T. J. Goering
Tropical root crops—cassava, potatoes, sweet potatoes, yams, and aroids—are a staple food of about one third of the population of tropical countries—generally the rural poor. An estimated 170 million tons of these crops, equivalent in calorie content to 50 million tons of grain, are produced annually. Typically, calories from root crops cost less than half as much as calories from traditional grains and pulses. Cassava accounts for nearly two thirds of production of all root crops and is a major source of calories for some 300 million people in the developing world. Occupying some 20 million hectares of cropland globally, this group of crops is worth more to the farmers producing them than either cocoa, rubber, tea, or coarse grains.
Root crops are widely cultivated in Southeast Asia (especially in Indonesia and Thailand), in South Asia (mainly in India), and in Western Africa and Latin America (particularly in Brazil and Colombia). About 95 per cent of production is directly consumed by the producers. Although these crops do not by themselves provide adequate nutrients, since most are high in starch and low in protein, they can frequently be combined with other local foods to provide nutritionally balanced diets. A particular advantage of cassava is that it can be grown successfully in a wide range of agricultural and climatic conditions. It is able to withstand drought and to thrive in relatively primitive farming systems, frequently under conditions of poor crop management and with few purchased inputs.
Despite the importance of these crops to the rural poor, they have not received much attention until recently, either from the agricultural research community or from development planners. Over the past few years, however, there has been a sharp increase in research work on root crops at national and international research centers, such as the International Center for Tropical Agriculture (CIAT) in Cali, Colombia and the International Institute for Tropical Agriculture in Ibadan, Nigeria. This research concentrates mainly on how to increase production and on how to expand the potential of such crops as sources of food, animal feed, or energy. Good progress is being made. At CIAT, for example, cassava yields have been tripled by using better varieties and improved, low-cost agricultural practices.
One opportunity for the expanded use of root crops, as efficient converters of solar energy into carbohydrates, lies in meeting the consumption needs of low-income people. However, the evidence shows that human consumption of these crops is unlikely to expand more quickly than population, mostly because as their incomes rise, people generally prefer less bulky, less perishable, and more nutritious food, such as wheat, rice, or maize. Thus, the substantial increase in yields that now appears possible will bring down the costs of producing these crops and make them potentially attractive for other purposes. There is, for instance, a growing market for root crops, especially for cassava, as feed for meat and poultry production—some five million tons of cassava were imported for feed by the European Community (EC) in 1978. These crops may also provide an attractive source of energy. Countries such as Brazil, for example, have begun to use cassava in the production of ethyl alcohol as a substitute for gasoline. The possibilities for using these crops also increase as fossil fuel costs rise and as population pressures push agricultural frontiers to lands that have increasingly limited potential to sustain production of traditional food crops. Expansion of root crop production depends crucially on combining the results of research aimed at increasing crop yields with greater efforts, at both national and international levels, to utilize these crops in a wide range of development projects.
Root crops as food
Consumption data on root crops tend to be unreliable, but it cannot be disputed that tropical root crops are an important and efficient source of calories in many of the poorest countries. The Food and Agriculture Organization (FAO) estimates that in recent years root crops have provided a substantial proportion of total calorie intake in several African countries, supplying as much as 60 per cent in Zaïre (see Table 1). Moreover, these crops are basic calorie sources in poor regions of other countries such as Brazil and Indonesia.
(Mid-1977, in millions)
|Daily per capita |
|Per cent of total |
calories from TRCs
Figures rounded to nearest 10.
Figures rounded to nearest 10.
Root crops generally compare poorly with grains in terms of protein, carbohydrates, iron, and thiamine, but they are good sources of calcium and, in the case of sweet potatoes, an exceptional source of vitamin A. This lack of protein in most root crops is a concern. However, there may be a greater role for root crops in the alleviation of nutritional deficiencies than is commonly believed. Nutritionists have frequently observed that food consumption by most adults in many developing countries tends to be roughly balanced in nutritional terms. (If calorie intake is adequate, so is the intake of most other nutrients.) If this is so—and case studies in Kerala (India), Northeast Brazil, and northwest Zambia, where root crops are important in the diet, suggest that it is—then the most useful way to improve nutrition may be to increase the quantity of root crops available for consumption and promote the use of other, nutritionally complementary local foods. This would seem to be more efficient and more likely to be acceptable than changing the composition of the diet radically, particularly if the latter required greater use of nonlocal foods. Small-farm cropping systems which include, for example, root crops and groundnuts or beans would be valuable parts of a food and nutrition program in these circumstances.
