2007 Schools Wikipedia Selection. Related subjects: Food and agriculture
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.
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.