A simple approach to modeling radiation interception by fruit-tree orchards

Abstract

The formulation and evaluation of a model of radiation interception by fruit-tree orchards is presented. The model computes radiation interception based on the proportion of the orchard floor that is shaded by the trees at any given time, calculated from geometric relationships of the length of the shadow cast by the trees and the orchard configuration. Inputs include tree dimensions, orchard configuration, daily global solar radiation and a correction factor that accounts for within canopy gaps. Evaluation of the internal consistency of the model and a sensitivity analysis were carried out. Then, a test of the performance of the model was done, comparing simulated values of fractional PAR interception with field measurements from a range of orchard conditions (species, orchard design, tree dimensions, and location), including orchards on steep terrain. Despite simplifications made to reduce input data requirements as well as the inherent variability among the orchards, the model simulated reasonably well the fractional interception of radiation on an hourly time step (mean absolute error, MAE = 10.08%; Willmott index of agreement, D = 0.94). When evaluated on a daily basis, the performance of the model improved considerably (MAE = 4.47%; D = 0.98). In both time scales, the model performed similarly for the different orchard conditions considered. The model can be used to estimate both PAR and global solar radiation interception, including different types of orchard configuration such as hedgerow, overhead trained, or isolated trees planted in rectangular patterns.