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.