Effect of low C/N crop residue input on N₂O, NO, and CH₄ fluxes from Andosol and Fluvisol fields

Crop residues are produced from agriculture in large amounts globally. Crop residues are known to be a source of nitrous oxide (N₂O); however, contrasting results have been reported. Furthermore, the effect of crop residues on nitric oxide (NO) and methane (CH₄) fluxes has not been well studied. We investigated N₂O, NO, and CH₄ fluxes after low C/N crop residue (cabbages and potatoes) inputs to lysimeter fields for two years using with automated flux monitoring system. Lysimeters were filled with two contrasting soil types, Andosol (total C: 33.1 g kg^-1; clay: 18%) and Fluvisol (17.7 g kg^-1; 36%). Nitrogen application rates were 250 kg N ha^-1 of synthetic fertilizer and 272 kg N ha^-1 of cow manure compost for cabbage, and 120 kg N ha^-1 of synthetic fertilizer and 136 kg N ha^-1 of cow manure compost for potato, respectively. Large N₂O peaks were observed after crop residues were left on the surface of the soil for 1 to 2 weeks in summer, but not in winter. The annual N₂O emission factors (EFs) for cabbage residues were 3.02% and 5.37% for Andosol and Fluvisol, respectively. Those for potatoes were 7.51% and 5.10% for Andosol and Fluvisol, respectively. The EFs were much higher than the mean EFs of synthetic fertilizers from Japan's agricultural fields (0.62%). Moreover, the EFs were much higher than the Intergovernmental Panel on Climate Change (IPCC) default N₂O EFs for synthetic fertilizers and crop residues (1%). The annual NO EFs for potatoes were 1.35% and 2.44% for Andosol and Fluvisol, respectively, while no emission was observed after cabbage residue input. Crop residues did not affect CH₄ uptake by soil. Our results suggest that low C/N crop residue input to soils can create a hotspot of N₂O emission, when temperature and water conditions are not limiting factors for microbial activity.