Microbial Organic Fertilizer Improved the Physicochemical Properties and Bacterial Communities of Degraded Soil in the North China Plain

Applying microbial organic fertilizer (MOF) effectively improves soil tilth and microbial diversity. However, there were few studies about the changes incurred in the physicochemical properties and bacterial diversity in the farmland of North China at a large-scale following MOF application. This study aimed to investigate the soil physicochemical properties and bacterial community following MOF application. A total of 910 t MOF was used on 173 hectares of degraded soil, and the results indicated increased nutrients in the top plough layer. Compared to controls, the treated samples had significant higher organic matter, total nitrogen, available phosphorus, potassium, and hydrolyzed nitrogen (p < 0.05). Furthermore, MOF application also induced a slight increase in the soil bacterial richness, but a significant decrease in the evenness was observed, where Firmicutes, Actinobacteria, and Bacteroidetes were enriched in the treated group, with Bacillus and Arthrobacter being the dominant genera, accounting for 0.291 and 0.136, respectively. Similarly, an increase in the proportion of Pseudomonas and Psychrobacillus was also observed at up to 0.038 and 0.034, respectively. The MOF treatment improved complex carbon metabolism and nitrogen reduction functions, inhibiting nitrogen oxidation as represented by nitrification. Redundancy and correlation analyses showed that total nitrogen, available phosphorus, and pH were the main factors driving the soil microbial community. This study concluded that MOF application could improve the soil's physicochemical properties and enhance the abundance and function of soil microbes, which is an effective method for improving the soil tilth and ecology of farmland in north China.