## 3 Results and Discussion
### The Impacts of Returning Biogas Slurry to the Field on the Yield of CO and Phosphorus Content  
The fresh weight of individual tea fruits, seeds, and peels showed an increasing trend with the increase in biogas slurry application, but compared to the control group, the application of biogas slurry slightly reduced the weight of the tea seeds while significantly increasing the weight of the peels (Figure 2a). The number of fruit sets of CO showed a significant increasing trend with an increase in biogas slurry application (Figure 2b). The average number of fruit sets in the area treated with biogas slurry was 176, which is an increase of 110 fruits per tree compared to the control group. Specifically, the number of fruit sets for ZY1, ZY2, ZY3, and ZY4 increased by 127%, 172%, 176%, and 193%, respectively. There was no significant difference in the number of fruit drops between the plots with and without biogas slurry application. As indicated by the number of fruit sets in each treatment group in Figure 2a, the theoretical yield of CO with biogas slurry application was significantly better than that of the control group. With an increase in the amount of biogas slurry, the yield of CO increased significantly. However, the effect of biogas slurry application on increasing the yield of CO is mainly manifested in the increase in peel weight, with no significant increase in the weight of the seeds. As shown in Table 4, with an increase in the application amount of biogas slurry, the phosphorus content in the leaves and fruits of CO increased accordingly, and the enhancement effect was more significant with an increase in the amount of biogas slurry. Compared to the blank control group, the application of medium and low concentrations of biogas slurry reduced the phosphorus content in the leaves and fruits of CO, whereas the application of high concentrations of biogas slurry effectively increased the phosphorus content in the leaves and fruits. However, there was no significant difference between different concentrations of biogas slurry applications, as well as between the biogas slurry application and the control treatment. Figure 2: The effects of different biogas slurry application rates on the fruit of CO at harvest. (**a**) Difference in the fruit yield of CO among different treatment groups, (**b**) Fruiting of CO in different treatment groups during the harvest period. Based on the results for the phosphorus content in the leaves, branches, and fruits of CO in this study, the application of biogas slurry can effectively increase the phosphorus content in the leaves and fruits. In particular, at higher application rates of biogas slurry, the increase in the phosphorus content in the leaves and fruits was more significant. This is consistent with the results of [PERSON] et al., who found that the application of biogas slurry can enhance plant phosphorus absorption [37]. In summary, this indicates that the application of biogas slurry improved the availability of phosphorus in the soil for CO plantations. The Impact of Returning Slurry to the Field on the Microbial Community of Phosphorus-Solubilizing Bacteria  
The high coverage estimate indicates the capture of Operational Taxonomic Units (OTUs) related to microbial phosphorus metabolism. Compared with CK, the return of biogas slurry to the field reduced the richness and diversity of the microbial community related to phosphorus metabolism in the soil (Table 5), with the low application rate of biogas slurry showing the most significant impact on the richness and diversity of the microbial community. After the return of biogas slurry to the field, the main phyla, such as _Actinobacteria_, Proteobacteria, _Chloroflexi_, and _Acidobacteria_, in the CO planting soil still accounted for approximately 80% of the level, but the biogas slurry enhanced the community abundance of dominant bacteria such as _Chloroflexi_bacterium_, _Acidobacteria_bacterium_, _Hymphicro-biales_bacterium_, _Terrabacteria_group_bacterium_ANGPI_, and _Actinobacteria_bacterium_ in the soil.