Method Examples Advantages Disadvantages Notes References Geometrical features External or exposed canopy surface; canopy height to between rows spacing Direct, simple, no complex inputs, or calculations needed Limited comparative value; difficult to find correlation with yields and ripening parameters; often canopy gaps are not accounted Sometimes exposed and external are erroneously used as synonyms [47 –49 ] Indices Y/PW (kg/kg); LA/Y (m2 /kg); PW/m (kg); LA/m (m2 ); LAD (m2 /m3 ); LLN (n), LAI (m2 /m2 ) Some very simple to be measured. Those expressing a ratio usually lead to a good general estimate of vine balance Source-sink vine balance not taken into account by the one-variable expressions; need of measuring or estimating LA is a deter for the using Recent apps have facilitated nondestructive LA estimates [40 , 50 –55 ] Amount and quality of light interception Good potential to differentiate training systems; in low to medium vigor conditions, good correlation with canopy photosynthesis Time-consuming; it usually requires diurnal trends; becoming less accurate with increasing LAI values Minimal equipment needed is a light bar with multiple sensors for rapid canopy scanning [56 –60 ] Canopy reconstruction (2D or 3D) and inference of physiology performance Fractions of external/sunlit LA; spatial distribution of light interception; estimates of canopy water use efficiency (WUE) Flexibility; helpful to amend and optimize canopy management practices Parametrization might be time consuming; light interception underestimated at the single organ level; assumption of independence between leaf orientation and 3D leaf positioning might be wrong [61 –67 ] Direct measurements of canopy gas exchanges Canopy net CO2 exchange rate, transpiration. Calculated canopy water use efficiency (WUE) It solves the problem of upscaling from leaf/shoot to canopy; long-term 24 h monitoring is possible Commercial versions are still unavailable, and setting requires a custom made approach; viable for experimental purposes only Air flow setting and degree of chamber perturbance must be carefully addressed [24 , 56 , 68 , 69 ] Modeling Simulated leaf area, photosynthesis, transpiration, respiration and dry matter accumulation, and partitioning trends and patterns Flexibility; dynamic trends of usually static variable or indices (e.g., leaf-to-fruit ratio) Independent outputs calibration required; several allometric relationships are usually required Balance between reasonably simple inputs and accurate enough outputs always difficult to find [47 , 70 –75 ]
