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ISHS Acta Horticulturae 1135: III International Symposium on Citrus Biotechnology

Understanding partial rootzone drying in citrus

Authors:   B.A. Contreras-Barragan, A. Kusakabe, J.C. Melgar, S.D. Nelson
Keywords:   deficit irrigation, water stress, water-saving irrigation, leaf function, tree growth, water movement, grapefruit trees
DOI:   10.17660/ActaHortic.2016.1135.15
Two greenhouse experiments were carried out to gain understanding of the effect of partial rootzone drying (PRD), a water-saving irrigation strategy, on growth and physiological parameters of split-root potted young grapefruit trees. In the first experiment, five treatments with the following tree evapotranspiration (ETc) requirements and allowable soil water depletion (AD) levels were applied: 1) optimum_PRD_10%_AD (no water on one side, 100% ETc applied on the other side when 10% of the available soil water was depleted), 2) optimum_PRD_30%_AD (no water on one side, 100% ETc applied on the other side at 30% AD), 3) deficit_PRD_10%_AD (no water on one side, 70% ETc applied on the other side at 10% AD), 4) deficit_PRD_30%_AD (no water on one side, 70% ETc applied on the other side at 30% AD), and 5) control (50% ETc on both pots). The irrigated side of the PRD-treated trees was alternated every month. All PRD-treated trees saved between 16 and 36% water compared to control trees. Leaf function and root hydraulic function were similar across treatments. Deficit_PRD_30%_AD trees reduced stem dry weight, but total tree growth and root length in all PRD-treated trees remained unchanged. Whole tree water use efficiency was increased in trees under deficit_PRD_30%_AD, respect to control trees. A second experiment was established to assess water movement between the wet and dry sides of the roots under PRD. Trees were grown under the treatments that maintained stem water potentials above -1.7 MPa in the previous experiment (control, optimum_PRD_10%_AD, deficit_PRD_10%_AD), and their roots in the wet side were immersed in a color dye solution. When available soil water in the wet side was high and root pressure conditions were met, color dye was detected in the roots in the dry side of optimum_PRD_10%_AD, which denotes water movement between the root sides under root pressure conditions.

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