Greenhouse gases in intensive agriculture: Contributions of individual gases to the radiative forcing of the atmosphere

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 equivalen ts per square meter per year) ranged from 110 in our conventional tillage s ystems to -211 in early successional communities. None of the annual croppi ng systems provided net mitigation, although soil carbon accumulation in no -till systems came closest to mitigating all other sources of GWP. In all b ut one ecosystem, nitrous oxide production was the single greatest source o f GWP. In the Late successional system, GWP was neutral because of signific ant methane oxidation. These results suggest additional opportunities for L essening the GWP of agronomic systems.