Humus is known to be good for the soil. The complex mixture of organic matter, such as dead animal and plant remains, serves as a food source for plants and soil microbes alike and is therefore a driving force for plant growth and soil health. It is primarily the humic substances contained in humus that ensure that moisture and nutrients are bound in the soil, convert microbial biomass into nutrient-rich biostimulants and make these available to plants. In practice, however, things often look different. Farmers try to compensate for the lack of nutrients in the soil with the help of fertilisers.

Artificial humic substances for agriculture

Researchers at the Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB) have now succeeded in artificially producing humic substances from biological residues and making them usable for agriculture. This was made possible by using a new, previously little-established process known as hydrothermal humification. ‘What nature can do in years with the help of microorganisms, we can achieve in minutes to hours in a controllable process with heat, pressure and water,’ explains Nader Marzban, post-doctoral researcher at the ATB and expert in biochar and humic substances.

Residue utilisation using hydrothermal humification

The ATB researcher has already demonstrated in studies that biological residues such as organic waste from agriculture and private households can be fully utilised using hydrothermal humification. In a high-pressure reactor, the biomass was mixed with water in a ratio of around 0.1 to 0.4. ‘The fibre components cellulose, hemicellulose and lignin are then broken down under high pressure (between 6 and 60 bar) and at a high temperature (between 160 and 240° C). Depending on the pH value and temperature in the reactor, we obtain either more hydrochar or artificial humic acid. Both are solids that range in colour from brownish to black,’ explains Marzban.

According to Marzban, these solids could be used as a fertiliser in agriculture, as tests with a humic-based microfertiliser have shown. ‘The initial results showed that adding just 0.01% of our humification products to the soil can significantly increase the germination index and help plants absorb more nutrients, such as phosphorus.’

Great potential for a sustainable and circular bioeconomy

The team led by the Potsdam expert is convinced of the potential of hydrothermal humification for the bioeconomy. ‘We are closing cycles and replacing fossil resources in the sense of a sustainable and circular bioeconomy. If we ensure that our humic acids are in no way inferior to natural deposits in terms of quality and benefits – and we can prove this – we have a fast, controllable process that uses renewable raw materials and enables cascading, i.e. multi-stage utilisation of this biomass,’ says Marzban.

According to the humic substances expert, other processes could also benefit from the new method - for example, by integrating it into biorefineries to convert solid and liquid residues into humic substances.

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