Abstract
Subcritical thermochemical conversion (STC) offers a sustainable approach for livestock manure valorization by transforming organic waste into subcritical fecal fertilizer (SFF). While aligning with circular economy and net zero goals, the effects of SFFs on soil gaseous reactive nitrogen (Nr) remain largely unexplored. Herein, pig manure (PM), cattle manure (CM), and their derived SFFs (PSF and CSF produced at 180 °C and 260 °C) were applied to rice paddies to assess impacts on Nr emissions. The results showed that SFFs exhibited enhanced stability, such as oxygen-containing functional groups, lower pH and higher C/N ratio. PSF and CSF application reduced cumulative NH3 volatilization by 45.2–48.6 % and 38.7–55.0 %, respectively, relative to the control. Moreover, PSF significantly decreased cumulative N2O emissions by 30.1–33.3 % compared to PM. Mechanistically, SFFs lowered floodwater pH and modulated inorganic N dynamics, suppressing drivers of NH3 and N2O production. STC preparation temperatures and manure source synergistically influenced emission patterns across crop growth stages. Critically, SFF application lowered environmental damage costs by 38.5–54.6 % while elevating net ecological benefits by 4.6–77.6 %. This study demonstrates that STC-mediated SFF enables dual mitigation of Nr emissions through soil-water biochemical regulation, providing a scalable strategy to enhance nutrient cycling and reduce pollution in livestock-intensive agriculture.