Long-term application of legume green manure improves rhizosphere soil bacterial stability and reduces bulk soil bacterial stability in rice

Overusing chemical fertilizers (CFs) causes soil degradation, which can be mitigated by partially substituting CFs with green manure. This study investigated the impact of traditional vs. improved fertilization schemes that included Chinese milk vetch (CMV) on soil properties and bacterial communities in rice rhizosphere and bulk soil from plots over 12 years under fertilization. The treatments included the conventional fertilization (CF₁₀₀), CMV (22.5 t ha⁻¹) with 100 % CF (CMV + CF₁₀₀), CMV with 80 % CF (CMV + CF₈₀), CMV with 60 % CF (CMV + CF₆₀), and CMV with 40 % CF (CMV + CF₄₀). CMV + CF40 increased the soil organic matter (SOM) content in the rhizosphere (bulk) soil by 38.02 % (37.86 %) compared to CF₁₀₀ (P < 0.05). The quality index in bulk soil increased by 5.49%–8.17 % through all CF combined with CMV. The rhizosphere bacterial diversity was 1.11%–2.30 % higher, and richness was 2.87%–4.93 % higher than in bulk soil. In the bulk soil, only the CMV + CF₄₀ increased the bacterial Shannon by 0.40 %, Ace by 0.84 %, and Chao1 indice by 0.89 %. Relative abundances of Geobacter in bulk soil were by 13.90%–52.27 %, Leptospirillum by 25%–77.12 %, and Desulfobacca by 7.42%–37.85 % higher than in the rhizosphere. The stability of the rhizosphere and bulk soil bacterial communities under the CMV input was predicted by the SOM and available phosphorus contents, as indicated by the degree of bacterial average variation. The CMV + CF₄₀ was recommended as the optimal alternative rate based on local soil ecological considerations.