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

The laser-induced fluorescence imaging system allows the recording of spectrally selected fluorescence images of the whole leaves or plants which is better and in contrast to the so far applied spot spectrofluorometer measurements. The fluorescence images of leaves of winter wheat (Soissons variety, Alsace) have been recorded at the four characteristic emission bands (440, 520, 690 and 740 nm) with a high resolution imaging device consisting of a frequency triplet or doubled Nd:YAG source For 355 nm or 532 nm excitation and of an intensified and gated CCD digitized camera. The effect of four different nitrogen treatments (0, 100, 140 and 180 kg/ha) on the fluorescence parameters (intensities F440, F520, F690, F740 and ratios F440/F520, F440/F690, F440/F740 and F690/F740) obtained by image processing has been analysed by statistical treatment, in a randomised blocks experiment. The measurements have been carried out on two leaf storeys weekly gathered during two months (May and June 1996). For 355 nm excitation, a significant decrease of the fluorescence ratios F440/F690 and F440/F740 was observed for increasing nitrogen concentration: the blue and green mean fluorescence intensities remained much the same, while the red and far-red chlorophyll fluorescence emissions were enhanced by the fertilisation. The fluorescence results are in excellent correlation with the crop yields.