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APPENDIX 4 - GLOBAL PRODUCTION AND CONSUMPTION OF ROOTS AND TUBERS


INTRODUCTION
ROOT AND TUBER CROP PRODUCTION: 1980-1992
ROOT AND TUBER CROP UTILIZATION: 1980-1992
FUTURE PROJECTIONS OF ROOT AND TUBER CROP PRODUCTION
DISCUSSION
REFERENCES

A TAC Secretariat desk study prepared in support of the Inter-Centre Review of Root and Tuber Crops Research in the CGIAR.

Resume

The purpose of this paper is to provide summary statistics on production and consumption trends in root and tuber crops to support the work of the Strategic Study of CGIAR Research on root and tuber crops. Following a brief description of the principal root and tuber crops grown in the developing countries, analysis of production and consumption trends since 1980 are presented. Global (developing country) and regional growth rates in production and consumption are presented and discussed on a crop-commodity basis. Future projections of production and consumption of root and tuber crops, based on recent studies by FAO and IFPRI, are also presented. Finally, preliminary analyses of alternative approaches to establishing priorities among root and tuber crops, and between root and tuber crops and the other major staple foods, are presented and discussed in the context of CGIAR goals of poverty alleviation and the management of natural resources.

INTRODUCTION

Roots and tubers provide a substantial part of the world's food supply and are also an important source of animal feed. On a global basis, approximately 55 percent of roots and tuber production is consumed as food; the remainder is used as planting material, as animal feed or in the production of starch, distilled spirits, alcohol and a range of other minor products. The patterns of utilization vary considerably among countries. In the developing countries, with the exception of China, Vietnam, Brazil and Paraguay, only small quantities (less than 20 percent) are fed to livestock and production is largely for on-farm food consumption. The relatively high costs of transport, processing and storage and the not inconsiderable time needed in preparation as food, frequently make roots and tuber crops less attractive to urban consumers (FAO, 1994). The consumption of roots and tubers as food is considerably smaller in developed countries, but their use as animal feed is relatively higher. A very small proportion of root and tuber production (5 percent approximately) is traded internationally and more than two-thirds of the exports are from developing countries; exports of cassava from Thailand account for more than half of the total. Cassava apart, only potatoes are traded in significant quantities and mainly among developed countries.

This paper addresses five major groups of roots and tuber crops, viz., Cassava (Manihot esculenta), Sweet potato (Ipomoea batatas). Potato (Solanum tuberosum), Yams (Dioscorea spp.) and edible Aroids (Colocasia esculenta and Xanthosoma spp.) known variously as Taro (Colocasia) and Tannia (Xanthosoma), but often referred to as cocoyams.

Cassava

Cassava's source of origin is tropical America; it is unknown in the wild state and its evolution as a species is directly linked to selection by man under cultivation. The exact time and location of domestication and its direct ancestors are not known. Cassava is the most widely cultivated root crop in the tropics and because of its long growth season (8 - 24 months) production is limited to the tropics and subtropics. It is grown across a broad range of agroclimatic conditions: from sea level to almost 2,000 metres in the American tropics and in areas with as little as 500 millimetres of rainfall to areas of tropical rain forest.

Important characteristics that earmark a role for cassava in tropical agriculture include: (i) high carbohydrate yield per unit of land and labour, (ii) adaptation to poor soils (low pH) and water stress (ability to withstand dry periods of up to five months) and (iii) compatibility with a wide variety of crops in rotational farming systems. Limitations include the high water content (60 - 70%) and bulkiness of the roots and root perishability after harvest. Cassava has been widely characterized as a subsistence crop and is typically grown by small-scale farmers, generally on agriculturally marginal lands. Fertilizer is seldom used in cassava production systems (less than 10% of farms) and few growers apply fungicides, insecticides or herbicides.

Sweet Potato

The centre of origin of sweet potato is Central America, but the crop is widely grown in many tropical and subtropical countries. Sweet potatoes are ranked seventh in world staple food production (expressed on a dry matter basis), after wheat, maize, rice, potato, barley and cassava. The crop is particularly important in South-East Asia, Oceania and Latin America. China still accounts for over 90% of total production; the other major sweet potato producing countries in Asia are: Indonesia, India, Japan, Vietnam, The Philippines and The Republic of Korea. Rwanda and Uganda are Africa's largest producing countries. Sweet potato production in Latin America and The Caribbean is relatively small.

Sweet potato is a perennial crop, but it is cultivated as an annual. It is grown between 40°N and 32°S latitude and at elevations up to 2,500 m. The plant is tolerant to a wide range of soil conditions, but is sensitive to water logging. The crop is generally grown on fairly infertile soils with little inputs of fertilizer. Tubers can be left in the ground after maturity, but once harvested they have a short storage life. For these reasons, sweet potatoes are generally grown as a subsistence crop for immediate consumption. A major cause of production loss arises from infestation of the tubers with the sweet potato weevil and related pests. The continuous reproduction of the weevil throughout the year makes control difficult. A notable feature of all statistics on this crop is that sweet potato production and consumption have continued to decline over the past two decades; whereas the significant reductions in production and consumption in China dictate the global downward trends, the reductions are also manifest in developing countries outside China.

Potatoes

The potato is of highland origin; domesticated in the Andes of South America, it became a major food crop in the cool highland areas of South America, Asia (Himalayas) as well as Central and Eastern Africa. In the eighteenth century the potato gradually became an important food crop for peasants and the urban poor in Europe and North America and many varieties now grown in the tropics originated in these temperate areas. More recently, potato production has spread from its traditional high altitude environment into warmer drier areas such as Peru's coastal valleys, the plains of India, Bangladesh and Pakistan and the irrigated oases of North Africa. Potato production has also expanded into the warm humid tropics; however, the prevalence of pests and diseases in these areas calls for high levels of pesticide use and varieties that are resistant or tolerant to pests and diseases.

In highland farming systems, potatoes are generally grown on small farms in a number of distinct parcels of land that, taken together, rarely exceed one to two hectares. Typically, the crop is rainfed and subject to many hazards including droughts and excessive rain, hail, frost and typhoon damage, depending on the location. Highland farmers generally retain a substantial part of the harvest to use as seed in the following season. Potatoes have also become an attractive winter crop in many arid, irrigated areas where they are grown on relatively large commercial farms. As harvest in these areas occurs at the beginning of summer, storage and marketing problems pose severe problems for this perishable crop; refrigeration is generally required both for seed and ware potatoes in these areas.

Yams

Yams are grown in many tropical regions throughout the world, but the main production centre is the savannah region of West Africa, where more than 90 percent of the crop is grown, mainly in Nigeria. White yam (Discorea rotundata) is believed to be indigenous to the area stretching from Côte d'Ivoire to Cameroon and is generally considered to be the best edible yam in that region. The yellow yam (Dioscorea cayenensis) is also indigenous in West Africa, whereas the water yam (Dioscorea alata) originated in South-East Asia. Yam production in Africa is concentrated in areas within 15 degrees of the equator.

Yams, like most African crops, are generally intercropped. They are normally grown in high rainfall areas with distinct wet and dry seasons; they grow best on loose, fertile, well drained soils. Production is labour-intensive because of the need for soil mounding before planting, for staking, weeding and above all for harvesting. A major constraint on yam production is the high cost and sometimes the unavailability of planting materials. The cost of planting materials can account for up to 60 percent of production inputs. High perishability and losses during storage (up to 50 percent) are a further constraint. Yam production systems have largely evolved within a subsistence economy and are not suited to large-scale mechanized production.

Aroids

Most of the cultivated edible aroids belong to two genera: Colocasia (Taro) and Xanthosoma (Tannia). Both taro and tannia are often referred to as cocoyams. Taro originated in India and South-East Asia and spread to Egypt about 2,000 years ago. Later it was grown in Spain from where it was taken to tropical America and later to West Africa. Tannia originated in tropical South America and the Caribbean. It is thought that the Spanish and Portuguese introduced it to Europe and later to Asia. The crop is thought to have initially spread to West Africa from the Caribbean around the middle of the last century. Cocoyams are typically grown as secondary crops in Nigeria and rank far behind yams and cassava in production and consumption; however, they constitute a staple food in parts of Ghana, Cameroon and Gabon.

Cocoyams normally produce optimum yields when planted in fertile soil with a high water retention capacity. The crop is well adapted to high rainfall and occasional flooding, to temperatures between 21 and 30°C and grows best at elevations below 1,000 m. Cultivation practices vary from region to region. Traditionally cocoyams are planted along the banks of streams, but in parts of West Africa they are grown in association with tree crops, especially cocoa. For edible aroids, as for most food crops in the tropics, labour is the main production input. Corms and cormels are used for propagation. The planting material is stored in the shade and after sprouting, cormels are selected for planting, usually on low mounds or ridges.

