Unravelling the effect of tree protection covers on the propagation of radiation within a cherry tree canopy

Abstract _ 

Crop protection covers are increasingly a necessary tool to face the increasing abiotic stresses under climate change, threatening both fruit quality and yield. Cover systems have been widely studied as they can modify the microclimate and consequently the ecophysiological responses of the crops growing underneath. The effects of covers on the propagation of radiation below the covers is crucial in determining the plant microclimate. Also the training system affects the canopy radiative regime via modifying the plant structural properties. Finally, the meteorological conditions and latitude affect the available radiation, resulting in very context specific modification of the microclimate.

In this study a 3D radiative transfer model (Discrete Anisotropic Radiative Transfer, DART) was used to represent the light propagation across a cherry orchard covered by a rain exclusion net.

The cherry orchard was represented by the repetition in all directions of a single tree, covered by a rain exclusion screen and in absence of covers. The DART scene was characterized by geometrical properties of the tree and the rain exclusion net, measured in the orchard, which were used for model calibration. The trunk and canopy volumes were described as a trapezoids based on trunk diameter and height, and crown dimensions, while the leaves as triangles with a certain leaf angle distribution.

The cherry tree canopy and cover were optically characterized based on spectrophotometric measurements, while the soil based on DART optical libraries. Field measured values of top of the canopy global short wave radiation recorded around noon were used as input for simulation of light propagation. The angles of incident sun rays were determined by DART starting  from time (date, local time zone) and scene location. The simulated radiation values obtained at three canopy heights were then were compared with ceptometer measurements performed at the same time. Following, sequence of simulations were run to obtain the spatial and temporal variations in light propagation during the growing season.

To the authors knowledge, this is the first application of a 3D radiative model on covered orchard systems. The proposed approach can give important insights into the effects of canopy covers on the radiative regime across climatic and context specific conditions. Considering the increasing use of covers to protect crops from climate change, the proposed approach may possibly contribute to drive agricultural advisers and farmers to more aware selections of the type of cover, according to their features.

The study was funded by the PRIN CHOICE project (Optimizing CHerry physiOlogIcal performanCE
through the correct choice of multifunctional covers