• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 List of Tables
 List of Illustrations
 Foreword
 Acknowledgement
 Introduction
 Trends in the use of roots and...
 Trends in the supply of roots and...
 Baseline projections of production...
 High demand and production growth...
 Roots, tubers, and the environ...
 Conclusions and recommendation...
 Supplementary tables
 References














Group Title: Food, agriculture, and the environment discussion paper
Title: Roots and tubers for the 21st century
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00085356/00001
 Material Information
Title: Roots and tubers for the 21st century trends, projections, and policy options
Series Title: Food, agriculture, and the environment discussion paper
Physical Description: viii, 64 p. : ill. ; 28 cm.
Language: English
Creator: Scott, Gregory J
Rosegrant, Mark W
Ringler, Claudia
International Food Policy Research Institute
International Potato Center
Publisher: International Food Policy Research Institute ;
International Food Policy Research Institute
Centro Internacional de la Papa
Place of Publication: Washington D.C
Lima Peru
Publication Date: c2000
Copyright Date: 2000
 Subjects
Subject: Root crops -- Economic aspects -- Developing countries   ( lcsh )
Tubers -- Economic aspects -- Developing countries   ( lcsh )
Food supply -- Developing countries   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 54-64).
Additional Physical Form: Also available online in pdf format at the IFPRI website.
Statement of Responsibility: Gregory J. Scott, Mark W. Rosegrant, Claudia Ringler.
General Note: "May 2000."
 Record Information
Bibliographic ID: UF00085356
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 44631084
lccn - 00423039
isbn - 0896296350

Table of Contents
    Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
    List of Tables
        Page v
    List of Illustrations
        Page vi
    Foreword
        Page vii
    Acknowledgement
        Page viii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
    Trends in the use of roots and tubers
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Trends in the supply of roots and tubers
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
    Baseline projections of production and use
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
    High demand and production growth scenario
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
    Roots, tubers, and the environment
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
    Conclusions and recommendations
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
    Supplementary tables
        Page 52
        Page 53
    References
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
Full Text
Food, Agriculture, and the Environment Discussion Paper 31


Roots and Tubers

for the 21st Century

Trends, Projections, and Policy Options

Gregory J. Scott
Mark W. Rosegrant
Claudia Ringler











SInternational Food Policy Research Institute
IFPRI 2033 K Street, N.W., Washington, D.C. 20006-1002 U.S.A.
SCentro Internacional de la Papa
Apartado 1558
Lima 12, Peru


May 2000






















Copyright 2000 International Food Policy
Research Institute

All rights reserved. Sections of this report may be
reproduced without the express permission of but
with acknowledgment to the International Food Pol-
icy Research Institute.

ISBN 0-89629-635-0


blind ii folio














Contents


Foreword vii
Acknowledgments viii
1. Introduction 1
2. Trends in the Use of Roots and Tubers 7
3. Trends in the Supply of Roots and Tubers 14
4. Baseline Projections of Production and Use 23
5. High Demand and Production Growth Scenario 34
6. Roots, Tubers, and the Environment 41
7. Conclusions and Recommendations 46
Appendix: Supplementary Tables 52
References 54















Tables


1. Production of, edible energy and protein in, and value of major roots and tubers
and cereals in developing countries, 1995-97 2
2. Percentage of calories and protein from consumption of roots and tubers as food,
1983 and 1996 3
3. Food and feed utilization of roots and tubers by region, 1983 and 1996 8
4. Per capital consumption of roots and tubers as food and feed, 1983 and 1996 9
5. Annual growth rates in area planted with and production of roots and tubers by
commodity and region, 1983-96 15
6. Production of roots and tubers by commodity and region, 1983 and 1996 15
7. Yields and annual growth rates in yield for roots and tubers, 1983-96 18
8. Total use of roots and tubers in 1993, and projected to 2020, baseline scenario 25
9. Projected annual growth rates for food, feed, and total use of roots and tubers,
1993-2020, baseline scenario 25
10. Projected annual growth rates for food, feed, and total use of wheat, maize,
rice, and all cereals, 1993-2020, baseline scenario 26
11. Per capital use of roots and tubers and cereals as food in 1993, and projected to
2020, baseline scenario 26
12. Food and feed use of roots and tubers in 1993, and projected to 2020, baseline
scenario 27
13. Production levels and annual growth rates of production for roots and tubers,
1993-2020, baseline scenario 30
14. Area planted and annual growth rates in area planted for roots and tubers,
1993-2020, baseline scenario 30
15. Yield and annual growth rates in yields for roots and tubers, 1993-2020,
baseline scenario 31
16. Estimated world prices for roots and tubers and selected other foods, late 1980s,
1993, and projected to 2020, baseline and HDP scenarios 32
17. Total value of selected IMPACT commodities for developing countries in 1993
and projected to 2020, baseline and HDP scenarios 33
18. Total use of roots and tubers in 1993, and projections to 2020, HDP scenario 35
19. Projected annual growth rates in food, feed, and total use of roots and tubers,
1993-2020, HDP scenario 35
20. Per capital use of roots and tubers as food in 1993, and projections to 2020, HDP
scenario 36



















21. Production levels and annual growth rates of production for roots and tubers,
1993-2020, HDP scenario 37
22. Area planted and annual growth rates in area planted for roots and tubers,
1993-2020, HDP scenario 37
23. Yields and annual growth rates in yield for roots and tubers, 1993-2020, HDP
scenario 38
24. Main agronomic characteristics of principal roots and tubers 52
25. Raw material characteristics of roots and tubers 52
26. Key IMPACT parameters for selected countries and regions 53




Illustrations


1. Edible energy produced by major roots and tubers and cereals 3
2. Production growth rates of major roots and tubers and cereals, developing
countries, 1961-63 to 1995-97 5
3. Per capital food and feed consumption of roots and tubers, selected countries
and regions, 1983 and 1996 9
4a. The relationship between per capital potato consumption and income 10
4b. The relationship between per capital cassava consumption and income 10
4c. The relationship between per capital sweetpotato consumption and income 11
5. Location of root and tuber production, 1996 16
6. Relative importance of major roots and tubers in countries and regions, 1996,
based on production volumes 17




Boxes

1. The Variety of Roots and Tubers 2
2. Case Studies on Factors Influencing R&T Use 12
3. The IMPACT Model 24















Foreword


The tremendous importance of roots and tubers as a source of income for poor farmers and of
food for the rural and urban poor is often overlooked in the debate about improving food
security and eradicating poverty in developing countries. Hopefully, the analyses in this
report, prepared jointly by the International Potato Center (CIP) and the International Food
Policy Research Institute (IFPRI), will help give these crops appropriate consideration in
future deliberations about the global food system at the national and international levels and
thereby improve efforts to ensure access to sufficient food and income for all people.
The assessment of past trends, future prospects, and policy options reported here stems
from the tradition of joint studies of roots and tubers in developing countries by the centers of
the Consultative Group on International Agricultural Research (CGIAR). While this report
builds on that previous collaboration, it also represents the first intercenter effort to produce
future projections of demand and supply for these crops.
This research began as a project on potato and sweetpotato, but when a recent intercenter
review of root and tuber crops in the CGIAR called for more formalized, albeit still informal
collaboration in this area, this initiative became part of a larger activity involving not just CIP
and IFPRI, but also the International Center for Tropical Agriculture (CIAT), the Interna-
tional Institute of Tropical Agriculture (IITA), and the International Plant Genetic Resources
Institute (IPGRI). The focus of the work also expanded to include cassava and yam. In so
doing, this report became the empirical foundation of a broader effort aimed at documenting
not just trends and projections but also describing research activities and organizations with
the overall objective of providing a vision for research on roots and tubers in the CGIAR.
Gregory J. Scott, Mark W. Rosegrant, and Claudia Ringler have synthesized a significant
amount of data and information on roots and tubers in an effort to provide a clearer vision of
their past, present, and future roles in the food systems of developing countries. How the
production and use of these commodities have changed and will continue to change over
time are all the more important to understand because of the contribution they make to the
diets and income-generating activities of the rural and urban poor in Asia, Africa, and Latin
America. This paper provides a fuller understanding of the prospects of roots and tubers for
food, feed, and other uses in developing countries in the decades ahead. In that regard, the
authors note that cassava, potato, sweetpotato, and yam will remain important commodities
in the coming years, particularly in many of those poorer regions and countries that merit
broader international support in their efforts to increase food production, reduce rural pov-
erty, and improve food security while protecting the environment.

Per Pinstrup-Andersen Hubert Zandstra
Director General, IFPRI Director General, CIP














Acknowledgments


We would like to express our sincere thanks to all those who contributed to the preparation of
this report and to our separate centers, CIP and IFPRI, for their support of this research. We
owe special appreciation to Rupert Best of the International Center for Tropical Agriculture
(CIAT) for his comments and corrections on the various preliminary versions of this docu-
ment and for supplying abundant source material on cassava in developing countries. Our
gratitude goes as well to Mpoko Bokanga of the International Institute of Tropical Agricul-
ture (IITA) for the very useful information on yam. We particularly wish to thank Luis
Maldonado and Victor Suarez for their work on several of the historical statistical tables.
Greg also would like to acknowledge Princess Ferguson for her editorial support in preparing
the numerous preliminary drafts of this report and Jo Sears for her help in completing the
final version. The authors also thank Uday Mohan for the technical editing of the manuscript
and Rajul Pandya-Lorch, head of IFPRI's 2020 Vision initiative, for her constant encourage-
ment and guidance throughout the process.
We are grateful to Roberta Gerpacio and Nicostrato Perez for their work on earlier
versions of this report. They contributed both model runs and written documents. We would
also like to thank C. M. Sourang of the International Fund for Agricultural Development for
his permission to cite "A Global Development Strategy for Cassava" (by Plucknett, Phillips,
and Kagbo) and "Global Cassava Market Study" (by dTp Studies), both of which are works
in progress. Similarly we are grateful to Reinhardt Howeler at CIAT for his permission to cite
"Strategic Environmental Assessment: An Assessment of the Impact of Smallholder
Cassava Production and Processing on the Environment and Biodiversity"-a draft report
by Howeler, Oates, and Costa Allem.















1. Introduction


The world food situation has been the focus of a
flurry of recent publications aimed at providing
greater insights into the evolution of global food
supply, demand, and trade over the next few
decades (Alexandratos 1995, 1996, 1997; Alex-
andratos and Bruinsma 1998; Delgado et al. 1999;
Pinstrup-Andersen, Pandya-Lorch, and Rosegrant
1999; Rosegrant, Agcaoili-Sombilla, and Perez
1995; TAC 1996, 1997a). Most of this analysis,
however, has focused on the past performance and
future prospects for cereals and livestock. This pa-
per analyzes recent trends in and alternative pro-
jections of the supply, demand, and trade for roots
and tubers (R&T). In doing so, it seeks to provide a
clearer vision of the contribution that these crops
can make to the food systems of developing coun-
tries through the year 2020. A key objective of this
paper is to clarify and, as much as possible, to
quantify the complexity and magnitude of that
contribution.
In 1995-97, the major R&T-cassava, potato,
sweetpotato, and yam-occupied about 50 million
hectares worldwide. Farmers produced 639 million
metric tons (mt) of these crops annually, 70 percent
of which were harvested in developing countries.'
(See Box 1 for an overview of the variety of R&T.)
Around 250 million mt of R&T were eaten in Asia,
Africa, and Latin America, and nearly 100 million
mt, almost all of it potatoes, in developed coun-
tries. The remainder was used as animal feed,
planting material, processed products (for example
starch), and other purposes. Production of the ma-
jor R&T in developing countries alone had an esti-
mated annual value of more than US$41 billion in
1995-97, nearly one-fourth the value of the major
cereals (Table 1).


Individually, cassava, potato, sweetpotato, and
yam rank among the most important food crops
worldwide and, in terms of annual volume of pro-
duction, cassava, potato, and sweetpotato rank
among the top 10 food crops produced in develop-
ing countries.

The Roles of R&T in Developing-
Country Food Systems
Many of the developing world's poorest producers
and most undernourished households depend on
R&T as a contributing, if not principal, source of
food and nutrition (see, for example, Alexandratos
1995, 100-102). In part, these farm households
value R&T because R&T produce large quantities
of dietary energy and have stable yields under con-
ditions in which other crops may fail (Alexandratos
1995, 189). R&T produce remarkable quantities of
energy per day, even in comparison to cereals. Po-
tatoes lead the way in energy production, followed
by yam (Figure 1). In addition, some R&T are an
important source of vitamins, minerals, and essen-
tial amino acids such as lysine (Low et al. 1997;
Spencer and Associates 1997; Woolfe 1987, 1992).
In many parts of Sub-Saharan Africa (SSA),
R&T are a major source of sustenance. They ac-
count for 20 percent of calories consumed in the
region (Table 2). In 31 African countries with an-
nual cassava production of more than 10,000 mt
each, annual per capital consumption averaged 140
kilograms (kg) during the last four decades (Phil-
lips 1998). Consumption in production centers and
among the rural poor in many parts of the region
greatly exceed this figure. Per capital consumption
levels for cassava and the importance of R&T in


I Unless cited otherwise, the source data on historic supply and demand of agricultural commodities is FAO 1999a (updated April
1999, accessed July).













Box 1: The Variety of Roots and Tubers


R&T are frequently grouped together because they are
bulky, perishable, and vegetatively propagated. At the
same time these crops are highly differentiated in terms
of origin, production and nutritional traits, and use.
More than 30 edible and nonedible species of R&T are
grown today. Foremost among them in terms of aggre-
gate output and estimated value of production are
cassava, potato, sweetpotato, and yam. Potato, cassava,
and sweetpotato originated in Latin America (Horton
1988). Yam includes some species that have moved
from Africa to North and South America, and others that
have traveled from Asia to Africa (Hahn et al. 1987).
Other prominent R&T include cocoyam, ginger,
taro, and yam bean, as well as Andean R&T such as
arracacha, mashua, oca, and ulluco. The latter group of
plants is grown in the Andean region, other parts of
South America, and East Asia. They are of minor im-
portance globally in terms of total production and com-
mercial value. Nevertheless, for particular countries,
regions, or agroecologies, one or more of these other
R&T can and do play an important role in food systems
(Hermann and Heller 1997; Horton 1988).
The variation in R&T growth patterns and produc-


tion requirements helps to explain how particular com-
modities wedged their way into distinct production
systems and varied consumption uses. For example,
while a potato crop grown under irrigation in the low-
land subtropics can mature in 100-120 days, cassava
can take 9 to 24 months (see Appendix, Table 24).
However, potato production requires adequate and
timely availability of water during the crop's vegetative
cycle, whereas cassava can be cultivated under near
drought-like conditions. Conversely, cassava has been
used more often for processed products because, among
other things, it has a higher starch content on average
(27-36 percent) than potato (13-16 percent) or sweet-
potato (18-28 percent) (Appendix, Table 25). More-
over, in spite of their bulkiness and perishability, most
R&T have proven remarkably mobile over millennia.
Other differences among R&T include such things as
their enormously dissimilar genetics; the diverse strat-
egies required for genetic improvement to take account
of their variable production systems and end-uses; the
distinctions between their pest and pathogen com-
plexes; and the differences in their policy environment
(see TAC 1997a, 20-24 for further details).


Table 1-Production of, edible energy and protein in, and value of major roots and tubers and
cereals in developing countries, 1995-97

Price Production Edible energy Edible protein Value
Commodity (US$/mt) (million mt) (trillion kilocalories) (million mt) (billion US$)
Cassava 53 165.3 142 0.7 8.8
Potato 157 105.3 65 1.8 16.5
Sweetpotato 88 137.0 127 1.9 12.1
Yam 130 31.5 28 0.5 4.1
Major R&T 439.1 362 4.9 41.4
Maize 126 257.6 786 20.1 32.5
Milled rice 284 350.0 851 15.7 99.4
Wheat 146 272.2 687 27.4 39.7
Major cereals 879.8 2,324 63.2 171.6

Source: Basic data from FAO 1998a (FAOSTAT June 1998, accessed July 1998).
Note: Coefficients for calculating edible energy and protein are based on Horton 1988. Prices are based on estimates for 1993 and 2020
IMPACT baseline scenario (see Chapter 4) interpolated for 1995-97.
aMilled rice is more readily comparable to the other commodities for the purposes of comparing international prices.









Figure 1-Edible energy produced by major
roots and tubers and cereals
250
216
200 182

159 152
150 135
S 121 121




50
'^DI




Source: Horton and Fano 1985.


the diet of many Africans, particularly less-well-
off consumers, have remained remarkably constant
despite drought, famine, wars, political and econ-
omic instability, regional population growth rates
that averaged nearly three percent per year during
the last 30 years, and growing urbanization. In ad-
dition, cassava leaf is an important source of pro-
tein in many parts of West and Central Africa
(Spencer and Associates 1997).
In much of Asia and Latin America, R&T pro-
vide an important, supplemental source of carbo-
hydrates, vitamins, and amino acids in food sys-
tems that are dominated by other commodities.
India, for example, is now among the world's larg-
est potato producers, having achieved a phenome-
nal growth rate in potato production of 6 percent
per year during 1962-96. India produced 25 mil-
lion mt in 1997-a level surpassed only by China
and the Russian Federation.2 Nearly all of India's
production is harvested in the cool, dry, winter
months, when cereals are in seasonally short sup-
ply in many parts of the country, and often in
water-scarce areas where irrigated rice cannot be
cultivated. Similar trends in production growth
(4.4 percent per year in 1962-96) have prevailed in


Table 2-Percentage of calories and protein
from consumption of roots and
tubers as food, 1983 and 1996
Calories Proteins
Country/regiona 1983 1996 1983 1996
(percent)
China 8.5 5.6 4.2 2.7
Other East Asia 1.9 1.8 1.1 1.4
India 1.9 1.3 1.2 0.9
Other South Asia 1.7 1.3 1.0 1.0
Southeast Asia 5.7 4.3 1.8 1.4
Latin America 4.8 4.3 2.8 2.6
WANA 1.9 2.3 1.4 1.6
Sub-Saharan Africa 18.7 20.1 6.6 8.0
Developing 6.3 5.4 2.9 2.6
Developed 4.3 4.3 3.4 3.3
World 5.7 5.1 3.1 2.8

Source: FAO 1999b.
Note: 1983 is average for 1982-84 and 1996 is average for 1995-
97 for all tables unless indicated otherwise; WANA is West
Asia and North Africa.
a Other East Asia includes Hong Kong, Macau, Mongolia, North
Korea, and South Korea. Other South Asia includes Afghanistan,
Bangladesh, Bhutan, Maldives, Nepal, Pakistan, and Sri Lanka.
Southeast Asia includes Brunei, Cambodia, East Timor, Indonesia,
Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand, and
Vietnam. Latin America covers Central and South America and the
Caribbean. WANA includes Algeria, Bahrain, Cyprus, Egypt, Gaza
Strip, Iran, Iraq, Jordan, Kuwait, Lebanon, Libya, Morocco, Oman,
Qatar, Saudi Arabia, Syria, Tunisia, Turkey, United Arab Emirates,
Western Sahara, and Yemen. Sub-Saharan Africa includes Central
West, Eastern, Northern, and Southern Sub-Saharan Africa.


Bangladesh, where results of a national rural nutri-
tion survey carried out during 1981-82 showed
that 15 percent of the vitamin C intake came from
potatoes (Scott 1988a).
Production and use of R&T tend to be concen-
trated in countries with lower per capital incomes
(Scott and Maldonado 1999). Within low-income
countries, R&T frequently play a relatively greater
role in the food systems in remote, often marginal,
areas with particularly low income levels and lim-
ited access to farm inputs. Production and use of
sweetpotato is thus more prominent in Sichuan
province, China (Gitomer 1996), in eastern India
(Dayal et al. 1995), or northern Uganda (Scott et al.
1999). Cassava is more prominent in northeast
Brazil (Ostertag and Herrera 1992) and northeast


2 On a per capital basis, 7 out of the world's 10 largest potato producers in 1997 were located in Eastern Europe and the Former
Soviet Union.








Thailand (Titapiwatanakun 1998), and potato in
the highlands of Guatemala (El Cid 1992) or Peru
(Scott 1985). In addition to their role as local sta-
ples or complementary sources of energy, R&T
serve as food security crops. They alleviate sea-
sonal shortages and fill food gaps caused by natural
or man-made disasters (see, for example, Tanganik
et al. 1999).
More than simply food crops for the rural poor,
R&T can also serve as sources of cash income for
low-income farm households and raw material for
processed products for both rural and urban con-
sumption. Growth in the latter uses of R&T is
relatively new and reflects the underlying dynam-
ism of the R&T sector in many developing coun-
tries. In Africa, cassava, in addition to being a
cheap, starchy staple, graduated from on-farm con-
sumption to cash crop for sale to both urban and
rural consumers (Nweke 1992; Nweke et al. 1994).
R&T have also increased in importance in
Asia. Potato production in Asia now accounts for
nearly 80 percent of total production in developing
countries. Asia's share of global potato output
soared from 7.5 percent in 1961-63 to 28.2 percent
in 1995-97. With rapid economic growth in many
parts of Asia, consumers have increasingly diver-
sified their food intake from strictly cereal-based
diets to greater consumption of potatoes, milk,
meat, and other commodities. Empirical evidence
shows that the overwhelming bulk of potatoes pro-
duced in Asia are sold for cash by small farmers
(Scott 1997). High yields mean that on-farm food
needs can be met by only a fraction of the harvest,
with strong off-farm demand using the surplus.
Feed, processed food, and other, nonfood uses
for cassava and sweetpotato have also expanded
considerably in Asia over the last three decades
(Pham et al. 1996; Scott 1992; Titapiwatanakun
1998). Rapid growth in demand for meat has cre-
ated growth opportunities for producers in more
remote areas to use R&T as animal feed. Such is
the case for cassava in northern Vietnam (Nguyen
1996) and sweetpotato in Sichuan province, China
(Huang 1999). Small farmers in China who have
long cultivated sweetpotato as a food security crop,
now process roughly half of their annual harvest of
118 million mt (1995-97 value) into animal feed.