ROOTS AND TUBERS: SIMILARITIES AND CONTRASTS

Root and tuber crops share some common characteristics but are also very dissimilar in many respects; see Table 1. Potatoes have a shorter vegetative period than most other root crops and do best under cool temperatures. They can be grown in areas with high daytime temperatures, but do not form good tubers if night-time temperatures exceed 20°C. For good yields, potatoes require high inputs of fertilizer and organic manure. While the optimum rainfall for potatoes is lower than other root crops, potatoes do require a regular watering and are highly susceptible to drought. Harvested tubers can be stored for long periods if they are free of pests and diseases and low temperatures and high humidity are maintained.

The other root crops have longer and more variable growing periods; cassava, at the extreme, requires 9-24 months depending on soil fertility and temperature. Other root crops also do better under higher temperatures; for example, the optimal temperature for yams is 30°C. Also by way of contrast, sweet potatoes and cassava, though responsive to fertilizer, can produce economic yields on poor unfertilized soils with little organic matter. Both crops are also highly drought-resistant. However, their harvested roots cannot be stored for longer than a few days, but they can be left, unharvested, in the ground for long periods. In contrast to cassava and sweet potatoes, yams and edible aroids require fertile soils and adequate moisture. Both yams and edible aroids can be left on the plant after maturity and harvested when needed. If care is taken to avoid damage to tubers, corms and cormels during harvesting, they store well.

Table 1. Characteristics of Root and Tuber Crops

Characteristics

Cassava

Potatoes

Sweet Potatoes

Tannia

Taro

Yam

Growth period (mo)

9-24

3-7

3-8

9-12

6-18

8-11

Annual or perennial plant

per.

ann.

Per.

per.

per.

ann.

Optimal rainfall (cm)

100-150

50-75

75-100

140-200

250

115

Optimal temperature (°C)

25-29

15-18

>24

13-29

21-27

30

Drought resistance

yes

no

yes

no

no

yes

Optimal pH

5-6

5.5-6.0

5.6-6.6

5.5-6.5

5.5-6.5

n.a.

Fertility requirement

low

high

low

high

high

high

Organic matter requirement

low

high

low

high

high

high

Growable on swampy,
water-logged soil
Planting material

no
stem

no
tubers
cutting

no
vine
cutting

no
corms/
cormels

yes
corms/
cormels

no
tubers

Storage time in ground
Postharvest storage life

long
short

short
long

long
short

long
long

moderate
variable

long
long

Source: Derived from Kay, D.E., 1973. Tropical Products Institute, London, as presented in Horton 1988.
n.a. = Data not available.

Root and tuber crops also vary considerably in nutritional value. All are low in protein content ranging from 0.9 g (Cassava) to 2.1 g (Potatoes) of protein per 100 g of edible food. Energy contents are high relative to other food crops and range from 76 (potato) to 124 K cal per 100 g of edible food (cassava). In terms of dry matter production per hectare, they outyield rice (1.9 t.ha-1), cereals (1.3 t.ha-1) and vegetable crops (1.6 t.ha-1) with annual dry matter production levels of 3.0, 2.4, 2.2 and 2.1 t.h-1 for cassava, yam, potato and sweet potato respectively (Horton and Fano, 1985). However, contrary to conventional thinking, root crops are not necessarily a cheap food. In most developing countries, yams, potatoes and edible aroids are costly sources of energy relative to cereals, sweet potatoes and cassava. Perishability and high transport and marketing costs make cassava expensive, especially as an urban food; however, cassava is consumed by both low income and high income urban households in South America.

ROOT AND TUBER CROP PRODUCTION: 1980-1992

In this study, data (FAO Agrostat) on root and tuber crop production over the period 1980 to 1992 were analysed. The results show that root and tuber crops are still a major source of food across the developing countries, albeit there are significant differences between countries and regions in the levels of production and patterns of utilization of the different crops. On aggregate, close to 36 million hectares of land in the developing world are devoted to root and tuber crops and yield a production in the region of 401 million metric tons each year (Table 2). With the exception of the potato, root and tuber crops are almost exclusively grown in the tropics albeit across a range of topographical, soil and climatic conditions. On the other hand, roughly 70% of the global potato crop is grown in the industrial countries, with Europe accounting for more than 80% of production1. Regional differences in root and tuber crop production across the developing world are also very pronounced (Table 3). Asia is by far the major source of root and tuber crops (226 million metric tons/16 million hectares approximately), followed by sub-Saharan Africa (108 million metric tons/15 million hectares), Latin America (46 million metric tons/4 million hectares) and the Near East/North African region (13 million metric tons/0.8 million hectares). Equally, there are very large differences between individual countries within each of the four regions. China, for example, dominates sweet potato production accounting for more than 90% of global production, whereas Nigeria is the major producer of yams. Nigeria (No. 3) is also among the top five cassava growing countries which includes Brazil (No. 1), Thailand (No. 2), Zaire (No. 4) and Indonesia (No. 5). China dominates potato production (34% approx.) within the developing countries; other major potato growing countries in order of levels of production output are India, Turkey, Iran and Colombia.

1Trends in potato production in developed countries have recently been studied by FAO/CIP (1995) and will not be discussed in this paper.

From a crop perspective, cassava production accounts for approximately 38% of the overall root and tuber crop production in the developing countries; sweet potato accounts for more than 31%, potatoes for 23%, whereas yams (6%) and aroids (2%) make relatively small contributions on a global scale. There are also quite large differences in average yields per hectare, among the crops. Sweet potato showed highest yields (13.9 MT.ha-1) in contrast to aroids with a yield average of 4.6 MT.ha-1. Within the four main regions studied there are also significant differences among the crops. For example, sweet potato is the dominant root crop in Asia, cassava the dominant crop in sub-Saharan Africa and Latin America, whereas the potato crop accounts for more than 97% of root and tuber crop production in the Near East/North African region.

Table 2: Root and Tuber Crop Statistics
Average annual production ('000 MT, '000 hectares and yield per hectare) in developing countries in the period 1990/92


Production
('000 MT)

Area
('000 Ha)

Yield
(MT. Ha)

Cassava

152,181

15,563

9.8

Sweet Potato

123,769

8,928

13.9

Potato

93,157

6,988

13.3

Yams

23,524

2,526

9.3

Aroids

8,533

1,839

4.6

Total

401,164

35,844

10.2

Source: FAO Agrostat.

PRODUCTION TRENDS

A number of time-series analyses of trends in the production and utilization of root and tuber crops have been published in recent years (FAO, 1992; Scott and Suarez, 1993; FAO, 1994; Wheatley and Scott, 1994). These analyses have focused primarily on the potato, cassava and sweet potato crops with little or no attention to yams and aroids, or the much lesser know Andean roots and tubers. A comprehensive three volume publication, 'Product Development for Root and Tuber Crops', published by CIP in 1993, presented reports on individual country data and developments in the major root and tuber crops across a broad range of countries in the developing world. These publications, and in particular the review papers cited above, have examined long-term (30 year) trends in the production and utilization of these crops. The purpose of this paper is to update these analyses by examining more recent trends (1980-92, and 1986-92) and future projections for root and tuber crop production and utilization, both on a regional basis and across the developing countries as a whole. Some limited information on root and tuber crop production on an agroecological zone basis is also presented.

Cassava

Average cassava production over the three year period, 1990/92, amounted to 152.181 million tons, representing an average annual yield of 9.8 MT.ha-1 over a total area of 15.563 million hectares, across the developing countries (see Table 3). Cassava production continued to expand at approximately 2.0% per annum over the 12-year and 6-year timeframes reviewed; approximately two-thirds of the increased production came from additional area planted with little indication of a significant expansion in crop yields. These increases in output are considerably lower than in earlier periods as reported by Scott and Suarez (1993); their analyses showed annual increases of the order of 3.5% per annum in the sixties and seventies, albeit there were signs of a reduction in output growth (2.75%) over the period 1974-1989. These reductions in output from the sixties to the nineties are characteristic of most food crops, and will be discussed later in the context of land areas planted to cereal based food crops versus root and tuber crops.

The results in Table 3 show some significant regional differences, not only in terms of cassava output but also in recent growth rates, particularly as regards area planted to cassava. For example, area planted to cassava in Latin America decreased annually (-0.3%) over the past twelve years and the very small annual increase in production (0.3%) resulted from increased yields (0.6%). By way of contrast, cassava production in sub-Saharan Africa increased at an annual rate of 3.4%, but much (65%) of the increased production came from additional area planted to the crop. Annual growth rates of cassava production in Asia over the study period averaged 1.2%, largely as a result of increased yields per hectare.

