Objectives Application of microbial fertilizers has displayed remarkable promotion effect on the growth and grain yield of maize, despite of fluctuations due to climate, soil conditions, managements, et al. Therefore, we searched the factors causing the fluctuations using meta-analysis method.

Methods There were total of 244 pairs of yield data collected from 38 literatures published from January 2000 to May 2022 in the study. Yield responses were quantified using meta-analysis under various climate conditions, soil properties, and planting managements. The relative importance of each variable was compared based on Random Forest method.

Results Application of microbial fertilizer increased maize grain yield by 13% on average in China. Compound microbial fertilizer outperformed single microbial fertilizer in terms of yield increase, in particular the Bacillus or Trichoderma-containing compound microbial fertilizers increased maize yield by 22%–29%, Acfinobacteria and Proteobacteria-included ones increased maize yield by 17%. The magnitude of yield increase was higher under warmer or less rainfall climate. The yield increase was 12% and 15% in regions of annual mean temperature ≤10℃ and >10℃, and that was declined from 20% to 11% when the average annual rainfall raised from ≤600 mm to >600 mm. Relative to the controls, application of microbial fertilizer increased maize yield by 30% in low-yielding fields, and the increase declined to 10% and 9% in the medium- and high-yielding fields, respectively. In the insufficient nutrient input systems, i.e. N application rate less than 100 kg/hm², P₂O₅ or K₂O less than 50 kg/hm², application of microbial fertilizer could increase maize yield by 16%−28%, and under sufficient nutrient supply such yield benefits were only 9%−10%. Yield responses to microbial fertilizer application were more obvious under higher planting density than under lower plant density, the yield increase was 77% under planting density beyond 80,000 plants per hectare, but declined to 9%−10% under low densities. According to the random forest analysis, the key variables affecting maize yield responses to microbial fertilizer were annual mean temperature, planting density, soil pH, annual rainfall, N and P application rates, soil total nitrogen, soil available potassium, and organic matter, of which the annual mean temperature being the most dominant factor.

Conclusions The application of microbial fertilizer is a reliable and green measurement for maintaining and further increasing maize yield, in practically under adverse environments. In all the main biological regions of maize production, Bacillus or Trichoderma-containing compound microbial fertilizer, and relatively higher plant density are conducive to optimize the maize yield benefits of microbial fertilizers.