Effect of Irrigation Management (System Type and Water Stress) on Yield and Physiological Indices of Grapes (Case Study:Naghang Region)

Change and decrease in atmospheric precipitation in recent years as well as increase in population and further demand for agriculture in the arid and semi-arid regions (such as Naghan) has led to a significant decrease in surface and groundwater resources. Therefore, achieving optimal utilization of water in agriculture, new irrigation systems has been considered to gain the most crop yield with less amount of water consumption. Also cultivated area can be expanded by these systems, containing lands with irregular topography, due to the high water distribution uniformity. Besides developing irrigation system, irrigation management is an important tool for increasing crop productivity. Researchers have shown that applying deficit irrigation (DI) under drip system, has led to improve the quality of grape yield, decrease water consumption and increase water efficiency. The aim of this study is to investigate the effect of irrigation system and water stress on water consumption, yield and physiological indices of grapes. The study field was located in Naghan, Chaharmahal & Bakhtiari Province, Iran. Experiences were done during summer 2016, in a completely randomized block design, with four replications in a grapevine garden The treatments included: CTRL, Furrow irrigation as common method in the area (control), surface irrigation with 100% water requirement (SI100), surface irrigation with 60% water requirement(SI60), drip irrigation with 100% water requirement(DI100) and drip irrigation with 60% water requirement (DI100).At the beginning of the experiences, 20 vine trees were selected with average of 60 years old. The field was divided into blocks, and the treatments were applied, randomly. Then the blocks were set up for the surface and drip irrigation. As the next step, required water was collected in a reservoir to obtain constant and reliable amount of water. In the control treatment, irrigation schedule of the gardeners (custom of the region) were considered in which irrigation event was at the beginning of the season. Also, drip and surface irrigation treatments were according to the soil water deficit. At the end of the experiment, water use efficiency, product performance, RWC, number of cubes per cluster, the weight of the cube in the cluster, cluster length, the number of main branches of the cluster and also qualitative properties such as soluble solids (Brix), total acid and pH of grape juice were measured. According to the results of qualitative traits, the amount of applied water significantly affected the grapes pH in the level of 5%. The lowest grapes pH was due to the control treatment and the highest to the surface irrigation 60%. Also, measuring total soluble solids (TSS) in grape indicated significant difference in 1% level which revealed that deficit and drip irrigation increased sugar in grapes and therefore quality of the crop. The results of quantitative traits showed the number of cubes in treatments had a significant difference at a probability level of 1%. Number of cubes in surface irrigation treatment 100% (SI100) had the highest value, while the quality of the crop was lower. The treatments differed significantly in weight of 100 cubes and the drip irrigation treatment 100% (DI100) did not have a significant difference with control treatment, while deficit irrigation resulted in reducing the crop weight. Relative water content of leaves (RWC) had the highest amount in the control treatment, while low water stress reduced this index. Wet and dry yields were highest in the control treatments (CTRL); while, the lowest amount was due to the low irrigation treatments of DI60 and SI60 with 19% and 34% reduction, respectively for the wet and dry yield. Drip irrigation with 100% water requirement (DI00) was not significantly different from the control treatment in most of the quality parameters, cluster and yield characteristics but had less water consumption and higher water use efficiency. Regarding the conditions of the region and the reduction of water resources, an accurate and efficient plan for irrigation is needed. So, the common method of irrigating in the region was assessed, as well as new methods of applying drip system and deficit irrigation. The results of this study indicate that drip irrigation system with 100% water requirement has no significant difference with the conventional irrigation method in the region, on quality and quantity of the gape yield. However, applying the drip system reduced the water consumption by 40%, and increased efficiency. Hence, drip irrigation system is suggested to be replaced by the traditional system.