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Title: Nitrous oxide, methane emission, and yield-scaled emission from organically and conventionally managed systems

Author
item Johnson, Jane
item Weyers, Sharon
item Archer, David
item Barbour, Nancy

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2012
Publication Date: 7/1/2012
Citation: Johnson, J.M., Weyers, S.L., Archer, D.W., Barbour, N.W. 2012. Nitrous oxide, methane emission, and yield-scaled emission from organically and conventionally managed systems. Soil Science Society of America Journal. 76:1347-1357.

Interpretive Summary: Nitrous oxide is about 300 times and methane is more than 20 times more potent as a greenhouse gas compared to carbon dioxide. Agriculture is a major source of nitrous oxide, which comes from fertilizer or manure application. Agriculture is also a source of methane coming as animal and manure management, while soils can either release or consume methane. Ideally, organic management would have few negative impacts by not using synthetic chemicals and by using manure. Organic producers have limited chemical options so they rely heavily on tillage for weed control. Conventional-production systems that use crop rotation with three or more crops and reduced tillage are also expected to improve soil quality. We selected conventionally- and organically-managed systems with the same tillage and crop rotations to compare the impact of applying manure or inorganic fertilizer on nitrous oxide or methane emission and overall soil quality. Soil quality is a concept describing the ability of soil to perform its desired function. Overall environmental benefits such as improved soil quality may be reduced if nitrous oxide or methane is increased. We expected soil quality index to improve over time for both management systems, but both declined. In the organically-managed systems, the desired benefits of improved soil quality and reduced nitrous oxide or methane intensity were undermined by the loss of productivity. This work provides information on the overall impact of management on greenhouse gas emission. It benefits producers, scientists, and policy-makers by providing guidance toward developing agricultural systems that reduce global warming risks without sacrificing productivity or profitability.

Technical Abstract: There is a gap in empirical greenhouse gas (GHG) data from many regions of the USA including the northern Corn Belt. This study compared nitrous oxide (N2O) emission in diverse, low-tillage conventionally- and organically-managed systems. Both systems had a four-year rotation, mole-knife, strip tillage and fertilizer applied based on fall soil test results. The conventionally-managed system received inorganic nitrogen fertilizer during the corn and wheat phase annually. The organically-managed system had manure added only once during the wheat phase. The corn phase of the rotation released the most nitrous oxide in the conventionally-managed system all three years and in two of three years in the organically-managed system compared to the other crops in rotation. In both systems N2O emission was associated primarily with spring thaw (0.21 to 1.54 kg N2O-N ha-1) and fertilizer application (0.24 to 1.03 kg N2O-N ha-1). The two systems did not differ in seasonal rotation average amount of N2O emission (4.21 kg N2O-N ha-1) during the three-year study. However, because the organically-managed system produced 1.5 times less plant biomass, there was more GHG emission per unit of biomass produced in two of the three years. The equivalent of 4.74% of the nitrogen fertilizer applied and 9.26% of manure N was measured as kg N2O-N over the entire three-year study. To achieve maximum environmental benefits from organic management, productivity must be maintained and N-use efficiency maintained.[GRACEnet publication]