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A Comparison Of Spectral Reflectance And Laser-induced Cholorphyll Fluorescence Measurements To Detect Differences In Aerial Dry Weight And Nitrogen Update Of Wheat

¹B. Mistele, ²U. Schmidhalter

1.
2. Technical University Munich

Chlorophyll fluorescence and spectral reflectance analysis are both powerful tools to study the spatial and temporal heterogeneity of plants` biomass and nitrogen status. Whereas reflectance techniques have intensively been tested for their use in precision fertilizer application, laser-induced chlorophyll fluorescence has been tested to a lesser degree, and there are hardly any comparative studies. Therefore, we used both techniques in field and laboratory experiments since more than eight years and compared their performance in detecting nitrogen uptake and aerial dry biomass of wheat with a particular focus on detecting possible disturbances by environmental factors. We tested both sensors in field experiments with tractor-based systems, mounted about 2 m above the canopy and measuring besides the tractor with an oblique angle of sensor view. Validation measurements were performed on large calibration areas of 25 m² in size. Fertilizer applications varied between 0-220 kg N ha^-1 and grain yields between 3-12 t ha^-1. The results obtained show that strong relationships exist between reflectance indices and total aerial N (R² = 0.90 to 0.99) and aerial dry biomass (0.77 to 0.92), from the end of tillering at growth stage GS 30 to flowering at GS 65, whereas laser-induced two-wavelength chlorophyll fluorescence detected total aerial N with R² of 0.78 to 0.86 and aerial dry biomass with R² of 0.77 to 0.85. Spectral reflectance measurements were influenced by both sensor geometry and solar angle. A strong influence of direct sunlight and temperature on the fluorescence ratio F₆₉₀/F₇₃₀ was evidenced. Therefore, a model was developed to describe the light-matter interaction in plant leaves. Both sensors were well suited to describe relative differences in aerial dry weight biomass and nitrogen uptake at relevant fertilizer application stages, but the spectral values were not always depicting a continuous evolution.

Keyword: Light intensity model, active light sensor, LIF, temperature model

B. Mistele U. Schmidhalter Pros and Cons of Reflectance and Fluorescence-based Remote Sensing of Crop Oral 2010

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