Sweet Potato

Sweet potato is second only to cassava in terms of production output (123.8 million metric tons per annum) and land area (8.928 million hectares) in the developing countries planted to this crop. However, in the period 1990-92, China accounted for more than 90% of total production. Annual yields averaged 15.7 MT.ha-1, but in countries other than China, yields were significantly lower; in Africa, for example, yields were as low as 4.7 MT.ha-1, in Latin America yields averaged 7.4 MT.ha-1 and in Asian countries other than China yields were 8.6 MT.ha-1. Reliable statistics are not available for the Near East/North African region as sweet potato production in this region is of very minor importance.

Levels of production of sweet potato dropped (-0.6% p.a.) across the developing world during the 12-year period, 1980-92. Area planted to the crop fell by 1.2% per annum and this was only partially offset by a modest annual increase (0.6%) in yields per hectare. The largest reduction in output occurred in Asia, particularly in those countries outside China (-1.7% p.a.) and in Latin America (-1.0% p.a.). On the other hand, sweet potato production increased in Africa as a result of a significant increase (2.6% p.a.) in area planted to the crop; in fact, the data suggest that yield per hectare declined marginally over the period. The data reported by FAO (1992) and Wheatley and Scott (1994) show that a reduction in sweet potato production had already become evident in the period 1973/75 - 1988/9, and that land area planted to the crop began to fall in the late sixties; however, yield increases over the periods analysed in these statistics offset the impact of reduced plantings.

Potatoes

The results in Table 3 show that potato production continues to expand across the developing countries at a significant level (2.8-3.1%). A little more than half (54%) of the increased production over the period, 1980-92, arose from an increase in the area planted, albeit a significant annual increase in crop yields was also manifest. These more recent annual trends are significantly lower than growth rates over the period, 1962-89, as published by Scott and Suarez (1993); however, as in the case of cassava, their analyses show that increases in potato production had begun to slow down in the late seventies and in the eighties (1988/90 vs. 1973/75).

Potato production in Asia continued to expand at a significant pace (2.9% - 4.0% p.a.) both within and outside China (see Table 3). Whereas yield increases grew at an annual rate ranging from 1.0 to 1.9%, roughly two thirds of the increased tonnage of potatoes came from expanded planting area. At the other end of the spectrum, there was a reduction in the area of land sown to potatoes in Latin America (-0.9% p.a.) over the study period; this was partially offset by increased yields resulting in a modest growth in output of 0.7% p.a. In the same period, potato production in the Near-East/North African region expanded rapidly (4.6% p.a.), albeit from a relatively low base (714,000 hectares) and the reported high yields per hectare (largely irrigated) continued to increase; potato exports to Europe may have been a significant factor in stimulating these increases as will be discussed later. On the other hand, potato production in sub-Saharan Africa remained low, both in terms of area planted (406,000 ha.) and total output (2,414 million MT); growth in output was also modest (1.2% p.a.). Yields per hectare were significantly lower than in other regions and changed little (0.6% p.a.) over the twelve year period.

Table 3: Regional Root Crop Statistics Average Annual Production (1990/92) and Annual Growth Rates, 1980-92 (D 1%) and 1986-92 (D 2%)

CROP

PRODUCTION (MT)

AREA ('000 Ha)

YIELD (MT.Ha-1)

MT

D 1

D 2

Ha

D 1

D 2

MT.Ha-1

D 1

D 2

CASSAVA


SS Africa

71,340.4

3.4

3.3

9,077.5

2.2

3.5

7.9

1.2

-0.2

Latin America

30,700.3

0.3

-0.8

2,641.8

-0.3

-0.5

11.6

0.6

-0.3

N. East/N. Africa

7.5

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

Asia incl. China

50,132.6

1.2

2.0

3,838.5

0.3

1.1

13.1

0.8

0.9

Asia minus China

46,849.3

1.3

2.2

3,608.5

0.4

1.1

13.0

0.9

1.1

Developing (93)

152,180.8

1.9

2.0

15,562.5

1.2

2.1

9.8

0.7

-0.1

SWEET POTATOES


SS Africa

6,249.8

1.5

0.9

1,327.1

2.6

1.3

4.7

-1.1

-0.4

Latin America

1,920.5

-1.0

-3.2

259.4

-1.6

-2.5

7.4

0.6

-0.8

N. East/N. Africa

131.5

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

Asia incl. China

115,466.9

-0.7

0.0

7,336.6

-1.7

-0.1

15.7

1.0

0.2

Asia minus China

9,146.9

-1.7

-1.4

1,069.2

-2.4

-1.1

8.6

0.8

-0.3

Developing (93)

123,769.4

-0.6

0.0

8,927.9

-1.2

0.0

13.9

0.6

0.0

POTATOES


SS Africa

2,414.4

1.2

1.0

405.9

0.6

1.0

5.9

0.6

0.0

Latin America

11,784.6

0.7

0.3

967.4

-0.9

-1.4

12.2

1.6

1.8

N. East/N. Africa

12,662.8

4.6

2.7

713.9

2.4

1.6

17.7

2.1

1.1

Asia incl. China

57,576.4

2.9

4.0

4,469.7

2.0

2.0

12.9

0.9

2.0

Asia minus China

25,509.8

3.7

3.6

1,651.7

2.1

1.9

15.4

1.5

1.7

Developing (93)

93,156.6

2.8

3.1

6,988.3

1.5

1.3

13.3

1.3

1.8

YAMS


 

SS Africa

22,552.1

7.7

15.6

2,382.2

4.5

7.6

9.5

3.0

7.5

Latin America

631.8

-0.2

-1.5

83.2

-1.1

-3.6

7.6

0.9

2.2

N. East/N. Africa

117.2

0.2

1.4

44.3

1.3

2.2

2.6

-1.1

-0.8

Asia incl. China

223.3

3.5

4.6

16.7

0.5

3.1

13.3

2.9

1.5

Asia minus China

223.3

3.5

4.6

16.7

0.5

3.1

13.3

2.9

1.5

Developing (93)

23,524.4

7.3

14.7

2,526.4

4.2

7.0

9.3

3.0

7.2

AROIDS


 

SS Africa

5,315.4

1.0

0.5

1,435.5

0.9

0.7

3.7

0.0

-0.2

Latin America

832.4

1.5

0.9

160.2

1.5

0.2

5.2

0.0

0.7

N. East/N. Africa

122.9

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

Asia incl. China

2,257.2

-1.0

-1.9

238.9

-1.4

-2.7

9.4

0.5

0.9

Asia minus China

1,082.8

-1.1

-2.7

156.5

-1.2

-2.8

6.9

0.1

0.1

Developing (93)

8,533.1

0.5

-0.1

1,838.8

0.6

0.2

4.6

-0.1

-0.2

Source: FAO Agrostat.
n.a. = Statistics based on few data, and consequently not reliable/available.

Yams

The growing of yams can be said to be almost exclusively confined to Africa which accounted for 96% of total production; the relatively small levels of production in Latin America (3%) and Asia (1%) have very little impact on the aggregate developing country statistics. Indeed, within Africa yam production is largely confined to a few countries, principally Nigeria (15.9 MT p.a.), Côte d'Ivoire (2.7 MT p.a.), Benin (1.1 MT p.a.) and Ghana (1.0 MT p.a.).

Perhaps, of greatest note is the comparatively rapid expansion in yam production over the period, 1980-92. The data in Table 3 show that global production expanded on average by 7.4% (sub-Saharan Africa 7.7%) each year, largely as a result of a significant increase (4.2%) in the area planted to yams, but also because of a sustained annual increase (3.0%) in crop yield per hectare over the twelve-year study period. Trends over the six-year period, 1986-92, if such short series data can be interpreted with confidence, suggest that yam production continued to expand even more rapidly in recent years, both in terms of area planted (7.0% p.a.) and yield per hectare (7.2% p.a.). China does not report yam production statistics and consequently the expansion of yam production in Asia relates solely to countries outside China; much of the expansion in production arose from increased (2.9% p.a.) yields per hectare. On the other hand, yam production in Latin America remained relatively static over the study period; the slight reduction in area planted to yams (-1.1% p.a.) was largely offset by an annual increase (0.9% p.a.) in crop yield. As few data have been published on yam production, hitherto, it has not been possible to adequately compare these recent production trends with earlier time-series data. Data published by Dorosh (1988) indicated that yam production per capita in West and Central Africa was declining by -0.3% and -1.2% respectively over the period 1964-74, and by -1.1% and -1.98% over the period 1974-84. To the extent that population growth in these areas was expanding rapidly in the sixties and seventies, it can be deduced that yam production was also expanding at a significant rate over the two decades in question.

