Detection of nutrient deficiencies of maize by laser induced fluorescence imaging

Laser-induced fluorescence is an active method of sensing the state of heath of the plants and the photosynthetic apparatus, as it is related not only to the pigment concentrations but also to the physiological activity. A high gain and high spatial resolution fluorescence imaging set up, consisting of a pulsed Nd:YAG laser for the excitation (355 nm) and of an intensified gated CCD numerical camera, has been used for monitoring various nutrient deficiencies of maize (Zed mays L.) by recording fluorescence images of-the leaves at 440, 520, 690 and 740 nm. The plant status was characterised by the fluorescence ratios F440/F520, F440/F690, F440/F740 and F690/F740. The experiments performed on field maize supplied with various amounts of nitrogen and on greenhouse maize with defined mineral deficiencies showed that all the deficiencies could be monitored by the fluorescence ratios and in some cases directly on the fluorescence images by considering the spacial distribution of the emission on the leaf-surface. From this work it appeared that the efficiency of detection depended on the period of measurements and on the age of the leaves. The fluorescence ratios F440/F690 and F440/F740 were found more sensitive to the growth conditions than the most frequently used chlorophyll fluorescence ratio F690/F740.