3. Production and consumption

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According to a recent FAO estimate, virtually every country in the world grows some species of root crop. Most of the root crops considered in this study require tropical conditions and are restricted to Africa, Asia and Latin America. Only potatoes and some varieties of sweet potato are grown in large quantities in the temperate zone. These root crops are often the main dietary staple for low-income consumers. They are grown by farmers as subsistence crops on small plots of land ranging from two to 20 hectares depending on the region.

It has been estimated that about 82 percent of Paraguayan farmers grow cassava as a subsistence crop on small holdings, and whenever they move on to virgin land they first plant cassava. In Latin America, 75 percent of the cassava farms are about 20 hectares or less, whereas in Java and Kerala the holding is about two hectares. In Thailand most producers have less than one hectare devoted to cassava. In 1982/83 the cultivation and harvesting of some 19 million tonnes of cassava in Thailand was carried out entirely by approximately 1.2 million smallholders who obtained yields of between 13 and 15 tonnes per hectare (FAO, 1984). Most of this production was processed, with 85 percent transformed into chips and pellets for animal feed and 15 percent used for starch production. Very little was used directly for human consumption.

In Africa these root crops are usually subsistence crops grown mainly as food, so the farmer keeps sufficient to feed his family and sells only the surplus. However, there is now a growing commercial market for them. Cassava is commercially processed into gari, a staple food in parts of Nigeria, and into kokonte in Ghana. In Brazil about 70 percent of the cassava harvest is marketed (Lynam and Pachico, 1982).

In subsistence production of cassava, yields are often low as a result of poor cultivation practices. Cassava is often grown on marginal land and as it grows relatively well on poor soils, with limited inputs, it is often planted as the last crop in a shifting cultivation system. On average, weeds reduce cassava yield by 59 percent. On newly cleared land no positive yield response is observed to either nitrogen or potash fertilizers. On poor land there may be some response to nitrogen, but fertilizer is not extensively applied. Even in Java in Indonesia, where land use is very intensive and the cost of fertilizer is heavily subsidized, only 8.1 kg of fertilizer/ha was used for cassava compared to 178.9 kg/ha average for all the other crops. In Brazil only about 9 percent of the cassava area is fertilized.

Most research to improve root crop production has been devoted to potato in temperate countries and in the tropics, especially at the International Centre for Potato Research (CIP) in Peru, and so it is not surprising that potato yields are much higher than those of the other root crops. In some parts of Latin America, however, it is still grown by subsistence farmers on a small scale, as part of a complex multiple-cropping system, on one to two hectare plots with low yields. In temperate zones and in cool highland areas, where it is usually grown under irrigation conditions and as a sole crop, yields are often very high. It is produced only in limited quantities in the tropics, cassava and sweet potatoes being the major crops there.

In 1982, the CIP estimated that there has been an overall increase in the total production of root crops in developing countries during the years from 1961 to 1979. However, when considered individually and regionally, production of crops like cassava has gone up, sweet potatoes have remained stagnant, while production of potatoes has decreased in industrialized countries, but increased in developing countries. Per caput production of root crops had fallen during this period in most developing countries. In sub-Saharan Africa, output of root crops, except sweet potato, failed to keep pace with population growth. In Latin America and the Caribbean, since 1970, production trends of starchy staples as a group have been negative (FAO, 1988a). Various reasons have been adduced for the decrease in production, including infestation by insects, parasites and diseases, bad weather and marketing problems.

That part of the root and tuber crop harvest which is produced by subsistence farmers for their own consumption does not enter the commercial marketing channels. It is thus difficult to obtain accurate data on total production of these crops. Today, FAO's statistics are the best available guide to global production of these crops.

Tables 3.1 and 3.2 provide production, acreage and yield figures for roots and tubers in various regions of the world. Among the five root crops listed, potatoes occupy a land area of about 20 million hectares or 44.3 percent of the total area of 46 million hectares devoted to world production of root crops. The potato is increasingly important in developing countries and is a good source of nutrients in the diet. Its protein: calorie ratio is as high as that of wheat (Table 4.10) and its productivity in terms of energy and protein per hectare per day is greater than that of most other staple food crops (Table 4.1).

Potato has the highest percentage of world production, accounting for 52.9 percent of the total in 1984, followed by cassava covering 14 million hectares (21.9 percent) and accounting for 30.9 percent of total production; then sweet potatoes covering about eight million hectares (16.9 percent) and accounting for 19.9 percent of total production. Yams cover about 3 million hectares (5.5 percent) with 4.3 percent of total production and the least important, taro, occupies I million hectares (2.5 percent) with 1.0 percent of total production.

Table 3.1 shows that potato is growing over a wide geographical spread in the countries producing this root crop, but the leading producers are all in temperate-zone areas (Table 3.3). Of the total of 130 potato-producing countries, 95 are developing countries and in 1978-81 they were able to produce less than 10 percent of the world production. However, by 1985 developing countries accounted for about one-third of world production, with China producing 60 percent of this contribution. The increase has been particularly significant in the Near East where production had gone up by 130 percent, in the Far East by 180 percent and in Africa by 120 percent. Potato is also a potentially high-yielding crop. The present average yield is only about 10 t/ha in developing countries but yields as high as 72 t/ha have been recorded on experimental research plots in the Netherlands and this could be further increased by the use of improved varieties under conditions of good husbandry (Doku, 1984). At present the normal recorded yield for the United States of America is about 27.3 t/ha.