It is estimated that these farmers convert another
20 to 30 percent of annual sweetpotato output into
starch for noodles and other processed products
(Huang 1999; Timmins et al. 1992). In Vietnam
during 1995-97, roughly 50 percent of the annual
cassava harvest of 2 million mt was processed into
feed and an additional 25 percent was used to make
starch (Goletti, Rich, and Wheatley 1999).
Roots and tubers also help alleviate poverty by
providing employment opportunities in produc-
tion, processing, and marketing. Farm surveys in
Bangladesh (Scott 1988a), Egypt (Crissman et al.
1991), Colombia (Rodriguez 1996), and Rwanda
(Braun, de Haen, and Blanken 1991), for example,
found that potato production requires between 120
and 450 labor days per hectare per crop, work to-
tals far greater than those for many other crops. In
South Asia, jobs in potato production particularly
help the landless, who make up a substantial per-
centage of the rural population (Scott 1988a). A
recent study of the potato sector in Bolivia esti-
mated that the crop generated over 12 million labor
days per year nationwide (Zevallos 1997). Surveys
on sweetpotato and cassava production have found
that labor is the most important cost of production
(see, for example, Achata et al. 1990; Pham et al.
1996; Cabanilla 1996). Root-crop processing for
feed or starch also is often highly labor-intensive,
thereby providing off-season employment and in-
come to the rural underemployed (see, for ex-
ample, Goletti, Rich, and Wheatley 1999; Nave
and Scott 1992; Nweke 1992; Simpson, Cheng,
and Miyazaki 1994; Timmins et al. 1992). More-
over, particularly in Sub-Saharan Africa, root and
tuber production, processing, and marketing pro-
vides important income-earning opportunities for
women (Gatumbi and Hagenimana 1998; Low
1998; Nweke 1992; Owori and Hagenimana 1998).
The role of R&T in developing-country food
systems also raises interest about the impact of
these crops on the environment. Recent case stud-
ies show instances of pesticide toxicity associ-
ated with potato production (Crissman, Antle, and
Capalbo 1998); water pollution from cassava pro-
cessing (Goletti, Rich, and Wheatley 1999); soil
erosion linked to cassava cultivation (Howeler
1996); and loss of biodiversity for potato (Brush,








Taylor, and Bellon 1992) and Andean roots and
tubers (Hermann and Heller 1997) as a result of
increased commercialization of production. But
R&T also hold the promise of helping to alleviate
environmental problems. Sweetpotato, for exam-
ple, can serve as a quick cover crop to reduce soil
erosion (Orno 1991). Production of potato using
botanical or true potato seed can increase genetic
diversity because each seed constitutes a distinct
genetic entity (Upadhya et al. 1995).3


Production Performance of R&T
During the past four decades, developing-country
food production policy has focused on achieving
growth in wheat, rice, and, more recently, maize.
With technological innovations resulting in high-
yielding varieties of these basic staple foods,
growth rates for cereal production in developing
countries, and particularly in Asia, rose rapidly.
Similar growth rates in production were achieved
for potato and yam, particularly during the last two
decades. Growth rates for cassava and sweetpotato
were much lower (see Figure 2). The tendency to
treat R&T as undifferentiated commodities has ob-
scured their variable performance and clouded un-
derstanding of their future prospects (McCalla
1998). Furthermore, in contrast to cereals, growth
rates for cassava, potato, and yam in developing
countries were driven by an expansion in area
planted rather than yields. Average yields for po-
tato and sweetpotato in developed countries
(cassava and yam are chiefly developing-country
crops) remain well above those in developing
countries, where yields fall far short of technically
feasible levels. As the recent review of R&T by the
Technical Advisory Committee (TAC) to the Con-
sultative Group on International Agricultural Re-
search (CGIAR) noted, ". . one of the greatest
similarities among root and tuber crops is unre-
alized yield potential that could be attained through
yet-to-be-developed technologies. . All too fre-
quently this is because the needed technology is


Figure 2-Production growth rates of major
roots and tubers and cereals,
developing countries, 1961-63 to
1995-97


Source: FAO 1999a.



not available to deal with yield-limiting factors
(water, nutrients) and yield-reducing factors
(disease, pests)." (TAC 1997b, 22). The review
went on to note that prospects for increasing yields
of R&T appear to be much greater than the "at-
tempts to increase the physiological yield potential
of crops already trapped on a yield plateau. .. ."
This observation suggests that achieving R&T
yield increases appears to be less formidable and
costly a task than achieving similar gains with
other crops.
Given the important contribution R&T can
make to the diets and livelihoods of over 2 billion
people in the tropics and subtropics, and the poten-
tial that exists for expanding production and use,
R&T have recently become the subject of increas-
ing attention (see, for example, dTp Studies 1998;
Horton 1981, 1988; Horton, Lynam, and Knipscher
1984; Plucknett, Phillips, and Kagbo 1998; Sarma
1989; Scott 1994a, 1997; TAC 1997b, 15; Woolfe


3 True potato seeds are the tiny seeds-smaller than tomato seeds-found in potato fruits. Potato plants and tubers grow from
these seeds. The tubers can then be consumed or replanted as potato seed (Upadhya et al. 1995).


~8bk








1987, 1992).4 And yet, there is a growing sense
that the role and importance of R&T in the global
food system are often poorly understood. This sit-
uation makes the present study on trends and future
prospects for R&T particularly timely and rele-
vant. A better understanding of the contribution
R&T can make to poverty alleviation, food se-
curity, economic growth, and environmental sus-
tainability in developing countries can improve the
livelihoods and well-being of more than a third of
the world's population. At the international and,
perhaps even more importantly, national level, re-
sults from the analysis presented here can help
guide investment decisions in agricultural re-
search, extension, and capacity development to
make R&T even more productive, marketable, and
accessible for developing-country populations.


Objective and Scope of This Study
This paper attempts to provide a better understand-
ing of the contribution roots and tubers will make
to global food systems in the decades ahead. It
analyzes trends and projections for the production
and use of the major R&T (potato, sweetpotato,
yam, and cassava) in developing countries and
discusses the factors that have influenced and will
influence the supply of and demand for these
commodities.
Given the important differences in the patterns
of production, use, and trade among R&T com-
modities, as well as differences at the regional and
national levels, the analysis will disaggregate R&T
by crop. Limited time, resources, and available
data prevent further specificity. It is hoped that this
study will serve as the basis for detailed reviews of
other R&T, both at the global and regional levels,
particularly in cases where such crops are impor-
tant for local food security.
The rest of this paper is divided into six chap-
ters. Chapter 2 discusses recent trends in the de-
mand and use of R&T. Chapter 3 examines pro-
duction trends for R&T, emphasizing the sharp re-


gional and commodity-specific differences among
these crops. Chapter 4 describes the IMPACT
global food projections model and then presents
baseline projections of demand and supply for
R&T to the year 2020. Chapter 5 offers projections
based on an alternative, high demand and produc-
tion growth scenario. Chapter 6 considers the en-
vironmental implications of R&T production and
use. The final chapter discusses the principal tech-
nological, institutional, and policy implications of
this analysis.
The paper argues for the sustained and possi-
bly increased importance of R&T in developing
countries in the decades ahead. It also contends that
achieving the potential for R&T is not a given.
Rather this will require continued investments in
agricultural research and institutional develop-
ment, and a policy framework conducive to R&T.
Improved technology that raises productivity
will be critical for increasing the availability of
R&T in developing countries in the next two
decades, as will post-production innovations. The
historical record suggests that it is feasible to ex-
pect such innovations to occur during the time
period in question. The paper points out that for
research planning and resource allocation pur-
poses, as well as for developing appropriate policy
measures, it is useful to distinguish between
supply-side constraints and demand-side con-
straints and to determine their relative importance
for particular R&T in specific developing-country
contexts. Ample scope exists for overcoming both
types of constraints.
The paper argues that policy issues for de-
veloping countries include (1) removing policy
distortions that bias market signals in favor of other
agricultural commodities, and (2) giving farmers
and entrepreneurs nondistorting incentives to in-
vest in production and post-production innovations
for R&T. Policy measures in industrialized coun-
tries include (1) removing subsidies on competing
crops, and (2) lifting trade restrictions on imports
from developing countries.


4 De Bruijn and Fresco (1989) estimated cassava alone as an important food crop for 500 million people in developing countries.
The 1993-94 national survey of consumer expenditures in India interviewed over 115,000 households as a representative sample
nationwide and found that over 85 percent-both rural and urban-reported consuming potato and that consumption was
remarkably widespread across states and throughout the year (GOI 1997). Potato consumption elsewhere, combined with
sweetpotato and yam in Asia, Africa, and Latin America, according to our estimates, put the aggregate figure between two and
three billion (see Gitomer 1996; Lev and Shriver 1998; Woolfe 1987, 1992).














2. Trends in the Use of Roots and Tubers


Utilization of R&T in developing countries con-
tinued to expand and diversify during the last two
decades. But both the growth in use and increase in
the number and relative importance of particular
end-use categories (food, feed, processed food
products, industrial inputs) evolved in a highly un-
even fashion across crops and geographic regions.
This evolution reflects a series of structural
changes in consumption and use of these com-
modities that began in some instances several
decades earlier. Five structural changes bear men-
tioning: (1) the continuous surge in potato demand,
particularly in Asia, beginning in the early 1960s
(Scott 1983a; FAO 1995b); (2) the shift in use of
cassava from food for domestic consumption to
feed for export beginning in the late 1960s in Thai-
land (Konjing 1989) and occurring more recently
(mid-1980s) for feed in Colombia; (3) the shift in
use of sweetpotato from food to feed in China in
the 1960s (Scott 1992); (4) the surge in yam con-
sumption in West Africa in the late 1970s (FAO
1998a); and (5) the growing importance of cassava
as a source of cash income and, hence, growing
demand for cassava roots and processed products
as purchased food in Sub-Saharan Africa since the
late 1970s and early 1980s (Nweke 1992). Growth
in total food and feed use was strongest for cassava
and potato. Uses of cassava and sweetpotato con-
tinued to diversify into feed and processed prod-
ucts, particularly in Asia and to a lesser extent
Latin America. The absolute increase in the con-
sumption of R&T as food was highest in Sub-
Saharan Africa. In light of these divergent ten-
dencies, trends in R&T use merit a disaggregated
analysis.


Total Consumption
Between 1983 (average of 1982-84) and 1996
(average of 1995-97), consumption ofR&T as food


in developing countries increased by 45 million mt,
or 22 percent, to 253 million mt (Table 3). Use of
R&T as animal feed increased by 32 million mt, or
50 percent, to 96 million mt during the same time
period. In 1996, cassava accounted for the largest
share of R&T consumed as food (93 million mt),
followed by sweetpotato (69 million mt) and potato
(65 million mt). The largest absolute increase in
food consumption was for potato (26 million mt),
followed by cassava (22 million mt). Consumption
as food increased most rapidly for yam, at 8.6 per-
cent per year during 1983-96, albeit from relatively
low levels. Consumption ofpotato as food increased
at 4.1 percent per year and consumption of cassava
increased at 2.1 percent annually. Consumption of
sweetpotato actually contracted by 1.8 percent an-
nually. However, sweetpotato use as animal feed
increased rapidly, at 3.4 percent per year during
1983-96, and it contributed the most (58 million
mt) to animal feed in 1996. This was followed by
cassava at 22 million mt and potato at 15 million mt.
China dominates sweetpotato feed use. Cassava in
Latin America and potato in China account for the
bulk of the remainder of R&T as feed. The data in
Table 3 illustrate the regional segmentation in R&T
use: for example, cassava and yam as food in Sub-
Saharan Africa, potato as food and sweetpotato as
food and feed in China; and cassava as food and feed
in Latin America.
Growth ofcassava as food has been particularly
rapid in Sub-Saharan Africa, at 3.1 percent per year.
The region has experienced low or negative eco-
nomic growth and booming populations, and has
continued to rely on R&T as major contributors to
food consumption. Cassava (62 percent) and yam
(33 percent) accounted for nearly all of the total
increase in human consumption of R&T in Sub-
Saharan Africa; the increase for potato was negligi-
ble and that for sweetpotato modest in absolute
terms (Table 3).










Table 3-Food and feed utilization of roots and tubers by region, 1983 and 1996

Cassava Potato Sweetpotato Yam All R&Ta
Country/region 1983 1996 1983 1996 1983 1996 1983 1996 1983 1996
(million metric tons)

Food
China 1.5 1.6 10.5 19.4 72.4 54.8 na . 85.7 77.0
Other East Asia . 0.8 0.9 0.6 0.3 ... ... 1.4 1.2
India 5.2 5.4 7.6 14.9 1.5 1.1 na na 14.4 21.3
Other South Asia 0.5 0.2 1.8 3.1 0.8 0.4 na na 3.4 4.3
Southeast Asia 14.1 16.1 0.7 1.6 4.4 4.0 . . 19.7 22.3
Latin America 10.3 11.4 8.4 11.2 1.0 0.9 0.2 0.3 20.3 24.3
WANA na na 6.8 11.6 0.1 0.2 na na 7.0 11.9
Sub-Saharan Africa 38.4 57.3 1.8 1.9 4.7 5.9 4.8 14.9 53.0 87.3
Developing 70.7 92.5 38.8 65.1 86.4 68.5 5.4 15.8 207.8 252.7
Developed 0.1 0.1 89.6 96.1 1.6 1.5 0.1 0.2 91.8 98.2
World 70.8 92.6 128.4 161.2 88.0 70.1 5.5 16.0 299.6 350.9

Feed
China 1.3 2.6 7.7 14.5 36.4 57.1 na na 45.5 74.3
Other East Asia na 0.1 0.2 0.1 0.2 0.1 na na 0.4 0.4
India na na na na na na na na na na
Other South Asia 0.2 0.1 ... .. ... ... . 0.2 0.1
Southeast Asia 0.7 0.6 ... . 0.3 0.3 . ... 1.0 1.0
Latin America 13.5 14.9 0.4 0.4 0.3 0.3 0.1 0.1 14.3 15.7
WANA na 0.1 0.1 0.1 na na na na 0.1 0.2
Sub-Saharan Africa 2.0 3.5 ... . 0.1 0.2 0.2 0.3 2.4 4.1
Developing 17.7 22.0 8.5 15.3 37.4 58.0 0.3 0.4 64.2 95.9
Developed 18.7 9.0 55.5 39.6 0.4 0.2 . . 74.6 48.9
World 36.4 31.0 64.0 54.9 37.8 58.1 0.3 0.4 138.8 144.8

Source: FAO 1999b.
Note: Ellipses (. .) signify very small values; na signifies no recorded use. WANA is West Asia and North Africa. Data for 1983 are averages
for 1982-84 and data for 1996 are averages for 1995-97. These values do not include locally produced R&T that are exported in fresh
or processed form. See Table 2 footnote for regional breakdown.
aAll R&T include cassava, potato, sweetpotato, yam, and other roots and tubers such as taro. For these other roots and tubers, utilization was less
than 1.5 million mt for all uses in all regions, except for food use in Sub-Saharan Africa. In 1983 use of other R&T as food in Sub-Saharan Africa
totaled 3.5 million mt, rising to 7.3 million mt in 1996.


Growth in R&T consumption in Asia was
mixed. Consumption of potato as food nearly
doubled in absolute terms in almost every part of
the region while consumption of sweetpotato as
food declined. This decline was more than offset
by an increase in use of the crop as animal feed in
China, where roots and vines annually provide an
additional 19 million mt of feed on a dry-matter-
equivalent basis.5 Consumption of yam is insignifi-
cant in Asia and consumption of cassava remained
flat, with the exception of Southeast Asia. Annual
growth in R&T consumption in Latin America was


moderate for food (1.4 percent) and nearly stagnant
for feed (0.7 percent). However, consumption of
potato as food increased by 33 percent to 11 mil-
lion mt in 1996.


Per Capita Consumption

As can be seen in Table 4, aggregate per capital
consumption of R&T as food has remained vir-
tually constant over the last decade and a half. In
developing countries, consumption fell slightly
from 60 kg per capital in 1983 to 57 kg per capital in


5 Total dry matter (DM) for sweetpotato includes vine DM equivalent to roughly 20 percent of the root-yield DM, although vine
DM content and total volume also vary by variety and cultural practices (Leon-Velarde et al. 1997). Moreover, in China, moisture
content in grains is traditionally not factored into conversion rates for R&T to grain equivalents (see Gitomer 1996, 21-22; Zhang
1999, 42).









Table 4-Per capital consumption of roots and tubers as food and feed, 1983 and 1996

Cassava Potato Sweetpotato Yam Total Food, Total Feed,
Country/region 1983 1996 1983 1996 1983 1996 1983 1996 1983 1996 1983 1996
(kilograms per capital)
China 2 1 10 16 70 45 na ... 82 63 44 60
Other East Asia ... .. 13 12 10 4 .... 24 17 7 5
India 7 6 10 16 2 1 na na 20 22 na na
Other South Asia 2 1 8 10 3 1 na na 14 13 1 0
Southeast Asia 37 33 2 3 12 8 .. ... 52 46 3 2
Latin America 29 25 24 25 3 2 1 1 57 54 40 35
WANA na na 28 34 ... ... na na 29 35 1 1
Sub-Saharan Africa 102 106 5 4 12 11 13 28 140 162 6 8
Developing 20 21 11 15 25 16 2 4 60 57 19 22
Developed . ... 75 75 1 1 . ... 77 76 63 38
World 15 16 28 28 19 12 1 3 64 61 30 25

Source: FAO 1999b.
Note: Ellipses (. .) signify very small values; na signifies no recorded use. For other roots and tubers, consumption was less than 2 kilograms
(kg) per capital for all uses in all regions, except for food use in Sub-Saharan Africa, where other R&T totaled 9.2 kg per capital in 1983,
rising to 13.5 kg per capital in 1996. WANA is West Asia and North Africa. Data for 1983 are averages for 1982-84 and data for 1996 are
averages for 1995-97. See Table 2 footnote for regional breakdown.
aAll R&T includes cassava, potato, sweetpotato, yam, and other R&T such as taro.


1996. In developed countries, per capital consump-
tion declined from 77 kg to 76 kg. In spite of this
apparent stagnation, the evolution of R&T use in
developing countries has been quite dynamic. It
has varied considerably across commodities by
form (that is, particular food, feed, processed prod-
uct, and seed forms); by end use; and by geo-
graphic region. Policy-oriented analyses and
comparisons with other agricultural commodities
therefore necessitate a disaggregated assessment of
R&T use.
On a regional basis, Sub-Saharan Africa
achieved both the highest level and the sharpest
absolute rise in per capital food consumption of
R&T between 1983 (140 kg) and 1996 (162 kg)
(Table 4, Figure 3). In 1996 the region consumed
almost three times the developing-country average.
The increase in Sub-Saharan African per capital
consumption is particularly remarkable given the
region's high population growth rate (nearly 3 per-
cent per year) during the same period. Per capital
consumption as food has also been increasing in
India and WANA, which experienced the largest
per capital percentage increases (almost all of it in
potato).
With the exception of China and Latin Amer-
S ica, use of R&T as animal feed is of little impor-
tance in most developing regions (Table 4). Per


Figure 3-Per capital food and feed consumption
of roots and tubers, selected countries
and regions, 1983 and 1996

180
0 Feed, 1983
160. I Food, 1983
0- D Feed, 1996
S* Food. 1996

o 120



40" -










averages for 1982-84 and data for 1996 are 1995-97 aver-




capita use of R&T as animal feed increased in
developing countries from 19 kg in 1983 to 22 kg
in 1996, and in China from 44 kg to 60 kg over the
same period. Feed use levels remained high in









Latin America, at 35 kg per capital in 1996. In
contrast, per capital feed use dropped steeply in
developed countries, from 63 kg in 1983 to 38 kg in
1996. Use of potatoes for pig feed declined sharply
in Europe, particularly in Western Europe, driven
by a decrease in the demand for pork (Delgado et
al. 1999) and by the structural shift in the pork
industry from a vast number of small, family-run
farms to relatively few, large, feed-intensive opera-
tions. These farm factories typically use other,
more efficient feed rations to reduce costs and cap-
ture economies of scale (Horton and Anderson
1992). Recent changes in the European Union's
Common Agricultural Policy also resulted in a
sharp decline in imports of cassava for feed (Henry
1998).
The share of calories and proteins in
developing-country diets coming from R&T re-
mains modest, with the exception of Sub-Saharan
Africa (Table 2; see also Horton 1988, 17). The
large share in Sub-Saharan Africa reflects the high
per capital consumption of R&T, the lesser impor-
tance of cereals, and the lower average number of
calories per capital in that region. These aggregate
figures on the calorie- and protein-shares provided
by R&T should be interpreted with caution, how-
ever, as they mask within-year (seasonal) and
within-region (national and subnational) varia-
tions. They also do not show R&T's contribution of
dietary essentials, such as calcium, potassium,



Figure 4a-The relationship between per
capital potato consumption and
income

Per capital consumption
(log scale)
3.0
2.5-
2.0-
1.5- *
1.0- -
0.5
0.0 ...


2.0 2.5 3.0 3.5 4.0
Per capital income (log scale)


4.5 5.0


Source: FAO 1999a (April 1999; accessed in July) and World Bank
1998.
Note: Per capital income is 1997 and per capital consumption is
1995-97 average.


iron, and ascorbic acid, that are less available in
other foods, particularly cereals.



Factors Influencing Changes in
Per Capita Use

Figure 4a presents the positive relationship be-
tween income and consumption of potato. At the
relatively low levels of per capital income (and per
capital food consumption) characteristic of many
developing countries, potato consumption is far be-
low the saturation point. Consumption of potato
increases as income increases. The relationships
for cassava and sweetpotato are different. As per
capital incomes increase, per capital consumption
declines, as shown in Figures 4b and 4c. This
income/consumption relation for cassava and
sweetpotato needs to be interpreted with caution.
Data on aggregate per capital food consumption can
mask shifts among food uses, for example from
fresh to processed foods.
In addition to per capital income, the growth
rates of per capital use of R&T are influenced by a
number of other measurable variables, including
existing use levels, relative prices, and availability
of substitutes. The growth rates are also a function
of tastes, preferences, and demographic and cul-
tural factors, but in less easily quantifiable ways.
Illustrations of how some of these factors played



Figure 4b-The relationship between per
capital cassava consumption and
income

Per capital consumption
(log scale)
3.0

12.5 + v

1.0 '*
0.5
0.01


2.5 3.0 3.5
Per capital income (log scale)


Source: FAO 1999a (April 1999; accessed in July) and World Bank
1998.
Note: Per capital income is 1997 and per capital consumption is
1995-97 average.


4.0 4.5 5.0









Figure 4c-The relationship between per capital sweetpotato
consumption and income
Per capital consumption
(log scale)
2.5
*4*
2.0- *
1.5
1.0
S*. 4

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Per capital income (log scale)

Source: FAO 1999b (April 1999; accessed in July) and World Bank 1998.
Note: Per capital income is 1997 and per capital consumption is 1995-97 average.


out in the use of R&T in various countries are
presented in Box 2. In the absence of more detailed
statistics, such as long-term time-series data on in-
ternational prices for R&T, local information can
shed light on the influence of R&T prices and other
agricultural commodity prices on the use of R&T.
Whereas potatoes are typically considered a
cheap, starchy staple in industrialized countries,
they tend to be high-priced and sometimes are lux-
ury vegetables in the developing world (Bottema et
al. 1989; Scott 1988a, 1988b). As economies in
Asia have developed rapidly during the last few
decades and incomes have increased, consumers
have increasingly diversified their diets, with addi-
tional consumption of potatoes among other foods.
As a result, potato production expanded rapidly in
a number of Asian countries during the 1960s and
1970s, bringing down relative prices versus
cereals, an outcome that fueled additional con-
sumption (Horton 1987).6 In other countries such
as Bolivia, relative price changes made potatoes
more expensive, discouraging increases in con-
sumption (Thiele et al. 1999).
The relationship between prices and sweet-
potato consumption is less clear (Horton 1989;
Overbeek 1994). Whereas a decline in relative
prices can spur some increase in consumption, as
in the case of Peru (Collins 1989) or, more re-
cently, Uganda (Scott et al. 1999), a major in-
crease in supply can quickly saturate the market.


