AGRICULTURAL SOILS & CO2
Today, soils store more carbon than all plants and the atmosphere combined. If we disturb them, this carbon escapes into the atmosphere as CO₂. This means we lose soils as an important CO₂ reservoir.
The diagram depicts a slope with three soil columns. On the left, an undisturbed soil formed in place: topsoil over subsoil, loess above, bedrock below. In the center, tillage and rainfall cause topsoil erosion and mixing with former subsoil; a tractor drives downslope. On the right, at the footslope, eroded materials accumulate: a newly formed topsoil overlies deposited subsoil, with a “buried former surface” indicated. Arrows above the left and right profiles denote CO₂ fluxes: photosynthesis upward and soil respiration. A note states the drawing is not to scale.
Exhibits in the exhibition. Foto: Nicola Pitaro (modif.)
HOW DOES CO₂ GET INTO THE SOIL?
Plants absorb carbon from the air in the form of CO₂ through photosynthesis. When they die, the ‘architects of the soil’, the microorganisms, begin their work: they decompose the plant residues, transferring some of the plants’ carbon into the soil. This creates valuable, nutrient-rich humus.
HOW IS CO₂ RELEASED FROM THE SOIL?
In healthy soils, the absorption of CO₂ into the soil is in a natural balance with soil respiration: during decomposition, microorganisms produce CO₂, which is released into the atmosphere.
If the protective, permanent vegetation cover is removed by tilling, fewer fresh plant residues enter the soil. The activity of the microorganisms changes: instead of forming more new humus, they decompose existing humus. In the process, the carbon stored in it is released as CO₂ – in addition to the natural soil respiration.
LOSS OF FERTILE AGRICULTURAL LAND
Many fertile soils are intensively farmed, making them susceptible to overuse and erosion. The latter is a particular problem on slopes in Central Europe: loosened by tillage, the topsoil with the fertile humus is washed down the slope by rainwater – especially when there is no protective vegetation cover.
While valleys are covered with fertile soil, the slopes lose more and more of their valuable topsoil. This loss can be compensated for by applying more fertiliser – which, however, places an additional burden on the environment – or by clearing new land for agricultural, which is often associated with deforestation.
Loess soils are an example of very productive soils which are used to grow a substantial proportion of the global food production. They were formed after the ice ages from fine dust deposited by wind in hilly landscapes. The fineness of the material and the location on slopes make loess soils particularly susceptible to erosion.
Erosion jeopardises the important function of loess soils for food production and CO₂ storage. We must prevent them from being lost. Once they are gone, they will not regenerate – at least not until the next ice age. Protecting soils means protecting the climate.
We can protect soils with sustainable and regenerative agriculture, e.g., by ploughing less, introducing plants that stabilise the soil and promoting humus formation.