Aroids

Edible aroids as defined in this paper, based on the FAO Agrostat aggregations, include Yautia/Tannia (Xanthosoma spp.) and Taro (Colocasia esculenta) commonly termed cocoyams, together with a grouping of very minor root and tuber crops (e.g., Arracacoa xanthorrhiza) not individually specified because of their relatively minor importance in international food production. Most of these and other minor crops (e.g, Alucasia, Cyrtosperma and Amorphophallus) are cultivated globally to a very limited extent, but are important food crops in certain communities in India, south-east Asia and the Pacific Islands. Much more important and more extensive in their cultivation, are Colocasia (Taro) and Xanthosoma (Tannia); these crops heavily dictate the edible aroid statistics reported in this section.

Edible aroid production across the developing countries averaged 8.533 million tons per annum in the period, 1990/92, and changed little (0.5% p.a.) over the previous decade; the slight increase reported arose largely from increased plantings with little change in crop yields. Sub-Saharan Africa (5.315 million MT) and Asia (2.257 million MT) dominated global production. Production increases (1.0% p.a.) in sub-Saharan Africa were offset by comparable decreases (-1.0%) in Asia, both changes principally due to fluctuations in land areas planted to these crops. Edible aroid crop production in Latin America, albeit very modest in quantity (832,000 MT p.a.), expanded at 1.5% per annum over the twelve-year study period as a result of increased plantings. As little has been published on production trends of these edible aroid crops, comparisons with earlier patterns of production are difficult.

ROOT AND TUBER CROP UTILIZATION: 1980-1992

Traditionally, root and tuber crops have been considered primarily as food crops with some by-products and wastes used for animal feed. In reality, these crops are applied to a wide variety of uses which vary considerably across countries and regions, and indeed among the individual crops. Over the past three decades, some notable changes in the utilization of these crops have occurred in individual countries. However, on a global basis (developing countries), the data published by Scott and Suarez (1993), show that, in general, the patterns of utilization of cassava, potato and sweet potato changed little over the timespan 1961/63 to 1988/90. In this paper the utilization of root and tuber crops over the period 1980-92 has been analysed; the results are shown in Table 4.

The table shows that, across the developing countries, food accounted for the highest share of all crops, averaging 68.9%, 50%, 62.8%, 58.6% and 84.9% for cassava, sweet potato, potato, yams and aroids. Little change occurred in these global food shares over the study period, with the exception of sweet potato, which decreased by 2.9% p.a.; Asia accounted for much of this change, not only through a reduction in sweet potato consumption in China, but also throughout the region.

The utilization of root and tuber crops as animal feed also changed little on a developing country basis, over the twelve-year period; the average shares for cassava, sweet potato, potato, yams and aroids were 14.8%, 40.3%, 13.2%, 1.0% and 3.0% respectively. The only noticeable change was a significant increase (5.7%) in sweet potato use as animal feed corresponding to a reduction in the food share referred to above; again almost exclusively originating in China and the rest of Asia. Another noticeable regional change was the reduction in yam consumption in Asia and the corresponding increase in use of the crop as animal feed; however, it should be recalled that yam production in Asia is only of very minor importance.

Looking across the different root and tuber crops, it is clear that little diversification has occurred in the use of yams and edible aroids; they continue to be grown essentially for food, at least on a regional basis. At the other end of the spectrum, both cassava and sweet potato utilization is more diversified across food, feed and industrial uses. These diversified utilization patterns are most obvious in Asia and Latin America. It should be noted that significant proportions of the potato crop are also used for livestock feed and in industrial use in China.

Table 4: Utilization of Root and Tuber Crops as Food, Feed and in Industrial Use: Average Percentage Shares (S%) 1990/92, and Annual Change 1980-92 (D %)

CROP

FOOD

FEED

INDUSTRIAL

S%

D

S%

D

S%

D

CASSAVA


SS Africa

82.7

0.1

2.3

-0.8

0.2

-0.6

Latin America

37.1

-0.1

47.0

0.1

6.0

0.1

N. East/N. Africa

7.9

n.a.

0.0

n.a.

0.0

n.a.

Asia incl. China

70.8

-1.5

9.2

3.7

10.6

13.8

Asia minus China

75.2

-1.3

2.8

0.4

11.8

14.6

Developing (93)

68.9

-0.1

14.8

-0.7

3.8

4.7

SWEET POTATO


SS Africa

58.3

n.a.

1.7

0.7

n.a.

n.a.

Latin America

48.3

0.1

10.6

-0.6

n.a.

n.a.

N. East/N. Africa

60.9

0.2

n.a.

n.a.

n.a.

n.a.

Asia incl. China

49.1

-3.0

41.2

5.7

4.6

-0.4

Asia minus China

40.3

-5.7

44.5

6.6

8.2

3.8

Developing (93)

50.0

-2.9

40.3

5.7

4.4

-0.3

POTATO


SS Africa

75.5

0.2

1.1

1.2

0.0

n.a.

Latin America

77.0

0.2

2.8

-2.1

0.9

n.a.

N. East/N. Africa

79.9

0.1

1.9

2.0

0.4

n.a.

Asia incl. China

53.9

0.4

21.2

-1.3

0.0

n.a.

Asia minus China

73.3

0.2

1.9

-2.2

0.1

n.a.

Developing (93)

62.0

0.3

14.8

-1.1

0.2'

n.a.

YAMS


SS Africa

57.8

0.6

0.6

4.2

0.0

n.a.

Latin America

72.8

3.3

14.9

-3.9

0.0

n.a.

N. East/N. Africa

90.0

n.a.

0.0

n.a.

0.0

n.a.

Asia incl. China

82.3

-0.3

5.0

-8.3

0.0

n.a.

Asia minus China

82.3

-0.3

5.0

-8.3

0.0

n.a.

Developing (93)

58.6

0.4

1.0

-4.6

0.0

n.a.

AROIDS


SS Africa

83.5

0.3

2.1

0.9

0.0

n.a.

Latin America

79.9

-0.1

0.9

3.6

0.0

n.a.

N. East/N. Africa

62.0

-1.2

0.0

n.a.

0.0.

n.a.

Asia incl. China

90.9

-0.1

4.0

0.6

0.0

n.a.

Asia minus China

85.2

-0.5

4.9

-0.1

0.0

n.a.

Developing (93)

84.9

0.1

3.0

1.2

0.0

n.a.

Source: FAO Agrostat.
n.a. = Statistics based on few data, and consequently not reliable/available.

Per capita consumption

Levels and changes in per capita consumption of the different root crops are shown in Table 5. Large differences emerged across the different regions and among the crops. At the global level, per capita consumption of cassava averaged 22.1 kilograms per person per annum in marked contrast with a per capita consumption of 1.8 kilograms per annum of edible aroids. Large regional differences in the per capita consumption of all crops were also manifest. With the exception of potatoes, the data showed a reduction in per capita consumption of all root and tuber crops over the 12-year timeframe. This essentially indicates that production levels did not match increases in population growth, possibly as a result of changes in dietary preferences, urbanization trends and the relative prices of alternative foods.

FUTURE PROJECTIONS OF ROOT AND TUBER CROP PRODUCTION

In recent years a number of studies have attempted to project future trends in the demand for and supply of the major food crops. These include two FAO studies, viz., (i) 'Medium-Term Prospects for Agricultural Commodities - Projections to the Year 2000' and (ii) 'Agriculture: Toward 2010', and a recent IFPRI study, 'Global Food Projections to 2020: Implications for Investment'. In all three studies the projections are based on past and current production trends tempered by assumptions relating to future population growth, changes in economic development patterns, food demand and anticipated dietary changes in the context of growing urbanization. A synopsis of the three studies is presented below.

Projections to the Year 2000

Production: This study projects that output of root and tuber crops in the developing countries will increase by 1.3% per annum, resulting in the production of 455,452 MT by the year 2000 (see Table 6). The bulk of this increase is forecast to occur in the Far Eastern countries, particularly in some of the major root crop producing countries such as India, Indonesia, the Philippines and Vietnam. Strong growth in potato and sweet potato production is anticipated in India and Indonesia, whereas growth in cassava is expected to be strongest in Vietnam. In contrast, it is projected that growth in root and tuber production in China will be modest (less than 1 % p.a.) and will depend entirely on increased yields, due to the continued replacement of sweet potatoes by cereals.

Growth rates of root and tuber crops in Africa (2.6% p.a.) are expected to result in a production of 150 million tons (approx.) by the year 2000, largely due to increased planting of potatoes, sweet potatoes and cassava. Regional output in Latin America is also projected to increase particularly in Brazil, Colombia and Peru. However, expansion of root and tuber crop production in the Near East countries is expected to slow down in comparison with the growth rates witnessed in the eighties.

