Determination of seasonal variations in solar energy utilization by the leaves of Washington navel orange trees ( Citrus sinensis L. Osbeck)
Abstract:Definition of both quality and quantity of energy consumption of crops by recently developed remote sensing methods has been an important factor in the control of sustainable bioenergy production in terms of food security. This study was conducted to find the critical physiological stages of orange trees from their energy supply and energy balances using remote sensing methods. The relationships between absorbed photosynthetically active radiation (APAR) and chlorophyll content (chl) of the leaves at different growth stages were investigated. Canopy reflectance by hand‐held spectroradiometer and total chl analysis at the laboratory were measured simultaneously from the random samples taken from four different parts of orange trees in orchards, each orchard being at a different age group. Reflectance measurements were conducted between 450nm and 900nm wavelength at four different bands (three visible bands and one near‐infrared band) at the four basic physiological periods of orange trees. Reflectance values measured in the field were converted to APAR (Wm −2 ) and the chl values were determined in mgml −1 . According to the statistical analysis, there was a strong relationship between APAR at the bands of 450–520nm (blue) and 630–690nm (red) and the chlorophyll content ( p ≤0.01; R 2 = 0.750 at blue wavelength and R 2 = 0.770 at red wavelength) in June (fruit setting stage). These results showed that the relationships between chl and APAR values were very strong despite low levels of APAR at this stage, in comparison to the other ones. Amongst all the stages, APAR values were the highest in November. Another important result was that Washington navel trees unexpectedly had the highest APAR during the dormancy stage. These results suggested that the relationships between PAR utilization and chlorophyll content were important for tree health and indirect yield of per annum plants such as citrus. The values obtained from the leaves of orange trees at different physiological periods were more important than those relationships for the trees of different ages.
Document Type: Research Article
Affiliations: 1: Akdeniz University, Remote Sensing Research and Application Centre, 07059 Antalya, Turkey 2: The Akdeniz Citrus and Greenhouse Research Institute, Antalya, Turkey 3: Akdeniz University, Faculty of Agriculture, Department of Agricultural Mechanization, Antalya, Turkey
Publication date: 2005-08-10