.

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ReturnForest Ecology and Management 241 (2007) 84–90
www.elsevier.com/locate/forecocopyComparison of litterfall production and leaf litter decomposition
between an exotic black locust plantation and an indigenous
oak forest near Yan’an on the Loess Plateau, China
Ryunosuke Tateno a,*, Naoko Tokuchi b, Norikazu Yamanaka c, Sheng Du c, Kyoichi Otsuki d,
Tetsuya Shimamura e, Zhide Xue f, Shengqi Wang f, Qingchun Hou gaFaculty of Agriculture, Kagoshima University, Kagoshima 890-0065, Japan
Field Science Education and Research Center, Kyoto University, Kyoto 606-8502, Japanc
Arid Land Research Center, Tottori University, Tottori 680-0001, JapandFaculty of Agriculture, Kyushu University, Fukuoka 861-2415, Japane
Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University, Uji 611-0011, Japanf
Northwest A & F University, Yangling, Shaanxi 712100, Chinag
Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi 712100, China

al

b

on

Received 6 April 2006; received in revised form 28 December 2006; accepted 29 December 2006rs

Abstractr'spe

Litterfall production, the amount of organic matter on the forest floor, and litter decomposition rates were studied in an exotic nitrogen (N)fixing black locust (Robinia pseudoacacia) plantation and an indigenous non-N-fixing oak (Quercus liaotungensis) forest near Yan’an, on the
Loess Plateau, China. The chemical composition of litterfall and soil was also examined. Litterfall production was similar in the two forests;
however, the amount of N in litterfall was greater in the black locust plantation than in the oak forest because of the high N concentration of black
locust leaves. The decomposition rate of black locust leaves was higher than that of oak leaves, most likely because of the higher N content of black
locust leaves. These results suggested that N cycling was greater and faster in the black locust plantation than in the oak forest. However, fasterdecomposition caused the disappearance of the organic layer from the forest floor in the black locust plantation. Furthermore, despite greater N
cycling in the black locust plantation, the soil N content was lower than in the oak forest. Our results indicated that the black locust plantation might
be more susceptible to soil erosion than the oak forest. In addition, our study suggested that the black locust plantation had advantages in short-term
N uptake, growth, and N cycling; however, it had disadvantages in soil development and regeneration and sustainable land management.
# 2007 Elsevier B.V. All rights reserved.

1. IntroductionthoKeywords: Organic matter cycling; Nitrogen fixation; Revegetation; Semi-arid

Au

Exotic species have been widely introduced for revegetationof arid and semi-arid areas. Functional differences in exotic
species often alter the productivity, decomposition, and nutrientand hydrological cycling of local ecosystems (Usher, 1988;
Vitousek, 1990; Ohte et al., 2003). Revegetation has oftencaused other problems, such as groundwater deficits resulting
from higher water consumption by the planted tree species (e.g.
Ohte et al., 2003). Ohte et al. (2003) reported that the water use* Corresponding author. Tel.: +81 99 285 8572; fax: +81 99 285 8572.
E-mail address: tateno@agri.kagoshima-u.ac.jp (R. Tateno).
0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2006.12.026

efficiency of an introduced Salix sp. was lower than that ofindigenous species. As a result of the extravagant water use anddeep rooting depth of Salix sp., areas dominated by thisintroduced tree tend to show groundwater deficits. Thus, it isimportant to investigate differences between exotic andindigenous species, not only in vegetation recovery ability,
but also in terms of functional differences and theirconsequences.
On the Loess Plateau in the semi-arid region of central
China, which is located in the middle reaches of the Yellow
River and covers most parts of Shanxi, Gansu, Ninxia, Shaanxi,
Henan, Inner Mongolia and Qinhai Provinces, the nitrogen (N)fixing exotic black locust (Robinia pseudoacacia) has been
widely used for revegetation (Zheng, 1985; Shan et al., 2003).

R. Tateno et al. / Forest Ecology and Management 241 (2007) 84–90

copy1998). Thus, organic matter and N-cycling dynamics are closely
related to regeneration processes and soil development. Therefore, understanding organic matter and N-cycling dynamics
within forests is important for both revegetation and sustainable
land management in arid and semi-arid areas.
The objective of this study was to compare the organic
matter turnover and N cycling between an indigenous oak forest
and a black locust plantation. We investigated organic matterand N cycling, litter decomposition, and the accumulation oforganic matter and N on the forest floor and in soil in both forest
types. We discussed the merits and detriments of black locust
plantations.
2. Materials and methods
2.1. Study sitesonalThe study sites were located on Mt. Gonglushan, near
Yan’an, Shaanxi Province, China (36825.400 N, 109831.530 E;
1353 m a.s.l.). On the Loess Plateau, the amount ofprecipitation and the occurrence of forest gradually decrease
northwestward, and Yan’an is located in the forest–grassland
zone (Cheng and Wan, 2002). The mean annual precipitation
and air temperature during 1982–2003 were 514 mm and10.2 8C, respectively, according to data from a local
meteorological station. Details of the study site were given
by Yamanaka et al. (2004) and Otsuki et al. (2005).
According to local farmers, this area was colonized 50–60
years ago and was cultivated after native oak forests werecleared. Cultivated lands in this area were not irrigated or
fertilized and were cultivated for about 30 years. Black locust
was planted on abandoned cultivated lands 20–30 years ago.
Considerable numbers of trees from the remaining oak forests
were cut for firewood and charcoal. According to tree-ring
analyses, the oak forests comprised 55–60-year-old secondary
forest and the black locust plantation was 29 years old at thetime of this study (Table 1; Du et al., 2007b).

th
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This species is native to North America and shows remarkable
growth in semi-arid environments (Zheng, 1985; Shan et al.,2003). The water use efficiency and drought tolerance of thisspecies are lower than that of indigenous species such as
Quercus liaotungensis and Acer stenolobum (Yamanaka et al.,2006; Du et al., 2007a). Recently, it was reported that a ‘‘drysoil horizon’’ near the forest limit for dryness develops in black
locust plantations, which results in wilting of the top of thecrown and causes the deaths of individual trees (Hou et al.,
1999; Wang et al., 2001). It is therefore necessary to reconsider
the use of non-indigenous trees for revegetation. Althoughprevious studies have reported on propagation, plantation
techniques and the physiological behavior in relation to nutrient
and water conditions (Li et al., 1996; Liu et al., 2003; Shanet al., 2003; Wang et al., 2003; Cao et al., 2005), N
accumulation and cycling have not been examined for R.
pseudoacacia in semi-arid areas. Production in semi-arid
ecosystems is thought to be co-limited by N and water
availability (Hooper and Johnson, 1999). Therefore, investigating the differences in organic matter and N cycling between
indigenous forests and exotic plantations may be useful indetermining alternate revegetation methods in this region.
In semi-arid ecosystems, soil organic matter and N pools tend
to be small compared to the flux of organic matter and N fromlitterfall (Crawford and Gosz, 1982). Understanding thedecomposition of litterfall is critical for predicting plant growthand N supply and cycling. Decomposition dynamics are strongly
affected by biotic and abiotic factors (e.g., Swift et al., 1979). For
example, decomposition and immobilization are closely related
to leaf properties, such as the carbon (C) to N ratio and specificleaf area, which vary widely among species (Takeda et al., 1987;
Hobbie, 1992; Berendse, 1994; Cornelissen, 1999; Osono and
Takeda, 2001), and environmental conditions, such as soil
moisture and temperature (e.g., Swift et al., 1979).
The balance between litter production and decomposition
controls the development of the soil organic layer and the patternof soil N accumulation. The soil organic layer plays a critical rolein species regeneration in arid and semi-arid environments(Pugnaire et al., 1996; Barritt and Facelli, 2001). The presence ofan organic layer has both negative and positive effects onunderstory development via plant regeneration processes, such as
germination, growth, and mortality. Furthermore, the organic
layer considerably increases the soil infiltration capacity andmitigates water and wind erosion (e.g., Pimentel and Kounang,85

2.2. Vegetation census
Six study plots were placed in an artificial R. pseudoacacia
plantation and an indigenous Q. liaotungensis forest in 2002.
The species and diameter at breast height (DBH) were recorded
for all trees >1 cm in DBH in each plot.

Au

Table 1
Stand structure of study plots

Mean DBH (cm)aMax DBH (cm)Mean height (m) a

Max height (m)Total BA (m2 ha1)

Max age (yr)Quercus liaotungensis
Q0
2375
Q1
4188
Q2
2713

7.6 (5.5)
4.3 (4.9)
5.1 (5.1)

23.9
29.4
23.8

5.0 (2.0)
5.2 (2.4)
7.7 (2.3)

9.2
11.1
11.7

16.3
14.1
12.9

55
59
60

Robinia pseudoacacia
R0
1713
R1
2736
R2
2736

8.6 (2.8)
10.0 (4.8)
10.6 (5.2)

15.3
20.7
24.6

8.2 (2.2)
9.0 (2.8)
8.3 (2.4)

12.8
13.6
11.6

22.1
24.0
26.1

27
–
–

Plot

a

Density (trees ha1)

Mean (S.D.).

R. Tateno et al. / Forest Ecology and Management 241 (2007) 84–90

2.3. Litterfall collection

We compared the amount of litterfall and organic layer andthe accumulation of N in the soil and the organic layer between
the black locust plantation and the oak forest using t-tests. A
two-way analysis of variance (ANOVA) was used to investigate
the effect of species and soil depth on the soil N content. We
used the software SPSS for Windows (SPSS Inc., Chicago,USA) for all statistical analyses.

Ten 0.25 m2 litter traps each were located in the black locust
plantation and the oak forest. Litterfall was collected monthly
from 2003 to 2004. All collections were sorted into leaves,
twigs, and other organs, and dried at 70 8C for 72 h. Eachfraction was weighed separately for each litter trap, ground into
powder, and analyzed for total N and C content using an NC
analyzer (NC-900; Shimadzu, Kyoto, Japan).

3. Resultspy

86

3.1. Stand structure

Five 1 m2 subplots were established in each forest to
estimate the extent of the soil organic layer. Organic matter was
carefully collected by hand and weighed after drying at 70 8C
for 72 h.
Mineral soil samples were collected from both forests. In
each forest, one soil sample was collected from each of six
depths (0–5, 5–10, 10–30, 30–50, 50–70, and 70–100 cm). The
samples were divided into fine soil (grains < 2 mm indiameter), gravel (>2 mm), roots, and litter. Fine soil was
ground into powder, and the total N and C contents were
determined using an NC analyzer (NC-900; Shimadzu, Kyoto,
Japan).

Stand structure of the study plots was summarized inTable 1. The mean DBH ranged from 8.6 to 10.6 cm in black
locust plantations and from 4.3 to 7.6 cm in oak forests. The
maximum DBH ranged from 15.3 to 24.6 cm in black locust
plantations and from 23.8 to 29.4 cm in oak forests. The
maximum height ranged from 11.6 to 13.6 m in black locust
plantations and from 9.2 to 11.7 m in oak forests. The total
basal area ranged from 22.1 to 26.1 m2 ha1 in black locust
plantations and from 12.9 to 16.3 m2 ha1 in oak forests.

alon

3.2. Litterfall production and N cycling

The amount of litterfall (mean  S.D.) was 3.8  0.6 t
ha1 year1 in the black locust plantation and 4.2  1.1 tha1 year1 in the oak forest; however, this difference was not
significant (t = 1.1, p > 0.05; Fig. 1a). The amount of leaf fall was
3.1  0.5 t ha1 year1 in the black locust plantation and3.3  0.5 t ha1 year1 in the oak forest; again, this difference
was not significant (t = 0.83, p > 0.05; Fig. 1a).
The amount of N in litterfall was significantly greater in theblack locust plantation (56.5  7.3 kg ha1 year1) than in theoak forest (39.1  15.5 kg ha1 year1; t = 3.20, p < 0.01;
Fig. 1b). Similarly, the amount of N in leaf fall was significantly
greater in the black locust plantation (43.3  4.9 kg ha1 year1)
than in the oak forest (25.5  4.3 kg ha1 year1; t = 8.68,
p < 0.001; Fig. 1b).
The percentage of N in black locust and oak litterfall was
1.49 and 0.93%, respectively, and the percentage of N in black
locust and oak leaf litter was 1.39 and 0.77%, respectively(Fig. 1c). The C:N ratio of black locust and oak litterfall was
31.9 and 58.4, respectively, and the C:N ratio of black locust
and oak leaf litter was 29.7 and 48.3, respectively.

rs

2.5. Litterbag methodco2.4. Analysis of organic and mineral soil layers

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th
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The leaf litter decomposition rate was measured using alitterbag method. During the period of leaf fall, we collected
newly fallen leaves from the forest floor and immediately driedthem at 70 8C. We filled 2-mm mesh nylon litterbags(10 cm  10 cm) with 2 g dry weight of leaf litter of R.
pseudoacacia or Q. liaotungensis. Litterbags of each species
were placed in both the black locust plantation and the oakforest on 20 November 2004. Litterbags were collected eighttimes: after 4, 5, 6, 7, 8, 9, 10, and 11 months. We collected 10
litterbags of each species from each forest at each samplingtime. The samples were weighted after drying at 70 8C for 72 h,
ground into powder, and stored in plastic bags until chemical
analysis. Total N and C contents were determined using an NC
analyzer (NC-900; Shimadzu, Kyoto, Japan).
The amounts of lignin contained in the leaf litter samples
were estimated by gravimetry according to a standardized
method using hot sulfuric acid digestion (King and Heath,1967).

3.3. Decomposition rate

2.6. Statistical analysis

Decomposition constants (k) of leaf litter were calculatedusing the exponential decay model (Olson, 1963) as follows:Wt¼ ektW0
where W0 is the original litter weight, and Wt is the litter weightafter a given period of time t. The data used for the calculationof decomposition constants were the mean remaining weight of
10 replications at each collection date.

The decomposition rate, k, of R. pseudoacacia was 0.47
year1 in the black locust plantation and 0.48 year1 in the oakforest (Fig. 2). The k of Q. liaotungensis was 0.15 year1 in theblack locust plantation and 0.21 year1 in the oak forest(Fig. 2). Thus, the k of R. pseudoacacia was greater than that of
Q. liaotungensis in both forest types. However, the effect offorest type was less important than that of species.
Initial N contents of leaf litter used for litter bag experimentwere 1.23 and 0.53% for R. pseudoacacia and Q. liaotungensis,
respectively. Initial C:N ratio of leaf litter were 34.7 and 81.3

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R. Tateno et al. / Forest Ecology and Management 241 (2007) 84–90

r'sFig. 1. (a) Amount of litterfall, (b) N in litterfall, and (c) the concentration of N in litterfall in an oak forest and a black locust plantation (mean  S.D.). Black bars(&) indicate total litterfall; white bars (&) indicate leaf fall.

thofor R. pseudoacacia and Q. liaotungensis, respectively. Initial
lignin content of leaf litter were 270.5 and 246.2 mg g1 for R.
pseudoacacia and Q. liaotungensis, respectively. Lignin to N
ratio of leaf litter was 22.1 and 46.7 for R. pseudoacacia and Q.
liaotungensis, respectively.

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3.4. Amount of organic matter and N on the forest floor andin soil
Whereas both the semi-decomposed, fragmented organic
matter layer (F horizon) and humus layer (H horizon) weredeveloped in the oak forest, only the F horizon was observed in
the black locust plantation. The total amount of organic matteron the forest floor was significantly lower in the black locust
plantation (5.5  1.1 t ha1) than in the oak forest (Fig. 3;
18.6  4.0 t ha1; t = 5.41, p < 0.05). The estimated turnoverrate (amount of organic matter on the forest floor/annual litter
fall) of the forest floor was 1.4 years in the black locust
plantation and 4.4 years in the oak forest.

N accumulation in the organic layer was 103  13 kg N ha1in the black locust plantation and 199  49 kg N ha1 in the oakforest; however, this difference was not significant (t = 2.675,
p = 0.12). The estimated turnover rate (annual litter fall/amountof organic matter on the forest floor) of the forest floor N was 1.8
years in the black locust plantation and 5.1 years in the oak forest.
The C:N ratio of organic horizons in black locust plantations was
19.5. The C:N ratio of organic horizons in oak forests was 52.6
and 20.0 for F and H horizons, respectively.
The soil N and C contents decreased with soil depth in bothforests (Fig. 4 a and b). The soil N contents were higher in the oakforest than in the black locust plantation. These differences weremore obvious in the shallow soil layers than in the deep layers.
The accumulation of N at a soil depth of 0–100 cm was
0.6627  0.0876 kg N m2 in the oak forest and 0.5619 
0.1676 kg N m2 in the black locust plantation. The accumulation of C at a soil depth of 0–100 cm was 9.9663 
0.7464 kg C m2 in the oak forest and 10.7560  2.1576 kg
C m2 in the black locust plantation. For both the N and C

R. Tateno et al. / Forest Ecology and Management 241 (2007) 84–90

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88

Fig. 3. Amount of the organic layer in the oak forest and black locust plantation(mean  S.D.). Black bars (&) indicate the F horizon; white bars (&) indicate
the H horizon.

4. Discussion

rsFig. 2. Changes in the remaining weight of leaf litter during 12 months ofdecomposition in litter bags (mean  S.E.). Open circles (OB) (*) and closed
circles (OO) (*) indicate leaves of black locust and oak, respectively, placed in
the oak forest; open squares (BB) (&) and closed squares (BO) (&) indicatesleaves of black locust and oak, respectively, placed in the black locust plantation. The decomposition rate constants (k) were 0.21, 0.48, 0.15, and 0.47 for
OO, OB, BO, and BB, respectively.

onalaccumulation at this depth, there were no significant differences
between the black locust plantation and the oak forest (t = 0.75,
p = 0.49 for N and t  0.49, p = 0.65 for C). The soil C:N ratio
increased with depth in both forests (Fig. 4c), and the soil C:N
ratio was higher in the black locust forest than in the oak forest.

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The litterfall production rate was only slightly higher in theoak forest than in the black locust plantation. In general, the leaf

Fig. 4. (a) Soil N content, (b) soil C content, and (c) soil C:N ratio in the oak forest and black locust plantation. Closed circles (*) indicate oak forest; open circles(*) indicate black locust plantation (mean  S.D.).

R. Tateno et al. / Forest Ecology and Management 241 (2007) 84–90

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Annual inputs of N to soil systems via litterfall were far
greater in the black locust plantation than in the oak forest.
Higher soil N accumulation by N-fixing trees has been reported
in many forested ecosystems (Boring and Swank, 1984a,b;Sanginga, 1990; Danso et al., 1992). N-fixing trees often areplanted as ‘‘fertilizers.’’ For example, Boring and Swank(1984a) reported that 33–75 kg N ha1 year1 N are fixed bysymbiotic N-fixers and accumulated in the soil each year in theAppalachian Mountains, USA, where the annual precipitation
is about 1800 mm. Because the forests studied here were about
30 years old, we expected that a substantial amount of N would
have accumulated in the soil, even though a considerable
amount had been removed by crop harvesting and erosion
during the period of cultivation. However, we found no
significant difference in soil N between the two forest types.
There are several possible explanations for this inconsistency. In arid and semi-arid environments, soil erosion
caused by precipitation and/or wind tends to be more severe
than in other ecosystems (Breshears et al., 2003). In particular,
erosion tends to occur when there is no vegetation or humus
cover (Pimentel and Kounang, 1998). Only an F layer wasobserved in the black locust plantation. The F horizon showed
high temporal variation and was very small just before leaf fall.
In contrast, the H horizon was quite stable. Thus, surface soil
erosion may have caused low N and C accumulation in thesurface soil of the black locust plantation. Furthermore,decomposed leaf litter may be blown away by wind. In thisregion, average of maximum daily wind strength from 19
March 2005 to 17 July 2005 were 1.9  0.7 and1.0  0.5 m s1 (mean  S.D.) in the black locust plantationand in the oak forest, respectively (Otsuki et al. unpublisheddata). The decomposing black locust leaf litter was thinner andmore fragmented than that of oak. Therefore, a considerable
amount of leaves may be removed by wind especially in black
locust plantations. Thus, the development of an organic soil
layer via decomposition may have been prevented in the black
locust plantation. In this area, where soil erosion caused bywater and wind is severe, black locust plantations may not beeffective as fertilizers.
In arid and semi-arid regions, revegetation is important for
maintaining local environments and restraining the expansionof desert areas. Over the short term, the high growth rate and Nfixing ability of black locust under severe conditions may makethis an advantageous species for revegetation (Zheng, 1985;
Shan et al., 2003). If the N fixed by this species was effectively
held in ecosystems via soil–plant systems, plantations of thisspecies would be desirable. However, it appears that black
locust plantations are disadvantageous, not only for soil
development and regeneration, but also for sustainable land
management. From the viewpoint of sustainability, black locust
plantations should be gradually shifted to forests of indigenous
tree species.

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N concentration of N-fixing trees is higher than that of non-Nfixing trees (Killingbeck, 1996; Aerts and Chapin, 2000). We
found a greater concentration of N in leaf litter of black locustthan in that of oak. As a result, the annual N cycling via litterfall
was higher in the black locust plantation than in the oak forest.
The amount of N cycling in both sites was comparable to that ofother ecosystems, such as wet temperate forests (Vitousek,
1982).
Decomposition is strongly affected by biotic and abiotic
factors (Swift et al., 1979). Our results suggest that the quality of
the leaf litter is more important than that of the site for litter
decomposition. This may be primarily because the leaf C:N ratio
and lignin/N ratio, which are good indicators of the decomposition rate (e.g., Swift et al., 1979), were lower in N-fixing
species than in oak. These results are consistent with previous
studies that have reported faster decomposition rates of N-fixing
than non-N-fixing species (Aerts and Chapin, 2000). Recent
studies reveals rapid initial decomposition does not always leadto low accumulation of organic matter. Forests with N-rich,rapidly decomposing litter often accumulate large amounts oforganic matter, especially if the litter is rich in lignin (Berg et al.,1996). Differences in lignin contents between two species were
far less than those of nitrogen contents, and it may suggest thatdifferences in N content was major factor influences on
decomposition rate in this study site. Furthermore, leaf anatomy
also affects the decomposition rate (Cornelissen et al., 1999).
Black locust leaves have a higher specific leaf area (SLA; unit
leaf area per unit leaf mass) than oak leaves (Yamanaka et al.,unpublished data), which may have contributed to the higher
decomposition rate of black locust.
Site conditions, such as soil moisture, temperature andfertility, also affect decomposition (Swift et al., 1979; Schuur,
2001 but see Prescott, 1995). Otsuki et al. (2005) reported thatthe soil moisture content of this black locust plantation was
significantly lower than that of the oak forest, which was causedby its sparser canopy. Furthermore, a higher soil temperature
was recorded in the black locust plantation than in the oak forest(Otsuki et al., 2005). Despite differences in environmental
conditions such as soil moisture and temperature, the forest
type did not affect the decomposition rate in this study.
As reflected by differences in the decomposition rate
between the species, there was a clear difference in soil organic
matter accumulation between the forest types. Whereas both F
and H horizons were observed in the oak forest, only an F
horizon occurred in the black locust plantation. There were few
seedlings and little understory vegetation in the black locust
plantation, whereas many seedlings and abundant understory
vegetation were evident in the oak forest (Yamanaka et al.,2004). In general, the accumulation of organic matter affects
seedling recruitment and mortality (e.g., Barritt and Facelli,2001). In the black locust forest, seedling mortality may be highbecause of the poorly developed organic layer. The differencesin litterfall production, decomposition, and organic matteraccumulation, which were mainly caused by functional
differences in the N-use strategy of these two species, may
be critical for the regeneration process in this area via theinterrelationship between plant and soil systems.

89

Acknowledgments
We received support from many institutes and individuals in
the People’s Republic of China. This work was supported in

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part by the Japan Society for the Promotion of Science-Chinese
Academy of Science (JSPS-CAS) Core-University Program‘‘Researches on Combating Desertification and Developmental
Utilization in Inland China.’’

