Improved Microbial Carbon Use Efficiency With Low Tillage Intensity: Evidence and Research Gaps

High microbial carbon use efficiency (CUE) in agricultural soils can limit the return of atmospheric carbon dioxide (CO₂) from organic matter mineralisation and potentially increase soil organic carbon (SOC) accumulation through the formation of microbial biomass and necromass. Therefore, soil management practices that increase microbial CUE are relevant for sustainable agriculture and climate change mitigation. We conducted an exploratory literature review and evidence synthesis to compare microbial CUE between conventional tillage (CT) and low-intensity tillage systems (reduced tillage, RT and no-tillage, NT). The synthesis of 50 paired observations from 11 studies showed an overall increase in microbial CUE of 12% in soils under low-intensity tillage compared to CT (p = 0.02). Separate tillage contrasts of RT and NT versus CT (i.e., RT/CT and NT/CT) also showed higher microbial CUE for soils under low-intensity tillage with p = 0.06 and p = 0.05, respectively. The increase in CUE is likely due to improved substrate availability for microbial growth and/or changes in the microbial community induced by the contrasting tillage systems. However, the limited availability of quantitative data linking tillage-induced changes in these drivers to microbial CUE constrains further analysis. We also extracted available SOC data from the eligible studies, but this data did not provide evidence that increases in microbial CUE were correlated with increases in SOC content. Future studies should extend the emerging empirical data set and clarify the abiotic and biotic drivers through which tillage practices can be refined for better SOC management and climate change mitigation strategies. Further studies should also aim to better understand the link between microbial CUE and SOC dynamics, which is important for the representation of CUE in global SOC models.