An energy balance approach for precision physiology-based management of apple orchards under netting

The aim of this research was to study the relationship between the radiant and heat flux components and leaf gas exchanges in apple orchard under netting. Net radiation (R_n), sensible heat (H) and latent heat (LE) fluxes were estimated from continuous monitoring of micro-environmental (global radiation, air and leaf temperature, relative humidity and wind speed) variables in a 'Gala' apple orchard growing under netting and open-air systems. Net photosynthesis (A_n), transpiration rate (E), stomatal conductance (g_s), and intrinsic water use efficiency (WUEi) were simultaneously recorded at leaf level by an IRGA system. Spectral solar irradiance was measured by a dual-system (UV-VIS-IR) spectrometer. Yield, fruit quality and tree growth parameters were estimated at harvest. Under sunny day conditions netting reduced by 18, 60 and 19% the R_n, H and LE fluxes, respectively. Reduction of daily cumulative fluxes of R_n and LE by netting was closely related to increases in A_n (R²=0.60 and 0.69, respectively) with positive effects on fruit growth and water use efficiency. From fitting a multiple regression model, it was estimated that maximum A_n would be achieved with a netting system that guarantees R_n and LE cumulative fluxes values in the ranges of 0.3-0.5 and 0.6-0.8 MJ m^‑2, respectively. Results suggest that energy balance components can be used for the development of more efficient netting systems (materials, installation system designs) to improve photosynthesis, productivity and water use efficiency in apple orchards.