Why is desert soil sterile


Torsten Mertz

To person

Born 1969 in Cologne, is a qualified geographer and works as an editor with a focus on the environment, sustainability and corporate responsibility in Munich. In 2006 his book "Schnellkurs ├ľkologie" was published.

The majority of our food grows in the earth, an intact soil ecology is important. But the heavy loads to which the floors are exposed are often overlooked.

(& copy AP)

We live on the ground, build our houses and roads on it and deposit our garbage in the ground. Without the fertile earth, which is a few meters thick, no life in the country would be possible, because the plants that feed us and the animals grow in it. So it is no coincidence that we refer to our planet as "earth", just like the most important source of our food, the soil. Soil degradation is a major human-made global environmental problem - and at the same time a danger that is not sufficiently perceived by the public.

The fertile skin of the earth

Except where bodies of water cover the earth and where bare rock emerges, the ground covers the entire planet with a living layer a few millimeters to many meters thick. The production of food and other agricultural products - apart from fishing - as well as forestry are dependent on it. Almost all vegetation, including grassland, cultivated plants and trees, needs the soil for water and nutrient supply as well as root space.

Soils are the result of the interaction of physical, chemical and biological factors that determine their composition and development on the basis of parent rock, climate and living organisms. The weathering of rocks can give rise to new minerals that bind water and absorb nutrients. In this way, the soil also becomes a natural filter that protects the groundwater from pollutants and a buffer that can store carbon dioxide from the atmosphere, for example.

Organic matter in the form of living and dead animals and plants (parts of plants) is of particular importance for the fertility of the soil. Dead organic matter is broken down by the organisms in the soil and converted into dark-colored organic compounds, the humic substances. The organisms living in the soil range from macrofauna (such as mammals) to mesofauna (such as earthworms) to micro-organisms. The latter - bacteria, fungi and algae - make up the largest part of the soil flora and fauna at around 80 percent. About 100 trillion bacteria and a billion fungi live in the top 30 centimeters of a square meter of soil. The soil fauna and flora is essential for the long-term fertility of the soil.

Danger to our livelihood

Around 15 percent of the world's soils are now considered degraded. Soil degradation is primarily a natural process. The soils are constantly changing due to weathering and the addition and removal of substances with water and air. However, these processes only run to a limited extent and for a very long time. Intensive land use measures accelerate degradation and lead to a reduction or loss of biological and economic productivity in cultivated areas, meadows and pastures, areas used for forestry and forests. It is expressed in
  • soil erosion caused by wind or water,
  • the deterioration in the physical, chemical, biological or economic properties of the soil,
  • the disappearance of the natural vegetation.
The main causes of soil degradation are overgrazing (around 35 percent), deforestation (30 percent) and overexploitation through arable farming (27 percent). In densely populated countries like Germany, sealing through settlement and road construction also leads to the loss of soil. The increase in population poses the greatest threat to soils. In order to feed the steadily growing number of people, either the area used for agriculture must increase by around 1.5 percent annually, or productivity per unit area would have to increase by this proportion. In the last few decades, however, arable land has barely increased in area. Because in the same order of magnitude as areas were gained - mostly at the expense of forests and grasslands - areas were lost again through subsequent degradation. However, this approach cannot be continued indefinitely: Destroyed soils only regenerate in geological periods, arable land is limited, and so more and more soils have to be used that are less and less suitable.