The United Nations' medium projection is for world population to reach about 7.9 billion by 2025 before hopefully stabilizing at about 10 to 11 billion toward the end of the 21st century. At least in the foreseeable future, plants — and especially cereals — will continue to constitute much of food supply, both for direct human consumption and as livestock feed to satisfy the rapidly growing demand for meat and milk products in the newly industrializing countries. It is likely that an additional 1 billion metric tons of grain will be needed annually by 2030 — a 50% increase over world cereal production in 2000 (FAO, 2003). Developing countries of Asia — because of rapid economic growth, urbanization, and large populations — will account for half of the increase in global demand for cereals. Most of this increase must be supplied through yield improvements on lands already in production, although the agricultural area is expected to expand in tropical lands in South America (cerrados) and Sub-Saharan Africa, and in temperate zones, mainly in North America.
There is concern in some circles that crop yields in the world's more intensively cultivated areas may be approaching their physical limitations. Many advances — such as introduction of fertilizer-responsive varieties, higher planting density, multiple cropping, and better management practices — may have represented one-time gains. Environmental constraints add additional uncertainty, as some of the most intensively cultivated areas now suffer repercussions from intensive use of irrigation, fertilizers, and crop protection chemicals.
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