Field-based 13C-15N labelling to investigate C and N allocation in crop–soil pools. Tillage practices in a dryland mixed farming did not influence C and N allocation. Only a small proportion (4–5%) of plant-assimilated C was allocated belowground. Only a small proportion (0.5–0.7%) of soil 15N tracer was allocated aboveground. Soil and agronomic functionality were similar across contrasting tillage systems.