Table 5: Annual Per Capita Consumption (Kg.c-1.a-1) in the period 1989/91 and Annual Change over the period, 1980-91 (D %)

CROP

Kg. c-1.a-1

D %

CASSAVA


SS Africa

116.6

0.4

Latin America

26.6

-1.7

N. East/N. Africa

n.a.

n.a.

Asia incl. China

7.3

-2.6

Asia minus China

11.6

-2.9

Developing (93)

22.1

-0.2

POTATO


SS Africa

3.8

-1.5

Latin America

21.5

-1.0

N. East/N. Africa

31.3

1.8

Asia incl. China

10.3

1.6

Asia minus China

9.7

2.5

Developing (93)

12.4

1.0

SWEET POTATO/YAMS


 

SS Africa

34.2

2.1

Latin America

4.2

-2.6

N. East/N. Africa

0.3

-0.6

Asia incl. China

21.0

-5.6

Asia minus China

4.2

-3.8

Developing (93)

19.1

-4.4

AROIDS


SS Africa

9.1

-1.8

Latin America

1.3

-0.7

N. East/N. Africa

0.3

-1.4

Asia incl. China

0.8

-2.5

Asia minus China

0.3

-2.5

Developing (93)

1.8

-1.4

Source: FAO Agrostat.
n.a. = Statistics based on few data, and consequently not reliable/available.

Consumption: The FAO Year 2000 study projects that consumption of root and tuber crops in the developing countries will increase by 1.8% p.a., but consumption per capita is expected to decline. The study suggests that this decline will reflect a movement towards more readily available and easily prepared cereal staples. In this context, mention is made of the high marketing and processing costs of roots and tubers coupled with inadequate storage. Urbanization in Africa is calculated to curtail consumption, particularly for cassava and yams, but will only have a small effect on potato consumption. Consumption in Latin America and the Caribbean is projected to increase by 1.8% p.a., mainly reflecting population growth (and in the case of cassava, increasing industrial use), but on a. per capita basis a long-term decline in root and tuber consumption is anticipated.

In the Far East, consumption of roots and tubers is projected to rise at 1% p.a. Highest growth is expected in Thailand where a major shift of supply from export to domestic markets is foreseen as a consequence of the reforms in the European Community marketing policies. In contrast, the domestic market for roots and tubers and in particular for sweet potatoes in China is expected to fall as higher incomes encourage a shift in patterns of consumption.

Table 6: Root and Tuber Crop Production - Projections to the Year 2000

Area

Projected Production
('000 MT)

Growth Rates
(%)

Africa

149,882

2.6

Latin America

57,217

1.7

Near East

12,215

2.0

Far East

234,101

0.6

Other developing

2,037

2.0

Total developing

455,452

1.3

Source: FAO Medium-term prospects for agricultural commodities - projections to the year 2000.

The study questions further expansion in use of roots and tubers as animal feed, mainly as a result of change in government policies. In the developed countries, the demand for roots and tubers as animal feed is expected to fall. Lower domestic grain prices and the slowing down of livestock production in the EC, as a result of the CAP reform, are expected to reduce import demand; this is expected to significantly effect cassava imports to the EC. These trends will be further aggravated by the Uruguay trade agreement, albeit the impact of these new arrangements was not considered in the study.

Trade: Only a very limited amount of roots and tubers is traded internationally. The vast majority of production in developing countries is utilized on-farm, because the inherent high degree of perishability and bulkiness of the product results in high transport costs. In the 80s, however, there was a noteworthy increase in international trade, largely, because of an expansion in the export of processed cassava from Thailand to the EC. By the late 80s, trade in cassava accounted for 75% of total trade in roots and tubers and reached 30 million tons, whereas trade in potatoes accounted for the remaining 25%. The FAO Year 2000 study projects a significant fall in cassava chips trade, but that trade in potatoes and cassava starch will increase substantially.

'Agriculture: Towards 2010'

The FAO study, 'Agriculture: Towards 2010', makes projections on root and tuber crop production over a 20-year horizon. A summary of the projections is shown in Table 7. In general, the projections anticipate significant growth in root and tuber production (more than cereals) with much of the expansion coming from increased yields. It is tacitly assumed that the application of existing technologies can dramatically increase yields, particularly in regions such as sub-Saharan Africa.

Potato yields across the developing countries are expected to grow by as much as 3.9% p.a., but a projected reduction of 1.9% in the area of land planted to the crop is expected to result in an overall production increase of the order of 1.9% p.a. However, the study anticipates significant regional differences in the growth of potato production, with an expected high growth in sub-Saharan Africa (3.4% p.a.) and a modest growth in Asia (1.6% p.a.), largely because of a reduction in the cultivation of potatoes in China. Annual production growth rates of 2.7% and 1.9% p.a. are anticipated in Latin America and the Near East/North African regions.

Cassava production is expected to grow at an even faster rate (2.1%), again with about half of the increase coming from increased productivity per hectare. Little change in output is anticipated in Asia (a negative 0.4% p.a. in fact), whereas rapid expansion (3.4% p.a.) is projected for Africa, much of it (62%) dependent on increasing the current low yields per hectare across the region. The study also projects significant increases in cassava production in Latin America (2% p.a.), arising, in near equal proportions, from increases in crop yields and in area planted to the crop.

The projections for yams and sweet potatoes were aggregated as a single crop group, in the FAO 2010 study. Given the diverse trends in the recent production histories of these crops (increased growth in yams vs. reduced sweet potato production), it is difficult to interpret the study's projections on these crops. Suffice to say that, on aggregate, the two crops are projected to increase by 1.5% p. a. across the developing world, with the largest increases anticipated in sub-Saharan Africa (3.7%) and Latin America (3.0%). Noticeably, the study projects a significant reduction in land area planted to these crops (-2.4% p.a.) and a rapid annual increase (4.0 % p.a.) in crop yields! This contrasts sharply with recent trends as reported in this study (Table 3). The edible aroid crops are also anticipated to increase at an annual rate of 1.9% p.a., arising from increased plantings and crop yields in nearly equal proportions.

Projection across Agroecological Zones

Of interest, in the context of ecoregional research and development programmes, the FAO 2010 study examined roots and tuber crop production on an agroecological basis and made projections across the different agroecological zones. The projections are based on average output and yields reported in the period, 1988-90, and arrived at through a process of objective and subjective appraisals of the growth potentials of the different land classes coupled with subjective expert opinion on likely advances in and application of production technologies. The projections suggest that, across the developing countries as a whole, cassava production will expand most rapidly in the moist semi-arid, humid and subhumid zones, whereas highest growth rates in potatoes are anticipated in the irrigated and moist semi-arid zones. The largest percentage growth rates for sweet potato/yam and edible aroids are projected on the fluvisol/gleysol soil classes and in the humid regions.

Table 7: Root and Tuber Crop Production: Projected Annual Growth Rates to 2010

CROP

PRODUCTION

AREA

YIELD

D %

D %

D %

CASSAVA


 

S.S. Africa

3.4

1.5

1.8

Latin America

2.0

0.9

1.0

N. East/N. Africa

0.0

0.0

0.0

Asia incl. China

-0.4

-1.3

0.9

Asia minus China

-0.3

-1.0

0.7

Developing (93)

2.1

0.9

1.2

SWEET POTATO/YAMS


 

S.S. Africa

3.7

1.8

1.9

Latin America

3.0

2.0

0.9

N. East/N. Africa

-1.0

-0.2

-0.7

Asia incl. China

0.7

-8.3

9.8

Asia minus China

2.9

1.8

1.2

Developing (93)

1.5

-2.4

4.0

POTATOES


 

S.S. Africa

3.4

1.3

2.1

Latin America

2.7

1.8

0.9

N. East/N. Africa

1.9

1.0

0.8

Asia incl. China

1.6

-4.9

6.7

Asia minus China

2.2

0.5

1.7

Developing (93)

1.9

-1.9

3.9

AROIDS


 

S.S. Africa

2.4

1.3

1.1

Latin America

1.2

1.1

0.1

N. East/N. Africa

1.1

1.1

0.0

Asia incl. China

0.8

-1.1

1.9

Asia minus China

2.7

1.7

1.0

Developing (93)

1.9

1.0

0.9

Source: FAO Year 2010 Study

By and large, the regional projections mirror the global trends with some notable exceptions. The study projects a reduction in both potato and cassava production in the subhumid and humid tropics of Asia when China is excluded. Within this region, cassava production is also projected to fall in the moist semi-arid zone. Projections on cassava, sweet potato/yams and edible aroids for the Near East/North African region are not discussed as the levels of output of these crops are of very minor significance in the region.

