Spectroscopic detection of nitrogen concentrations in sagebrush

The ability to estimate foliar nitrogen in semi-arid landscapes can yield information on nutritional status and improve our limited understanding of controls on canopy photosynthesis. We examined two spectroscopic methods for estimating sagebrush dried leaf and live shrub nitrogen content: first derivative reflectance (FDR) and continuum removal. Both methods used partial least squares (PLS) regression to select wavebands most significantly correlated with nitrogen concentrations in the samples. Sagebrush dried leaf spectra produced PLS models (R-2 = 0.76-0.86) that could predict nitrogen concentrations within the data set more accurately than PLS models generated from live shrub spectra (R-2 = 0.41-0.63). Inclusion of wavelengths associated with leaf water in the FDR transformations appeared to improve regression results. These findings are encouraging and warrant further exploration into sagebrush reflectance spectra to characterize nitrogen concentrations.