Laser-induced fluorescence imaging for monitoring nitrogen fertilizing treatments of wheat

ABSTRACT The laser-induced fluorescence imaging system allows the recording of spectrally selected fluorescence images ofthe whole leaves or plants which is better and in contrast to the so far applied spot spectrofluorometer measurements. Thefluorescence images of leaves of winter wheat (Soissons variety, Alsace) have been recorded at the four characteristicemission bands (440, 520, 690 and 740 nm) with a high resolution imaging device consisting of a frequency triplet ordoubled Nd:YAG source for 355 nm or 532 nm excitation and ofan intensified and gated CCD digitized camera. The effectof four different nitrogen treatments (0, 100, 140 and 180 kg/ha) on the fluorescence parameters (intensities F440, F520,F690, F740 and ratios F4401F520, F440/F690, F4401F740 and F690/F740) obtained by image processing has been analysedby statistical treatment, in a randomised blocks experiment. The measurements have been carried out on two leaf storeysweekly gathered during two months (May and June 1 996). For 355 nm excitation, a significant decrease of the fluorescenceratios F4401F690 and F4401F740 was observed for increasing nitrogen concentration: the blue and green mean fluorescenceintensities remained much the same, while the red and far-red chlorophyll fluorescence emissions were enhanced by thefertilisation. The fluorescence results are in excellent correlation with the crop yields.Keywords: wheat, plant stress, nitrogen fertilisation, fluorescence imaging