In geography, arable land (from Latin arare, to plough) is an agricultural term, meaning land that can be used for growing crops.
Of the earth's 148,000,000 km² (57 million square miles) of land, approximately 31,000,000 km² (12 million square miles) are arable; however, arable land is currently being lost at the rate of over 100,000 km² (38,610 square miles) per year. A major element of arable land loss comes from deforestation (starting in the Middle Ages in Europe as well as Asia). Such deforestation continues to the present day primarily in tropical countries by commercial over-exploitation of tropical forest. At times, deforestation can be so extreme that it leads to desertification, or the total loss of arable land, as has occurred in portions of the central highland plateau of Madagascar following extensive slash-and-burn activity.
A smaller, but important loss of arable land arises from the lack of renewal of rich flooding sediment due to flood control works. Part of the arable land on earth is around the largest rivers on earth; for example, the Nile River, the Mississippi River, the Tigris and Euphrates Rivers, the Yellow River, the Amazon River, the Ganges and the Rhine River.
The most productive partion of arable land is that from sediments left by those rivers and the sea in the geological times. In modern times, the rivers do not generally flood as much agricultural land, due to the demands of flood control to support instensive agriculture required of a heavily-populated Earth.
The Nile continues to flood regularly, overspilling its banks. When the flood is over, the waters recede, leaving behind rich silt. This silt provides 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 new deposits of silt arrive following the next flood. Flood-control projects in the region, such as levees, may increase human comfort but cause substantial adverse impact to the quantity and quality of arable land.