THROUGH PLANTS INTO THE SOIL
Biochar (biological charcoal)
The illustration shows a green rural landscape with forest, fields, machinery, and a pyrolysis plant. Six numbered steps depict the biomass-to-biochar cycle: 1) Plants grow in the forest and absorb CO2; translucent arrows indicate gas exchange. 2) During harvesting, wood and plant residues are collected and transported to a pyrolysis facility. 3) Inside the plant, biomass is heated to about 400–900 °C without oxygen; a cutaway diagram shows a heating loop, the pyrolysis chamber, and an outlet producing biochar, while waste heat is fed to district heating and to preheat new biomass. 4) The biochar is cleaned, packaged, and hauled by truck to a farm. 5) On a field, a tractor incorporates the biochar into the soil; a magnified view shows porous black particles with retained nutrients around plant roots. 6) The text explains the benefits: the contained carbon remains in the soil for centuries, improving soil structure, water and nutrient retention, potentially boosting yields and reducing fertilizer needs.
Plants remove CO₂ from the atmosphere through photosynthesis and incorporate the carbon (C) into their biomass, such as leaves and roots. Through pyrolysis, i.e. heating without oxygen, biomass waste (e.g., from the wood industry) is converted into stable charcoal. The charcoal is mixed into arable soil, where it remains unchanged for a long time. This permanently stores the carbon (from the CO₂) contained in the charcoal. Alternatively, biochar can also be incorporated into products such as concrete.
The practice of adding charred plant residues to the soil to improve its quality was already being used centuries ago by indigenous peoples in the Amazon region. Today, biochar is also used in modern agriculture, albeit on a relatively small scale.
Biochar stores CO₂ and can also improve soil quality by binding nutrients and thus promoting plant growth.
The long-term effects of biochar on agricultural soils in our latitudes still need to be investigated further. For example, it is unclear how much it improves soil quality and whether it could also have a negative impact on soil chemistry and soil ecosystems. One example is the possibility that biochar could also retain pollutants in the soil.
Biochar not only stores CO₂ but it can also help retain nutrients and water in the soil. This can promote plant growth. Photo: ANGHI (iStock)
Exhibits
Concrete with biochar
Biochar
BIOCHAR…
… IN SOIL
Biochar is a dark, lightweight material consisting mainly of carbon (C) which originally comes from CO₂ in the air. This makes biochar a tool for CO₂ storage – but that’s not all: it also improves the soil, as it contains countless tiny pores that can bind water and nutrients and hold them for long periods of time – like a sponge that has been soaked in water.
This retention function can be exploited in agriculture, in the garden or even in flower pots. Before being applied to the soil, the biochar has to be
‘charged’: it can be mixed with compost, soaked in liquid fertiliser or, if nothing else is available, urine. The charged biochar is then mixed with the soil. There, it slowly releases nutrients to the plants over time, as they are not immediately washed out. Biochar thus supports plant growth, reduces the need for fertiliser and stores CO₂ at the same time.
… AND IN CONCRETE
Biochar can also be added to products such as concrete in the form of small pieces as a filler. This only slightly alters the concrete, which has comparable technical properties to conventional concrete. The biochar remains in the concrete for long periods of time, permanently storing the carbon it contains. It also replaces less climate-friendly fillers, thereby reducing CO₂ emissions during concrete production.