Effects of the combination of beneficial microbes and nitrogen on sunflower seed yields and seed quality traits under different irrigation regimes

► We evaluated the effect of beneficial microbes on sunflower seed traits. ► The mixed application of BM with N fertilizer improved sunflower productivity. ► The highest protein and oil yields were obtained from mixed fertilization treatments. ► The lowest saturated FA obtained in the presence of BM alone or in the mixed forms. ► The combined application of BM and fertilizer increased the level of unsaturated FA. The environmental and economic impacts of fertilizer application have encouraged agronomists and growers to evaluate the use of alternative nutrient sources. To study the response of sunflower seed yield and seed quality traits to beneficial microbes (BM) and N fertilizer under water deficit conditions, experiments were carried out at the Eslam Abad-Gharb Agricultural Research Station, Kermanshah province, Iran, during 2006 and 2007. A two-year field experiment was performed using split plots laid out in randomized complete block design with three replicates. The main plot conditions were irrigation at 85% (I1), 70% (I2), and 55% of field capacity (I3). The subplot conditions included six levels of fertilization: control (C), recommended nitrogen (N), Azotobacter and Azospirillum (AA), AA+100% recommended N (AA100), AA+75% recommended N (AA75) and AA+50% recommended N (AA50). The results showed that the grain yield of sunflowers improved when sunflower plants were grown with a combination of N fertilizer and BM. However, there were no significant differences in grain yield among the AA50, AA75 and AA100 treatments under different irrigation regimes. The mean increases in the grain yield under the AA, AA50, AA75, AA100 and N treatments were approximately 13, 24.4, 26.4, 26.2 and 19.5% compared with the control treatment, respectively. The highest and lowest total oil concentrations were obtained from the I1 and I3 conditions, respectively. The existence of a water deficit strikingly decreased the total oil, oleic acid (O) and linoleic acid (L) concentrations of the seeds. However, it increased the protein, palmitic acid (P), and stearic acid (S) in sunflower seeds. The presence of BM improved the seed oil concentration, O, and L levels, especially when the sunflower plants were subjected to water shortage conditions.