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

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

Results Compared to CF, BS significantly reduced available phosphorus (Olsen-P) content by 15.17% and increased organic phosphorus (Org-P) content by 29.58% during rice tillering stage, while significantly enhancing straw yield without notable effects on rice yield or plant phosphorus content. Compared to BS, BD significantly elevated Sol-P and aluminum-bound P (Al-P) contents during tillering 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 Substituting entire chemical nitrogen fertilizers with biogas slurry is beneficial for facilitating the conversion of insoluble phosphorus within the soil. Elevating the frequency of biogas slurry applications can not only effectively boost the levels of available phosphorus in the soil but also augment the complexity and stability of phosphorus-solubilizing microbial communities. Hence, it is advisable to utilize biogas slurry that contains an equivalent nitrogen content to chemical fertilizers and to adopt a multiple-application approach in paddy soils.