Investigating the Effect of Partial Root Zone Drying (PRD) Deficit Irrigation at Different Irrigation Intervals on Water Use Efficiency and Growth Parameters of Sunflower Plant

According to the Statistical Center of Iran, the country's population between 1957 and 2017, has increased approximately from 19 people to 80 million. With population growth, the water demand is increased and water resources are threatened cumulatively. Agriculture is recognized as the main water consumer in the country. Due to the arid and semi-arid climate of the country, it is essential to use water reduction strategies such as deficit irrigation (DI) and partial root zone drying (PRD) deficit irrigation in agriculture. In case of water shortages, DI is an optimal solution for production, which is usually accompanied by a reduction in product per unit area. The base of PRD is keeping dry the half of root while irrigating the other half. The plant root in the wet area absorbs enough water. The other part of the root in dry soil, with a reaction to dryness and sending symptoms to the stomata, affects their opening size and reduces water losses. Sunflower is one of the four major oil producing plants in the world. The high volume of this product's import causes the country's strong dependence on oil import and the currency's outflow from the country. Although all living and non-living stresses are considered to be major factors in reducing production, water deficit stress is one of the main factors limiting the production of sunflower; Therefore, studying the reaction of this plant to different drought stress conditions and providing a solution to reduce the negative effects of dryness would be essential.

The present study was conducted on sunflower plant (Hysun 25) in a research farm of Sari Agricultural Sciences and Natural Resources University (SANRU) in 27 plots (5 × 5 square meters). Each plot consisted of 6 rows of planting at a distance of 75 cm from each other and 5 meters long. Sunflower seeds were planted at a depth of 4 cm from the soil and at a distance of 20 cm from each other. The experiment was conducted by using split-plot design, with three main factor (irrigation interval) and three sub-factor (irrigation water amount) in randomized complete block design in three replication. The irrigation intervals were irrigation after 20, 35 and 50 mm evaporation from class-A evaporation pan (F-20, F-35 and F-50 respectively). The sub-factor was irrigation water in levels of 100%, 75% and 55% of water demand (FI, PRD-75 and PRD-55 respectively). Controlling the volume of water delivered to each treatment was carried out using a volumetric flow meter. The application of irrigation treatments was carried out six weeks after planting. The irrigation for FI was conducted regularly at both sides of the root and for PRD it alternatively changed at the right and left sides of the root. The studied traits were irrigation water use efficiency (IWUE, kg/m3), height (H, cm), the flower diameter (D, cm), the seeds number per flower (SN), the 1000 seeds weight (W, gr) and the chlorophyll index (SPAD). Statistical analysis of data conducted by SAS software using Duncan test (1% level). Diagrams extracted by Microsoft Excel software.

Evaluation of irrigation interval factor based on the experiment two years data, indicated that the best results for plant growth parameters was for F-20. Also, the best results for sunflower plant growth parameters was for FI. According to the significant difference between FI and PRD-55 at most of the growth parameters, it’s suggested to conduct PRD-75 for PRD. For the irrigation interval factor, there was significant difference for most of the plant growth parameters between F-20 and F-50. Therefore, considering this case as well as the problem of increasing the operating cost by reducing the irrigation interval, F-35 is recommended for irrigation interval. It’s concluded that there was significant difference between all of the irrigation interval treatments by analyzing the IWUE trait. The highest amounts was for F-50 and the lowest was for F-20. Despite the increase in the value of IWUE in PRD-75 in comparison with other treatments for each two years of the experiment, this difference was not significant. According to the non-significant difference between F-35 and F-50 for IWUE at the second year of the experiment and this trait relative increase at PRD-75 in comparison with two other treatments, it’s suggested to conduct PRD-75 with F-35 to have higher IWUE.

Simultaneous analysis of sunflower’s IWUE and its growth parameters showed that it could be possible to save in irrigation water use and increase the IWUE with the lowest decrease in the sunflower plant growth parameters by applying PRD-75 and F-35.