Nitrous Oxide Emissions in a Corn-Soybean Cropping System with and without Tile Drainage.

Little is known about the effect of split-N applications in reducing nitrous oxide (N₂O) emissions from corn (Zea mays L.) or what contribution soybeans (Glycine max L. Merr.) has in the rotation. Similarly, studies evaluating the effect of soil drainage on N₂O emissions are lacking.  Our objective was to quantify in-season N₂O emissions in a corn-soybean rotation under tile-drainage and natural (no tile) conditions with different N fertilization management. Emissions were measured under drained and undrained soils during 2014 near Wells, MN. Corn received 134 kg N ha^-1 as a single pre-plant application or as a split application (1/3 pre-plant and 2/3 at V4 development stage) and check (zero N) plots were present for both crops.  In the first year of a multi-year study, drainage did not impact corn and soybean yield and the drainage-by-N interaction effect for corn was also not significant.  Nitrogen increased corn yield for the single- (11.5 Mg ha^-1) and split-application (11.4 Mg ha^-1) relative to the check (8.9 Mg ha^-1).  In corn, a significant drainage-by-N interaction effect indicated that N treatment had no effect on cumulative N₂O emissions (kg N₂O-N ha^-1) in drained conditions, but in undrained conditions N fertilizer increased emissions 3.2 times for the single- and 2.9 times for the split-application relative to drained conditions. Also, in undrained conditions, the single N application emitted greater N₂O-N (4.2 kg ha^-1) than the other treatments which emitted similar amounts: split-N 2.7 kg ha^-1 and unfertilized check 1.5 kg ha^-1.  Soybean cumulative emissions (kg N₂O-N ha^-1) were unaffected by drainage (0.6 for drained and 0.9 for undrained) and were similar to the unfertilized corn (0.8 for drained and 1.5 for undrained).  These data indicate that split-N application in poorly to somewhat-poorly drained soils with no tile-drainage can help reduce N₂O emission without negatively impacting corn yield.