Finally, the IFPRI Study, 'Global Food Projections to 2020: Implications for Investment', has published aggregate projections on root and tuber crop production (all crops) to the year 2020 (Rosegrant et al 1995). The study suggests that production will grow at a rate of 1.64% p. a., of which 37% will come from increased area planted and the balance of 63 % from increased yields. With the exception of rice, the study projects that roots and tubers will fail to match the productivity increases anticipated in the cereal crops; this projection is not consistent with the FAO 2010 Study, but the differences in the projected growth rates are not very great.

DISCUSSION

Statistical parameters on root and tuber crops in the developing countries are difficult to estimate with any degree of precision (Horton, 1988). The difficulty arises from the very nature of the crop (subterranean root and tuber growth), the extended planting and harvesting seasons, and the predominance of traditional production and harvesting systems and storage practices associated with resource-poor farmers and isolated marginal land areas where the crops are normally cultivated. In many developing countries and particularly in Africa, root crop statistics are based on extrapolations from small, often dated surveys (Dorosh, 1988). It is also suggested that government agencies tend to underestimate root crop production and consumption, because root crops are grown in isolated areas on small, irregular plots, frequently as intercrops, relay crops, secondary crops or backyard garden crops. (Horton, 1988) A further difficulty arises when time series analyses are undertaken. The FAO Production Yearbook publications are the commonly used reference source. However, it should be remembered that FAO continually revises and updates its estimates and does so retrospectively; consequently, recently updated Agrostat data are most accurate in time series analyses. This also implies that short timespan series analyses probably reflect trends more accurately than do long span analyses. However, in general, time series analyses should be interpreted with caution.

By and large, the trends reported in this study are consistent with most earlier studies, if not in the absolute levels of change, certainly in the direction of the changes indicated. The main trends may be summarized as follows:

Production:

(i) Root and tuber crops continue to be a major staple food across the developing world, yielding a total production in excess of 400 million metric tons of product, which in addition to its main use as human food, alternatively is used as animal feed or as a base material for a wide range of industrial processing.

(ii) In order of global production output per annum across the developing countries, the crops ranked as follows: 1. Cassava (152,181 MT), 2. Sweet Potato (123,769 MT), 3. Potato (93,157 MT), 4. Yams (23,524 MT), and 5. Edible Aroids (8,533 MT).

(iii) With the exception of sweet potato production, output of the major root and tuber crops expanded over the past decade, at moderate (cassava: 2%) to intermediate (potato: 3.1%) and at very high (yams: 7.3%) rates of annual growth.

(iv) Growth rates over the past decade were considerably lower than in the sixties and seventies (cf. Scott and Suarez, 1993), but the fall-off in production growth rates is in line with the general reduction in agricultural output of all agricultural crops over the period in question. The increase in yam production is a notable exception.

(v) Crop yields changed very little over the twelve-year period (1980-92) with the exception of yams (3% p.a. increase) and to a lesser extent potatoes (1.3% p.a. growth).

(vi) Expansion in area planted to roots and tubers was the main component of increased production.

(vii) Strong regional differences in production output and annual growth rates, and to a lesser extent in land area changes and crop yields, were evident in the study period. Asia was the major producer of root and tuber crops, and in particular of sweet potato and the potato crop, whereas cassava production was the most important root crop in Africa. Yams, and to a lesser extent edible aroid crops, all be they minority crops on a global basis all made important contributions to food production in Africa, and particularly in Nigeria. Asia headed the list in terms of improvements in crop yields.

Utilization:

(viii) Root crops continue to be predominantly used as a source of food; on a global basis the sweet potato crop is most prominent as regards the extent and range of its utilization as animal feed and in industrial processing, in addition to its use as a staple food. However, cassava and potatoes also make important contributions to the animal feed industry, and in the case of cassava to industrial processing. Yams and the edible aroid crops continue to be almost exclusively used as food for human consumption.

(ix) Globally, across the developing countries, the only major shifts in root crop utilization patterns appear to be in Asia, principally with regard to diversification in cassava use. However, global and regional statistics can mask developments at the level of individual countries; this will be discussed later.

(x) Annual per capita consumption of root crops averaged 55 kilograms in the period 1980/91. Large differences in consumption levels were evident not only among the crops, but also between the regions across the developing world. The consumption of roots and tubers is particularly prominent in Africa.

(xi) In general, per capita consumption levels fell over the study period with the exception of the potato, indicating that production level increases are not matching population growth. However, the effects of urbanization coupled with possible changes in dietary preferences (convenience foods) may also have had a significant bearing on the reduction in per capita consumption levels.

Projected Growth:

(xii) The three projection studies reviewed in this paper envisage modest to fairly significant expansion in root and tuber crop production in the future, albeit the three studies encompassed quite different time horizons. On a global basis, the growth projections averaged 1.3% p.a., 1.8% p.a. and 1.6% p.a. in the FAO Year 2000, FAO Year 2010 and IFPRI Year 2020 studies, respectively. Implicit in all three studies is the projection that crop yield increases will grow significantly in the future, an assumption that has clear implications for the development and/or transfer of production technologies.

(xiii) The FAO 2010 Study implies that root and tuber crop production growth rates will marginally outpace growth in cereals, whereas the FAO Year 2000 and IFPRI Year 2020 studies indicate growth rates somewhat less than cereals, rice not included.

Another major observation that is evident in this study is that aggregate analyses, such as those presented here, can mask significant developments at the level of individual countries. Firstly, it is obvious in the data presented that aggregated global (developing country) statistics do not reflect the wide variation that exists from region to region. Perusal of the data on the individual countries within the regions studied further emphasizes this point. In the context of capturing the dynamics and embryonic development of any given industry, particularly as they relate to future research needs and priorities, global and regional analyses such as those presented here, have considerable limitations. Evidence to support this point emerges strongly in the studies published by Scott and Suarez (1993), Wheatley and Scott (1994), Henry and Gottnet (1995) and indeed in several of the papers presented in the CIP publication, 'Product Development for Root and Tuber Crops', volumes I, II and III. A review paper, 'Potatoes in the 1990s', currently being prepared by FAO and CIP, further exemplifies this point in the context of developments in international trade in potatoes.

Whereas international trade in cassava peaked in the early nineties, and is currently facing a nose dive in the exports of cassava pellets to Europe as animal feed, growth in cassava based extracts and in particular in starch is expanding. For example, starch production in Thailand has been increasing in recent years at a rate of 8% p.a. and a considerable amount of research on the development of modified starches for a variety of industrial uses is being undertaken both in the public and private sectors (Cenpukdee et. al. 1992). Several countries (e.g., Indonesia, Vietnam, Colombia and Nigeria) are researching the use of root crop flours as a substitute for cereal flours and starches and a number of successes have been reported (Berrios and Beavogui, 1992; Odaga and Wanzie, 1992; Damardjati et. al. 1994 and Gitomer, 1994).

Starch extraction from root crops expanded rapidly in some individual countries (Thailand, Brazil and Indonesia) during the 1980s (Wheatley and Scott, 1994). However, seasonal variation in product supply and lack of storage are major bottlenecks in the development of this industry. It highlights the need for R & D on primary processing and cost-effective storage systems. More fundamentally, sustained or expanded root and tuber crop consumption will increasingly demand research on postharvest technologies to meet the growing trends in diet diversification which follow economic growth and urbanization. Wheatley and Scott (1994) have discussed this subject at some length; they report interesting case studies and development examples from Indonesia, China, Hong Kong and Singapore in Asia and from Colombia, Guatemala, Costa Rica and Panama in South America. All of these examples of embryonic developments in the processing and diversification of root and tuber crops, have clear implications for the importance of postharvest research, not only to secure a future niche for roots and tubers in the food chain, but also for the long-term competitiveness of this group of crops in future land use systems.

Assessing the Priority of Root and Tuber Crop Research

In the context of establishing priorities for national and/or international agricultural research, several and indeed contradictory arguments can be advanced to support and/or to undermine support for research on roots and tubers. Some of the arguments will be briefly discussed, all in the context of the major goals of the CGIAR, viz., improving sustainable food security through the alleviation of poverty and the conservation of natural resources.

