Greenhouse Gases in Intensive Agriculture: Contributions of Individual Gases to the Radiative Forcing of the Atmosphere

TLDR

Agriculture is a major source of greenhouse gases, notably CO₂, N₂O, and CH₄, influencing global fluxes. Between 1991 and 1999, we quantified gas fluxes and other GWP contributors in cropped fields and adjacent unmanaged ecosystems. Net GWP varied from 110 g CO₂‑eq m⁻² yr⁻¹ in conventional tillage to –211 g CO₂‑eq m⁻² yr⁻¹ in early successional communities, with no annual cropping system providing net mitigation, no‑till systems approaching mitigation, nitrous oxide as the dominant GWP source, and late successional systems achieving neutrality through methane oxidation, indicating opportunities to lower agronomic GWP.

Abstract

Agriculture plays a major role in the global fluxes of the greenhouse gases carbon dioxide, nitrous oxide, and methane. From 1991 to 1999, we measured gas fluxes and other sources of global warming potential (GWP) in cropped and nearby unmanaged ecosystems. Net GWP (grams of carbon dioxide equivalents per square meter per year) ranged from 110 in our conventional tillage systems to -211 in early successional communities. None of the annual cropping systems provided net mitigation, although soil carbon accumulation in no-till systems came closest to mitigating all other sources of GWP. In all but one ecosystem, nitrous oxide production was the single greatest source of GWP. In the late successional system, GWP was neutral because of significant methane oxidation. These results suggest additional opportunities for lessening the GWP of agronomic systems.