[Effects of Different Microbial Fertilizers on Soil Quality and Maize Yield in Coastal Saline Soil]

Microbial fertilizers have the characteristics of high efficiency and environmental protection in improving saline soils, and the application of functional microbial fertilizers is of great significance for the green abatement of saline barriers and the improvement of soil quality in coastal areas. The experiment was based on moderately saline soil in the coastal area of Hebei Province, with corn as the indicator crop, on the basis of conventional chemical fertilizer application. Different microbial fertilizer treatments, namely, T1 （conventional chemical fertilizer 750 kg·hm^-2 + compound microbial agent 75 kg·hm^-2）, T2 （conventional chemical fertilizer 750 kg·hm^-2 + Bacillus megaterium 300 kg·hm^-2）, T3 （conventional chemical fertilizer 750 kg·hm^-2 + B. mucilaginosus 300 kg·hm^-2）, T4 （conventional chemical fertilizer 750 kg·hm^-2 + organic silicon fertilizer 600 kg·hm^-2）, T5 （conventional chemical fertilizer 750 kg·hm^-2 + bio-organic fertilizer 600 kg·hm^-2）, T6 （conventional fertilizer 750 kg·hm^-2 + active microalgae 15 kg·hm^-2）, and CK （only fertilizer 750 kg·hm^-2）, were used for these seven treatments, to study the effects of different microbial fertilizers on soil nutrients, salinity, bacterial community, and corn yield and economic efficiency during two critical periods （V12 stage and maturity stage） of corn. The results showed that compared with that in CK, T1 significantly increased soil total nitrogen （TN） and available phosphorus （AP） contents during the whole growth period. Over the whole reproductive period, soil organic matter （OM） at maturity increased by 10.35% over the V12 stage compared to that in CK, but there was no significant difference between treatments. Compared with that in CK, T5 and T6 significantly reduced soil total salinity and Ca²⁺ content during the whole growth period by an average of 14.51%-18.48% and 24.25%-25.51%. T1 significantly increased the bacterial diversity index over the whole growth period by 45.16% compared to that in CK. The dominant soil phyla were Actinobacteria, Proteobacteria, Acidobacteria, and Chloroflexi, and the dominant genera were Bacillus and Geminicoccaceae. The most abundant functions of the bacterial community in the study area were chemoheterotrophy and aerobic chemoheterotrophy, with average relative abundances of 28.89% and 27.11%, and T3 and T6 significantly improved soil N cycling function. The results of redundancy analysis （RDA） indicated that Na⁺, SO₄^2-, pH, and EC were important factors driving the structure of the bacterial community, and correlation heatmaps showed that Na⁺, SO₄^2-, pH, and EC were significantly and positively correlated mainly with the phylum Planctomycetota, whereas soil OM and TN were significantly and positively correlated with Cyanobacteria. Compared with that in CK, T6 increased the relative abundance of Cyanobacteria and optimized the bacterial community structure during the whole growth period. Using recommended dosages of bacterial fertilizers T1 and T6 increased maize yield by 7.31%-24.83% and economic efficiency by 9.05%-23.23%, respectively. The preliminary results of soil chemical properties and yield correlation analysis revealed that EC, AP, HCO₃^-, and Mg²⁺ were the obstacle factors limiting soil productivity in coastal areas. In conclusion, the use of the compound bacterial agent （T1） and active microalgae （T6） at the recommended dosage can significantly enhance soil nutrients, reduce salinity, and improve the structural diversity of soil bacterial communities, which not only ensures the increase in maize yield and efficiency but also realizes the efficient use of microbial fertilizers and the improvement of soil quality.