Evidence from several countries including the
Philippines (Cabanilla 1996), Rwanda (Tardif-
Douglin 1991), and Peru (Collins 1989) suggests
that consumers are much less inclined than in the
case of potato to appreciably expand their con-
sumption of sweetpotato in fresh form as a result of
a decline in price. The same holds for cassava in
Latin America and Asia.
Lifestyle changes, historical and cultural fac-
tors, and evolution in tastes also influence R&T
consumption trends. The rapid increase in urban-
ization in developing countries over the last three
decades, the greater participation of women in the
labor force, and the pervasive exposure to adver-
tisement of food commodities and to the eating
habits of tourists and foreign residents have in-
creased the proportion of purchased foods in total
food intake. These changes in consumption pat-
terns have affected the demand for R&T in various
ways.
In much of Asia, particularly China, consump-
tion of preferred foods, such as potato (FAO
1995b; Ye and Rozelle 1993; Zhang et al. 1999)
and meat (Delgado et al. 1999) has increased,
whereas the consumption of less preferred com-
modities, such as fresh sweetpotato, has declined
(Woolfe 1992). The divergence in consumption
trends among R&T crops in urban settings likely
has been reinforced by the association of potatoes
with Western, more modern, tastes, and of sweet-


6 More recent evidence from a number of countries further substantiates this relationship between declines in relative prices
(versus cereals) and increases in per capital potato consumption (Bouis and Scott 1996; Byerlee and Sain 1991; Scott 1999).












Box 2: Case Studies on Factors Influencing R& T Use


Potato in Peru. Although the potato is part of the tradi-
tional Peruvian diet and has long been ranked as the
country's most important food crop, per capital con-
sumption dropped from a high level of 100 kg in the
early 1960s to about 45 kg by the mid-1 980s. The princi-
pal forces driving the contraction in potato consumption
included (1) years of overvalued exchange rates that
made cereal imports cheap, combined with food sub-
sidies that lowered domestic cereal prices, and (2) price
controls, restrictive credit policies, and anti-middlemen
marketing regulations that discouraged production,
marketing, and consumption of potatoes (Horton 1987).
By the late 1980s, the overall economy had gone into a
tailspin, per capital incomes had declined sharply, and
the relative potato/rice price had reached historic high
levels in the capital city of Lima, where roughly half the
country's effective demand is concentrated. Projections
for future growth in production and consumption of
potatoes were modest at best.
After 1990, the government adopted a series of
market-liberalizing policies. As the economy recovered,
potato production and productivity increased and its
relative price versus rice declined. As a result, per capital
consumption rebounded to 65 kg by 1995 (see Byerlee
and Sain 1991 for a similar situation in Ecuador).

Sweetpotato as Animal Feed in Sichuan Province,
China. With rapid economic growth and rising incomes,
demand for meat products in China increased by 6.3
percent per year during 1982-94 (Delgado et al. 1999).
The need for animal feed rose sharply as a result. More
than 57 million mt of sweetpotato roots alone were used
annually as animal (largely pig) feed, during 1995-97.
Several factors account for this development: (1) China
is now the world's largest pig producer; (2) more than 80
percent of pig production takes place at the household or
village level (Ke 1997); (3) the largest pig-producing
province in China is Sichuan; (4) Sichuan is not only a
maize-deficient province, but geographically isolated
from both domestic, maize-surplus provinces and inter-
national markets; and (5) processing sweetpotato roots
and vines into feed adds value to the commodity and
creates employment at the farm level. Sichuan province
alone produces more sweetpotato (Gitomer 1996) than
all other developing countries combined (Scott and Mal-
donado 1999). In rural Sichuan, which is poorer than the
more affluent coastal provinces, farmers and village-
level enterprises use sweetpotato to sustain feed security
at the farm level. This strategy helps to reduce China's
potential dependence on feed imports. According to


Simpson, Cheng, and Miyazaki (1994) China used some
75 million mt of cereals as feed in the early 1990s. Esti-
mates based on Food and Agriculture Organization of
the United Nations (FAO) Food Balance Sheet data show
that sweetpotato (both roots and vines) provide large
amounts of additional feed on a dry-matter equivalent
basis. Furthermore, the extraction of starch from roots to
make noodles for sale and the use of the remaining mash
to feed pigs is a highly lucrative combination, more so
than pig production alone (Peters 1997).

Cassava as Food and Processed Food Products in
Nigeria. According to Ouraga-Djoussou and Bokanga
(1998), annual consumption of cassava in Nigeria
doubled to 250 kg per capital between 1983 and 1994.
Cassava production increased from 14.4 million mt to
31.1 million mt during 1982-97 (FAO 1999a). The in-
crease in consumption and output of cassava can be
attributed to several factors. Given Nigeria's low per
capital income and rapid population growth, cassava has
served as both a basic staple and a food security crop; the
ban on cereal imports between 1987 and 1990 provided
an added stimulus to production (Adeniji et al. 1997).
The crop's multiple uses have also facilitated greater
consumption. Roots are consumed in fresh, boiled form;
as toasted granules widely known as gari; as chips/flour
(or laiun); and as unsteamed wet paste (orfiifu) (Nweke
1994). Cassava leaf is also eaten, often in the form of a
sauce with meat or fish on rice, boiled roots, orfiJfu.
Because the demand for cassava as a food com-
modity has remained strong, commercial sales of both
processed products and fresh roots as raw material for
food processing have become a highly profitable under-
taking, due in part to technical improvements in process-
ing and the introduction of high-yielding varieties
(Nweke, Ezumah, and Spencer 1988). Increasing urban-
ization has prompted entrepreneurial farmers to expand
production close to major cities and towns in order to
capitalize on the concentration of prospective con-
sumers. According to estimated expenditure elasticities
for processed cassava (gari), urban households treat it as
a normal good (Nweke et al. 1994). More recent esti-
mates, based on the six-country Collaborative Study of
Cassava in Africa (COSCA), indicate that expenditure
elasticities for rural households hover around 1.0 for
fresh and processed cassava (Ezemenari, Nweke, and
Strauss 1998), which is similar to the elasticities for
high-value foods. Hence, continued urbanization and
improvements in income are likely to translate into con-
tinued strong demand for cassava in Nigeria.








potato in fresh form with traditional, local customs,
and times of hardship or food scarcity (Gitomer
1996; UPWARD 1991). The picture for cassava is
more mixed. In urban Latin America-Colombia
or Brazil, for example-fresh cassava is often con-
sidered a tasty and nutritious food (see, for exam-
ple Janssen 1986; Lynam 1989a). In West Africa,
urban consumers regard cassava in processed form
as a highly preferred food. In West Africa as well,
yam is a high-status, preferred food wherever it
forms part of the diet, for example, in Nigeria,
Ghana, and C6te d'Ivoire. Some evidence suggests
that yam actually retains a higher status in urban
areas than do other staples (Bricas and Attaie 1998
and Nweke et al. 1994).
Cultural factors influencing consumption of
R&T are both traditional and modem in nature.
The rituals associated with yam in several West
African countries certainly contribute to its con-
tinued place of prestige in the diets of many con-
sumers in that region (Bricas and Attaie 1998). For
potato, the explosive growth of fast food restau-
rants and snacks has given the commodity a new
image, reinforced by advertising and promotional
campaigns (Scott 1994a; Scott, Basay, and Mal-
donado 1997; Zhang et al. 1999). Consumers typ-
ically not only like the taste of such products but
also consider their consumption fashionable and
cosmopolitan as well as convenient for shorter
lunch hours. But traditional images of sweetpotato,
particularly in Asia, are also often associated with
positive traits such as medicinal uses (Gitomer


1996). The modem quest for healthy foods has
given new impetus to the consumption of sweet-
potato leaves or tips in some Asian countries, in-
cluding Korea and Japan, even though consump-
tion of fresh roots has declined considerably in
these countries (Woolfe 1992). Cassava's cultural
recognition remains high and positive in much of
rural and urban Sub-Saharan Africa. Currently, re-
searchers are attempting to develop easier forms of
preparation for cassava and yam and to improve
their preservation in an effort to better cater to the
tastes, preferences, and pocketbooks of the re-
gion's growing number of urban consumers
(Legros et al. 1995; Westby and Graffham 1998).
The driving forces behind the trends in R&T
use include different growth rates in income and
population across regions and countries and the
increasingly complex structure of R&T food and
feed demand. The ability of R&T to lend them-
selves to both traditional and more modem uses
has facilitated their rapid growth in food and feed
use in several developing-country regions.
Given rapid population growth over the next
few decades, aggregate production will have to in-
crease substantially simply to maintain existing per
capital use levels for R&T. Income increases and
emerging new uses will likely raise aggregate de-
mand for R&T still further. Other factors, such as
changing tastes and preferences due to rising in-
comes and increasing urbanization, will stimulate
additional demand for these crops. The next chap-
ter reviews trends in the production of R&T.















3. Trends in the Supply of Roots and Tubers


Growth in Production of R&T

Rates of growth for area, yield, and production of
major R&T have varied substantially by crop and
country over the past two decades. Annual produc-
tion growth for R&T during 1983-96 averaged a
modest 2.1 percent in developing countries. This
overall rate of growth masks significant differ-
ences across R&T and regions ranging from a rapid
8.3 percent annual rate of growth for yam in Sub-
Saharan Africa, to a -6.8 percent per year decline
for sweetpotato in East Asian countries other than
China (Table 5). Thus, the analysis of the dynamics
of R&T production requires a variety of vantage
points from which to draw a comprehensive pic-
ture of the evolution of these crops.
In the last two decades, yam and potato
achieved the highest annual growth rates in pro-
duction among R&T in developing countries: 8.0
percent and 4.1 percent, respectively (Table 5).
Yam production grew from a small base and
increased largely in one region (West Africa).
Cassava production grew at a more modest pace,
1.8 percent annually. Growth in sweetpotato pro-
duction was flat over the period, with an initial
decline in production followed by a recovery to
earlier levels.
In developing countries, total production of
R&T crops increased by 30 percent, from 344 mil-
lion mt in 1983 to 449 million mt in 1996 (Table 6).
Production increases varied substantially by com-
modity. The production increase was largest for
yam in percentage terms. Output reached 32 mil-
lion mt in 1996, a 170 percent increase over the 13-
year period, albeit from low production levels. The
crop contributed 19 percent to the total increase in
R&T output. Sweetpotato production, on the other
hand, barely increased during the same period, ris-
ing by 1.8 percent to 134 million mt in 1996.
Cassava and potato contributed 33 percent and 42


percent, respectively, to growth in R&T output.
Production of cassava grew by 27 percent between
1983 and 1996 to 164 million mt, and production
of potato grew by 68 percent to 108 million mt.
On a per capital basis, production of R&T in
developing countries increased from 99 kg in 1983
to 101 kg in 1996. Developing-country production
of cassava remained virtually constant at 37 kg per
capital, supported mainly by the per capital produc-
tion growth in Sub-Saharan Africa. Per capital pro-
duction of potato increased by 6 kg to reach 24 kg
in developing countries in 1996, and yam produc-
tion per capital grew by 4 kg to reach 7 kg. Yam
production is significant only in Sub-Saharan Af-
rica where it reached 56 kg per capital in 1996, up
from 28 kg per capital in 1983. Between 1983 and
1996 sweetpotato production declined from 38 kg
to 30 kg per capital.
Production of individual R&T tends to be
highly skewed toward particular countries and re-
gions. Figure 5 shows the locations of R&T produc-
tion in 1996. More than 60 percent of global potato
production was harvested in developed countries,
followed by China with a 17 percent share and India
with 7 percent. Potato production has been shifting
back toward developing countries; they have in-
creased their share of global output from 11 percent
in 1961-63 to 37 percent in 1995-97 (Scott and
Maldonado 1998). Slightly more than half the
global production of cassava takes place in Sub-
Saharan Africa, followed by Southeast Asia with 23
percent and Latin America with 20 percent. Sweet-
potato production is concentrated in China, which
has an 88 percent share of global production.
Ninety-six percent of the world's yam is produced in
Sub-Saharan Africa (mostly West Africa).
The importance of particular crops in specific
regions and subregions can also be seen from the
share of each crop in total R&T production (Figure
6). In WANA, virtually all R&T production con-










Table 5-Annual growth rates in area planted with and production of roots and tubers by
commodity and region, 1983-96

Cassava Potato Sweetpotato Yam All R&Ta
Country/region Production Area Production Area Production Area Production Area Production Area
(percent per year)
China -0.53 -0.47 4.60 3.03 0.21 -0.84 na na 1.20 0.30
Other East Asia na na -1.00 -2.09 -6.77 -5.69 na na -3.24 -3.26
India 0.30 -1.94 5.12 3.77 -2.50 -3.33 na na 3.35 1.73
Other South Asia -6.64 -4.69 3.73 2.69 -4.25 -3.16 na na 1.50 1.13
Southeast Asia 0.17 0.18 5.42 2.53 -0.73 -1.31 4.28 -0.55 0.22 -0.02
Latin America 0.80 0.02 1.95 0.32 -1.18 -1.60 2.97 1.22 1.09 0.05
WANA na na 4.75 2.59 3.67 3.46 na na 4.71 2.59
Sub-Saharan Africa 3.56 2.38 0.62 0.70 1.75 2.64 8.32 4.70 4.32 2.75
Developing 1.83 1.37 4.08 2.42 0.14 -0.50 7.96 4.49 2.06 1.31
Developed na na -0.83 -1.40 -1.00 -2.00 2.73 1.61 -0.84 -1.40
World 1.83 1.37 0.60 -0.07 0.12 -0.52 7.91 4.48 1.07 0.61

Source: FAO 1999a.
Note: na signifies no recorded production. WANA is West Asia and North Africa. Data for 1983 are averages for 1982-84 and data for 1996
are averages for 1995-97. See Table 2 footnote for regional breakdown.
aAll R&T includes cassava, potato, sweetpotato, yam, and other R&T such as taro.



Table 6-Production of roots and tubers by commodity and region, 1983 and 1996

Cassava Potato Sweetpotato Yam All R&T"
Country/region 1983 1996 1983 1996 1983 1996 1983 1996 1983 1996
(million metric tons)
China 3.8 3.6 27.3 48.9 114.6 117.8 na na 147.1 171.7
Other East Asia na na 1.2 1.1 1.1 0.5 na na 2.4 1.5
India 5.5 5.7 10.7 20.4 1.6 1.2 na na 17.8 27.3
Other South Asia 0.7 0.3 2.4 3.8 0.9 0.5 na na 4.2 5.1
Southeast Asia 36.9 37.7 0.8 1.6 5.1 4.6 ... . 43.4 44.6
Latin America 28.9 32.1 11.4 14.7 2.2 1.9 0.7 1.0 43.9 50.5
WANA na na 8.3 15.1 0.1 0.2 na na 8.5 15.4
Sub-Saharan Africa 53.8 84.7 2.3 2.5 5.4 6.8 10.7 30.3 75.6 131.0
Developing 129.8 164.3 64.3 108.1 131.6 133.9 11.7 31.6 344.4 448.8
Developed na na 209.2 187.6 2.2 1.9 0.1 0.2 211.9 190.0
World 129.8 164.3 273.5 295.6 133.7 135.8 11.8 31.8 556.4 638.8

Source: FAO 1999a.
Note: Ellipses (. .) signify very small values; na signifies no recorded production. WANA is West Asia and North Africa. 1983 is average for
1982-84 and 1996 is average for 1995-97. See Table 2 footnote for regional breakdown.
aAll R&T includes cassava, potato, sweetpotato, yam, and other R&T such as taro.


sists of potato. Potato is also of relatively high
importance in India and other South Asian coun-
tries and in East Asian countries other than China.
Production of cassava plays a major role in South-
east Asia (86 percent of R&T production), Latin
America (65 percent), and Sub-Saharan Africa (68
percent). Yam production accounts only for 24 per-


cent of R&T output in Sub-Saharan Africa, but it
has become increasingly concentrated in this re-
gion. China continues to dominate sweetpotato
production, which accounts for almost 70 percent
of the country's R&T output. Sweetpotato also
plays a major role in R&T production in the rest of
East Asia.










Figure 5-Location of root and tuber production, 1996

Potato


China 16.5%


dia 6.9%

West Asia and
Developed North Africa 5.1%
63.4%
Latin America 5.0%
S' Other South Asia 1.3%
Sub-Saharan Africa 0.8%
Southeast Asia 0.5%
Other East Asia 0.4%







Sweetpotato

dia0.9%
West Asia and North Africa 0.1%
Latin America 1.4%
SOther South Asia 0.4%
n/ 6n Sub-Saharan Africa 5.0%

Southeast Asia 3.4%

Other East Asia 0.3%
developed 1.4%








All roots and tubers


Cassava


Latin America
/ 19.5%


SOther South
Asia 0.2%

Southeast Asia 23.0%



SChina 2.2%
India 3.5%


Southeast Asia
0.1%


India 4.3%
Other East Asia 0.2%
Other South Asia 0.8%
Southeast Asia 7.0%

West Asia and
North Africa 2.4%
Latin America 7.9%

Sub-Saharan Africa 20.5%


Source: FAO 1999a.
Note: 1996 is average of 1995-97. See Table 2 footnote for regional breakdown.









Figure 6-Relative importance of major roots
and tubers in countries and regions,
1996, based on production volumes


Percent


E Sweetpotato N Yam E Cassava E Potato


Source: FAO 1999a.
Note: 1996 is average of 1995-97. See Table 2 footnote for
regional breakdown.



Sources of Growth in Output

Expansion in area and higher yields have con-
tributed almost equally to output growth for R&T
during 1983-96. Increase in area accounted for 57
percent of total output growth and yield improve-
ments accounted for the remaining 43 percent. The
role of area expansion as a source of output growth
is significantly larger for R&T than for other major
food crops. This is due, in part, to the location of a
significant share of the harvested area for R&T in
Sub-Saharan Africa. Twenty-six and 34 percent of
total R&T area could be found in this region in
1983 and 1996, respectively. Other factors con-
tributing to this evolution include the relatively low
investments in agricultural R&D for these crops
compared to investments in wheat, maize, and rice,
for example. The greater adaptability of some R&T
to marginal areas, combined with their flexible
growth cycle, also facilitated area expansion in
some countries and regions.


Globally, the area harvested in R&T increased
during 1983-96 from 45.8 million hectares to 49.5
million hectares. The largest expansion of R&T
area occurred in Sub-Saharan Africa, from 11.9
million hectares in 1983 to 16.9 million hectares in
1996. The distribution of area planted in R&T
across regions largely coincides with that of pro-
duction and use levels because only a small propor-
tion of R&T output is traded internationally.

Sub-Saharan Africa
In Sub-Saharan Africa, the increase in cassava out-
put has been driven largely by growth in area
planted. A synthesis of the results from the com-
prehensive COSCA study found that the most im-
portant reasons for farmers to increase cassava pro-
duction are famine, hunger, and drought (Spencer
and Associates 1997). Cassava's low input require-
ments, a trait that fits well with the region's
resource endowments (relatively abundant land,
relatively scarce labor), make it suitable for the
difficulties African farmers face. The shortage of
chemical inputs and organic matter and the limited
irrigation facilities in the region also make cassava
a crop of choice for African farmers. Moreover, as
farm size shrinks under population pressure, food
requirements per hectare of land cultivated rise,
increasing the prospects that farmers will shift to
crops with higher output of energy per hectare as
one strategy for overcoming hunger.7 Food short-
ages precipitated by a combination of political and
civil unrest, wars, economic stagnation, erratic
rainfall patterns, and rapid population growth have
had a much greater influence on R&T production
in this region than anywhere else.
Another important reason for cassava's bur-
geoning presence in Sub-Saharan Africa is the
crop's resistance to pests and diseases (Spencer
and Associates 1997). Higher prices, increased
market access for farmers, and higher yields have
also played a role in cassava's emergence as a cash
crop in much of the region (Nweke 1992). This
commercialization of the crop is particularly sig-
nificant, given that the share of the urban popula-
tion is expected to increase from 30 to 50 percent
by 2020 (FAO 1998b).


7 Ruthenberg (1980, 361) predicted a shift in cropping patterns to more energy productive crops as farm size in developing
countries declined and population growth pushed up food (that is energy production per hectare) requirements per given land area.









Table 7-Yields and annual growth rates in yield for roots and tubers, 1983-96

Cassava Potato Sweetpotato Yam All R&T,
Yield Growth Yield Growth Yield Growth Yield Growth Yield Growth
Country/region 1983 1996 rate 1983 1996 rate 1983 1996 rate 1983 1996 rate 1983 1996 rate
(mt/ (percent (mt/hectare) (percent (mt/hectare) (percent (mt/ (percent (mt/ (percent
hectare) per year) per year) per year) hectare) per year) hectare) per year)
China 15.6 15.5 -0.06 11.3 13.8 1.52 16.7 19.1 1.06 na na na 15.3 17.1 0.89
Other East Asia na na na 13.3 15.4 1.12 20.0 17.2 -1.15 na na na 15.8 15.9 0.02
India 17.5 23.5 2.28 14.0 16.5 1.30 7.4 8.3 0.85 na na na 13.7 16.9 1.60
Other South Asia 11.5 8.8 -2.05 9.7 11.1 1.01 10.4 9.0 -1.12 na na na 10.1 10.6 0.36
Southeast Asia 12.1 12.1 -0.01 9.1 13.1 2.82 6.2 6.7 0.59 2.6 4.7 4.85 10.7 11.0 0.24
Latin America 10.8 12.0 0.78 11.1 13.7 1.63 7.2 7.6 0.43 6.7 8.4 1.73 10.3 11.8 1.04
WANA na na na 14.8b 19.4b 2.10 21.8b 22.4b 0.21 na na na 15.0 19.5 2.06
Sub-Saharan Africa 7.1 8.2 1.15 6.1 6.0 -0.08 5.0 4.5 -0.86 6.4 9.9 3.46 6.4 7.8 1.53
Developing 9.3 9.9 0.46 11.6 14.2 1.62 13.8 15.0 0.64 6.5 9.9 3.32 10.6 11.7 0.74
Developed na na na 16.0 17.2 0.57 16.3 18.6 1.02 18.1 20.9 1.10 16.0 17.2 0.57
World 9.3 9.9 0.46 14.6 16.0 0.67 13.8 15.0 0.64 6.5 9.9 3.29 12.2 12.9 0.46

Source: FAO 1999a.
Note: na signifies no recorded production, mt is metric ton. WANA is West Asia and North Africa. 1983 is average for 1982-84 and 1996 is
average for 1995-97. See Table 2 footnote for regional breakdown.
aAll R&T includes cassava, potato, sweetpotato, yam, and other R&T such as taro.
bFAO indicates very high yields in Egypt on small areas.


