Excavated soil from construction sites usually ends up in landfills, but it has great potential. Researchers at the Technical University of Munich (TUM) show how excavated soil can be enriched with organic waste so that it can be reused in cities. By adjusting the mixture, the specific properties can be adapted to each use case, such as fertile green spaces or for the protection of groundwater.
Astrid Eckert / TUM In urban areas, soil is often moved in opposite directions: on the one hand, excavated material is removed from construction sites and often ends up in landfills. As such, soil accounts for a quarter of waste in the EU. On the other hand, soil from outside the city is used to enrich the soil in urban areas, for example for parks. This so-called "land take" is to be reduced to net zero by 2050 as part of the EU Soil Strategy in order to protect areas surrounding cities.
An alternative to land take are the so-called "constructed soils" where these excavated, often degraded soils are enriched with other components. Researchers from the Technical University of Munich (TUM) now characterize different constructed soils using urban organic waste products and identify their potential in urban landscape planning.
The team took excavated soil samples from construction sites in Munich and Augsburg and mixed them with greenwaste compost, and a compound called biochar. Biochar consists of organic waste products, e.g. from biogas production, which would usually go unused and into the waste stream.
Improved fertility and groundwater protection
The constructed soils, made from excavated soil and these compounds showed increases in several indicators for soil functionality: they are more fertile as they have up to quadrupled nitrogen content and improved carbon accrual. Furthermore, they may aid in protecting groundwater as they can immobilize up to 90% of pollutants, such as heavy metals.
"Repurposing both the soil and the waste products is a win-win-situation: we keep waste out of landfills and can create soil as a basis for diverse purposes in urban spaces," explains Lauren Porter, first author of the publication, who works at the Chair of Urban Productive Ecosystems at TUM.
Nadja Berger, doctoral candidate at the Chair of Restoration Ecology , has already tested the artificially produced soils as a substrate for plants in greenhouses. The results show that plants from wetlands thrive on these soils and can withstand various stress factors such as heat, flooding, and pollutants.
Astrid Eckert / TUM Constructing soils for each purpose
Beyond circularity, constructed soils offer a crucial added benefit: they can be customized to each specific use-case. For instance, if the soil is to be used in a roadside strip, the pollutant-binding property of the soil can be enhanced, while in green areas where plants should thrive, increased fertility can be prioritized. Based on the characterization presented by the researchers, practitioners can construct the soils to achieve the desired functions, by using more biochar or compost, depending on the application area.
"In the long term, our findings can support city and building planners," says Lauren Porter. "The better they know the respective soils, the more successful they can be tailored to each use and aid in closing the resource cycle for soils."
Porter, L., Bucka, F.B., Páez-Curtidor, N. et al. Constructing (multi)functional soil using urban organic and sediment wastes. Nat Cities (2025). https://doi.org/10.1038/s44284-025-00332-9
Nadja K. Berger, Lauren Porter, Leonardo H. Teixeira, Johannes Kollmann. Testing native plants for multifunctional infiltration swales: Effects of substrate amendments and flooding. Urban Forestry & Urban Greening (2025). https://doi.org/10.1016/j.ufug.2025.129177
Nadja K. Berger, Johannes Kollmann, Leonardo H. Teixeira. Native plant communities designed for infiltration swales can tolerate urban heat, flooding, and pollution. Basic and Applied Ecology. 2025. https://doi.org/10.1016/j.baae.2025.12.003
The research took place at chairs at the TUM School of Life Sciences . The professorship of Urban Productive Ecosystems and the chair of Soil Science are part of the World Agricultural Systems Center Hans Eisenmann-Forum at TUM. The research was funded by the Research Training Group 2679 Urban Green Infrastructure .