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PHYSIOLOGIA PLANTARUM 123: 459–466. 2005
Printed in Denmark – all rights reserved

doi: 10.1111/j.1399-3054.2005.00481.x
Copyright # Physiologia Plantarum 2005

Application of silicon enhanced drought tolerance in Sorghum bicolor
Taiichiro Hattoria,*, Shinobu Inanagaa, Hideki Arakib, Ping Ana, Shigenori Moritac, Miroslava Luxovád and Alexander LuxeaArid Land Research Center, Tottori University, 1390 Hamasaka, Tottori, Tottori 680-0001, Japan
Faculty of Agriculture, Yamaguchi University, 1677-1 Yoshida, Yamaguchi, Yamaguchi 753-8515, Japanc
Field Production Science Center, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Midori-cho,Nishitokyo, Tokyo 188-0002, Japand
Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 14, SK-842 23 Bratislava, Slovak RepubliceDepartment of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B-2, SK-842 15
Bratislava, Slovak Republic*Corresponding author, e-mail: hat@alrc.tottori-u.ac.jpbReceived 28 July 2004; revised 22 November 2004

The effects of silicon application on the drought tolerance ofsorghum (Sorghum bicolor (L.) Moench) were investigated fortwo cultivars differing in drought susceptibility. Silicon application ameliorated the decrease in dry weight under drought
stress conditions, but had no effect on dry matter production
under wet conditions. Under dry conditions, silicon-appliedsorghum had a lower shoot to root (S/R) ratio, indicating
the facilitation of root growth and the maintenance of thephotosynthetic rate and stomatal conductance at a higher

Introduction
Sorghum (Sorghum bicolor (L.) Moench) is one of themost important crops of arid regions in Africa and Asia.
Insecure water supply as a result of fluctuating precipitation and/or limited irrigation often causes a decrease insorghum yield. Thus, it is important to enhance thedrought tolerance of this economically important crop.
The application of certain mineral elements to various
crops can influence their drought tolerance or traits
involved in drought tolerance. For example, Purcell andKing (1996) found that nitrogen supply to soybean
enhanced its drought tolerance through an improvement
in nodule activity. Phosphorus influences osmotic adjustment in leaf tissues in sorghum and bean (Alkaraki et al.
1996) and root characteristics in white clover (Singh andSale 2000). Potassium contributes to the maintenance oflevel compared with plants grown without silicon application.
The diurnal determination of the transpiration rate indicatedthat the silicon-applied sorghum could extract a larger
amount of water from drier soil and maintain a higher stomatal conductance. Very similar effects of silicon application
were observed for both cultivars regardless of their droughtsusceptibility. These results suggest that silicon application
may be useful to improve the drought tolerance of sorghum
via the enhancement of water uptake ability.

osmotic adjustment in pearl millet (Ashraf et al. 2001)
and to root growth in hibiscus (Egilla et al. 2001).
Calcium increases antioxidant activity under drought
stress conditions in liquorice (Li et al. 2003). The modification of fertilizer composition is therefore considered
to be a useful method to improve crop productivity
under drought conditions. However, few effects on
drought tolerance have been reported for elements
other than the major nutrients.
Certain seed plant species, mainly from the families
Gramineae and Cyperaceae, accumulate large amountsof silicon. They are sometimes referred to as silicon
accumulators. Silicon application to these plants ensuresbetter growth, especially during environmental stress.
Silicon application has been reported to alleviate thedecrease in dry matter accumulation or photosynthetic

Abbreviations – ANOVA, analysis of variance.; DAS, days after sowing.; LAR, leaf area ratio.; NAR, net assimilation rate.; RGR, relative
growth rate.; S/R ratio, shoot to root ratio.; WUE, water use efficiency.
Physiol. Plant. 123, 2005459

rate caused by high salt concentration in various speciesof cereals (Matoh et al. 1986, Ahmad et al. 1992, Lianget al. 1996), high temperature (Okamoto 1969) and the
toxicity of some heavy metals (Jarvis and Jones 1987,
Hammond et al. 1995, Gu et al. 1998). A recent review
on this subject is given in Ma (2004).
Silicon application may also be effective in enhancing
the drought tolerance of plants. Under water stress conditions, such as soil drying and high water demand fromthe atmosphere, silicon-applied cereal crops have beenreported to be able to retain a higher leaf water potential
than crops grown without silicon application (Yoshida
1965, Matoh et al. 1991, Agarie et al. 1998). The
formation of a silica – cuticle double layer on leaf epidermal
tissue has been considered to be responsible (Yoshida 1965,
Matoh et al. 1991). The active reaction of stomata toatmospheric humidity in rice (Agarie et al. 1998) and thedecrease in the specific leaf area in wheat (Gong et al. 2003)
have also been suggested to be involved in the inhibition ofleaf water deficit. However, these data are insufficient toclarify completely the mechanism of improvement indrought tolerance caused by silicon application. As paststudies have focused attention mainly on the preventionof excess water loss, as mentioned above, the effects ofsilicon application on water uptake ability, which cannot
be ignored in a discussion of drought tolerance, remain
unknown.
Endodermal tissue, which plays an important role inwater transport across the root (Steudle and Peterson
1998), is known to accumulate large amounts of silicon
in mature drought-tolerant sorghum cultivars (Lux et al.
2002). A similar observation has previously been
observed in rice (Lux et al. 1999). These data, together
with the high speed of silicon uptake and deposition bysorghum root (Lux et al. 2003), and the effects of losing
root cell wall in sorghum (Hattori et al. 2003), suggest
the possibility that silicon plays an important role inwater transport and/or root growth of sorghum underdrought conditions.
In terms of the effect of silicon on sorghum, information
regarding drought tolerance and water uptake ability islacking. In the present study, we focused on the effects ofsilicon application on the growth and water relations ofsorghum under water-limited conditions to verify whether
silicon may be useful to enhance the drought tolerance of
this species. To achieve this purpose, the effects of silicon
were assessed for two cultivars differing in drought tolerance. The silicon-induced physiological reactions of sorghum were analysed from the viewpoint of water relations,water use efficiency (WUE) and photosynthesis.

Materials and methods
Plant materials, growth conditions and silicon treatments
Two sorghum cultivars differing in drought tolerance
were used as plant materials in the present study. Seedsof the two sorghum cultivars were provided by the Soil &Water Research Center, Agricultural Research Corporation, Sudan. Gadambalia is a local cultivar in Sudan and460

is drought tolerant. Tabat is a drought-sensitive cultivar
released for the irrigated regions. The morphological andphysiological adaptations of both cultivars on exposure
to drought stress have been reported previously (Salihet al. 1999, Tsuji et al. 2001, 2003).
Pot experiments were conducted in a glasshouse at theArid Land Research Center, Tottori University, Tottori,
Japan. Plastic pots filled with 15.0 kg sand dune Regosol(collected from Tottori sand dunes) were used for theexperiment. The pots were covered with aluminium foil
to prevent an increase in soil temperature caused by solar
radiation. Each pot was fertilized with nitrogen, phosphorus and potassium at a rate of 1.0, 1.0 and 3.3 g perpot, respectively. As the source of potassium, potassium
silicate was used in the silicon-applied treatment (1 Si)
and potassium chloride in the silicon-deficient treatment(– Si). In the 1 Si treatment, 5.0 g of silicon was added toeach pot. Trace element fertilizer containing 0.21 g g1 of
MgO, 0.0045 g g1 of MnO and 0.0045 g g1 of B2O3 wasalso supplied to each pot at a rate of 1.5 g per pot. The
soil pH in all pots was adjusted to pH 7.6 with calcium
hydroxide. Five seeds of sorghum were sown per pot
and, thereafter, seedlings were thinned to a single planton the 12th day after sowing (DAS). At 23 DAS, 100 ml
of potassium silicate solution (100 mg l1) was applied topots of the 1Si treatment. Potassium chloride solution
was applied to the pots of the –Si treatment to yield thesame total potassium as in the 1Si treatment. The pH inboth solutions was adjusted to pH 5.5 with HCl prior toapplication. Plants were grown until 50 DAS.
Dry treatments
The sorghum seedlings contained in pots were adequately irrigated to yield a soil water content of
0.08 g g1 until 24 DAS. Dry treatment was initiated at
25 DAS. During the period of dry treatment until
50 DAS, the water content of the pot soil was adjusted
gravimetrically every day to 0.03 g g1 for the dry treatment and 0.08 g g1 for the wet treatment. Plastic sheetscoated with aluminium film were placed on the soil
surface to prevent evaporation from the pots.

Growth analysis, photosynthetic rate and WUE
The photosynthetic rate, transpiration rate, stomatal
conductance and intercellular CO2 concentration of thethird-last fully expanded leaves were measured underclear and sunny weather using a portable photosynthesis
system (LI-6400, LI-COR Inc., Lincoln, NE) at 39 and
40 DAS. The leaf water potential of the same leaves wasmeasured by a pressure chamber (Model 1000, PMS
Instrument Co., Corvallis, OR) during the daytime(10.00–14.00 h) at 46 DAS. The leaf blade, stem androot system were separately sampled at 50 DAS. The
leaf area was measured with a leaf area meter (AAL410, Hayashi Denko Inc., Tokyo, Japan) and the dryweight of each organ was measured after drying
Physiol. Plant. 123, 2005

samples in an oven at 80 C for 72 h. At least three plantsfrom each treatment were used for statistical analysis.
Growth analysis was performed on the basis of dry weight
and leaf area measured before and after the dry treatment.
The relative growth rate (RGR), net assimilation rate (NAR)
and leaf area ratio (LAR) were calculated according to thefollowing formulae:
RGR ¼

1nw2  1nw1
t2  t1

NAR ¼

w2  w1 1nL2  1nL1
t2  t1
L2  L1

Statistical analysis
Data were analysed statistically by analysis of variance(ANOVA), with subsequent comparison of means by theleast significant difference (LSD) test.

1nw2  1nw1
L2  L1
LAR ¼

w2  w1
1nL2  1nL1
where wi and Li are the total dry weight (g) and leaf area(m2) on day ti, respectively. The days t1 and t2 are the initialand last days of the dry treatment period, respectively.
Diurnal changes in the water content of the soil (average value of a whole pot) and the transpiration rate perunit leaf area were calculated from the transition of the
pot weight and leaf area at 49 DAS. The water content
was converted to water potential according to the watercontent–water potential curve of the soil (Inoue andNomura 1983). WUE was also calculated according to
the following formula:
WUE ¼

The silicon concentration of the third-last fully
expanded leaves was measured according to Lux et al.
(2002). Briefly, the dried powdered plant sample wasashed in a muffle oven at 500 C for 5 h. The plant ash
was dissolved in diluted HCl (1 : 1; 10 ml) at 100 C. The
process of dissolving in HCl and evaporation to dryness
was repeated three times. Then, diluted HCl (1 : 1; 15 ml)
was added and the sample was heated at 100 C, filtered,placed into a ceramic crucible and ashed again in theoven at 540 C for 5 h. After cooling, the weight of Si wasdetermined gravimetrically.

w2  w1
T

Results
Silicon concentration in soil and leaves
The soluble silicon concentration in sand dune Regosol fromthe Tottori region used for the experiment was 21.1 mg kg1
dry soil for the – Si treatment and 30.6 mg kg1 for the 1 Si
treatment. The silicon concentration in leaf blades wasincreased by silicon fertilizer application regardless of thesoil water regime (Tables 1 and 2). There were no significant
differences in the silicon concentrations between thecultivars.
Dry matter production

where T is the total amount of water used for transpiration during the dry treatment period.

Measurement of silicon concentration
The silicon concentration in the soil taken from the pots in
the 1 Si and – Si treatments was measured by the submerged soil incubation method according to Nonaka and
Takahashi (1988). An air-dried 10 g soil sample was submerged in 60 ml of distilled water in a 100 ml polyethylene
container and placed in an incubator at 40 C for 1 week.
After 1 week, the silicon concentration of the supernatant
was measured by the molybdenum blue method.

Silicon application did not influence the dry weight of theplants before the initiation of the dry treatment (data notshown). The effect of silicon application on plant size
became visibly clear as the plants grew (Fig. 1). At
50 DAS, the dry weight of plants given the 1 Si/dry treatment was significantly higher than those given the – Si/dry
treatment (Tables 1 and 2). In the – Si/dry treatment, theplant dry weight decreased by 77–80% compared with the– Si/wet treatment. In contrast, in the 1 Si/dry treatment,
the plant dry weight decreased by only 53–54% comparedwith the 1 Si/wet treatment. The effect of silicon on the
dry weight showed a similar tendency for both cultivars,
but the increase in shoot dry weight was relatively higher
in cv. Gadambalia than in cv. Tabat. In the wet treatment,

Table 1. Effects of silicon application on shoot dry weight (SDW), root dry weight (RDW), total dry weight (TDW), shoot to root (S/R) ratio
and silicon concentration (%) in leaves of cv. Gadambalia. Data are the means of three replications. Different letters indicate significant
differences by LSD (P , 0.05). *, y, NS, significant at the 0.1% and 5% level and not significant by analysis of variance (ANOVA), respectively.
Treatment

SDW (g)RDW (g)

TDW (g)S/R ratio

Si concentration (%)

1 Si, wet
– Si, wet
1 Si, dry
– Si, dryDry
SiliconDry  silicon
LSD (0.05)

43.9a
37.4a
19.2b
8.6c
*
y
NS
9.3

25.0a
22.6a
13.1b
3.7c
*
y
NS
6.7

69.0a
60.0a
32.2b
12.3c
*
y
NS
15.7

1.76a
1.66a
1.50a
2.41b
y
NS
y
0.58

1.85a
1.09b
1.56ab
0.61c
y
*
NS
0.47

Physiol. Plant. 123, 2005

461

Table 2. Effects of silicon application on shoot dry weight (SDW), root dry weight (RDW), total dry weight (TDW), shoot to root (S/R) ratio
and silicon concentration (%) in leaves of cv. Tabat. Data are the means of three replications. Different letters indicate significant differencesby LSD (P , 0.05). *, y, z, NS, significant at the 0.1%, 1% and 5% level and not significant by analysis of variance (ANOVA), respectively.
Treatment

SDW (g)RDW (g)

TDW (g)S/R ratio

Si concentration (%)

1 Si, wet
– Si, wet
1 Si, dry
– Si, dryDry
SiliconDry  silicon
LSD (0.05)

38.8a
36.0a
14.7b
9.3b
*
NS
NS
5.9

32.7a
33.8a
18.0b
6.4c
*
NS
NS
11.3

71.5a
69.8a
32.7b
15.8c
*
z
NS
12.1

1.25ab
1.10ab
0.82a
1.44b
NS
NS
z
0.46

2.03a
1.09bc1.59ab
0.98c
NS
y
NS
0.57

the dry weight was not affected by silicon application. A
significantly lower shoot to root (S/R) ratio was observedin 1 Si/dry plants compared with – Si/dry plants. The
effect of silicon application on the S/R ratio was unclear
in the wet treatment. These tendencies were similar inboth cultivars.
In both cultivars, RGR was not affected by siliconapplication in the wet treatment (Table 3). Although
RGR was reduced in the dry treatment in both cultivars,
silicon application significantly alleviated the decrease in
RGR (Table 3). LAR was higher in the – Si/dry treatment than in the 1 Si/dry treatment (Table 3).
Assimilation rate and stomatal conductanceThe decrease in NAR due to drought stress was significantly ameliorated by silicon application (Table 3). However, silicon had no effect on NAR in wet conditions.
The photosynthetic rate, transpiration rate and stomatal
conductance of sorghum measured in the daytime (10.00–14.00 h) were maintained at a significantly higher levelin the 1 Si/dry treatment than in the – Si/dry treatment(Fig. 2). The parameters observed in the – Si/dry treatment were only 30–40% of those found in the –Si/wet

treatment, whereas, in the 1Si/dry treatment, the values
were at least 75% of those in the 1Si/wet treatment. The
influence of silicon application on the intercellular CO2
concentration (Ci) was undetectable regardless of the soil
water status. These tendencies were quite similar for both
cultivars (only data from Gadambalia are shown in
Fig. 2).
WUE and water relations
The WUE in the dry treatment was significantly higher
than that in the wet treatment in both cultivars (P , 0.05,
tested by ANOVA). However, silicon application itself had
no effect on WUE in both wet and dry treatments(Fig. 3). The diurnal transition of the soil water potential
and transpiration rate per unit leaf area showed different
trends in relation to silicon application in the dry treatment, but not in the wet treatment (Table 4, Fig. 4). The
soil water potential in the 1 Si/dry treatment was slightly
lower than that in the – Si/dry treatment during 09.00–
11.00 h; thereafter, it markedly decreased at 13.00 h.
Despite the lower soil water potential, sorghum plants
in the 1 Si/dry treatment maintained the same or higher
transpiration rate than those in the – Si/dry treatment.
The leaf water potential in the daytime was not significantly different between the 1 Si/dry and – Si/dry plants(Fig. 5). In the wet treatments, the leaf water potentials
were higher than those in the dry treatments, but noeffect of silicon was detected. These characteristics ofthe leaf water potential and diurnal changes in transpiration rate were commonly observed in both cultivars (onlydata from Gadambalia are shown in Figs 4 and 5).

Discussion

Fig. 1. Effect of silicon application on the growth of sorghum under
dry conditions. Sorghum plants (cv. Gadambalia) were grown insilicon-applied soil (left) and non-applied soil (right). Plants were
47 days old (22 days after the initiation of dry treatment).

462

Silicon is an abundant element in soil, but plant-available silicon is usually present at rather low concentrations in soil solution. If there is plenty of available siliconin the plant rhizosphere, sorghum absorbs more siliconthan normal from the soil solution. Supplemental application of silicon increased the shoot silicon concentrationand led to higher dry matter production under drought
conditions in the present study (Tables 1 and 2, Fig. 1).
The similar dry weight for 1 Si/wet and – Si/wet treatments also indicated that the chloride anion added withpotassium to the – Si treatments in this study did not
Physiol. Plant. 123, 2005

Table 3. Effects of silicon application on the relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) during thedry treatment in two sorghum cultivars differing in drought tolerance. Data are the means of three replications. Different letters indicate
significant differences by LSD (P , 0.05). *, y, z, NS, significant at the 0.1%, 1% and 5% level and not significant by analysis of variance(ANOVA), respectively.
Gadambalia

Tabat

Treatment

RGR(g g1 day1)

NAR(g m2 day1)

LAR(  104 m2 g1)

RGR
(g g1 day1)

NAR(g m2 day1)

LAR(  104 m2 g1)

1 Si, wet
– Si, wet
1 Si, dry
– Si, dryDry
SiliconDry  silicon
LSD (0.05)

0.157a0.149a0.126b
0.083c
*
*
y
0.020

28.3a
25.1ab
21.3b
10.9c
*
y
z
4.61

55.9a
59.5a
59.5a
76.5b
y
y
z
7.94

0.160a0.171a0.127b
0.106c
*
NS
y
0.014

29.4ab
34.3a
24.2b
15.0c
y
NS
z
9.2

55.0a
51.1a
52.7a
70.6b
z
z
z
10.6

have a negative effect on the dry matter production ofsorghum (Tables 1 and 2).
Several reports have described the effect of several otherelements on drought tolerance (e.g. Egilla et al. 2001, Li
et al. 2003). In terms of the improvement in growth under
dry conditions, these elements seem to achieve this throughthe enhancement of dry matter production itself, rather
than through the enhancement of properties responsiblefor drought tolerance. All of these elements improved dry
matter production in both wet and dry conditions (e.g.
Rodriguez et al. 1996). Silicon is distinct from theseelements, as silicon-induced acceleration of dry matterproduction in sorghum is observed only when the plants
are subjected to drought (Tables 1 and 2). The specificity ofthe effect of silicon to dry conditions indicates that siliconaffects certain traits restricting dry matter production
under water-limited conditions. This is discussed below.
The results of growth analysis indicated that theenhancement of drought tolerance observed in the 1Si/
dry treatment was due to a higher dry matter production
per unit dry weight (RGR), which was accounted for by
the higher assimilation rate (NAR) or photosynthesis
rate (Table 3, Fig. 2). Although the plants in the –Si/dry
treatment had a higher LAR, indicating a larger leaf area
per unit dry weight, it did not result in an increase in the
total amount of dry matter production compared withthe 1 Si/dry plants, which had higher NAR. The analysisof the characteristics related to WUE may also provide

Fig. 2. Effects of siliconapplication and dry treatment
on the photosynthetic rate (P),transpiration rate (T),stomatal conductance (gs) andintercellular CO2
concentration (Ci) in the thirdlast fully expanded leaf of cv.
Gadambalia (drought-tolerantsorghum cultivar). Data are
the means of three replications.
Different letters in the figure
indicate significant differencesby LSD (P , 0.05).
Physiol. Plant. 123, 2005

463

Fig. 3. Effects of silicon application and dry treatment on the water
use efficiency of the two sorghum cultivars differing in droughttolerance. Data are the means of three replications. Different lettersin the figure indicate significant differences by LSD (P , 0.05) for
each cultivar.

an interpretation for the high drought tolerance of plants(Passioura 1977). The dry matter production of plants isdetermined by water consumption (transpiration) and
WUE in addition to other factors. In the present study,
although the WUE of sorghum increased with soil desiccation regardless of the cultivar, there were no significant
changes in WUE with silicon application under either
dry or wet conditions (Fig. 3). The higher dry matterproduction was achieved by an increase in transpiration
rather than WUE. Thus, higher stomatal conductance,
allowing a higher transpiration rate, was the main reason
for the silicon-induced enhancement of photosynthesis
under drought conditions. As stomatal conductance ismainly affected by leaf water status, we discuss the water
relations of leaves below.
The transpiration rates in the 1 Si/dry treatment wereconsiderably high around noon compared with those in
the – Si/dry treatment (Figs 2 and 4, Table 4). The leaf
water potential in the – Si/dry treatment decreased toalmost  2.0 MPa at midday (Fig. 5), which is the criticalleaf water potential of sorghum leading to the closure ofstomata (Tsuji, W. et al. 2004, unpublished data). In
contrast, the leaf water potential in the 1 Si/dry treatment was above the critical potential. This indicatedthat, in the 1 Si/dry treatment, water uptake from theroots was more balanced with the high transpirational
demand in the daytime and this prevented stomatal closure due to leaf water deficit, even when the soil was
drying. One reason for the high water uptake may be thelower S/R ratio in the 1 Si/dry treatment (Tables 1 and2), consequently allowing an increase in the root surface
area per unit of leaf area. The lower S/R ratio in the
1 Si/dry treatment may compensate for the slower waterflow from bulk soil to roots by expansion of the extractable root surface area (Sperry et al. 2002). In addition,
hydraulic resistance in the water pathway through plants
may play an important role in the increased water
uptake, as certain nutrient elements can influence thehydraulic resistance of roots (Passioura 1988). Further
physiological and ecological studies are needed to understand the drought-specific effects of silicon because themechanism responsible for this phenomenon remains
incompletely elucidated.
The observation that silicon increased the transpiration
rate (Figs 2 and 4, Table 4) contradicted previous reports,
which showed that silicon application in rice led to adecrease in transpiration via the formation of a cuticle –silica double layer, maintaining a high leaf water potential(Yoshida 1965, Matoh et al. 1991). Although there was a
possibility that water loss from the cuticle might also havedecreased with silicon application in sorghum plants, its
effect on the total transpiration rate would have been quite
small compared with that in rice. According to Matohet al. (1991), the contribution of cuticular transpiration
was about 25–39% of the total transpiration in rice,whereas it was only 3–9% in sorghum (Hattori, T. et al.
2004, unpublished data). The decrease in water loss fromthe cuticle would be masked by the increased transpirationfrom the stomata caused by silicon application.
The performances of the two cultivars were not significantly different with regard to the response to soil drying(Tables 1 and 2), except for the S/R ratio (P , 0.01, tested by
ANOVA). Salih et al. (1999), Tsuji et al. (2001) and Tsuji
et al. (2003) investigated the same two sorghum cultivars
from a physiological and morphological viewpoint underdrought conditions. They reported that cultivar differences

Table 4. Effects of silicon application and dry treatment on leaf area (LA), water uptake (WU) and transpiration rate per leaf area (T) during09.00–13.00 h in two sorghum cultivars differing in drought tolerance. Data are the means of three replications. Different letters indicate
significant differences by LSD (P , 0.05). *, y, z, NS, significant at the 0.1%, 1% and 5% level and not significant by analysis of variance(ANOVA), respectively.
Gadambalia

Tabat

TreatmentLA(m2 plant1)

WU(mol H2O plant1 h1)T(mmol H2O m2 s1)LA
(m2 plant1)

WU(mol H2O plant1 h1)T(mmol H2O m2 s1)

1 Si, wet
– Si, wet
1 Si, dry
– Si, dryDry
SiliconDry  silicon
LSD (0.05)

0.249a0.242a0.105b
0.066c
*
y
z
0.018

4.79a
4.40b
1.65c
0.64d
*
*
z
0.34

5.35a
5.07ab
4.36b
2.70c
*
y
z
0.75

0.259a0.243a0.093b
0.072c
*
z
NS
0.020

4.40a
4.10b
1.42c
0.75d
*
*
NS
0.28

4.73a
4.68a
4.23a
2.90b
*
y
y
0.50

464

Physiol. Plant. 123, 2005

Fig. 4. Effects of siliconapplication and dry treatment
on the diurnal change intranspiration rate per unit leaf
area and the soil water
potential in cv. Gadambalia(drought-tolerant sorghum
cultivar). The soil water
potential was calculated fromthe weight of the pots. The
transpiration rate was derived
from the decrease in pot weight
and the total leaf area. Data
are the means of three
replications. Vertical bars
represent the LSD (0.05) for
each measurement. PWP,
permanent wilting point.

in relation to drought tolerance resulted mainly from water
uptake from the deep soil. In the present study, as therooting zone was restricted by the limited pot volume, theavailability of water was identical between the cultivars.
This may have diminished the difference in dry matterproduction under drought conditions. With regard to silicon application, cultivar differences were ambiguous. Sili-

con application, however, apparently enhanced the dry
matter production in both cultivars under drought conditions (Tables 1 and 2). This suggests that silicon application
may be useful for the alleviation of drought stress in sorghum, irrespective of cultivar. Further research and field
experiments are being performed at present to clarify thecultivar differences with respect to the effects of silicon.
Acknowledgements – This work was supported by a grant for the
21st Century COE program from the Japan Society for the Promotion of Science and by a Research Fellowship from the Japan
Society for the Promotion of Science for Young Scientists.