Evidence from the COSCA study further indi-
cates that the increased area planted is in many
instances replacing fallow land. New cassava pro-
duction is also crowding out other crops, especially
yam in the humid zone and maize in the nonhumid
zone (Spencer and Associates 1997).
On the post-production side, a key food se-
curity role played by cassava in Sub-Saharan
Africa is its ability to be stored in the ground for 36
months or more after the formation of the edible
roots is complete. Hence, cassava cultivation
serves as something of a household food bank that
can be drawn upon when adverse agroclimatic con-
ditions or civil unrest limit the availability of and
access to other foods. The wide variety of food
products that are made from the roots and the
highly nutritious leaves widely consumed as a reg-
ular part of the diet, particularly in Central, South-
ern, and West Africa, are added reasons why
cassava cultivation is expanding (NR1 1992).
About 95 percent of the world's yam output is
produced in Sub-Saharan Africa. Nigeria, Ghana,
and C6te d'Ivoire account for more than 80 percent


of the worldwide yam harvest (Lev and Shriver
1998). The growth in area planted to yam acceler-
ated in recent years and accounted for 56 percent of
total output growth during 1983-96.8 In West Af-
rica, particularly in Nigeria, the increase in area
planted represents an expansion in yam cultivation
from its traditional growing area in the humid for-
ests to the moist savannahs (Manyong et al. 1996).
Higher solar radiation, less pressure from pests and
diseases, and lower costs of production due to less
labor-intensive cultivation practices appear to have
induced this shift.
Increases in yam area and production have also
been driven by strong demand for the tubers in
fresh form as food and a growing interest in their
use as raw material for processed food products
(Attaie, Zakhia, and Bricas 1998).
Sweetpotato production in Sub-Saharan Africa
during 1983-96 has been entirely driven by growth
in area planted; average yields actually contracted
in this period (Tables 5 and 7). Most of the growth
in production occurred in Eastern, Central, and
Southern Africa in response to steadily increasing


s Global and regional statistics for yam are highly influenced by data for Nigeria that show serious inconsistencies between
production and consumption estimates (see Bricas and Attaie 1998 and Dorosh 1988).









pressure on local food systems due to population
growth, civil war, and economic hardship (see, for
example, Bashaasha et al. 1995; Tardif-Douglin
1991). In the Kivu region, Democratic Republic of
the Congo, for example, sweetpotato has been used
as a staple food for disaster relief (Tanganik et al.
1999). Declines or stagnation in output of other
staples have also contributed to the interest by
farmers and consumers in sweetpotato in some
countries, for example Malawi (Phiri 1998). Cash
sales of the roots and a nascent processing sector
have added to the momentum in production in
Uganda (Scott et al. 1999) and Kenya (Gatumbi
and Hagenimana 1998).
For potato in Sub-Saharan Africa, pressure on
land to produce more food and the absence of gov-
ernment intervention in output markets for table
potatoes (Rasolo et al. 1987; Scott 1988b, 1994b)
have led to an increase in area planted of 0.7 per-
cent per year during 1983-96. However, average
yields remain too low to foster greater market par-
ticipation by small-scale farmers in East and
Southern Africa, mainly due to unfavorable grow-
ing conditions and lack of access to improved seed
and chemical fertilizers.

Asia
In 1996, 29 percent of the global area harvested for
potato was located in developing Asia, up from 19
percent in 1983. Most of the rest, 59 percent, was
harvested in the industrialized countries. Follow-
ing the break-up of the Former Soviet Union,
China became the world's largest potato producer.
In 1997, India ranked third after the Russian
Federation. In China, India, and Asia in general,
expansion in area planted has been driven in large
part by strong off-farm demand. On the supply
side, the potato's highly flexible vegetative cycle,
which allows it to fit into a wide variety of crop-
ping systems, has been another factor influencing
area expansion. In the Indian Indo-Gangetic plain,
where area expansion has been particularly rapid,
potato can be harvested between rice and other
crop harvests (Bardhan Roy et al. 1999). The
spread of potato cultivation in the region has also
been facilitated by ample availability of irrigation,
chemical fertilizers, and cold storage facilities, and
improvements in cultivation techniques and road
and rail transport. And with relatively high yields


in 100-120 days, potato represents an extremely
lucrative crop for even the small farmers who
dominate production in many Asian countries
(Bardhan Roy et al. 1999; Bottema et al. 1989;
Dahiya and Sharma 1994; Scott 1983b, 1988a).
Seventy-eight percent of global area planted to
sweetpotato is located in Asia, 68 percent alone in
China, down from 83 percent in 1983. Some of the
same factors that contributed to expanded potato
production have led to a decline in area planted
in sweetpotato. With the spread of irrigation, farm-
ers in some parts of China (Stone 1984; Ye and
Rozelle 1993; Zhang 1999, 46) and Korea (Chin
1989) switched to crops with higher returns per
hectare. Moreover, with increasing economic
growth and rapid urbanization in many parts of
Asia, consumers decreased their demand for tradi-
tional starchy staples, such as fresh sweetpotato, in
favor of meat, bread, potato, and other preferred
foods. Hybrid maize or imported feed rations
displaced sweetpotato as a feed source as countries
such as Korea (Chin 1989) and Taiwan (Chiang
1992) became more integrated into the global
economy. An exception is sweetpotato production
in Sichuan province, China (see Box 2). Bulkiness,
perishability, and erratic year-to-year, season-to-
season movements in supply and prices made it
difficult to establish local sweetpotato-based agro-
industries in the Philippines (Cabanilla 1996), In-
donesia (Setyono, Damardjati, and Malian 1992),
and elsewhere in Asia (Woolfe 1992).
Growth in area planted to cassava in Asia has
been negative primarily due to the contraction in
demand for cassava chips and pellets in the Euro-
pean Union. Stagnant demand for meat in indus-
trialized countries, in particular pork, has also con-
tributed to this trend (Delgado et al. 1999). Use of
cassava as feed in developed countries in 1996 was
less than half the 1983 level of 19 million mt (Table
3). In India, cassava has come under increasing
pressure from competing raw materials in the mar-
kets for processed products (Balagopalan, Pad-
maja, and Kurup 1992) and has been hurt by ad-
verse policies, including subsidies favoring
substitute crops such as Hevea brasiliensis (natural
rubber) (Best 1996).
Since the early 1990s, however, the cassava
industry in South and particularly Southeast Asia
has aggressively pursued alternative market outlets









(Dang, Le, and Henry 1996; FAO 1994, 1995a;
Titapiwatanakun 1996). The growth in the use of
cassava for starch and as raw material for livestock
production has raised expectations that the sector's
decline may have bottomed out, and that cassava
production may rebound, capitalizing on the same
favorable set of factors that led to spectacular
growth in the 1970s and 1980s (Konjing 1989).
These factors include climate conditions that facili-
tate low-cost solar drying, ample transportation in-
frastructure, technology transfer through joint ven-
tures, well-organized commodity associations, and
attractive returns to production (Titapiwatanakun
1998).

Latin America
In Latin America, area planted to R&T has been
either flat or negative. Production of cassava and
sweetpotato stagnated or contracted due to urban-
ization and its associated shifts in eating habits.
Moreover, imports of wheat flour for food, and
maize or concentrates for feed, provided stifling
competition for R&T in countries such as Peru
(Blondet and Espinola 1998; Meerdink 1995). In
other countries, such as Argentina, sweetpotato use
was confined to niches for processed products in
the domestic market or to exports of fresh roots.
Weak demand, high relative prices, and more at-
tractive returns to other crops have dampened po-
tential production increases (Brescia and Parellada
1994; Maggi 1990). Where cassava production did
increase-on the north coast of Colombia and in
northeast Brazil-it followed the pattern first es-
tablished in Thailand. Markets for cassava as ani-
mal feed and links between small farmers and these
alternative commercial outlets provided the incen-
tives for growers to expand output, often through
yield-increasing technologies. This pattern offers
promise to cassava-producing countries where the
absence of emerging markets has led to a decline in
cassava production (Henry 1992).
Potato production in Latin America increased
by more than 3 million mt and yam by 0.3 million
mt during 1983-96, with growth in area account-
ing for 16 percent and 41 percent of this increase,
respectively. The continued popularity of yam as a
food item and source of cash income was largely
confined to Jamaica and Haiti. The emergence of a


fast-food sector and processing industry in the re-
gion spurred domestic output of potato (Scott,
Basay, and Maldonado 1997). However, the elim-
ination of credit schemes (as part of a broader ef-
fort to reduce public spending and government par-
ticipation in the marketplace) raised the costs of
production per hectare, driving many smaller po-
tato producers out of the sector (Rodriguez 1996).
The more efficient farms were able to respond to
growing market opportunities by expanding area
planted.



Sources of Productivity Growth

Although growth in area planted has contributed
more to increases in R&T production in develop-
ing countries than improvements in yields, note-
worthy increases in productivity have taken place
in some countries and regions (Table 7).

Sub-Saharan Africa
Yield growth rates in Sub-Saharan Africa have
been disappointing except in the case of yam. In-
creases in yield are often difficult to achieve in the
region because of nutrient-poor soils, lack of ir-
rigation, and weak infrastructure (Spencer and
Badiane 1995). In addition, R&T have suffered
from the tendency of governments, with a few
noteworthy exceptions, to focus their policies and
resources on cash crops for export, or, in parts of
East and Southern Africa, on cereals. One conse-
quence of this relative neglect is that national re-
search programs for R&T are often poorly funded
and understaffed.
But as population growth and urbanization
have continued apace, many governments and re-
searchers are reappraising the potential of R&T to
help meet food, feed, and income requirements in
the decades ahead (Adeniji et al. 1997; Bashaasha
and Mwanga 1992). Research on R&T has focused
more on efforts to control pests and diseases
through a combination of better biological control,
improved cultural practices, and the introduction
of disease-resistant varieties. Several of these pro-
duction interventions have been successful (see,
for example, Rueda et al. 1996). But with the note-
worthy exception of integrated pest management









for cassava mealybug (Norgaard 1988), the area
cultivated using these new technologies has been
limited to date.

Asia
Yields have increased more rapidly in Asia. In the
case of potato, yield increases have been catalyzed
in part by the introduction of high-yielding vari-
eties, which made the crop more profitable for
farmers (see, for example, Bofu et al. 1996; Scott
1988a). Introduction of improved seed multiplica-
tion techniques meant that farmers could achieve
higher yields by having seed available at optimum
planting time. In the Indo-Gangetic plain, these
techniques were complemented by the expansion
of cold storage facilities for seed and table potatoes
(FAO 1995b). Potato yields also benefited from the
earlier introduction of improved rice and wheat
varieties. Successful adoption of the cereals
prompted increases in the supply of chemical fer-
tilizers, irrigation, and rural infrastructure, with
subsequent spillover benefits to potato, which also
is an input-intensive crop. After taking hold in
prime locations, potato production expanded to
somewhat less favorable soils, which led to a slow-
down in yield improvement.
Production growth for sweetpotato is now pos-
itive in China, although it had contracted. The re-
bound is largely due to the explosive demand for
meat and animal feed in the feed-deficit, inland,
sweetpotato production centers. Growth in demand
both at home and abroad for processed food prod-
ucts made from sweetpotato has also contributed to
the upsurge in sweetpotato output (Fuglie et al.
1999; Zhang 1999). Improved, small-scale pro-
cessing of sweetpotato roots has also boosted pro-
duction by making household or village-level pro-
cessing less onerous and more profitable
(Wheatley, Liping, and Bofu 1997). In addition,
new varieties have been adopted more widely, in
part because of the rebound in off-farm demand.
But China's earlier isolation from Western science
and sweetpotato's much lower priority than cereals
or industrial crops such as cotton have handicapped
more rapid improvements in productivity.
Cassava productivity has followed trends simi-
lar to sweetpotato productivity. Cassava and, even
more so, sweetpotato have been neglected in hard-


pressed national agricultural research programs.
Policies that have favored cheap imports or domes-
tic products that could serve as substitutes have
also hurt the potential for improving cassava
productivity.

Latin America
For the region as a whole, cassava and sweetpotato
productivity has been affected by weak demand.
Most farmers have had little incentive to use yield-
increasing technologies because potential commer-
cial opportunities have yet to be exploited. Existing
market outlets are limited and relatively thin, with
the exception of cassava for feed or processed food
in Colombia and northeast Brazil. Remaining
growers are generally resource-poor farmers who
choose to cultivate these commodities in part to
avoid the financial risks associated with more in-
put- and cash-intensive crops. As area planted with
cassava and sweetpotato has declined or at best
stagnated, cultivation often has been pushed onto
or confined to more marginal soils. Productivity
increases therefore have become more difficult to
achieve. With a few notable exceptions, for exam-
ple cassava in Colombia, weak national research
programs have further handicapped productivity
improvements for these crops. R&T are also often
overlooked in policy deliberations regarding ex-
change rates and trade and tariff agreements. Be-
cause the farmers who make up these commodity
subsectors typically have smallholdings and are
poorly organized, they lack the political clout of
more formidable farmers' groups, such as the na-
tional rice-growers' associations, to press for more
public and private sector investments.
For potato and yam, improvements in yields
have been larger. Average potato yields in Mexico
are now 20 mt per hectare, after increasing at more
than 4.1 percent per year during the last decade.
Strong off-farm demand, fueled by contracts with
agro-industry, have helped catalyze this upward
trend. Potato productivity in Mexico has also bene-
fited from the introduction of improved varieties;
the spread of potato cultivation to lowland, irri-
gated farming areas; the high returns per hectare
that have attracted large, highly technical com-
mercial growers to the sector; and the spillover
benefits-fertilizers, pesticides, and local infra-








structure-associated with the spread of improved
cereal varieties (Biarnms, Colin, and Santiago Cruz
1995). Colombia has witnessed similar develop-
ments, though production remains concentrated in
highland and rainfed areas (Rodriguez 1996). In
contrast, yield growth for potato in Bolivia and
Ecuador, for example, has been negative or stag-
nant during the last decade, with average produc-
tivity in Ecuador still nearly 30 percent below
levels reached in the early 1980s. Complex agro-
ecologies; a heterogeneous set of target farmers in
terms of size, education, and market orientation;
slower introduction of and demand for new prod-
ucts; and trade and exchange rate policies that have
favored cereal crops have all played a role in this
negative trend (Zevallos 1997).
In summary, trends in production, area


planted, and yield for R&T have been highly vari-
able by crop and by region. Increases in potato and
yam production have been most impressive in Asia
and Sub-Saharan Africa, respectively. Cassava
output growth has been strongest in Sub-Saharan
Africa.9
For cassava and sweetpotato in Asia and Latin
America, trends have been more mixed. Issues that
need to be explored include the potential for in-
creased productivity, the reduction in per unit costs
to make these crops economically attractive
sources of raw material, and the increased ability
of existing public and private organizations to re-
spond to the demand for new uses. The following
chapter will address these issues and assess future
prospects for R&T in a framework that encom-
passes all the major food commodities.


9 In WANA, potato production nearly doubled during 1983-96, from 8.3 million mt to 15.1 million mt (Table 6). Area planted
expanded at an annual rate of 2.6 percent in response to both strong domestic demand (see, for example, Fuglie 1994) and shifts in
government policy in countries like Egypt that served to spur exports (Pautsch and Abdelrahman 1998). Yields increased at a rate
of 2.1 percent per year. With access to irrigation facilities, chemical fertilizers, and improved seed (from foreign and local sources)
farmers in the region had both the incentive (strong off-farm demand) and technical capability to raise productivity.















4. Baseline Projections of Production and Use


Changes in the volume, rate of growth, form, and
location of R&T production and use have con-
tinued to evolve in a highly heterogeneous fashion
over the last two decades. Two aspects of this evo-
lution have been particularly noteworthy: the ver-
satile uses of R&T and the adaptability of these
crops to the emerging needs of local food systems
in developing countries. These aspects of R&T will
be even more important in the face of future in-
creases in population, urbanization, and persistent
poverty in the midst of rising incomes. Assessing
the future role of R&T in the global food system
requires careful consideration of the relative
capacity of these different food commodities to
respond to the challenges ahead. For this assess-
ment to be transparent, key assumptions about the
most likely track for the global economy and popu-
lation growth, as well as the most likely responses
of particular food commodities to these trends,
need to be made explicit. The rationale behind
these assumptions also need to be delineated.
In this and the following chapter two alternative
scenarios for the role of R&T in the food systems of
developing countries up to 2020 will be analyzed.
The baseline projections are presented in detail in
this chapter, and the alternative high demand and
production growth projections are presented in
Chapter 5. These global projections of food supply
and demand are based on IFPRI's International
Model for Policy Analysis of Agricultural Com-
modities and Trade (IMPACT), which is continually
refined and updated and covers 37 countries or
country groups and 18 commodities, including all
cereals, soybeans, the major R&T, meats, and milk
(see Box 3). The assumptions behind the estimates
are based on assessments of the future outlook for


production and use of R&T; the prospects for expan-
sion in area planted and increases in productivity;
and the implications of these growth patterns for
future net trade, international prices, and value of
production ofthese commodities.


Baseline Scenario to 2020
Under the baseline scenario, projections for R&T
are driven by conservative estimates of the effects
of income growth on the demand for these com-
modities (see Appendix, Table 26) and of the
effects of technological change and other parame-
ters on increases in production and yield. As a cor-
ollary, the rate of growth of output is modest in
relation to recent historical trends.
Total use of R&T in developing countries is
projected to increase by 232 million mt to 635
million mt, or by 58 percent, between 1993 (1992-
94 average) and 2020 (Table 8). The largest in-
crease in terms of volume is projected for cassava:
103 million mt, or 44 percent of the total increase
in R&T use over the period. Potato ranks second,
with 68 million mt, or 29 percent of the increase in
R&T use. Sweetpotato and yam will account for an
additional 62 million mt, about 27 percent.10
Total demand for cassava is expected to in-
crease at 1.9 percent per year during 1993-2020 in
developing countries; potato at 2.0 percent per
year; and sweetpotato and yam combined at 1.3
percent per year. These rates of growth compare
well with projected increases in demand of major
cereals during this period: demand for wheat is
projected to grow at 1.8 percent annually; maize at
2.2 percent annually; and rice at 1.2 percent an-
nually (Tables 9 and 10).


10 IMPACT implicitly assumes that the relative importance of the volume of production (fresh weight) of sweetpotato versus yam
in Sub-Saharan Africa will remain roughly constant during 1993-2020. The results presented here are based on the June 1998
IMPACT baseline.











Box 3: The IMPACT Model


IFPRI's IMPACT model is specified as a set of country-
level demand and supply equations linked to the rest of
the world through trade. Food demand is a function of
commodity prices, per capital income, and population
growth. Feed demand is a function of livestock produc-
tion, feed prices, and feeding efficiency. Total demand
equals the sum of food, feed, and other demand. Crop
production is determined by the area and yield response
functions; area is projected as a function of crop prices,
investment in irrigation, and estimated rates of loss of
land to urbanization and land degradation. Crop yield is
a function of crop price, input price, investment in irri-
gation, and yield growth due to technological change.
Growth in productivity due to technological change is,
in turn, estimated by its component sources, including
advances in management research and, in the case of
food crops, plant breeding research. Other sources of
growth considered in the model include private-sector
investments in agricultural research and development,
agricultural extension and education, markets, in-
frastructure, and irrigation (see Rosegrant, Agcaoili-
Sombilla, and Perez [1995] for details on the method-
ology).


The projections presented in this paper go beyond
past estimates of future R&T supply and demand in
a number of important respects. Previous attempts
typically focus on a single root and tuber crop, for ex-
ample, potato (see FAO 1995b; Henry and Gottret
1996) or aggregate R&T into one commodity. These
approaches do not allow for the estimation of the possi-
ble linkages among R&T and between R&T and other
food commodities.I Previous projections have relied
heavily on past commodity trends and are seldom ex-
plicit about key parameters, such as income elasticities
of demand. Given concerns about the accuracy of time-
series data on production and use of R&T (Alex-
andratos 1995, 100), IMPACT integrates an analysis of
past trends and projections with a synthesis of surveys
and case studies of these commodities. Previous at-
tempts at multicommodity projections were often
carried out without the full collaboration of R&T spe-
cialists. Given the relative shortage of published infor-
mation on projections of supply and demand for R&T,
consultation with specialists, as is the case here, repre-
sents an important aspect of any modeling exercise for
these commodities.


I' Although sweetpotato and yam are combined in this analysis some results are disaggregated outside IMPACT
when discussing the findings and associated contributing factors at the regional and subregional level. Cassava refers
to cassava and other roots and tubers, including aroids such as taro; however, cassava alone accounts for more than
97 percent of the cassava total.


Demand for potato in developing countries is
expected to increase by 2.3 percent annually for
food and 0.4 percent annually for feed during
1993-2020 (Table 9). These projected food and
feed growth rates are well below the annual rates
achieved during 1983-96 of 4.1 percent and 4.6
percent, respectively. The combined annual growth
in use of sweetpotato and yam is projected at 0.4
percent for food and 1.8 percent for feed over the
next two decades compared with annual growth in
human consumption of -1.8 percent and 8.6 per-
cent per year, and annual growth in feed demand of
3.4 percent and 2.7 percent during 1983-96. Ac-
cording to IMPACT, cassava demand will grow at
2.0 percent annually for food and 1.6 percent per
year for feed in developing countries (Table 9).
These are virtually the same rates of growth
achieved during 1983-96.


Per capital consumption of cereals as food is
expected to decline slightly in both developed and
developing countries, from 144 kg in 1993 to 140
kg in 2020, and from 172 kg to 170 kg, respectively
(Table 11). But per capital consumption of R&T as
food is projected to increase, albeit marginally, in
both developed and developing countries, from 77
kg to 78 kg and from 56 kg to 58 kg, respectively.
Declines in per capital R&T demand in China,
Southeast Asia, Latin America, and Sub-Saharan
Africa will be more than offset by increases in
India and other South Asian countries, and in East
Asian countries other than China.


Sub-Saharan Africa
Sub-Saharan Africa is expected to experience the
most rapid growth in food demand in all R&T










Table 8-Total use of roots and tubers in 1993, and projected to 2020, baseline scenario

Cassava, Potato Sweetpotato and yamb All R&T
Country/region 1993 2020 1993 2020 1993 2020 1993 2020
(million metric tons)

China 5.1 6.4 42.7 63.3 108.0 126.9 155.9 196.7
Other East Asia 1.8 1.9 2.6 3.7 0.9 1.2 5.4 6.7
India 5.7 7.3 16.3 37.1 1.2 1.2 23.2 45.6
Other South Asia 0.9 1.4 3.5 7.6 0.5 0.7 4.9 9.7
Southeast Asia 18.9 24.4 1.4 2.7 5.3 7.7 25.6 34.8
Latin America 30.3 42.9 13.0 20.4 2.5 3.6 45.8 67.0
WANA 0.9 1.0 12.8 22.0 0.1 0.2 13.8 23.2
Sub-Saharan Africa 87.7 168.1 2.8 6.3 36.0 74.5 126.4 248.9
Developing 152.0 254.6 95.2 163.2 155.5 217.3 402.7 635.1
Developed 20.7 20.5 190.1 206.2 2.5 2.7 213.3 229.4
World 172.7 275.1 285.3 369.4 158.0 220.0 616.0 864.5

Source: IMPACT Simulations, June 1998.
Notes: Total use includes food, feed, and other uses. WANA is West Asia and North Africa. See Table 2 footnote for regional breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.



