Abstract:To achieve the previsual detection on nitrogen(N) stress, the microelectrode technique was used to measure the membrane potential, membrane capacitance and light induced responses of leaf membrane potentials under four different levels of Ntreatment, respectively. No obvious difference was found in the membrane potential between Nstress and Nsufficient cucumber leave. It shows that the membrane potentials were not suitable for early diagnosis of Nstress in cucumber plants. The research on the changes of membrane capacitance found that it was sensitive to Ndeficiency. The measurement of membrane capacitance could be used for previsual diagnosis of severe and moderate Ndeficiency 2d before the appearance of visually morphological changes. The research on the changes of magnitude of leaf membrane potential response to light found that it was sensitive to Nexcess. The measurement of the magnitude of leaf membrane potential response to light could be used for previsual diagnosis of Nexcess at least 7d before the appearance of visually morphological changes. It shows that the microelectrode technique is suitable for early diagnosis of Nstress in cucumber plants.