Modified fungal diversity in dense clay subsoils after deep-banding organic substrate

Context Deep-banded nutrient rich amendments can overcome crop productivity constraints of Australian dense clay subsoils. However, knowledge on essential microbial community in field trials is limited. Methods We examined subsoils that had been deep-ripped 2 years earlier with various types of amendments (organic, a blend of organic and inorganic, and purely inorganic). Subsoil samples (15–25 cm) were collected encompassing the amendment band (0 cm), as well as at increasing distances from it (14 and 28 cm). Bacterial 16S rRNA, fungal ITS amplicon sequencing, and SOM/TOC measurements on amendment band samples were done to assess microbial communities. Key results While no variations were detected in bacterial communities across treatments, soils enriched with organic substrates diverged significantly in fungal diversity compared to the control, concentrated primarily within the amendment bands. Fungal response to these organic amendments was primarily dominated by an enrichment of filamentous saprotrophic fungi. Conclusion Changes in fungal diversity and the enrichment of saprotrophic fungi is primarily attributed to the introduction of organic substrates into the subsoil. However, despite the absence of SOM/TOC differences between treatments, SOM/TOC levels were initially expected to rise in response to organic amendments. Consequently, variations in fungal communities may have initially arisen from heightened SOM/TOC levels but persisted even as these levels returned to baseline, suggesting a lasting legacy effect. Implications A single application of deep-banded organic amendments was effective in enriching agriculturally significant fungi within dense clay subsoils after 2 years. This can further aid crop productivity by fostering soil structural improvements and optimising nutrient cycling, even after the organic amendments are undetectable.