Studies on emissions of nitrous oxide (N
2O) from agricultural soils mostly focus on fluxes between the soil and the atmosphere or are limited to the atmosphere in
the topsoil. However, in soils with shallow water tables, significant N
2O formation may occur closer to the groundwater. The aims of this study were (i) to determine the importance of subsoil N
2O formation in a sandy soil; and (ii) to obtain a quantitative insight in the contribution of subsoil N
2O to the overall losses of N
2O to the environment. We applied
15N labeled fertilizer at a rate of 5.22 kg
15N ha
−1; 50% as Ca(NO
3)
2 and 50% as NH
4Cl, on a mesic typic Haplaquod seeded with potatoes (
Solanum tuberosum L.), and traced soil N
2O concentrations and fluxes over a one-year period. Throughout the year, total N
2O and the amount of
15N recovered in soil N
2O were highest in the subsoil, with a maximum concentration at 48 cm depth in mid-February of 19900 μl m
−3 and 24 μg
15N m
−3, respectively. The maximum concentration coincided with the highest water-filled pore space of 71%. The cumulative flux of
N
2O was 446 g N
2O-N ha
−1, the recovery of
15N in this flux was 0.06%. During the summer, maximum fluxes followed high soil N
2O concentrations. During winter, no such relation was found. We concluded that the formation of N
2O was the highest in the subsoil, largely controlled by water-filled pore space rather than NO
3− concentration or temperature. Although high subsoil N
2O concentrations did not lead to high surface fluxes of N
2O in the winter, artificial draining may lead to high indirect N
2O emissions through supersaturated drainage water.
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