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Fig. 5. Effects of silicon application and dry treatment on the leaf
water potential. The leaf water potential was measured at 46 days
after sowing (DAS) with the same leaves as used for photosynthetic
measurement. Data are the means of three replications. Different
letters in the figure indicate significant differences by LSD (P , 0.05)
for each cultivar.
Physiol. Plant. 123, 2005

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Edited by M.T. Tyree

466

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Soil Science and Plant Nutrition (2006) 52, 540–544

doi: 10.1111/j.1747-0765.2006.00057.x

ORIGINAL ARTICLE
Effects
R.
Nakazawaof porous
et al.
glassLtd
material on tomato growthBlackwell
Publishing

Effects of the application of porous glass material treated withphosphate on the growth of tomato plants and the phyto-available
phosphate in soil
Ryoji NAKAZAWA1, Hisashi TOMEMORI1, Atsuko HIRANO2,
Hidetoshi MOCHIZUKI1, Ping AN1 and Shinobu INANAGA1
1

Arid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680-0001, and 2Graduate School of Agriculture,
Tottori University, Koyamacho-minami 4-101, Tottori 680-8553, Japan

Abstract
We have previously reported the ability of porous glass material (PGM) to adsorb phosphate and thatcalcium contributed to this process. In the present investigation, the possible use of PGM to improve water
quality (wastewater in particular) and the subsequent use of phosphate-adsorbed PGM as fertilizer were
examined. We confirmed the phyto-availability of phosphate adsorbed onto PGM using tomato cultivation
and an assay of truog-phosphate levels. Adsorption and release of phosphate in PGM was controlled by particle
size. The findings suggest the possibility of using PGM of different particle sizes for efficient phosphate
recycling in soil-water/plant systems.
Key words: phosphate, porous glass material, recycling, tomato, truog-phosphate.

INTRODUCTION
Eutrophication in a closed water system is caused bywastewater produced by households, industry andlivestock. Phosphate in wastewater is a key substancethat contributes to eutrophication. To solve this problem,
prevention laws applied to closed water systems tomaintain water quality have been legislated, and theselaws have controlled the emission of phosphate. Nevertheless, the contamination of phosphate in closed water
systems is still occurring (Kunimatsu 1995).
In contrast, phosphate is a key nutrient for the
maintenance of crop productivity. Exhaustion of theorigins of phosphate fertilizer (phosphate deposits) is,
however, predicted to occur at some point in the twentyfirst century (Koshino 1994).
To deal with the above problems, we have proposed
the establishment of a recycling system of phosphate in
the soil-water/plant system (Inanaga et al. 2005). In thissystem, phosphate-adsorption materials are added to
the wastewater produced by households, industry andCorrespondence: P. An, Arid Land Research Center, Tottori
University, Hamasaka 1390, Tottori, 680-0001, Japan. Email:an.ping@alrc.tottori-u.ac.jp
Received 24 January 2006.
Accepted for publication 25 April 2006.

livestock effluents. Following this, the phosphate-adsorbed
materials are collected and used as phosphate fertilizer.
In a previous paper, it was reported that porous glassmaterial (PGM) adsorbed phosphate (Inanaga et al. 2005).
Porous glass materials are recycled materials made fromwaste glasses and foaming agents (such as crushed shells andCaCO3) (Hara et al. 1998). Porous glass materials are lightweight and have many pores. In addition, we found thatthe adsorption of phosphate is caused by the calcium inthe foaming agents (Inanaga et al. 2005). From the above
results and the finding that plants can use calcium-binding
phosphate in soil (Takahashi 1998), it is expected that
PGM can be used as the phosphate-adsorption materials in the above phosphate-recycling system. However,
several investigators have reported that in phosphateadsorption materials, phosphate adsorption is causedby the aluminum and iron in these materials (e.g. Yanagida
and Jiang 1994; Tanada et al. 2003) and is, thus, notavailable for use by plants (Takahashi 1998). In this paper,
we confirm the phyto-availability of phosphate-adsorbed
PGM using cultivation examination and soil analysis.

MATERIALS AND METHODS
Preparation of porous glass material
Porous glass materials (Fig. 1) were provided by the
Ehime Recycling Institute Company (Niihama, Ehime,© 2006 Japanese Society of Soil Science and Plant NutritionEffects of porous glass material on tomato growth

Figure 1 Porous glass materials without being crushed.

Japan). The manufacturing of PGM occurred, briefly,
as follows. First, wood and metal impurities were
removed from waste glasses and then the glasses werecrushed to approximately 10 mm in diameter. Next,
the crushed glasses were milled to pieces of approximately
500 µm in diameter. Crushed shells (oysters with themain component being CaCO3) were also milled briefly
and mixed with the milled glasses to 0.005 g g−1, andthen the mixture was burned at 900°C for 30 min. The
PGM were crushed and sieved and PGM that were < 1,
1– 2 or 2 –4 mm in diameter (not enough material > 4 mm
was collected) were used in the following experiments.

Phosphate-adsorption experiments
One gram of PGM (< 1, 1–2 and 2–4 mm diameter) was
soaked in 5 mL of 1–100 mg L−1 phosphate (PO4-P)
solution (as KH2PO4) for 24 h and then the upper solution was obtained and filtered using 0.2 µm membranefilters (Millipore IC-Millex-LG, Tokyo, Japan). The
phosphate concentrations in the filtrates were measured
using the molybdenum-blue method (Aso et al. 1985).

Cultivation experiments
First, phosphate-adsorbed PGM was prepared. One
gram of PGM (2 –4 mm diameter) was soaked in 5 mLof 100 mg L−1 phosphate solution for 24 h, and then theupper solution was obtained and filtered using 0.2 µm
membrane filters. The phosphate concentrations in thefiltrates were measured using the molybdenum-blue
method. This procedure was repeated six times to complete the phosphate-adsorption reaction. The remaining
PGM was rinsed in 1.5 L kg−1 of 0.8 L L−1 ethanol andthen the ethanol was removed and dried up. At thistime, the retention of phosphate onto PGM was 646(mg P kg−1 PGM). As a control, distilled-water-treated
PGM was prepared using the above procedure but with© 2006 Japanese Society of Soil Science and Plant Nutrition541

the addition of distilled water rather than phosphate
solution. The phosphate-adsorbed PGM and the distilledwater-treated PGM were used in the following cultivation experiments.
For the cultivation experiments, Tottori sand dunesand was used as the medium. The soil texture of thesoil was S (sandy). The sandy soil consisted of 0.96 g g−1
of sand and 0.04 g g−1 of silt and clay. The truogphosphate level was below the quantification limit, so
the soil was classed as being deficient in phosphate.
Porous glass material was added to air-dried sandy
soil to 0.20 g g −1 and distilled water was also added
to pF = 1.5. The mixtures were placed into 230-mL
pots. Treatments were as follows: (1) no phosphate
fertilizer + distilled-water-treated PGM (–P+G), (2) nophosphate fertilizer + phosphate-adsorbed PGM (–P+GP),(3) phosphate fertilizer + distilled-water-treated PGM(+P+G), (4) phosphate fertilizer + phosphate-adsorbed
PGM (+P+GP), (5) phosphate fertilizer alone (+P). For
each group, there were 15 replicates. The application of‘phosphate fertilizer’ in (3), (4) and (5) was conductedby irrigation of 40 mL of 2.25-fold strength Hoaglandsolution into pots at 0, 15 and 30 days after the sowing
of tomato (Lycopersium esculentum L. Fukuju-2) seeds.
At this time, the total phosphate (100 mg P2O5 per pot)
in Hoagland solution was applied to the sowing seeds.
‘No phosphate fertilizer’ in the –P+G and –P+GP
treatments was conducted by application of Hoaglandsolution containing no phosphate. Tomato plants weregrown in a plastic greenhouse for 44 days and thenharvested. Following this, the plant materials weredried at 80°C for 72 h and the dry weights of shoots
and roots were measured.
To estimate the effects of the application of phosphateadsorbed PGM on the phyto-available phosphate insoil, we determined the truog-phosphate levels (Nanjo
1997) and the pH(H2O) (Kamewada 1997) in the soilof each treatment as outlined above.
In the present study, we focus on two aspects of thefertilizer effects of PGM. One aspect is whether or not
plants can use the phosphate that is adsorbed onto
PGM. To determine this, we compared the results oftreatments –P+G and –P+GP. The second aspect isthat, after plants make use of phosphate provided from
phosphate-adsorbed PGM, phosphate-free PGM remains.
Does the phosphate-free PGM negatively affect soil
phosphate fertility? To examine this, we comparedtreatments +P+G, +P+GP and +P.
We selected tomato as the plant material. PGMs
release silicate as well as adsorb phosphate (Murakami
2003), and silicate is considered to be beneficial for
certain plant species (Takahashi 1999). For example,
silicate improves photosynthesis and provides tolerance
to disease, environmental stress and insects; it also

542 R. Nakazawa et al.

Table 1 Phosphate adsorption of porous glass materials of different particle sizes
Particle sizes ofporous glass materials

Initial phosphateconcentrations (mg L−1)

Phosphate concentrations
after 24 h (mg L−1)

Adsorption
ratio (%)

Phosphate contents in porous
glass materials (mg kg−1)

1
10
100
1
10
100
1
10
100

0.90 ± 0.01
7.26 ± 0.00
70.4 ± 0.00
0.76 ± 0.02
6.86 ± 0.01
64.9 ± 0.01
0.67 ± 0.01
5.81 ± 0.04
47.3 ± 0.04

10.5 ± 0.80
27.4 ± 0.32
29.6 ± 0.13
23.9 ± 1.92
31.4 ± 0.55
35.1 ± 1.11
33.2 ± 1.37
41.9 ± 3.76
52.7 ± 4.17

0.52 ± 0.04
13.7 ± 0.16
148 ± 0.67
1.19 ± 0.10
15.7 ± 0.27
176 ± 5.53
1.66 ± 1.37
18.3 ± 2.30
237 ± 20.9

< 1 mm

1– 2 mm

2– 4 mm

Data are mean ± standard error (n = 3).

increases crop yield in plants such as rice and cucumber.
Therefore, to make it easier to analyze the fertilizer
effects of PGM, we selected tomato plants because
these plants do not appear to be affected by silicate application (Takahashi 1999). In addition, tomato plants are
sensitive to a low concentration of phosphate (Tadano1999), so it is easy to prepare phosphate-deficient tomato
plants.

RESULTS AND DISCUSSION
To preliminarily determine the amount of PGM to be
applied to the soil, the effects of PGM on soil physicalproperties (saturated hydraulic conductivity and waterholding capacity; soil water characteristic curves) were
determined. The results showed that 0.2 g g−1 PGM did
not affect these soil properties (data not shown). Therefore, the amount of PGM applied to the soil in thefollowing experiments was 0.2 g g−1. In addition, because
the truog-phosphate level in soil treated with 0.2 g g−1
of +GP alone was not significantly different to that in
the +P treatment, we expected to be able to determine theside effects of PGM as well as the provision of phosphatefrom the comparison between those two treatments.
In another preliminary experiment, we compared thephosphate adsorption of PGM of different particle sizes(< 1, 1–2 and 2–4 mm diameter). The highest adsorption was in the 2–4-mm particles at each phosphateconcentration, followed by the 1–2-mm and < 1-mm
particles (Table 1). These results show that larger-sized
PGMs have a higher phosphate adsorption. In general,
smaller-sized absorbents have a larger surface area andhigher adsorption capacity. In contrast, PGMs havenumerous pores of ∼1 mm in diameter, as shown in
Fig. 1, but these pores were destroyed in the smallersized material. The findings show that the phosphateadsorption of PGM is affected by physical factors, suchas the number of pores, as well as chemical factors,

Figure 2 Effects of the application of porous glass materials
on the growth of tomato plants. Results are mean ± standard
error (n = 15). Letters (a–d, A–D) indicate significant
differences between shoots and roots, respectively (P < 0.05).

such as the Ca contents of the material as previously
reported (Inanaga et al. 2005). As the application oflarger-sized (2–4 mm) PGM in polluted water systems
may be more efficient in improving water quality, weused 2–4-mm particles of PGM.
The results of the cultivation experiments are shownin Fig. 2. Comparisons of –P+G and –P+GP showedthat the total growth (shoot + root) observed in the–P+GP treatment (0.277 g per plant) was approximately
5.7-fold higher than that observed in the –P+G
treatment (0.049 g per plant). This result indicates that
phosphate is provided by phosphate-adsorbed PGM,
which alleviates phosphate deficiency. In addition,
plants in the –P+G treatment were the smallest of allplants from all treatments, and the typical symptom ofphosphate deficiency (discoloration of leaves to red or
purple) was observed (Fig. 3) (Takahashi 1998). Fromthese results, it is confirmed that plants in the –P+G
© 2006 Japanese Society of Soil Science and Plant NutritionEffects of porous glass material on tomato growth543

Table 2 Effects of phosphate-treated porous glass materials
on phyto-available phosphate and pH(H 2O) in sandy soil
Treatments
–P+G
–P+GP
+P+G
+P+GP
+P

Truog-phosphate†(mg P2O5 100 g soil−1)

pH(H2O)†

0.96 ± 0.37
20.3 ± 2.29
24.8 ± 1.01
37.4 ± 1.60
18.5 ± 0.09

7.7 ± 0.1
7.2 ± 0.1
7.8 ± 0.1
7.3 ± 0.0
6.5 ± 0.0†
Truog-P and pH(H 2O) in sandy soil alone were0.60 ± 0.09 mg P2O5 100 g soil−1 and 6.1 ± 0.0, respectively. Data aremean ± standard error (n = 3). ±P, presence or absence of phosphate
fertilizer application; +G, application of porous glass materials treated
without phosphate; +GP, application of porous glass materials treatedwith phosphate.

Figure 3 Tomato plants grown under conditions of phosphate
deficiency, with phosphate-adsorbed (left) or distilledwater-treated (right) porous glass materials.

treatment suffered from phosphate deficiency. Next, we
compared the +P+G and +P+GP treatments and showedthat there was no significant difference (Fig. 2). This
result indicates that phosphate-free PGM does notnegatively affect soil phosphate fertility.
In contrast, when we compared +P+G, +P+GP and +P,
the growth of +P+G and +P+GP was slightly lower thanthat of +P (Fig. 2). We assume that there are two reasonsfor this phenomenon. One is that phosphate from the
Hoagland solution is adsorbed by PGM, and the otheris that PGM release a substance that is toxic to tomato
plants. However, from the finding that there is no
significant difference between treatments +P+G and +P+GP,
the first reason is rejected, and the second reason isbelieved to be more likely. In a previous paper (Inanaga
et al. 2005), we reported the alkalization of a solution
by soaking PGM within the solution. The mechanism
for this is proposed as follows (Maruta 1975): CaCO3 is
added as a foaming agent and is converted to CaO, andCO2 gas is generated by burning. Foams are generated
by CO2. CaO reacts with H2O and synthesizes Ca(OH)2.
This substance may cause the alkalization. Sandy soil
has a neutral pH, so it may be greatly affected by PGM;
however, the alkalinity of the materials may be usefulfor improving acidic soils. In the present study, thenegative effects of PGM on plant growth are slight, so it isdifficult to analyze the detailed mechanism that is
responsible. This should be analyzed in future studies.
The results of truog-phosphate levels in the treatmentswith phosphate and/or PGM are shown in Table 2. The
truog-phosphate level in –P+GP was higher than that in© 2006 Japanese Society of Soil Science and Plant Nutrition–P+G, and was not significantly different to that of +P.
The highest growth rate was seen in +P, and +P was
treated as the model for standard chemical fertilization.
These results indicate that phosphate-adsorbed PGMs
have the same potential as chemical phosphate fertilizer
to act as fertilizers. However, there is no correlation
between plant growth and truog-phosphate levels. Thismay be because of the release of inhibitors to plant
growth from PGM causing alkalinity, as mentioned
above. To clarify this point, the pH(H2O) in treatmentswith phosphate and /or PGMs was measured. The pH(H2O)
was raised by the application of PGMs (Table 2). These
results indicate that the alkalinity of PGMs may affectplant growth. If so, it may be appropriate to apply the
PGM to acidic water systems and to acidic soils. In
addition, comparisons between +P+G and +P showedthat truog-phosphate levels increased as a result of theapplication of PGM that had not been treated withphosphate. This indicates that the alkalinity of PGMs
may increase the solubility of phosphate fertilizer andinsoluble phosphate (such as Al-P and Fe-P) in the soil.
Smaller-sized PGM adsorbs lower amounts of phosphate (Table 1). This result indicates that phosphateadsorbed on larger-sized PGM may be released bycrushing to smaller-sized PGM. To confirm this, phosphate-adsorbed PGM (2–4 mm diameter) was crushed
to ∼1 mm in diameter and truog-phosphate levels inthe sandy soil that was applied to the crushed materials
were measured. The resulting truog-phosphate level was
36.8 ± 2.1 mg P2O5 per 100 g of soil (pH[H2O] = 8.5),
which was higher than that in soil that was applied tophosphate-adsorbed PGM (2–4 mm diameter) alone(Table 2). From these results, the efficiency of therecycling system of phosphate, from the point of viewof the mass balance of phosphate, may be improved by
the use of larger-sized PGM in the improvement ofwater quality followed by the use of smaller-sized PGM
as phosphate fertilizer.

544 R. Nakazawa et al.

Next, we discuss the practical use of wastewater
treatment using PGMs. Techniques for the removal ofphosphate from water systems, including coagulating
sedimentation (e.g. Kitao 1978), activated sludge processing(e.g. Inamori and Sudo 1982), crystallization (e.g. Sunahara 1988) and removal with adsorbents (e.g. Tanada et al.
2003; Yanagida and Jiang 1994) have been reported. In
the present study, we review these protocols from theviewpoints of suitability to different types of wastewater.
Among these protocols, it is considered that activatedsludge processing is appropriate for the treatment ofwastewater containing large amounts of organic contaminants rather than removal using adsorbents (including PGMs)
and crystallization. Crystallization is appropriate
for the treatment of a great deal of wastewater containing high levels of phosphate, such as industrial wastewater, because of the high initial cost, compared withremoval using adsorbents. Based on these findings, forexample, removal using adsorbents (including PGMs) may
be appropriate as an additive treatment after the primary
treatment of wastewater by, for example, activated sludge
processing. Additionally, because the previously reported
adsorbents consist of aluminum and iron (e.g. Tanada
et al. 2003; Yanagida and Jiang 1994), very little ofthe phosphate adsorbed by these materials is phytoavailable; however, the phosphate adsorbed by PGMs isphyto-available and can be used as fertilizer. Very littleof the phosphate-containing sediment obtained in coagulating sedimentation is phyto-available because of asimilar reason. Thus, PGM is advantageous compared withthe other adsorbents and coagulating sedimentation.
In the present study, we applied large amounts of
PGMs (20% w/w) to soil. In future, for the practical useof PGMs in the field, the amount of PGM application
should be reduced to improve the phosphate-adsorption
capacity. For example, we have previously suggested
that PGMs that have a high phosphate-adsorption
ability can be manufactured by using large amounts of
CaCO3 as the foaming agent (Inanaga et al. 2005) andenlarging the particle size, as shown in the present
study, also increases the phosphate-adsorption capacity.
In addition, the use of PGMs in nursery bed for raisingseedlings may be also useful.
In conclusion, it is confirmed that phosphateadsorbed onto PGM is available to plants. The findingsof the present study suggest that at least some phosphate fertilizer can be provided by PGM and that using
PGM of different particle sizes may aid the efficient
recycling of phosphate in soil-water/plant systems.

ACKNOWLEDGMENTS
We thank the Ehime Recycling Institute Company forprovision of porous glass materials. This research was

supported by the 21st Center Of Excellence (COE)program “Arid Land Science Program” and a Tottori
Prefecture Grant Aid for Environment Science.

