Response of citrus trees to deficit irrigation during different phenological periods in relation to yield, fruit quality, and water productivity

Four strategies of deficit irrigation based on a different water-stress ratio (WSR) applied in each phenological stage, and a control treatment were implemented in 11-year-old citrus trees (Citrus sinensis L. Osb. Cv. Navelina) grafted onto carrizo citrange (C. sinensis L. Osb. × Poncirus Trifoliata L. Osb.). The midday stem-water potential and stomatal conductance were measured during the periods considered, and these parameters were used to estimate the plant-water status. Integrated stem-water potential (Ψ_Int) and integrated stomatal conductance (g_Int) were calculated for all treatments and used as a water-stress indicator for the crop. Reference equations were formulated to quantify the relations between water-stress indicators (WSR, Ψ_Int, g_Int) and the crop response, expressed as yield, yield components, and fruit-quality parameters under limited seasonal water availability. Significant differences in yield were found in the second year of experiment between the stressed treatments and control, although these differences were evident during the first year. The main effects were detected in treatments with a water-sever stress applied during the flowering and fruit-growth phases. When this degree of stress was applied during the maturity phase, it was reflected mainly in fruit-quality parameters (total soluble solids, and titrable acidity). These results lead to the conclusion that, in mature orange trees, deficit irrigation affects yield and fruit quality, while enabling water savings of up to 1000 m³ ha⁻¹. Therefore, yield declined on average 10-12% but boosted water productivity 24% with respect to the fully irrigated treatment. Regarding the water-stress indicators used, Ψ_Int and g_Int showed highly significant correlations with the yield and fruit-quality parameters.     

Positive Impact of Deficit Irrigation on Physiological Response and Fruit Yield in Citrus Orchards： Implications for Sustainable Water Savings

Different strategies of deficit irrigation based on water stress dynamics were applied in an 11-year old citrus trees （Citrus sinensis L. Osb. cv. Navelina） grafted on carrizo citrange （Citrus sinensis L. Osb.×Poncirus Trifoliata L. Osb.）. The trees were subjected to two irrigation treatments： （1） sustainable deficit irrigation （SDI） established with water supplied at 60% of the crop evapotranspiration （ETc） and （2） low frequency deficit irrigation （LFDI） irrigated according to the plant water status. In addition, a treatment irrigated at 100% of ETc was included as a control （C）. Midday stem-water potential （ψUstem）, stomatal conductance （gs）, and micrometric trunk diameter fluctuations were measured during the maximum evapotranspirative demand period to evaluate the plant-water status, and establish the main relationships among them. The seasonal pattern of the studied variables had a behavior consistent with the contributions made by the volumes of applied irrigation water. Especially significant close relationships of ψstem with gs, and with the maximum daily shrinkage （MDS） were found. The lowest ψstem and gs values were registered in the treatments with lowest irrigations levels （SDI and LFDI）, being the MDS was significative higher than in the C treatment. The LFDI showed an oscillating behavior in these parameters, which was on line with the supplied irrigation restrictions cycles. Thus, according to the results of the present experiment the physiological stress indexes based in MDS or ψstem allow establishing different irrigation restriction cycles, encouraging important water saving without significant impact on yield and the fruit quality parameters.