A field experiment on sorghum (Sorghum bicolor L.) with diverse levels of fertilization, carried out in the spring of 2022 in a randomized complete block design (RCBD) with factorial arrangement, had three replications and two factors at the field of Ibn-Al-Bitar Vocational Preparatory School, District Al-Hussainiya, Kerbala, Iraq. The first factor comprised three sorghum cultivars (V1 = Al-Khair, V2 = Rabeh, and V3 = Bohuth-70), while the second was combinations of nitrogen and bio-fertilizers (F0 = recommended dose of N 320 kg ha^-1, F1 = 3/4 of the recommended amount of N with Azotobacter, F2 = 1/2 of the recommended dosage of N + Aotobacter, F3 = 1/4 of the recommended dose of N + Azotobacter, and F4 = Azotobacter + No nitrogen fertilizer). The results showed that the sorghum cultivar Bohuth-70 was significantly superior for enhanced plant height (204.63 cm), number of leaves plant^-1 (9.807), 1000-grain weight (35.27 g), and the grain yield (6.192 Mg.ha^-1). However, cultivar Al-Khair produced the highest mean leaf area (4,929 cm²) and grains per head (4,428 grains.head^-1). Cultivar Rabeh excelled in performance, with the highest mean value for stem diameter (24.67 mm) and head length (31.29 cm). The F0 treatment recommended dose of N 320 kg ha^-1 was considerably superior in the number of leaves (9.867 leaves plant^-1), stem diameter (24.8 mm), and grain yield (6.145 Mg.ha^-1). The F1 treatment of 3/4 of the recommended dose of N with Aotobacter excelled in plant height (166.57 cm), leaf area (4,936 cm²), and number of grains (3,916 grain head^-1). However, the F2 treatment 1/2 of the recommended dose of N + Aotobacter was notably superior in head length (30.18 cm) and 1000-grain weight (29.93 grains). As for the interaction, the sorghum cultivar Bohuth-70 with F0 treatment excelled in the number of leaves plant^-1 (10.33 leaves) and the grain yield (7.157 Mg.ha^-1), while the cultivar Al-Khair with F1 treatment excelled in stem diameter (26.70 mm) and leaf area (5,164 cm²).

Keywords: Sorghum (Sorghum bicolor L.), cultivars, nitrogen fertilizer, biofertilizer, growth and yield, Azotobacter

Key findings: Nitrogen and biofertilizer (Azotobacter) significantly affected the growth and yield traits. The studied cultivars also showed varied responses to various fertilization levels. It might be possible to reduce chemical fertilizers and replace them with biofertilizers.