Leaf area index (LAI) is one of the key biophysical variables required for crop modeling. Direct LAI measurements are time consuming and difficult to obtain for experimental and commercial fruit orchards. Devices used to estimate LAI have shown considerable errors when compared to ground-truth or destructive measurements, requiring tedious site-specific calibrations. The objective of this study was to test the performance of a modified digital cover photography method to estimate LAI in apple trees using conventional digital photography and instantaneous measurements of incident radiation (I_o) and transmitted radiation (I) through the canopy. Leaf area of 40 single apple trees were measured destructively to obtain real leaf area index (LAI_D), which was compared with LAI estimated by the proposed digital photography method (LAI_M). Results showed that the LAI_M was able to estimate LAI_D with an error of 25% using a constant light extinction coefficient (k = 0.68). However, when k was estimated using an exponential function based on the fraction of foliage cover (f_f) derived from images, the error was reduced to 18%. Furthermore, when measurements of light intercepted by the canopy (I_c) were used as a proxy value for k, the method presented an error of only 9%. These results have shown that by using a proxy k value, estimated by I_c, helped to increase accuracy of LAI estimates using digital cover images for apple trees with different canopy sizes and under field conditions.

A study was conducted in a commercial sweet cherry orchard in central Chile. The objective was to evaluate the rain cover effect on changes in the microclimate, vegetative growth, plant physiology and fruit quality of ‘Rainier’, ‘Bing’ and ‘Sweetheart’ sweet cherry trees. The data were compared to a control without a rain cover. The results showed that, under the rain cover, there was a 50–60% reduction in total solar radiation, as well as an increase in air temperature (+0.6 °C) and a decrease in relative humidity (−4.7 percentage points) in the upper canopy zone. Regarding the trees under rain cover, a greater shoot length (28–58%) and leaf area (24–54%) were observed among cultivars compared to the control; the trunk cross-sectional area was only significant in ‘Rainier’, it being 1.2 times greater under rain cover. CO₂ assimilation showed no differences, but an increase in the leaf transpiration rate was observed. The fruit firmness and sugar content in fruits were negatively affected by the rain cover, those characteristics being of major relevance for the cherry growers. Additionally, the contents of anthocyanins and carotenoids and the antioxidant capacity were significantly lower only in ‘Rainier’ under rain cover, while the total phenol content decreased in all three cultivars. The rain cover did not negatively affect the tree physiology, but it can be detrimental in bicolor cultivars with a yellow flesh due to a lower color and phenolic compounds development.

Zusammenfassung: Chile ist der größte Fruchtexporteur der südlichen Halbkugel. Exportiert wurden in der Saison 2017/18 780.000 t Äpfel, 751.000 t Weintrauben, 166.000 t Süßkirschen, 155.000 t Avocados, 105.000 t Heidelbeeren und 180.000 t Kiwi. Chile ist – nach China, Italien und Neuseeland – im Moment der viergrößte Kiwiproduzent.Der Obstbau in Chile konzentriert sich auf die vier mittleren, klimatisch gemäßigten Zonen Valparaiso, Metropolitana, O’Higgings und Maule am 34–36°S Breitengrad des langestreckten Landes.Kiwi- und Birnenanbau gingen stark zurück von 12.000 ha auf nur 6000 ha bzw. von 17.000 ha auf heute ca. 9000 ha und Avocado von 39.000 ha auf 29.300 ha. Die Heidelbeerfläche beträgt 15.600 ha und die Apfelfläche über Jahre konstant 36.000 ha. Bei Süßkirschen wird die Fläche von 25.000 ha (2500 ha unter Folie) nach Süden in die Regionen Bio-Bio und Araucania ausgeweitet.Der Apfelanbau ist geprägt durch Frost- und eine hohe Sonnenbrandgefahr, genügend Niederschläge und ausreichend Kältereiz, die zu Erträgen von 60–110 t Äpfel/ha bzw. 10–15 t/ha bei Süßkirschen führen. Ziel ist – bei nur 18 Mio. Einwohnern Chiles – einen hohen Anteil Premiumfrüchte für den Export im Winter auf der nördlichen Hemisphäre zu erzielen – China, USA und Europa sind die Hauptabnehmer.