Synergy of thiencarbazone-methyl isoxaflutole and nitrogen fertiliser reduces soil microbial nutrient cycling functions: Mitigation strategies

The synergy between the herbicide mixture thiencarbazone-methyl·isoxaflutole (TMI) and nitrogen fertiliser may inhibit soil microbial nutrient cycling functions. A field experiment was conducted to examine the co-effects of TMI and nitrogen fertiliser on microbial functions and to identify the underlying pathways. The mitigating effects of nitrapyrin and nanostructure-modified attapulgite on microbial functions were also assessed. TMI residues exhibited significant negative correlations with nitrite-reduction genes nirS and nirK , carbon-fixation gene cbbL , and phosphorus-solubilisation gene phoD , with variance analysis confirming the inhibition. The synergy between TMI and available nitrogen amplified the inhibition of these functional genes, as revealed by interaction detector. Structural equation model further revealed a pH–denitrification feedback triggered by TMI and available nitrogen, and the feedback reduced cbbL and phoD abundance by lowering Shannon diversity. Both modified attapulgite and nitrapyrin enhanced functional gene abundance, with modified attapulgite showing superior performance through combining strong ecological benefits, lower herbicide application rates and reduced input costs. This study highlights the practical potential of modified attapulgite as a cost-effective solution to mitigate herbicide‑nitrogen stress and improve soil microbial function in maize fields.