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Rye Cover Crop Effects on Direct and Indirect Nitrous Oxide Emissions

Parkin, Timothy B., Kaspar, Thomas C., Jaynes, Dan B., Moorman, Thomas B.
Soil Science Society of America journal 2016 v.80 no.6 pp. 1551-1559
Glycine max, Secale cereale, United Nations Framework Convention on Climate Change, Zea mays, agroecosystems, corn, cover crops, crop rotation, denitrifying bacteria, emissions factor, greenhouse gas emissions, leaching, nitrate nitrogen, nitrates, nitrogen, nitrogen cycle, nitrous oxide, rye, soil, soil minerals, soybeans, winter
Winter cover crops can have a pronounced effect on N cycling in agricultural ecosystems. By reducing available soil mineral N during active growth and by providing a substrate for denitrifying bacteria after they are killed, cover crops can potentially influence soil N₂O emissions. However, there have been conflicting reports regarding cover crop effects on increasing or decreasing N₂O emissions. In this study, direct soil emissions of N₂O were measured for a 10-yr period in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation, with and without a winter rye (Secale cereale L.) cover crop. Additionally, NO₃ leaching losses during the period were measured and used to estimate indirect N₂O emissions by applying the Intergovernmental Panel on Climate Change (IPCC) EF₅ emission factor of 0.0075 kg N₂O-N kg⁻¹ NO₃–N leached. Direct N₂O emissions measurements were measured using vented static chambers from March 2004 through December 2012. Annual N₂O emissions in corn years were significantly greater than emissions in soybean years (P = 0.013). Under corn annual direct N₂O emissions ranged from 2.3 to 12.5 kg N₂O-N ha⁻¹ yr⁻¹, and under soybean annual emissions ranged from 1.02 to 6.94 kg N₂O-N ha⁻¹ yr⁻¹. Cumulative direct N₂O emissions were calculated each year by numerical integration and summed to compute 10-yr cumulative emissions for the rotation. Total direct emissions during the 10-yr period in the rye and no-rye treatments were not significantly different. The rye cover crop did effect estimated indirect emissions (P = 0.046), which were 1.25 kg N₂O-N ha⁻¹ yr⁻¹ in the rye treatment and 2.69 kg N₂O-N ha⁻¹ yr⁻¹ in the no-rye treatment. There was no significant difference (P = 0.155) between 10-yr cumulative total N₂O emissions (direct + indirect) of the rye cover crop treatment (55.7 kg N₂O-N ha⁻¹) and the no cover crop treatment (63.8 kg N₂O-N ha⁻¹).