TABLE 3.1 - World area, production and yield of root crops in 1984

TABLE 3.2 - World area and production of root crops in 1984 (in percentages)

TABLE 3.3 - Leading root crop producers in 1984 (percentage of total)

In spite of the low production, potato has become an acceptable foodstuff in a number of developing countries, including China, Bolivia, Colombia, Ecuador, India, Guatemala, Kenya and Rwanda (see Table 3.4). After China, India is the leading producer, accounting for 3.6 percent of world production, followed by Turkey (1.1 percent), Brazil and Colombia (0.8 percent). Together these four countries account for over 50 percent of the production in developing countries but only 7 percent of the world production.

Present research projects at CIP include breeding varieties to tolerate tropical temperatures at altitudes down to 1 000 ft (300 m) or even lower. Great progress has recently been made in the field of tissue culture and genetics and it may not be long before the potato also becomes a common tropical root crop. This will materially assist the provision of additional food for the ever increasing population in this part of the globe. At present potatoes provide only a small percentage of dietary calories in most developing countries, as indicated in Table 3.4. Cassava and sweet potatoes are more important root crops providing a range from 57.9 percent of the calories in Zaire to 35.2 percent in Angola.

Over the last 20 years (1965-84), cassava production worldwide has increased by over 330 percent. This corresponds to an annual growth rate of 4.3 percent which is substantial for any food crop (Chandra, 1988). Calculated recent changes in world production in 1986 with reference to base year 1984 showed that production of cassava has increased by 5.2 percent, yam by 4.8 percent and taro by 3.7 percent. While world production (including temperate-zone production of sweet potato and potato) has decreased by 3.8 percent and 1.8 percent respectively, the position of these two crops in some developing countries continues to strengthen. Production of sweet potato between 196971 and 1981-83 grew by 3.4 percent per annum in sub-Saharan Africa (FAO, 1986a) and by percentages varying from 6.3 percent per annum (Viet Nam) to 1.1 percent per annum (Thailand) in selected countries of Asia (FAO, 1987b). The increase in potato production for some Asian countries was 7.8 percent per annum for India, 6.2 percent for China, 10.2 percent for Sri Lanka and 13.8 percent for Viet Nam, between 1970-72 and 1982-84. Since 1970 there were also significant gains in potato production in Cuba, Colombia, Venezuela and most of Central America, owing to the adoption of new technologies.

TABLE 3.4 - Ten developing market economies with highest calorie Intake derived from root crops (in percentages)

Nigeria is the highest producer of yams, producing about 73 percent of the world total, most of which is used locally as food. Other leading producers are the West African countries of Côte d'Ivoire (9.2 percent), Ghana (3.4 percent), Benin (2.7 percent), Togo (1.8 percent) and Cameroon (1.6 percent). Virtually all the world production of yam is from West Africa, with D. rotundata the most important variety and D. cayenensis the least important. The other developing countries that produce some yam are in Central and South America, e.g. Haiti, Chile and Ecuador.

The Samoan islanders of the South Pacific region derive nearly 16 percent of their calorie intake from the consumption of cocoyam (aroids), but these root crops are less important in Africa. In Ghana they contribute about 11 percent of calories to the diet but in Nigeria and Côte d'Ivoire their contribution is only about two percent of calorie intake (see Table 3.4.). In Latin America and the Caribbean the production of aroids rose at less than one percent per year between 1969-71 and 1982-84 and did not keep pace with population growth. Similarly in Oceania annual growth in aroid production was sluggish at 1.3 percent and in South and Southeast Asia growth in production during recent years has been negligible.

Mention must be made of banana and plantain which have made a significant contribution to some subsistence economies, especially as the labour cost is relatively lower even than for that of cassava. Labour requirements for the production of various root crops in Nigeria, for example, are shown in Table 3.5.

Plantains and cooking bananas are grown and utilized as a starchy staple mainly in Africa, where production in 1985 was almost 17 million metric tonnes out of total developing-country production of 24 million metric tonnes. Of this total, South American production contributed about 4 million tonnes with the remainder produced in Asia, Central America and Oceania. In most of these regions annual production growth rates between 1969-71 and 1982-84 were only 1.7 to 1.8 percent, and well below the rate of population increase. Although overall production in South and Southeast Asia remained low, the annual rate of growth in production was more encouraging at 4.9 percent total for both plantain and banana.

TABLE 3.5 - Labour requirements for production of various staple crops in Nigeria


Working days/ha

Working days/mt

Working days/mcal

















Source: Nweke, 1981.

Cultivation of ensete, Ensete ventricosum, is limited to Ethiopia, where it is a staple food crop of the people of the southern highlands. It resembles a banana plant and is often called the " false banana". It does not produce an edible fruit and is harvested as a food source before flowering. The starchy portions of the swollen pseudo-stem and the underground corm are edible. It has been estimated that between 7 to 8 million people in the south and southwestern part of Ethiopia depend on fermented starchy staples prepared from ensete (FAO, 1985b).

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