Fruitful soils securing food for the world’s population and form the basis for the production of vegetable raw materials such as cotton or oils, and serve as a carbon sink. Nevertheless, more valuable soil is being lost worldwide – at least more than is being newly formed. The main cause of the increasing loss of soil is modern agriculture and the increasingly intensive use of land in many parts of the world. These makes wind and rain easy to remove material.
The global erosion rate is around 2.4 tons of soil per hectare per year, Swiss researchers write in the journal “Nature Sustainability”. To get an idea of the global condition of soils, David Wuepper from ETH Zurich and his colleagues analyzed a huge set of satellite-based and other data, in which the erosion rates of the soils at more than 35 million locations around the world were recorded.
The researchers investigated the extent to which the economic situation of a country, its environmental policy and the various agricultural methods in the individual countries influence soil erosion.
In fact, they have identified specific “country effects” as the cause of the erosion. Soil loss was most pronounced on the Caribbean island of Hispaniola, the eastern half of which is occupied by the Dominican Republic, while Haiti is in the west of the island. Although the climate and topography are almost identical in both countries, more than 150 tons of soil per hectare are lost in Haiti every year.
In contrast, the erosion rate in the neighboring country is only about a fifth. The annual loss there is less than 30 tons per hectare. Already along the political border, the erosion rate leaps by more than 50 tons of material per year. The reason: In Haiti, unlike in the neighboring country, there are only a few forests that protect the soil.
The Swiss researchers were able to find climate effects in many parts of the world. In addition to Haiti, Brazil and Mexico has the highest erosion rates in the western hemisphere. The damage is lowest in Argentina, Ecuador and the United States.
In Asia, soil loss is greatest in China, Burma and Indonesia, while it is lowest in South Korea, Laos and Cambodia. In Africa, Zimbabwe and Cameroon have the highest erosion rates, while Mozambique, Tanzania and the West African countries between Benin and Sierra Leone have the least losses. In Europe, Italy and Greece lose most of their land.
The condition of the soil in Germany has recently been examined by employees of the Thunen Institute, which belongs to the Federal Ministry of Agriculture. Over the past six years, they have taken more than 120,000 soil samples from more than 3,100 locations in Germany.
The researchers paid particular attention to the soil’s organic carbon content. The undoubtedly largest stores for carbon are the bog soils. Although they only make up about six percent of the agricultural area, the bogs in the top two meters contain up to a thousand tons of organic carbon per hectare.
In comparison, the German grassland soils contain an average of 88 tons of carbon per hectare. In the case of mineral soils using arable land, the carbon content drops to an average of only 61 tons per hectare.
However, there are large fluctuations in mineral soils. They range from a carbon content of 31 tons per hectare in the sandy soils of Mecklenburg-West Pomerania to 400 tons in the old moraine landscapes of the foothills of the Alps.