Bioimpedance Analysis of Cucumber Plants Exposed to Different Nitrogen Doses Under Greenhouse Conditions

Nitrogen (N) availability is critical for cucumber (Cucumis sativus L.) growth and yield in greenhouse production. In this study, we investigated the effects of different N doses on the bioimpedance spectroscopy (BIS) parameters of cucumber plants (ES.22.17 F1 genotype), focusing on extracellular fluid resistance (R1), intracellular fluid resistance (R2), vacuole fluid resistance (R4), and cell membrane capacitances (Cm, Ct). The results showed that low N supply significantly increased R1 and reduced Cm in the leaves, indicative of decreased nitrate (NO3−) concentration and impaired membrane fluidity. Higher N supply lowered resistance and increased cell membrane capacitance, reflecting improved ion transport and storage efficiency. A strong positive correlation was observed between total N and NO3− content (r = 0.9), while NO3− content negatively correlated with extracellular fluid resistance (R1, r = −0.8) and vacuole fluid resistance (R4, r = −0.9). The optimal N supply for cucumber plants was associated with R1 values of 47,121.07–52,953.93 Ω, R4 values of 0.348–0.529 Ω, and Cm values of 3.149 × 10⁻10–3.781 × 10⁻10 F. These BIS parameters showed high sensitivity to plant N status, highlighting BIS as a promising, minimally invasive technique for real-time nutrient monitoring. By integrating BIS data and horticultural best practices, growers can refine N fertilization strategies for better resource efficiency and potentially higher yields and fruit quality.