Objective The aims were to clarify the effects of the combined application of organic materials and microbial inoculants on maize growth and soil improvement efficiency, in order to provide a theoretical basis for the practice of sustainable green agriculture.

Method An indoor pot experiment was conducted, the treatments included the conventional fertilization (CK) as a control, different types of organic materials (maize straw, MS; wheat straw, WS; biochar, BC) were applied in combination with varying concentrations of microbial agents (0%, 25%, 50%, 75%, 100%), resulting in a total of 16 treatments. The maize growth, plant nutrient (total nitrogen, phosphorus, and potassium) contents and soil properties were tested.

Result The results showed that all three organic materials with different concentrations of microbial agents significantly improved the growth, soil physicochemical properties, maize nutrient content, and microbial community population of maize. Specifically, the MS3 treatment (conventional fertilization + maize straw + 50% bacterial agent) increased leaf area by 58.11%, while the BC3 treatment (conventional fertilization + biochar + 50% bacterial agent) elevated available phosphorus by 99.64%. The WS5 treatment (conventional fertilization + wheat straw + 100% bacterial agent) increased fungal population by 58.02%. Notably, the BC5 treatment (conventional fertilization + biochar + 100% bacterial agent) exhibited the most comprehensive improvements: stem thickness, shoot dry weight, root dry weight, organic matter, total nitrogen and available potassium increased by 35.89%, 75.48%, 81.79%, 249.56%, 91.68%, and 280.65%, respectively. Additionally, shoot total phosphorus content, shoot total potassium content and root total potassium content increased by 112.15%, 18.15%, and 84.36%, respectively, while bacterial, fungal and actinomycete populations increased by 263.24%, 90.94% and 210.93%, respectively. A comprehensive evaluation of soil indicators using the membership function method confirmed that the BC5 treatment most effectively improved the maize growth environment.

Conclusion The synergistic application of organic materials and microbial agents significantly enhanced soil physicochemical properties and nutrient availability. The BC5 treatment demonstrated superior crop growth performance and the most substantial soil improvement. Therefore, the integration of conventional fertilization with biochar and a 100% bacillus agent is recommended as an effective fertilization strategy for achieving high-yield and high-quality maize production in the Huang-Huai-Hai region.