Symposium no. 32
Paper no. 683
Presentation: poster
Towards sustainable use of deserts
FARSHAD A. (1), ERIAN W.F. (2), ZAREI ABARGHUEI S.H. (3) and
SHRESTHA D.P. (1)
(1) International Institute for Geo-information Science and Earth Observation (ITC),
Enschede, The Netherlands
(2) University of Cairo, Cairo, Egypt
(3) MollaSadra College, Yazd, Iran
Abstract
Resource mismanagement in most arid parts of the world is alarming. In these
areas, harsh climatic conditions such as very low rainfall (0-100 mm), high
temperatures with remarkable fluctuations between day and night as well as summer
and winter, strong wind and sand storms are common. Besides, they are characterized
by the presence of salt-affected soils and lack of fresh water. In some of these deserts
such as the Chutt in Southern Tunisia, the Central and Lut in Iran, villagers have to
fetch water from long distances. However, in this connection, socio-economic
conditions play a vital role.
The results of such climatic conditions coupled with the occurrence of gypsiferous
marls, shale and limestone have led to the formation of climofunctional and
lithofunctional soils. Though, soil surveyors are often reluctant when working with saltaffected soils, one most significant criteria for interpretation purposes are obtained if
(soil) family and eventually series differentiate (e.g., particle size class, horizon
thickness and arrangement) are used.
The idea of combating desertification started a few decades ago by applying such
techniques as mulching and plantation. In spite of these, the process of desertification
continued as no other appropriate measures were taken to stop resource degradation.
This is evidenced in the case of most present day deserts, except for the playas, which
are mainly geological in their origin.
Resource degradation (as a result of inherent fragility) is a fact that mankind should
learn to live with, for it seems very difficult, if not impossible, to stop it. However,
resource degradation can be controlled or slowed down, even if not to stop it fully. This
means that besides the conservation measures, which should retard or stop desert from
further advancement, the existing deserts should be put to relevant uses. With advances
in technology, bringing deserts into one use or the other is a possibility. A
demonstration of this is seen in the following: desert reclamation projects in Egypt,
Ministry of Jehad-e-Keshavarzi project in combating desertification in Iran, and
irrigation projects in Southern Tunisia, Egypt, and Iran where higher salt content in the
irrigation water up to 5,000 mg L-1 are used to irrigate highly tolerant crops, in soils
with adequate drainage.
Keywords: aridification, sustainability, indigenous knowledge, desert, salt-affected
soils, degradation, reclamation
683-1
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
Introduction
Almost all researchers and responsible organizations, who have defined the term
desertification, believe that the end product, desert land, is biologically non-active. The
surface area affected by desertification within the dry part of the world is about 4 billion
ha, some 75% of the total dry-land surface area, excluding hyper-arid deserts.
Obviously, neglecting deserts in such a populated world would mean a great loss.
The idea of combating desertification started a few decades ago, applying such
techniques as mulching and plantation. These were more to prevent deserts of further
encroachment, as the process of desertification kept continuing, simply because there
were no appropriate measures taken to stop the resource degradation. Often, it has been
shown that resource degradation is like an unwanted illness that soon or later comes
forth as we are becoming more and more careless with our resources.
Despite the argument that traditional farming systems were environmentally more
sound than the modern systems, land degradation, although much slower than today, has
always been active (Farshad, 1997). The present deserts, except for those playas which
are mainly geological in origin (Krinsely, 1970) are formed because of long-term
mismanagement, where the mankind seems to be responsible for. However, resource
degradation, particularly in the arid regions of the world, can be controlled or slowed
down, since it is not possible to stop fully.
There is no doubt that much has been done in the field of mapping, assessment and
monitoring of desertification, using satellite based remote sensing techniques (Shrestha,
1989; Abdel-Hamid and Shrestha, 1992; Rahman et al., 1995; Mohammad et al., 1996;
Zarei, 1998; Karavanova et al., 2001). With increasing spatial resolution, and
application of scanning techniques for recording surface features, assessment and
monitoring land degradation can be more efficiently used. Besides the improvement of
spectral resolution of many presently available sensor systems, the use of middle
infrared and thermal wave bands can give valuable information with respect to moisture
stress in plant and in assessing evapo-transpiration. For early warning system remote
sensing techniques have proved to be an efficient tool (Groten, 1996).
