Nitrous oxide emissions from soybean in response to drained and undrained soils and previous corn nitrogen management.

While corn (Zea mays L.)-soybean (Glycine max. Merr. L) is a predominant rotation system in the US Midwest the residual effect of nitrogen (N) fertilization to corn on the following year's soybean and N2O emissions under different soil drainage conditions has not been studied. Our objective was to quantify agronomic parameters and season-long N2O emissions from soybean as affected by N management (0-N and optimum N rate of 135 kg N ha-1 as single or split application) during the previous corn crop under drained and undrained systems. Urea was applied to corn, and residual N effects were measured on soybean the following year in a poorly drained soil with and without subsurface tile drainage. Drainage reduced N2O emissions in one of three growing seasons but had no effect on soybean yield or N removal in grain. Nitrogen management in the previous corn crop had no effect on soybean grain yield, N removal, or N2O emissions during the soybean phase. Even though soybean symbiotically fixes N and removes more N in grain than corn, N2O emissions were more than two times greater during the corn phase (mean = 1.83 kg N ha-1) due to N fertilization than during the soybean phase (mean = 0.80 kg N ha-1). Also, N2O emissions in the corn years were increased possibly due to decomposition of the previous year's soybean crop residue compared to corn residue decomposition in the soybean years. Tile drainage, especially where wet soil conditions are prevalent, is a viable option to mitigate agricultural N2O emissions.

Corn Nitrogen Management Influences Nitrous Oxide Emissions in Drained and Undrained Soils.

To date, no studies have evaluated nitrous oxide (NO) emissions of a single versus a split-nitrogen (N) fertilizer application under different soil drainage conditions for corn ( L.). The objective of this study was to quantify season-long cumulative NO emissions, N use efficiency, and soil N dynamics when corn received a recommended N rate as single or split-N application in Minnesota soils with and without tile drainage over two growing seasons. Preplant urea was broadcast incorporated, and in-season split-N was broadcast as urea plus urease inhibitor. Tile drainage reduced NO emissions during periods of excess moisture but did not affect grain yield or other agronomic parameters. Conversely, when precipitation was adequate and well distributed, tile drainage did not affect NO emissions, but it did enhance grain yield. Averaged across years, the undrained soil emitted 1.8 times more NO than the drained soil (2.36 vs. 1.29 kg N ha). Compared with the Zero-N control, the Single Preplant and Split N applications emitted 2.1 and 1.6 times more NO, produced 1.4 and 1.3 times greater grain yield, and resulted in 1.5 and 1.4 times more residual soil total inorganic N, respectively. Per unit of grain yield, the Split application emitted similar amounts of NO as the Zero-N control. Averaged across years and drainage, the Split application emitted 26% less NO than the Single Preplant application (1.84 vs. 2.48 kg N ha; < 0.001) with no grain yield differences. These results highlight that soil drainage can reduce NO emissions and that a split N application may be a feasible way to achieve NO reduction while enhancing grain yield.