Scouting ecophysiological variables to manage Regulated Deficit Irrigation in almond

In semi-arid areas, almond orchards face adverse conditions caused by climate change. Sustainable irrigation strategies and innovative approaches monitoring plant functionality can reduce water consumption increasing water use efficiency. The use of proximal and remote sensors is critical to assess the most appropriate time windows and the intensity of water restriction. The present study aims to monitor the response of almond trees subjected to differentiated irrigation regimes and identify optimal thresholds of ecophysiological variables, linked with tree functionality, to manage irrigation. The trial was carried out on an almond orchard cv. Guara where irrigation was differentiated during the kernel filling period supplying 100% (CTRL), 80% (mRDI) and 60% (sRDI) of Crop Evapotranspiration (Etc). Results showed a good relationship among variables describing plant functionality and pedoclimatic variables such as air temperature, vapor pressure deficit and soil water content. Stomatal conductance (gs), stem water potential (Ψs), photosynthesis (Pn) and PKo/Kc (variable describing the electron flux exiting PSII and the carboxylative activity of RuBisCO), were generally higher in fruit growth phase declining during kernel filling and raising again during post-harvest irrigation. Values of gs, Ψs PKo/Kc and Pn in mRDI were slightly lower than CTRL and higher than sRDI in almost the entire kernel filling period. Yields, volume and dry weight of fruits were similar among the treatments, but sRDI showed a higher number of tight-hull fruits (approximately 20% more than the control). These preliminary results suggest that in almond both gs, Ψs, Pn and PKo/Kc are responsive to pedoclimatic variations, showing values closely related to the water-functional state of plants. The mRDI treatment allowed the greatest water saving without affecting yields and fruit quality. Considering the development of new sensor able to monitor the above-mentioned variable in a quick and low-cost way, the use of plant-based thresholds for managing irrigation is desirable.