The roles of organic amendments and microbial community in the improvement of soil structure of a Vertisol

- Two organic amendments and two biocides were applied to a Vertisol.
- Straw improved aggregation but straw-derived biochar did not.
- Fungicide suppressed aggregation but bactericide did not.
- Fungi played a vital role in aggregation.

Poor soil structure is a serious problem of Vertisol which makes it difficult for agricultural workability and crop growth. Thus, improving soil structure is mandatory as it mediates a range of soil biological and physical processes. This study evaluated the roles of organic amendments and microbial community in the improvement of soil structure of an expansive clay soil, locally called as Shajiang black soil in China. Two organic amendments were straw and straw-derived biochar. Two biocides were fungicide and bactericide. Thus, this study involved 9 treatments: 1) the soil without amendment and biocide as a control, and the soil with 2) fungicide, 3) bactericide, 4) straw, 5) straw + fungicide, 6) straw + bactericide, 7) biochar, 8) biochar + fungicide, 9) biochar + bactericide. Straw amendment significantly enhanced soil respiration, microbial biomass carbon (MBC), and phospholipid fatty acid (PLFA), and hence improved aggregation (P < 0.05). But biochar had no impact on soil microbial activity as well as on soil aggregation in comparison to the control (P > 0.05) due to its recalcitrant nature. The fungicide application significantly suppressed macroaggregates production, which confirmed dominant positive role of fungi in aggregation. On the contrary, bactericide application did not reduce aggregation, even enhanced it by creating less competitive environments for fungi. Pearson correlation analysis between mean weight diameter (MWD) and PLFA indicated that aggregation was related to fungi (r = 0.926) much closer than bacteria (r = 0.453). Our study exhibited that straw amendment technique has the potential to be an option to improve soil structure of Shajiang black soil by promoting fungal abundance.