Objective To clarify the effects of applying bio-organic fertilizers in pear orchards and to establish a scientific fertilizer application regime.

Methods Two typical pear orchard sites were selected for this study. Different application rates of bio-organic fertilizer were set as follows: 3750 (SF1), 7500 (SF2), and 11250 kg/hm² (SF3), with no application as a control (CK). The effects of different treatments on soil physical and chemical properties and soil bacterial community structure were investigated. The correlation between soil properties and bacterial communities was analyzed to comprehensively evaluate the soil improvement effects of bio-organic fertilizers in different pear orchard sites.

Results The application of lignite organic fertilizer has significantly enhanced the physical structure of the soil. Notably, the water retention capacity of both gravelly and loamy soils has improved markedly, with soil bulk density also significantly lower than that of the control treatment. Specifically, the SF2 treatment resulted in a reduction of 21%, while the RF3 treatment led to a 14% decrease. Furthermore, the levels of organic matter, alkali-hydrolyzable nitrogen, available phosphorus, and readily available potassium in the soil have all seen notable increases. The enhancement of organic matter and alkali-hydrolyzable nitrogen content in gravelly soil is significantly greater than that observed in loamy soil. At the phylum level, the dominant phylum in both gravelly and loamy soils is Proteobacteria, and the application of lignite organic fertilizer has exerted a significant influence on bacterial β-diversity in both soil types. The relative abundance of Proteobacteria in gravelly soil has significantly decreased by 8.3% compared to the control group, while in loamy soil, an increasing trend in the relative abundance of Proteobacteria is observed with higher fertilization rates, with the RF3 treatment exceeding the control group by 3.2%. Simultaneously, after fertilization in gravelly soil, the relative abundances of Bacteroidetes and Actinobacteria increased by 5.7% and 2.5%, respectively, compared to the control group. Correlation analysis reveals that soil bulk density is a key factor influencing changes in bacterial communities, while soil organic matter and readily available nutrients also exert a certain influence on the structure of bacterial communities.

Conclusion The application of lignite improved soil physical properties, increased soil quick-acting nutrient content, and altered soil bacterial community composition, contributing to the healthy development of the soil. Based on the effects of various treatments on soil, the recommended lignite application rates are 7500 kg/hm² for sandy soil and 11250 kg/hm² for loamy soil.