Production capacity evaluation of the citrus tree by the optical method

In order to evaluate citrus tree productivity by remote sensing, a nondestructive method that estimated the leaf area index per tree crown area (LAI_tca) using a plant canopy analyzer (PCA: LAI-2000, LI-COR, Inc.) was examined. The measurement by the PCA was carried out in 2003 and 2004 on 7 kinds of Satsuma mandarin (Citrus unshiu Marc.) tree of which cultivar, tree age and size differed. The cultivars used for the experiments were Otsu No.4, Sugiyama unshiu and Okitsu wase. To begin with, PCA measured the incident light to the treetop, and next, it measured the transmitted light of the tree at the 30cm interval (30, 60, 90, 120, 150, 180cm) on 4 azimuths (NE, NW, SE, SW) from the trunk. The measurement was carried out under cloudy conditions in order to minimize the effect of the direct light to the PCA. After the measurement, total leaf numbers, average of individual leaf area, tree crown radius in the 16 or 8 azimuths and tree height of the trial tree were measured. From total leaf area, tree crown area and tree height, LAItca and leaf area density (LAD) were calculated. The LAI_tca is the result of dividing the total leaf area by the tree crown area, and the LAD is the result of dividing the LAI _tca by tree height. The leaf area index (LAI) by the PCA was recalculated except for the values of the measuring point which was outside the tree crown area. In the relationship between LAI by PCA and LAI_tca, there was an underestimation tendency of about 37%, but the very high correlation was shown when the lower LAD trees were removed. The possibility of LAI by PCA using this measurement method as an effective index for LAI _tca in productivity evaluation of the citrus tree was indicated.