In a raster based Geographic Information System (GIS), change detection for
monitoring desert encroachment is not a difficult task. Normalized difference vegetation
index can be used as an indicator for the study of desertification. By map overlay of the
vegetation indices of different dates the increase or decrease of vegetation cover within
an area and the trend of the change pattern can be determined and monitored.
Furthermore, the use of Global Positioning System (GPS) helps in accurately locating
and delineating desert encroachment areas. This is especially useful in infrastructurefree regions where orientation is a difficult task due to insufficient landmarks for the
purpose of mapping.
On the other hand, much has been learnt from desert encroachment, planting
tamarix, holoxylon, atriplex (Zarei, 1998). The main aim however, has been to stop
deserts of further moving, but gradually next to the limited conservation activities other
remedies were also thought of, namely making use of the desert at its capacity. In this
way, it was accepted that deserts are not dead bodies and that they can still be put to use.
Management-Oriented Problems in Deserts
Harsh climatic conditions, salt-affected soils and lack of fresh water are the main
problems of the deserts in arid parts of the world. Here, deserts are characterized by
683-2
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
very low rainfall (0-100 mm), high temperature with remarkable fluctuations between
day and night, and also summer and winter, strong wind and sand storms.
As a result of such harsh climatic conditions, and also because of the occurrence of
lithologic formations such as gypsiferous marls, shales and limestones, climofunctional
and lithofunctional soils occur extensively. These are characterized by an ochric
epipedon (poor in organic matter content) which either directly overlies a C layer
(Entisols or Vertisols) or, in a more developed form, is underlied by a subsurface
horizon such as salic, gypsic or calcic (Aridisols). In general, Aridisols, if occurring as
AC profiles, are poor in fertility, and if having any of the salic, gypsic and/or calcic
subsurface horizons (as ABC profiles) they then may be toxic or very difficult to
manage.
It is obvious that here too, soil variability must be taken into consideration. Soil
surveyors are often reluctant when working with salt-affected soils, as they are quickly
classified as Salids, not sufficiently expressive for further interpretations. However,
besides such subgroups as Typic, Aquollic, Sodic and Fluventic (Farshad, 1997) which
give important criteria for interpretation purposes, family and eventually series
differentiae such as particle size class, mineralogy, horizon thickness and arrangement
can be vital when interpretation of soil survey results for irrigation and reclamation of
these soils.
Obviously, the deserts lack fresh water, which is seen as the most serious problem
by inhabitants (if any). In some of these deserts such as the Chutt in southern Tunisia,
the Central and Lut in Iran and the ones in Egypt, the inhabitants have to fetch water
from long distances.
Business-as-Usual
The way we people, in particular in arid parts of the world, make use of resources is
threatening. An example of the mismanagement of groundwater in Iran, Yazd province,
demonstrates how aridification is accelerated.
The provincial capital Yazd, about 600 km southeaster of Tehran, is an ancient
town within the fringe of the Iranian Central Desert, known for its traditional irrigation
systems (ghanats). The mean annual rainfall is below 100 mm, with high intensity. The
mean annual temperature is about 20°C, with a maximum of over 45°C in July and a
minimum of –16°C in January and February, with a frost period of over 40 days.
Summers are very long with very hot days. The annual evaporation is very high,
varying from 2,500 to 3,500 mm (Ghobadian, 1982). Thus, agriculture in Yazd cannot
be practiced without irrigation. As a consequence of the climatic conditions, surface
water is very limited. In other words, all water needed in agricultural and industrial
sectors must come from non-renewable aquifers. Although from 750,000 ha, the total
surface area of the province, some 110,000 ha are used for farming, many deep wells
have been excavated to satisfy the needs of the above mentioned sectors. The
excavation of too many wells has caused not only the extinction of the traditional
irrigation systems (ghanats) but also drying out of a great number of aquifers. This is
shown in many places by subsidence of the ground surface, leading to the formation of
cracks, which have damaged infrastructure and led to obvious gully and tunnel erosion
(Farshad, 1997). In short, as a result of removal of natural vegetation, overgrazing,
agricultural activities such as excessive use of fertilizers and misuse of irrigation water,
and overexploitation of vegetation for domestic use, the desert is expanding.