REFERENCES
Aso S, Goto I, Takagi T, Takenaga H, Yosiba M 1985:
Molybdenum-blue method. In Textbook for Inorganic
Chemistry Experiment, Ed. S. Aso, pp. 175 –177. Department of Agricultural Chemistry, Tokyo University ofAgriculture, Tokyo.
Hara Y, Onizuka K, Yoshitake S, Aso N, Yoko M 1998:
Example of greening of slope faces by using foamed
glass materials. 33rd Summary of Japanese GeotechnicalSociety (JGS), 2253 – 2524.
Inamori Y, Sudo T 1982: Trend of biological removal ofphosphate. J. Water Waste, 24, 1095 –1110.
Inanaga S, Nakazawa R, Tomemori H et al. 2005: Mechanismof phosphate-adsorption onto porous glass materials.
Man. Environ., 31, 11–16.
Kamewada K 1997: pH (glass electrode method). In Analysis
of Soil Environment, Eds T Kaneno, pp. 195 –197.
Hakuyusha, Tokyo.
Kitao T 1978: Evaluation and problem of protocols for removalof nitrogen and phosphorous. Kogai-to-Taisaku, 14, 822–831.
Koshino M 1994: Phosphate fertilizer. In Encyclopedia of Soil,
Plant Nutrition, and Environment, Eds T Matsusaka
and A Awahara, pp. 256 – 257, Hakuyusha, Tokyo.
Kunimatsu T 1995: Water resource and water quality. In
Agriculture and Environment, Eds K Kyuma and O Soda,
pp. 73 –147. Huminkyoukai, Tokyo.
Murakami M 2003: Basic research on improvement of soil andwater by using porous glass materials (Master thesis). Graduate
School of Agriculture, Tottori University, Tottori, Japan.
Maruta S 1975: Alkali-earth metals. In Summary of Inorganic
Chemistry, pp. 48 – 52. Sankyoshuppan, Tokyo.
Nanjo M 1997: Phyto-available phosphate. In Analysis of Soil
Environment, Eds T Kaneno, pp. 267–269, Hakuyusha, Tokyo.
Sunahara K 1988: Removal of phosphorous by crystallization.
Suisituozakukennkyu, 11, 617 – 621.
Tadano T 1999: Tolerance to phosphate-deficiency. In Plant
Nutrition and Fertilizer Science, Ed. M Chino, pp. 133 –138. Asakurashoten, Tokyo.
Takahashi E 1999: Silicate. In Plant Nutrition and Fertilizer
Science, Ed. M Chino, pp. 95 – 98, Asakurashoten, Tokyo.
Takahashi K 1998: Phyto-available phosphate. In Encyclopedia
for Soil Science and Plant Nutrition, Eds S Fujiwara, T Anzai,
Y Ogawa and T Kato, p. 101, Nobunkyo, Tokyo.
Takahashi K 1998: Phosphate-deficiency. In Encyclopedia for
Soil Science and Plant Nutrition, Eds S Fujiwara, T Anzai,
Y Ogawa and T Kato, p. 135, Nobunkyo, Tokyo.
Tanada S, Kobayama M, Kawasaki N et al. 2003: Removal ofphosphate by aluminium oxide hydroxide. J. Colloid.
Interface Sci., 257, 135 –140.
Yanagida T, Jiang Y 1994: Effects of heating temperature andadditives on phosphate sorption coefficient of heatedmaterials from the volcanic ash soils. Jpn. J. Soil Sci.
Plant Nutr., 65, 171–174.
© 2006 Japanese Society of Soil Science and Plant Nutrition

ReturnPlanta (2004) 219: 450–458
DOI 10.1007/s00425-004-1245-2

O R I GI N A L A R T IC L E

Yanhua Qi Æ Yasuo Yamauchi Æ Jianqun Ling
Naoyoshi Kawano Æ Debao Li Æ Kiyoshi Tanaka

Cloning of a putative monogalactosyldiacylglycerol synthase genefrom rice (Oryza sativa L.) plants and its expression in response
to submergence and other stresses
Received: 28 January 2004 / Accepted: 24 February 2004 / Published online: 16 April 2004
 Springer-Verlag 2004

Abstract Suppression subtractive hybridization was used
to construct a subtractive cDNA library from plants of
non-submerged and 7-day-submerged rice (Oryza sativa
L., FR13A, a submergence-tolerant cultivar). One cloneof the subtractive cDNA library, S23, was expressed
abundantly during submergence. The full length of S23
was ampliﬁed using 5¢- and 3¢-rapid ampliﬁcation of
cDNA ends, and found to consist of 1,671 bp with anopen reading frame of 1,077 bp (181–1257) encoding 358
amino acids. Its deduced amino acid sequence showed ahigh homology with monogalactosyldiacylglycerol synthase (UDPgalactose: 1,2-diacylglycerol 3-b-D-galactosyl transferase; EC 2.4.1.46, MGDG synthase) from
Arabidopsis thaliana; therefore, we named the gene OsMGD. Time-course studies showed that the expressionof OsMGD in the rice cultivars FR13A and IR42 (submergence-susceptive cultivar) during submergence was
gradually increased and that expression in FR13A washigher than in IR42. The expression of OsMGD in
FR13A was inﬂuenced by benzyladenine and illumination. The accumulation of OsMGD mRNA in both
FR13A and IR42 was also increased by ethephon, gibberellin, drought and salt treatment, but cold stress had
no eﬀect on the expression of the gene. These results
suggest that the expression of OsMGD mRNA requires
benzyladenine or illumination, and that the process isalso mediated by ethephon and gibberellin. Salt anddrought stress have an eﬀect similar to that of submerY. Qi Æ Y. Yamauchi Æ N. Kawano Æ K. Tanaka (&)
Laboratory of Plant Biotechnology, Faculty of Agriculture,
Tottori University, Koyama, 680-8553 Tottori, Japan
E-mail: jotanaka@muses.tottori-u.ac.jp
Tel.: +81-857-315638
J. Ling
Department of Applied Biological Resource Sciences,
School of Agriculture, Ibaraki University, Ami-machi,
Inashiki-gun, 300-0393 Ibaraki, Japan
D. Li
Institute of Biotechnology, Zhejiang University,
Huajiachi Campus, 310029 Hangzhou,
People’s Republic of China

gence. Furthermore, the enhanced expression of OsMGD may relate to photosynthesis, and play animportant role during submergence.
Keywords Monogalactosyldiacylglycerol synthase ÆOryza Æ OsMGD Æ Stress Æ Submergence Æ Suppression
subtractive hybridization
Abbreviations BA: N6-Benzyladenine Æ GA:
Gibberellin Æ MGD: Monogalactosyldiacylglycerol
synthase Æ RACE: Rapid ampliﬁcation of cDNA ends

Introduction
Submergence tolerance of rice is an important trait for
agricultural production. Two important factors, thelimitation of gas diﬀusion under water and reduced
irradiance, which impair photosynthesis and eﬃcientutilization of carbohydrates, inﬂuence rice plant survival
during submergence (Ram et al. 2002). Thus, survival
during submergence may largely depend on an accumulation of a high concentration of carbohydrate prior tosubmergence and a capacity for maintaining energy
production through rapid alcoholic fermentation underoxygen shortage. Under submergence conditions, glycolysis and alcoholic fermentation pathways become
more active for energy production in plants (Arumugam
Pillai et al. 2002). Increased alcoholic fermentation is thus
a way to alleviate the adverse eﬀect of anoxia on reduced
production of energy for growth and maintenance processes during submergence. Genes related to anaerobic
metabolism (such as those for glyceraldehyde-3-phosphate dehydrogenase, enolase, alcohol dehydrogenase,pyruvate decarboxylase and aldehyde dehydrogenase)are strongly induced under submergence (Umeda andUchimiya 1994; Sachs et al. 1996; Nakazono et al. 2000).
The potential capacity for internode elongation isimportant for plant response under submergence (vander Knaap et al. 1998). To avoid drowning, deepwater
rice has evolved the capacity to elongate very rapidly

451

when it becomes submerged (van der Knaap et al. 1997).
Internode elongation is partially induced by oxygen
stress (Raskin and Kende 1984a). It was also found thatinternode elongation during submergence is controlled
by the ratio of gibberellin to abscisic acid (HoﬀmanBenning and Kende 1992), and that gibberellin activity
could be enhanced by ethylene (Raskin and Kende
1984b). Submergence and gibberellin or ethylene treatment produce some similar eﬀects on plants: they promoted rapid internode elongation and induced
accumulation of expansin mRNA before the rate of
growth started to increase (Cho and Kende 1997).
During submergence, an ortholog of replication protein A1 (RPA1) and a putative type-1a plasma membrane receptor were also induced by gibberellin (van derKnaap et al. 1997, 1998). Submergence or ethylene
treatment enhanced expression of the genes for 1-aminocyclopropane-1-carboxylate synthase (ACS) andoxidase (ACO) (Zarembinski and Theologis 1997;
Mekhedov and Kende 1996). A novel ethylene-regulated
gene, OsUsp1, which encoded a plant protein related to aprokaryotic universal stress protein family, was also
expressed during submergence (Sauter et al. 2002).
Although numerous studies of submergence tolerance
have been carried out, the molecular aspect is not yet
clearly understood (Chang et al. 2000; Van Der Straeten
et al. 2001; Arumugam Pillai et al. 2002). To further
understand the mechanism of submergence tolerance, we
studied some genes related to submergence tolerance.
The present paper reports a new gene (OsMGD) in rice
isolated by suppression subtractive hybridization (SSH)
and the pattern of OsMGD expression in response tosubmergence, phytohormone, salt, drought, cold, dark
and illumination treatments.

FR13A were subjected to the following treatments for 0,6, 18, 30, 42, and 54 h: darkness (the growing plants wereplaced in a black box), darkness plus N6-benzyladenine(BA; 100 lM), light (white ﬂuorescent lamps: 23–
50 lmol photons m)2 s)1) and light plus BA (Yamaryoat al. 2003). Leaves of the rice plants grown under thediﬀerent conditions were harvested, frozen in liquid
nitrogen and stored at )80C until use.
RNA isolation
Total RNA was extracted by the SDS–phenol method(Bachem et al. 1996). Poly(A)+RNA was puriﬁed fromtotal RNA using the Oligotex-dT 30 super kit (Roche).
Suppression subtractive hybridization
PCR-based suppression subtractive hybridization (SSH)
was performed according to Diatchenko et al. (1996). SSH
was carried out using a PCR-Select cDNA Subtraction
Kit (Clontech) following the manufacturer’s instructions.
Aliquots (1.5 lg) of mRNA from non-submerged andsubmerged (for 7 days) rice plants were prepared as driverand tester RNA samples, respectively. After SSH, theproducts of PCR were sub-cloned into the pCR 2.1-TOPO
vector (TOPO TA Cloning kits; Invitrogen). Positive
colonies were picked out randomly for plasmid extraction, and digested with EcoRI. Northern blot hybridization was carried out to conﬁrm the positive clone forsubmergence induction, and the plasmid was isolatedusing the Miniprep Kit (PE Applied Biosystems).
Northern blot analysis

Materials and methods
Plant growth
Seeds of the rice (Oryza sativa L.) cultivars FR13A (submergence tolerant) and IR42 (submergence susceptive),
obtained from the International Rice Research Institute(IRRI), were soaked in water at 30C for 3 days, forgermination. The germinated seeds were transplanted
into a pot containing vermiculite. The seedlings were
irrigated at 1-week intervals using HYPONEX nutrient
solution diluted 1,000-fold with water. Three-week-old
seedlings were submerged completely, about 20 cm under
the water surface, for 1–7 days in a tank in a greenhouse.
The water temperature was 25–30C. Seedlings of thesame age were either irrigated every day for 7 days withwater containing 10)2 M ethephon, 10)5 M gibberellicacid (GA3) (Raskin and Kende 1984a, 1984b), or a highconcentration of salt (0.25 M NaCl), or they were subjected to drought (not irrigated) for 7 days. Cold treatment was performed at 4C for 1 day. The seedlings werealso grown under normal conditions as a control for
Northern blot analysis. Two-week-old seedlings ofTotal RNA (30 lg) was run in 1.5% formaldehyde–
agarose gels as described by Sambrook and Russell(2001), and blotted onto Hybond+ membranes (Amersham–Pharmacia). The digoxigenin (DIG)-labeled PCR
product was used as a probe for Northern hybridization
following the manufacturer’s instructions (PCR DIG
Probe Synthesis kit; Roche). The membranes were washed twice with a solution containing 2·SSC (sodium
chloride–sodium citrate buﬀer) and 0.1% SDS for
10 min at room temperature and twice with a solution
containing 0.1·SSC and 0.1% SDS for 20 min at 65C.
The DIG Luminescence Detection Kit (Roche) was used
for signal detection.
Isolation of full-length cDNA
5¢- and 3¢-rapid ampliﬁcation of cDNA ends (RACE;
Chenchik et al. 1998) were carried out to obtain the5¢- and 3¢-terminals of the OsMGD gene using a
SMART RACE cDNA Ampliﬁcation kit (Clontech)following the manufacturer’s instructions. An mRNA

452

sample (1 lg) from a 7-day-submerged rice plant(FR13A) was converted into ﬁrst-strand cDNAs. We
designed one gene-speciﬁc primer GSPR1 (5¢-ACAATTTGCAGCCCATC GCTGGT-3¢) and one nested
gene-speciﬁc primer NGSPR1 (5¢-CCCTCTGAACAAAGGACGACAGG-3¢) in antisense orientation for the
5¢-RACE. The gene-speciﬁc primer GSP2 (5¢-CTGTCGTCCTTTGTTCAGAGGG-3¢) and the nested speciﬁcprimer NGSP2 (5¢-ACCAGCGATGGGCTGCAAATTGT-3¢) in sense orientation were used for 3¢-RACE.
The universal primer sequence and the nested universal
primer (NUSP) for 5¢-RACE and 3¢-RACE refer to theuser manual of the kit. The up-regulated clone S23 oflength 672 bp (Fig. 1a, from 906 to 1577) was separated
from the subtractive cDNA library. After sequencing
S23, a fragment containing 1,577 bp (Fig. 1a, 1–1577)
was ampliﬁed out using the primer pair GSPR1 and
USP. Nested PCR primers, NGSPR1 and NUSP, wereused for the reaction, since the PCR products wereshown more clearly than GSPR1 and USP in a 1.5%
agarose gel (data not shown). A 139-bp fragment of the3¢-terminus (Fig. 1a, 1533–1671) was ampliﬁed using
GSP2 and USP. A nested PCR using NGSP2 and NUSP
for 3¢-RACE further conﬁrmed the 3¢-terminal sequence.
Fig. 1 a Nucleotide anddeduced amino acid sequencesof the rice (Oryza sativa)
OsMGD cDNA (numbered on
the left and right of thesequence, respectively). The
positions of RACE primers arelabeled (arrows). GSP2 andNGSP2 are used in 3¢-RACE.
GSPR1 and NGSPR1 are usedin 5¢-RACE; the latter two
primers are the reverse
complementary sequences of
NGSP2 and GSP2. GSP3 and
GSPR4 are used to amplify thefull length of OsMGD cDNA.
The positions of nine a-helices
are indicated by straight lines
under the amino acid sequence,
and were determined using thesecondary sequence prediction
program available at thefollowing internet address:
http://npsa-pbil.ibcp.fr/cgi-bin.
The sequence of OsMGD
cDNA was registered in
GenBank under accession
number AB112060.
b Comparison of OsMGD
and genome fragment
AAAA01000356. (From NCBI,
http://www.ncbi.nlm.nih.gov/
BLAST/Geno-me/
PlantBlast.html. Plant choices:
Oryza sativa ssp. indica WGS
contigs.) E1–7, exons 1–7; I1–
6, introns 1–6. The numbers on
the genome and OsMGD
indicate the sites of the exons
and introns

GSP3 (5¢-CTTTTTTTTTTTTTTTTTTTTTTGCTGCTG-3¢) and GSPR4 (5¢-GAATGGATATGTTACAAGTCGAGAG-3¢) were applied to obtain the full-length
cDNA. All PCR reactions were performed with
the Advantage 2 PCR Enzyme system (Clontech) in a
Takara PCR Thermal Cycler using the following
protocol: 94C for 5 s, 68C for 10 s and 72C for 3 minfor 35 cycles. Nested PCR reactions were performedby the same protocol for 20 cycles. The PCR productwas sub-cloned into pCR 2.1-TOPO vectors andsequenced.
cDNA sequence analysis
Sequencing was performed using the BigDye Terminator
Cycle Sequencing Ready Reaction Kit, v 2.0 in an ABIPRISM System 3100 (Applied Biosystems), and following
the cycle sequencing protocol for 25 cycles: 96C for 10 s,
50C for 5 s and 60C for 4 min. The M13 forward primer(CTGGCCGTCGTTTTAC) and M13 reverse primer(CAGGAAACAGCTATGAC) were respectively used inthese reactions. The Genetyx-SV-RC version6 (Software
Development Co., Tokyo, Japan) and DDBJ Homology

453

Search systems were used for sequence analysis. Comparison between the gene and Oryza sativa genome wascarried out using NCBI (http://www. ncbi. nlm.nih.gov/
BLAST/Genome/PlantBlast.html; plant choices: Oryza
sativa ssp. indica WGS contigs).

Results
cDNA clone of the OsMGD gene
The OsMGD cDNA contained 1,671 bp, with start codon
at 181 bp and stop codon at 1,257 bp, coding 358 aminoacids. The theoretical isoelectric point (pI) of the putative
amino acid sequence is 8.33 and molecular weight (MW) is
39.9 kDa. The ﬂank of the start codon ATG is AACATGG (Fig. 1a, 177–183), according to the ‘‘Kozak’’
rule. The putative amino acid sequence of the OsMGD
gene may contain nine a-helices, according to secondary
sequence prediction (Fig. 1a). In addition, the 1–23 site of
the 5¢-untranslated region in the OsMGD sequence(CTTTTTTTTTTTTTTTTTTTTTT) is very interesting.
It looks like an antisense strand. Further study is necessary to understand if this sequence has any biological
function. Based on the OsMGD cDNA sequence and asearch of the genomic database for Oryza sativa (Indica
cultivar), it was found that the OsMGD gene is well located in the 8580–4934 region of rice genome fragment
AAAA01000356. Following the GT-AG rule, it was
conﬁrmed that there are seven exons and six introns in the
OsMGD gene: the exon regions are in 8580–8279, 7299–
7134, 7036–6895, 6477–6253, 6148–6086, 5980–5906,
5599–4934 and the intron regions are in 8278–7298, 7133–
7035, 6894–6476, 6252–6147, 6085–5979, 5905–5598 ofgenome fragment AAAA01000356 (Fig. 1b).
Comparison of the deduced amino acid sequence of
OsMGD with MGDG synthases from other plants
The deduced amino acid sequences of OsMGD and
MGDG synthases from Cucumis sativus, Spinacia oleracea and Arabidopsis thaliana are aligned in Fig. 2.
Seventy regions are completely identical in the four
species. The putative amino acid sequence of OsMGD
showed high homology to csMGD A (58.6%), soMGD A (58.4%), atMGD A (59.5%), and atMGD B(74.0%). In Arabidopsis thaliana, at least two classes of
MGDG synthase homologues can be distinguishedaccording to the length of the N-terminal portion of the
hypothetical precursors (Miege et al. 1999). Experimental evidence indicated that type A exhibits a transit
sequence of about 100 amino acids, with a cleavage site.
On the other hand, the N-terminal sequence of type B isshorter (about 40 amino acids) than that of type A anddoes not exhibit any predictable cleavage site, as determined by the ChloroP program (Shimojima et al. 1997;
Emanuelsson et al. 1999). The putative amino acid sequence of OsMGD has a strong transmembrane helix,

from amino acids 18 to 40 in the N-terminus (by http://
www.ch.embnet.org/cgi-bin/ TMPRED_form _parser).
The most likely cleavage site is between positions 45 (A)and 46 (G) of the putative amino acid sequence (byhttp://www.cbs.dtu.dk/services/singnalP). The putative
amino acid sequence of OsMGD is shorter by about
107–167 amino acid residues than the MGDG synthasesof Cucumis sativus, Spinacia oleracea and Arabidopsis
thaliana. However, the 5¢-untranslated region (5¢-UTR;
179 bp) of the OsMGD cDNA contains an upstream inframe stop, TAG, at position 55–57 bp, that underlines
the function of the subsequent ATG in starting thetranslation and eliminates the probability that thecDNA is not full length. So OsMGD seems not to belong to the type-A or type-B MGDG synthases mentioned above. It is therefore suggested that OsMGD
might be a new type of MGDG synthase.
Time-course of expression of the OsMGD genein cultivars FR13A and IR42 during submergence
The northern blot analysis of OsMGD during submergence (0–7 days) is shown in Fig. 3. The expression of
OsMGD in FR13A and IR42 gradually increased withtime of submergence. The expression of OsMGD mRNAin submerged (7th day) FR13A and IR42 seedlings was
about 3-fold and 1.7-fold higher, respectively, than in
non-submerged rice. Although the level of OsMGD
mRNA was higher in FR13A than in IR42 at the 7th
day of submergence, it had already reached a peak at the
4th day of submergence in IR42 and declined thereafter.
Expression of the OsMGD gene in the rice cultivar
FR13A in response to dark, dark/BA, light,
and light/BA treatments
The expression of OsMGD was greatly reduced in 2week-old FR13A rice plants that were kept in the dark
and irrigated with water for up to 54 h (Fig. 4a).
However, when plants were irrigated with 100 lM BA
solution in the dark, the OsMGD expression increased
remarkably (Fig. 4b). The level of OsMGD expression
remained fairly constant throughout the time course
when plants were kept in the light and irrigated withwater (Fig. 4c) but increased when irrigated with BA in
the light (Fig. 4d).
Expression of the OsMGD gene in responseto phytohormone treatments and various stresses
Expression of OsMGD in rice plants (FR13A and IR42)
was also inﬂuenced by phytohormone treatments andvarious stresses (Fig. 5). Accumulation of mRNA was
greatly increased by submergence, ethephon, GA treatment (GA3), and drought or salt stresses. Moreover,expression in FR13A was higher than in IR42 under454
Fig. 2 Alignment of thededuced amino acid sequencesof OsMGD and MGDG
synthases from various plants.
csMGD A, Cucumis sativus
MGD A (GenBank U62622);
soMGD A, Spinacia oleracea
MGD A (GenBank
AJ249607); atMGD A,
Arabidopsis thaliana MGD A(At number, At4g31780);
atMGD B, A. thaliana MGD
B (At number, At5g20410);
OsMGD, Oryza sativa MGD(GenBank AB112060). The
black shading indicates identicalamino acids

these conditions. The OsMGD gene did not accumulate
in cold-treated rice plants.

Discussion
We constructed a subtractive cDNA library from nonsubmerged and submerged (7 days) rice plants. Using
the cDNA library, a new submergence-related gene,
OsMGD, was isolated and identiﬁed. The OsMGD geneencoded a putative polypeptide of 358 amino acids(Fig. 1). The putative polypeptide is highly homologous
to the monogalactosyldiacylglycerol synthase (UDP
galactose: 1,2-diacylglycerol 3-b-D-galactosyl transferase; EC 2.4.1.46, MGDG synthase) enzymes of Cucumis
sativus, Spinacia oleracea and Arabidopsis thaliana, andwe suggest that OsMGD might have a similar function.
The lipid MGDG is a major structural component ofphotosynthetic membranes in chloroplasts. Its formation is catalyzed by MGD synthase (Jarvis et al. 2000).

455

Fig. 3a,b Northern blot analysis of OsMGD gene expression in ricecultivars FR13A (a; submergence tolerant) and IR42 (b; submergence susceptive) during submergence from 0 to 7 days. Sub0–Sub7
From non-submerged to submerged for 7 days. Thirty microgramsof total RNA from samples submerged for diﬀerent times was
loaded on each lane and probed with clone S23 using the PCR DIG
Probe Synthesis kit. 28S rRNAs on Hybond+ membrane were
stained with methylene blue. Relative levels of mRNA wereanalyzed by Scion image and Excel software

MGDG synthase transfers a galactose from UDPgalactose to 1,2-diacylglycerol in the chloroplast envelope (Joyard and Douce 1987). MGDG is not only aFig. 4a–d Northern blot
analysis of OsMGD gene
expression in the rice cultivar
FR13A in response to dark,
dark/BA, light, and light/BA
treatments. a,b Seedlings wereplaced in the dark for 0, 6, 18,30, 42 and 54 h, and soakedwith water (a) or BA (100 lM)
solution (b). c,d Seedlings were
illuminated with whiteﬂuorescent lamps: 23–
50 lmol m–2 s–1 for 0, 6, 18, 30,
42 and 54 h, and soaked withwater (c) or BA (100 lM)
solution (d). DW Dark/water,
DBA dark/BA, LW light/water,
LBA light/BA. The northernblotting procedure was same as
in Fig. 3

major constituent of the chloroplast membrane but also
has an important role in photosynthesis (Murphy 1982;
Murata et al. 1990). The small galactose of the headgroup and large unsaturated fatty acid chains of MGDG
give it a cone-like molecular shape and a consequentpredisposition to form non-lamellar, hexagonal-phaseaggregates. The molecular shape of MGDG may be
important for the structural organization of thylakoid
membranes. Evidence also suggests that MGDG is more
directly involved in certain photosynthetic reactions(Tremolieres et al. 1994). In addition, photosynthesis has

456
Fig. 5a,b Northern blot
analysis of OsMGD expression
in rice cultivars FR13A(a; submergence tolerant)
and IR42 (b; submergencesusceptive) subjected tophytohormone treatments andvarious stresses. Sub0No-submergence, Sub7
submergence for 7 days, Eth10)2 M ethephon, GA 10)5 M
gibberellic acid, Salt 0.25 M
NaCl, Drou drought (notirrigated) for 7 days, Cold
exposed to 4C for 1 day. The
northern blotting procedure
was same as in Fig. 3

a great eﬀect on tolerance to submergence (Ram et al.
2002). Though the photosynthetic rate of the rice seedlings was reduced during submergence, the photosyn-

Fig. 6 A proposed model of the relationship between glycolysis
and MGDG synthesis (refer to Shen and Wang 1991; Kelly andDormann 2002; Ichihara 2001). Gal Galactose, Gal-1-P galactose1-phosphate, Glu-1-P glucosel-1-phosphate, UDP uridine diphosphate, TCA cycle tricarboxylic acid cycle, ACP acyl carrier protein,
G-3-P glycerol-3-phosphate, LPA lysophosphatidic acid, PA
phosphatidic acid, DG 1,2-diacyl-sn-glycerol, DGD2 an Arabidopsis
gene encoding a UDP-galactose-dependent digalactosyldiacylglycerol synthase, 16:0 length of carbon chain: number of double bonds

thetic rate of FR13A remained higher than that of thesubmergence-sensitive cultivar IR42 (Kawano et al.
2002a, 2002b; Ella at al. 2003). The expression of the
OsMGD gene in FR13A was higher than in IR42 during
submergence (Fig. 3), indicating that OsMGD may be
important for maintaining photosynthetic activity.
The transcripts of OsMGD were inﬂuenced by BA
and illumination treatments (Fig. 4). In the presence ofexogenous BA, OsMGD expression was raised even in
the dark (Fig. 4b), a response identical to that of the
MGD gene of cucumber (Yamaryo at al. 2003). Thismight explain why the OsMGD transcripts were increased during submergence: though the light level under water is weaker than in air, the endogenous
cytokinin may be stimulated during submergence, which
would result in the increased expression of OsMGD.
It has been found that many submergence-related
genes are regulated by phytohormones (see Introduction). Our data show that the expression of OsMGD isalso induced by ethylene and gibberellin (Fig. 5). An
increase in the rate of ethylene production was observed
when deepwater rice was submerged (Raskin and Kende
1984a). The striking eﬀects of total submergence on rice
plants, elongation and chlorosis, were reproduced byapplying ethylene under pressure (0.35 Pa) to non-submerged rice plants (Jackson et al. 1987). The elongationof internodes in rice is regulated by cooperative action
between GA and ethylene (Raskin and Kende 1984b), so
the expression of OsMGD may be mediated by GA andethylene.
It was indicated that OsMGD was induced not only
by submergence but also by drought and salt stress(Fig. 5). Both drought and salt stresses lead to dehydration in cells and there are many common mechanismsof response to these stresses (Hayashi et al. 2001). There
have been some reports that salt tolerance might well be
associated with membrane lipids. A salt-induced decrease in chloroplast lipids has been found (Harwood1984). Moreover, severe reduction in galactolipid synthesis after salt stress has been observed in both olive(Zarrouk et al. 1995) and oilseed rape (Najine et al.
1995). Under drought stress, MGDG synthase activity

457

in rape (Brassica napus) was reduced (Benhassaine-Kesriet al. 2002). These results seem to contradict our datathat OsMGD mRNA is increased by drought and salt
treatment. The decrease in MGDG may trigger the
expression of OsMGD in preparation for translation to
MGDG synthase. Since the MGDG synthase gene belongs to a multigene family, the relationship between
transcription and translation seems to be complicated. It
is possible that the OsMGD gene is related to resistibility
to submergence, salt and drought stresses.
Signiﬁcant changes in several aspects of plant membrane lipids have been noted in response to lowtemperatures. In the eukaryote tomato, MGDG biosynthesis was inhibited at low temperature (Yu andWillemot 1996). This corresponds to our result that the
OsMGD gene was not expressed at 4C in rice plants.
Furthermore, the OsMGD gene also seems to be
associated with glycolysis (see Fig. 6). Figure 6 shows a
proposed model to elucidate the relationship between
glycolysis and MGDG synthesis. UDP-galactose (UDPGal) is a substrate for MGDG and digalactosyldiacylglycerol (DGDG) synthesis (steps e, f). Moreover, UDPGal is an intermediate product for the entry of Gal into
glycolysis (steps a–c). A key step of glycolysis is fromglyceradehyde-3-phosphate to glycerate-1,3-bisphosphate, catalysed by glyceradehyde-3-phosphate dehydrogenase (step d). The expression of the OsGAPDH
gene coding glyceradehyde-3-phosphate dehydrogenase
is dramatically increased by submergence and anaerobiosis (Umeda and Uchimiya 1994; Sachs et al. 1996;
Arumugam Pillai et al. 2002). Moreover, acetyl-CoA
may be supplied as a substrate for the tricarboxylic acidcycle and lipid biosynthesis (Mellema et al. 2002).
According to the above-mentioned relationship and thefact that the expression of OsMGD increased during
plant submergence (Fig. 5), we suggest that MGDG
synthesis and glycolysis might be associated and that
OsMGD may play an important role during submergence.
A submergence-related gene, OsMGD, and its increase during submergence of rice plants are reported
here for the ﬁrst time, and this ﬁnding will supply a new
train of thought in the study of submergence tolerance.
More work is in progress to understand OsMGD genefunction, and submergence-related genes could be discovered in succession by utilizing this subtractive cDNA
library.

