The Effect of Deficit Irrigation and Partial Root Zone Drying Irrigation on Tree and Fruit Growth Characteristics of Valencia Orange

Due to poor seasonal distribution of rainfall in Mazandaran province and shortage of water resources for citrus irrigation in recent years, these trees are generally subject to water stress in the warm seasons. In order to study water deficite stress on quantitative and qualitative yield of oranges, a completely randomized block design with four treatments and four replications was conducted at Ramsar citrus and subtropical fruits research center in 2018-2019. Experimental treatments included full irrigation (FI), deficite irigation (DI), partial rootzone drying irrigation (PRD) and fixed partial rootzone drying irrigation (FPRD) at 50% level of full irrigation. At the end of study, quantitative and qualitative characteristics of tree and fruit, including leaf relative swelling, leaf water potential, length and branch diameters, fruit diameter, relative growth rate of the fruit, leaf elements, weight of the shed fruits and width and thickness of skin and fruit volume, yield, vitamin C, soluble solids (TSS), titrable acidity (TA), color index (Chroma, CI, h, L) were measured and the comparisons between treatments were performed by SNK test at 5% level. The results showed that there was no significant differences between treatments in terms of shoot length and diameter, amount of leaf elements, relative water content of leaves, and fruit weight. Although, there was no significant difference among treatments in terms of fruit quality, but PRD, FPRD and DI treatments had good quality compared to FI treatment. Comparison of leaf water potential of relative growth rate and fruit diameter showed significant differences among treatments. FPRD, PRD and DI methods reduced water consumption and increased water use efficiency. Regarding to the fruit color index, the highest fruit market value was observed in DI method. The PRD method slightly reduced fruit weight but increased TSS and TA, which are important in fruit juice production.