In view of the characteristics of Ultisols (red soils) in southern China, this study developed two types of rice-specific biochar-based fertilizers (BBOF: bio-organic-inorganic biochar-based fertilizer; BBF: inorganic biochar-based fertilizer) using rice straw biochar as the base and coating technology. Pot and field experiments were conducted to evaluate their effects on soil chemical properties, microbial communities and rice yield under different pH value, nutrient statuses, and cadmium (Cd) pollution levels. Conventional fertilizer (CF) was used as the control, with three carbon treatments for experiments: direct biochar application (BC), BBOF, and BBF. The results showed that both BBF and BC improved rice yield under field conditions, with BBF enhancing the three key yield components; however, BBF had limited effects on soil improvement. BBOF and BC significantly increased soil pH and soil organic carbon contents(SOC) in the weakly acidic (WA) soil and the strongly acidic soil (SA) with Cd pollution(P<0.05), demonstrating effective acid regulation and carbon sequestration, but had limited effects in low-nutrient acidic (LN) soils. The impact of carbon treatments on soil nutrients varied with soil type: in WA soils, all three treatments significantly increased available phosphorus (AP), available potassium (AK), and dissolved organic carbon (P<0.05); in SA soil, AK was significantly reduced (P<0.05); and in LN soil, ammonium nitrogen(NH₄⁺-N) and nitrate nitrogen levels were notably altered, with BC also significantly increasing AK content (P<0.05). Other soil properties showed no significant response to biochar treatments. Compared with BC, biochar-based fertilizers reduced the amount of exogenous biochar applied and thereby decreased soil Cd input, indicating higher environmental safety. Microbial community analysis revealed that none of the biochar treatments had significant effects on fungal communities (P>0.05), but all affected bacterial communities, with an impact intensity order of BC>BBOF>BBF and a soil bacterial communities response order of LN>SA>WA. Both BC and BBOF regulated bacterial communities in a similar way by significantly increasing the relative abundances of key phyla (Myxococcota, Methylomirabilota, and Acidobacteria) and important functional families (Rokubacteriales_unclassified, Anaeromyxobacteraceae, Bradyrhizobiaceae, and Nitrospiraceae), while significantly decreasing the relative abundances of Planctomycetota (phyla level) and Subgroup_7_unclassified and Isosphaeraceae (family level) (P<0.05). Correlation and redundancy analyses indicated that shifts in soil bacterial communities were closely related to changes in soil chemical properties, with different driving factors identified across soils: AP in WA, SOC in SA, and NH₄⁺-N in LN. This suggests that the regulatory effects of carbon treatments are highly soil-dependent. In conclusion, the bio-organic-inorganic biochar-based fertilizer demonstrated advantages in improving soil environmental conditions and regulating microbial communities in rice-growing red soils, showing potential to replace direct application of biochar. However, its yield enhancement effects and application strategies require further study and optimization.