Agroecosystem modeling of reactive nitrogen emissions from U.S. agricultural soils with carbon amendments

Abstract Fertilizer-intensive agriculture is a leading source of reactive nitrogen (Nr) emissions that damage climate, air quality, and human health. Biochar has long been studied as a soil amendment, but its influence on Nr emissions remains insufficiently characterized. More recently, the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel, resulting in a solid zero-valent carbon (ZVC) byproduct whose impact on soil emissions has yet to be tested. We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US. fertilized soils. Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely (− 17% to + 27% under 5 ton ha −1 applications, − 38% to + 18% under 20 ton ha −1 applications) and depend mostly on how nitrification is affected. Low-dose biochar application (5 ton ha −1 ) stimulated emissions of all three nitrogen species in 75% of simulated agricultural areas, while high-dose applications (20 ton ha −1 ) mitigated emissions in 76% of simulated areas. Applying zero-valent carbon at 20 ton ha −1 exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha −1 . Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils (pH < 5.84) with low organic carbon (< 55.9 kg C ha −1 ) and inorganic nitrogen (< 101.5 kg N ha −1 ) content. Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts. Graphical Abstract