Large nitrous oxide emissions from arable soils after crop harvests prior to sowing.

Global agriculture is the largest anthropogenic source for nitrous oxide (N₂O) emissions. During crop rotations, periods with arable soils without crops, thereafter called "bare soils" are often impossible to avoid after the crop is harvested, prior to sowing of the next crop. However, such periods are underrepresented in studies focussing on N₂O emissions. Here, we present continuous, high-temporal-resolution N₂O fluxes during bare soil periods after four major crops, using the eddy-covariance technique at two sites in Switzerland. Overall, periods with bare soil were net sources for N₂O as well as for carbon dioxide (CO₂) and methane (CH₄). Daily average sums of N₂O emissions varied between 10 ± 2 and 38 ± 5 g N₂O-N ha^-1 d^-1 after the respective rapeseed, winter wheat, pea, and maize harvests. While CO₂ emissions contributed 86-96% to the total GHG budgets, N₂O fluxes accounted for 2% after pea, but for 10-12% after rapeseed, winter wheat, and maize. In contrast, CH₄ fluxes were negligible (< 2%). N₂O fluxes during bare soil periods increased for all cropland sites with increasing water-filled pore space, particularly at high soil temperatures. Thus, our study emphasizes the significance of avoiding bare soil periods to mitigate N₂O emissions from croplands.

Supplementary information: The online version contains supplementary material available at 10.1007/s10705-024-10395-0.