Relationships between soil health tests and relative abundances of N-metabolism genes in no-till, plowed, and undisturbed reference soils

Farmers are increasingly recognizing the importance of building healthy soils to enhance farm resilience and profitability. Advances in metagenomic DNA sequencing of soil microbial communities offer opportunities to explore relationships between genes linked to key soil functions and established soil health metrics. Since soil nitrogen (N) is critical for crop growth, our study aimed to assess soil health and N transformation gene abundances and correlate soil health with genes involved in inorganic and organic N transformations on commercial dairy farms in Pennsylvania. Soils from three conventional no-till farms and three organic farms using plow-tillage were evaluated with an array of soil health tests as well as metagenomic sequencing. Undisturbed soils from fencerows or farm edges served as reference soils with native properties. Soil health variables of reference soils were more similar to those of no-till soils than to the tilled organic soils. Reference soils had greater relative abundances of microbial genes related to organic N use, while no-till and tilled organic soils exhibited greater abundances of genes related to inorganic N transformations. Carbon and N mineralization and autoclave citrate-extractable (ACE) protein were positively correlated with abundances of genes involved in organic N use, with ACE protein negatively associated with genes involved in inorganic N transformations. Differences in soil health metrics and N use microbial profiles between reference and cropped soils offer insights into the status of microbial communities before and after agricultural disturbance, likely reflecting the history of external N inputs and internal N cycling.