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ReturnPlant Prod. Sci. 8(5) : 553 — 562 (2005)

Development and Distribution of Root System in Two Grain
Sorghum Cultivars Originated from Sudan under Drought Stress
Wataru Tsuji1, Shinobu Inanaga1, Hideki Araki2, Shigenori Morita3, Ping An1 and Kaori Sonobe1{lArid Land Research Center, Tottori University, 1390, Hamasaka, Tottori, 680-0001, Japan;
2Faculty ofAgriculture, Yamaguchi University, 1677-1, Yoshida, Yamaguchi, 753-8515, Japan;
3Graduate School ofAgricultural and Life Sciences, The University of Tokyo, 1-1-1,
Midori-cho, Nishitokyo, Tokyo, 188-0002, Japan)

Abstract: The difference in rooting pattern between two grain sorghum cultivars differing in drought tolerance
was investigated under drought stress. The cultivars, Gadambalia (drought-tolerant) and Tabat (drought-

susceptible), were grown in bottomless wooden or acrylic root boxes to examine root parameters. Gadambalia
consistendy exhibited higher dry matter production and leaf water potential than Tabat under drought stress inboth root boxes. In the experiment with wooden root boxes, under a drought condition, Gadambalia extracted
more water from deep soil layers (1.1-1.5 m), which was estimated from the reduction in soil water content, than
TabaL This was because Gadambalia had a significantly higher root length density in these soil layers. The highroot length density was due to enhanced lateral root development in Gadambalia. In the other experiment withacrylic root boxes, though total root length in the upper soil layer (0-0.5 m) was declined by limited irrigation inboth cultivars, the reduction in Gadambalia was moderate compared with that in Tabat owing to the maintenanceof fine root growth. Unlike Tabat, Gadambalia had an ability to produce the nodal roots from higher internodes
even under drought, which resulted in the high nodal root length of Gadambalia. The growth angle of nodal
roots was significantly correlated with root diameter, and the nodal roots from the higher internodes had large

diameters and penetrated into the soil more vertically. These results indicate that the responses of roots (i.e.

branching and/or growth of lateral root, and nodal root emergence from higher internodes) to soil dryness
could be associated with the drought tolerance of Gadambalia.
Key words : Branching of root, Drought stress, Drought tolerance, Growth angle of nodal root,

Plagiogravitropism, Root diameter, Root length density, Sorghum bicolor (L.) Moench.

Water deficiency is a serious limitation to cropi.e., the contribution of root development especially

production in large areas of the world. Sorghumin the deep soil profile. However, little is known about[Sorghum bicolor (L.) Moench] is one of the mostthe contribution of root system to drought tolerance inimportant crops in arid and semi-arid regions where

sorghum cultivars.

precipitation is low and highly variable. For sorghum

Root distribution of monocotyledonous plants

production in these areas, the cultivars are expected

is the result of growth of different types of roots

to be tolerant to less rainfall and/or limited irrigation.

(Klepper, 1991). Depth and expansion of a root

We previously studied dry matter production andsystem are primarily determined by the trajectoryshoot water relations in response to water shortage inof the axile roots consisting of seminal and nodal

sorghum cultivars from Sudan (Tsuji et al., 2003) toroots. Furthermore, rooting depth of the axile roots

understand eco-physiological strategies for drought

is determined by the growth direction and the length

adaptation of the African sorghum. Under soil dryingof the roots (Araki et al., 2000). In a field experiment,

conditions, a local cultivar with drought tolerance

Nakamoto et al. (1991) observed that cultivars of(Gadambalia) could maintain higher leaf watermaize and foxtail millet, whose nodal roots orientatedpotential and photosynthetic rate than a drought-

downward, exhibited high root length density insusceptible cultivar (Tabat) improved for irrigateddeep soil layers. A positive correlation was reported

cropping. These differences were likely influenced by

between "Root Depth Index" and growth angle of

the ability to extract water under soil drying condition,

wheat seminal roots (Oyanagi et al., 1993a), which

Received 19 April 2005. Accepted 11 June 2005. Corresponding authon W. Tsuji (tsun@alrc.tottori-u.ac.jp, fax +81-857-29-6199). This
research was supported in part by a grant for the 21st Century COE program from the Japan Society for the Promotion of Science,
Japan.

Abbreviations : BI, branching index; RLD, root length density; SDW, shoot dry weight; SRL, specific root length; TRL, total root
length; VWC, volumetric water content; 0, growth angle of nodal roots; 0m, mean growth angle of nodal roots; <FLl leaf water potential.

554

Plant Production Science Vol.8, 2005

are the deepest axile roots in the wheat root systemthan 95% of incident solar radiation. The soil at the(Morita et aL, 1993; Araki and Iijima, 2001). Growthexperimental site was sandy with about 98% sand todirection of axile roots in cereals is determined bya depth of about 5.0 m. The two sorghum cultivars

plagiogravitropism (Oyanagi et al., 1993b). The

and two water regimes were arranged in a completely

intensity of the plagiogravitropism in axile roots is

randomized design with three replications in theaffected by genotypes (Nakamoto, 1991; Oyanagi etfollowing two experiments.

al., 1993a; Araki and Iijima, 2001), environmental
factors such as soil temperature (Tardieu and Pellerin,

Experiment 1. Soil water content and root distribution

1991) and soil moisture (Nakamoto, 1993; Oyanagi etin the soil profileal., 1995), and internode positions from which axile

The two sorghum cultivars were grown in bottomlessroots emerged (Nakamoto et al., 1991; Araki et al.,wooden root boxes (0.3 m wide, 0.9 m long, 1.8 m

2000). The growth direction of axile roots, which ishigh) made of veneer plywood boards (12 mm thick).

determined by genotype-dependent plagiogravitropism

The root boxes were filled with air-dried sandy soil atand influenced by environmental factors, can be said
to determine the shape of the root system.

a bulk density of 1.5 Mg m~3. A compound fertilizer
containing major elements (N: P2O5: K2O = 0.13:

Root distribution in soil is also determined by the

0.13: 0.16 g g"1) was applied to the root boxes at theextent of branching and elongation of lateral roots.

rate of 15 g per root box as top dressing. A compound

Lateral roots compose a great proportion of root

trace element fertilizer mainly containing MgO: MnO:

length in cereal crops (Yamauchi et al., 1987a). In

B2O3: = 0.14: 0.003: 0.003 g g1 and calcium hydroxidewater-limited environments, growth of the lateral

were also applied to each root box at rates of 10 g androots is important for crops to acquire more water

25 g, respectively, to supplement the fertility and tofrom a dry soil. Water extraction from given depths

adjust the pH (7.6) of the acidic sandy soil. The root

was closely related to root length density (Fukai andboxes were buried in soil by 1.7 m deep to fix them

Cooper, 1995). The growth of the lateral roots is highly

and prevent any increase in soil temperature caused

influenced by soil moisture (Kono et al., 1987; Pardales

by solar radiation. An observation pit was dug along

and Kono, 1990). Banoc et al. (2000a) indicated thatthe sidewall (0.3 m wide, 1.8 m high) of the root

branching ability of the root would be involved in thebox. Ten seeds of sorghum per root box were sown

genetic differences in adaptation to fluctuating soilin the central part of the root boxes, and seedlings

moisture (dry-submerged cycle) in rice cultivars.

were thinned to two plants per root box four wk after

The objective of this study was to investigate thedevelopmental patterns of the root systems of twosorghum cultivars differing in drought tolerance undersowing. Irrigation water was adequately applied until

the start of the soil water treatments. Fifty-two days

after sowing, the last irrigation of root boxes to 0.35 m3

drought stress. We compared the root distribution

m*3, which is more than moisture holding capacity after

profiles in the soil and their modification by soil

24 h was made. Thereafter, daily irrigation was applied

drying. As the factors determining the developmental

only to the wet treatment, while irrigation in the dry

pattern of roots, growth angle, length, initiation oftreatment was completely withheld until the end of thenodal roots, and the extent of branching of lateralexperiment at 145 d after sowing.

roots were also examined, and how the developmental

At the flowering stage, 55 d after the start of water

responses of roots to soil dryness contribute to drought

treatments, water potentials of flag leaves were

tolerance of the sorghum cultivars was discussed.
Materials and Methods
Plant materials and experiment sitemeasured with a pressure chamber (Model 1000,
PMS Instrument Co.) between 1100 and 1400. At

early maturity stage, four holes (28 mm diameter)

were made at depths of 0.3, 0.7, 1.1 and 1.5 m on the

Two grain-sorghum cultivars, Gadambalia (droughtsidewall, facing the observation pit beside the root

tolerant) and Tabat (drought susceptible), were usedbox, to measure soil water content using a profilein the present study. Seeds of both cultivars wereprobe (Type PR1/4, Delta-T Devices). After accessprovided by the Agricultural Research Corporation

tubes were horizontally inserted into each hole,(ARC), Sudan. Gadambalia is a local drought-resistant

output values were measured at four positions in thecultivar, and Tabat is an improved cultivar released

tube. The average output values (V) were converted

for irrigated cultivation (Salih et al., 1999; Tsuji etto volumetric water content (VWC) according to aal., 2003). Root distribution in the soil profile andcalibration formula, VWC =1.4053V-0.1486 (r =rooting pattern of the axile and lateral roots were0.995). After measurement of VWC, larger holes (0.15

separately examined in a plastic greenhouse, underm diameter) were perforated at the same position

two contrasting soil water regimes (wet and dry), at thefor collecting roots. A metallic cylinder (0.15 m in

Arid Land Research Center, Tottori University, Japan.

diameter, 0.38 m length) was inserted into the soil

The study plot (110 m2) was covered with a transparent

to sample a soil core with roots. After collection ofplastic vinyl sheet that permitted transmission of more

the soil core, a soil column of 20 mm adjacent to theTsuji et al.

Development and Distribution of Root System in Sorghum under Drought StressOrigin*Coordinate A
X/
Steel meshFig. 1.

555

Coordinate B

Root-crossed position

Measurement of growth angle of nodal roots (0). Root-crossing positions on each inner and outer steel meshes

were recorded in the root box (Left). Model (Right) used for calculating 0 according to a formula (see Materials andMethods) when one corner of the root box was determined as the origin O (0, 0, 0), and then coordinates A (plantbase), and B (a root-crossing position on the meshes) were shown by (ax, ay, az) and (bx, by, bz), respectively.

wall of the root box was cut to remove roots bristlingcompartments. Three plants at intervals of 0.1 m werealong the wall. The soil samples were carefully washedgrown between the inner two steel meshes (Fig. 1).

with showering tap water on a fine meshed sieve (lessThe soil and fertilizers applied were the same as thosethan 0.5 mm), and the collected roots were preservedin Experiment 1 with wooden root boxes. We appliedin FAA solution (Formaldehyde: Acetic acid: 70%

1.0 L of water to each root box from the top every day.

ethanol = 1: 1: 18). The root lengths were measured

The plants were subjected to two different irrigation

with a root length scanner (Root Length Scanner,

treatments from 25 d after sowing. The wet treatment

Commonwealth Aircraft Co. Ltd.) to calculate the root

received 1.0 L water every day, while the dry treatment

length density (RLD). After measurement, the roots

0.5 L water every two days.

were dried in an oven at 80°C for 3 d, and weighed.

At the late vegetative stage on 25 d after the startSpecific root length (a ratio of root length to root dryof water treatments, water potentials of the highest

weight, SRL) was calculated from the root length andfully expanded leaves were measured with a pressure

dry weight. SRL is an indicator of root morphology

chamber (Model 1000, PMS Instrument Co.) between

which shows the thickness of roots and/or extent of1000 and 1400. At the flowering stage, 52 d after the

branching (Eissenstat, 1992). Dry weights of excisedstart of water treatments, the acrylic boards wereshoots were also weighed after dried in the oven atremoved to observe elongation direction and initiation

80°C.

of the nodal roots. At this time, Tabat in the dry

Experiment 2. Rooting pattern of nodal and lateralroot system was carefully washed with running tap

treatment was still in the vegetative stage. The wholeroots

water. The position of the plant base (coordinate A)

The sorghum plants were grown in bottomlessand the crossing position of the nodal roots on theacrylic root boxes (0.5 m wide, 0.5 m long, 0.5 m

steel meshes (coordinate B) were recorded with three-high), which were placed on the sandy soil. The root

dimensional c6ordinates (Fig. 1). One corner of theboxes were covered with aluminum foil to prevent theroot box was determined as the origin O (0, 0, 0), andrise in soil temperature caused by solar radiation. Fourthen coordinate A and B were shown by (ax, a^ aj andsteel-wire meshes (4x4 mm) fixed by steel frames were(bx, by, bz), respectively. Growth angle of each nodal

vertically inserted at intervals of 0.15 m to observe

root (0) was calculated by the following formula:

the growth angle of nodal roots (Fig. 1). The steel
meshes separated the rooting zone into three large

6 = tan'[k-bj/{(ax-bx)2+(ay-by)2)1/2] (0°^ 6 £ 90°)

556

Plant Production Science Vol.8, 2005

Table 1.

Shoot dry weight (SDW) and leaf water potential (fL) of two sorghum cultivars under wet and dry treatments inwooden and acrylic root-box experiments.

Cultivar

Treatment

Gadambalia

Tabat

—

SDW

(g)

(MPa)

Wooden root-box

Acrylic root-box

Wooden root-box

Wet

51.83±7.33

19.69±2.64b-1.09±0.03a-1.64±0.04a

Dry

49.87±2.76

12.39±1.35C-1.16±0.01a-2.15±0.09b

Wet

63.08±6.4226.99 ±1.56a-1.09±0.04a-1.45±0.07a

Dry

44.78±3.78

4.47± 1.23d-1.34±0.01b-2.91±0.08c

5.82

0.08

0.23

LSD0,5

Wooden root-box

The SDW and leaf water potential were measured at late ripening and flowering stage, respectively, in the wooden rootbox, and at flowering and late vegetative stage, respectively, in the acrylic root-box experiment. Data are means of three
replications ± standard errors. Values within a column followed by the different letter are significantly different according
to LSD test at the 0.05 probability level. The letters and LSD value are not shown for the SDW in the wooden root-box
experiment since interaction between cultivars and treatments was not found by analysis of variance (ANOVA, P=0.16).

VWC (m3 m3)

where, 6 represents the angle between soil surface andthe line joining with the base of plant and the rootcrossing points on the mesh, so the greater 9 indicates

0that the nodal roots elongated vertically. Mean growth

0 -angle of nodal roots (0m) was calculated for each

0.02

0.06

0.3 -

After the determination of 0, internodes from which
nodal roots emerged were traced. The number ofM

jv \ \

diameter of nodal roots at 5 mm from the base was{ \simultaneously measured with a digital vernier caliper.

0.7 -The data above were limited to those from the nodalf1

measured with a scale and a root length scanner (Root":respectively. Branching index (BI; Morita and Collins,i1990) was calculated as:j

BI = Lateral root length/Nodal root length

i
1
1.5 -

BI indicates branching ability of parental roots and/or

the oven at 80°C to obtain the dry weight, SRL wasweighed after drying in the oven at 80°C.
Results

1.

Leaf water potential and shoot dry weight
Water potential of the leaves (fL) was lowered bylimited water application more severely in the plants

N

Fig. 2.

p

\
\

\

I

TDry

vJV
^ \
\

\\
*

v\ ij \\
\\
\!

i

j

PWP

growth of lateral roots. After drying the roots in
calculated. Dry weights of excised shoots were also

\

:

1.1

—A— TWet\

1 S\ Xand lateral roots were classified and their lengths were
Length Scanner, Commonwealth Aircraft Co. Ltd.),\

GWet-o- GDryi\nodal roots in each internode was also counted. The

In the root systems preserved in FAA solution, nodal

0.14

:

replicated plant.

roots, i.e., no data were obtained for the seminal roots.

0.10

MHC

Change in volumetric water content of soil (VWC)

across soil depths in two sorghum cultivars, Gadambalia(G) and Tabat (T) under wet and dry treatments. Dottedlines indicate permanent wilting point (PWP) and moistureholding capacity after 24 h (MHC) of the sandy soil filled
in root boxes. The * symbol indicates soil depths at which
differences between cultivars under drought condition
were significant at the 0.05 probability level.

grown in the acrylic root boxes than in those grown in

the wooden root boxes (Table 1). In the wooden rootbox experiment, *FL was hardly affected by the limited

A similar trend was observed in dry matter

irrigation in Gadambalia, but significantly dropped to

production (Table 1). In wet conditions, shoot dry-1.34 MPa in Tabat. In the plants grown in the acrylic

weight (SDW) of Tabat was consistently higher thanroot boxes, the fL of Tabat dropped to below -2.9 MPathat of Gadambalia in both the wooden and acrylic

by drought, but that of Gadambalia only to -2.2 MPa.

root-box experiments. However, the SDW of Tabat inTsuji et al.

Development and Distribution of Root System in Sorghum under Drought Stress

RLD (cm cm"3)

SRL (m g1)

0.5

()

557

1.

0

40

80

120

/^

0.3-

\\
\
\ \ \

t It*
f

1

\\ \

/ / /

/
0.7-

1

\)\ \
\

1.1 - *

\
\

/

/
/

1.5-

/
/
/

/

I

\
\
\

-•- G Wet\b■

-O-GDry-A- TWet-A- TDry

1
\
1
1

\

$

Tt

/

Fig. 3.

\ I

\

y

"d

\

^ \

}

I
!

|> i
■

(S

1
1
1
1
o

Change in root length density (RLD) and specific root length (SRL) across soil depths in twosorghum culdvars, Gadambalia (G) and Tabat (T) under wet and dry treatments. The * symbol
indicates soil depths at which differences between treatments in Gadambalia were significant at the 0.05
probability level.

Table 2.

Total, nodal and lateral root length, branching index (BI) and specific root length (SRL) of whole root system of twosorghum cultivars under the wet and dry treatments.

Cultivar

Gadambalia

Tabat

Total root

Nodal root

Lateral rootBIlength (m)length (m)length (m)(m m1)

Wet

626.3±191.8

21.2±1.6

605.1 ±190.2

27.6±6.5

47.5± 6.2

Dry

349.9± 28.7

13.0±2.7

336.9± 30.7

28.5±6.645.9± 1.1

867.2 ±126.0

20.9±1.0

846.4± 126.9

41.3±8.2

53.5±10.7

205.2 ± 70.9

9.3±0.8

195.9± 70.7

26.9 ±7.9

36.5± 5.1

Treatment

Wet
Dry

,

SRL

Data are means of three replications ± standard errors.

the dry treatment was significantly low compared withacross soil depths (Fig. 3). However, the response tothat in the wet treatment. In Gadambalia, the SDW in

drought was markedly different between the cultivars.

the dry treatment was hardly affected by the drought

In the dry treatment, Tabat had a slightly higher RLD

in the wooden root-box experiment, and was slightly

than in the wet treatment, though this increase waslower than that in the wet treatment in the acrylic root-

not significant at the 5% level. Although the RLDbox experiment.

of Gadambalia in the wet treatment decreased with

2.

with increasing depth, especially in the deeper (1.1-1.5

increasing depth, that in the dry treatment increased
Water uptake and root distribution in the soil
profilem) soil layers (P<0.05). The specific root length (SRL)

In the wet treatment, the soils in the wooden rootof Tabat was not affected by drought stress, but that ofboxes with the two cultivars planted on them showed

Gadambalia tended to increase in the dry treatment

similar volumetric water content (VWC) at each soil

at 0.7-1.5 m depths, indicating that fine roots in these

depth (Fig. 2). Soil below 0.7 m in the dry treatment

layers increased in response to the drought stress (Fig. 3).

was significantly drier in the boxes with Gadambalia

than those with Tabat. In the wet treatment, both
cultivars exhibited a similar root length density (RLD)3.

Root length and branching

Detailed analysis on the length of the nodal andlateral roots was carried out for the roots in thePlant Production Science Vol.8, 2005

558

Gadambalia

Dry: y=13.89x + 12.07

Dry :y=19.25x+1.85

Tabat

r=0.66"'
•

i

60-

•s

9
30-

f •t.7

Wet:y=l3.06x+12.48

Wet :y=13.43x+10.93

r=0.75***

T-0.85""*0-012345012345

Basal diameter (mm)Fig. 4.

Relationships between growth angle (0) and basal diameter (5 mm from thebase) of nodal roots of twosorghum cultivars under wet (closed circle) and dry (open circle) treatments. Regression lines are solid andbroken for wet and dry treatments, respectively. The *** symbol indicates the relationship were significant at
the 0.001 probability level.

experiment with the acrylic root boxes. In the wet
condition, Tabat developed the longest roots and40-

showed the highest branching index (BI) and SRL(Table 2), indicating a higher branching ability thanGadambalia in non-stressed conditions. However, theseparameters in Tabat were the lowest in the drought
stress treatment. Although the total root length was
reduced by drought in both cultivars, the reduction

in Gadambalia was only 44.1%, while it was 76.3%
in Tabat. Response of nodal and lateral roots to thedrought stress also differed with the genotype. By

dry treatment, the lengths of nodal and lateral roots

were decreased by 38.7 and 44.3%, respectively, in
Gadambalia, and 55.5 and 76.9%, respectively, in

Wet

Tabat. The BI and SRL of Gadambalia were lower thanGadambalia

those of Tabat in the wet treatment. These parameters

were not affected by the drought stress in Gadambalia,

Dry

Fig. 5.

