Terrestrial and Remote Indexes to Assess Moderate Deficit Irrigation in Early-Maturing Nectarine Trees

Monitoring plant water status is relevant for the sustainable management of irrigation under water deficit conditions. Two treatments were applied to an early-maturing nectarine orchard: control (well irrigated) and precise deficit irrigation (PDI, based on soil water content thresholds). Moderate water deficits generated by PDI were assessed by comparing terrestrial: stem water potential (Psi(stem)) and gas exchange parameters, with remote: canopy temperature, normalized difference vegetation (NDVI), and soil adjusted vegetation index (SAVI), plant water status indicators. The Psi(stem) was the only indicator that showed significant differences between treatments. NDVI and SAVI at the postharvest period were appropriate indexes for estimating winter pruning, although they did not serve well as plant stress indicator. Vapor pressure deficit along with Psi(stem) values were able to predict remote sensing data. Psi(stem) and canopy to air temperature difference values registered the highest signal intensity and NDVI the highest sensitivity for detecting water deficit situations. The results suggest that care should be taken when using instantaneous remote indicators to evaluate moderate water deficits in deciduous fruit trees; more severe/longer water stress conditions are probably needed. The proposed PDI strategy promoted water saving while maintaining yield, and could be considered a promising tool for semi-arid agrosystems.