Table 9-Projected annual growth rates for food, feed, and total use of roots and tubers, 1993-
2020, baseline scenario

Cassavaa Potato Sweetpotato and yamb All R&T
Country/region Food Feed Total Food Feed Total Food Feed Total Food Feed Total
(percent per year)

China 0.17 1.61 0.84 2.20 0.27 1.47 -1.02 1.81 0.60 0.00 1.55 0.86
Other East Asia 0.83 0.21 0.05 1.31 1.20 1.29 0.84 1.47 0.86 1.22 1.20 0.83
India 0.93 na 0.93 3.09 na 3.09 0.14 na 0.14 2.42 na 2.54
Other South Asia 2.03 na 1.62 2.97 na 2.95 1.31 na 1.18 2.63 na 2.58
Southeast Asia 0.97 0.89 0.96 2.31 2.58 2.30 1.31 2.41 1.39 1.13 1.45 1.14
Latin America 0.70 1.75 1.30 1.69 1.62 1.69 1.09 2.01 1.32 1.18 1.75 1.42
WANA 1.34 0.43 0.68 2.02 1.59 2.02 1.52 na 1.51 2.00 0.60 1.95
Sub-Saharan Africa 2.49 1.53 2.44 3.10 1.81 3.10 2.74 1.89 2.73 2.55 1.56 2.54
Developing 1.99 1.62 1.93 2.33 0.37 2.02 0.44 1.81 1.25 1.62 1.57 1.70
Developed -0.50 0.01 -0.04 0.37 0.22 0.30 0.28 0.61 0.33 0.36 0.15 0.27
World 1.98 0.95 1.74 1.20 0.26 0.96 0.43 1.80 1.23 1.30 1.07 1.26

Source: IMPACT Simulations, June 1998.
Notes: na signifies no recorded use. Total use includes food, feed, and other uses. WANA is West Asia and North Africa. See Table 2 footnote
for regional breakdown.
"These figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.


categories with the total R&T growth rate averag-
ing 2.6 percent per year through 2020. Growth in
total use (food, feed, and other uses) in Sub-
Saharan Africa will account for nearly 122 million
mt or 53 percent of the increase in demand for all


R&T crops in developing countries during 1993-
2020. The increase in use will come largely from
cassava, 80 million mt (66 percent of the total), and
yam roughly 33 million mt (31 percent) (Table 8)
and will be overwhelmingly for food (Table 12).










Table 10-Projected annual growth rates for food, feed, and total use of wheat, maize, rice, and
all cereals, 1993-2020, baseline scenario

Wheat Maize Rice All Cereals
Country/region Food Feed Total Food Feed Total Total Food Feed Total
(percent per year)
China 0.90 3.46 1.11 -0.50 3.46 2.53 0.58 0.58 3.37 1.37
Other East Asia 1.20 2.55 1.64 0.29 2.15 1.86 0.44 0.64 2.22 1.44
India 1.90 3.65 1.98 0.81 7.39 2.44 1.56 1.56 4.96 1.69
Other South Asia 2.77 2.83 2.77 2.21 2.88 2.34 1.84 2.30 2.85 2.32
Southeast Asia 2.28 2.46 2.29 0.84 2.81 2.27 1.23 1.31 2.66 1.53
Latin America 1.36 2.19 1.44 1.22 2.00 1.74 1.66 1.36 2.04 1.70
WANA 2.02 2.45 2.05 1.22 2.40 2.01 2.19 1.98 2.47 2.12
Sub-Saharan Africa 3.30 3.65 3.30 2.58 3.43 2.64 3.20 2.91 3.45 2.92
Developing 1.67 2.92 1.77 1.07 2.92 2.24 1.23 1.43 2.81 1.75
Developed 0.31 0.42 0.35 0.00 0.70 0.66 0.29 0.21 0.59 0.49
World 1.29 1.08 1.22 0.94 1.72 1.49 1.19 1.21 1.41 1.27

Source: IMPACT Simulations, June 1998.
Note: Total use includes food, feed, and other uses. Rice demand for animal feed is negligible. All cereals includes wheat, maize, rice, and
other coarse grains. See Table 2 footnote for regional breakdown.



Table 11-Per capital use of roots and tubers and cereals as food in 1993, and projected to 2020,
baseline scenario

Cassava" Potato Sweetpotato and yamb All R&T Cereals
Country/region 1993 2020 1993 2020 1993 2020 1993 2020 1993 2020
(kilograms per year)
China 2 2 14 20 45 28 61 50 214 206
Other East Asia I 1 18 21 6 6 24 27 157 149
India 6 5 13 21 1 1 20 27 163 175
Other South Asia 3 3 9 11 2 1 13 15 159 170
Southeast Asia 32 30 3 3 10 10 45 43 169 169
Latin America 25 21 22 24 3 3 50 48 128 129
WANA 1 1 28 28 ... ... 29 29 214 210
Sub-Saharan Africa 131 124 3 3 36 36 169 164 112 119
Developing 24 28 13 16 19 14 56 58 172 170
Developed ... . 75 77 1 1 77 78 144 140
World 19 23 27 27 15 12 61 62 165 165

Source: IMPACT Simulations, June 1998.
Notes: Ellipses ( .) signify very small values. WANA is West Asia and North Africa. See Table 2 footnote for regional breakdown.
"These figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.


Continued strong growth in food demand for
cassava (2.5 percent per year) reflects the impor-
tant role that cassava plays in many African diets
and the relatively high rates of population growth
projected for the region. The growth rate in food
demand also stipulates that cassava will maintain
its importance in regional diets as Sub-Saharan


Africa continues to urbanize and increase its share
of processed food products for consumers in the
countryside and the cities. In major cassava-
producing countries such as Nigeria, the bulk of
annual production is already processed into food
products (Adeniji et al. 1997). Finally, despite
what some might consider relatively high growth









Table 12-Food and feed use of roots and tubers in 1993, and projected to 2020, baseline
scenario

Cassava, Potato Sweetpotato and yamh All R&T
Country/region 1993 2020 1993 2020 1993 2020 1993 2020
(million metric tons)
Food
China 2.7 2.8 15.9 28.5 53.2 40.3 71.7 71.6
Other East Asia 0.1 0.1 1.8 2.5 0.5 0.7 2.4 3.2
India 5.4 6.9 11.8 26.9 1.1 1.2 18.4 35.0
Other South Asia 0.7 1.3 2.5 5.6 0.4 0.6 3.7 7.4
Southeast Asia 15.0 19.5 1.2 2.2 4.6 6.6 20.8 28.2
Latin America 11.5 13.9 9.9 15.6 1.6 2.1 23.0 31.6
WANA 0.2 0.3 10.5 18.0 0.1 0.2 10.8 18.5
Sub-Saharan Africa 67.0 130.2 1.4 3.1 18.2 37.9 86.6 171.2
Developing 103.3 175.9 55.0 102.5 80.5 90.5 238.8 368.9
Developed 0.4 0.4 96.2 106.2 1.7 1.8 98.3 108.4
World 103.7 176.3 151.2 208.7 82.2 92.3 337.1 477.3

Feed
China 1.9 3.0 12.3 13.3 49.4 80.2 63.7 96.4
Other East Asia ... ... 0.4 0.6 0.1 0.1 0.5 0.7
India na na na na na na na na
Other South Asia 0.1 . na na . ... 0.1
Southeast Asia 0.7 0.9 . ... 0.3 0.6 1.0 1.5
Latin America 13.7 21.9 0.4 0.7 0.4 0.6 14.5 23.2
WANA 0.6 0.7 0.1 0.1 na na 0.7 0.8
Sub-Saharan Africa 5.0 7.5 ... ... 0.4 0.7 5.4 8.2
Developing 22.0 33.9 13.3 14.7 50.7 82.3 86.0 130.9
Developed 19.4 19.4 37.0 39.3 0.4 0.5 56.8 59.2
World 41.4 53.4 50.3 53.9 51.1 82.8 142.8 190.1

Source: IMPACT Simulations, June 1998.
Notes: Ellipses (. .) signify very small values; na signifies no recorded use. WANA is West Asia and North Africa. See Table 2 footnote for
regional breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.


rates, annual average per capital consumption of
cassava as food in Sub-Saharan Africa is actually
projected to decline slightly, from 131 kg per year
in the base period to 124 kg per year by 2020
(Table 11).
The projected rate of growth for sweetpotato
and yam as food is 2.7 percent per year during
1993-2020 (Table 9). This increase is driven
largely by the projected high population growth
rate and modest per capital income growth in West
Africa, where production of these crops, particu-
larly yam, will remain concentrated. Additional
factors that will contribute to the growth rate in-
clude increased purchases of fresh sweetpotato by
low-income, urban consumers as a cheap, starchy
staple (see, for example, Hall, Bockett, and Nahdy


1998); the recurrent use of sweetpotato as a crop
for food security and disaster relief; and, the mod-
erate expansion of the use of processed food com-
modities made from sweetpotato as market niches
emerge with population growth and urbanization
(Gatumbi and Hagenimana 1998). The projected
annual growth rate of potato as food (3.1 percent)
reflects increasing urbanization and changes in
tastes in the region and the relatively low level of
per capital demand for potato as food (2.7 kg per
year) in the base period (Tables 9 and 11).

Asia
Potato for food and sweetpotato for feed-the lat-
ter almost exclusively in China-dominate pro-
jected use patterns for R&T in Asia. Of the pro-









jected total increase in demand of 79 million mt of
R&T in Asia by 2020, some 48 million mt (61
percent) will be contributed by potato, another 22
million mt (28 percent) by sweetpotato, and the
remaining 9 million mt (11 percent) by cassava.
Annual growth rates in R&T food demand will be
driven largely by increased consumption of po-
tatoes (Table 9). Growing urbanization, rising in-
comes, and a desire by consumers to increasingly
diversify diets will help spur continued growth in
demand for processed potato products (Pacific-
Vision 1995a, 1995b; Scott 1994a; VIPDT 1999; Ye
and Rozelle 1993; Zhang et al. 1999). Estimated
growth rates of roughly 3.1 percent per year for
India and 2.2 percent for China conform with the
potato's status as one of the most preferred of the
complementary vegetables in Asia and, in some
areas in South Asia, as a seasonal staple. Continued
increases in potato demand are also consistent with
the effects on consumption of past increases in in-
come and estimated income elasticities of demand
(see, for example, Bouis and Scott 1996; Goletti
1993). Results from IMPACT suggest that per
capital food demand for potato in developing Asia
will increase from 11 kg in 1993 to 17 kg in 2020, on
average, and growth in food demand for potato is
projected at higher levels than growth for the major
cereals (Tables 9 and 10). However, even in those
countries with projected high growth rates in potato
demand, estimated per capital consumption levels in
2020 will still be a third or less of current consump-
tion levels in developed countries (Table 11).
Growth in sweetpotato use will be concen-
trated in China (which produces very little yam)
and, to a lesser extent, in Southeast Asia. Projected
growth in feed demand for sweetpotato in China
(1.8 percent per year) continues a trend already
well documented in field studies, which describe a
growing tendency of farmers and small-scale vil-
lage enterprises to use both roots and vines as ani-
mal feed, particularly in Sichuan province (see, for
example, Jiang, Rozelle, and Huang 1996; Peters
1997). Despite overall negative growth in total de-
mand for sweetpotato as food (-1.0 percent per
year), some local processing of sweetpotato into
food will likely continue (Fuglie et al. 1999; Jiang,

12 Lucier et al. (1991) report that over 52 percent of the U.S.
describes similar trends for Western Europe.


Rozelle, and Huang 1996; Zhang 1999), given that
these activities in many instances complement
sweetpotato processing for feed at the small-
entrepreneur level (Peters 1997). As for cassava,
feed use and processed products will increasingly
replace direct consumption as food. This pattern
has already become evident in Vietnam (Goletti
and Wheatley 1999; Howeler 1996), Thailand (Ti-
tapiwatanakun 1998), and Indonesia (Wheatley
and Scott 1994).

Latin America
In Latin America, the increase in total R&T de-
mand will be dominated by cassava (12.6 million
mt or about 60 percent of the total increase in R&T
demand) and potato (7.4 million mt or 35 percent
of the total increase). Demand growth for cassava
as feed (1.8 percent per year) is projected to be
stronger than growth for food (0.7 percent per
year) (Table 9). This slow growth in food demand
will follow recent trends: per capital food demand
declined from 29 kg in 1983 to 25 kg in 1993 and is
projected to decline further to 21 kg by 2020 (Table
11). Lynam (1989a, 1989b) and Ostertag and Her-
rera (1992) point to the increasing availability and
use of cassava substitutes such as wheat flour, es-
pecially in urban areas, a trend facilitated in recent
years by trade liberalization. Although new or im-
proved forms of processed cassava for human con-
sumption have been developed, their entry into the
market has been sufficient only to slow the decline
in per capital food demand for cassava. Feed use
has been and will continue to be more dynamic,
because cereal-feed-deficit countries (such as Co-
lombia; see, for example, Balcazar 1997) or re-
gions within countries (like northeast Brazil; see,
for example, Ospina and Wheatley 1992) exploit
cassava as a local substitute for maize.
Per capital food demand for potato stood at 22 kg
in 1993 and is projected to rise, albeit modestly, to
24 kg in 2020 (Table 11). Population and income
growth combined with high levels of urbanization,
will spur a greater intake of processed potatoes in
countries like Colombia (Rodriguez and Rodriguez
1992), following a trend already manifest in some
developed countries.12 Potato will not be used

potato crop is used for processed food products. Hesen (1991)








much for animal feed in the region: a mere 0.6
million mt out of a total use of 15.6 million mt in
2020; nor is this projected to change in the future
(Table 12). Per capital consumption levels for
sweetpotato and yam as food (roughly 3 kg in both
1993 and 2020) are low when compared to cassava
and potato (Table 11). The growth rate in food
demand for potato is highest of all R&T and sur-
passes those for the cereals (Tables 9 and 10).


Baseline Projections for Production, Area,
and Yield

According to the baseline scenario, production of
cassava in developing countries will grow at an
annual average rate of 1.7 percent during 1993-
2020 (Table 13) compared to the annual growth
rate of 1.8 percent achieved during 1983-96 (Table
5). Production growth for sweetpotato and yam is
projected at 1.3 percent per year during 1993-
2020, and for potato at 2.0 percent. Thus, growth in
potato production is expected to slow down consid-
erably from the rate of 4.1 percent per year during
1983-96.
Total R&T production in developing countries
will increase by some 230 million mt by 2020 ac-
cording to the baseline scenario (Table 13). More
than half of that increase (122 million mt) is
projected to occur in Sub-Saharan Africa and will
consist largely of cassava (81 million mt) and yam
(roughly 30 million mt).13 Over the next two
decades, the source of output growth will shift
away from expansion in area planted toward in-
creases in yields (66 percent of total output growth)
for total R&T (Tables 14 and 15). The projected
growth rate for cassava production in Sub-Saharan
Africa of 2.5 percent per year actually constitutes a
33 percent decline compared to the rate of increase
during 1983-96 (Table 5). The growth rate for
sweetpotato and yam production is also projected
to decline between 1993 and 2020 to 2.7 percent
annually (Table 13). Discrepancies between pro-
duction and use data for yam in Nigeria (Bricas and
Attaie 1998), agroclimatic constraints on further


expansion in area planted for yam (M. Bokanga,
personal communication, September 1998), and
slower development of high-yielding varieties
(Spencer and Badiane 1995) all support the more
conservative projected growth rate for sweetpotato
and yam.
Projected increases for R&T production in
Asia will be led by potato. In fact, about 48 million
mt out of the 68 million mt increase in potato pro-
duction in developing countries will come from
developing Asia. The bulk of this production in-
crease will be driven by improvements in yields
(Tables 14 and 15). With access to irrigation,
chemical inputs, and relatively abundant labor,
prospects for yield improvements are good. In
Bangladesh, India, and Pakistan, the introduction
of improved varieties and the expansion of cold
storage facilities have provided additional incen-
tives to growers (FAO 1995b). The liberalization
of the internal market for cold storage has brought
an expansion and modernization of India's storage
industry that appears capable of keeping up with
farm production of potatoes (Fuglie et al. 1997).
Some farmers in Bangladesh and India, in fact,
currently report yields double their respective na-
tional averages of 11 mt/ha and 16 mt/ha (see, for
example, Dahiya et al. 1997; Khatana et al. 1997).
Given that anywhere from 65 to 90 percent of the
potato harvest in South Asia is sold for cash (Bot-
tema et al. 1989; Dahiya and Sharma 1994; Fuglie
et al. 1997; Kokab and Smith 1989), growers have
a strong commercial incentive to improve
productivity.
Sweetpotato production in China is projected
to grow at 0.6 percent per year, due entirely to
increases in yields because area planted is pro-
jected to contract. As irrigation and improved road
networks penetrate into more isolated areas,
growers will switch from sweetpotato to produc-
tion of higher value-added crops unless new tech-
nology (for example improved varieties for use as
feed), institutional development (such as improve-
ments in small agro-enterprise management and
marketing), and appropriate policies in support of
these initiatives are implemented. Increases in pro-


13 The figure of 30 million mt is for yam alone and assumes that the division of total sweetpotato and yam production conforms to
the proportion in 1993.










Table 13-Production levels and annual growth rates of production for roots and tubers, 1993-
2020, baseline scenario

Cassava, Potato Sweetpotato and yamb All R&T
Production Growth Production Growth Production Growth Production Growth
Country/region 1993 2020 rate 1993 2020 rate 1993 2020 rate 1993 2020 rate
(million mt) (percent/ (million mt) (percent/ (million mt) (percent/ (million mt) (percent/
yr) yr) yr) yr)

China 4.8 6.5 1.18 42.5 63.4 1.49 108.5 128.3 0.62 155.8 198.3 0.90
Other East Asia na na na 2.4 3.2 1.13 0.8 1.1 1.18 3.2 4.3 1.14
India 5.8 7.0 0.71 16.3 37.3 3.10 1.2 1.2 0.12 23.3 45.5 2.51
Other South Asia 0.8 1.3 1.56 3.5 7.5 2.90 0.5 0.7 1.00 4.8 9.4 2.53
Southeast Asia 42.0 48.2 0.51 1.3 2.3 2.06 5.3 7.5 1.29 48.6 58.0 0.65
Latin America 30.3 41.7 1.19 12.6 20.0 1.72 2.6 3.5 1.19 45.5 65.3 1.35
WANA 0.1 0.2 1.60 13.0 22.4 2.02 0.1 0.2 1.35 13.3 22.8 2.01
Sub-Saharan Africa 87.8 168.6 2.45 2.6 5.9 3.01 36.0 74.2 2.71 126.4 248.7 2.54
Developing 172.4 274.7 1.74 94.3 162.0 2.02 155.9 217.8 1.25 422.6 654.5 1.63
Developed 0.4 0.4 0.68 191.0 207.4 0.31 2.1 2.1 0.12 193.4 210.0 0.31
World 172.7 275.1 1.74 285.3 369.4 0.96 158.0 220.0 1.23 616.0 864.5 1.26

Source: IMPACT Simulations, June 1998.
Notes: na signifies no recorded production. WANA is West Asia and North Africa. See Table 2 footnote for regional breakdown.
'These figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.




Table 14-Area planted and annual growth rates in area planted for roots and tubers, 1993-
2020, baseline scenario

Cassava" Potato Sweetpotato and yamb All R&T
Area Growth Area Growth Area Growth Area Growth
Country/region 1993 2020 rate 1993 2020 rate 1993 2020 rate 1993 2020 rate
(million ha) (percent/yr) (million ha) (percent/yr) (million ha) (percent/yr) (million ha) (percent/yr)

China 0.3 0.3 0.08 3.1 3.2 0.17 6.2 5.6 -0.39 9.6 9.1 -0.19
Other East Asia na na na 0.2 0.2 -0.41 . 0.1 0.30 0.2 0.2 -0.25
India 0.2 0.2 0.02 1.0 1.4 1.19 0.1 0.1 -0.16 1.4 1.8 0.90
Other South Asia 0.1 0.1 0.21 0.3 0.4 0.89 0.1 0.1 0.10 0.5 0.6 0.67
Southeast Asia 3.5 3.5 0.04 0.1 0.1 0.59 0.8 0.8 0.04 4.4 4.4 0.06
Latin America 2.7 2.7 -0.01 1.0 1.1 0.41 0.3 0.3 -0.23 4.0 4.1 0.07
WANA .. ... 0.12 0.7 0.8 0.55 .. ... 0.13 0.7 0.8 0.54
Sub-Saharan Africa 11.9 15.9 1.09 0.4 0.6 1.25 4.2 5.7 1.16 16.5 22.2 1.11
Developing 18.8 22.9 0.73 6.8 7.8 0.51 11.9 12.8 0.27 37.5 43.5 0.55
Developed . ... -0.04 11.6 11.0 -0.19 0.1 0.1 -0.09 11.7 11.1 -0.19
World 18.8 22.9 0.73 18.4 18.8 0.09 12.0 12.9 0.27 49.2 54.6 0.39

Source: IMPACT Simulations, June 1998.
Notes: Ellipses ( .) signify very small values; na signifies no recorded production. WANA is West Asia and North Africa. ha stands for
hectares. See Table 2 footnote for regional breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.









Table 15-Yield and annual growth rates in yields for roots and tubers, 1993-2020, baseline
scenario

Cassava' Potato Sweetpotato and yamh All R&T
Yield Growth Yield Growth Yield Growth Growth
Country/region 1993 2020 rate 1993 2020 rate 1993 2020 rate rate
(mt/ha) (percent/yr) (mt/ha) (percent/yr) (mt/ha) (percent/yr) (percent/yr)
China 15.1 20.2 1.10 13.7 19.6 1.32 17.5 23.1 1.02 1.09
Other East Asia na na na 13.2 20.0 1.55 15.9 20.2 0.89 1.40
India 23.6 28.4 0.69 15.6 25.9 1.89 8.4 9.1 0.29 1.60
Other South Asia 9.4 13.5 1.35 10.9 18.5 1.99 9.1 11.6 0.90 1.84
Southeast Asia 12.1 13.7 0.46 12.5 18.6 1.46 6.8 9.5 1.25 0.60
Latin America 11.3 15.6 1.21 12.9 18.3 1.30 7.6 11.2 1.43 1.27
WANA 32.5, 48.3, 1.48 18.6' 27.6, 1.46 17.8 24.7 1.23 1.46
Sub-Saharan Africa 7.4 10.6 1.34 6.5 10.4 1.74 8.6 12.9 1.54 1.41
Developing 9.2 12.0 1.00 13.8 20.7 1.50 13.1 17.0 0.97 1.08
Developed 12.1 14.7 0.72 16.5 18.9 0.50 17.9 18.9 0.22 0.49
World 9.2 12.0 1.00 15.5 19.6 0.87 13.2 17.0 0.96 0.87

Source: IMPACT Simulations, June 1998.
Notes: na signifies no recorded production. WANA is West Asia and North Africa; ha is hectares. See Table 2 footnote for regional breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.
,FAO indicates very high yields in Egypt in small areas.


duction of cassava will also largely come from in-
creases in yield.
In Latin America, cassava production will in-
crease at a moderate rate (1.2 percent per year)
during 1993-2020. This increase will be driven by
growth in yields, even as market demand for tradi-
tional cassava production remains weak, compared
to potential growth opportunities in alternative
markets. A similar scenario plays out in the case of
sweetpotato and yam, but from a much lower level
of output in the base period. For potato, annual
growth in yields and area planted, 1.3 and 0.4 per-
cent, respectively, combine to form the annual pro-
duction growth rate of 1.7 percent. Improvements
in the management of pests and diseases-late
blight, for example-will facilitate productivity
increases. Demand for both fresh and processed
potato products will induce farmers to adopt yield-
increasing technologies-a tendency supported by
falling tariffs (Scott, Basay, and Maldonado 1997).


