Urea Decreases Nitrous Oxide Emissions Compared with Anhydrous Ammonia in a Minnesota Corn Cropping System
2010
Venterea, Rodney T. | Dolan, Michael S. | Ochsner, Tyson E.
Quantifying N₂O emissions from corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields under different fertilizer regimes is essential to developing national inventories of greenhouse gas emissions. The objective of this study was to compare N₂O emissions in plots managed for more than 15 yr under continuous corn (C/C) vs. a corn–soybean (C/S) rotation that were fertilized during the corn phase with either anhydrous NH₃ (AA) or urea (U). During three growing seasons, N₂O emissions from corn following corn were nearly identical to corn following soybean. In both systems, however, N₂O emissions with AA were twice the emissions with U. After accounting for N₂O emissions during the soybean phase, it was estimated that a shift from C/S to C/C would result in an increase in annual emissions of 0.78 kg N ha⁻¹ (equivalent to 0.11 Mg CO₂–C ha⁻¹) when AA was used, compared with only 0.21 kg N ha⁻¹ (0.03 Mg CO₂–C ha⁻¹) with U. In light of trends toward increased use of U, these results suggest that fertilizer-induced soil N₂O emissions may decline in the future, at least per unit of applied N, although further study is needed in different soils and cropping systems. While soil CO₂ emissions were 20% higher under C/C, crop residue from the prior year did not affect soil inorganic N or dissolved organic C during the subsequent season. We also compared different flux-calculation schemes, including a new method for correcting chamber-induced errors, and found that selection of a calculation method altered N₂O emissions estimates by as much as 35%.
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