The research priority of root and tuber crops as a source of human food, as animal feed or as industrial raw material may be described in terms of output parameters, measures of utilization and demand, and productivity indices (input/output ratios). The discussion which follows will focus primarily on the utilization of root crops for human consumption and animal feed in that, to date, the use of root crop products (principally starch) in industrial processing is of very minor significance on a global basis. Crop output parameters include: (i) Gross output of harvested material (metric tons), (ii) Dry matter percentage (% DM), and (iii) Output expressed in terms of food/feed energy (Kcals) and protein (Kg); ideally crop by-products (vines, stalks, etc.) should be included in these measurements but few reliable data are available. Utilization parameters include: (i) Total consumption (metric tons), (ii) Food and feed utilization shares (%), (iii) Per-capita consumption (Kg.C-1), and (iv) Proportion of dietary calorie supply (%). Productivity indices ideally should include output per unit area of land, labour and capital, taking into account input costs such as seed, fertilizer and biocides, to facilitate gross and net margin profit analyses; however as the economics of root crop production in the tropics are very poorly documented, few estimates of these measures of productivity are available.

Each of these parameters has merit in projecting the relative importance of each crop from a particular perspective. However in making comparisons among crops, or as between root and tuber crops and cereals for example, some common value denominators are needed. A widely used congruent in priority analysis of agricultural research is the economic value of production expressed in a standard currency; it is the starting point of the 1992 CGIAR Priorities and Strategies analysis which expressed the gross value of production of the major food commodities in US dollar terms. One of the limitations of this approach, as cited in the CGIAR Priorities and Strategies study, is the difficulty in getting comparable information on crop prices that reflects the true value of each commodity to the consumer across so many diverse socio-economic environments within the developing countries. This is particularly difficult for root and tuber crops which for the most part are consumed on-site by the producer; consequently, international trade in these commodities is non-existent (yams and edible aroids) or very limited (cassava, potatoes and sweet potatoes). As a result, relevant and reliable price data are very difficult to obtain.

An alternative approach would be to compare the crops in terms of energy and protein production relative to human dietary needs. However, this approach also has its limitations in that no single crop adequately meets the balanced requirements of the human diet, which in addition to protein and energy includes specific essential amino acids, minerals, trace elements and vitamins. Root and tuber crops vary considerably in these different components and in turn are markedly different from other staples, most noticeably in terms of protein content. Food protein is particularly important for the poor as their choice of food is often limited to one or two staple crops. Consequently, priority ranking of food crops is arguably better based on an index which takes into account the energy content of the protein fraction of the crop.

Output Parameters. Rankings of root and tuber crops on edible energy, edible protein, protein adjusted energy and economic value of production (VOP) are shown in Table 8. Values for rice and wheat are also listed for comparison. The economic values of production are based on the commodity prices being used in the current CGIAR Priorities and Strategies Study2. The estimated VOP figures rank the five crops in the order: cassava (30%), potato (30%), sweet potato (27%), yam (9%) and aroids (3%). Ranking on edible energy places cassava first (40%), followed by sweet potato (35%), potato (17%), yam (6%) and aroids (2%). However, when the energy values are adjusted for protein and indexed to cassava, sweet potato moves to the top of the list; in this ranking the value for edible aroids, albeit retaining the lowest rank, increases significantly.

2 Based on the prices being used in the current CGIAR Priorities and Strategies Study, viz.: Wheat US$ 144 per ton; Rice US$ 292 per ton; Cassava (fresh) US$ 68 per ton; Potato US$ 110 per ton; Sweet potato US$ 76 per ton; Yam US$ 137 per ton. In the absence of published price data on edible aroids this group of crops has been assigned the same value as yam, viz., US$ 137 per ton.

Table 8: Edible Energy, Edible Protein, Edible Energy Adjusted for Protein3 and Value of Production (VOP) of Root Tuber Crops, Rice and Wheat (1990/92)

3 Edible Energy Adjusted for Protein (EAP): EAP =a E, where E = Edible energy (Kcal) and a = 4p/e; p and e = grams of protein (p) and food energy (e) per 100 grams of edible portion.


Edible Energy
(Trillion Kcal)

Edible Protein
(Million Tons)

Edible Energy Adjusted
for Protein

VOP4
(US $ Million)

Cassava

130,617

594

130,617

10,348,308

Sweet Potato

114,511

1,733

187,798

9,406,444

Potato

57,944

1,593

148,916

10,247,270

Yam

20,584

393

40,756

3,222,788

Aroids

6,826

171

32,628

1,169,021

Root Crops

330,482

4,484

540,706

34,393,831

4 The value of production data should be interpreted with caution as there is some uncertainty about the prices used.

Cereals

Wheat

587,221

23,422

3,270,821

33,526,224

Rice

805,750

14,851

1,756,353

96,794,788

Rice indexed Comparisons

Rice

1.0

1.0

1.0

1.0

Wheat

0.73

1.58

1.86

0.35

Root Crops

0.41

0.30

0.31

0.36

Of wider interest, perhaps, is the comparison of root and tuber crops as a commodity group with other staple foods such as rice and wheat. In terms of value of production (VOP), Table 8 shows that root and tuber crops on aggregate sum to 36% of the value of rice whereas wheat has a rice indexed value of 35%. In food energy terms, roots and tubers are marginally higher in relative value (41%) whereas wheat because of its higher protein content increases to 73 % of the value of rice. As might be expected these differences are much more noticeable when the crops are compared on a protein adjusted energy basis. On this basis the rice indexed value of root and tuber crops drops to 31% whereas wheat increases to 186%. It is interesting to note that the estimated values of root crops relative to rice fall within a very narrow range (31-41%) irrespective of the congruent used in the comparisons.

Productivity indices. As stated earlier, priority ranking on output criteria only captures one perspective of the production process. Input costs are also critically important, particularly in the context of a priority setting exercise which has as one of its major goals the alleviation of poverty. Comparable input costs from Africa (FAO, 1985) and South America (FAO, 1989), based on IITA and CIAT data, suggest the following average cost differentials relative to cassava, viz., cassava 1.0, potato 2.74, sweet potato 1.25, yam 3.34, and edible aroids 0.73; the South America study did not include input costs for edible aroids, but did provide estimates for rice production which would suggest a weighting of 1.5 relative to cassava costs. Applying these weights to the output data in Table 8 results in the rankings listed in Table 9.

As would be expected cassava heads the list on cost adjusted value of production and energy output terms, whereas sweet potato has highest rank on protein adjusted energy output; this simply reflects its relatively high protein content. It should be noted that, adjusting for input costs does change the relative values of the crops significantly. The aggregate cost adjusted values for root and tubers relative to rice are 0.48, 0.35 and 0.38 for Energy, Protein adjusted Energy and Value of Production respectively; these are not greatly different from the respective values in Table 8, and suggest that root and tuber crops have a value somewhere between 30 to 48% of the value of rice depending on which index is chosen for comparison. The proximity of the rice-indexed cost-adjusted edible energy and protein-adjusted energy values relative to value of production in dollar terms would seem to suggest that market price does reflect the nutritional value of the crops. However, it should be borne in mind that the part-whole correlations among these indices will intrinsically engender some degree of proximity between the values. It may be argued that the cost adjusted rankings, and in particular the cost adjusted energy ranking, have greatest relevance to the poor, who on the one hand don't have the resources to engage in high input farming systems, and on the other hand have most urgent food energy and protein needs. On the other hand, value of production (VOP) as it relates to economic development also has relevance for the poor, particularly in countries where there is an equal distribution of wealth across the different sectors of society.

Table 9: Ranking of Root and Tuber Crops on Cost Adjusted Edible Energy, Protein Adjusted Energy and VOP (1990/92)


Edible Energy
(Trillion Kcal)

Protein Adjusted Energy
(Trillion Kcal)

VOP4
(US $ Million)

Cassava

130,617

130,617

10,348,308

Sweet Potato

91,609

150,238

7,525,155

Potato

21,148

54,349

3,739,880

Yam

6,163

12,202

964,907

Edible Aroids

9,351

44,696

1,601,399

Roots and Tubers

258,888

392,102

24,179,649

Rice

537,167

1,170,902

64,529,858

R&T/Rice

0.48

0.35

0.38

4 The value of production data should be interpreted with caution as there is some uncertainty about the prices used.

In addition to the costs considered above, productivity returns to land and labour should also be taken into account. Availability of land and labour are often major constraints of the poor; labour to the extent that family labour demands need to be abated to accommodate needed improvements in education standards. In this context, published rankings of some of the major food crops on Edible Energy per hectare per day (Horton, 1984), and FAO estimates of the labour demands of different food crops (FAO, 1994), are interesting. However, the basis of these calculations is not described and consequently it is difficult to decide how to use the estimates appropriately.

