Unit 7: Agriculture // Section 2: Earth's Land Resources
How much of Earth's surface can be used for agriculture? The basic limits are temperature, topography, climate, soil quality, and available technologies, including scientific understanding of issues like plant and animal genetics. As technology improves over time, the zone where agriculture can be practiced successfully expands. For example, development of the horse collar in China allowed farmers to use livestock to pull ploughs and thus to farm in heavier soils than they could till by hand. Many social, political, and economic factors also shape agricultural land use, including land tenure patterns, population density, and environmental regulations.
As of the year 2000, about 37 percent of Earth's land area was agricultural land. About one-third of this area, or 11 percent of Earth's total land, is used for crops. The balance, roughly one-fourth of Earth's land area, is pastureland, which includes cultivated or wild forage crops for animals and open land used for grazing (footnote 2).
To help governments with land-use planning, the United Nations Food and Agricultural Organization (FAO) has developed a system called Agro-Ecological Zoning that characterizes land's suitability for agriculture based on physical parameters like climate, soil, and topography (footnote 3). Based on current soil, terrain, and climate data, FAO estimates that more than three-quarters of Earth’s land surface is unsuitable for growing rain-fed crops (i.e., raising crops without irrigation). Most of the remainder is subject to some soil, terrain, and/or climate limitations. On average, only about 3.5 percent of Earth’s surface is suitable for agriculture without any physical constraints (Fig. 2).
Figure 2. Distribution of climate and soil/terrain constraints by region
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Source: © 2000. International Institute for Applied Systems Analysis and Food and Agriculture Organization.
These physical constraints mean that not all farmland is equally productive, even with modern techniques and inputs. In areas where land is less productive, agriculture requires more techniques and inputs to address limitations such as poor soil quality. Less productive agricultural land generally has low market value, so in many countries farming must compete with other uses such as residential or commercial development or recreation. However, in areas that have received few modern inputs, such as many parts of Africa, fertilizer and other technologies can greatly increase productivity and raise the value of agricultural land.
In regions where productivity is rising faster than demand, such as the United States, the European Union, and Japan, land is being withdrawn from cultivation. These areas rely on agricultural intensification to keep output high as their farmed lands shrink. In contrast, land is being converted for agriculture in many parts of the developing world. Both trends are causes for concern. Agricultural intensification has serious environmental impacts, as we will see in the following sections, while land conversion is a major cause of deforestation. Clearing forests for agriculture alters ecosystems that provide important services such as sequestering carbon or absorbing floodwaters.
Another 30 percent of the world's land area is forested, with half of global forests managed at least partly for wood production (other forest functions may include land conservation or protecting indigenous plants and animals) (footnote 4). Forestry is generally a much less intense form of land use than agriculture because tree crops have longer rotation periods than agricultural commodities, so soils are less disturbed and fewer cultivation inputs like fertilizer are needed. However, some forestry practices—such as building roads through forest tracts and clear-cutting on hillsides where trees stabilize soil—can disrupt ecosystems on a scale comparable to farming.