683-3
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
The Sharra district is a part of the Gharachai river basin. It is located at about 50 km
east of the city of Hamadan. The occurrence of salt-affected soils in this area is well in
accordance with its historic background, which also was studied using archaeological
and carbon dating techniques. In contrast, no salt-affected soils occur in the HamadanBahar area. This, the surroundings of the ancient city of Hamadan, is located at about
400 km southwest of Tehran at the skirts of the granitic Alvand mountain, a NW-SE
oriented stretch of the central Zagros mountain ranges. Water scarcity is a major
constraint for agricultural development. A negative balance of 34 Mm3 y-1 was
calculated for the Hamadan-Bahar area, whereas the water budget for a part of the
Sharra area shows a deficit of more than 120 Mm3. An observation well in the village of
Shirin-abad, in the Sharra area, showed a 13 m drop of groundwater level in a period of
six years, between 1986 and 1991 (Farshad, 1997). The mean annual precipitation in the
Alvand mountain is about 500 mm, as compared with 300 mm in the Sharra area. A
comparison between the above mentioned areas, Yazd with <100 mm mean annual
rainfall, Sharra with some 300 mm, and Hamdan-Bahar area with 500 mm,
demonstrates that groundwater is under pressure. In the same way that the Yazd area
has moved from being desert’s margin to desert, the Sharra area is now taking a position
like desert’s margins.
Alternatives; Making use of the Deserts’ Potentials
Looking to what has so far been done in deserts of the world, it can be concluded
that with the advances in technology the possibility of putting deserts to one or another
use does not anymore sound strange.
Case of Egypt; desert reclamation projects
In a promising project, Egyptian government decided to reclaim and cultivate new
lands. Many circumstances urged taking such a decision (Erian, 1998), that are: (1) to
re-distribute the population, concentrated in the narrow and limited area of the Nile
valley; (2) to control further environmental pollution; (3) to encourage local production
and control the steadily increasing imports; and (4) to encourage investments and partly
solve the problem of unemployment
The Sugar Beet Area, Zone III, is one of these areas, which covers an area of about
25,000 ha. The area has a Mediterranean climate. The annual rainfall is about 180 mm
and most of the precipitation falls in winter between October and March. The mean
annual temperature is 20.4oC. The maximum monthly temperature is 26.6oC in August
and the minimum is 13.7oC in January. Soils of the area are classified as Aridisols, with
torric and scattered patches of aquic moisture regimes. The soil temperature regime is
thermic.
The investigated area has salty groundwater that seems unsuitable for irrigation,
hence Nile water is pumped from the El Nubariya canal to El Nasr and Maryut.
The goals of these policies could be summarized as follows:
• Forming agricultural communities in the new lands capable of using advanced
technology to reach high production as well as the best methodology for
cultivation.
• Forming stable rural communities that may draw the population from the
densely populated regions to the new lands where infrastructure and social
services are provided to connect the new communities with the Nile Delta.
683-4
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
Next to the above mentioned semi-governmental project, there are also several
people coming together as companies and investing in different parts of the desert
(Shawki Elghazali et al., 1998; Abdelrahman, 1998).
Case of Iran
Traditional approach, an example of making use of the deserts’ potentials
Kashan, a town surrounded by mountains to the west and south, and the central
desert to its east and north east, lies between 51 and 27 East longitude and 33 and 59
North latitude, with an average altitude of 1,000 m asl. It is located 220 km south of
Tehran. The mean annual rainfall is about 140 mm from which about 85 mm or 60%
fall during the growing period, from November through April of the following year.
Knowing that the least amount of rainfall for rainfed cereals in the area is about 250
mm, it is evident that agriculture in Kashan with 140 mm cannot be practiced without
irrigation.
The Aran-Bidgol Township is located 10 km north of Kashan (250 km south of
Tehran), at the margin of the desert (Kawir-e-Markazi). The Center for dune
stabilization, established some thirty years ago as a division of the Ministry of
Agriculture and Fisheries, is situated somewhere to the north of Mohammad-abad, one
of several villages surrounding the township (Farshad and Zinck, 1998).
