Effect of irrigation and ZnO and SiO2 nano and conventional fertilizers levels on yield, yield components and water use efficiency of sunflower

Water deficiency is one of the most limiting factors of crop production throughout the world. Moreover, addition of fertilizers to supplement farm fertility is essential for crop production. In particular, microelements have important roles in seed formation and seed yield. Foliar sprays with fertilizers including microelements such as Zn and Si have been shown to be convenient for field use, have a good effectiveness and very rapid plant response. Hence, studying the effects of irrigation and fertilizer on agriculture is important in arid regions like most parts of Iran. Sharing 2.8% of total world oilseeds (around 107 million ton), sunflower is the fifth most important edible oil producer, following soybean, rape, cotton and peanut.
In order to investigate the effect of ZnO and SiO2 nano and conventional fertilizers application on yield, yield components and water use efficiency of sunflower in water deficit stress conditions an experiment was conducted as a split-plot based on a Randomized Complete Block Design with three replications at experimental field of Islamic Azad University, Birjand Branch, Birjand, Iran in 2014. The main plot was devoted to irrigation at two levels (irrigated after 100 and 200 mm cumulative evaporation from evaporation pan) and the sub-plot was devoted to foliar spray of ZnO and SiO2 at seven levels (nano ZnO, nano SiO2, ZnO, SiO2, nano ZnO nano SiO2, ZnO SiO2 and control or wihtout foliar spray). Measuring traits included the head diameter, seed number per head, 1000-seed weight, seed yield, biological yield, oil yield and water use efficiency for seed, biomass and oil. MSTAT-C statistical software used for data analysis and means compared with Duncan multiple range test at 5% probability level.
Results showed that water deficit stress decreased head diameter, seed number per head, 1000-seed weight, seed yield, biological yield, oil yield and water use efficiency for seed, biomass and oil by 16.9, 39.5, 18.5, 50.3, 33.3, 51.5, 73.7, 62.9 and 75%, respectively as compared to no-stress conditions (irrigation after 100 and 200 mm cumulative evaporation from evaporation pan). It can be said probably the stomata closure and as a result, the decrease in CO2 inflow to the plant decreased leaf area and duration and photosynthesis rate under limited irrigation conditions. Therefore, seed yield decreased because of the decrease in plant growing period, seed filling, head diameter, seed number per head and 1000-seed weight and probably the increase in unfilled head percentage. Also foliar application of conventional ZnO fertilizer significantly increased head diameter, seed number per head, seed yield and oil yield by 10.2, 42.9, 59.7 and 70.3%, respectively as compared to no-foliar application treatment. Zinc fertilizer has positive effect on auxin biosynthesis that can stimulate cell division and better absorption of minerals and thus increase the plant growth (Marschner, 2012). It seems that ZnO fertilizer mainly by increasing the seed number in head significantly seed yield increased. Probably zinc element participates in protein synthesis of the pollen tube during pollination, which leads to increase the seed number in head. The highest water use efficiency for seed and oil with means of 0.125 and 0.056 kg. m-3 respectively, was observed in treatment of ZnO application that was 77.8 and 75% higher compared to the control treatment, respectively. This result can be related to higher seed and oil yield in this treatment compared to other treatments of fertilizer.
It seems the use of zinc oxide fertilizer due to its role in improving the functioning of physiological and biochemical in plant (Malakoti & Lotfolahi, 2004) has increased photosynthetic capacity and especially by increasing the fertilization of flowers and seed number per head caused a significant increase in seed yield. Moreover, water deficit stress by stomata closure and decreasing in the photosynthetic capacity of plant and source power was significantly reduced seed number per head and 1000-seed weight and finally seed yield and oil yield of sunflower. In total, it is recommended treatment of irrigation after 100 mm cumulative evaporation from evaporation pan and foliar application of conventional ZnO for the cultivation of sunflower under conditions of this research.