The presented study sought to use the plant growth-promoting microorganism (PGPM) as a biofertilizer in maize (Zea mays L.) seeds and determine its effects on the growth and productivity of maize, with two levels of mineral fertilizer (25% and 50% of chemical fertilizer) under Iraqi conditions. Laboratory studies confirmed no antagonism between Azotobacter chroococcum and other microorganisms used in this study. Field experiments carried out during crop season 2021 were in two different regions, Mosul (36°20′6″N, 43°7′8″E) and Kirkuk (35°28′5.02″N, 44°23′31.99″E) in the north of Iraq. The result showed biofertilizer superiority when combined with 25% and 50% doses of the recommended mineral fertilizer for maize growth and yield traits in the experiments in both locations. In Kirkuk city, the biofertilizer combined with 25% chemical fertilizer recorded superiority without significant difference from the biofertilizer combined with 50% mineral fertilizer. However, in Mosul city, the biofertilizer combined with 50% chemical fertilizer expressed a more superior and significant difference than other treatments for growth and yield traits in maize. The difference between the two regions might be due to chemical fertilizer residues in the soil.

Keywords: Maize (Zea mays L.), biofertilizer, plant growth-promoting microorganisms (PGPM), Azotobacter chroococcum, bio-agents, mineral fertilizer, growth and yield traits

Key findings: Biofertilizer treatment with 25% and 50% doses of the recommended mineral fertilizer lead to significantly enhance the growth and yield parameters of maize. However, the use of mineral fertilizer depends upon the available fertilizer residues in the soil.