Wet

Dry

Tabat

Mean of the growth angle of nodal roots (0m) of

but decreased by the drought stress in Tabat.

two sorghum cultivars under wet and dry treatments. 0m

4.

surface. Data are means of three replications ± standard

is represented by mean degree of deflection from the soil

Growth angle and initiation of nodal roots

The growth angles of nodal roots (0) determined

errors.

at the inner and outer meshes were highly correlatedwith each other (r = 0.895 at P<0.001). Therefore,
only the angles determined at the inner meshes are

relatively high 6 was observed in Tabat grown in thepresented in this paper.

wet soil since the plants had roots with large diameters.

In the whole root system, there were close

The slope of the regression lines of 6 against therelationships between 6 and basal diameter of thebasal root diameter was not affected by the drought

nodal roots in both cultivars and treatments (Fig.

treatment in Gadambalia (Fig. 4). In Tabat, the slope4). In the wet treatment, there was no genotypic

was slightly increased by the drought treatment, butdifference in the mean growth angle of nodal roots

6m was significantly reduced due to the emergence of(0m) and the slope of the regression line, i.e.,

fewer nodal roots with large diameters (Figs. 4, 5).

increment of 0 per unit root diameter (Figs. 4, 5). A

Table 3 shows the 0 of the roots emerged from eachTsuji et al.

Table 3.

559

Development and Distribution of Root System in Sorghum under Drought Stress

Growth angle of nodal roots (0) at each internode in two sorghum cultivars under wet and dry treatments.
0 (degree)

Cultivar

Gadambalia

Tabat

Internode

Treatment

3rd

4th

5th

6th

7th

25.2±2.734.4±3.540.7±0.7

44.0±1.952.0±2.3

55.6±2.730.4±4.729.0±1.234.8±3.2

47.0±1.450.5±0.755.3±0.0

29.6±0.3

36.0±l.l

46.5±5.0

58.6±7.0

64.6±0.1

67.7±0.0

28.7±2.4

41.6±4.3

49.6±4.7

-

-

1st

2nd

Wet

20.6±2.9

Dry

26.1 ±2.9

Wet25.4±2.624.3±2.9Dry13.0±0.4

22.5±0.5

8th

The 0 is represented by degree of deflection from the soil surface, that is, the bigger the growth angle, the deeper the nodal roots
elongate vertically. Dashes mean no emergence of nodal roots. Data are means of three replications ± standard errors.

Table 4.

Number of nodal roots in total and at each internode of two sorghum cultivars under wet and dry treatments.
Number of nodal roots

Cultivar

Gadambalia

Tabat

TreatmentInternode

1st

2nd

3rd

4th

5th

6th

7th

8th

Total

Wet

3.3±0.4

3.1±0.1

3.1±0.4

3.1±0.1

3.8±0.1

4.0±0.2

2.0±0.7-22.7±1.2

Dry

3.0±0.2

2.4±0.7

3.1±0.2

3.4±0.3

3.8±0.3

3.7±0.4

1.9±1.0-

21.3±0.2

Wet

2.1±0.3

2.8±0.5

3.6±0.4

3.1±0.1

3.6±0.3

3.4±0.4

1.7±1.1

0.6±0.5

20.8±0.6Dry

2.8±0.5

2.9±0.4

3.3±0.4

3.3±0.2

1.0±0.5-13.3±0.9

Dashes mean no emergence of nodal roots. Data are means of three replications ± standard errors.

internode. The 0 consistently increased as the rooting

Gadambalia extracted more water, especially frominternodes were acropetally advanced irrespective ofdeep soil, under drought stress. Salih et al. (1999)

cultivars and treatments. The diameter of the nodal

reported that Gadambalia had higher efficiency inroots at higher internodes was also larger. The 0 of

extracting soil water from 0-0.9 m depth than Tabatroots emerged from the same internode was notalthough Gadambalia had a lower RLD. The present

different so much between Gadambalia and Tabat

study indicated that Gadambalia extracted more water

irrespective of treatments. Gadambalia produced

than Tabat from deeper soil layers (Fig. 2). Gadambalia

roots at the 6th and 7th internodes even in thegrown in a root box had an extended RLD in 1.1-1.5

dry treatment as in the wet treatment (Table 4). Inm depth in response to drought, but Tabat did notcontrast, emergence of the roots from the higher(Fig. 3). The increased SRL of Gadambalia in the soilinternodes (6-8th) was inhibited by dry treatment indeeper than 0.7 m indicated a vigorous development

Tabat. This explains why the 0m of Tabat in the drytreatment was reduced by drought stress.
Discussion

Tabat is a cultivar adapted to irrigation, whichof fine roots under the dry condition (Fig. 3). The
increased RLD (Fig. 3) would adaptively enhancewater uptake from deeper soil layers, and allow better
water relations in the shoot. This character might
contribute to the drought tolerance of Gadambalia.

exhibited higher performance in dry matter

Grain sorghum genotypes with drought tolerance fromproduction than Gadambalia on a well-irrigated soil

Australia also had a higher RLD in deep soil layers(Table 1, Tsuji et al., 2003). In the dry condition,

below 1.0 m than susceptible genotypes under drought

however, a reverse was the case. In Tabat, the SDW

stress conditions (Wright and Smith, 1983; Ludlow

and *fL were significantly reduced by drought stresset al., 1990; Santamaria et al., 1990). These reports,

even in the wooden root-box experiment, in which

together with ours, indicate that adaptive responses

plants were exposed to moderate drought stress. Inof the root development to soil dryness would be

Gadambalia, the drought stress hardly influenced thean important trait for drought tolerance in grain

SDW and fL in the wooden root-box experiment,sorghum.

but affected them in the acrylic root-box experiment.

Lateral roots occupy a great proportion in the total

In addition, depletion of soil water in the root boxes

length of the root system (Yamauchi et al., 1987b), andwith Gadambalia planted on it was greater than thatare responsible for a large portion of water extracted

in the root boxes with Tabat under the water-limitedby the whole root system (Varney et al., 1993). The

condition (Fig. 2). These results indicated that

responses of roots to drought stress differed between

560

Plant Production Science Vol.8, 2005

the sorghum cultivars used in this study even in

nodal roots irrespective of cultivars and treatments

the shallow soil layer. The smaller decrease in Total(Fig. 4). Similar correlations were also observed inroot length (TRL) under the drought condition inother cereals such as lowland and upland rice, maize,

Gadambalia could be attributed to retention of aand foxtail millet (Yamazaki et al., 1981; Yamazakihigh BI and SRL on the nodal roots (Table 2). On

and Kaeriyama, 1982; Nakamoto et al., 1991; Araki etthe contrary, the significant reduction of TRL in theal., 2002). In sorghum cultivars, the growth angles ofdrought-stressed Tabat was attributed to the lower

nodal roots are likely to be established by common

BI and SRL indicating that growth and initiation ofmorpho-physical processes proposed by Abe andthe lateral roots were suppressed by drought stress. A

Morita (1994) that the growth direction of axile roots

drought-tolerant cultivar of upland rice also exhibited

may be primarily limited by their diameter. The nodal

an extensive increase in the number of high-orderroots emerging from higher internodes had large

lateral roots produced by first-order lateral roots

diameters and elongated downward irrespective ofunder fluctuating soil moisture (Banoc et al., 2000a).

cultivars and watering treatments (Table 3). Even in

Morita et al. (1997) reported that moderate soil drying

the dry treatment, the nodal roots emerged from theinhibited the elongation of primary seminal roots in

6-7th internodes with the highest 6 in Gadambalia, but

wheat, but accelerated the compensatory branching of

not in Tabat. Stable emergence of the nodal roots atlateral roots. These changes in root growth appeared

higher internodes in Gadambalia accounted for the

to be adaptive for water acquisition after rewatering

higher 0m under drought stress (Fig. 5) and would be(Morita et al., 1997). The crops including sorghum

partly responsible for the high RLD in deep soil layers.

may be required to obtain the ability to generate

The hydrotropism induced by a water gradient in theand elongate the lateral roots under lowered soil

medium influenced the growth angle of nodal roots

water potential to keep BI higher to achieve drought

in maize (Leopold and LaFavre, 1989; Nakamoto,tolerance. Otherwise, water extraction would be1993) and wheat (Oyanagi et al., 1992). However, thisdepressed by lack of roots resulting in a poor water

tropism might have little effect on the growth direction

status in the shoot and low productivity.

of nodal roots in sorghum since the 6 of each nodal

The decrease of nodal root length also accounted
for the decrease of TRL in the dry treatment (Table 2).

root was similar between the watering treatments ineither cultivar (Table 3).

The reduction of the nodal root length was moderate

Water acquisition from deeper soil layers might be

in Gadambalia compared with that in Tabat. The

determined not only by the root length or root surface

inhibition of nodal roots elongation under drought

area but also by the physiological function of the roots,

stress has also been observed in sorghum (Pardales

e.g. hydraulic conductivity (Sperry et al., 2002). Salihand Kono, 1990), sweet potato (Pardales et al., 2000)

et al. (1999) reported that Gadambalia took up more

and rice (Banoc et al., 2000b). The greater decreasewater from deep soil layers despite its lower RLD thanof nodal root length in Tabat would be partly due toTabat. Furthermore, Gadambalia, unlike Tabat, wasthe reduction of the number of nodal roots (Table

not affected by drought stress in cross sectional area4). Interestingly, the emergence of nodal roots

and capacity of late metaxylem vessels, which implied

from higher internodes was suppressed by drought

high hydraulic conductive potential of the nodal roots

stress in Tabat (Table 4), but was hardly affected inof Gadambalia. Functional aspects of roots may also

Gadambalia. Initiation and/or differentiation of

be involved in the high ability to extract water fromprimordia are sometimes delayed or suppressed bydeep soil layers, and hence, the drought tolerance ofenvironmental stresses (Nemoto et al., 1995). So

Gadambalia. Further research to clarify the function offar, knowledge on nodal root emergence under soilroots in water extraction by the sorghum cultivars is in

drying is limited. Although a number of studies haveprogress.

been made on physiological processes involved in
the differentiation of lateral roots, for example, theConclusion

function of growth regulators like hormonal substrate,

The two sorghum cukivars with contrasting drought

turgor maintenance by osmotic adjustment, and atolerance differed in the responses of their rootrole of carbon allocation (e.g. Wightman et al., 1980;

systems to soil drying. The drought tolerance ofWestgate and Boyer, 1985; Banoc et al., 2000a), it isGadambalia is derived from deep rooting attributestill unknown what determines differentiation of nodal

and an ability to produce thick nodal roots elongatingroots in water-limited conditions.

downward from higher internodes, as well as enhanced

In cereals such as maize, foxtail millet and wheat,

lateral root branching in deep soil layers under

growth angle of nodal and seminal roots characterizeddrought condition. In general, thick nodal roots

the root distribution profiles (Nakamoto et al., 1991;

persist longer and produce more and larger branch

Oyanagi et al., 1993a, 1993b; Araki and Iijima, 2001).

roots, thereby increasing root length density (Nguyen

In the cultivars used in this study, there was a close

et al., 1997). Therefore, information on such nodal

positive correlation between 9 and basal diameter ofroot emergence would facilitate breeding programs

Tsuji et al.

Development and Distribution of Root System in Sorghum under Drought Stressand management practices for improving droughttolerance in sorghum.

561

Nakamoto, X, Shimoda, K. and Matsuzaki, A. 1991. Elongation
angle of nodal roots and its possible relation to spatial root
distribution in maize and foxtail millet. Jpn. J. Crop Sci. 60 :Acknowledgements

The authors are grateful to Dr. Anthony Egrinya
ENEJI and Dr. John GORHAM, visiting professors,
Arid Land Research Center, Tottori University, Japan,
for their invaluable comments and critical reading of
the manuscript.

gravitropic behavior of nodal roots in maize. Plant Soil 152 :

261-267.
Nemoto, K., Morita, S. and Baba, T. 1995. Shoot and root
development in rice related to the phyllochron. Crop Sci. 35 :24-29.

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rice: its variation and contribution to root system formation.

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Which roots penetrate the deepest in rice and maize rootsystems? Plant Prod. Sci. 3 : 281-288.
Araki, H. and Iijima, M. 2001. Deep rooting in winter wheat:rooting nodes of deep roots in two cultivars with deep andshallow root systems. Plant Prod. Sci. 4 : 215-219.

Araki, H., Morita, S., Tatsumi, J. and Iijima, M. 2002. Physiol-

morphological analysis on axile root growth in upland rice.
Plant Prod. Sci. 5: 286-293.
Bafioc, D. M., Yamauchi, A., Kamoshita, A., Wade, L. J. andPardales, J. R. Jr. 2000a. Genotypic variations in response oflateral root development to fluctuating soil moisture in rice.
Plant Prod. Sci. 3: 335-343.
Bafioc, D. M., Yamauchi, A., Kamoshita, A., Wade, L. J. andPardales, J. R. Jr. 2000b. Dry matter production and rootsystem development of rice cultivars under fluctuating soil

moisture. Plant Prod. Sci. 3 : 197-207.
Eissenstat, D. M. 1992. Costs and benefits of constructing rootsof small diameter. J. Plant Nutr. 15 : 763-782.
Fukai, S. and Cooper, M. 1995. Development of droughtresistant cultivars using physio-morphological traits in rice.

Field Crops Res. 40 : 67-86.
Klepper, B. 1991. Crop root system response to irrigation. Irrig.
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Kono, Y, Tomida, K., Tatsumi, J., Nonoyama, T., Yamauchi, A.

and Kitano, J. 1987. Effects of soil moisture conditions on thedevelopment of root system of soybean plants (Glycine max

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Leopold, A. C. and LaFavre, A. K. 1989. Interractions between

red light, abscisic acid, and calcium in gravitropism. Plant
Physiol. 89:875-87.
Ludlow, M. M., Santamaria, J. M. and Fukai, S. 1990.
Contribution of osmotic adjustment to grain yield in Sorghum

bicolor (L.) Moench under water-limited conditions. II . Water
stress after anthesis. Aust. J. Agric. Res. 41 : 67-78.

Morita, S. and Collins, H. P. 1990. A method to describe root
branching. Jpn. J. Crop Sci. 59 : 580-581.

Morita, S., Okuda, H. and Abe, J. 1993. Spatial distribution andstructure of wheat root system. In Korean Society of Crop
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in Asia. Korean Society of Crop Science, Seoul. 399-404.

Morita, S., Okuda, H. and Abe, J. 1997. Root system morphologyof wheat grown under different soil moisture andtranspiration rates after rehydration. J. Agric. Meteorol. 52 :819-822.

543-549.

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Nguyen, H. T., Babu, R. C. and Blum, A. 1997. Breeding fordrought resistance in rice: Physiology and molecular genetics

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Oyanagi, A., Sato, A. and Wada, M. 1992. Effect of water

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Oyanagi, A, Nakamoto, T. and Morita, S. 1993b. The gravi tropic
response of roots and the sharping of the root system incereal plants. Environ. Exp. Bot. 33 : 141-158.

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between hydrotropism and gravitropism in the primaryseminal roots of Triticum aestivum L. Ann. Bot. 75 : 229-235.
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Crop Sci. 39:168-173.
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Contribution of osmotic adjustment to grain yield in Sorghum

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Sperry, J. S., Stiller, V. and Hacke, U. G. 2002. Soil water uptake
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Growth and gas change of three sorghum cultivars underdrought stress. Biol. Plant. 46 : 583-587.
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Hormonal factors controlling the initiation and development

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of lateral roots. II

Plant Production Science Vol.8, 2005

. Effects of exogenous growth factors

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Wright, G. C. and Smith, R. C. G. 1983. Differences between
two grain sorghum genotypes in adaptation to drought stress.

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Jpn.J. Crop Sci. 56 : 608-617.
Yamazaki, K., Morita, S. and Kawata, S. 1981. Correlations

between the growth angles of crown roots and their diameters
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*In Japanese with English summary

Yamauchi, A., Kono, Y. and Tatsumi, J. 1987b. Quantitative

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Science and Plant Nutrition

23

Soil Sci. Plant Nutr.f 48 (1), 23-29, 2002

22Na+ and 36C1" Mobility in Salinized Excised Leaves of
Several Crop Plants
Satoshi Yamada, Atsushi Takeoka, and Masuo Yamanouchi
Faculty ofAgriculture, Tottori University, Tottori, 680-8553 Japan

Received May 1, 2001; accepted in revised form October 16, 2001

Excised leaves of several crop plants were cultured in a nutrient solution containing 22Na*(816 Bq mL"1) or 36C1" (802 Bq mL"1), and the mobility of 22Na* and 36Cr between and withinorgans was investigated. Though 22Na+ and 36C1" seemed to be taken up depending on thetranspiration in all the examined crops, the distribution pattern of 22Na* and 36CF and theconcomitance between them varied among the crops as follows: 1) Though 22Na* and 36CF
were taken up concomitantly in rice and maize, 22Na* and 36C1~ were well distributed all overthe leaf in rice and reached the lower half of the leaf blade but moved only over a short dis

tance from the midrib and the brims of the leaf blade in maize. 2) In soybean, 22Na+ and
36CF were well distributed all over the leaf, and the possibility of the preferential intrusionof 36C1~ to the leaf was indicated. 3) In adzuki bean, 22Na* and 36CF were intensely distrib
uted first to the petiole, then to the leaf veins, and finally to the mesophyll. The concomi
tance between 22Na+ and 36C1" could not be determined. 4) In pumpkin, 22Na* and 36CF wereretained in the petiole for transfer to the leaf blade, and 86C1" was taken up preferentially.
These results suggested that in the excised leaves, the mobility of Na+ and Cl" was affected
not only by the transpiration but also by the transport of Na+ and Cl~ from the xylem to surrounding tissues and / or by the structure of leaf tissues.

Key Words: 36C1" distribution, excised leaf, leaf structure, 22Na* distribution, transpiration.

Since salinized agricultural lands, crop productivity is
usually reduced by the restriction of water absorption

among the crops. Therefore, it was suggested that only
passive processes such as mass flow could not accountand /or the disturbance in nutrient absorption, it is im

for Na+ transport, and that Na+ retention, Na+ exclusion,

portant to investigate the mechanisms of nutrient ab

or Na+ transfer from the xylem flow to the xylem paren

sorption under salinized conditions for the improvement

chyma cells might occur. However in the previous study,of the productivity. Many studies on the characteristics

it was impossible to investigate in detail the mobility ofof mineral absorption under salinized conditions have

22Na+ within organs such as that between the leaf veinbeen centered on whole plant experiments which are

and mesophyll, since the level of 22Na+ in the segments

important to analyze the responses of crops to salinizedof petioles or leaf sheaths and leaf blades was deter

conditions in terms of productivity (Francois and Maas

mined by using a 7-counter.

1994). However, investigations on mineral absorption of

PLB and DP systems enable to investigate the mobili

whole plant do not enable to reveal the autonomous

ty of elements absorbed from the xylem flow between

mobility of the ions in each individual organ, since theand within organs by neglecting the effects of stems andmobility of ions is assumed to be regulated by adjacentroots, since the proximal ends of the petioles or leafor separate organs.

sheaths were soaked in the nutrient solution.

In a previous paper, the distribution pattern of 22Na+ in

The objective of this study was to investigate thethe petiole or leaf sheath with the leaf blade (hereafterreferred to as PLB) and the detached petiole or leaf

22Na+ and 36C1" mobility between and within organs in
PLB and DP subjected to NaCl treatment. Five main

sheath without the leaf blade (hereafter referred to as

glycophytes were examined and the salt-tolerant andDP) was investigated in several crops (Lopez et al.

1999), where the distribution pattern of 22Na+ and thesensitive varieties were also examined for 3 out of the 5crops. PLB and DP were cultured in a nutrient solution

relationship between the amount of transpiration and thecontaining 22NaCl or Na36CI, the amount of transpiration

amount of 22Na+ absorbed in these excised leaves varied

was measured and the distribution of 22Na+ and 36C1" inNil-Electronic Library Service

Japanese Society of

Soil

Science and Plant Nutrition

24"

S. YAMADA, A. TAKEOKA, and M. YAMANOUCHI

Rice (var. Pokkali)

Rice (van Yamahikari)

Maize (var. White Dento)

\
24h

48h

24h

Soybean (var. SJ2)

24h

48h

48h

24h

24h

Adzuki bean (var. Kantoh No. 2)

24h

48h

48h

Soybean (var. Chasengoku)

48hAdzuki bean (var. Hikari)

24h

48h

Pumpkin (var. Sunbell)

24h

48h

Fig. 1. Distribution of ^Na* in the petiole and leaf sheath with leaf blade (PLB) or without leaf blade (DP) revealed by radioluminography using an imaging analyzer. Images of PLB and DP are shown on the left and right sides of each window, respectively. For
maize and pumpkin, the photographs of fresh specimens of PLB and DP are shown on the left side of each image.

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25

22Na* and 36CI~ Mobility in Salinized Excised Leaves

these plant parts was visualized by radioluminography.

the vial with the nutrient solution without PLB or DP for 24

or 48 h (g). Methods of visualization of 22Na+ and ^CP was
described previously (Yamada et al. 2000).

The room temperature for 22Na+ and 36C1" uptake and

MATERIALS AND METHODS
Plant materials.

for the determination of the amount of transpiration was

The plant materials used wererice (Oryza sativa L. salt-tolerant variety: Pokkali andadjusted to 25°C and the light intensity was 500-600

jxE s"1 m-2salt-sensitive variety: Yamahikari), maize (Zea mays L.

van White Dento), soybean (Glycine max Mem salt-tol
erant variety: SJ2 and salt-sensitive variety: Chasen-

RESULTSgoku), adzuki bean (Phaseolus angularis L. salt-tolerantvariety: Kantoh No.2 and salt-sensitive variety: Hikari),

22Na+distribution

In the PLB of both varieties of rice, 22Na+ was welland pumpkin (Cucurbita pepo L. van Sunbell).

Plant culture and 22Na+ and 36Cr uptake. The
method were previously described (Yamada et al. 2000)
except for the use of a nutrient solution containing 40

distributed all over the leaf sheaths and leaf blades aftermM NaCl labeled with 22NaCl (816 Bq ml/1) or Na36Cl

rice, the 22Na+ density increased gradually distally,(802 Bq mL"1) for 22Na+ and 36C1~ uptake, respectively.
Determination of the amount of transpiration and visualization of 22Na+ and ^Cl".

24 h and the distribution became denser in both organs

after 48 h (Fig. 1). In the DP of these two varieties ofthough 22Na+ was also well distributed all over the leaf
sheaths and the distribution became denser with time.

After

In the PLB of maize, 22Na+ reached the middle part ofplant culture, PLB and DP prepared as described previ

the leaf blade to be distributed along the midrib after 24

ously (Lopez et al. 1999) were transferred to 20 mL

h and the 22Na+ intrusion continued upward along thevials containing 2-3 mL of salinized nutrient solution.

midrib and the brims of the leaf blade after 48 h, while

At 24 or:48 h after transfer to the vials, the amount ofin DP, 22Na+ was distributed all over the leaf sheath andtranspiration was calculated by the following equation.

the distribution became denser with time.

In the PLB and DP of both varieties of soybean, 22Na+

Amount of transpiration (mL) = A — B

was well distributed all over the petioles and leaf blades

A: weight loss of the vial with the nutrient solution for theculture of PLB or DP for 24 or *48 h (g). B: weight loss ofafter 24 h, and the distribution became slightly denser inall these two organs in van SJ2 while the' density of

Rice?
var. Pokkali

Pumpkin

Maize

var.Yamahikari

3fc.

2-

OD

1 -

0

I
Adzuki bean

Soybeantvar. SJ2

var. Kantoh No.2

var.Chasengoku

var.Hikaris

0.5PLB PP

24hFig. 2.

PLB

DP

48h

PLB DPPLB DP

24h

48h

0-

PLB

DP

24h

PLB DPPLB DPPLB DP

48h

24h

48h

Amounts of transpiration at 24 and 48 h after 22Na+ absorption. Bars in figure indicate SD value (n = 3).

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26

S. YAMADA, A. TAKEOKA, and M. YAMANOUCHI

Rice (var. Pokkali)

24h

Rice (var. Yamahikari)

48h

24h

Soybean (var. SJ2)

-,

24h

24h

Adzuki bean (var. Kantoh No. 2)

48h

24h

48h

Soybean (var. Chasengoku)

48h

24h

48h

Maize (var. White Dento)

48h

Adzuki bean (var. Hikari)

24h

48h

Pumpkin (var. Sunbell)

24hFig. 3.

