Inter-relationships between canopy features and fruit yield in citrus as detected by airborne multispectral imagery.
Ye, Xujun*,1, Sakai, Kenshi1, Asada, Shin-Ichi2, Akita, Tetsuya1, Sasao, Akira1, 1 Tokyo University of Agriculture and Technology, Fuchu, Tokyo, Japan2 Kanagawa Prefectural Agricultural Research Institute, Odawara, Kanagawa, Japan
ABSTRACT- The objective of this study was to investigate the alternate bearing dynamics in citrus crops. Airborne multispectral images with high spatial resolution were acquired over a Satsuma Mandarin (Citrus unshiu Marc.) orchard at four time periods in 2002 and 2003. On the images, thresholded pixel counts (TPCs), indicators of the relative leaf areas of several leaf types in each canopy, for 48 tree samples were extracted. Correlation analyses between each of the TPCs and the fruit yields of citrus in 2002, 2003 and 2004 were conducted. Results indicated that some TPCs show a higher correlation with fruit yield than those corresponding to the entire canopy size, particularly the TPCs extracted from the visible red, green and blue wavelengths. The mature leaves before the fast vegetative growth (May) were found to be significantly correlated with the fruit yield of the same growing season, whereas the younger leaves during this period were more significantly correlated with the fruit yields of the previous and the following growing seasons. This information implies an unmatched energy allocation dynamics between different leaf types within the canopy, which may lead to an unsynchronized leaf energy contribution, direct (mature leaves) or delayed (younger leaves), to the fruiting of citrus crops. In addition, the models based on the TPCs demonstrated the potential of airborne multispectral imagery to forecast the fruit yield of citrus. The obtained yield estimates can provide valuable information for planning fruit harvest schedules and generating prescription maps for tree-specific management practices on an individual tree basis.
Key words: alternate bearing dynamics, canopy-yield interrelationship, modelling
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