Effects of grapevine (Vitis vinifera L.) water status on water consumption, vegetative growth and grape quality: An irrigation scheduling application to achieve regulated deficit irrigation

Precision irrigation in grapevines could be achieved using physiologically based irrigation scheduling methods. This paper describes an investigation on the effects of three midday stem water potential (midday Ψ_S) thresholds, imposed from post-setting, over water use, vegetative growth, grape quality and yield of grapevines cv. Cabernet Sauvignon. An experiment was carried out on a vineyard located at the Isla de Maipo, Metropolitana Region, Chile, throughout the 2002/03, 2003/04 and 2004/05 growing seasons. Irrigation treatments consisted in reaching the following midday Ψ_S thresholds: −0.8 to −0.95 MPa (T1); −1.0 to −1.2 MPa (T2) and −1.25 to −1.4 MPa (T3) from post-setting to harvest. Results showed significant differences in grape quality components among treatments and seasons studied. In average, T3 produced smallest berry diameter (6% reduction compared to T1), high skin to pulp ratio (13% increment compared to T1) and significant increments in soluble solids and anthocyanins. Improvements in grape quality attributes were attributed to mild grapevine water stress due to significant reductions in water application (46% for T2 and 89% for T3 less in average, both compared to T1). This study found significant correlations between midday Ψ_S and berry quality components, no detrimental effects on yield by treatments were found in this study. This research proposes a suitable physiological index and thresholds to manage RDI and irrigation scheduling on grapevines to achieve high quality grapes on mild water stress conditions.     

Positive impact of regulated deficit irrigation on yield and fruit quality in a commercial citrus orchard [Citrus sinensis (L.) Osbeck, cv. salustiano]

The impact that different regulated-deficit irrigation (RDI) treatments exert on a 12-year-old orange orchard (Citrussinensis L. Osbeck, cv. salustiano) was studied from 2004 to 2007. The experiment consisted of a control irrigation treatment which was irrigated at 100% of the crop evapotranspiration (ET_c) values for the whole season, and three deficit treatments imposed as a function of the water-stress index (WSI), which is defined as the ratio of the actual volume of water supply to the ET_c rate. In our case, these WSI values were 0.75, 0.65, and 0.50, respectively. The stem-water potential at noon (Ψ_Stem) was used as a parameter to estimate the water status of the plant. Yield and fruit quality was evaluated at harvest in each treatment (taking into account the temporal variability of the results due to the climatic characteristics of each of the years of this study) and an overall analysis was made using the whole dataset. Significant differences were found in fruit quality parameters (total soluble solids and titrable acidity), which also showed significant regression coefficients with the values of the integrated stem-water potential. These results led us to conclude that in mature orange trees grown under these conditions, regulated-deficit irrigation has important and significant effects on the final fruit quality, but the effects are not so clear-cut in tree yield, where the differences in the case of reducing a 50% of the crop ET_c, were not considered to be statistically significant despite an approximate 10% decrease in fruit yield. A global rescaled distance cluster analysis was performed in order to summarize the main relationships between the variables evaluated and to establish a different correlation matrix. Finally, a classification tree was derived and principal-component analysis was undertaken in order to identify and evaluate the variables which had the strongest effect on the crop response to different irrigation treatments.