48h

Distribution of 36C1" in PLB or DP revealed by radioluminography using an imaging analyzer. The other parts in the legend

are the same as those in Fig. 1.

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27

22Na+ and 36C1~ Mobility in Salinized Excised Leaves

36CP distribution pattern was vary similar to that of

22Na* did not change in van Chasengoku after 48 h.
In the PLB and DP of both varieties of adzuki bean,

22Na+ (Fig. 3).

22Na+ was intensely distributed to the petioles and leaf

In the PLB and DP of both varieties of soybean, 36C1~

veins to some extent after 24 h, and densely distributed

was well distributed all over the petioles and leaf bladesalso to the mesophyll after 48 h. After 48 h, the distribu

after 24 h, and the distribution became slightly denser intion of MNa+ was slightly denser in van Kantoh No. 2

van SJ2 while the density of 36CP did not change in van
Chasengoku after 48 h, though the difference in the 36C1~

than in van Hikari.

In the PLB of pumpkin, 22Na+ was distributed almost
only all over the petiole after 24 h, and a slight distribu

density between the leaf veins and mesophyli was lesspronounced in var SJ2 than in van Chasengoku.

tion of 22Na+ to the leaf veins was detected after 48 h,

In the PLB and DP of both varieties of adzuki bean,

while in DP, 22Na+ was sparsely distributed distally after

36C1" was distributed all over the petioles and leaf blades

24 h and the distribution became denser with time.

after 24 h, and the distribution became slightly denser inAmount of transpiration for 22Na+ absorption
In the two varieties of rice, the amount of transpiration increased with time in PLB but was constant in DP,
and was slightly larger in van Yamahikari than in van

var. Kantoh No. 2 while the 36C1" density did not change
in var. Hikari after 48 h. The difference in the 36C1" density between the leaf veins and the mesophyll was simi
lar in the two varieties of adzuki bean.

In the PLB of pumpkin, 36C1" was intensely distribut
ed all over the petiole and to some extent to the leaf

Pokkali after 24 and 48 h (Fig. 2).

In maize and pumpkin, though the amount of transpi
ration in PLB and DP increased with time, the differ
ence in the amount of transpiration between PLB andDP was the smallest in these crops.

In the PLB and DP of soybean and adzuki bean, theamount of transpiration increased with time and theveins and mesophyll after 24 h, and the distribution
became slightly denser in the leaf veins and mesophyll

after 48 h, while in DP, 36C1~ was distributed all over thepetiole after 24 h and the distribution became slightly
denser with time.

ies of each species.

Amount of transpiration for 36C1" absorption
The amounts of transpiration in the 36CF absorption

36Cr distribution
In the PLB and DP of the two gramineous crops, theabsorption experiment, except that the amount of tran
spiration was smaller in both varieties of soybean andincrements were almost similar between the two variet

experiment were almost the same as those for the 22Na+

Rice

var. Pokkali

32-

•3

1-

I

S N. |

Soybean

«

O

21-

0-

PLB DP

24h

Fig. 4*I

1.51.0-

I

0.5-

0

var. Kantoh No.2

PLB DPPLB DPPLB DP

I 1

48h

24h

48h

1

*

Adzuki bean

var.Chasengoku

var. SJ2

3

Pumpkin

Maize

var.Yamahikari

var.Hikari

PLB DPPLB DPPLB DPPLB DP

24h

48h

24h

48h

Amounts of transpiration at 24 and 48 h after 36C1~ absorption. Bars in figure indicate SD value (n = 3).

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S. YAMADA, A. TAKEOKA, and M. YAMANOUCHI

28

was larger in both varieties of adzuki bean than those inrelated to the leaf structure and was clearly observed in

the 22Na+ absorption experiment (Fig. 4).

pumpkin and indistinctly in soybean.

As described above, although the distribution patternof Na+ and C\~ varied among the crops, the concomi

tance between Na+ and Cl~ also seemed to vary among

DISCUSSION

the crops. In rice and maize, 22Na+ and 36CV were taken

In this study, 22Na+ and 36C1" mobility between andup concomitantly (Figs. 1 and 3). In soybean, the densi

within organs in the excised leaves treated with NaClty of both 22Na+ and 36C1~ seemed to be almost saturated

was investigated and the distribution of 22Na+ and 36C1~

after 24 h, though the amount of transpiration for thewas visualized by radioluminography using an imaging

36C1~ absorption experiment was remarkably smaller

analyzer (Imaging Analyzer BAS

2000, Fuji Film,than that for the 22Na+ absorption experiment (Figs. 2

Tokyo, Japan). In this method, the monochrome densityand 4). Therefore, it is possible that CF might have been

expresses the radiant energy of 22Na+ and 36C1~ captured

taken up preferentially to PLB. In adzuki bean, since thein the imaging plate, and the radiant energy of these two

distribution of 22Na+ tended to become denser with time

radioisotopes is different. Therefore, the amounts ofwhile the 36C1~ density was assumed to be alreadyalmost saturated after 24 h (Figs. 1 and 3), 36C1" was

22Na+ and 36C1" could be compared based on the densityof each isotope as indicated in Figs. 1 and 3, respective

apparently taken up preferentially to the leaf blade.

ly. Since the density of 22Na+ and 36C1~ was assumed to

However, since the amount of transpiration for the 36Cfroughly depend on the amount Of transpiration, theabsorption experiment was roughly double of that for

amount of 22Na+-and 36Cf absorbed was assumed to depend on the amount of transpiration. Though the amountthe 22Na+ absorption experiment (Figs^ 2 and 4), thepreferential intrusion of 36Cr could not be confirmed. Inof net 22Na+ and 36Cr absorbed could not be compared,
the mobility rate of MNa+ and 36C1~ could be estimated

22Na+ and 36C1~ should be examined under the sameby the difference in the isotope density from 24 to 48 hamount of transpiration. The difference in the amount ofafter MNa+ and 36C1" absorption.

transpiration between the two experiments in soybean

The results of the 22Na+ and 36C1" distribution (Figs. 1
and 3) indicate that the distribution patterns of Na+ andCr varied among the crops; Na+ and CP were distributin the experimental conditions such as the humidity andthese two leguminous crops, the concomitance between

and adzuki bean was attributed to the subtle differences
solar radiation-intensity from the window of the labora

ed all over the leaf in rice and soybean, upward along

tory. The density of 36C1" was almost constant in soy

the midrib and the brims of the leaf blade in maize,

bean and adzuki bean with an increase in the amount ofintensely distributed to the-petioles, to some extent totranspiration with time, which indicated that Cl" exclu

the leaf veins and subsequently to the mesophyll insion from the leaf blade occurred in the PLB of soybean

adzuki bean, and the transport was restricted to the leaf

and adzuki bean. In pumpkin, since the difference in theblade in pumpkin. A considerable factor responsible for

36Cr density between the leaf blade and petiole wasmuch smaller than that of the 22Na+ density (Figs. 1 andthe variation in the distribution pattern was the transportsystem of these ions from the xylem to the surrounding3), it was considered that CT intrusion occurred preferparenchyma tissues. In a previous paper, it was reported

entially into the petiole and leaf blade. The studies inthat 22Na+ was retained in the lower part of the petioles

which the Na+/Cl~ ratio of several highly salinizedcrops was examined, revealed that the Na+ / Cl" ratio inof PLB and DP and that the transport was restricted to
the leaf blades in pumpkin (L6pez et al. 1999). And it

leaves was 0.97 ± 0.14 in rice, 0.22 ± 0.12 in soybean

was also reported that Na+ was excluded from the leaves

and 0.64 ± 0.20 in adzuki bean (Yamanouchi et al.

of beans (Kramer et al. 1977) and corn (Yeo et al. 1977)

1990a). Yamanouchi et al. (1990b) stated that in pumpby the reabsorption of Na+ from the xylem sap to thesurrounding tissues in the proximal region of the roots.

kin, the total amount of Na+ absorbed was remarkably
small compared with that of CF, Na+ markedly accumu

The rate of transport of Na+ and Cl" from the xylem sap

lated in the stem and the transport was restricted to theto the surrounding tissues might vary among the examleaf blade, resulting in high concentrations of K+, Ca2+,

ined crops. The other considerable factor was the strucand Mg2+ without concomitance between Na+ and Cl~.

ture of the leaves. In this study, MNa+ and 36C1" distri

Namely in a whole plant, Na+ and CT were taken up

bution became gradually and distally denser in rice andconcomitantly in rice and CF was taken up preferential

maize, which might be due to the similarity in the distri

ly in soybean, adzuki bean, and pumpkin. It is interest

bution of bundle sheaths. In adzuki bean, ^Na* and 36CF

ing to note that the concomitance between Na+ and Cl~

were intensely distributed to the petiole first, subse

in whole plant occurred in the excised leaves of rice andquently to the leaf veins, and finally to the mesophyll,

pumpkin in this study.

and this phased distribution pattern might be closely

In the current study, the excised leaves of the salt-tol-

NII-Electronic Library Service

Japanese Society of Soil

Science and Plant Nutrition

29

22Na+ and 36CP Mobility in Salinized Excised Leaves

erant and sensitive varieties were examined for rice,-L6pez R, Yaraada 5,-and Yamanouchi M 1999: Comparison ofsoybean, and adzuki bean. In the salt-tolerant varieties

sodium uptake by and transport in detached plant partsof rice such as Pokkali, the restriction of Na+ accumulation in shoots was due to the Na+-holding capacity and

Yamada S, Takeoka A, and Yamanouchi M 2000:32P mobility in

Na+-excluding capacity of the roots (Yamanouchi 1989).

The salt-tolerant varieties of soybeansuch

as SJ2

showed lower concentrations of Na+ and Cl~ in the leaf
blade or stem than

the sensitive varieties such as

Chasengoku (Yamanouchi et al. 1989a), and the salt-tol

erant varieties of adzuki bean such as Kantoh No. 2

showed a lower concentration of Na+ in the leaf blades
which depended on the Na+-excluding capacity and / or
the rate of Na+ translocation to leaves (Yamanouchi etal. 1989b). Hence, salinity tolerance can be partly attrib
uted to the mechanisms of Na+ and C\~ partition in thewhole plant. In the PLB and DP systems in this study,
Na+ and Cl" mobility in leaves could be investigated byneglecting the effects of stems and roots and it was

revealed that the Na+ and Cl" mobility in the excised
leaves was not different between the examined varietiesof rice, and was almost the same between the examinedvarieties of soybean and adzuki bean. In conclusion, it
can be stated that the leaves themselves only hardly dis

among several crops. Soil Sci. Plant Nutr., 45, 659-668
detached leaf of several crop plants. Soil Sci. Plant Nutr.t
46,969-974

Yamanouchi M 1989: The mechanisms of salinity tolerance inrice plants. Relationships between the varietal difference ofsalinity

tolerance and characteristics

of absorption

andtranslocation of sodium ion (2). Jpn. J. Soil Sci. Plant Nutr.,
60, 210-219 (in Japanese with English summary)

Yamanouchi M, Fujiyama H, Kimura Y, and Nagai T 1990a: The
effects of sodium chloride on the absorption and the translocation of several ions in sugar beets, rice plants, soybeans, azuki beans, and kidney beans. The effects of sodium
chloride on the absorption and the translocation of several
ions in plants (2). Jpn. J. Soil Sci. Plant Nutr., 61, 173-176(in Japanese with English summary)

Yamanouchi M, Fujiyama H, Koyama Y, and Nagai T 1989a:
The mechanisms of salinity tolerance for soybean (Clycine

max L.). Relationships between the varietal difference ofsalinity tolerance and the characteristics of absorption andtranslocation of sodium ion (6). Jpn. J. Soil Sci. Plant Nutr.,
60, 437-442 (in Japanese with English summary)

Yamanouchi M, Fujiyama H, Matsumoto N, and Nagai T 1990b:
The effects of sodium chloride on the absorption and theplay the salt-excluding mechanism and can not accounttranslocation of several ions in Cucurbitacea plants. The

for the salinity tolerance for rice, soybean, and adzuki

effects of sodium chloride on the absorption and the transbean.

location of several ions in plants (1). Jpn. J. Soil Sci. Plant
Nutr., 61, 1-7 (in Japanese with English summary)

Yamanouchi M, Susaki S, Wakusima T, and Fujiyama H 1989b:

REFERENCES

The

mechanismsof salinity

tolerance

for

azuki

bean

(Phaseolus angularis L.). Relationships between the varietal

difference of salinity tolerance and characteristics of absorp
Francois LE and Maas EV 1994: Crop response and manage

tion and translocation of sodium ion (3). Jpn. J. Soil Sci.

ment on salt-affected soils. In Handbook of Plant and Crop

Plant Nutr., 60, 325-334 (in Japanese with English sum

Stress, Ed. M Pessarakli, p. 149-182, Marcel Dekker, Inc.,New York / Basel / Hong Kong

Kramer D, Lauchli A, and Yeo AR 1977: Transfer cells in rootsmary)

Yeo AR, Kramer D, Lauchli A, and Gullasch J 1977: Ion distri

bution in salt stressed mature Zea mays roots in relation toof Phaseolus coccineux: Ultrastructure and possible func

ultrastructure and retention of sodium. J. Exp. Bot., 28, 17-tion in exclusion of sodium from the shoot. Ann. Bot., 41,291031-1040

Nil-Electronic Library Service

ReturnReturnReturn

A Study on a Water Maker System using Peltier Devices
Tsutomu Hayashi1, Wei Liu2, Kengo Nojima3, Yutaka Hara1 & Kotaro Tagawa4
1

2

Department of Applied Mathematics and Physics, Tottori University, Japan
Post Doctoral 21 Century COE, Tottori University, Japan, liu@svr01.damp.tottori-u.ac.jp
3
Industrial Research Institute of Tottori Prefecture, Japan
4
Faculty of Regional Sciences, Tottori University, Japan

Keywords: Water maker system, Peltier devices, Arid regions, Coefficient of performance
Abstract: This research aims to develop a water maker system, which condenses water vapor in the atmosphere, forirrigation water and drinking water in the arid regions. In this study, the water maker system using the Peltier
device as a freezer function only by direct-current source was made. The experiment was conducted in the following
environmental conditions: 20 ºC (40, 60, 80% RH) and 30 ºC (40, 50, 60% RH), which could be controlled in thelaboratory. In each environment, the effect of the surface area of a heat exchanger and change of air flow rate on
the water production rate was investigated. In this study, the characteristics of the water maker system wereclarified.

1. Introduction
It is necessary to obtain a stable reserve of drinking
water, medical water, and irrigation water for humanlife in arid regions. The problem is serious in the area
where rain falls little; therefore it is important todevelop the permanent water maker system in place ofexisting groundwater. Since humidity changes withthe difference in temperature between day and night,
fog is generated at night in some arid regions along theseashore. It is then possible to obtain the permanentand economical water maker system if water vapor in
the atmosphere is condensed efficiently.
It is important to produce refrigeration with thecoefficient of performance (COP) for water makersystem [1], and the compressor (COP=2-5) with large
cooling capability is used for a common dehumidifier.
However it is not environmentally friendly since thechlorofluocarbon is used.
Moreover, social
maintenance is inadequate, and periodic maintenanceand quick repair are difficult in arid regions.
In this research, the water maker system with theeasy structure using the Peltier device was made. It
aims to develop the water maker system suitable for thearid regions.
A Peltier device is a small andlightweight device, which can make a difference oftemperature only via passing direct-current source.
Although COP (COP=0.3-0.6) is small, not using
chlorofluorocarbon and not having a movable part, it issuitable for the arid regions.
This study investigated the following: the effect ofchange of the surface area of a heat exchanger and the
air flow on water production rate under the different

temperature and humidity environment in order toclarify main characteristics of the water maker systemusing Peltier device.

2. Experimental details
Figure 1 shows the experimental setup. The watermaker system consists of a heat exchanger (Copper),eight Peltier devices, two sets of cooling and fan units
fin (ALPHA, FH10040A), and a ventilation fan (FAN362). The size of the Peltier device used in the study
is 40mm × 40mm × 4.2mm as shown in Figure 2 [2].
Three heat exchangers, 80mm, 120mm and 160mm inwidth b [mm], were tested in the experiment. The
surface area for 160mm heat exchanger was too big tocool the air sufficiently, thus 80mm and 120mm heatexchangers were used in this study. Experiments
were performed in a chamber, in which the temperatureand humidity were kept at constant conditions asfollows: 20 ℃ with 40, 60, 80% RH, and 30 ℃ with40, 50, 60% RH. In this experiment, electric power
was supplied to the system by a stabilized DC source.
The input voltage applied to the Peltier device was set
at 10V. The air flow rate was controlled by thevoltage (0V, 4 -14V/piece: interval 2V) change of aventilation fan. We measured the air temperature inthree locations using thermocouple: inlet, middle, andoutlet of the heat exchanger. The effect of heatexchanger size, air flow rate, and environment
condition on water production rate were studied.

On the water surface: a=7.5, b=237.3 (-30 to 100ºC)
On the ice surface:
a=9.5, b=265.3 (-50 to 0ºC)
Vapor pressure Pw is shown as
Pw = Pa × (

ϕ

100

)

(2)

φ[%] is relative humidity.
Absolute humidity
ω [kg/kg’] is the mass of water vapor present in 1kg
dry air. It is expressed as follows:Pwω = 0.622 ×(3)
P − Pw
Here, P [Pa] is atmospheric pressure.
Enthalpy is total heat of the moisture air, and is thesum of sensible heat and latent heat. Enthalpy H [J/kg]
is given by the following formula.
H = 1.005 × T + ω × (2500 + 1.861× T )Figure 1.

Schematic diagram of experimental setup(4)

The amount of cooled air is decided by theperformance of refrigeration. Heat during the coolingprocess can be calculated multiplying by the differenceof enthalpy before and after air cooling. Amount ofheat required cooling air Q [W] is obtained by thefollowing formula.
Q = M × (H1 − H 2 )(5)where, M [kg/s] is the mass rate of air flow. H1 andH2 are enthalpy of before and after air cooling.
If amount of absorbing heat of the Peltier device Qp
is known, assuming Q=Qp, theoretical water production
per 1 second Mw [kg/s] can be obtained by thefollowing formula:
M w = M × (ω1 − ω 2 )(6)

4. Results and discuss

Figure 2. Dimensions of heat exchanger and Peltier
devices

3. The calculation
production rate

methodfor water

4.1. Natural convection

Water production rate by cooling can be calculated
from the performance of the refrigeration. Before
describing the calculation method, the various amountsof states of moist air are explained [3], [4]. Saturation
vapor pressure Pa [Pa] is given by the following
approximation formulas, when temperature T [ºC] is
known.
aT

Pa = 6.11× 10 (T +b )In this research, two ventilation cases: naturalconvection and forced convection were studied. In
the natural convection case, the ventilation fans were
removed from the system. In the forced convection
case, air wind speed in outlet was controlled between
0m/s and 1.6m/s to investigate the effect of the air flow.

(1)

Figure 3 shows water production rate and the cooled
air temperature in the natural convection case. The
cooled air temperature was measured in outlet of heatexchanger as shown in Figure 1, and the averageexperimental value for the last 30 minutes in the second
half was used when the experiment conditions was in astationary state.
When not ventilating in eachenvironment condition, the water production rate withthe large surface area of the heat exchanger widthb=120mm had exceeded that with b= 80mm.

rate when air temperature is set in this range in actualuse. The maximum of water production rate in theexperiment was 65.5g/h in environment condition of 20ºC and 80% RH (b= 120mm).
Figure 6 shows that water production rate and thecooled air temperature vary with air flow rate in theenvironment condition of 20 ºC and 80% RH. In theexperiment, although ventilation was performed, sincesome air wind speed was too low to measure, and it isregarded as 0m3/s in Figure 6.

Figure 3. Water production rate and the cooledtemperature in the natural convection case

Figure 4. Photograph of the heat exchanger with the
frost

Figure 5. Water production rate, air flow rate and thecooled temperature in the forced convection caseMoreover, in the 20 ºC environment condition, thecooled air temperature was less than the freezing pointon all the conditions except b= 120mm, 80% RH, andthe frost adhered to the heat exchanger as shown in
Figure 4.

4.2. Forced convection
Figure 5 shows the maximum water production ratein each environment and the air flow rate at that time,
and the cooled air temperature. The overall trend
showed no significant difference when b= 80mm andb= 120mm, as the experiment of values in these cases
came to be dependant upon the cooling capability of
the Peltier device. This is because the Peltier device
with small absorbing heat cannot enlarge the air flow
rate, the influence of the air flow rate does not appear
between b= 80mm and b= 120mm (except 20 ºC, 80%
RH). Water production rate was the maximum whencooled air temperature was between 2.5 to 4.8 ºC (anaverage of 3.5 ºC) below the dew point as shown in
Figure 5. It is necessary only to control the air flow

Figure 6. Water production rate and the cooled airtemperature vary with air flow rate

The water production rate increased with increasing
air flow rate. However, the water production rate
started to decrease when the cooled air temperatureneared the dew point with increasing air flow rate.
The difference of the water production rate had arisen
between b= 80mm and b= 120mm as the air flow
became high.
Since wind speed at b= 80mm
increased about 1.5 times than that at b= 120mm in thecase of the same air flow rate as shown in Figure 7,
therefore the influence of wind speed appeared when
the air flow rate was more than 0.003m3/s.
Figure 8 shows comparison of the experimental andcalculated value for water production rate and the air
flow rate in each environmental condition.

The measured value for the temperature inclined
high, since the cooled air temperature measured in theheat exchanger central part, and the cooled airtemperature rose by condensation heat. Actually inthe experiment, even if the cooled air temperature had
exceeded the dew point, condensation occurred, andcondensation stopped at about 3 ºC more than the dew
point. To compare with a calculation value, themeasured cooled air temperature value subtracted 3 ºCfrom the experimental value as shown in Figure 8.
The calculation value shown as a solid line computedfrom a formula (6), when assuming absorbing heat
80W which multiplied electric power 160W to a Peltier
device by COP=0.5 of the Peltier device. When an
experiment value was compared with a calculation
value, it was observed that the maximum waterproduction rate in the experiment approachedcalculation value with high relative humidity,
producing high water efficiency.

5. Conclusions

Figure 7. Comparison of the wind speed between
b=80mm and b=120mm

A trial production for the water maker system using
the Peltier devices was conducted; its performance wasinvestigated. The following results were elucidated.
(1) Equipment efficiency is dependent on
absorbing heat of the Peltier device, noappreciable difference exists in the maximum
water production rate and the air flow rate
between b=80mm and b=120mm.
(2) Water production rate becomes the maximum,
when the cooled air temperature is in the range
2.5 to 4.8 ºC (an average of 3.5 ºC) below thedew point.
(3) For the water maker system, producing water
efficiency becomes large with high relative
humidity.

6. References[1] Jesse S. Doolittle, 1960, Thermodynamics forengineers, International textbook company,
Pennsylvania.
[2] Tsutomu Hayashi et al. 2004, A Study on a Water
Maker System using Peltier Devices, The Japan
Society of Mechanical Engineers Branchconference, Japan, No.045-2 (I), pp.109-110.
[3] Virgil M. Faires, 1962, Thermodynamics, Maruzen
Company Limited, Tokyo.
[4] Yunus A. Cengel & Michale A. Boles, 1994,
Themodynamics: An Engineering Approach,
McGraw-Hill, Inc.

Acknowledgement
Figure 8. Comparison of the experimental andcalculated value for water production rate and the air
flow rate

This study was carried out under the Cooperative
Research Program of Arid Land Research Center,
Tottori University. As a part of the 21st century COE
program, the gratitude was expressed by all authors.

