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Arable land

2007 Schools Wikipedia Selection. Related subjects: Food and agriculture

   Modern arable agriculture typically uses large fields like this one in
   Dorset, England.
   Enlarge
   Modern arable agriculture typically uses large fields like this one in
   Dorset, England.
   Percentage of arable land by country, from CIA figures
   Enlarge
   Percentage of arable land by country, from CIA figures

   In geography, arable land (from Latin arare, to plough) is a form of
   agricultural land use, meaning land that can be used for growing crops.

   Of the earth's 57 million square miles (148,000,000 km²) of land,
   approximately 12 million square miles (31,000,000 km²) are arable;
   however, arable land is being lost at the rate of over 100,000 km²
   (38,610 square miles) per year.

   Most of the arable land on earth is around the largest rivers on earth;
   for example, the Nile River, the Tigris and Euphrates Rivers, the
   Yellow River, the Amazon River, the Ganges and the Rhine River. These
   rivers flood regularly, overspilling their banks. When the flood is
   over, the rivers recede, leaving behind rich silt. This silt is
   excellent fertilizer for crops. Even if the land is overfarmed, and all
   the nutrients are depleted from the soil, the land renews its fertility
   when the next flood comes. Thus, flood control projects such as levees
   may increase human comfort, but cause substantial adverse impact to the
   quantity and quality of arable land.

Unarable land

   On unarable land, farming is not possible. Unarable land usually has at
   least one of the following defiencies: 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 (making sunlight into
   food), reducing productivity. Plants can starve without light.
   Starvation and nomadism often exists on marginally arable land.
   Unarable land is sometimes called 'wastes', 'badlands', 'worthless' or
   'no man's land'.

   In rare cases, unarable land can 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 unarable land arable often
   involves digging new irrigation canals and new wells, aquaducts,
   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.

   Some examples of infertile unarable land being turned into fertile
   arable land are:
     * Aran Islands: This island off the west coast of Ireland, (not to be
       confused with the Isle of Arran in Scotland's Firth of Clyde), was
       unarable because it was too rocky. The people covered the island
       with a shallow layer of seaweed and sand from the ocean. This made
       it arable. Today, crops are grown there.
     * Israel: Israel was mostly unarable desert until desalination plants
       were built on the coast. The plants turn salt water into fresh
       water for farming, drinking, and washing. They created their own
       large fresh water source.

   Some examples of fertile arable land being turned into infertile
   unarable 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 turn 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 practised by many natives.
     * Romans' destruction of Carthage: At the end of the Punic Wars,
       legend has it that the victorious Romans sowed the earth with salt,
       to symbolize total victory. The Roman symbol meant that Carthage
       would never grow back - their civilization ended. (Whether this
       actually happened is debatable due to the logistics involved. Salt
       was very valuable and was used as money at the time, and it would
       have taken a lot of salt to ruin the whole area.) Crops won't
       generally grow in highly saline soil. This is why salt water from
       the ocean can't be used to water crops.
     * Each year more arable land is lost to desertification and erosion
       from human industrial activities. 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.
     * Urban sprawl: In the United States, about 2.2 million acres (8,900
       km²) of land was added to urban areas between 1992 and 2002, much
       of it farm land now paved.

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   with only minor checks and changes (see www.wikipedia.org for details
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