Abstract Background and aims This study was the first to test the efficiency of monitoring root electrical capacitance (C R *) non-destructively in the field to evaluate crop development under different environmental conditions. Methods A free-air CO 2 enrichment (FACE) experiment was performed with two winter wheat cultivars, two levels (low and high) of nitrogen supply and two (ambient and elevated) of [CO 2 ] in three replicate plots over two years. The validity of C R * as a proxy for root uptake activity was confirmed by tracking the ceptometer-based leaf area index (LAI). Results Repeated C R * measurements clearly demonstrated the seasonal dynamics in root development, with a peak at flowering, and the delayed growth in the second year caused by the unfavourable meteorological conditions. From the vegetative to flowering stages, C R * was strongly correlated with LAI (R 2 : 0.897–0.962). The positive effect of higher N supply and elevated [CO 2 ] on crop growth was clearly indicated by the higher C R * values, associated with increased LAI, shoot dry mass (SDM) at flowering and grain yield (GY). The maximum C R * was closely related to GY (R 2 : 0.805 and 0.867) when the data were pooled across the N and CO 2 treatments and the years. Unlike C R * and GY, SDM and LAI were significantly lower in the second year, presumably due to the enhanced root/shoot ratio induced by a severe spring drought. Conclusions The present results convincingly demonstrated the potential of the in situ root capacitance method to assess root responses dynamically, and to predict crop GY.