Abstract. Enhanced weathering (EW) and biochar amendment are proposed carbon dioxide removal (CDR) techniques with potential co-benefits for soil health and plant productivity. However, knowledge gaps remain regarding their impacts on soil carbon dynamics and heavy metal mobility. This study investigates the effects of basalt and biochar amendments on soil CO2 efflux (SCE), soil base cation dynamics, biomass yield and heavy metal uptake in clover (Trifolium pratense) and mustard (Brassica juncea) field plots. Despite potential CO2 uptake through weathering, we found that basalt increased SCE in both crops, suggesting increases in soil organic matter (SOM) decomposition and/or rhizosphere respiration. Biochar enhanced plant biomass and reduced plant uptake of several trace metals in both mustard and clover plants, while basalt did not affect any of the 33 assessed elements in aboveground plant biomass. While basalt alone increased CO2 efflux, co-application with biochar tempered this response, potentially mitigating a basalt-induced priming of soil organic matter decomposition. Hence co-application of biochar with basalt countered the basalt-induced rise in soil CO2 emissions, while biochar also reduced plant trace metal uptake, highlighting biochar’s potential to mitigate both environmental and food safety risks.
Vienne et al. (Mon,) studied this question.