The impact of deficit irrigation strategies on sweet cherry (Prunus avium L) physiology and spectral reflectance

by Antunez-Barria, Alejandro Jose

by Alejandro Jose Antunez Barria, Ph.D. Washington State University December 2006 Co-Chairs: Claudio O. Stockle and Matthew D. Whiting Prudent irrigation management of sweet cherry trees (Prunus avium L.) requires periodic monitoring of plant water status to avoid physiological stress. In recent years, on several fruit crops, various deficit irrigation techniques have been shown to be effective for saving water resources and having little impact on yield and quality. However, to date, little research has been conducted on sweet cherry water management. The purpose of this research was to investigate the physiological response of sweet cherry to deficit irrigation strategies that varied in placement of water. Additionally, correlations between sweet cherry canopy water status and leaf spectral reflectance were investigated. Lastly, a weighing lysimeter system was designed and utilized to accurately estimate transpiration of young potted trees, in real time. v In the field, sweet cherry trees were subjected to three season-long irrigation strategies: control (C) receiving 100% weekly replacement evapotranspiration (ET), deficit irrigation (DI) receiving 50% replacement of ET to the entire rootzone, and partial root-zone drying (PRD) receiving 50% ET to half of the rootzone per irrigation. In general, there were subtle treatment effects on leaf net photosynthetic rate (Pn), stomatal conductance (gs), leaf evaporation (E), water use efficiency (WUE), chlorophyll fluorescence and assimilation response parameters to carbon dioxide (CO2) and photosynthecic active radiation (PAR). However soil water was conserved by PRD and DI vs. C by approximately 20%, we found no clear physiological benefit to PRD. Leaf spectral reflectance shows promise as a tool to estimate plant water stress. Close correlations were found between reflectance and stem water potential (?stem) in the visible range. The best correlation model predicting ?stem used six wavelengths between 550 and 710 nm. Throughout the 2004 growing seaon, transpiration from C trees was 846 mm m?2, and deficit-irrigated trees exhibited 31% to 35% less transpiration. Stomatal conductance was reduced by irrigation treatments and correlated with vapor pressure deficit and air temperature. Overall, sweet cherries show tolerance to mild water stress and there is a potential to adopt deficit irrigation strategies in commercial production systems. vi