[Effect of Long-term Dairy Manure Amendment on N₂O and NO Emissions from Summer Maize-Winter Wheat Cropping Systems]

Annual nitrous oxide (N₂O) and nitric oxide (NO) emissions were measured within a 27 year fertilization experiment in Guanzhong Plain. Gas samples were collected using static chambers from June 2017 to June 2018. The primary objectives of this study were to quantify the variations in N₂O and NO emissions and evaluate the effect of manure amendment on gas losses. Three treatments were set up in the field using a completely random block design. The control treatment (CK) remained unfertilized throughout the year. The synthetic fertilizers (NPK) and NPK plus dairy manure (NPKM) treatments received an annual nitrogen (N) input at a rate of 353 kg·hm^-2. In the summer maize season, the NPK and NPKM treatments received urea as a N source at 188 kg·hm^-2. In the winter wheat season, the NPK treatments received urea at 165 kg·hm^-2. The NPKM treatment received the same amount of N as the NPK treatment but with 30% from urea and 70% from dairy manure. The results showed that N₂O and NO emissions from the CK treatment were consistently low during the experimental period. Large emission peaks were captured in the NPK and NPKM treatments, mostly responding to fertilizer application and irrigation. The largest N₂O and NO peaks were up to 103.0 g·(hm²·d)^-1 and 71.0 g·(hm²·d)^-1, respectively, and both occurred in the NPKM treatment during the summer maize season. The NO/N₂O ratio was negatively related to soil water-filled pore space (P<0.01) at soil temperatures above 20℃ for the NPK and NPKM treatments, indicating the regulatory effect of soil temperature and water content on gas fluxes. Annual N₂O emissions from the CK, NPK, and NPKM treatments were 0.21 kg·hm^-2, 2.32 kg·hm^-2, and 2.15 kg·hm^-2, respectively, with a non-significant difference between the NPK and NPKM treatments (P=0.74). Annual NO emissions from the CK, NPK, and NPKM treatments were 0.23 kg·hm^-2, 0.80 kg·hm^-2, and 1.46 kg·hm^-2, respectively, with a significant difference between the NPK and NPKM treatments (P<0.05). We concluded that long-term dairy manure amendment did not influence N₂O emissions but increased NO emissions.