A Three-Dimensional Model of the Light Regime in an Avocado Orchard

Hadari Matan
M.Sc.Thesis, 2005

(together with Zur Benjamin & Broday David)


One of the major limiting factors in agricultural production in general, and in Avocado orchard in particular, is the availability of solar radiation in the wavelengths relevant to photosynthesis (400-700nm) at different canopy regions. The dense and vigorously growing Avocado canopy, if not managed correctly, results in large sized trees that tend to shade themselves and the neighboring trees. Insufficient light in Avocado orchards has been observed to reduce fruit yield, deteriorate its quality, and allocate it at the top of the trees. Various canopy management strategies were devised during the years, based mainly on the growers intuition and on “thumb rules” adopted from work done on apples during the 70`s and the 80`s. Most of these practices, however, were not supported by quantitative measurements or simulation models. The progress in computer software and hardware enables us to inspect the dynamics of solar radiation, and to calculate light interception and penetration for a large variety of canopy management strategies. The model presented here uses the state of the science illumination software “Radiance”, complimented by an additional code enabling simulation results (radiation readings) to be collected and analyzed over the whole growing season. Since Radiance is originally meant for architectural purposes (mainly for internal illumination), it holds the ability to deal with complex shape models produced by commercial software (AutoCAD, 3DMax, etc.).

Field measurements of light intensity were conducted in a commercial Avocado Cv. “Hass” orchard in kibbutz “Shomrat”, Israel. The measurements were found in good agreement with model predictions of light intercepted at the canopy surface, and used for calibrating the code regarding the extinction of light within the canopy. In particular, a large number of measurements was conducted in order to gain better understanding of the attenuation of light as it penetrates into the Avocado canopy. Numerous orchard models were tested in order to examine various agrotechnical practices that can effect light interception. We aimed at three major goals: maximizing the total intercepted radiation, maximizing light intensity (PPF), and maximizing the total radiation at the lower 2 m of the canopy. For that purposes, results indicate that the tree height should be reduced and that trees should be pruned at a sharp angle. However, the intercepted light does not provide clear cutting outcomes as for which practice is superior, and a new concept – the “potentially productive canopy volume” (PPCV), was introduced. The PPCV is defined as the volume maintaining a threshold level radiation for a given exposure time. The extinction coefficient measured in the field has been adopted for use by the software by means of a material (“mist”) with favorable extinction properties. Thus, it enabled us to analyze the penetration of solar radiation into the canopy. The results of the PPCV analysis indicate that maintaining high PPCV for long times is possible in the high density small-tree orchard.

According to our simulation results, high density planting seems to be a promising practice for maintaining most of the canopy potentially productive for long times, thus producing fruits (income) at high efficiency.