Introduction

Root and tuber crops are highly important food resources. They comprise several genera and supply the main part of the daily carbohydrate intake of large populations. These carbohydrates are mostly starches found in storage organs, which may be enlarged roots, corms, rhizomes or tubers. Many root and tuber crops are grown in traditional agricultural systems or are adapted to unique ecosystems and do not enter world trade; however, some are grown worldwide. With some important exceptions, root and tuber crops are more important for food production in tropical than in temperate climates.

There are many crop species that produce edible roots and tubers. Food and Agriculture Organization (FAO) statistics indicate that in 1997 root and tuber crops were cultivated over more than 49 M ha and the total production was greater than 650 Mt (FAOSTAT, 1998). Potato (Solanum tuberosum L.), cassava (Manihot esculenta), sweet potato (Ipomea batatas), yam (Dioscorea subsp.), radish (Raphanus sativus), carrot (Daucus carota subsp.) and kohlrabi (Brassica oleracea) are the most widespread root and tuber crops used for food production. Among these, potato and cassava are by far the most widely cultivated species in the world as their current production accounts for 72% of the total harvest of root and tuber crops. Potato makes the largest contribution to the total production of tuber and root crops, but its global production share decreased from about 60% in the 1960s to 45% in the 1990s. Cassava became

┬ęCAB International 2000. Climate Change and Global Crop Productivity

more important and its global production share grew from 15 to 25% over the same 37 years (Fig. 9.1). This reflects the faster growth of populations and their food demand in developing vs. developed countries. Cassava is mainly cultivated in tropical regions, whereas potato is an important crop in the temperate zones. Production of these crops steadily increased by about 4Mt per year from 1961 to 1997 (Fig. 9.2). This increase was due mainly to increased yields per unit of land, as the global area cultivated did not change (Fig. 9.3). Several factors may have caused these yield increases, including improved crop varieties, crop management, increased use of fertilizers, reduced losses from pest and disease infestations, improved harvesting and conservation methods and extended irrigation. The continuous increase in atmospheric carbon dioxide concentration ([CO2]) may also have contributed.

Years

Fig. 9.1. Changes in relative contribution of potato and cassava as percentage of total tuber and root crop global production from 1961 to 1997.

Years

Fig. 9.1. Changes in relative contribution of potato and cassava as percentage of total tuber and root crop global production from 1961 to 1997.

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Years

Fig. 9.2. Global production (Mt) of tuber and root crops from 1961 to 1997.

Years

Fig. 9.2. Global production (Mt) of tuber and root crops from 1961 to 1997.

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Fig. 9.3. Average yield per unit land (closed circles, t ha-1) and the total cultivated area (open circles, Mha) of tuber and root crops in the world, from 1961 to 1997.

Years

Fig. 9.3. Average yield per unit land (closed circles, t ha-1) and the total cultivated area (open circles, Mha) of tuber and root crops in the world, from 1961 to 1997.

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