N₂O emission characteristics and mitigation methods in South Loess Plateau under rain-fed winter wheat conditions

Quantifying N₂O emissions and searching for appropriate emission-reduction measures have gained high international interest in global climate change studies. Therefore understanding the impacts of human activities on N₂O emissions from arable soils was vital for mitigating any negative effects on climate change. In this paper, N₂O emissions from soil under different nitrogen treatments: no nitrogen (CK), conventional treatment of 220 kg(N)·hm^-2 (CON), optimized treatment with 150 kg(N)·hm^-2 and straw return (OPT), optimized treatment with DCD (OPT+DCD) and optimized treatment by coated slow release fertilizer OPT(SR), in central Shaanxi of South Loess Plateau were observed during winter wheat season using the static opaque chamber/gas chromatography (GC) method. Results showed that in the first month of winter wheat growth, emissions were of large amount and lasted for longer times. In the last month, emission peaks rapidly occurred and disappeared after precipitation. Then during other times of winter wheat season, emissions were generally low. During seedling to re-greening stage, OPT+DCD and OPT(SR) significantly reduced N₂O emission. Then during re-greening to maturing stage, emissions under the three optimized treatments were not significantly different. In terms of total emissions of different treatments of winter wheat, all the three optimized treatments reduced N₂O emission, increased crop yield and decreased N2O intensity (N₂O emission for per unit grain yield). Compared with CON, the optimized treatments of OPT, OPT+DCD and OPT(SR) reduced N₂O emission by 29.2% (P < 0.01), 38.7% (P < 0.01) and 39.3% (P < 0.01), respectively, with not significant differences among the three optimized treatments. Compared with CON, the optimized treatments of OPT, OPT+DCD and OPT(SR) increased crop yield by 3.8% (P > 0.05), 15.2% (P < 0.05) and 9.5% (P < 0.05), respectively. Also compared with CON, the optimized treatment of OPT reduced N₂O intensity by 31.7% (P < 0.05). Then compared with OPT, OPT+DCD and OPT(SR) reduced N₂O intensity by 22.1% (P < 0.05) and 18.9% (P < 0.05), separately. The results suggested that returning straw to soils in combination with reducing nitrogen application rate to 150 kg(N)·hm^-2 most reduced N₂O emission. Using slow release fertilizer or adding certain amounts of DCD increased crop yield.