Another productivity parameter which may well become increasingly important in priority analysis in the future is the energy balance ratio of crop production systems, particularly in the context of the sustainable management of natural resources. Food crop production systems differ markedly in their energy balances. Leach (1976) has reported energy balance ratios (Er = Mj.ha-1 OUT/Mj.ha-1 IN) for a range of farming systems in the tropics and in temperate regions. Subsistence cassava (Er = 62) and rice (Er = 17.3) production systems are shown to be far more efficient in energy terms than, for example, main crop potato production in lowland Britain which has an estimated energy ratio of 1.57. Typically, energy balance ratios for tropical crop production systems involving some fertilizer inputs and machinery, range from 5 to 10. This energy balance perspective has relevance to long-term research priorities, which in the context of sustaining natural resources may dictate greater emphasis on the photosynthetic capture of C4 crops and the genetic manipulation of germplasm to enhance pest and disease resistant capacity, thereby reducing the need for pesticide and herbicide inputs.

Demand perspectives: Finally, demand side perspectives should also be considered in priority setting judgements. In this context, it must be recognized that root and tuber crops do not make a major contribution to the human diet on a global (developing countries) basis. Horton (1988), calculated that root and tuber crops collectively contribute 6.7% of total dietary calorie intake in the developing countries. Sweet potato (2.7%), cassava (2.1%) and potato (1.3%) contributed more than 90% of root and tuber sourced calorie intake. However, regional differences were quite large. For example, cassava accounted for 9.6% of total calorie intake in Africa and 3.7% in South America, whereas the potato contributed 2.9% of total calorie intake in Asia.

These regional differences not only reflect consumer preferences, but also agroecological and soil suitability to grow different crops. However, traditional consumer preferences strongly influence demand for foods and particularly for foods of root and tuber origin. Of important relevance to future research priorities in this context is the extent to which the continuous expansion of urbanization will effect the demand for root and tuber crops. It is argued that research and development of postharvest technologies will open up new urban markets for convenience foods based on root and tuber crops; reference to recent developments in Asia is cited by Scott and Suarez (1993) to advance this view. On the other hand, there are a number of studies (FAO 1985) which show that the storage and marketing costs of root and tuber crops are very high compared to staple foods such as rice. At issue therefore, is the question - can postharvest research on the storage and processing of root and tubers commercially enhance these crops to more effectively compete on the urban markets. Of more immediate interest are the questions -should the CGIAR Centres expand their activities in postharvest technology; and how should this work be facilitated in partnership with the private sector which ultimately must become involved in commercial development and marketing?

The foregoing analyses and discussion provides a starting point and some instrumental perspectives on the task of determining the research priorities of root and tuber crops. Several additional judgements need to be made in the context of the CGIAR Priorities and Strategies exercise. These include considerations such as (i) Technology gap potentials, (ii) Application of existing technologies, (iii) Strength of NARS in root and tuber crop research, (iv) Comparative advantage of the CGIAR Centres, and (v) Alternative sources of technology supply. All of these considerations raise important questions that are very difficult to answer with relevant and conclusive evidence.

Further, a dimension not easily captured in a global approach to the setting of agricultural research priorities is the development dynamics of the production-consumption chain, the starting point of most priorities and strategies market research in industry. Post-factum regional statistics may capture some of the fluxes; e.g., growth in use of root crops for animal feed in China. However, emerging developments usually have their origin in localized initiatives which as they evolve develop appropriate momentum and change. Given that agricultural research priorities are all about likely future change, perhaps they are best identified in the market place, viz., from the bottom up. In this context and in hindsight, it may have been better to have undertaken this analysis on a country basis, selecting those countries that grow most and are exploiting more fully alternative uses of root and tuber crops, and sequentially develop appropriately weighted aggregate regional and global parameters and perspectives from that basis. Certainly, growth projections developed from a selected country perspective may provide better insights to potential and likely changes. On the other hand, the global projections in the FAO and IFPRI studies do not anticipate significant growth differentials among the major food crops, other than what might be expected from past trends.

REFERENCES

Berrios, D. and M. Beavogui. 1992. Trials for the Introduction of Sweetpotato in Bread Making in Burundi. In: Scott, G., P.I. Ferguson and J.E. Herrera (eds.) 1992. Product Development for Root and Tuber Crops. Vol. III - Africa. Proceedings of the Workshop on Processing, Marketing, and Utilization of root and Tuber Crops in Africa, held October 26 - November 2, 1991 at International Institute for Tropical Agriculture (IITA), Ibadan, Nigeria. CIP, Lima, Peru. 506p. + xxiii. pp. 373-376.

Cenpuykdee, U., C. Thiraporn, and S. Sinthuprama. 1992. Cassava Processing and Utilization in Thailand. In: Scott, G., S. Wiersema and P.I. Ferguson (eds.) 1992. Product Development for Root and Tuber Crops. Vol. I - Asia. Proceedings of the International Workshop held April 22 - May 1, 1991 at Visayas State College of Agriculture (VISCA), Baybay, Leyte, Philippines, sponsored by the International Potato Centre (CIP), the Centro Internacional de Agricultura Tropical (CIAT), and the International Institute for Tropical Agriculture (IITA), CIP, Lima, Peru. 384p. + xxii. pp. 51-60.

CIP. 1993. Product Development for Root and Tuber Crops. Volumes I, II and III. Edited by Scott, G.J., S. Wiersema and P.I. Ferguson. CIP, Lima, Peru.

Damardjati, D.S., S. Widowati, T. Bottema and G. Henry. 1994. Study on Cassava Flour Processing and Marketing in Indonesia. Paper presented at International meeting on cassava flour and starch, CIAT, Cali, Colombia 11-15 January 1994.

Dorosh, P. 1988. The economics of root and tuber crops in Africa. RCMP Research Monograph, IITA, Ibadan, Nigeria.

FAO, 1985. Report of the Workshop on Production and Marketing constraints on Roots, Tubers and Plantains, Kinshasa, Zaire, 1985.

FAO, 1989. Roots, tubers and plantains in food security. FAO Economic and Social Development Paper No. 79.

FAO, 1990. Roots, Tubers, Plantains and Bananas in Human Nutrition. FAO Food and Nutrition Series: No. 24.

FAO, 1992. The World Sweet Potato Economy. Published by the Commodities and Trade Division, FAO, Rome.

FAO, 1993. Agriculture: Towards 2010. FAO, Rome.

FAO, 1994. Medium-Term Prospects for Agricultural Commodities Projections to the year 2000.

FAO, 1994. Tropical root and tuber crops: Production perspectives and future prospects. FAO Plant Production and Protection Paper, No. 126. FAO, Rome.

FAO/CIP, 1995. Potatoes in the 1990s: Current Status and Future Prospects of the World Potato Industry. (In press).

Gitomer, C. 1994. Potato and Sweetpotato Production in China: Systems, Constraints, and Potential. (In press).

Henry, G. and V. Gottnet. 1995. Global cassava sector trends: Reassessing the crops future. CIAT internal cassava programme paper, 1995.

Horton, D. 1988. Underground Crops: Long-term trends in production of roots and tubers. Winrock International, Morrilton, AR, USA.

Horton, D. and H. Fano. 1985. Potato Atlas. International Potato Center (CIP). Lima. Peru.

Kay, D.E. 1973. Root Crops. Tropical Products Institute, London.

Leach, G. 1976. Industrial energy in human food chains. In Food Production and Consumption: the efficiency of human food chains and nutrient cycles. Ed. by A.N. Duckham, J.G.W. Jones and E.H. Roberts. North Holland Publishing Company. 1976.

Odaga, A. and R. Wanzie. 1992. The Use of Sweetpotato in Bakery Products in Cameroon. In: Scott, G. P.I. Ferguson and J.E. Herrera (eds.) 1992. Product Development for Root and Tuber Crops. Vol. Ill - Africa. Proceedings of the Workshop on Processing, Marketing, Utilization of Root and Tuber Crops in Africa, held October 26 - November 2, 1991 at International Institute for Tropical Agriculture (IITA), Ibadan, Nigeria. CIP. Lima, Peru. 506p. + xxiii.

Rosegrant, M.W., Mercedita Agcaoili - Sombill and Nicostrato, D. Perez (1995). Global Food Projections to 2020: Implications for Investment. IFPRI Draft Food Agriculture and the Environment Discussion Paper, 2020 Vision.

Scott, J.S. and V. Suarez, 1993. Transforming Traditional Food Crops: Product Development for Roots and Tubers. Proceedings of an International Workshop on Root and Tuber Crop Processing, Marketing and Utilization in Africa. Published by the International Potato Centre (CIP), Lima, Peru. 1993

Wheatley, C.C. and G.J. Scott, 1994. Global Markets for Roots and Tubers in the 21st Century. Proceedings of the Tenth Symposium of the International Society for Tropical Root Crops (ISTRC)1, Brazil. November 1994.


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