But some dietary problems are likely to remain. The nutritional deficiencies of the young and of pregnant and lactating women who depend on root crops for their food tend to be widespread and, in many cases, serious. It is demonstrably true that if a child eats mainly cassava or other high-calorie, low-protein root crops, he is almost certain to suffer from protein deficiency. (Despite this, experience in some developing countries suggests that even where root crops provide an important part of the diet, child mortality—one measure of nutritional adequacy—may still below if other protein-rich foods are also consumed.) An appropriate course of action to counter the nutritional deficiencies of these particular groups would be to concentrate on improving existing diets by supplementing them with other protein-rich in digenous foods. Thus, the addition of a handful of groundnuts to the daily diet of children over six months of age in nutritionally-deficient areas of Africa could solve a large portion of their nutritional problems.
Experience in some countries has also shown that root crops can be used to improve nutrition when they are combined with other crops in the production of composite flours. In parts of Africa, for instance, it has been suggested that a mixture of 70 per cent cassava flour and 30 per cent groundnut flour would contain more protein, calorie density, and niacin than the maize flour frequently used as the food staple. The use of these composite flours may help to reduce foreign exchange expenditure on wheat imports, by substituting flour components derived from local sources. This also may have the effect of stimulating local agricultural production, processing, and employment. Careful examination of typical diets for particular socioeconomic groups or geographic regions is needed before unequivocal recommendations can be made about how the root crops can be produced and utilized so as to contribute to nutritional improvement. Further research is also needed to determine the extent to which heavy intake of cassava may restrict the intake of iodine by the human body, a possibility supported by some studies done in West Africa.
Use as feed and starch
Thus far, the export of cassava pellets to the EC for use in the manufacture of livestock feed is the most dynamic element in the expanding global use of root crop products. The shipment of five million tons in 1978 reflects an annual growth rate in recent years of nearly 20 per cent. Exports are dominated by Thailand and, to a much smaller extent, Indonesia. Because Thailand has extensive lands well suited to cassava production and because the Thai Government assists farmers by providing a good physical infrastructure, cassava has become one of the country’s most important export commodities.
The size of exports of root crops to the EC has been determined by several factors, particularly by their quality and price competitiveness compared with alternatives. As a general rule, cassava prices must be at least 20 per cent less than cereal and soybean meal prices if cassava is to represent an economic substitute in the preparation of livestock feeds. But assuming that cassava will continue to be cheaper than its alternatives as a source of feed, its share of the EC market will be heavily influenced by political factors. Growing pressures by some EC members to grant increased protection to community grain producers has already led to some limitations on cassava imports.
The use of root crops as animal feed in developing countries appears to have considerable potential. The carbohydrates in cassava roots, for example, are highly digestible and could provide a valuable complementary source of energy to the typical tropical forages, which tend to be fibrous, bulky, and not very palatable. If tropical forages are supplemented with cassava products, therefore, the resulting feed generally has a marked positive impact on livestock performance. Recent work in Venezuela has also demonstrated that good quality protein is obtainable at reasonable cost from cassava leaves, and can be used to feed livestock. Cassava leaves have been utilized too, in Thailand, for export as commercial feed supplements.
Thus, in general, cassava products can be substituted for alternative sources of nutrients to feed different species of livestock in both tropical and temperate countries, although research work is not sufficiently advanced to permit precise specification of rations under particular circumstances. Continued research is required if these possibilities are to be brought into practical commercial use.
