Model-based studies have shown that large scale application of Negative Emission Technologies (NETs) is of critical importance to limit future temperature rise well below 2⁰C. Two key examples of NETs are biochar, the carbon-rich (by)product of biomass combustion, and Enhanced Silicate Weathering (ESW), the spreading of finely ground silicate minerals. When applied to agricultural soils, ESW not only consumes CO2, but also increases soil pH and releases essential nutrients, thereby potentially enhancing crop production. However, a parallel release of heavy metals may contaminate soils and groundwater. Biochar application to agricultural soils increases the stable Soil Organic Matter (SOM) pool, and enhances the capacity of soils to bind nutrients and heavy metals, which can both be released by ESW. Moreover, the combined application of ESW and biochar may promote the formation of organo-mineral associations and soil aggregates. Through the promotion of SOM stabilisation mechanisms, combined ESW and biochar applications may synergistically sequester a larger amount of carbon in soils than single applications. However, biochar and ESW have so far only been studied separately.

The aim of this research is to experimentally study whether, and through which mechanisms, synergies between ESW and biochar occur. We hypothesise that the combined application of ESW and biochar provides synergistic effects on three key ecosystem services provided by soils, namely carbon sequestration, nutrient cycling, and heavy metal immobilisation. Three types of silicate minerals combined with high quality biochar will be applied to both sandy and clayey soils in carefully designed laboratory and lysimeter field experiments, to quantify their net carbon sequestration and effects on crop growth. Moreover, by using high resolution imaging techniques, this study will provide molecular scale understanding of SOM-mineral-biochar interactions in soils. This research will be the first experimental study on ESW and biochar combinations, and mechanistic understanding of their potential synergies is of critical importance to design application strategies that enhance essential ecosystem services, thereby paving the way for a transition towards carbon negative agricultural systems.