Abstract
Abstract. Apple trees often produce high amount of fruits, which results in small, low quality fruits. Thinning in apple orchards is used to improve the quality of the apples by reducing the number of flowers or fruits the tree is producing. The current method used to estimate how much thinning is necessary is to measure flowering intensity, currently done by human visual inspection of trees in the orchard. The use of images of apple trees from ground-level to measure flowering intensity and its spatial variation through orchards has been researched with promising results. This research explores the potential of UAV RGB high-resolution imagery to measure flowering intensity. Image segmentation techniques have been used to segment the white pixels, which correspond to the apple flowers, of the orthophoto and the single photos. Single trees have been cropped from the single photos and from the orthophoto, and correlation has been measured between percentage of white pixels per tree and flowering intensity and between percentage of white pixels per tree and flower clusters. The resulting correlation is low, with a maximum of 0.54 for the correlation between white pixels per tree and flower clusters when using the ortophoto. Those results show the complexity of working with drone images, but there are still alternative approaches that have to investigated before discarding the use of UAV RGB imagery for estimation of flowering intensity.
Highlights
Thinning ensures the production of less but bigger fruits, with better qualities (Link, 2000)
With accurate spatial information about flowering intensity in the orchard, thinning can be optimized for the spatial variation of the orchard by applying different amount of chemical thinning according to the tree’s flowering intensity, because the total number of flowers indicates the maximum number of fruits that can be produced each year
The R2 obtained for correlation between flowering intensity and percentage of white pixels using Otsu’s segmentation was 0.14 when the orthophoto results were used and 0.41 when the results based on the UAV photos were used (Figure 3)
Summary
Thinning ensures the production of less but bigger fruits, with better qualities (Link, 2000). With accurate spatial information about flowering intensity in the orchard, thinning can be optimized for the spatial variation of the orchard by applying different amount of chemical thinning according to the tree’s flowering intensity, because the total number of flowers indicates the maximum number of fruits that can be produced each year. This would reduce the input of chemicals in the crop and would reduce or avoid having trees with unequal bearing of fruits, and hand thinning. With knowledge regarding spatial variability the farmer can use the information to decide to use fertilizer where it is more needed, and use less fertilizer where it is less needed, in trees carrying a lower amount of fruits
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