RESEARCH & EVENTS
Figure
2. Timelapse K cb of Nonpareil, Vela and Shasta trees at low tree density( 308 tree / ha) from November 2022 to July 2023, demonstrating differences due to variety.
per day, late in the afternoon to avoid the occurrence of sun-flair. Under-canopy images were processed by splitting the original RGB images into red, green and blue channels. The blue channel was converted into a binary image( sky vs canopy) using the thresholding algorithm developed by Otsu( 1979). The image was then divided into 25 sections( as a 5 by 5 grid, Figure 1) and the proportion of canopy in each grid was used to calculate the leaf area index of the image using the method described by Macfarlane et al.( 2007). Leaf area index was converted to density coefficient( K d
), from which basal crop coefficient( K cb
) was derived, using the methodology of Allen and Pereira( 2009).
RESULTS Shasta and Vela are two new almond varieties with strongly contrasting tree habits. Shasta grows upright trees which open with the weight of crop due to tip bearing, whilst Vela trees are quite spreading. Trees of Nonpareil, the current industry standard variety, are relatively upright and compact. Figure 2 displays K cb calculated from under-canopy camera images for Nonpareil, Shasta and Vela trees planted at 6.5 x 5m( 308 trees / ha). The comparison indicates that K cb
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measured using timelapse cameras was highest in Nonpareil and Shasta, while Vela gave lower values. The decline in K cb at the end of the growing season also occurred earlier in Vela and later in Shasta, when compared to Nonpareil, despite there being no difference in management, and Shasta being the earliest variety harvested and Vela the latest.
CONCLUSION This project demonstrated that an under-canopy camera system is able to monitor canopy growth in orchards to support improved irrigation scheduling. Under-canopy cameras were positioned approximately 1m from the trunk, suggesting that the commercial use of such sensors within an orchard environment would not be disrupted by orchard machinery and standard management practices. Permanently installed undercanopy timelapse imagery systems demonstrated their ability to track changes in canopy size and water requirement, particularly in the latter half of the season.
REFERENCES
ALLEN, R. G. & PEREIRA, L. S. 2009. Estimating crop coefficients from fraction of ground cover and height. Irrigation Science, 28, 17-34.
MACFARLANE, C., HOFFMAN, M., EAMUS, D., KERP, N., HIGGINSON, S., MCMURT- RIE, R. & ADAMS, M. 2007. Estimation of leaf area index in eucalypt forest using digital photography. Agricultural and Forest Meteorology, 143, 176-188.
OTSU, N. 1979. A Threshold Selection Method from Gray-Level Histograms. IEEE Transactions on Systems, Man, and Cybernetics, 9, 62-66.
industry. australianalmonds. com. au
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