ReturnA Study on Water Making System Using Renewable Energy
in Tottori Sand Dune
(Analysis of the System Efficiency by Simulation)
Tsutomu Hayashi*1, Kenji Tanaka*1, Yutaka Hara*1, Wei Liu*2, Kengo Nojima*3 & Kotaro Tagawa*4*1

Department of Applied Mathematics and Physics, Tottori University, Japan*2
Post Doctoral, 21 century COE program, Tottori University, Japan*3
Industrial Research Institute of Tottori Prefecture, Japan*4
Faculty of Regional Sciences, Tottori University, Japan

Abstract
Objective of this study is development of a water making system that can produce
good quality water useful in arid region for drinking, medical treatment and irrigation, using electric
power generated by renewable energy (especially, wind energy). A simple and tough water maker
was composed of eight Peltier devices, copper heat exchanger and fans. The best driving
environment and the operating condition of the system were examined by indoor experiments. Our
research group is planning to conduct the outdoor experiments with the water making system at
Tottori Sand Dune. A meteorological observation system has already been installed at the site andhas been collecting the meteorological data. In this research, water production rate was simulated
based on the indoor experiments data and the observed meteorological data. In the simulation, theoperation of water maker was assumed to be controlled by both the dew point and the battery level.
The water production rates were calculated at the different settings of dew point and wind turbine
performance. The system obtained the highest efficiency at the controlled dew point of 10°C whenusing the meteorological data of November, 2004.
Keywords:

Water Making System, Water Maker, Peltier Device, Renewable Energy

1. INTRODUCTIONSIn arid region, obtaining a stable reserve of water is one of themost important problems for people living there. In this research,a system which can easily produce clean water from water vapor
in the atmosphere has been studied and developed. Most of thearid regions are blessed with renewable energy such as windenergy or solar energy. Therefore, wind power and/or solar
power is appropriate for the energy source of the water making
system and the development of a sustainable system is expected.
At the arid regions along the west coast of a continent, where
rainfall is small but humidity is high, night fogs often occur due
to the large temperature difference between daytime and night.
Especially in such arid regions, the water making system might
operate efficiently by condensing water vapor at night.
In our research group, a simple and tough water maker with
Peltier devices has been proposed, and the characteristic of thewater maker was clarified by indoor experiments. Now, theauthors are planning to conduct outdoor experiments with thewater making system consisted of the water maker and ameteorological observation system at Tottori Sand Dune. The
meteorological observation system has already been installed at
the site and has been collecting the meteorological data. Also,
the amount of water production has been calculated by using theindoor experiment data and the observed meteorological data,

based on assumption that electric power to the system is supplied
only wind turbine. In this research, the influence of the electric
power generated by the wind turbine on the water production
rates was examined. Moreover, the optimal operating conditions
for the control of the system were clarified.
2. THEORY OF THE WATER MAKING BY COOLING
Water vapor in the atmosphere can be condensed by coolingthe moisture air below the dew point. Amount of heat required
to cool air can be calculated multiplies by mass flow rate and thedifference of enthalpy before and after cooling air. Therefore,amount of heat required to cool the air in one-second q [kJ/s] isgiven by the following formula,q = ma × ( h1 − h2 )(1)where, ma [kg/s] is mass flow rate of air, h1 [kJ/kg]，h2 [kJ/kg]
are enthalpy before and after cooling air. Amount of heatremoved from air is decided by performance of the refrigeration.
If amount of absorbing heat of Peltier device qp[kJ/s] is known,
assuming q = qp, the amount of air cooled is decided. In otherwords, air flow rate is given by the following formula.

m a = q p /( h1 − h2 )(2)Since the amount of air cooled was decided, water production1

rate per one-second mw [kg/s] is obtained by the following
formula,mw = ma (x1 − x2 )(3)

where, x1 [kg’/kg]，x2 [kg’/kg] are absolute humidity before andafter cooling air.
3. WATER
MAKER
AND
METEOROLOGICALOBSERVATION SYSTEM
3.1 Water maker
Figure 1 shows the schematic diagram of the water makerusing the Peltier device in the research. On both sides of theheat exchanger, four Peltier devices (two series, 4 parallel, 8
piece in total), and cooling fin and fan were set up. The heatexchangers with two types of width (b=80,120mm) were used inexperiment. The ventilation fan was set up directly in the upperof the heat exchangers, one fan was used in the case of b=80mm,
and two fans were used in the case of b=120mm. Also, whenthe experiments were performed with no ventilating, the fanswere removed. The indoor experiments were carried out in aconstant temperature and relative humidity chamber, in which
the temperature and relative humidity were set six environmentsof 20°C with 40, 60, 80%RH, and 30°C with 40, 50, 60% RH.
The influences of the heat exchanger width and air flow rate on
water production rate during one hour under each condition were
investigated [2]. Fig. 2 shows the comparison between theexperimental values and the calculated values of the waterproduction rate and the air flow rate in the environment of 20°C
with 40, 60 and 80%RH. The experimental values of the
maximum water production rate approached the calculated
values as high relative humidity increases, and the efficiency of
the water production increased as shown in Fig. 2.

3

Air flow rate [m /s]

Water production [g/h]Fig.1 Schematic diagram of water maker

Sampling

Wind speed
Wind direction
Temperature
Humidity
Amount of insolation
Amount of rainfall

Every one second
Every one second
Average for ten minutes
Average for ten minutes
Average for ten minutes
Integrate for ten minutes

20͠,80%20͠,60%20͠,40%20͠,80%0.0075

20͠,60%0.005

b=80 120mm

20͠,40%

40%
60%
80%

0.002500Calculated
value(80W)

2

4

6
8
10
12
14
Cooled air temperature [͠]

16

18

20

Fig.2 Experimental and calculated values of waterproduction and air flow rate

3.2 Meteorological observation system
The schematic diagram of the meteorological observation
system is shown in Fig. 3, and the measurement items are shownin Table 1. The system was set up in Arid Land ResearchCenter of the Tottori University. The system was consisted ofanemovane, humidity/temperature meter and photovoltaic
module were installed, and the hyetometer was set up beside thesystem. The height of the observation pole was 4.5m and theanemovane was set at the top of the pole. The electric power
for the system was supplied by the battery charged with the solar
pane. And the obtained data was saved in the memory of thelogger box.
Table 1. Measurement items
Measurement items

70
60
50
40
30
20
10
0
0.01

Anemovane

Pyranometer
Humidity/Temperature meter
Logger box
Photovoltaic module
HyetometerFig.3 Schematic diagram of meteorological observation system2the case of relative humidity control 90%RH, however, it is lessthan case of no relative humidity control. Therefore, althoughwater production rate can expect to increase when relative
humidity adds to controlled condition, it decreases if relative
humidity is set too high. From Fig. 7, energy efficiency was
improved in each relative humidity control condition whencontrolled dew point became high. And energy efficiency also
improves when relative humidity adds to controlled condition.
From Figs. 6 and 7, the energy efficiency is high whencontrolled dew point is high, but water production rate decreases
when it become too high. In this research, it is assumed that
prototype water maker is used. However, when extended watermaker is used in practice, the energy efficiency became more
important as it is possible that the number of sheets of Peltier
device increases.

4. CONDITIONS FOR THE CALCULATION
It is assumed that the electric power for the water maker is
supplied by only wind turbine and the operation of water maker
is controlled by both the dew point and the battery level. The
control by the dew point is performed when the dew point ismore than datum value, and the control by the battery is
performed when battery level is more than 10%. The case of
three types of wind turbines (rated power 220W, 340W and
460W) were assumed as shown in Fig. 4. Also, the battery withthe capacity 200Ah was assumed. The water production rate
was calculated by using the indoor experiments data and theobserved meteorological data at Tottori Sand Dune (November,2004). In the calculation, the air was cooled to 3°C below thedew point based on the results of indoor experiments and thecontrolled dew point was varied 3°C to 12°C in each windturbine. Moreover, the calculation was carried out in the caseof adding the operating conditions for the relative humidity,
controlling when relative humidity is more than datum value(70%RH, 80%RH and 90%RH).

6
November, 2004

Water production‫[ޓ‬kg]

500
460W
340W
220W

Power [W]

400

5

300

4
3
2
460W
340W
220W

1
0
3

200

4

5

6

7

8

9

10

11

12

Controlled dew point‫]͠[ޓ‬

Fig.5 Water production by difference of wind turbine

100

5
2

4

6
8
10
Wind speed [m/s]12

November, 2004
Rated power 340W

14

Water production [kg]00

Fig.4 Power curve of wind turbines

5. RESULTS AND DISCUSSION
The results of calculation when controlled dew point is variedin each wind turbine are shown in Fig. 5. The water production
rate is calculated using the data of November, 2004. The waterproduction rate rises as the size of the wind turbine becomeslarge. And the fluctuation band of water production rate becomeslarge as the size of the wind turbine becomes large. That is, theoperation by the dew point is important when electricity
generated becomes large contrasts to the electric consumption of
the equipment.
The results of calculation are shown in Fig. 6 in the case ofusing of the wind turbine with rated power 340W and adding thecontrol of the relative humidity. And, Fig.7 shows the energy
efficiency with the condition as shown in Fig.6. Energy
efficiency is given by dividing the water production rate by the
input electricity to equipment,
Ee = M w / Win
(4)

4
3
2

No relative humidity control
More than 70%RH
More than 80%RH
More than 90%RH

1
0
3

4

5

6

7

8

9

10

11

12

Controlled dew point [͠]Fig.6 Water production by relative humidity control

Energy efficiency [kg/kW]

0.35

where Ee [kg/kW] is energy efficiency of the system, MW [kg] ismonthly water production, and Win [kW] is input electricity toequipment.
In the case of 80%RH, Fig. 6 shows that water production rateis increasing compared with no relative humidity control. In

November, 2004

0.3 Rated power 340W
0.25
0.2
0.15
No relative humidity control
More than 70%RH
More than 80%RH
More than 90%RH

0.1
0.05
0
3

4

5

6

7

8

9

Controlled dew point [͠]Fig.7 Energy efficiency

3

10

11

12

Evaluated valueof system efficiency [kg2/kW]

Therefore, the efficiency of water making system is evaluatedfrom water production rate and energy efficiency.
The system efficiency ES [kg2/kW] is defined as multiply waterproduction rate by energy efficiency.
E s = M w × Ee
(5)The evaluated values of the system efficiency in each control
condition are shown in Fig. 8. In each relative humidity control,
the evaluated values of the system efficiency were obtained thehighest value in about 10°C when relative humidity control was
other than 90%RH. Furthermore, the maximum value of thesystem efficiency was obtained maximum when controlled
relative humidity was 80%RH and the controlled dew point was
10°C. In the case of this controlled condition, monthly waterproduction was 3.5 kg, and energy efficiency was 0.27 kg/kW.
The result of a calculation at that case for one month is shownin Fig. 9. The water production range shown in figure is waterproduction rate in the case of assuming to operate without
dependence on the battery level. In this case, monthly waterproduction is 8.5 kg. Thus it produces 40% of 8.5 kg in thecase of electric power supplied by only wind turbine (rated
power 340W). Although there are many water production
ranges in the first half of November, it is recognized that water
making system cannot be operated because of the shortage of theelectricity generated. In the latter half of November, battery
level (electricity generated) is enough, but there are few
production possibility boundaries. So, it is recognized that thesystem cannot operate.

1
0.9
0.8
0.7
0.6
0.5 November, 2004
Rated power 340W
0.4
No relative humidity control
0.3
More than 70%RH
More than 80%RH
0.2
More than 90%RH
0.1
0
3
4
5
6
7
8
9

10

11

12

Controlled dew point [͠]Waterproduction [kg/day]Electric
energy [kWh/day]

6. CONCLUSIONSAs a result of calculation based on the indoor experiments data
and the observed meteorological data for the water maker using
the Peltier device, the following results were elucidated.
(1) Water production rate increases when electricity
generated by a wind turbine becomes large, and thedependence on the control conditions of water production
rate becomes high.
(2) By adding relative humidity control, improvement ofenergy efficiency can be expected and the increase ofwater production rate can also be expected.
(3) The highest efficiency of the system is obtained at thecontrolled dew point of 10°C and controlled relative
humidity of 80%RH in the case of the meteorological
data at Tottori Sand Dune in November, 2004.

25
20
15
10
5
0
2.5
2.0
1.5
1.0
0.5
0
1.5

Controlled relative humidity: 80%RH

Controlled dew point :10 ͠
Dew point
Humidity

100
80
60
40
20
0

Relative humidity [%RH]

Dew point [͠]Fig.8 Evaluated value of system efficiency

Electricity generated
Battery level

Water production range
Water RTQFWEVKQP

1
0.5
0

5

10

15

20

25

30

Day

Fig.9 Calculated value in Tottori Sand Dune

ACKNOWLEDGEMENT
This study was carried out under the Cooperative Research
Program of Arid Land Research Center, Tottori University. As
apart of the 21st century COE program, the gratitude wasexpressed by all authors.
REFERENCES[1] Ichimatsu Tanishita, Engineering Thermodynamics,
Syoukabou company, pp.221-227 (1995).
[2] Tsutomu Hayashi et al, A Study on a Water Maker System
Using Peltier Devices, The Japan Society of MechanicalEngineers Branch Conference, Japan, No.045-2(Ι),
pp.109-110 (2004).

4

ReturnCharacteristics of a Straight-Bladed Vertical Axis Wind Turbine in
Periodically Varying Wind
In-Seung KANG1, Kenichi ARIYASU1, Yutaka HARA1,
Tsutomu HAYASHI1 and Ion PARASCHIVOIU1,2
1

Department of Applied Mathematics and Physics, Tottori University,
4-101 Koyama-cho, Tottori 680-8552, Japan2
Department of Mechanical Engineering, Ecole Polytechnique Montreal,
P.O. Box 6079, Station Centre-ville, Montreal, Quebec, Canada H3C 3A7
Abstract
An experimental study of the torque characteristics for a straight-bladed vertical axis
wind turbine (VAWT) in periodically varying wind speed is presented. The amplitude of theperiodically varying wind speed was fixed at 2m/s with the average wind speed of 8m/s and thecycles of 2.9 s, 4.5 s, and 5.9 s were chosen. The VAWT with NACA 0012 blade sections (chord
length = 0.075m) having the rotor radius of 0.3 m and the rotor height of 0.469 m was rotated by ainduction motor. We studied several experimental models by changing the number of blades (2 to
5 blades) in order to investigate the influence of rotor solidity on the wind turbine performance.
The averaged torque curve in the case of the periodically varying wind is almost the same as thetorque in the case of the constant wind speed. However, in the case of five-blade rotor, the torquein the periodically varying wind became larger than that in the constant wind near the
tip-speed-ratio region where the maximum torque was obtained. The torque and rotational speed
follow the change of the wind speed. This trend is better if the rotor solidity becomes larger.
Keywords:

Wind Turbine, VAWT, Solidity, Periodically Varying Wind, Torque Characteristics

1. INTRODUCTION
Recently, straight-bladed vertical axis wind turbines(VAWT), whose torque characteristics are independent ofwind direction variation, have been attracting people's
attention due to the possibility to be suitable for thechangeable wind conditions. One of our goals of study isdevelopment of a practical VAWT having high efficiency even in
bad wind conditions like changeable wind direction. We alreadyconducted experiments[1] in order to investigate the solidity
dependence of our trial models of VAWT by using a wind tunnel.
However, wind used in such wind tunnel test is constant speed ingeneral, and experiments to investigate the response of a windturbine to the wind speed variation have hardly been reported sofar. Our group carried out the measurements of aerodynamic
forces acting on a two-dimensional blade in a periodicallyvarying wind to investigate the behaviors of the aerodynamic
force coefficients in the wind speed variation[2].
In this study, the torque characteristics of the straight-bladedvertical axis wind turbine are measured in both theperiodically varying wind (PVW) and the constant velocity wind(CVW) in order to compare the rotor behaviors in the different
wind conditions. The number of blades of the rotors and thecycle of the PVW are changed as the parameters in a series ofexperiments to investigate the dependence of VAWT on them.

Fig. 1 Diagram of the rotor of VAWT with 5 blades
Table 1 Specification of the VAWT
Number of Blade：B

2～5

Rotor Radius：R

0.300mRotor Height：H

0.4688m

Blade Chord Length：c

0.075mProjected Area：A=2RH

0.281 ㎡

Material

CarbonBlade Airfoil

NACA 0012

2. EXPERIMENTAL SETUP AND METHOD
Figure 1 shows a diagram of the rotor of VAWT with five
blades. The cross-sectional form of the blade is symmetrical
NACA 0012 airfoil. The number of blades can be changed fromtwo to five. The specification of the rotor is shown in Table 1,
and the photographs of the rotors with different numbers of
blades are shown in Fig. 2.
The diagram of our experimental system is shown in Fig. 3.
The wind tunnel used in the experiment is the Eiffel type, and its
outlet is a 1.5 m × 1.5 m square. The center of the windturbine rotor is located at 1.5m downstream from the center ofthe wind tunnel outlet. The rotor axis is held by two ballbearings, and is combined through couplings with both thetorque detector and the induction motor which is controlled byan inverter. Rotational number of the rotor was fixed in every
about 30 rpm in the range from 30 rpm to 510 rpm. The obtained
torque data were corrected by adding the braking torquemeasured when the axis from which all blades were removed
was rotated at the same rotational number.

The periodically varying wind was generated by variation of
the pitch angle of the axial blower in the wind tunnel. The
average wind speed of the PVW is 9 m/s and the amplitude isabout 2 m/s. The cycle (Tw) of the PVW was set to 5.9 s, 4.5 s,
and 2.9 s. Wind speed was measured at the wind tunnel outlet
using a hot-wire anemometer.
3. EXPERIMENTAL RESULTS AND DISCUSSIONSThe time-averaged power coefficients (Cp) measured in theconstant velocity wind (CVW) and the periodically varying wind
(PVW) are shown in Fig. 4 and Fig. 5, in which only the resultsin the cases of 2-blade and 5-blade rotors are given. The windspeed of the CVW is 9m/s; the cycle of PVW in Fig. 4 is Tw =5.9 s and that in Fig. 5 is Tw = 2.9 s. As shown in Fig. 4 and Fig.
5, roughly speaking, the time-averaged Cp measured in the PVW
and the Cp in the CVW are almost the same. This tendency is thesame in the cases of 3-blade and 4-blade rotors, too. However, if
seen in detail, the Cp in the PVW is somewhat larger than that in
the CVW at the tip speed ratio of λ = 0.8-1.5 in the case of
2-blade rotor and at λ = 1.5-1.7 in the case of 5-blade rotor.
0.1
2Blade-PVW

0.08

5Blade-PVW
2Blade-CVW
5Blade-CVW

0.06

3bladesCp

2 blades

0.04
0.02
0
0

0.2

0.4

0.6

0.8

-0.02

4 blades

1

1.2

1.4

1.6

1.8

2

1.6

1.8

2

λ

5bladesFig. 4 Power characteristics (Tw = 5.9 s)
Fig. 2 Photos of the rotors with different number of blades
0.1

2Blade-PVW
0.08

5Blade-PVW
2Blade-CVW

Cp

0.06

5Blade-CVW

0.04

0.02

0
0
-0.02

0.2

0.4

0.6

0.8

1

1.2

1.4

λ
Fig. 5 Power characteristics (Tw = 2.9 s)

Fig. 3 Experimental setup

0.18

18

PVW

16

CVW

0.14

14

Wind Speed

12

0.1

10

0.08

8

0.06

6

0.04

4

0.02

2

Cq

0.12

0

Wind Speed(m/s)

0.16

0
0

0.2

0.4

Time/Tw

0.6

0.8

1

Fig. 6 Comparison of torque variations in PVW and CVW(5 blades, Tw = 2.9 s, λ = 1.5)

Fig. 7 Dependence of torque characteristics on tip speed ratio(2 blades, Tw = 2.9 s)

Fig. 8 Dependence of torque characteristics on the number of
blades (Tw = 2.9 s, λ = 1.5)

Fig. 9Deviation of the rotational speed in each case ofdifferent number of blades (Tw = 2.9 s, λ = 1.5)

Figure 6 shows the comparison of torque variations of 5-blade
rotor in the CVW and the PVW when the cycle of PVW is 2.9 sand λ = 1.5. In this figure, the ensemble-averaged wind speed
is also shown together with the ensemble-averaged torquecoefficients (Cq). The data used for the ensemble average in thecase of Tw = 2.9 s includes nine cycles. The abscissa of thegraph in Fig. 6 is non-dimensional time on the basis of the cycleof PVW. The torque coefficient (Cq) in the PVW fluctuateslarger than the Cq in the CVW. The averaged value (0.075) of Cq
in the PVW is larger than that (0.070) in the CVW. Thistendency is observed in the case of Tw = 5.9 s as well. This
corresponds to the superiority of Cp around λ= 1.6 in the PVW
in the case of 5-blade rotor in Fig. 5.
The ensemble-averaged torque variations under the conditionsof 2-blade rotor and Tw = 2.9 s are shown in Fig. 7, in which thedata for λ = 0.5 and 1.5 are compared. In the case of 2-blade
rotor, when the wind speed is small, the Cq fluctuates larger at
any value of λ. That is, the torque coefficient of a VAWT is
influenced by wind speed variation. This tendency is observed in
the case of Tw = 5.9 s, too.
Figure 8 shows the torque behaviors of the rotors withdifferent numbers of blades in the periodically varying wind of
Tw = 2.9 s. The tip speed ratio in Fig. 8 is λ = 1.5. Clear
dependence of the torque variations on the number of blade isobserved. The Cq of the 2-blade rotor, as seen in Fig. 7, increases
in the domain of low wind speed. On the other hand, the Cq of
5-blade rotor gradually increases in the domain of high windspeed and decreases in the low wind speed domain rapidly. Thisdifference is observed in PVW of Tw = 5.9 s, too. Obviously, theaveraged value (0.067) of Cq of 5-blade rotor is larger than that
(0.035) of 2-blade rotor.
Deviation of the rotational speed which has been measured
simultaneously with the torque of Fig. 8 is shown in Fig. 9. This
figure shows that the follow-up nature of the VAWT to the windspeed variation becomes higher as the number of blades
increases.

0.18

18

Tw=5.9s
Tw=2.9s

0.14

Cq

16
14

Wind Speed

0.12

12

0.1

10

0.08

8

0.06

6

0.04

4

0.02

2

0
-0.02

Wind Speed(m/s)

0.16

0

0

0.2

0.4

0.6

0.8

1

-2

Time/Tw

Fig. 10 Dependence of torque characteristics on the cycle of
PVW (5 blades, λ = 1.5)
0.035

Tw=5.9s
Tw=4.5sTw=2.9s

0.03

RMS

0.025
0.02
0.015
0.01
0.005
0
2

3

4

5

Blade Namber

Fig. 11 Root mean square of the torque coefficient in each caseunder the condition of λ=1.5
The torque coefficients in the cases of Tw = 5.9 s and 2.9 s arecompared in Fig. 10 under the conditions of 5 blades and λ =1.5. The Cq in the case of Tw = 2.9 is larger than the Cq in thecase of Tw = 5.9 s in the domain of non-dimensional time from
0.6 to 0.75. On the other hand, in the domain from 0 to 0.2, theCq in the case of Tw = 2.9 s is smaller than that in the case of Tw= 5.9 s. That is, when the variation of wind speed becomes faster,even if the amplitude of the periodic varying wind holds thesame level, the torque variation acting on the wind turbine might
become larger.

Root mean square of the torque coefficient in each case under
the condition of λ=1.5 is shown in Fig. 11. As seen in Fig. 10,
the torque fluctuation of 5-blade rotor gets larger as the cycle of
PVW becomes short. However, the case of 2-blade rotor shows
the contrary tendency. In addition, obvious tendency can not befound in the case of 3 blades and 4 blades.
5. CONCLUSIONSThe torque characteristics of straight-bladed Vertical Axis
Wind Turbines (VAWT) were measured in both the periodicallyvarying wind (PVW) and the constant velocity wind (CVW) in
order to compare the rotor behaviors in the different windconditions. The averaged Cp in PVW is almost the same as thatin CVW. However, in the 5-blade case, the Cp in PVW became
larger than the Cp in CVW at the rotational conditions near λ=1.6. The follow-up nature of the VAWT to the wind speed
variation becomes higher as the number of blades increases.
Torque fluctuation of the 5-blade rotor gets larger as the cycle of
PVW becomes short, although the 2-blade rotor shows thecontrary tendency.
ACKNOWLEDGEMENT
This study was carried out as a part of the 21st century COE
program "Program for Arid Land Science". The authors
express the gratitude.
REFERENCES[1] Hayashi, T., Hara, Y., Moriya, T., Tagawa, K. and Nozima, K.,
The Study on the Solidity Dependency of the Straight-Bladed
Vertical Axis Wind Turbine, Proceedings of the 42nd general
meeting and lecture meeting of Chugoku-Shikoku branch of
JSME, No.045-1, 307-308 (2004).
[2] Hara, Y., Kang, I., Moriya, T., Ariyasu, K. and Hayashi, T.,
Development of a Measuring System with Two Force Sensors
of Aerodynamic Forces Acting on a Two-Dimensional Wing,
The Sixth KSME-JSME Thermal and Fluids Engineering
Conference (CD-ROM), JE-08, (2005).

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