Effect of Azotobacter Chroococcum and Nitrogen Fertilization on Some Morphophysiological Traits, Grain Yield, and Nitrogen Use Efficiency of Safflower Genotypes in Rainfed Conditions

The effects of Azotobacter chroococcum (A. chroococcum) and nitrogen (N) fertilization on root morphological traits, plant physiology, N uptake of plant, yield components, grain yield, and nitrogen use efficiency (NUE) of six safflower genotypes in rainfed conditions were examined. A factorial experiment was conducted based on the three replications of randomized complete block designs in two cropping years, 2015–2016 and 2016–2017, at Sarableh Agricultural Research Station, Ilam Province, western Iran. Experimental factors included seed inoculation with A. chroococcum using N chemical fertilizer at four levels (two treatments without using N fertilizers urea included control and seed inoculation with A. chroococcum and another two treatments received urea included seed inoculation with A. chroococcum + 50% N of urea source and 100% N of urea chemical source), and six safflower genotypes (312-S6-697, PI-401478, PI-253895, PI-306974, Padideh, and Sina). The results indicated that the highest grain yield, number of grains per boll, and photosynthesis rate were obtained with no significant differences in the treatments of 100% N fertilizer and seed inoculation with A. chroococcum + 50% N fertilizer use. Besides, inoculation with A. chroococcum + 50% N fertilizer had higher NUE than 100% N fertilizer application. Comparing the average genotypes suggested that Sina cultivar with the highest grain yield and NUE was recognized as the best cultivar among the studied genotypes. Therefore, the appropriate cultivars (Sina) with recommended 50% N fertilizer application with A. chroococcum was used to reach the sustainable agriculture under rainfed safflower cultivation. Abbreviations A. chroococcum: Azotobacter chroococcum; BBCH scale: Biologische Bundesantalt, Bun-dessortenamt and Chemische Industrie; N: Nitrogen; NUE: Nitrogen use efficiency