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

Soil erosion affects 20% of croplands worldwide. However, understanding the effect of soil erosion on N2O 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 N2O emissions from croplands. There are, however, indications that the erosion state itself strongly impacts N2O emission, similar to the N fertilizer form. Therefore, our investigations aimed to further explore these indications.We measured N2O fluxes for three years and at five sites within an erosion affected field experiment. N2O 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 N2O 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 N2O emission (6.2 & PLUSMN; 0.21 kg N2O-N/ha y  1) compared to mixed (5.5 & PLUSMN; 0.18 kg N2O-N/ha y  1) and mineral (1.9 & PLUSMN; 0.17 kg N2O-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 N2O emissions. Regarding the erosion status, we observed the highest N2O emissions in the depositional soil (2.8 & PLUSMN; 0.21 kg N2O-N/ha y  1), followed by the non-eroded (1.9 & PLUSMN; 0.17 kg N2O-N/ha y  1) and the extremely eroded soil (0.6 & PLUSMN; 0.03 kg N2O-N/ha y  1). These differences in N2O 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 N2O emissions from croplands.