Methane-Derived Zero-Valent Carbon Solids Inhibit Nitrification and Decrease Nitrous Oxide Flux from Agricultural Soils

Abstract Zero-valent carbon (ZVC) is a byproduct of hydrogen production by pyrolysis of methane or other hydrocarbons, and its production may increase as part of the energy transition. Its pyrogenic nature has prompted comparisons to biochar for agricultural soil amendment, which motivates proactive assessment of its potential impacts on microbial ecosystem services such as nitrogen (N) cycling. Past research with pure bacterial cultures suggested that ZVC could inhibit nitrification, which would enhance soil retention and plant utilization of applied N fertilizers. Here, we conducted soil microcosm studies to verify this effect in a more realistic system and determine whether it may translate to climate benefits by decreasing soil nitrous oxide (N2O) emissions. ZVC-amended microcosms were prepared with clay or sandy soils to assess response variability, and biochar-amended microcosms were included for benchmarking. ZVC hindered nitrification in both soils, resulting in lower N2O cumulative fluxes by up to 15 ± 2% compared to unamended controls. Though NH4+ application caused changes in the soil microbial community after 30-day incubation, ZVC or biochar amendment had minimal impact on community structure or relative abundance and expression of archetypal nitrogen cycling genes (amo and nor) compared with unamended controls. Similar to biochar, ZVC decreased ammonium bioavailability for nitrification by electrostatic physisorption. Overall, this study de-risks ZVC as agricultural soil amendment and suggests that it could be a greener alternative to chemical nitrification inhibitors, with potential climate benefits.