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 N 2 O emissions under different soil drainage conditions has not been studied. Our objective was to quantify agronomic parameters and season-long N 2 O 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 N 2 O 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 N 2 O emissions during the soybean phase. Even though soybean symbiotically fixes N and removes more N in grain than corn, N 2 O 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, N 2 O 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 N 2 O emissions.