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The plant debris accumulated throughout the year is composted to form the finest humus.
The fertility of our soils is declining year on year, while the effects of climate change are becoming more frequent and intense. One possible solution to this is humus.
Humus – what is it exactly?
Plants take in CO2 from the air and transform it into sugars and subsequently organic matter. Valuable humus forms as a result of the interplay between plants and plant debris and soil organisms. A healthy ecosystem made up of microorganisms, fungi, insects and other creatures plays a crucial role here. Roots, animal waste, plant debris and dead soil organisms are continually metabolized and deposited in the soil. Humus therefore refers to all the dead and decomposed organic material in the soil. Plants and their fruits can only thrive and mature to their fullest extent in soil that is living and rich in humus. Thanks to its stable, crumbly structure, humus loosens heavy soil so that plants can better take root in it. It is also an important store of water for plants during dry periods. For that reason, in our medicinal herb garden and on our Sonnenhof farm, we have put the focus on healthy soil from the start. Both use Demeter-certified farming methods, which prioritise healthy soil. In order to grow the best raw materials for our Dr. Hauschka natural cosmetics, WALA medicines and fresh organic vegetables, our gardeners and farmers enrich the soil with different types of composts, green manure and biodynamic compounds.
Fascinatingly fertile soil in the rainforest
South American peoples from centuries gone by were masters of humus formation. The most fertile soils on earth date back to this period: Terra Preta.
Terra Preta is a Portuguese phrase meaning ‘black earth’. This soil, which is very rich in humus, was discovered in the Amazon region. Gerald Dunst finds this fascinating: ‘It’s not possible to form humus using natural processes there. Acidic soil, heavy rainfall, high temperatures and high humidity make that unattainable. Organic material that falls on the soil is very quickly washed away. That is why farming on cleared rainforest soil is not possible. Within two years, the soil becomes barren and unsuitable for growing crops or use as pasture land.’
So, why is it that scientists were able to find the most fertile soil in the world on the very same patch of earth? It turns out that this soil had been artificially created by humans. The indigenous peoples’ secret involved mixing residue from charcoal production into the soil. This resulted in soil that can store nutrients while also providing a perfect habitat for the microbiology that is so important for humus formation. Thanks to this practice, the soil of the indigenous South American peoples became more fertile with each passing year. In the eyes of humus expert Dunst, this sends one of the most wonderful messages: ‘Human civilisation can help to make soil more fertile.’
Humus as a climate saviour
Dunst has a clear-cut answer to the question of whether soil can save the climate: ‘Without a doubt.’ Nowadays, even sceptical scientists are no longer discussing whether humus formation can help to protect the planet by sequestering carbon, but the extent to which it can do so. Soil is therefore an important means of removing CO2 from our atmosphere, as it can function as a large carbon sink. Plant photosynthesis leads to carbon being sequestered in the plant material on the arable land. Dead plant debris is then converted to humus on the arable land, resulting in the storage of the carbon. According to Gerald Dunst, humus formation is also an effective way to combat the existing and intensifying effects of climate change: ‘The higher the proportion of humus, the better the soil can deal with extreme weather events such as torrential rain and drought, as the soil stores the water more effectively.’ Soil therefore functions as a sponge.
Gerald Dunst is a humus expert and CEO of the company Sonnenerde from Austria’s Styria region.
Photo: Sonnenerde GmbH
Humus formation is also possible in your own garden
In many places, the humus content of the soil has shrunk to two percent or less. In areas where there are sandy soils, the humus content is sometimes one percent or less: ‘By definition, that is essentially desert. There is an urgent need to act.’
But this means that we should be all the more encouraged by the advantages of humus formation: increased soil fertility and biodiversity due to thriving soil life and an enhanced ability to absorb water. In this respect, earthworms are a miracle of nature. They loosen the soil and enable it to store water. Just a handful of earthworms can be found in a cubic metre of soil low in humus, while soil that is rich in humus can be home to up to 600.
Soil that is rich in humus is a paradise for earthworms. The tunnels they create act as water tanks in the soil.
Photo: Daniel Wagner
Small gardens can also play a part in combating soil erosion, whereby soil particles are carried away by wind and water. As far more organic matter is produced in a garden than the soil really needs, you can form a lot of humus here. ‘On top of that, a garden should not always be kept clean and clinical. Nature can be given a bit more space.’ It is also important to till the soil just as much as is needed for sowing or planting. For the humus expert, the most important thing is that: ‘soil should never see the sun,’ as the biology of the soil on the surface is immediately killed by UV rays and dries out.
TEXT: Daniel Wagner