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.     

Photosynthesis, yield, and chemical composition of Tieguanyin tea plants (Camellia sinensis (L.) O. Kuntze) in response to irrigation treatments

Tieguanyin Oolong tea (Camellia sinensis (L.) O. Kuntze) is a name brand important commodity for Anxi county, Fujian province in China. Four-year-old tea plants at a tea plantation in Anxi were subjected to six different irrigation treatments (i.e. 5, 10, 15, 20, and 25 d irrigation intervals for T₁ to T₅ with a rate of 3.5 kg water per plant, plus a non-irrigated control). After 50 d of irrigation treatments, leaf water potential was −1.70, −2.34, −2.48, −2.89, −3.55, and −4.92 MPa for treatment T₁, T₂, T₃, T₄, T₅, and control, respectively. Leaf biomass yield increased by 32.8%, 21.9%, and 21.3% for T₁, T₂, and T₃, respectively, compared to control. The net photosynthesis (Pn), stomatal conductance (gs) and transpiration (E) decreased with irrigation interval increasing. Tea polyphenol (TP) and free amino acid (AA) decreased when the irrigation intervals were increased, but caffeine (CA) content apparently increased as the irrigation intervals were increased. To balance irrigation water demand and tea yield and quality, it is recommended that the irrigation interval should be set at 10 d with a rate of 3.5 kg water per plant for the optimal production in Anxi, Fujian province of China.