CANOPY STRUCTURE AND RADIATION REGIME IN GRAPEVINE .2. MODELING RADIATION INTERCEPTION AND DISTRIBUTION INSIDE THE CANOPY

A 3D version of the radiation model of SINOQUET and BONHOMME (1992) wa s used to simulate the light microclimate of grapevine. It was tested against measurements of radiation interception and distribution within two canopy systems (Open Lyre and Geneva Double Curtain) exhibiting d ifferent vigor levels. The agreement between the model and the measure ments was generally good. Discrepancies may have arisen from incorrect assumptions concerning leaf azimuth distribution and leaf dispersion as well as a lack of accuracy in the description of the distribution o f leaf area density inside the canopy. The model also permitted to ass ess light partitioning between main and lateral shoot leaves which can influence global canopy photosynthesis and berry ripening. As an exam ple of application, the model was used to evaluate the consequences of lateral leaf removing on the interception efficiency of the canopy an d the light environment of the fruit zone. The possible use of a geome trical approach to simulate the radiation interception at the canopy s cale was also discussed.