Objectives We studied the effects of different biogas slurry application modes and rates on soil phosphorus availability and rice yield, and explored the underlying mechanism from the perspectives of periodical P supply and soil microbial community characteristics.

Methods A experiment was conducted in paddy fields of the Hangjiahu Plain with five treatments: blank control (CK), conventional chemical fertilization (CF), single applicaiton of full biogas slurry (BS), split application of full biogas slurry (BD) and split application of reduced biogas slurry (BL). Soil physicochemical properties, P fractions, phosphatase activities, abundance and community composition of phoC- and phoD-harboring functional microbes, as well as rice biomass and plant P content, were analyzed using chemical assays and high-throughput sequencing at the tillering and maturity stages.

Results Compared with CF, the BS treatment significantly reduced soil available phosphorus (Olsen-P) content by 15.17% and increased organic phosphorus (Org-P) content by 29.58% at the rice tillering stage, while significantly enhancing straw yield without notable effects on grain yield or plant P content. Compared with BS, the BD treatment significantly increased water-soluble P (Sol-P) and aluminum-bound P (Al-P) contents at the tillering stage, while reducing Org-P content at maturity. Both alpha diversity and co-occurrence network analyses indicated that higher application frequency enhanced the diversity and network complexity of phosphate-solubilizing microbial communities. LEfSe analysis revealed that BS significantly increased the relative abundance of Rhizobiaceae, whereas BD notably enriched Rubrobacter. Redundancy analysis (RDA) demonstrated that Sol-P was the dominant factor driving phoC-harboring microbial community shifts, while Olsen-P and occluded P (O-P) jointly influenced phoD-harboring microbial community dynamics.

Conclusions Complete substitution of chemical nitrogen fertilizer with biogas slurry facilitates the transformation of insoluble phosphorus in paddy soils. Increasing the frequency of biogas slurry applications not only effectively enhance soil P availability but also augments the complexity and stability of phosphorus-solubilizing microbial communities. Hence, isplit application of biogas slurry with an equivalent nitrogen input to chemical fertilizer is an effective strategy for improving soil phosphorus availability in paddy fields.