عنوان مقاله [English]
Introduction: Since Iran is located in arid and semi-arid region of the world, so consumption and saving of water must be taking into account. Water is often a valuable natural resource, thus proper application methods - for increase water efficiency can be very important. Regulated deficit irrigation (RDI) is one of the most important methods to increase water use efficiency and fruit quality. Apple is one of the most important fruit trees from economical point of view. Studies showed that regulated deficit irrigation led to growth reduction in apple trees and sometimes fruit quality increased. The aim of this study was to evaluate the effect deficit irrigation on vegetative growth and fruit quantity and quality of Golden delicious apple trees in Gahvareh region of Kermanshah province.
Materials and Methods: This experiment was conducted on 10 years old Golden delicious apple trees in a randomized complete block design with 5 irrigation treatments and three replications during 2006. Three apple trees assigned to each experimental unit. Irrigation treatments were: T1= early deficit irrigation (40% water requirement), T2= early deficit irrigation (60% water requirement), T3= late deficit irrigation (40% water requirement), T4=late deficit irrigation (60% water requirement), T5=control (C) (100% water requirement). Early deficit irrigation starts 55 days after full bloom (15th Jun) and continued 60 days (16th Aug), while late deficit irrigation starts 115 days after from full bloom (16th Aug) and continued 40 days near to harvesting time (23th Sept). Control trees were full irrigated based on water requirement, which calculated based on national water document of Iran and irrigation amount was calculated based on the following formulas: Q=0.0184.L.H3/2
Where Q is volumetric flow rate (liter/Second), L is parshall flume crown length (cm) and H is water height (cm). Irrigation time was calculated based on national water document of Iran and volumetric flow rate as this formula Q.t = di.a, where Q is volumetric flow rate (liter/Second), t is time based on second, di is net water requirement and a is irrigated area. To evaluate irrigation effects some vegetative (shoot growth and trunk cross sectional area); reproductive (fruit volume, fruit weight and yield) and quality (Total soluble solid, total sugar, nitrogen, phosphorous, potassium and calcium) traits were measured.
Results and Discussion: Results showed that deficit irrigation had no effect on trunk cross sectional area, but shoot growth was affected significantly by deficit irrigation by. So, regulated deficit irrigation (RDI) can be used to control excessive vegetative growth in apple trees. There were no significant differences of fruit volume and weight of trees under deficit irrigation than the control exception to secondary 40% treatment. Fruit yield did not have significant differences under early and late 60% treatment in compare to the control. Where yield reduction was only 4 and 8 % in late and early 60% deficit irrigation respectively in compare to full irrigated trees. Water deficit had positive effect on qualitative traits of apple fruit, So that total soluble solids (TSS) and total sugar concentration (TSC) of fruit were higher in trees subjected to deficit irrigation as compared to the control. Regulated deficit irrigation led to 7-18% and 1.8-15% increase in total soluble solid and total sugar content in compare to full irrigated trees. Relative water content (RWC) was significant based of the time of applying deficit irrigation. Deficit irrigation did not have significant effect on fruit minerals such as P and K in compare to the control, but N content had significant reduction in deficit irrigation treatments in compare to the control and Ca fruit content of control trees had significant different in compare to trees were subjected to early deficit irrigation (40% of water requirement).. RDI favored reproductive growth over vegetative growth by suppressing vegetative growth. Water saving in deficit irrigation was 41, 27, 18 and 12 percent in early 40%, 60% and late 40% and 60% of water requirement respectively. Therefore, regulated deficit irrigation (RDI) applied with good intensity and at the right time not only reduces the amount of water used but also increased the yield performance and some fruit qualitative properties. RDI can be used to control vegetative growth and improve yield efficiency of apple trees.
Conclusions: Regulated deficit irrigation is more effective for water saving with a higher WUE and not reduction of fruit quality rather than to contain excessive vegetative growth in apple trees. Therefore, RDI can be suggested for commercial use and can be adapted successfully for the regions in similar soil and climate conditions. In general water deficit irrigation can cause increases quality of fruit in the Golden Delicious apple trees. Therefore, it is recommended to apply 60% of the water requirement for this cultivar.