Industrial starches derived from root crops differ only slightly from those derived from grains; their share of the market is therefore determined largely by their price. Starch imports in the two largest markets, Japan and the United States, have been in the range of 100,000 tons annually in each in recent years, with cassava starch accounting for three quarters of this amount. (Other starch imports include potato, arrowroot, and sago.)
Prospects for international trade in cassava starch, however, appear to be limited. Imports of cassava starch into the United States have declined in recent years because of higher freight costs, erratic supplies, and the increased availability of locally produced corn starch that can be modified to meet particular needs. This decline seems likely to continue. Prospects of starch imports into Japan may be somewhat brighter, because of Japan’s proximity to the major source of supply, Thailand, which accounts for about one half of the world’s cassava and sago starch exports and has large excess production capacity.
In contrast to the export market, local starch industries which supply domestic needs could be expanded in some countries which produce root crops. The range of starch production technologies here is wide, and there seem to be some economies of scale in starch manufacture. Where small-farm production and the creation of rural nonfarm employment are important development objectives, deliberate government policy to support investment and research in these processing technologies is likely to be required to improve the quality and efficiency (and thus the viability) of small-scale starch plants in rural areas.
|Asia, centrally planned||9.3||14.5||—||85.8||1.8||111.5|
|(Per cent of total)||41||15||7||34||3||100|
indicates data are insignificant.
Includes taro, minor roots, and tubers.
Includes Egypt, Libya, and the Sudan.
indicates data are insignificant.
Includes taro, minor roots, and tubers.
Includes Egypt, Libya, and the Sudan.
Other industrial processing
One of the possibilities for making use of root crops in industry is as a base for fermentation processes involved in the manufacture of high-value products, such as single-cell protein (SCP) and ethyl alcohol. Research on these processes has expanded in recent years in response to sharply higher relative prices for petroleum—the usual base for the manufacture of these products. Production of glucose sugar from cassava or other root crops is as technically feasible as the more common practice of using corn or wheat starch. The major consideration is the relative price of starch from these various sources. A doubling or tripling of cassava yields would make the use of cassava starch economically attractive.
An interesting question for food planners is the potential role of root crops in meeting future protein requirements of humans through traditional sources, such as meat, or through nontraditional protein. Production of single-cell protein, now used largely for animal feed, exceeds one million tons annually. Single-cell protein is generally produced from a petroleum base, but the technology used is equally suited to a base of organic materials such as root crops, provided they are sufficiently cheap and supplies are adequate. Typically, raw materials costs make up at least 60 per cent of total production costs and are therefore critical in determining the economic viability of the process. And because production costs per unit of output decline sharply as plant size increases, a basic question is whether efficient, smaller-scale SCP plants are technically and economically feasible. Research at CIAT, with support from Canada’s International Development Research Center, is underway to provide answers to these questions.
Several root crops, and cassava in particular, have been used at various times and places for more than 50 years in the production of ethyl alcohol. Each ton of fresh roots can produce up to 160 liters of alcohol. The product can substitute for up to 20 per cent of gasoline by volume without needing a change in the carburetion systems of most engines. Much of the research on the alcohol production process in recent years has been underwritten by the Brazilian Government as part of its National Alcohol Program, which aims to produce alcohol for blending with gasoline or for use in all-alcohol powered engines. Although most of the installed production capacity in Brazil’s alcohol industry is based on the use of sugar cane, greater use of cassava is expected in the future because of its wider adaptability to soil and climatic conditions. Japan has long derived much of its industrial alcohol from the sweet potato.
Root crops have a potential role in a considerable range of agricultural and rural development projects. Opportunities for commercial development are exemplified by the growing volume of cassava exports from Thailand that will be used as animal feed. A strategy which uses these crops to improve the conditions of the rural poor should reflect several factors: the need for low development costs per beneficiary, the relative abundance of labor during much of the year, the limited access of the poor to good land, and their negligible cash reserves. A sound strategy should also ad dress the frequent calorie shortages of this group, and should recognize that many of the future poor must seek livelihoods on lands of limited natural fertility in a sociopolitical environment where support services for agriculture are frequently deficient.
