title: Digital cover photography for estimating leaf area index (LAI) in apple trees using a variable light extinction coefficient.
abstract: 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 (Io) 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 (Ic) 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 Ic, helped to increase accuracy of LAI estimates using digital cover images for apple trees with different canopy sizes and under field conditions.
authors: Research and Extension Center for Irrigation and Agroclimatology (CITRA), Universidad de Talca, Talca 3460000, Chile. cpoblete@utalca.cl.
authors: Carlos
authors: C
authors: Poblete-Echeverría
authors: Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Melbourne, VIC 3010, Australia. sigfredo.fuentes@unimelb.edu.au.
authors: Sigfredo
authors: S
authors: Fuentes
authors: Research and Extension Center for Irrigation and Agroclimatology (CITRA), Universidad de Talca, Talca 3460000, Chile. sortega@utalca.cl.
authors: Samuel
authors: S
authors: Ortega-Farias
authors: Centro de Pomaceas, Universidad de Talca, Talca 3460000, Chile. jgonzalezt@utalca.cl.
authors: Jaime
authors: J
authors: Gonzalez-Talice
authors: Centro de Pomaceas, Universidad de Talca, Talca 3460000, Chile. ayuri@utalca.cl.
authors: Jose Antonio
authors: JA
authors: Yuri
mesh_terms: D055592:Biophysical Phenomena; D003201:Computers; D018556:Crops, Agricultural; D027845:Malus / Q000502:physiology*; D010781:Photography; D018515:Plant Leaves / Q000502:physiology*
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