Soil erosion commonly appears after conversion of forests to agricultural land, sweeping away fertile soil and pesticides.
When forests are cleared, the exposed topsoil often begins to erode, increasing sedimentation into watercourses (for example, rivers). The situation worsens if there are no forests left along the banks of rivers to hold soil carried by rain. Coffee, cassava, cotton, corn, palm oil, rice, sorghum, soybean, tea, tobacco, and wheat are some of the crops whose cultivation causes soil erosion.
Since 1960, an estimated one-third of the world’s arable land has been lost through erosion and other degradations. The problem persists, with a reported loss rate of about 10 million hectares per year.
In reality, the situation may be much more worrying. Over the last five decades, increases in agricultural productivity have made it possible to produce more crops on the same amount of land. But because agricultural land is often degraded and almost useless, producers keep moving to more productive land. Globally, the land used and abandoned in the last 50 years may be equal to the amount of land used today.
The Cerrado: From savannah to desert
In the Brazilian Cerrado, the combined effects of deforestation and increased soil temperatures have made it difficult for rainwater to sink into the soil. When plantation areas of up to 10,000 hectares are exposed following deforestation, the soil becomes extremely vulnerable to wind and water erosion. As a result, desertification has become a serious threat to these areas, which experience a long dry season.
In the Santarem region, intensive rainfall causes erosion, especially near streams and rivers. The sediment is transported downstream, where it makes the rivers and coves turbid.