Effects of deep incorporation of organic materials on microbial community characteristics in albic soil

In order to investigate the effects of deep incorporation of organic materials on microbial community characteristics in the plow layer and subsoil of albic soil, a two-year field experiment was conducted. The experiment included the following treatments: deep tillage at 35 cm (DT, no organic material), deep tillage at 35 cm plus straw (DTS), deep tillage at 35 cm plus manure (DTM), deep tillage at 35 cm plus straw and manure (DTSM), with conventional shallow tillage at 15 cm (CT, no organic materials) as the control. The results show that compared to the CT treatment, DTM and DTSM significantly increase the content of AK (available potassium) and pH in the plow layer, while DTSM significantly increases the content of AN (available nitrogen) (P<0.05). In the subsoil, the contents of SOC (soil organic carbon), TN (total nitrogen), AN, and AK are significantly higher in the DT, DTS, DTM, and DTSM treatments compared to CT (P<0.05). Deep incorporation of organic materials significantly influences soil microbial community characteristics in both the plow layer and subsoil. The dominant bacterial phyla are Proteobacteria, Actinobacteriota, and Acidobacteriota, while the fungal communities are primarily dominated by Ascomycota and Mortierellomycota. DTSM treatment significantly increases the Chao1 and Shannon indices in the plow layer and the Shannon index in the subsoil (P<0.05). Principal coordinate analysis (PCoA) indicates differential effects of the treatments on soil microbial communities. A pronounced shift in bacterial community characteristics is observed in DTSM and DTM treatments, which clearly separate from the clusters of the CT and DT treatments. In contrast, CT and DT treatments maintain highly similar bacterial and fungi community profiles. Redundancy analysis indicates that changes in microbial community in the plow layer are significantly positively correlated with AN, AK, and pH (P<0.05), while in the subsoil, they are significantly positively correlated with SOC and TN (P<0.05). Random forest model analysis showed that pH value and available potassium (AK) were the key factors affecting bacterial and fungal communities, with contribution degrees of 0.25 and 0.28, respectively. In conclusion, the application of organic fertilizer alone or combined with straw (DTSM/DTM) represents the optimal strategy for enhancing nutrient content and microbial community characteristics in albic soil.