If the welfare of low-income people is to be improved, relatively simple, low-risk technologies are needed to provide greater returns from the limited resources under their control. Root crops, by virtue of their importance to smallholders throughout the world, are well suited both to improving agricultural growth and to increasing the income opportunities of the poor. But if these benefits are to be fully realized, deliberate efforts must be made by governments and donor agencies to influence several factors—including the emphasis on research concerning root crop production and utilization, the type of cropping system utilized in rural development programs, and the scale and type of technology used in processing root crops.
In many small farms, cropping systems should be designed to provide both adequate incomes and a nutritionally balanced diet for the family. This is frequently difficult to achieve. Many small-scale farmers, having experienced the vagaries of the markets for their cash crops, often prefer the security of producing most of their own food, even if it means sacrificing some income. The first priority in the design of a cropping system for low-income families may well be to provide a variety of crops to ensure the family’s food security, then allocate the balance of the holding to cash crops. The portion of the typical smallholding allocated to basic food production is likely to be small if root crops are included in the cropping program. With, for example, annual cassava yields of 10-20 tons per hectare and maize yields of 1-2 tons per hectare, approximately one half a hectare divided between these two crops, intercropped with beans, would provide for the basic calorie and protein needs of a typical smallholder family. The low-risk nature of cassava production makes this crop an ideal “safety net” to ensure some food supplies in risky agricultural and climatic situations. These “nutritional dimensions” of any proposed cropping programs require the explicit attention of project analysts. Precise cropping possibilities can only be determined according to the characteristics of specific locations.
Because the direct consumption of root crops by producers is likely to expand only slightly more rapidly than their increase in numbers, improved technologies will be needed to increase other forms of utilization. This requires technologies to make these crops more widely available for urban consumption as well as to make industrial processing of these crops more efficient. Since root crops are bulky, their marketing and transport costs are now relatively high compared with other food groups. However, these costs can be reduced through drying processes and improved market infrastructure and transport. Improved storage technologies already exist that can slow post-harvest deterioration of the fresh product. Further research on the use of root crops in composite or fortified flours is a necessary part of this overall effort to reduce the cost of calories and to increase the availability of food nutrients to low-income consumers.
Using root crops for some nonfood purposes may require a choice at the national level between promoting small-scale technology, which will directly benefit the local area, or emphasizing large-scale production, which will maximize returns and economies of scale. At one extreme, smallholders can supply fresh roots to small-scale processing facilities, as is done in the cassava/chip industry in Thailand and the cassava flour/starch industry in Northeast Brazil. At the other extreme of the technological spectrum are plantation production systems producing fresh roots for large-scale, capital-intensive facilities designed to produce industrial starch or alcohol. The choice of technology for processing is perhaps the most important factor in determining the distribution of benefits from development programs based on root crops, since the type of technology chosen is an important determinant of the systems that will be used to produce the raw material. Large-scale processing generally leads to pressures for large-scale production systems and to reduced opportunities for small-holder participation.
The export market for root crops depends on their cost competitiveness. There is a need for dependable supplies of processed cassava, generally in the form of pellets, that are large enough to enable exporters to benefit from the important economies of scale which exist in shipping (by sea) and handling. Therefore, individual country export programs should probably be based on annual root production of at least 250,000 tons, equivalent, at 20 tons of fresh roots per hectare, to 12,500 hectares of crop. This would require about two pelletizing factories, each with an annual pellet production capacity of 60,000 tons. Total establishment costs for a factory of this size using imported machinery are in the range of US$750,000, although locally fabricated machinery is available in some countries and might result in considerable cost savings. In a number of countries where root crops are staple food items, higher yields, more production and lower prices would be required to compete in the international market with cassava supplies from traditional exporters.
Existing production technology, effectively applied, already provides a sound basis on which to build rural development projects which incorporate the use of root crops. But realization of the full potential of these crops as sources of food nutrients and industrial raw materials rests upon the achievement of reduced unit costs of the energy produced from them and improved returns per unit of land and labor. These goals can only be realized when farm yields more closely approach those promised in experimental work. The need for continued research into increasing production and the uses of these crops and for effective agricultural extension services is clear.