Wheat is grown from the Arctic Circle to the Equator (Fig. 5.1) and from sea level to 3000 m altitude. However, it is best suited to 30-50° N or 25-40° S latitudes (Briggle and Curtis, 1987; Gooding and Davies, 1997). Production of wheat has increased more than that of any other crop of consequence in the last century. In 1900 production was 90 Mt; by 1954 it was 200 Mt, due to
©CAB International 2000. Climate Change and Global Crop Productivity (eds K.R. Reddy and H.F. Hodges)
doubling the area under cultivation (90 to 190 Mha). By the early 1990s, total production was 600 Mt, achieved by increased productivity. Production is largely from Asia (China, 100 Mt; India 50 Mt), former USSR (100 Mt), North America (USA, 65 Mt; Canada, 23 Mt) and the European Union (100 Mt; including France, 65 Mt). There is little production in Africa, although it is a major crop in North Africa. Currently, 2.2 x 109 ha of land are used for wheat cultivation. Five exporters dominate world trade (USA, Canada, European Union, Australia and Argentina). Some relatively small producers are of considerable importance, because their exports balance poor harvests in other areas. Wheat has been the main provider of food for the increasing world population (1.5 billion in 1900; 5.5 billion in 1993; probably reaching 11 billion by the mid-21st century). Wheat is imported by many countries, including the former USSR, China, Japan, Egypt and Indonesia. Many developing economies with rapidly growing populations would be particularly susceptible to decreased wheat production. Increased world cereal production of 35-40% will be required, and wheat should make up a larger proportion than other cereals (Ansart, 1997).
Productivity of wheat was c. 11 ha-1 as a global average during the first half of the 20th century, but has risen to 2.5 t ha-1 currently (Slafer et al., 1996). In areas that are climatically favourable for wheat production, such as western Europe, with cool, moist, long growing seasons and days and fertile soils, productivity of modern, semi-dwarf varieties under intensive management (fertilizers, pest and disease control) has risen to over 10tha-1, with peak yields to > 12 t ha-1 and country-wide yields of 7 t ha-1. However, worldwide the crop is grown extensively with limited inputs and yields are small. In the last decade, the rate of increase in productivity may have slowed and the area under cultivation has decreased by 8%. This trend, if maintained, may result in shortages. Over the last two decades, investment in agriculture has decreased and prices to producers have dropped, both disincentives to production (Evans, 1998). Global storage of wheat was about 35% of production in the early 1980s, due to cumulative effects of worldwide increases in productivity resulting from governmental subsidies to research, development and to farmers. Stocks are now about 18% of consumption, just above the FAO recommended 15% (Ansart, 1997). There is urgent need to ensure greater investment in wheat production to meet the known demands of population increase and possible effects of GEC.
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