Similar strong impact of N fertilizer form and soil erosion state on N2O emissions from croplands.

• Soil erosion states strongly impact N 2 O emission similar to N fertilizer form. • Organic fertilizer resulted in highest N 2 O emission compared to mixed and mineral. • Depositional soil resulted in highest N 2 O emission compared to non-eroded and eroded. • Site-specific differences in soil properties induced by erosion influence N 2 O emission. Soil erosion affects 20% of croplands worldwide. However, understanding the effect of soil erosion on N 2 O emissions, which is one of the most potent greenhouse gases, is still limited. This limitation is likely because the small-scale differences in soil properties and fertility induced by erosion (i.e. ranges of erosion states) have barely been considered in studies quantifying N 2 O emissions from croplands. There are, however, indications that the erosion state itself strongly impacts N 2 O emission, similar to the N fertilizer form. Therefore, our investigations aimed to further explore these indications. We measured N 2 O fluxes for three years and at five sites within an erosion affected field experiment. N 2 O emissions were quantified using a manual chamber system. Three sites were established on a summit position (Albic Luvisol; non-eroded) but differed in N fertilizer forms (organic biogas fermented residues, calcium ammonium nitrate and a mixture of both fertilizers). Two additional sites were established on an extremely eroded soil (Calcaric Regosol) and wet depositional soil in a depression (Endogleyic Colluvic Regosol) to measure the effect of soil erosion states on N 2 O emissions. Both additional sites were fertilized with calcium ammonium nitrate only. In case of the non-eroded soil (summit), organic fertilization resulted in the highest cumulative N 2 O emission (6.2 ± 0.21 kg N 2 O-N/ha y−1) compared to mixed (5.5 ± 0.18 kg N 2 O-N/ha y−1) and mineral (1.9 ± 0.17 kg N 2 O-N/ha y−1) fertilization. These high emissions were probably caused by soluble C and N substrates from organic fertilizer, resulting in microbial activities favoring high N 2 O emissions. Regarding the erosion status, we observed the highest N 2 O emissions in the depositional soil (2.8 ± 0.21 kg N 2 O-N/ha y−1), followed by the non-eroded (1.9 ± 0.17 kg N 2 O-N/ha y−1) and the extremely eroded soil (0.6 ± 0.03 kg N 2 O-N/ha y−1). These differences in N 2 O emissions were mainly due to the site-specific, erosion induced differences in soil properties such as soil texture, soil organic C and total N contents and stocks, water-filled pore space and soil pH. These results indicate that soil erosion state may indeed be of similar importance, as N fertilizer form, for the magnitude of N 2 O emissions from croplands. [ABSTRACT FROM AUTHOR]