RADIOMETRIC ESTIMATION OF BIOMASS AND NITROGEN-CONTENT OF BARLEY GROWN AT DIFFERENT NITROGEN LEVELS

Field measurements of red (655 nm) and near-infrared (NIR: 805 nm) canopy reflectance from barley grown at different nitrogen levels are related to changes in biomass accumulation and total nitrogen content of the plant material. Crop biomass and the NIR reflectance or the NIR/red index are highly correlated. The variation in reflectance and index accounted for by the biomass is between 93 and 99 per cent. In the different nitrogen treatments the percentage nitrogen content of the crop is negatively correlated with the biomass accumulation, and the nitrogen content declines in a exponential manner. The correlation coefficient between plant nitrogen content and biomass declines from -0-99 to -0-92 with increasing nitrogen application rates. However, at any given chronological age the total plant nitrogen content and the accumulated biomass are strongly correlated in a curvilinear manner. Hence on each sampling date the NIR and NIR/red reflectance are closely related to percentage plant nitrogen in a curvilinear manner similar to the relationship between biomass and percentage plant nitrogen. Sequential reflectance measurements related to the chronological age of the plants are satisfactory for a model assessing the total nitrogen content of the barley plants. Information about the developmental stage of the barley plants should improve the model assessing biomass accumulation by reflectance measurements. The plants should be described by parameters that take the nutritional status of the crop into account. Parameters such as numbers and survival of tillers numbers and duration of leaves, plant height and flowering should be used for a satisfactory definition of the developmental stage of the plants. © 1990 Taylor & Francis Group, LLC.