According to definitions and survey recommendations by the Food and Agriculture Organization (FAO), used by for example Eurostat and the World Bank, arable land is agricultural land occupied by crops both sown and harvested during the same agricultural year, sometimes more than once. Land is also considered arable if used as temporary meadows for mowing or pasture, market and kitchen gardens; as well as temporarily fallow land — not seeded for one or more growing seasons, yet not left idle for more than five years.
Permanent crops that occupy the land for a number of years, and don't need replanting after each annual harvest — like coffee, rubber, flowering shrubs, fruit, nut trees and vines — are not counted as existing on arable land, but as existing on permanent cropland.
Permanent pastures and meadows used for grazing, land mowed for hay or silage not included in a crop rotation scheme, and abandoned land resulting from shifting cultivation is also not counted as arable, along with lands with built-on and barren areas, forests and woodlands.
Arable land area
Although constrained by land mass and topology, the amount of arable land, both regionally and globally, fluctuates due to human and climatic factors such as irrigation, deforestation, desertification, terracing, land reclamation and urban sprawl. In 2008, the world's arable land amounted to 1,386 M ha, out of a total 4,883 M ha land used for agriculture.
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Land which is unsuitable for arable farming usually has at least one of the following deficiencies: no source of fresh water; too hot (desert); too cold (Arctic); too rocky; too mountainous; too salty; too rainy; too snowy; too polluted; or too nutrient poor. Clouds may block the sunlight plants need for photosynthesis, reducing productivity. Starvation and nomadism often exists on marginally arable land. Non-arable land is sometimes called wasteland, badlands, worthless or no man's land.
However, non-arable land can sometimes be converted into arable land. New arable land makes more food, and can reduce starvation. This outcome also makes a country more self-sufficient and politically independent, because food importation is reduced. Making non-arable land arable often involves digging new irrigation canals and new wells, aqueducts, desalination plants, planting trees for shade in the desert, hydroponics, fertilizer, nitrogen fertilizer, pesticides, reverse osmosis water processors, PET film insulation or other insulation against heat and cold, digging ditches and hills for protection against the wind, and greenhouses with internal light and heat for protection against the cold outside and to provide light in cloudy areas. This process is often extremely expensive. An alternative is the Seawater Greenhouse which desalinates water through evaporation and condensation using solar energy as the only energy input. This technology is optimized to grow crops on desert land close to the sea.
Some examples of infertile non-arable land being turned into fertile arable land are:
- Aran Islands: These islands off the west coast of Ireland, (not to be confused with the Isle of Arran in Scotland's Firth of Clyde), were unsuitable for arable farming because they were too rocky. The people covered the islands with a shallow layer of seaweed and sand from the ocean. This made it arable. Today, crops are grown there.
- Israel: Israel's land primarily consisted of desert until the construction of desalination plants along the country's coast. The desalination plants, which remove the salt from ocean water, have created a new source of water for farming, drinking, and washing.
- Slash and burn agriculture uses nutrients in wood ash, but these expire within a few years
- Terra preta, fertile tropical soils created by adding charcoal.
Some examples of fertile arable land being turned into infertile land are:
- Droughts like the 'dust bowl' of the Great Depression in the U.S. turned farmland into desert.
- Rainforest Deforestation: The fertile tropical forests are converted into infertile desert land. For example, Madagascar's central highland plateau has become virtually totally barren (about ten percent of the country), as a result of slash-and-burn deforestation, an element of shifting cultivation practiced by many natives.
- Each year, arable land is lost due to desertification and human-induced erosion. Improper irrigation of farm land can wick the sodium, calcium, and magnesium from the soil and water to the surface. This process steadily concentrates salt in the root zone, decreasing productivity for crops that are not salt-tolerant.
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