The fungal community structure and soil fertility in rhizosphere soil have an important effect on the health of Panax notoginseng (P. notoginseng). The attack of pathogenic fungi and the imbalance of soil fertility can easily lead to diseases. The effect of Bacillus subtilis on improving the community structure of soil fungi has been confirmed, and the corresponding biological agent products have been commercialized. A pot experiment carried out in a greenhouse explored the effect of a biological agent and fertilizer on the fungal community in the rhizosphere of P. notoginseng. In the experiment, fertilization and the addition of biological agents were set up with three gradients, respectively, and the full coupling experiment was adopted, and the blank control group (CK) was set up at the same time. Therefore, there were thirteen treatments in the experiment. NH4 decreased between 36.42% and 11.56%, AP increased between 6.03% and 92.46%, AK increased between 2.99% and 25.40%, TN increased between 0.10% and 9.41%, and TP increased by 18.25% to 47.73% The addition of Bacillus subtilis biological agent decreased the Chao1, Shannon, Simpson, and ACE index of fungi in the rhizosphere soil of P. notoginseng. The Chao1 index decreased between 0.39% and 78.22%; the ACE index decreased between 0.43% and 78.24%. The main pathogenic fungi Cylindrocarpon and Fusarium of P. notoginseng were different in the experimental results. Cylindrocarpon decreased under F1C1, F2C1, and F3C2 treatments, while Fusarium increased under F1C1, F2C2, F3C1, and F3C3 treatments and decreased Fusarium content in rhizosphere soil of P. notoginseng in other treatments. RDA analysis (Redundancy analysis) showed that NH4-N was negatively correlated with the main pathogen Cylindrocarpon, Fusarium, and Ilyonectria, while AP and AK were positively correlated with Cylindrocarpon, Fusarium, and Ilyonectria. The results of the GRA-TOPSIS analysis showed that the score of F3C2 was the highest, while F2C3 and F2C1 ranked second and third, respectively. The calculation results of the theoretical model based on GRA-TOPSIS analysis showed that the GRA-TOPSIS score was highest when the theoretical optimal fertilizer application rate and bacteria application rate were 116.31 kg hm⁻² and 15.83 kg hm⁻², respectively.

In semi-arid agricultural ecosystems, excessive chemical fertilization has led to severe soil degradation. However, the mechanism by which organic fertilizer substitution affects microbial community construction in alkaline black soil through activated carbon components remains unclear. This study conducted a field experiment in the black soil zone of Northeast China to evaluate the effectiveness of organic fertilizer (OF) substitution. Four treatments were set up: no fertilization control (CK), single application of chemical fertilizer (T0), and substitution of 25% (T25) and 50% (T50) of chemical nitrogen fertilizer with organic fertilizer. The results showed that organic fertilizer substitution significantly optimized soil pH and significantly reduced C/N ratio compared to the control group, creating a favorable environment for nutrient mineralization. It is worth noting that the carbon pool management index (CPMI) under T25 treatment reached its highest level (an increase of 135.44% compared to T0), and significantly enriched active organic carbon components, especially particulate organic carbon (POC) and easily oxidizable organic carbon (ROC). Contrary to the traditional view that higher diversity is better, organic fertilizer substitution reduces bacterial alpha diversity but induces deterministic screening of functional groups. Redundancy analysis (RDA) and Mantel test showed that specific activated carbon components drove the enrichment of nutrient cycling bacteria genera (Sphingomonas, MND1, Gemmatimonas) and saprophytic fungi (Mortierella), while significantly inhibiting pathogenic bacteria (Fusarium). Although T50 treatment limited crop productivity due to the mismatch of carbon and nitrogen supply and demand, T25 achieved the highest maize yield and nitrogen fertilizer utilization efficiency by synchronizing nutrient release with crop demand. The conclusion indicates that 25% organic fertilizer substitution is the best strategy for this region, and its mechanism for improving soil productivity is not simply to increase microbial diversity, but to drive microbial restructuring towards more efficient functional networks through activated carbon input.

This study addresses the global issue of soil degradation and the decline in soil quality caused by excessive fertilizer use. Field experiments were conducted in the Northeast Black Soil Region and the North China Plain to evaluate the potential of organic fertilizer as a substitute for chemical fertilizers. Four treatment groups were established: control with no fertilization (CK), pure chemical fertilizer (T0), 25% organic fertilizer substitution (T25), and 50% organic fertilizer substitution (T50). The study systematically analyzed changes in soil physical and chemical properties, organic carbon fractions, microbial communities, and maize yield. The results showed that organic fertilizer substitution significantly reduced soil bulk density and pH, while increasing available phosphorus, potassium content, and various active organic carbon components (DOC, MBC, POC, ROC) by 28.21%–52.97%. The T25 treatment resulted in a 194.1% and 30.17% increase in carbon pool management index and activity index, respectively, while also promoting microbial diversity and the abundance of functional microbial groups. Nitrogen fertilizer utilization efficiency increased by 17.95%–33.33%, and maize yield traits were significantly optimized. In conclusion, 25% organic fertilizer substitution is the optimal ratio for improving soil quality, microbial activity, and maize yield.