The Sombak 7 km to the east and the Chartaghi (also known as ghool-abad) 15 km
to the north of the township are the two duneland areas known to people for their good
quality watermelon.
Four topographic levels can be distinguished, starting from the Ghamsar mountains
(2,000 m asl) in the southwest to the Salt Lake (800m asl) located to the north of the
Kashan catchment. The fourth level is a lacustrine plain (the Salt Lake coastal area) and
the other levels form extensive piedmont landscape, on the lowest part of which the
dunelands are located (Motamed, 1988).
Owing to hydrologic structure and the low topography, the groundwater table is
high. soils, formed in materials consisting of a varying cover of 1 to 5 meters aeolian
lying on a loamy sand to sandy loam layer, classified as Quartzipsamments. In the
Chartaghi area, soils are rather saline with higher gypsum content than the soils in the
Sombak area.
Although these areas are not used as intensively as in the past, some farmers still
use the land, particularly in the Sombak area, to grow watermelon. These areas are
cultivated on the basis of a traditional way: bringing the crop into contact with water.
The geomorphologic setting and hydrological condition of these areas must have been
known to local people since centuries.
In order to cultivate the area, huge amount of sand must be removed until the loamy
sand to sandy loam layer is reached wherein seeds are sown. Very large pool-like (e.g.,
about one tenth of a hectare = two djeribs) holes are excavated in the sand dunes, that is,
removing the sand from the planned surface and pile it all around the pit. The in this
way formed walls are then planted with some plant residues acting as windbreaks.
Normally, sof is used for this purpose, although by law it is prohibited to cut this plant,
which is a resistance type to the prevailing dry conditions and the strong winds of the
region. Once the pit is ready, the pit floor is parceled, for which plant residues are used
too, and sown. The Center for dune stabilization has been successful in stabilization of
683-5
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
a large part of the desert dune by planting Haloxylon saliconicum (tagh), Calligonum
crinitum (eskanbil) and Atriplex sp. and by means of chemical mulching.
Several reasons can be thought of why the Sombak area is used more seriously than
the Chartaghi area, the most important of which are: the accessibility and the distance to
the township and the salinity problem in the Chartaghi. In the past, groups of farmers
traveled on their donkeys to the Chartaghi area and settled there for a few months until
the watermelon was harvested. Obviously, after such a long period away from home the
farmers had grown long hair and beards, and looked like "monsters". This is said to be
the root of the name ghool-abad, a kind of nickname for the Chartaghi region. In
Persian, Ghool-abad means a place developed by monsters. The watermelon which is
produced in this way is fed by the groundwater, which is at a depth of about 70 cm. The
yield, if the watermelon plants are not harmed by sand attacks, can easily reach to 100
kharwars (each khrwar = 120 kg).
Newly established projects, associated with combating desertification
In different parts of Iran, such as some areas in Kashan, Kerman and Yazd,
combating desertification is still in function. The different combating projects
concentrate on vegetation cutting control, range management, water resource
development, soil protection and dune stabilization, and some integrated land
management (Zarei, 1998). Some of the plants so far cultivated in extensive areas of the
deserts in different parts of Iran are Atriplex lentiformis, A. canenses, Holoxylon
persicum and H. aphylum, Tamarix spp., Zygophyllum eurypterum, Stipgarostis
pennuata, Calligonum spp., Calotropis procera, Accaccia spp., Prosopis spicigera,
Nitraria schoberi and Panicum spp.
In a study to find out the reasons why the planted Atriplex lentiformis in the
Abarkooh area in Yazd is drying out, the effect of a number of soil attributes such as
soil depth, salinity and alkalinity on the performance of the plant were examined. Land
use requirements of the plant for the ongoing land utilization type (LUT), formulated on
the basis of grazing (maily camel), were set up to carry out a physical land evaluation.
This suitability evaluation indicates the areas suitable for growing Atriplex, which may
not be the same as the places where they are grown at present. The drop of groundwater
table depth showed to be a very important factor in the death of the plants (Alavipanah,
1991; Zarei, 1998). The effectiveness of agroforestry systems has not been sufficiently
tested, although indigenous systems of limited number of trees in pasture and croplands
can be a witness (Baumer, 1990; Young, 1997). In indigenous agroforestry systems, the
main components are pasture and animal, simply because of the shortage of water, on
one hand and the lack of organic matter, on the other. The lack of water seems to be
taken care of either manually, or by pot irrigation, the ancestor of the current driplet
irrigation and growing limited number of trees to prevent the competition between trees
and crops. The produced manure is to compensate the lack of the soil organic matter
content.
