Background and Aims Crop responses to elevated atmospheric CO2 are likely to be different in semi-arid cropping systems of Australia. This experiment aimed to investigate the interactive effects of atmospheric CO2 and nitrogen (N) fertiliser on carbon (C) and N partitioning in the soil-plant system of Wheat (Triticum aestivum L.) and field pea (Pisum sativum L.). Methods Plants were grown with 40 or 100 mg N kg−1 under ambient CO2 (390 ppm) or elevated CO2 (eCO2; 550 ppm) using free-air CO2 enrichment (SoilFACE). Repeated 13CO2 pulse labelling was used to quantify C transfer via plant to the soil. Destructive sampling was performed at grain filling and maturity. Results eCO2 increased shoot biomass of field pea (36 %) and wheat (55 %) but only increased root biomass of wheat (13.5 %) in the 25–50 cm soil layer. Total N content of both species was greater under eCO2, and for field pea it indicated enhanced biological N2 fixation. However, eCO2 increased the C:N ratio of wheat even at the high N level. Greater 13C in soil of wheat grown under eCO2 indicated a minor increase in soil C via rhizodeposition. Conclusions Increased biomass and C:N ratio of wheat could have implications for residue decomposition. eCO2 and low N tended to increase grain yield but the increase was highly variable and not significant. Additional N content of field pea under eCO2 exceeded the N that would be removed in wheat grain, albeit with lower than expected grain yield due to dry conditions.