Losing Agricultural Land

Historically, world food production increased primarily by expanding the amount of land devoted to agriculture. When the world’s population began to increase more rapidly in the late eighteenth and early nineteenth centuries, during the Industrial Revolution, pioneers could migrate to uninhabited territory and cultivate the land. Sparsely inhabited land suitable for agriculture was available in western North America, central Russia, and Argentina’s pampas.

Two centuries ago, people believed that good agricultural land would always be available for willing pioneers. Today few scientists believe that further expansion of agricultural land can feed the growing world population. At first glance, new agricultural land appears to be available because only 11 percent of the world’s land area is currently cultivated. However, in recent decades, population has increased much more rapidly than agricultural land.

World Population Growth, Agricultural Land, and Food Production

The food production index is set at 10 in the year 2005.

Loss of Land to Urbanization

The von Thünen model shows the influence of proximity to urban markets in the form of agriculture practiced on a piece of land. The expansion of urban areas has contributed to reducing agricultural land.

Loss of farmland to urban growth is especially severe at the edge of the string of large metropolitan areas along the East Coast of the United States. As urban areas grow in population and land area, farms on the periphery are replaced by urban land uses. A serious problem in the United States has been the loss of 200,000 hectares (500,000 acres) of the most productive farmland, known as prime agricultural land, as urban areas sprawl into the surrounding countryside.

Some of the most threatened agricultural land lies in Maryland, a small state where two major cities—Washington and Baltimore—have coalesced into a continuous built-up area (see Chapter 13). In Maryland, a geographic information system (GIS) was used to identify which farms should be preserved. Maps generated through GIS were essential in identifying agricultural land to protect because the most appropriate farms to preserve were not necessarily those with the highest-quality soil. Why should the state and nonprofit organizations spend scarce funds to preserve “prime” farmland that is nowhere near the path of urban sprawl? Conversely, why purchase an expensive, isolated farm already totally surrounded by residential developments, when the same amount of money could buy several large contiguous farms that effectively blocked urban sprawl elsewhere?

To identify the “best” lands to protect, GIS consultants produced a series of soil quality, environmental, and economic maps that were combined into a single composite map. The map shows that 4 percent of the state’s farmland had prime soils, significant environmental features, and high projected population growth, and 25 percent had two of the three factors. Maryland officials are making use of the results of the GIS as part of an overall strategy to minimize sprawl.

Protecting Farmland in Maryland

Prime farmland is typically flat and well drained. Significant environmental features include water quality, flood control, species habitats, historic sites, and especially attractive scenery.

Desertification

In some semiarid regions, agricultural practices contribute to a loss of soil moisture and protective plant cover, allowing deserts to spread. A lack of water pushes many people from their land. For example, hundreds of thousands have been forced to move from the Sahel region of northern Africa because of drought conditions. The people of the Sahel have traditionally been pastoral nomads, a form of agriculture adapted to dry lands but effective only at low population densities. Human actions that cause land to deteriorate to a desertlike condition is called desertification, or more precisely semiarid land degradation. The capacity of the Sahel to sustain human life—never very high—has declined recently because of population growth and several years of unusually low rainfall. Consequently, many of these nomads have been forced to move into cities and rural camps, where they survive on food donated by the government and international relief organizations.

Semiarid lands that can support only a handful of pastoral nomads are overused because of rapid population growth. Excessive crop planting, animal grazing, and tree cutting exhaust the soil’s nutrients and preclude agriculture. The Earth Policy Institute estimates that 2 billion hectares (5 million acres) of land have been degraded around the world. Overgrazing is thought to be responsible for 34 percent of the total, deforestation for 30 percent, and agricultural use for 28 percent. The U.N. estimates that desertification removes 27 million hectares (70 million acres) of land from agricultural production each year, an area roughly equivalent to the size of Colorado.

Bushes Planted to Prevent Desertification

Gansu, China.

Desertification (Semiarid Land Degradation)

Excessive water threatens other agricultural areas, especially drier lands that receive water from human-built irrigation systems. If the irrigated land has inadequate drainage, the underground water level rises to the point where roots become waterlogged. The U.N. estimates that 10 percent of all irrigated land is waterlogged, mostly in Asia and South America. If the water is salty, the plants may be damaged by the salt. The ancient civilization of Mesopotamia may have collapsed in part because of waterlogging and excessive salinity in its agricultural lands near the Tigris and Euphrates rivers.

Pause & Reflect 9.4.2

Have you seen loss of farmland near where you live? For what new purpose is the land used?