Baseline Projections for World
Prices and International Trade
IMPACT projections indicate that global produc-
tion of R&T will grow fast enough for real world
prices of these commodities to fall between 1993
and 2020. According to the baseline scenario, aver-
age root and tuber prices are projected to decline
by 19 percent: potato prices by 14 percent; sweet-
potato and yam by 23 percent; and cassava and
other roots and tubers by 15 percent (Table 16).
This slow decline in prices will not be accom-
panied by a significant increase in aggregate world
trade of major R&T according to the baseline sce-
nario. In fact, as a share of developing country
R&T production, trade in R&T is projected to
decline over time.
Developing countries as a group will remain
net R&T exporters and developed countries net
importers. Total net exports are projected to de-










Table 16-Estimated world prices for roots and tubers and selected other foods, late 1980s, 1993,
and projected to 2020, baseline and HDP scenarios

Price (US$ per metric ton) Price changes (percent)
Commodity 1987/89" 1989/91b 1993c 2020Ad 2020B1 1993/2020Af 1993/2020Bg
Potato 180 110 160 137 145 -14 -9
Sweetpotato and yam -91h 70" 82h -23 -10
Sweetpotato' 82 76 80 56 69 -30 -14
Yam' 105 137 135 105 115 -22 -15
Cassava and other R&T 54i 46 48i -15 -11
Cassava 66 68 -
All roots and tubers 113 91 99 -19 -12
Wheat 144 144 148 133 133 -10 -10
Maize 104 124 126 123 123 -2 -2
Other grains 122' 105h 106" -14 -13
Barley 128 114 -
Sorghum 93 124
Millet 132 158 -
Milled rice 284 292 286 265 266 -7 -7
Soybean 265 234 263 234 235 -11 -11
Beef 2,023 1,768 1,771 -13 -12
Beef and buffalo meat 1,458" 2,226 -
Pigmeat 1,366 1,209 1,212 -11 -11
Sheep and goat meat 1,652" 2,099" 2,032" 1,842" 1,845" -9 -9
Poultry 1,300 1,157 1,159 -11 -11

Sources: 1987/89: TAC (1996, Annex II); 1989/91: Rao (1993); 1993, 2020A, 2020B: IMPACT Simulations, June 1998.
Note: signifies not applicable/available.
aPrices used in 1992 analysis (TAC 1996, Annex II, Table 9).
bPrices used by Rao (1993).
cBase period prices used in present study.
dBaseline scenario.
"High demand and production growth scenario.
f'993/baseline scenario percent change in price, rounded to nearest percent.
91993/high demand and production growth scenario percent change in price, rounded to nearest percent.
hComposite price.
'Disaggregation of sweetpotato and yam outside of IMPACT, but based on historical trends and IMPACT simulations.
jComposite price: cassava and other roots and tubers such as taro.


crease slightly from 19.9 million mt in 1993 to 19.4
million mt in 2020 under the baseline scenario. The
slight decrease in net cassava exports largely re-
flects the current declining trend in cassava ex-
ports from Southeast Asia to the European Union
and the almost offsetting exports of cassava prod-
ucts to other regions (Goletti and Wheatley 1999;
Titapiwatanakun 1998). Potato imports by the
developing world will show the biggest absolute
increase in R&T trade, rising by nearly a third,
from 0.9 million mt in 1993 to 1.2 million mt in
2020. The biggest increases in potato imports are
projected for Southeast Asia and Sub-Saharan
Africa (0.3 million mt each), the former region will
import mostly processed food products and the lat-
ter a mix of food products and seed. China and
India are expected to become net exporters on the


order of 100,000 mt per year, but in absolute per-
centage terms this will represent less than one half
of one percent of their projected domestic produc-
tion in 2020.
Net exports of sweetpotato and yam by de-
veloping countries are projected to increase by 40
percent or 162,000 mt, a tiny fraction of total pro-
duction in these countries. It should be noted that
trade among developing countries causes their ag-
gregate net exports of sweetpotato and yam (and
other commodities) to be lower than the exports of
some individual developing countries. China, for
example, is expected to export 1.4 million mt of
sweetpotato by 2020.
Net exports of cassava and other roots and tu-
bers by developing countries are projected to
decrease slightly, by 290,000 mt or 1.4 percent,









Table 17-Total value of selected IMPACT commodities for developing countries in 1993 and
projected to 2020, baseline and HDP scenarios

1993 2020A 2020B
Percent Percent of Percent Percent of Percent Percent of
Commodity Value, of total subtotal Value" of total subtotal Values of total subtotal
(US$ million) (US$ million) (US$ million)
Potato 15,094 4.1 6.6 22,193 3.9 7.0 28,131 4.9 8.6
Sweetpotato and yam 14,185 3.9 6.2 15,248 2.7 4.8 18,879 3.3 5.8
Yam aloneb 4,209 1.1 1.8 6,642 1.2 2.1 7,693 1.4 2.4
Cassava and other 9,307 2.5 4.0 12,636 2.2 4.0 13,937 2.4 4.2
R&T
All R&T 38,586 10.5 16.7 50,076 8.8 15.8 60,946 10.5 18.6
All cereals 176,622 48.0 76.7 241,253 42.6 76.3 242,195 41.9 73.8
Soybeans 15,176 4.1 6.6 24,839 4.4 7.9 24,958 4.3 7.6
Subtotal 230,384 316,168 328,099
All meat 137,752 37.4 249,862 44.1 250,467 43.3
Total 368,136 100.0 100.0 566,030 100.0 100.0 578,567 100.0 100.0

Source: IMPACT Simulations, June 1998.
Note: 2020A: baseline scenario; 2020B: high demand and production growth scenario (HDP).
aValue is calculated using production data (1993: IMPACT base year values; 2020A: IMPACT baseline scenario; 2020B: IMPACT HDP scenario)
multiplied by price (see Table 16).
bDisaggregation for yam outside of IMPACT, but based on historical trends and IMPACT simulations.


from 1993 levels. This decrease will come about
largely because India will switch from being a
small net exporter to a small net importer. The
opposite trend is projected for China. Latin Amer-
ica will see imports of cassava and other roots and
tubers rise to 1.2 million mt by 2020. The major
beneficiaries of a more diversified world market
for cassava and other roots and tubers will be
Southeast Asia and Sub-Saharan Africa.
An important development for the international
R&T market is the projected increase in total use of
R&T in some developing country regions at rates
higher than the projected production growth rate in
these regions. This trend will benefit traditional net
potato exporters such as Canada, the United States,
and the Netherlands. Eastern Europe will become a
net exporter of potato at 411,000 mt, while Japan
will increase its imports of all roots and tubers by 23
percent, from 1.5 million mt in 1993 to 1.9 million
mt by 2020, under the baseline scenario.


The Value of R&T Crop Production
in the Baseline Scenario

Policymakers and researchers are also interested in
the projected value of root and tuber crops in the
decades ahead. The projections of the rate of


growth of supply, demand, and world market
prices for R&T permit the estimation of the future
value of root and tuber crops alone and in relation
with the estimated values for other major food
commodities produced in developing countries.
The IMPACT baseline scenario shows that the
share of R&T in the total value of the major food
commodities will decrease from 10.5 percent to 8.8
percent between 1993 and 2020, and R&T's share
in the major food and feed crops will shrink from
16.7 to 15.8 percent (Table 17). The bulk of the
change in the projected future values of R&T is
due to the decline in the estimated world prices for
cassava and sweetpotato and the relatively strong
projected prices for maize and rice in 2020.
In summary, the projected baseline growth
rates for supply and demand of R&T vary accord-
ing to crop, region, and use. Furthermore, in sev-
eral instances the projected growth rates in supply
are rather conservative when compared with recent
historical trends. This is most notably the case for
potato. Nevertheless, even the baseline estimates
indicate that the role of R&T in the food systems of
developing countries will not deteriorate signifi-
cantly over the next two decades.
The next chapter presents the outcome of an
alternative scenario, based on more optimistic
growth prospects for R&T.















5. High Demand and Production Growth Scenario


Past projections for some R&T in developing
countries-most notably potato-have often
underestimated actual increases in demand and
supply (see Scott 1983a). These low projections
have resulted from income elasticities of demand
based on data from industrialized countries and the
assumption that consumers in Africa, Asia, and
Latin America will behave in a fashion similar to
their developed-world counterparts (Horton 1981).
In many cases, they have not. Estimates of actual
income elasticities of demand for specific roots
and tubers in developing countries are relatively
few and far between, which partly accounts for the
need to "extrapolate" from the experience of indus-
trialized countries. Furthermore, the estimates that
do exist are for particular time periods, often for a
subsection of the population (for example, rural
households), and invariably for fresh products.
Moreover, trends beginning in some cases as early
as the 1960s indicate that the structure of demand
and supply for R&T in the developing world is
undergoing fundamental shifts (Scott and Suarez
1992). As consumption of processed products in-
creases, the small number of estimates for fresh
roots and tubers becomes less and less appropriate.
If the continued rapid increase in potato demand,
for example, particularly in Asia and parts of
WANA, is sustained for several more years, the
upward shift in income elasticities may be even
greater than accounted for in the baseline scenario.
These upward shifts make it necessary to ex-
plore a high demand and production growth (HDP)
scenario that incorporates a more sustained in-
crease in supply and demand for those developing
countries and regions currently experiencing rapid
growth in the R&T sector. This chapter examines
the impact of this faster supply and demand growth
on the regional and global supply/demand situation
in 2020.
On the demand side, the HDP scenario incor-


porates food demand elasticities for potato that are
0.20 higher than in the baseline scenario for Egypt,
India, and Turkey and 0.10 higher for China (se-
lected baseline elasticities are given in the Appen-
dix, Table 26). For sweetpotato feed in China the
HDP scenario incorporates a higher ratio of sweet-
potato per unit of livestock output. And for cassava
and other roots and tubers, the HDP scenario uses
demand elasticities that are 0.35 higher than in the
baseline for Nigeria and central-west Sub-Saharan
Africa, and 0.20 higher for the rest of Sub-Saharan
Africa. On the supply side, area growth rates for
potato are assumed to increase by 0.50 percent per
year more than in the baseline scenario for China,
Egypt, and India, and by 0.20 percent per year
more for Turkey. Yield growth in China is assumed
to be 0.70 percent per year above the baseline rate
of growth, reflecting more rapid technological
change. For cassava and other roots and tubers,
area growth for Sub-Saharan Africa is assumed to
increase by an additional 0.30 percent per year. The
HDP scenario thus incorporates the assumption
that the accelerating growth in supply and demand
for R&T seen in the early 1990s tapers off more
gradually than in the baseline scenario.


HDP Projections for R&T Use
According to the HDP scenario, total use of R&T
in developing countries is projected to increase by
74 percent between 1993 and 2020, or an addi-
tional 64 million mt compared to the baseline sce-
nario (Tables 8 and 18). More than half of the addi-
tional increase (35 million mt) is attributable to
faster growth in use of potato, with the remainder
roughly evenly divided between cassava and other
roots and tubers (16 million mt) and sweetpotato
and yam (13 million mt). Average annual increases
in total use of potato during 1993-2020 are con-
siderable: 2.8 percent versus 2.0 percent in the










Table 18-Total use of roots and tubers in 1993, and projections to 2020, HDP scenario

Cassava, Potato Sweetpotato and yamb All R&T
Country/region 1993 2020 1993 2020 1993 2020 1993 2020
(million metric tons)

China 5.1 7.5 42.7 89.2 108.0 136.8 155.9 233.6
Other East Asia 1.8 1.9 2.6 3.6 0.9 1.1 5.4 6.7
India 5.7 7.4 16.3 44.6 1.2 1.2 23.2 53.3
Other South Asia 0.9 1.4 3.5 7.5 0.5 0.7 4.9 9.5
Southeast Asia 18.9 25.3 1.4 2.7 5.3 7.7 25.6 35.7
Latin America 30.3 43.2 13.0 20.6 2.5 3.5 45.8 67.3
WANA 0.9 1.0 12.8 23.9 0.1 0.2 13.8 25.1
Sub-Saharan Africa 87.7 181.2 2.8 6.3 36.0 77.4 126.4 265.0
Developing 152.0 270.2 95.2 198.6 155.5 229.9 402.7 698.7
Developed 20.7 20.6 190.1 204.8 2.5 2.6 213.3 228.0
World 172.7 290.8 285.3 403.5 158.0 232.5 616.0 926.7

Source: IMPACT Simulations, June 1998.
Notes: WANA is West Asia and North Africa. See Table 2 footnote for regional breakdown.
'These figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.


Table 19-Projected annual growth rates in food, feed, and total use of roots and tubers, 1993-
2020, HDP scenario

Cassava, Potato Sweetpotato and yamb All R&T
Country/region Food Feed Total Food Feed Total Food Feed Total Food Feed Total
(percent per year)

China 0.00 2.77 1.40 2.78 2.74 2.76 -1.03 2.24 0.88 0.22 2.35 1.51
Other East Asia 0.87 0.21 0.11 1.30 1.31 1.26 0.74 1.23 0.74 1.17 1.12 0.81
India 1.01 na 1.01 3.80 na 3.80 0.12 na 0.12 2.99 na 3.13
Other South Asia 2.10 . 1.69 2.90 na 2.89 1.08 . 0.95 2.57 . 2.53
Southeast Asia 1.11 0.91 1.09 2.40 2.38 2.55 1.28 2.25 1.35 1.23 1.40 1.23
Latin America 0.78 1.73 1.33 1.71 1.58 1.71 1.04 1.80 1.24 1.23 1.73 1.44
WANA 1.51 0.42 0.73 2.33 1.56 2.33 1.45 na 1.44 2.31 0.59 2.24
Sub-Saharan Africa 2.80 1.53 2.73 3.15 1.78 3.14 2.93 1.72 2.87 2.83 1.55 2.78
Developing 2.24 1.72 2.15 2.75 2.66 2.76 0.50 2.23 1.46 1.88 2.17 2.06
Developed -0.52 0.03 -0.03 0.34 0.20 0.28 0.22 0.37 0.23 0.33 0.14 0.25
World 2.23 1.02 1.95 1.39 1.01 1.29 0.49 2.21 1.44 1.49 1.49 1.52

Source: IMPACT Simulations, June 1998.
Notes: Ellipses (. .) signify very small values; na signifies no recorded use. WANA is West Asia and North Africa. Total use includes food,
feed, and other uses. See Table 2 footnote for regional breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.


baseline scenario. The HDP growth rate for use is
more modest for sweetpotato and yam: 1.5 percent
per year versus 1.3 percent. Annual growth in the
use of cassava and other roots and tubers is esti-
mated at 2.2 percent, versus 1.9 percent in the base-


line scenario (Tables 9 and 19). For cassava and
potato, these HDP growth rates are still below re-
cent historical trends.
Asian countries, particularly China, will expe-
rience the bulk of the additional increase in food









Table 20-Per capital use of roots and tubers as food in 1993, and projections to 2020, HDP
scenario

Cassava, Potato Sweetpotato and yamb All R&T
Country/region 1993 2020 1993 2020 1993 2020 1993 2020
(kilograms per year)
China 2 2 14 23 45 28 61 53
Other East Asia 1 I 18 21 6 5 24 27
India 6 6 13 25 1 1 20 32
Other South Asia 3 3 9 11 2 1 13 15
Southeast Asia 32 31 3 3 10 10 45 44
Latin America 25 22 22 24 3 3 50 49
WANA 1 1 28 31 ... .. 29 31
Sub-Saharan Africa 131 135 3 3 36 38 169 176
Developing 24 30 13 18 19 15 56 62
Developed ... ... 75 76 1 1 77 77
World 19 24 27 28 15 12 61 65

Source: IMPACT Simulations, June 1998.
Notes: Ellipses ( .) signify very small values. WANA is West Asia and North Africa. See Table 2 footnote for regional breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.


and feed demand for potato projected in the HDP
scenario. In comparison to the baseline scenario,
per capital consumption of potato in 2020 will in-
crease by 3.3 kg to 23 kg in China, by 4.2 kg to 25
kg in India, and by 2.5 kg to 31 kg in WANA
(Tables 11 and 20). For South Asia and WANA,
where some estimates of expenditure elasticities
for potato have been estimated using household
survey (Bouis and Scott 1996; Goletti 1993) and
time-series data (Fuglie 1994), the HDP increases
reflect the available empirical evidence. A com-
bination of field surveys (Ye and Rozelle 1993),
marketing and demand studies (Pacific-Vision
1995b; Zhang et al. 1999), and commercial updates
(VIPDT 1999) suggest that the higher R&T
projections for China in effect do reflect recent
trends. In short, a historical perspective shows that
the additional per capital food demand for potato
projected for Asia by the HDP scenario is a plausi-
ble alternative to the baseline.
The HDP scenario also indicates a substantial
increase in the use of sweetpotato as animal feed in
China: 2.2 percent per year during 1993-2020
compared to 1.8 percent per year in the baseline
scenario (Tables 9 and 19). The projected slower
decline in the world market price of maize over the
next 20 years (when compared to Rosegrant,


Agcaoili-Sombilla, and Perez 1995, 26) might
make sweetpotato a more competitive feed source.
Genetic improvements in sweetpotato varieties and
improvements in feed preparation at the household
and village levels could further boost the use of
sweetpotato as feed.
Sub-Saharan Africa will account for nearly all
of the additional demand for cassava under the
HDP scenario: 13 million mt of the projected total
increase of 16 million mt. As a result, per capital
food demand for cassava in Sub-Saharan Africa
will increase from 131 kg in 1993 to 135 kg in 2020
under the HDP scenario, instead of declining to
124 kg as projected under the baseline scenario
(Tables 11 and 20). Total use of sweetpotato and
yam in Sub-Saharan Africa in 2020 will increase
by 3 million mt compared to the baseline scenario
(Tables 8 and 18), and per capital food demand will
increase from 36 kg in the baseline scenario to 38
kg under the HDP scenario (Tables 11 and 20).



HDP Projections for Production,
Area, and Yield

Annual average growth rates for production of
R&T in developing countries during 1993-2020










Table 21-Production levels and annual growth rates of production for roots and tubers, 1993-
2020, HDP scenario

Cassava, Potato Sweetpotato and yamb All R&T
Production Growth Production Growth Production Growth Production Growth
Country/region 1993 2020 rate 1993 2020 rate 1993 2020 rate 1993 2020 rate
(million mt) (percent/yr) (million mt) (percent/yr) (million mt) (percent/yr) (million mt) (percent/yr)

China 4.8 6.6 1.21 42.5 87.8 2.72 108.5 136.0 0.84 155.8 230.4 1.46
Other East Asia na na na 2.4 3.3 1.18 0.8 1.1 1.36 3.2 4.4 1.22
India 5.8 7.1 0.76 16.3 43.3 3.67 1.2 1.3 0.44 23.3 51.7 3.00
Other South Asia 0.8 1.3 1.61 3.5 7.7 2.98 0.5 0.7 1.27 4.8 9.7 2.62
Southeast Asia 42.0 48.2 0.51 1.3 2.3 2.08 5.3 8.0 1.49 48.6 58.5 0.68
Latin America 30.3 42.0 1.22 12.6 20.2 1.76 2.6 3.7 1.41 45.5 65.9 1.39
WANA 0.1 0.2 1.61 13.0 23.4 2.21 0.1 0.2 1.55 13.3 23.9 2.19
Sub-Saharan Africa 87.8 183.8 2.77 2.6 6.0 3.06 36.0 78.0 2.90 126.4 267.7 2.82
Developing 172.4 290.3 1.95 94.3 194.0 2.71 155.9 230.2 1.45 422.6 714.6 1.96
Developed 0.4 0.4 0.67 191.0 209.5 0.34 2.1 2.3 0.36 193.4 212.2 0.34
World 172.7 290.8 1.95 285.3 403.5 1.29 158.0 232.5 1.44 616.0 926.7 1.52

Source: IMPACT Simulations, June 1998.
Notes: na signifies not applicable. WANA is West Asia and North Africa. See Table 2 footnote for regional breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.








Table 22-Area planted and annual growth rates in area planted for roots and tubers, 1993-
2020, HDP scenario

Cassava, Potato Sweetpotato and yamb All R&T
Area Growth Area Growth Area Growth Area Growth
Country/region 1993 2020 rate 1993 2020 rate 1993 2020 rate 1993 2020 rate
(million ha) (percent/yr) (million ha) (percent/yr) (million ha) (percent/yr) (million ha) (percent/yr)

China 0.3 0.3 0.09 3.1 3.7 0.67 6.2 5.6 -0.36 9.6 9.6 0.02
Other East Asia na na na 0.2 0.2 -0.39 . 0.1 0.44 0.2 0.2 -0.20
India 0.2 0.2 0.03 1.0 1.6 1.71 0.1 0.1 -0.04 1.4 2.0 1.31
Other South Asia 0.1 0.1 0.22 0.3 0.4 0.92 0.1 0.1 0.22 0.5 0.6 0.71
Southeast Asia 3.5 3.5 0.03 0.1 0.1 0.58 0.8 0.8 0.15 4.4 4.4 0.06
Latin America 2.7 2.7 -0.01 1.0 1.1 0.43 0.3 0.3 -0.10 4.0 4.1 0.09
WANA ... 0.12 0.7 0.8 0.67 .. ... 0.22 0.7 0.8 0.66
Sub-Saharan Africa 11.9 17.2 1.39 0.4 0.6 1.27 4.2 5.9 1.26 16.5 23.7 1.36
Developing 18.8 24.2 0.94 6.8 8.6 0.84 11.9 13.1 0.35 37.5 45.8 0.74
Developed -0.07 11.6 11.0 -0.18 0.1 0.1 0.06 11.7 11.2 -0.17
World 18.8 24.2 0.94 18.4 19.6 0.23 12.0 13.2 0.34 49.2 57.0 0.54

Source: IMPACT Simulations, June 1998.
Notes: Ellipses ( ...) signify very small values; na signifies no recorded production. WANA is West Asia and North Africa; ha stands for
hectares. See Table 2 footnote for regional breakdown.
-These figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.