Cases of southern Tunisia, Egypt, and Iran, also at research level
In Iran, like many other countries such as Southern Tunisia, Egypt, and Israel,
saline water is used to irrigate cotton, maize and fodder sorghum (Soil Institute of Iran,
1970; Abdelrazek, 1998). In general, irrigation water containing 600 mg L-1 of total
dissolved solids may be used to irrigate almost all crops (National Academy of
Sciences, 1974). Higher salt content in the irrigation water, up to 5,000 mg L-1, is
683-6
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
reported to have been used to irrigate highly tolerant crops, in soils with adequate
drainage. However, the type and concentration of salt in the water is important.
According to the report of National Academy of Sciences (1974), sea water, with a
total salt content of about 35,000 mg L-1, is said to exceed the tolerance of even the
most salt-tolerant crop studied to date. The most salt-tolerant crop is known to be the
Suwanee Bermuda grass, which can tolerate about 12,000 mg L-1. In the Intecol
congress held in Florence in Italy (19-26 July 1998), however, interesting results of
some researches carried out on growing halophytes in different parts of the deserts in
saudi Arabia, and the United Arab Emarates were presented by several research workers
(Boer, 1998; Lieth, 1998). Halophytes are plants which can tolerate elevated salinity
concentrations in water and soil (UNESCO and MAB, 1998). According to the
halophyte database (HALOPH) by Aronson (Lieth 1998), there are 1,560 species of
halophytes. Lieth and Moschenko, in the above mentioned publication
(UNESCO&MAB) foresee good results, pumping seawater on desert land to produce
cash crop halophytes.
Case of Saudi Arabia
To be self sufficient in food and fodder production, the Ministry of Agriculture,
Saudi Arabia started soil survey and land classification project in cooperation with the
UN Food and Agriculture Organization. One of the main objective of the project is to
find suitable land for cultivation in the desert. The land is distributed to potential
farmers who grow cereals or fodder for livestock. Irrigation is done by pumping the
groundwater. Efficient use of the groundwater is of prime importance for the sustainable
use of the resources.
Conclusions
Worldwide, there are enough examples demonstrating that resource degradation, as
a result of inherent fragility, is a fact that mankind should learn to live with, for it seems
very difficult, if not impossible, to stop it. However, resource degradation can be
controlled or slowed down, if sustainability is respected. This means that continuous use
of resources without taking account of appropriate conservation measures accelerates
their degradation. This will retard or may stop desert from further advancement, but
does not yet solved the problem of the existing deserts. Neglecting deserts in the
populated world of today would mean a great loss of territory. Through a few examples
of deserts, it is shown that benefiting from indigenous knowledge and the advanced
technology, can help put parts of deserts, if not all, to relevant uses.
References
Abdel-Hamid, M.A. and D.P. Shrestha. 1992. Soil salinity mapping in the Nile Delta,
Egypt using remote sensing techniques. International Archives of Photogrammetry
and Remote Sensing, vol. XXIX, part B7, ISPRS Commission VII/4, Washington
D.C., USA., August 1992, pp.783-787.
Abdelrahman, S.I. 1998. Land planning for sustainable development of Mersa Shaa’b
area, southeastern Desert of Egypt–An integrated RS and LIS approach. A poster
presentation in SLM congress, ITC, Journal 3/4, Enschede, The Netherlands.
683-7
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
Abdelrazek, M.A.A. 1998. Land evaluation for sustainable land use planning in the NE
part of the Fayoum depression, Egypt. Unpublished M.Sc. Thesis. ITC, Enschede,
The Netherlands. 198 p.
Alavipanah, S.K. 1991. Effect of physicochemical properties of the salt-affected soils
on the yield of Atriplex lentiformis in the margin of Kavir-e-Abarkooh. Tarbiat
Modarres University, Tehran, Iran (Persian text). 175 p.
