Nature-based solutions to optimize the functions of soils in future cities – OPTISOIL

From a perspective of sustainable development, the cities of tomorrow have to be more resilient and adaptive. Operational solutions are urgently needed to face ongoing and future climate changes, but also to reduce anthropic pressure on natural resources. In such a view, urban greenspaces are a key element of future cities as they imply the production of organic wastes – e.g. woody wastes - and also provide ecosystem services. To date, recycling by composting and biomethanisation are not well adapted to woody residues. Production of biochar (heating without O2) can consist in a valuable way to ecologically and economically valorizate these wastes. In addition, its incorporation into soils is now recognized as a valuable material to store carbon in soils and to promote soil functions such as water retention and belowground biodiversity. Hence, biochar can be a tool to recycle woody residues while promoting a new bioeconomic sector but also ecosystem services provided by soil from urban greenspace area. Yet biochar alone is unlikely to promote alone soil fertility in urban green spaces as a consequence of their intrinsic low nitrogen content. OPTISOIL proposes to grow nitrogen-fixing plants in these urban green spaces to counterbalance this limitation. This project aims to document the combined effect of the addition of biochar and N2-fixing plants on the functions of a degraded soil (e.g. technosol) and to estimate the ecological imprint and economic prospects related to these nature-based solutions.
OPTISOIL will develop fundamental and applied research on the use and impact of biochar and N2-fixing plants on :
(i) the biogeochemical cycle of the soil, in particular through the study of the degradation of biochar and of the factors controlling CO2 emissions at short and long time scales;
(ii) soil water retention by coupling geophysical tools to propose a unique spatial and temporal field monitoring for such an experimental ;
(iii) above-ground and below-ground life to determine additional carbon stocks but also changes in soil biodiversity, a substrate for numerous ecosystem services;
(iv) the ecological footprint and the techno-economic impacts will also be evaluated in order to assess the sustainability of the proposed natural solutions and their potential for developing a new economic sector.
Overall, according to its resolutely multidisciplinary approach, the OPTISOIL project will involve research aligning the interests of different scientific disciplines (organic geochemistry, geophysics, microbiology and economics) and of public and private stakeholders in the management of green spaces.