Plants allocate recently photo-assimilated carbon (C) to aboveground and belowground organs to support their structural and non-structural components and metabolic processes1, 2, influencing the C source sink balance3 and nutrient cycling in terrestrial ecosystems4. Of the total belowground C allocation, a significant amount can be translocated from roots to soil (e.g. as exudates) and subsequently respired as CO25,6,7. Root exudates are energy-rich substrates which influence the growth and activity of microbes, mineralisation of soil organic matter (SOM), and uptake of soil-released nitrogen (N) by plants4. Thus, belowground C allocation is a key process in influencing the coupled source–sink activities between shoots, roots and soil microorganisms with implications for C and N cycling, N use efficiency and biomass productivity in agro-ecosystems2, 8, 9. However, the responses of these agro-ecosystem dynamics to management practices, including the relationship between belowground C allocation and crop N uptake, are not well understood4, 7, 10. A better understanding is needed of the potential of management practices to enhance plant C input and N use efficiency in crop–soil systems