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The net greenhouse gas emissions from upland soils, as indicated by global warming potential (GWP), mainly depend on the soil carbon sequestration and nitrous oxide (N 2 O) emissions. The annual changes in surface (0-20 cm) soil organic carbon (SOC) content from 2010 to 2017 and the N 2 O emissions from 2014 to 2017 were measured within a long-term fertilization experiment. The objective was to quantify the effect of stalk incorporation on the soil carbon sequestration, annual N 2 O emissions, and GWP of a winter wheat-summer maize field in the Guanzhong Plain. The field experiment included three treatments:conventional fertilization (CF), conventional fertilization plus maize stalks (CFS), and an unfertilized control (CK). The CF and CFS treatments received the same amount of urea per year, with nitrogen (N) input at 165 kg·hm -2 and 188 kg·hm -2 in the winter wheat season and summer maize season, respectively. The CF treatment retained the stubbles (about 10 cm above ground) when harvesting the winter wheat and summer maize crops. The CFS treatment retained the same wheat stubbles and all maize stalks (containing approximately 40 kg·hm -2 of N). The CK treatment was unfertilized throughout the year, with the stubble management the same as that in the CF treatment. The results showed that the CK treatment displayed few changes in SOC content and low N 2 O emissions, with GWP varying from 0.04 to 0.11 t·(hm 2 ·a) -1 . The SOC contents in the CF and CFS treatments increased linearly with the fertilization years ( P <0.001), and their SOC sequestration rates were 0.69 t·(hm 2 ·a) -1 and 0.97 t·(hm 2 ·a) -1 , respectively. The N 2 O emissions from the CF and CFS treatments varied from 1.65 to 5.36 kg·(hm 2 ·a) -1 and from 3.08 to 7.73 kg·(hm 2 ·a) -1 , respectively. The annual N 2 O emissions from the CFS treatment were 43%-94% higher than those from the CF treatment, whereas the difference was only significant between 2015 and 2016 ( P <0.05). The GWP of the CF and CFS treatments varied from -1.95 to -0.28 t·(hm 2 ·a) -1 and from -2.59 to -0.35 t·(hm 2 ·a) -1 , respectively. The cumulative GWP of the CFS treatment was 42% lower than that of the CF treatment between 2014 and 2017. In summary, the studied winter wheat-summer maize field acted as a sink of greenhouse gases under the conventional fertilization regime. The stalk incorporation further favored greenhouse gas mitigation despite the trade-offs between SOC sequestration and N 2 O emissions.

Annual nitrous oxide (N 2 O) 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 N 2 O 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 N 2 O 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 N 2 O and NO peaks were up to 103.0 g·(hm 2 ·d) -1 and 71.0 g·(hm 2 ·d) -1 , respectively, and both occurred in the NPKM treatment during the summer maize season. The NO/N 2 O 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 N 2 O 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 N 2 O emissions but increased NO emissions.

The primary aim of this study was to quantify the effects of long-term organic amendments on soil nitrous oxide (N 2 O) emissions. Using static chamber-gas chromatograph technique, we measured N 2 O fluxes from winter wheat-maize rotation system and related environmental factors in the Guanzhong Plain for one year (October 2014 to October 2015). Field experiments were based on the "Chinese National Loess Fertility and Fertilizer Effects Long-term Monitoring Experiment". Four treatments were control (CK, 0 kg·hm -2 ), NPK (NPK, 353 kg·hm -2 ), NPK combined with maize straw[NPKS, (353+40) kg·hm -2 ] and cattle waste[NPKM, (238+115) kg·hm -2 ]. During the experimental period, N 2 O fluxes from CK treatment were small[<2.9 g·(hm 2 ·d) -1 ]; while emissions from fertilized treatments peaked after fertilization[up to 113.4 g·(hm 2 ·d) -1 for NPKS] and irrigation[up to 495.0 g·(hm 2 ·d) -1 for NPKM] during winter wheat and maize seasons, respectively. N 2 O flux was significantly correlated to soil water-filled pore space for all treatments ( r >0.28, P <0.05). Annual N 2 O emissions were (0.1±0.0), (2.6±0.1), (3.4±0.7) and (2.9±0.3) kg·hm -2 for CK, NPK, NPKS and NPKM, respectively. The fertilized treatments released higher N 2 O emissions than CK treatment ( P <0.05), indicating that fertilization stimulated N 2 O emissions. However, the differences in N 2 O emissions were not significant among the fertilized treatments ( P =0.06), suggesting that organic amendments did not increase N 2 O emissions obviously. The direct emission factors were 0.72%, 0.83% and 0.80% for NPK, NPKS and NPKM, respectively, all of which were lower than the IPCC default of 1%. The yield-scaled N 2 O emission for NPKM was the lowest among the fertilized treatments.

With static-closed-chamber and GC (Agilent 4890), the nitrous oxide (N2O) flux in spring wheat field ecosystem in the Sanjiang Plain of Northeast China was continuously observed in situ from May 2004 to October 2006. The results showed that the N2O flux presented obvious seasonal and inter-annual variation, which was mainly related with precipitation and field water management. The diurnal variation of N2O flux had correlations with the air temperature and the temperature at 5 cm underground. Wheat field ecosystem was the strong sources of atmosphere N2O during plant growth season. The N2O flux decreased obviously in fallowing period, was weaker in freezing period, and increased slowly when soil thawing. The average N2O flux in wheat growth season was 0.190 mg x m(-2) x h(-1), the flux was 0.077 mg x m(-2) x h(-1) from after-reaping to before-freezing period, and 0.017 mg x m(-2) x h(-1) in freezing and thawing period.