Aims <p>This study evaluated the suitability of root electrical capacitance measurements for nondestructive plant phenotyping in a free-air CO₂ enrichment (FACE) experiment.</p> Methods <p>A two-year FACE study was conducted with maize grown under ambient and elevated [CO₂], and low and high nitrogen supply in three replicate plots. The saturation root electrical capacitance (C_R*) was monitored during the plant growth cycle. Aboveground plant parameters were measured in situ at flowering.</p> Results <p>Capacitance measurements revealed a seasonal pattern in root development with a peak at flowering, and the positive effect of higher nitrogen dose and [CO₂] enrichment on plant growth. At anthesis, C_R* was significantly (<i>p</i> &lt; 0.001) and linearly correlated with stem basal area (R²: 0.51–0.68), aboveground biomass index (basal area × plant height; R²: 0.47–0.62) and leaf chlorophyll concentration (R²: 0.40–0.56). However, the best correlation (R²: 0.73 and 0.74) was found for plant leaf area, which is closely related to root water uptake, suggesting that the applied current signal penetrated the roots, and that the capacitance method directly measured root status in the field. In addition, C_R* at flowering was a reasonable early predictor of maize grain yield (R²: 0.58 and 0.64) under our experimental conditions.</p> Conclusions <p>The electrical capacitance method proved to be a practical high-throughput tool for phenotyping not only the root but the whole plant in the field. Being noninvasive, it is particularly beneficial in FACE systems, where destructive sampling and soil disturbance should be minimized. It would also provide cost-effective support for breeding stress-tolerant and climate-resilient crops.</p> Graphical Abstract <p></p>