Spectrometric Estimation of Total Nitrogen Concentration in Douglas Fir Foliage

[L. Johnson & C. Billow, International Journal of Remote Sensing 17:489-500]

picture of douglas fir foliage on lab table

A laboratory spectrophotometer was used to acquire absorbance spectra of 97 Douglas fir foliage samples, from seedlings cultivated under differing fertilization.

Wavelength dependence of correlation between first-derivative absorbance spectra and total nitrogen concentration for each sample preparation, 2000 - 2498 nm. Locations of nitrogen-hydrogen absorption features shown by arrows at top of plot.


Laboratory measurements of total nitrogen (mg g-1) versus predictions generated by stepwise regression from fresh-leaf first-derivative absorbance spectra for seven cross-validation sets.

Conclusions:

  • Fresh-leaf spectral properties influenced by total nitrogen concentration, particularly >2000 nm.

  • Sampling drying and grinding increased correlation between spectra and chemistry (vs. fresh), but had little effect on shape of correlogram.

  • Stepwise regression may be used to estimate total nitrogen concentration from fresh-leaf spectra, with standard errors ranging from 1.5-2.4 mg g -1.

  • Ability to extract biochemical information from fresh-leaf spectra, shown here, is a necessary but insufficient condition regarding use of remote sensing for canopy-level estimation.


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