The need for cheap and affordable alternate sources of plant nutrient inputs to boost the nutrient level of degraded arable farmlands has been a major concern for soil scientists, agronomists, and local farmers. In 2018, a greenhouse and laboratory pot experiment was carried out under control conditions for 21 weeks to evaluate the effect of plant growth-promoting rhizobacteria (Azospirillium brasilense), spent grain (SG) organic wastes from the beer industry, and chemical fertilizer (CF) on the soil fertility–plant nutrition, corn (Zea Mays L.) germination rate in calcareous soil. The treatments consisted of CK (control), SG (spent grain, 20 g kg ⁻¹ soil), Az (Azospirillium seed inoculation), CF (100% of NPK recommended fertilizers), bio-organic (Az with SG), bio-mineral (Az with CF), and organo-mineral (50% of SG +50% of CF). These treatments were arranged in a randomized complete block design and replicated three times. Results showed that after 10 and 21 weeks, SG application significantly increased soil organic carbon by 69% and 67.8%, total nitrogen (TN) by 87.66% and 85.44%, and raised available P (P) by 75.7% and 87.23%, respectively. The final germination percentage (FGP), germination index (GI), coefficient of velocity of germination (CVG) and plant height were significantly higher in the amended pots than that of the control pots after 21 days of planting. The SG with Az treatments had the highest GI, CVG, and FGP of 9.23, 0.19 day ⁻¹, and 100 %, respectively, while the least values were obtained in the CF 2.37, 0.12 day ⁻¹, and 61.6%, respectively. The highest values of N/P ratio, available Fe ^2＋, Zn ²⁺, and Mn ²⁺ were 401, 20.35 mg kg ⁻¹, 7.27 mg kg ⁻¹, and 16.58 mg kg ⁻¹ respectively, as well as bio-fertilizers enhanced the dehydrogenase and urease enzymes by 1117.3 μg TPF ml ⁻¹, and 275.4 mg NH ₃ ⁻Hg ⁻¹h ⁻¹ respectively, after 21 weeks of seed sowing. The final results among all treatments were in the order of SG > Bio-organic > Az > Organo-mineral > Bio-mineral > CF > CK. In conclusion, the application of SG and Az is recommended to improve TN and P use efficiencies, micro-nutrients uptake, plant seed germination performance of maize, and enhancement of calcareous soil properties.