Exploring the relationships between leaf nitrogen content, biomass and the near-infrared/red reflectance ratio

Abstract

The relationship between above-ground vegetation biomass (biomass) and reflectance in red (R) and near-infrared (NIR) wavelengths is well documented. In recent work it has been observed that the accuracy of biomass estimation using these relationships is higher than that based solely on traditional ground data measurement. It was posulated that the accuracy of these estimates allowed field assessment of leaf nitrogen content to be undertaken when leaf nitrogen, green reflectance and near-infrared reflectance were not strongly related because of the relationships between biomass and leaf nitrogen. This paper presents the results of a pilot study that sought to explore the links between biomass, leaf ‘kjeldahl’ nitrogen, R and NIR reflectance. It was observed that biomass was related to R and NIR reflectance and leaf kjeldahl nitrogen, but the variance in each relationship was high, despite taking into account leaf and soil moisture and site topography. It is proposed that much of the unexplained variance is due to different proportions of live, dead, erectophile and planophile biomass at each site.