Relationship between Chlorophyll Content and Canopy Reflectance in Washington Navel Orange Trees (citrus Sinensis (l.) Osbeck)

Understanding the spectral features of Washington navel trees is important to remotely measure and monitor the canopy properties and biochemical changes in plantations. Satellite and ground based passive remote sensing techniques have been widely used in many plant species. However, the use of these techniques in orange trees is limited. In this study, relationships between total chlorophyll (Chl) contents and canopy reflectances (RF) were used to determine the most suitable growth and development stage that could be used to measure and monitor the canopy properties and biochemical changes by remote sensing technologies in Washington navel orange trees (Citrus sinensis (L.) Osbeck). Plant materials consisted of four different age groups of 15, 20, 25 and 30 years old orange trees. Spectral measurements in the range of 450-900 nm were made at four different growth and development stages; viz., flowering, fruit setting, fruit maturity and dormancy using a portable spectroradiometer and total chlorophyll contents of the leaves at these stages were assessed with a spectrophotometer. The highest relationship between Chl and RF at blue and red bands was r= 0.845 and 0.860 at the 0.01 level, respectively, at the fruit setting stage of the 20 years old trees. Again at this stage, fruit setting, total Chl and RF values among the 40 orange trees were significantly correlated at the blue and red bands with the r values of 0.787 and 0.812 at the 0.001 level, respectively. Results of the present study suggested that the most suitable growth and development stage was the fruit setting stage for passive remote sensing techniques to determine and monitor the canopy properties and biochemical changes of orange trees.