Mechanistic study on the optimization of soil ecological structure and promotion of rapeseed (Brassica napus L.) growth by co-application of organic fertilizer and biochar

Despite the continuous diversification of amelioration strategies for acidic red soils in recent years, a distinct research gap persists: the lack of data-driven quantitative evidence to elucidate the cascading response pathway linking soil physicochemical remodeling, rhizosphere microbial succession, and crop economic traits. To bridge this gap, we hypothesized that the co-application of organic fertilizers and biochar induces distinct, source-dependent responses in soil acidity neutralization and microbial community restructuring, thereby driving specific variations in crop performance. This study aimed to evaluate these responses and decipher key biological associations utilizing multivariate data models. Experimental data revealed that both individual and integrated regimes effectively mitigated acidic stress (elevating pH from 4.93 to 5.04–6.47) and substantially boosted organic matter content (18.24–73.82%). Furthermore, Principal Coordinate Analysis (PCoA) showed clear separation of rhizosphere bacterial communities among treatments, and ANOSIM further confirmed significant differences in community structure ( R = 0.881, p = 0.001). Crucially, crop agronomic outcomes exhibited strong source-dependent patterns rather than a uniform superiority of combined applications. Subsequent statistical association analyses pinpointed that specific integrated treatments enriched the phylum Firmicutes, whose relative abundance exhibited a highly significant positive coupling with seed oil accumulation ( r = 0.838, p < 0.05). Ultimately, this study provides a novel strategic framework and robust data support for the precision management of fertilization in rapeseed ( Brassica napus L.) production within acidic red soil ecosystems.