Table 23-Yields and annual growth rates in yield for roots and tubers, 1993-2020, HDP
scenario

Cassava, Potato Sweetpotato and yamb All R&T
Yield Growth Yield Growth Yield Growth Growth
Country/region 1993 2020 rate 1993 2020 rate 1993 2020 rate rate
(mt/ha) (percent/yr) (mt/ha) (percent/yr) (mt/ha) (percent/yr) (percent/yr)
China 15.1 20.3 1.12 13.7 23.7 2.04 17.5 24.2 1.20 1.44
Other East Asia na na na 13.2 20.2 1.57 15.9 20.4 0.92 1.43
India 23.6 28.7 0.73 15.6 26.3 1.94 8.4 9.6 0.48 1.66
Other South Asia 9.4 13.7 1.39 10.9 18.8 2.05 9.1 12.1 1.05 1.89
Southeast Asia 12.1 13.8 0.49 12.5 18.7 1.49 6.8 9.7 1.34 0.62
Latin America 11.3 15.7 1.23 12.9 18.5 1.33 7.6 11.4 1.51 1.29
WANA 32.5c 48.6c 1.50 18.6, 28.1' 1.53 17.8 25.4 1.33 1.53
Sub-Saharan Africa 7.4 10.7 1.36 6.5 10.5 1.77 8.6 13.2 1.62 1.44
Developing 9.2 12.0 1.00 13.8 22.7 1.85 13.1 17.6 1.10 1.21
Developed 12.1 14.8 0.74 16.5 19.0 0.52 17.9 19.4 0.30 0.52
World 9.2 12.0 1.00 15.5 20.6 1.06 13.2 17.6 1.09 0.98

Source: IMPACT Simulations, June 1998.
Notes: na signifies no recorded production. WANA is West Asia and North Africa. ha stands for hectares. See Table 2 footnote for regional
breakdown.
aThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the
total.
bEstimates for Sub-Saharan Africa are largely for yam, given the roughly 80/20 distribution in favor of yam production in the region, according to
FAO 1999a. Estimates for Asia and WANA are for sweetpotato only, and in Latin America estimates are 68/32 for sweetpotato versus yam.
IFAO indicates very high yields in Egypt on small areas.


are higher for all commodities under the HDP sce-
nario compared to the baseline (Tables 13 and 21).
For developing counties as a whole, total root
and tuber production under the HDP scenario is
projected to expand at 2.0 percent per year between
1993 and 2020. This figure is about 20 percent
higher than the annual growth rate of 1.6 percent
projected by FAO for the period 1988/90-2010
(Alexandratos 1995), but just below the recent his-
torical growth rate of 2.1 percent (Table 5).
According to the HDP scenario, the largest in-
crease in production of R&T in Asia will be for
potato and sweetpotato. Almost 80 percent of the
additional potato output of 32 million mt in de-
veloping countries, compared to the baseline sce-
nario, will be harvested in China (24 million mt)
and 19 percent in India (6 million mt) (Tables 13
and 21). The difference between HDP and baseline
production in China and India results from addi-
tional area planted and a larger increase in average
yields (Tables 14 and 22 and 15 and 23). As robust
as the potato area and production growth rates for
China and India appear, the HDP projections con-
stitute a slowdown in recent trends. Chinese pro-


duction, for example, drops from an annual growth
rate of 4.6 percent per year for 1983-96 (Table 5)
to 2.7 percent per year for 1993-2020 (Table 21).
The additional production of sweetpotato in
China of almost 8 million mt by 2020 under the
HDP scenario will account for nearly all of the
increase in Asia and for more than 60 percent of the
increase for all developing countries (Tables 13
and 21). This added output will be used largely for
animal feed. The higher production of sweetpotato
and yam will result mostly from increases in yield.
Area planted with sweetpotato and yam is pro-
jected to decline by 0.6 million hectares between
1993 and 2020 (Table 22). The higher yields for
sweetpotato in China (Table 23) can well material-
ize through greater use of improved germplasm
bred specifically for use as feed. China has con-
siderable potential for yield improvement because
it has had limited access to improved germplasm
for sweetpotato. Davis and Ryan (1987) estimated
that benefits from investments in sweetpotato re-
search in China would outweigh those for any of
the other 22 commodities they studied, except for
rice, wheat, and potato. The relatively higher feed








demand projected for sweetpotato under the HDP
scenario could accelerate investments in this crop
as growers seek out yield-increasing technology
and cost-reducing procurement, processing, and
feeding practices linked to specific postharvest
uses, such as pork production.
Sub-Saharan Africa will account for prac-
tically all the additional output of cassava. The 15
million mt difference between HDP and baseline
cassava production in Sub-Saharan Africa in 2020
will come from an additional 1.3 million hectares
under cultivation and a slight increase in yield
(Tables 14 and 22 and 15 and 23). Annual growth
in area will increase to 1.4 percent from 1.1 percent
under the baseline scenario.
It might be argued that the projected increase
in area planted to R&T will be limited by disap-
pearing agricultural frontiers and limits to the crop-
ping index (the ratio of crop area harvested to ara-
ble land). This would affect Sub-Saharan Africa
the most because some 7 million of the estimated 8
million hectare expansion of R&T area in develop-
ing countries is projected to take place in that re-
gion during 1993-2020. However, the overall
projected increase in area planted to R&T is insig-
nificant when compared to the 3.3 billion hectares
of potential land area available for crop production,
not to mention possible further intensification of
the cropping index (Rosegrant et al. 1997).


HDP Projections for World Prices
and International Trade
The faster growth scenario for R&T means that
R&T prices will decline more slowly to 2020 (Ta-
ble 16). On average, world prices for R&T will fall
by 12 percent under the HDP scenario, instead of
by 19 percent. The more modest price declines
reflect the stronger demand, particularly for sweet-
potato as feed in China. The HDP scenario has only
minor effects on the commodity composition and
volume of R&T trade.
The level of net exports of cassava and other
roots and tubers by developing countries increases


only slightly (by 81,000 mt), but the mix of impor-
ters and exporters changes. China switches from
being a net exporter to a net importer. Net exports
of cassava by Sub-Saharan Africa rise fivefold to
2.6 million mt.14 China's altered trade position
suggests that feed demand simply outpaces feed
supply given the prices generated by the HDP sce-
nario. In contrast, the more abundant supply of
cassava and other roots and tubers in Sub-Saharan
Africa facilitates exports from that region. A simi-
lar situation arises in the case of sweetpotato and
yam for China and Sub-Saharan Africa.
Net imports of potatoes by developing coun-
tries jump from 1.2 million mt under the baseline
scenario to 4.6 million mt under the HDP scenario
as China, India, and WANA switch from being net
exporters to net importers. Strong demand in de-
veloping countries under the HDP scenario gener-
ates greater imports of processed potato products
from Europe and North America. Overall, how-
ever, international trade will remain a minor share
of developing-country production of R&T and will
continue to be highly skewed toward cassava and
Southeast Asia under the HDP scenario.15


The Value of R&T Production
Under the HDP Scenario
The more robust demand and production growth
rates and the resulting higher prices under the HDP
scenario lead to a larger value for R&T production
in 2020. Under the HDP scenario, the share of
R&T in the total value of the major food crops plus
soybean and selected meat commodities remains at
10.5 percent, the share R&T contributed in 1993.
R&T's share in the value of crop production (that is
cereals, soybean, and R&T), however, increases
from 16.7 percent in 1993 to 18.6 percent in 2020
(Table 17). In terms of individual commodities,
potato's share in the total value of major foods rises
to 4.9 percent in 2020 from 4.1 percent in 1993.
Yam also increases its value share, but sweetpotato
declines in relative importance. Cassava and other
R&T slip in value, but by an insignificant amount


14 These absolute figures for net exports should be interpreted with caution given that they represent only a small percentage of
total output and use.
15 These trade estimates must be interpreted with caution given uncertainties about the accuracy of the published trade data (see
for example, Scott, Basay, and Maldonado 1997).









(Table 17). The bulk of the increase in R&T value
is located in Asia and Sub-Saharan Africa. The
value of R&T in Latin America declines in relative
importance across all commodities.
To summarize, although the HDP growth rates
for supply and demand of R&T are notably higher
than those in the baseline scenario, they reflect
recent accelerating trends in output and use, partic-
ularly in the cases of potato and yam.
Both scenarios project that the largest absolute
increase in R&T production by 2020 will take
place in Sub-Saharan Africa. China will account
for the bulk of the projected sweetpotato output.
China and India together will harvest between 62
percent (baseline) and 68 percent (HDP) of the
future supply of potatoes in developing countries.
Cassava production will expand the most-by 80-
100 million mt-in Sub-Saharan Africa. The pro-
jected expansion in area planted falls well within


the range available for crop cultivation, even after
taking into account area expansion for the other
major food crops.
Increases in R&T production will be driven by
demand for food in the cases of potato (both fresh
and processed) and yam. The demand for feed and
starch (in both food and industrial products) will be
met mostly by cassava and sweetpotato.
In the baseline scenario R&T will decline in
economic importance vis-a-vis the other major
food commodities over the next two decades,
though the decline relative to other food and feed
crops will be marginal. Under the HDP scenario,
the economic importance of R&T will either re-
main unchanged or, in the case of food and feed
crops, increase slightly. This latter finding con-
trasts with earlier projections that estimated signi-
cant declines in the importance of R&T (see, for
example, Alexandratos 1995; McCalla 1998).















6. Roots, Tubers, and the Environment


Prospects for continued increases in supply and
demand of R&T in developing countries have
raised concerns about the impact of their output
and use on the environment (see for example
Bardhan Roy et al. 1999; Crissman, Antle, and
Capalbo 1998; Goletti, Rich, and Wheatley 1999;
Howeler 1996). Cultivation of some R&T can help
slow soil erosion (see, for example, Oro 1991)
and new technologies may systematically increase
the level of genetic diversity under cultivation
(Upadhya et al. 1995). Technological progress, in-
stitutional innovations, and changes in policy can
and should be geared toward sustaining the re-
source base while increasing supply and demand.
This chapter briefly examines the environmen-
tal problems and potential associated with R&T.
Not intended as an exhaustive review of the litera-
ture, it identifies instead a cross-section of issues,
technologies under development, and associated
policies that can help ensure that increased R&T
production and use are environmentally sustain-
able. It should be noted that many of these prob-
lems or potential opportunities are by no means
exclusive to R&T.

Pesticides
Improper use of pesticides is a major environmen-
tal concern in potato cultivation. Pesticide use is far
less frequent and less potent with the other R&T.
The vast majority of resource-poor farmers who
cultivate cassava, sweetpotato, and yam have lim-
ited access to these products or cannot justify their
use given other demands on their limited cash
resources.
The most widespread and intensive use of
pesticides in developing countries is for controlling


late blight potato disease caused by phytophora
infestans. Farmers in some countries spray their
potato fields up to 15 times during a single grow-
ing season of 4 to 6 months in order to combat
this disease (Hijmans, Forbes, and Walker 1999).
Pesticide sales to potato producers in develop-
ing countries exceeded an estimated US$150 mil-
lion in 1991 (Oerke et al. 1995, 459). Pesticides
can also constitute a formidable health risk to farm
families and farm workers engaged in potato pro-
duction (Antle et al. 1998).
With the emergence of new, more virulent
strains of phytophora, the fear now is that late
blight and other pests and diseases will develop
resistance to the current array of pesticides. Conse-
quently, even heavier applications of chemicals
may end up providing even less protection against
plant damage, resulting in greater loss of food
(Erselius et al. 1999) and potentially greater harm
to human life (see, for example, Cole et al. 1999).16
Pesticides are also used against other potato
diseases and pests, such as insects. In spite of the
extremely high cost and potentially harmful conse-
quences of many of these chemicals, users con-
tinue to apply them because the risk and value of
crop losses are so high.
Concerns with environmental and health im-
pacts, combined with a growing appreciation of the
damage different pests and pathogens can do to
R&T, have led to the development and diffusion of
an array of alternative technologies. These include
disease-resistant varieties (Landeo et al. 1997),
pheromone traps (Alvarez et al. 1996), targeted use
of natural predators, and integrated crop manage-
ment techniques that combine reduced applications
of pesticides with improved cultivars and natural
barriers to pest infestation. Increased production


16 The estimated value of the loss of production in developing countries in 1997 due to late blight was US$2.5 billion (CIP 1998,
16-17).








and use of potatoes may well boost the total cost of
pest damage and the potential for adverse environ-
mental effects from improper use of pesticides, but
it will also increase the rewards associated with
more environmentally friendly agricultural and
postharvest practices.
Moreover, as Lee and Espinoza (1998) note in
their case study of Colombia and Ecuador, changes
in government policy, including greater market de-
termination of exchange rates, liberalized trading
regimes, elimination of government-administered
pricing systems for imports such as pesticides,
decrease in agricultural credit subsidies, and other
domestic sectoral reforms can help discourage in-
efficient use of pesticides. Policies that facilitate
farmer education and training programs as well as
increase governments' ability to establish, monitor,
and enforce appropriate regulations regarding
proper pesticide use are also needed.


Fertilizers
Excessive, deficient, or incorrectly proportioned
doses of chemical fertilizer represent various forms
of environmental risk. For example, too much fer-
tilizer may result in residues contaminating local
water supplies, including ponds otherwise avail-
able for fish farming. Conversely, too little fertil-
izer can result in low yields, declining soil fertility,
and, eventually, soil exhaustion. The nonavail-
ability or high price of fertilizer is more of a prob-
lem in Sub-Saharan Africa than in Asia or Latin
America (Scott 1988a; Tardif-Douglin 1991). Afri-
can farmers on average use less than a tenth of the
fertilizer per hectare that Asian farmers use.
Inefficient use of fertilizer has been identified
in diagnostic studies of potato production in a num-
ber of countries, including Bangladesh (Scott
1988a), Mexico (Biarnms and Duchenne 1995), and
Pakistan (Iqbal et al. 1995), and documented in
farm surveys for cassava in Thailand (Howeler
1996). Improperly balanced fertilizer applications
are of special concern in the case of cassava be-
cause so much of area planted is already produced
on highly acid and infertile soils (Howeler, Oates,
and Costa Allem 1999). The environmental and
economic costs of nitrogen fertilizer use on R&T in
developing countries have only recently become
the focus of attention for researchers (Bowen et al.


1999). But based largely on an analysis and extrap-
olation of recent trends in nitrogen use in
developed countries, Frink, Waggoner, and Aus-
ubel (1999) suggest that farmers in developing
countries, for example, China, are gradually ensur-
ing that fertilizer applications conform to the
proper proportions of nitrogen, phosphorus, and
potassium.


Soils
Soil disturbance is a problem common to all R&T
production (TAC 1997b). Regular working of the
soil can degrade soils by decreasing soil carbon
levels and fostering water and wind erosion. The
effects can become accentuated as fallow periods
decline and cropping intensity increases.
The degree of potential soil degradation is
higher on hillside or highland fields where severe
slopes can intensify the erosive effects of rainfall
(or irrigation) and wind. Because some R&T are
frequently cultivated on such fields-and cassava
is grown on more marginal soils to begin with-
the soil erosion associated with these crops can be
substantial, though the association is not inevitable
(see, for example, Howeler 1996; Howeler, Oates,
and Costa Allem 1999). Although potato produc-
tion in hilly areas can exacerbate erosion problems,
some mid-elevation and highland cultivation of po-
tatoes, particularly in Asia, is carried out in ter-
raced fields otherwise used for irrigated rice. The
latter form of potato cultivation causes less ero-
sion. The case of sweetpotato is more complex,
particularly for those varieties that produce abun-
dant, rapidly growing vines (L6on-Velarde et al.
1997). This foliage can provide a quick crop cover
over fragile fields and thereby naturally slow, if not
reduce, soil erosion (Orno 1991).
As population increases in the countryside, and
as the demand for food on and off the farm expands
accordingly, cultivation of some R&T can also in-
fringe on forests or high altitude natural grasslands,
such as the paramos in the Andes. Expanded
cassava production in northeast Thailand resulted
in serious deforestation (Howeler, Oates, and Costa
Allem 1999). A combination of better technology
to increase net returns on existing farmland and
policies that discourage cultivation of food crops in
national parks, forests, and other preserves can pre-








vent R&T-related degradation in these areas (see
Duffy 1999).
Results of the COSCA surveys carried out in
C6te d'Ivoire, Democratic Republic of Congo,
Ghana, Nigeria, Tanzania, and Uganda indicate
that in Sub-Saharan Africa cassava production is
replacing fallow land, and that cassava producers
are cultivating their plots more intensively, that
is with shorter fallows (Spencer and Associates
1997). The danger is that when the fallow period
becomes too short, rapid soil degradation may re-
sult. One possible solution is to integrate small-
scale livestock production and cassava cultivation
more closely, so that cassava foliage serves as live-
stock feed and livestock manure provides organic
matter to help sustain soil fertility (Christiaesen,
Tollens, and Ezedinma 1995). Another possibility
involves returning the leaves and stems to the soil
(Howeler, Oates, and Costa Allem 1999). Further-
more, good agronomic practices such as closer
plant spacing, reduced tillage, and use of contoured
grass hedgerows can be very effective in reducing
erosion and possibly increasing cassava yield and
total income (Howeler, Oates, and Costa Allem
1999). The set of best practices is highly site-
specific, requiring both the identification of appro-
priate, improved procedures through farmer par-
ticipation and government initiatives such as land
titles, educational programs, and credit schemes
that provide incentives for adoption.
Potato cultivation in input-intensive crop rota-
tion systems, like those involving irrigated rice in
South Asia, has come under closer scrutiny be-
cause it extracts considerable nutrients from the
soil. But preliminary research results suggest that
the problem-from the farmer's perspective-
may not be as acute as originally thought (Bardhan
Roy et al. 1999). At least some farmers appear to
grow potatoes in these systems in part because po-
tato production halts continuous flooding and al-
lows farmers to interrupt continuous rice produc-
tion, which is associated with nutrient depletion,
absence of soil aeration, and soil compaction
(Pingali 1998).


Water and Air Pollution
The spread of pesticide or fertilizer residues into
water supplies through irrigation systems or field


run-off has attracted growing attention in recent
years (see, for example, Ducrot, Hutson, and
Wagenet 1998). Not only does this form of water
pollution damage plants, insects, and livestock, it
also poses a threat to the drinking water supply of
farm households. The trade-off between food pro-
duction, pesticides, and human health is most acute
in the case of potato production, which relies on
chemicals more than any other R&T (Antle et al.
1998).
Water pollution is not restricted to production,
but also includes postharvest activities. Recent re-
search on cassava processing in Vietnam highlights
the adverse impact that a rapid increase in small-
scale processing of cassava roots into starch has on
local water supplies (Goletti, Rich, and Wheatley
1999; Howeler, Oates, and Costa Allem 1999). In
the absence of proper treatment facilities, the water
used in starch processing contaminates local water
supplies. Similar pollution problems have also
been noted in processing the Andean root crop,
canna, into starch in Vietnam (Hermann, Quynh,
and Peters 1999). With the expansion of potato
processing in developing countries (Scott 1994a;
Scott, Basay, and Maldonado 1997) and the con-
struction of large-scale processing facilities to sat-
isfy increasing demand and capture economies of
scale, concerns have emerged about plant efflu-
ents. These problems mirror those associated with
large-scale potato processing in some developed
countries (New York Times 1994).
The sheer volume of water required to culti-
vate potatoes under desert conditions has also
emerged as an issue, particularly in areas such as
the newly reclaimed land in Egypt, where produc-
tion and processing of potatoes are drawing on
groundwater from newly dug wells (Chilver, El-
Bedewy, and Rizk 1997). The possible medium- to
long-term implications for local water supplies re-
main unclear.
Roots and tubers have also attracted attention
of late for their potential role in the development of
urban and peri-urban agriculture (see, for example,
Brochier et al. 1992; Nweke et al. 1994). Given the
increasing pressure on urban water systems in
developing countries and the practice of using a
wide variety of water sources to cultivate and pro-
cess R&T in urban and peri-urban settings (see, for
example, Villamayor 1991), the implications for








local water supplies and human health merit closer
monitoring (Howeler, Oates, and Costa Allem
1999).
Finally, some traditional cassava-processing
techniques in West Africa can involve prolonged
exposure to inhalation of smoke. Studies have
shown that this can be hazardous to women's and
infants' health. New, improved processing tech-
niques for cassava have gone a considerable way
toward reducing the time required to produce pro-
cessed cassava products and hence toward decreas-
ing environmental and human health problems
(Jeon and Halos 1992).



Biodiversity

A number of studies covering developed and
developing countries have shown that as potato
production becomes more technical, commercial,
and oriented towards processing, producers have
tended to reduce the number of varieties grown
(Brush, Taylor, and Bellon 1992; Walker 1994).
Similar concerns about the loss of genetic diversity
in farmers' fields have been expressed about
cassava (Howeler, Oates, and Costa Allem 1999),
sweetpotato (Prain and Campilan 1999), and yam.
The risk in the Andean region in particular-the
center of origin for the potato and for several other
R&T-is that more native varieties could go out of
cultivation, only to be maintained in gene banks or
lost forever (Alvarez and Repo 1999). One produc-
tion initiative that not only enables small, resource-
poor farmers to produce more food, but also in-
creases the level of genetic diversity is botanical
seed or true potato seed. With this technique, each
seed is a genetically different entity (Upadhya et al.
1995). Hence, greater use of true potato seed would
increase the number of different entities under
cultivation.
The aroids such as taro, and the Andean roots
and tubers such as canna or ulluco, present an even
more formidable challenge. These crops have only
recently attracted the attention of the global scien-
tific community (NRC 1989). They are typically
grown on a limited scale (Hermann and Heller
1997) and are often produced in heretofore isolated
Localities that can be threatened by rapid exposure
to the full force of market penetration. Small,


resource-poor growers of canna and ulluco may
lack access to improved production and posthar-
vest technology, credit to facilitate adoption, and
related initiatives such as government-supported
market promotion schemes, leaving them ill-
equipped to compete with other food commodities
produced on much larger farms and strictly for the
market. As a result, these Andean R&T face the
risk of extinction.
Increases in productivity will be a key require-
ment for improving the competitiveness of R&T in
the decades ahead. One essential aspect of that ef-
fort will be the accelerated movement of germ-
plasm across borders and between continents. For
example, quicker transfer of germplasm native to
Latin America to Sub-Saharan Africa would help
raise cassava yields in the latter region (Spencer
and Associates 1997). Concerns regarding protec-
tion of farmer's rights and national germplasm col-
lections (see, for example, Schneider and Yaku
1996) can and must be addressed to ensure con-
tinued rapid transfer of materials between coun-
tries and regions.



Biotechnology

The advent of genetically modified plants has
become reality in the case of potato (see, for ex-
ample, Qaim 1999) and sweetpotato (see, for
example, Cipriani et al. 1999; Newell, Lowe, and
Merryweather 1995; Prakash, Egnin, and Jaynes
1998). Although these innovations offer tremen-
dous promise for both R&T production (reduced
application of pesticides, for example) and use (re-
duction in the level of trypsin inhibitor in sweet-
potato for feed, for example), they raise a whole
array of new issues, ranging from unanticipated
effects on the environment to the distribution of
economic benefits from such advances. These
questions potentially stretch across the entire food
system, from preproduction, or seed stage, to final
use. The range of concerns includes property rights
for specific postharvest traits (for example, starch
properties for cassava, sweetpotato, yam, or An-
dean roots and tubers), specific processing tech-
niques, and as yet unknown uses of some parts of
particular R&T plants. The limited knowledge and
capabilities in most developing countries regarding








the regulation, accelerated development, and sub-
sequent introduction of these new technologies
suggest that, as with cereals (Morris and Byerlee
1998), the response to this challenge will require a
combination of new technologies, policies, and in-
stitutional strengthening, with a critical role for the
international agricultural research centers
(IARCs). Efforts are already underway in this
direction at the international agricultural research
system level with the formation of the Committee
on Inter-Centre Root and Tuber Crops Research
(CICRTCR) in the CGIAR. This committee is for-
mulating plans for intercenter synergy in, among
other things, the area of biotechnology (Scott et al.
2000). The plans include collaborative efforts to
access laboratory facilities in developed countries,
and thereby reduce the cost of developing bio-
technology for developing countries, as well as


studies of and methodologies for risk assessment of
related technological innovations.
In summary, production and use of R&T in
developing countries have drawn attention to the
potential benefits and raised a series of concerns
regarding their impact on the environment and hu-
man health. The available evidence indicates that
the incidence of potential environmental effects
varies from crop to crop. Pesticides and fertilizer
use, for example, are much more important in the
case of potatoes and problems of soil erosion more
acute in the case of cassava. While the environ-
mental problems discussed merit greater attention
in the future, there are also clear signs that new
technology, institutional innovations, and better
policies can not only meet the challenge but also
more effectively exploit the potential of R&T and
thus help sustain the natural resource base.















