Surface and subsurface N 2 O losses from dairy cropping systems

Dairy rotations rely on corn silage, which is estimated to have significant nitrous oxide (N 2 O) emissions. This study examined whether including legumes within rotations can reduce N 2 O emissions from the soil surface and dissolved in tile-drainage water. Emissions of N 2 O were measured from the soil surface and in tile drainage. Cropping systems were: corn–corn (CC), corn + cover crop-corn (C + cc), soybean–corn (SC) and alfalfa–alfalfa (AA) on a clay soil. Liquid dairy manure provided 2-year total N inversely related to legume cropping: 310 (CC), 280 (C + cc), 110 (SC), 50 kg N ha −1 (AA). Losses of N 2 O via tile drainage were 0.1–0.3% of total emissions. Ratios of N 2 O-N to NO 3 − -N in drainage were at least 63% lower than the IPCC default value (0.0075). Reductions of N 2 O emissions were only observed from established alfalfa in year 2. Compared to the SC treatment, which had the highest emissions in year 2, the AA treatment had 62% lower surface N 2 O and 88% lower dissolved N 2 O flux. Alfalfa had low yield in the first year, which led to high yield-scaled N 2 O emissions; thus, alfalfa may need to be grown 4 years to achieve a similar average yield scaled emission factor as CC. Silage corn had consistently high yield, averaging 317 kg ha −1 yr −1 for N yield, which was 36% higher than AA. As a result, CC had the lowest N 2 O emissions scaled by N-yield over the 2 years, averaging 2.6% of N-yield, which was 59% lower than AA on average.