Baumer, M. 1990. Agroforestry and desertification. ICTA, Wageningen, The
Netherlands.
Boer, B. 1998. Investigations on the growth of halophytes in the Arabian peninsula.
Personal communication during an Intecol presentation, Florence, Italy.
Erian, W.F. 1998. The use of the sustainable development multi-indicators for
evaluating the stabilization in some new rural communities in desert areas in Egypt.
SLM Congress, ITC Journal, Enschede, The Netherlands.
Farshad, A. and J.A. Zinck. 1997. Indigenous knowledge and agricultural sustainability.
ITC Journal, Vol.3 and 4 (Final proceedings on CD), Enschede, The Netherlands.
Farshad, A. 1997. Analysis of integrated soil and water management practices within
different agricultural systems under semiarid conditions of Iran and evaluating their
sustainability. Publication No. 57. ITC, The Netherlands. 395 p.
Ghobadian, A. 1982. Central Iranian Plateau: Natural resources of Yazd province in
relation to desert problems. Jundishapur University, Ahvaz, Iran and Ostandari-eYazd, Iran (Persian text). 349 p.
Groten, S.M.E., 1996. Satellite monitoring and aerial photograph analysis for early
warning of migration risks. Paper presented at the International symposium on
"Environmentally induced population displacements and environmental impacts
resulting from mass migrations", Geneva.
Krinsely, D.B. 1970. A Geomorphologic and Paleoclimatological Study of the Playas of
Iran. Part II. Geological Survey. United States Department of the Interior,
Washington, D.C. 486 p.
Karavanova, E.I., D.P. Shrestha and D.S. Orlov. 2001. Application of remote sensing
techniques for the study of soil salinity in semiarid Uzbekistan, pp. 261-273. In
E.M. Bridges, I. Hannau, L.R. Oldeman, F. Penning de Vries, S. Scherr and S.
Sombatpanit (eds.). Responses to Land Degradation. Oxford and IBH Publishing
Co. Pvt. Ltd.
Lieth, H. 1998. Extending terrestial production with “sustainable, seawater irrigated,
halophyte crops”, pp. 258. Introduction to the workshop on sustainable halophyte
problems. Proceedings of VII International Congress of Ecology (Intecol).
Mohammad, S.O., A. Farshadand and J. Farifteh. 1996. Evaluating land degradation for
assessment of land vulnerability to desert conditions in the Sokoto area, Nigeria.
Land Degradation and Development 7:205-215.
Motamed, A. 1988. A Study on the Source and Distribution of the Aeolian Sand in
Kashan, South of Masileh. University of Tehran. Tehran, Iran. 73 p.
National Academy of Sciences. 1974. More water for arid lands, Promising
technologies and research opportunities. Report of an Ad Hoc Panel of the
683-8
17th WCSS, 14-21 August 2002, Thailand
FARSHAD ET AL.
Advisory Committee on Technology Innovation Board on Science and Technology
for International Development Commission on International Relations. Washington
D.C. USA. 153 p.
Rahman, A., M.A. Jabbar, M.S. Islam and D.P. Shrestha. 1995. Study of land
degradation by integration and analysis of remotely sensed data in geographic
information systems: A case study of Hathazari Thana in Bangladesh. Asian-Pacific
Remote Sensing Journal 7(2):109-116
Shawki Elghazali, M., A. Nasr and Y. Elmandili. 1998. Sustainable land management
for reclaimed farms in Egypt: Dina Integrated Farms. A poster presentation in the
SLM congress, ITC Journal 3/4, Enschede, The Netherlands.
Shrestha, D.P. 1989. Soil degradation, recognition of their processes and mapping by
remote sensing techniques. Proceedings: 14th UN/FAO workshop on Remote
Sensing Applications to Land Resources, Rome, Italy.
UNESCO and MAB 1998. Sustainable Use of Halophytes. University of Osnabrueck,
Germany.
Young, A. 1997. Agroforestry for Soil Management. 2nd edition. ICRAF and CAB
International.
Zarei, S.H. 1998. The relationship between a selected number of soil attributes and the
performance of Atriplex and Holoxylon planted as combating means in
desertification. Unpublished M.Sc. Thesis, ITC, Enschede, The Netherlands. 143 p.
683-9