Search

This work aimed to assess the performance of different thermal infrared (TIR)-based physiological indicators (PI) as an alternative to the stem water potential (Ψs) and stomatal conductance (gs) to monitor the water status of grafted drip-irrigated 'Regina' cherry trees. In addition, we evaluated the usefulness of piecewise linear regression for finding PI thresholds that are important for post-harvest regulated deficit irrigation (RDI) management. With this purpose, an irrigation experiment was carried out in the post-harvest period. Trees were submitted to three Ψs-based water-stress treatments: T0 (fruit grower management treatment, or control) (Ψs > − 1.0 MPa, without-to-low water stress); T1 (low-to-mild water-stress treatment = − 1.0 > Ψs > − 1.5 MPa); and T2 (mild-to-severe water-stress treatment = − 1.5 > Ψs > − 2.0 MPa). The results indicated that the trees were more stressed in T2 than in T0. In the former, averages of Ψs and gs were − 1.75 MPa and 372 mmol m−2 s−1, whereas they were − 1.56 MPa and 427 mmol m−2 s−1 in T0. The piecewise model allowed determining the water-stress thresholds of almost all studied PI. The breakpoints yielded by this analysis indicated that trees at Ψs lower than − 1.5 MPa had a gs lower than 484 mmol m−2 s−1. These results also showed that TIR-based PI, whose equations incorporate a temperature normalization, are a better indicator of cherry tree water status than those without normalization. The derived TIR-based PI threshold values could be used as a reference for managing drip-irrigated 'Regina' cherry trees. [ABSTRACT FROM AUTHOR]

A study was carried out to calibrate and validate the aerodynamic temperature method for estimating the spatial variability of the sensible (H) and latent (LE) heat fluxes over a drip-irrigated merlot vineyard located in the Maule Region, in Chile. For this study, measurement of energy balance components and meteorological data were collected from the 2006 to 2010 growing seasons. The experimental plot was composed of a 4.25 ha of 'Merlot' vineyard, which was equipped with an Eddy-Covariance system and an automatic weather station. The k-fold cross-validation method was utilized to tune and validate a vineyard surface aerodynamic temperature (Taero) model, considering all of the days when Landsat scenes and ground measurements of meteorological data and surface energy balance (SEB) were available. Then, the satellite-based estimations of Taero were utilized to calculate the surface aerodynamic resistance (rah) and, subsequently, heat fluxes of H and LE. Results indicated that the estimated H and rah values were not significantly different to those measured in the vineyard (95% significance level) showing a root mean square (RMSE) and mean absolute error (MAE) between 34-29 W m-2 and 1.01-0.78 s m-1, respectively. Satellite-based computations of LE were somewhat higher than those measured at the time of satellite overpass (RMSE = 63 W m-2; MAE = 56 W m-2), presumably due to the biases embedded in the net radiation (Rn) and soil heat flux (G) computations. The proposed SEB method based on Taero is very simple to implement, presenting similar accuracies on ET mapping to those computed by complex satellite-based models. [ABSTRACT FROM AUTHOR]

As blueberries are susceptible to water stress and their future cultivation in semiarid Mediterranean areas will be challenged by drought, irrigation management strategies will be needed to optimize water productivity and maintain sufficient levels of fruit yield and quality. This study aim was to evaluate the effect of different irrigation levels on plant water status, yield, fruit quality, and water productivity in a drip-irrigated rabbiteye blueberry (Vaccinium ashei Reade 'Tifblue') orchard. Four irrigation treatments based on crop evapotranspiration (ETc) were applied to blueberry plants during two consecutive growing seasons (2012/2013 and 2013/2014): 125 (farmers' irrigation management, T 1), 100 (T 2), 75 (T 3), and 50 (T 4) % ETc. During the study, the average values of midday stem water potential (Ψ stem) were −0.85, −0.86, −0.97 and −1.11 MPa for the T 1 , T 2 , T 3, and T 4 treatments, respectively. Fruit weight (FW), yield (Y), fruits per plant (FP), soluble solids (SS), and the water stress integral (WSI) were significantly affected by the irrigation treatments. The water productivity (WP), juice pH, and weight/volume ratio were statistically similar among the treatments. The highest values of Y, FP, and FW were observed in the T 1 and T 2 treatments, while the lowest values were found in the T 4 treatment. In addition, the Y, FP, FW and WSI in the T 1 and T 2 treatments were significantly similar, but the total water application in the T 2 treatment was between 20% and 27% lower than that in the T 1 treatment. For the T 1 and T 2 treatments, the values of Y were between 8.8 and 9.4 kg plant −1, and the Ψ stem was >−0.85 MPa during the two growing seasons. The interaction between irrigation treatments and growing season was only significant for the FW, with the lowest values observed in the T 4 treatment during the 2012/2013 growing season. • Irrigation at 100% evapotranspiration (ETc) reduced water use without affecting yield and quality. • Irrigation at 100% ETc reduced the water use between 950 and 1130 m3 ha−1 season−1. • Irrigation at 100% ETc maintained midday stem water potential >−1.0 MPa. • Irrigation at 50% ETc significantly decreased fruit weight and yield. • Irrigation at 50% ETc increased soluble solids and the water stress integral. [ABSTRACT FROM AUTHOR]