7. Conclusions and Recommendations


This paper has analyzed supply and demand trends
and future projections for R&T in order to provide
a clearer vision of the contribution that these crops
can make to the food systems of developing coun-
tries over the next two decades. The paper has also
stressed the important differences among these
crops and the multiple roles they play in today's
food systems. The analysis has shown that R&T
will continue to play a significant role in devel-
oping-country food systems because 1) they con-
tribute to the energy and nutrition requirements of
over 2 billion people in developing countries today
and will continue to do so over the next two
decades; 2) they are produced and consumed by
many of the world's poorest and most food inse-
cure households; 3) they are an important source of
employment and income in rural, often marginal
areas, including for women; and 4) they adapt to a
wide range of specific uses, from food security
crop to cash crop, from food crop to feed crop,
from the latter to raw material for industrial uses,
and from fresh food to high-end processed product.
To realize R&T potential in these areas, a combina-
tion of new technologies and improvements in the
institutional and policy environment will be
required.
With the foregoing in mind, the key questions
addressed in this study can be reconsidered: 1)
How have R&T contributed to the food systems of
developing countries? 2) What role(s) will R&T
play in the next two decades? And 3) What are the
factors that have influenced and will influence the
supply of and demand for these commodities?

The Changing Roles of R&T in
Developing-Country Food
Systems
The supply of and demand for R&T began to
change significantly in the 1960s and 1970s. These


changes-surging potato production in WANA,
South Asia, and China, for example-accelerated
over the next two decades, particularly during the
1990s. With a few noteworthy exceptions, the
trend throughout has been toward greater diver-
sification in use and greater specialization in pro-
duction by crop and region.
In much of Asia and WANA, rising incomes,
growing urbanization, and a desire by consumers
to diversify away from strictly cereal-based diets
have increased demand for potato as food in fresh
and, more recently, in processed form. The same
forces have influenced cassava and sweetpotato
use in different ways. Growers, traders, and entre-
preneurs capitalized on the raw material charac-
teristics of these crops by shifting use toward
starch, feed, and processed food products. In Sub-
Saharan Africa, population growth, low and stag-
nant per capital incomes, and rapid urbanization
have generated tremendous demand for a cheap,
starchy staple to feed poor rural and urban con-
sumers alike. Political instability and highly vari-
able climatic conditions favor cassava as a low-
cost, reliable source of carbohydrates, particularly
in Central and West Africa. Yam continues to be
consumed as a food crop in fresh form, but on a
more modest scale compared to cassava.
In Latin America, changing diets in some
countries (for example Colombia and Mexico) and
the emergence of the fast food and snacks subsec-
tor in others (for example Argentina, Brazil, and
Peru) have increased potato consumption. Many
small producers have been driven out of produc-
tion by rising costs per hectare and, most recently,
by falling tariffs for imports of fresh potatoes and
processed potato products. Cassava demand stag-
nated, with declines in fresh consumption offset by
increases in feed use and processing for food and
industry uses. Sweetpotato consumption stagnated
as well due to weak demand. Growers had little








incentive to adopt yield-increasing technology, ex-
cept where they had access to markets. Increases in
yam output were confined largely to Haiti and
Jamaica.
Small farmers produce most of the potatoes in
Asia and WANA. In most developing countries
small farmers produce potatoes primarily for cash,
though they have increasingly turned to sales of
other R&T as a supplemental source of cash in-
come. These farmers capitalize on the income-
generating potential of potato, including its short
vegetative cycle and broad adaptability. Relatively
abundant labor supplies, new production tech-
nologies, improvements in infrastructure and input
supply systems, and expansion ofpostharvest facil-
ities, particularly cold storage, further facilitate
their efforts to increase production and improve
productivity. The lucrative export market to Eu-
rope provides an added incentive in North Africa.
The principal policies that helped generate the rise
in potato output and productivity includes limited
intervention in output markets, credit and tax
schemes to build and equip storage facilities, and
programs to expand production and marketing
infrastructure.
Sweetpotato production in China fell rapidly
from the late 1970s to the late 1980s, primarily
because the consumption of sweetpotato roots in
fresh form declined. As cereal production in-
creased and the overall economy grew rapidly, in-
comes improved and consumers switched from
fresh sweetpotato to more preferred foods. But
continued economic growth, diversification of
diets, and the demand for meat and processed prod-
ucts led to a rapid increase in demand for sweet-
potato as animal feed and starch. Growth rates for
sweetpotato production began rising again in the
early 1990s. New production technology (such as
improved sweetpotato varieties and cleaner plant-
ing material) also contributed to increased yields
and improved profitability, offering postproduc-
tion employment opportunities to poor farm house-
holds in the process.
In the past, growth in cassava output in Sub-
Saharan Africa has been driven primarily by sub-
sistence demand for food in low-income house-
holds. In recent years, cash sales have assumed
near equal importance. Cassava production-
particularly in West Africa-has increased due to a


combination of additional factors, including the
crop's ability to do well even on poor soils, with
minimal rainfall and little or no purchased inputs;
better production technologies (high-yielding vari-
eties and integrated pest management techniques);
improvements in postharvest practices; and policy
measures intended to promote development of the
local cassava processing industry.

The Roles for Roots and Tubers
by 2020
IMPACT simulations indicate that R&T will play
economically important and increasingly diver-
sified roles in developing-country food systems
over the next two decades.
In Asia, potato will serve as a complementary
vegetable, occasional seasonal staple in parts of
South Asia and China, and, increasingly, as raw
material for processed food products. These multi-
ple uses will reflect the continuing segmentation of
the market into city versus countryside and low-
income versus high-income. Increases in output
and productivity for potato will translate into con-
siderably higher levels of total production. But the
rise in annual per capital intake will be much more
modest, reaching only a third of the consumption
levels in Europe or North America by 2020. Potato
will not be traded in appreciable quantities. Nev-
ertheless, higher potato production and consump-
tion will help sustain food self-sufficiency, reduce
the need for imports of cereal substitutes, and save
foreign exchange in the process.
Sweetpotato in China and to a lesser extent in
Vietnam will serve a much more diversified role in
response to location-specific market requirements.
In maize-deficit areas, such as Sichuan province,
sweetpotato will be used for feed. In other loca-
tions like Shandong province, sweetpotato will be
processed into starch for food products such as
noodles. Improvements in sweetpotato productiv-
ity (yields and quality), processing (economic and
technical efficiency), and product development
(new uses for starch) will propel the evolution in
sweetpotato use. The associated growth in employ-
ment and improvements in incomes will help al-
leviate rural poverty. Growth in sweetpotato feed
use will reduce the need for and cost of imports. Its
role as a food security crop will be limited to the








most isolated, resource-poor, and least-developed
food systems in Asia. In Indonesia, Thailand, and
Vietnam cassava will follow a development path
similar to that of sweetpotato in China.
In Sub-Saharan Africa cassava and yam will
continue to be used overwhelmingly as food. Pro-
cessed food products made from cassava will re-
main important in rural diets, particularly in West
and Central Africa, where they will serve as a basic
staple. Continued high rates of population growth
and urbanization, combined with comparatively
low levels of per capital income and limited eco-
nomic growth, will promote growth in the use of
cassava as food and catalyze its sustained penetra-
tion into urban markets. In East and Southern Af-
rica, cassava will be used more as a supplementary
staple and as a food security crop. The gradual
emergence of processed food products from
cassava in urban areas will open up new commer-
cial outlets in cities and towns. Growth rates in
cassava area planted and yields will be driven by
the introduction of new, high-yielding, disease-
resistant varieties; low-cost methods of pest con-
trol; and the spread of improved processing tech-
niques to East and Southern Africa. Yam in West
Africa as well as sweetpotato and potato in East
and Southern Africa will also witness steady in-
creases in consumption, but more modest in vol-
ume terms than for cassava. This consumption
trend will be reinforced by market niches among
higher-income consumers for processed food prod-
ucts and snacks made from yam and potato and
among lower-income consumers for processed
food and snacks made from sweetpotato. Improved
production and postharvest technologies as well as
institutional and policy innovations will facilitate
the increases in output and productivity that match
the increases in consumption.
Cassava and potato will dominate R&T use in
Latin America. Cassava will be used in processed
form (both for food and industry) and as feed. In
contrast potatoes will continue to be used in fresh
form, though the use of potato in processed and
snack form will also continue to increase. Better
varieties will increase yields and, for cassava in
particular, the strengthening of small agro-
enterprises will increase production further.
Prices of all R&T commodities are projected to
decline by 2020, by 14-23 percent, depending on


the commodity. The global impact of increased
production and lower prices on R&T trade will be
minimal. The decline in the economic value of
R&T in developing countries, in relation to cereals,
meat, and soybean, will be modest; the rise in im-
portance of potato and yam will compensate for the
fall in importance of cassava and sweetpotato.

The Influence of Technology,
Institutions, and Policy
By 2020, we envision that the environmentally
sound production of a diversified range of high-
quality, competitive products for food, feed, and
industry will integrate R&T into emerging mar-
kets. R&T adaptation to marginal environments,
their contribution to household food security, and
their great flexibility in mixed farming systems
make them an important component of a targeted
strategy for improving the welfare of the rural poor
and linking smallholder farmers to emerging mar-
kets (Scott et al. 2000).
Although the projections for future production
and use of roots and tubers in developing countries
are realistic, they are by no means guaranteed. The
continuous generation and diffusion of improved
production and postharvest technology is essential
if the root and tuber sectors in Asia, Africa, and
Latin America are to flourish. Additional socio-
economic research on the most effective and effi-
cient ways to facilitate development and adoption
of this improved technology will also be required.
These efforts will only prove successful provided
there are substantial levels of public and private
investment in agricultural research at both the na-
tional and international levels in the decades ahead.
Past analysis of such investments has shown that
they can offer high rates of return (see, for exam-
ple, Norgaard 1988; Johnson 1999; Walker and
Crissman 1996).
Emerging from this review of the production
and use patterns for the major R&T is a dichoto-
mous vision for capitalizing on the emerging op-
portunities for these crops. Potato and yam pri-
marily face supply-side constraints; cassava and
sweetpotato face mainly demand-side constraints.
Given the linkages between production and post-
harvest activities, however, efforts to improve
R&T should use a systems approach.









The removal or reduction of barriers to in-
creased output of potato and yam-for example,
through the development of disease- or drought-
tolerant varieties, better pest management, im-
proved systems for diffusing planting material, and
policies and procedures aimed at stabilizing the
within-year and year-to-year flow of supply onto
the market-can enable producers to find outlets
for their increased production of these com-
modities more easily. Producers can also identify
and exploit the latent demand for feed and pro-
cessed food products made from cassava and
sweetpotato by lowering costs, raising quality, and
improving availability. To minimize or overcome
these constraints will require improved germ-
plasm, more technically and economically efficient
procedures for producing raw material and finished
products, strengthened grower-to-processor link-
ages, and small-to-medium-scale enterprises for
producing and marketing the products.
In addition to these concerns, a recent review
of current research on R&T in the CGIAR identi-
fied the following commodity-specific priorities
(Scott et al. 2000).


Research and Policy Priorities
* Cassava. Research priorities involve market
appraisals and identification of linkages between
producers, processors, and policymakers that
capitalize on cassava's potential for expanded use
in processed form. Such market-driven initiatives
should be bolstered by germplasm research-
including biotechnology research-on specific
end uses (such as starch), tissue culture, rapid mul-
tiplication of planting material, pest and disease
resistance (most notably cassava bacterial blight
and cassava green mite), and appropriate tech-
nologies and procedures to ensure that cassava pro-
duction and processing have a benign impact on
the environment, with particular regard to soil ero-
sion and water quality.
* Potato. Research priorities include enhancing
resistance to prevalent diseases such as late blight
by combining conventional plant breeding tech-
niques and biotechnology; improving informal
seed systems; and developing effective integrated
crop management. Research on risk assessment for


biotechnology and the impact of potato improve-
ment on poverty, the environment, and human
health also merit high priority, as does research on
the demand and use of processed products.

* Sweetpotato. Concerted international efforts
are under way to increase dry matter content and
yield, exploit national and international germplasm
for appropriate postharvest characteristics, includ-
ing starch quality and pre-beta carotene content,
and systematically support national efforts to foster
greater product development for sweetpotato by
small- and medium-scale farmers and entrepre-
neurs. Because sweetpotato cultivation is often
concentrated in the poorest growing areas and
among farmers with limited-resources, an evalua-
tion of the impact of sweetpotato research on the
food consumption and income-earning activities of
the poorest countries is warranted.

* Yam. Areas of concentration for yam research
include genetic improvement through more effi-
cient germplasm screening; breeding for host-plant
resistance to pests such as nematodes; reducing the
high cost of planting material and labor-intensive
field operations; and exploiting the crop's potential
to be used in processed form.

While each of the major R&T has its
commodity-specific priorities, recent appraisals of
international agricultural research have stressed
the need for and potential benefits from closer col-
laboration among IARCs (Strong et al. 1998). The
recent TAC review of R&T highlighted the poten-
tial gains from capturing the synergies among the
interested organizations involved with these com-
modities (TAC 1997b). At present, areas of poten-
tial gain include phytosanitary regulations, which
affect the international exchange and transfer of
germplasm and the speed of varietal improvement;
biotechnology, which, among other things, in-
volves the sharing of information and techniques
for cryopreservation of germplasm (the storage of
plant cuttings at -190' C) so as to reduce the cost
and improve the quality of the preserved R&T; and
postharvest technology and marketing. The latter
area entails collaborative assessments of the mar-
ket for R&T and related products (Ferris et al.
1999; Prain et al. 1999); joint capacity building
through methodology development in the area of









market analysis (Scott 1995) and product develop-
ment (Wheatley et al. 1995); the exchange of infor-
mation about procedures, processes, and products;
and mobiliztion of regional interaction between
scientists and their respective organizations (Scott,
Ferguson, and Herrera 1992; Scott, Wiersema, and
Ferguson 1992; Scott et al. 1992). These collabora-
tive efforts can produce gains from synergy. But
equally if not more important, these efforts would
help fill the gap left by the absence of the private
sector in R&T development.17
The private sector has underinvested in R&T
for three key reasons: (1) These crops are produced
and consumed in developing countries, with the
exception of potato (and, in the case of sweet-
potato, Japan and the United States), hence there
are few spillover benefits for industrialized coun-
tries. (2) While some R&T commodities have ex-
port potential, their commercial prospects abroad
are generally more modest than for other agri-
cultural products. As a result, the outlook for for-
eign exchange earnings is less attractive. And
(3) R&T are cultivated and used by low-income
households with limited means to purchase new
technology. Moreover, most R&T producers are
rarely organized into effective national organiza-
tions. These circumstances and the limited re-
sources national agricultural research institutes
have for R&T research (TAC 1997b), call for the
creation of an advocacy group on behalf of these
commodities in addition to closer collaboration. In
individual countries such a body would serve as the
rough equivalent to a growers' association or in-
dustry representative. It would seek to promote the
needs of producers, traders, processors, and con-
sumers of R&T in domestic policy deliberations,
public resource allocation, private investment deci-
sions, and trade negotiations. In that spirit, and in
the case of cassava, Plucknett, Phillips, and Kagbo
(1998, 12) have called for R&T supporters to
"keep the needs of industry before the public and
decision makers . [and] . for research and
development, provision of infrastructure and in-
vestments, and changes in policies to grasp the new
[commercial] opportunitiess]" In a similar vein, a


focal point is needed at the international level for
gathering support and capturing the synergies of all
those organizations working on R&T for the bene-
fit of developing countries (Scott et al. 2000).
Policymakers should take increased cog-
nizance of the growth prospects for particular
R&T, and for particular uses in particular regions.
Policymakers can do so by ensuring that the na-
tional and international databases for these crops
are improved, particularly for R&T production and
use in Sub-Saharan Africa (see, for example
Minde, Ewell, and Teri 1999). More disaggregated
and continuously updated projections at the re-
gional and subregional levels for particular R&T
can also be useful to prospective investors, multi-
lateral agencies, and bi-lateral donors. Policy-
makers in developing countries should eliminate
measures like overvalued exchange rates or sub-
sidies on imported food, in order to benefit from
the full potential of R&T (see, for example, By-
erlee and Sain 1991).
Policymakers can also foster R&T develop-
ment by removing policy distortions that promote
artificial economies of scale in livestock produc-
tion (Delgado et al. 1999). Policies that promote
only large-scale, feed-lot hog production in China
offer a prime example of the constraints placed on
sweetpotato production for household- and village-
level processing into pig feed. Policymakers can
include R&T in national five-year plans in order to
give research on these crops more legitimacy and
public support. They can also encourage efforts to
seek more nontraditional funding for research and
development of R&T (Spencer and Associates
1997).s8 Policymakers can also facilitate the use of
R&T as a means of alleviating poverty among the
poor and most vulnerable groups in a variety of
ways. For example, innovations and their benefits
should be made available to all groups, including
women. Credit schemes would enable women en-
trepreneurs to purchase improved cassava-
processing equipment in Sub-Saharan Africa
(Spencer and Associates 1997). Policymakers in
developing countries must also be more vigilant in
negotiations over tariff and nontariff barriers for


17 Potato is perhaps the exception, albeit on a limited basis (Qaim 1999).
18 In one practical example, financially consistent measures have been developed to cost and sell planting materials for potato
(Espinosa, Crissman, and Hibon 1996). Revenues can then be recycled to support potato research and development, which are
often entirely dependent on annual government appropriations and/or donor financial support.









R&T and their substitutes because these mecha-
nisms can affect resource-poor households (Scott,
Basay, and Maldonado 1997). Policymakers also
need to be more sensitive to the allocation of re-
sources within national R&T programs in order to
ensure that postproduction activities-often most
closely linked to income generation-are not un-
derfunded in relation to production research.
In the environmental arena, policymakers can
promote conservation of the natural resource base
by making sure that research and extension efforts
provide small farmers with viable technical alter-
natives to resource-depleting practices for soil, wa-
ter, and forest resources, and by fostering farmer-
based organizations to help disseminate the alter-
native technologies. Policies that discourage the


improper use of pesticides and fertilizers should
complement these efforts.
Policymakers in industrialized countries can
also help improve the growth prospects for R&T in
developing countries in a variety of ways. These
include abandoning trade arrangements that limit
import demand for R&T (see, for example, Henry
1998), eliminating subsidies on exports of com-
peting food products (Spencer and Badiane 1995),
and facilitating technology transfer (small- to
intermediate-scale processing equipment, for ex-
ample) to strengthen production and use of R&T in
developing countries. Finally, access to developed-
country markets can also help maintain genetic
diversity for R&T in developing countries (Fano et
al. 1998).


















Appendix: Supplementary Tables



Table 24-Main agronomic characteristics of principal roots and tubers

Cocoyam Taro
Cassava tanniaa) Potato Sweetpotato cocoyamm)
(Manihot (Xanthosoma (Solanum (Ipomoea (Colocasia Yam
Characteristics esculenta) nigrum) tuberosum) batatas) esculenta) (Dioscorea spp.)
Growth period (months) 9-24 9-12 3-7 3-8 6-18 8-11
Annual or perennial plant Per. Per. Ann. Per. Per. Ann.
Optimal rainfall (centimeters) 100-150 140-200 50-75 75-100 250 115
Optimal temperature (C) 25-29 13-29 15-18 >24 21-27 30
Drought resistant Yes No No Yes No Yes
Optimal pH 5-6 5.5-6.5 5.5-6.0 5.6-6.6 5.5-6.5 n.a.
Fertility requirement Low High High Low High High
Organic matter requirement Low High High Low High High
Growable on swampy, waterlogged soil No No No No Yes No
Planting material Stem Corms/cormels Tubers, Vine cuttings Corms/cormels Tubers
Storage time in ground Long Long Short Long Moderate Long
Postharvest storage life Short Long Long Short Variable Long

Sources: Derived from D. E. Kay, Root crops, London: Tropical Products Institute, 1973, as presented in Horton (1988).
Note: n.a. = Data not available.
aWhole tubers, cut tubers, or botanical seed.







Table 25-Raw material characteristics of roots and tubers

Aroids Cassava Potato Sweetpotato Yam

Dry matter (%) 22-27 30-40 20 19-35 20-42
Starch (%FW) 19-21 27-36 13-16 18-28 18-25
Total sugars (%FW) 2.0 0.5-2.5 0-2.0 1.5-5.0 0.5-1.0
Protein (%FW) 1.5-3.0 0.5-2.0 2.0 1.0-2.5 2.5
Fiber (%FW) 0.5-3.0 1.0 0.5 1.0 0.6
Lipids (%FW) 0-1.5 0.5 0.1 0.5-6.5 0.2
Vitamin A (pg/100g FW) 0-42 17 Trace 900 117
Vitamin C (mg/100g FW) 9 50 31 35 24
Ash (% FW) 0.5-1.5 0.5-1.5 1.0-1.5 1.0 0.5-1.0
Energy (kJ/100g) 390 607 318 490 439
Antinutritional factors Oxalate crystals Cyanogens Ylycoalkaloids Trypsin inhibitors Alkaloids, tannins
Starch extraction rate (%) n.a. 22-25 8-12 10-15 n.a.
Starch grain size (micron) 1-12 5-50 15-100 2-42 1-70
Amylose (%) 3-45 15-29 22-25 8-32 10-30
Maximum viscosity (BU) n.a. 700-1,100 n.a. n.a. 100-200
Gelatinization temp. (oC) 68-75 49-73 63-66 58-65 69-88

Source: Wheatley et al. 1995, Bradbury and Holloway 1988.
Note: n.a. = Data not available. FW = fresh weight; pg = microgram; mg = milligram; BU = Brabender units; kJ = kilojoule.











Table 26-Key IMPACT parameters for selected countries and regions

Average annual Income elasticities of demand,
growth rate, Sweetpotato and
1993-2020 Cassavab Potato yam
Countries/region Population Income 1993 2020 1993 2020 1993 2020
(percent)
Brazil 1.12 3.2 -0.08 -0.18 0.40 0.30 -0.10 -0.25
Nigeria 2.67 3.2 0.30 0.20 0.20 0.18 0.50 0.40
Central and Western Sub-Saharan Africa 2.70 3.8 0.10 -0.05 0.40 0.38 0.30 0.20
Egypt 1.56 3.2 0.05 -0.15 0.40 0.25 0.10 0.00
Turkey 1.24 4.5 0.00 -0.20 0.35 0.20 0.10 0.00
India 1.30 5.1 0.15 -0.05 0.55 0.45 -0.10 -0.30
Thailand 0.63 5.4 -0.05 -0.10 0.40 0.25 -0.10 -0.25
China 0.72 5.6 -0.05 -0.15 0.45 0.35 -0.20 -0.35

Source: IFPRI IMPACT, June 1998.
aEstimates for the baseline scenario.
bThese figures are for cassava and other roots and tubers such as taro. For developing countries, cassava alone accounts for over 97 percent of the


















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Gregory J. Scott is a senior economist at CIP; Mark W. Rosegrant is a senior research fellow and Claudia
Ringler a research analyst in the Environmental and Production Technology Division at IFPRI.




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