School of Environmental Sciences, University of Guelph, Guelph, Ontario N1G2W1, Canada; Agri-Environment Branch, Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9 5PX, Northern Ireland, UK.
School of Environmental Sciences, University of Guelph, Guelph, Ontario N1G2W1, Canada.
Sci Total Environ. 2022 Apr 1;815:152744. doi: 10.1016/j.scitotenv.2021.152744. Epub 2021 Dec 31.
Nitrous oxide (NO) emissions are highly variable in space and time due to the complex interplay between soil, management practices and weather conditions. Micrometeorological techniques integrate emissions over large areas at high temporal resolution. This allows identification of causes of intra- and inter-annual variability of NO emissions and development of robust emission factors (EF). Here, we investigated factors responsible for variability in NO emissions during growing and non-growing seasons of corn and soybeans grown in an imperfectly drained silt loam soil, in Ontario, Canada. We used quasi-continuously (at half-hourly to hourly intervals) NO fluxes measured via the flux-gradient technique over 11 years for corn and 5 years for soybeans and evaluated the uncertainty of default IPCC and Canada-specific EFs. In the growing season, emissions were controlled by soil nitrate content, soil moisture and temperature in the fertilized corn, while moisture and temperature regulated NO emissions in the unfertilized soybeans. In the non-growing season, nitrogen (N) input from the crop residue did not affect the emissions, pointing to freeze-thaw cycles as mechanisms for enhanced NO emissions. The non-growing season contribution to annual emissions was 38% in corn and 43% in soybeans. On average, annual emissions were 2.6-fold higher in corn than soybeans. Observed mean NO EFs were 0.84% (0.12-2.02%) for growing season and 1.69% (0.29-7.32%) for yearly emissions. The growing season EF derived from long-term NO emissions was 0.9 ± 0.14%. The interannual variability in NO emissions and EFs can be attributed to management practices and annual weather variability. The default IPCC approach based on overall N input had poorer performance in predicting annual NO emissions compared to the current Canadian methodology, which includes management and environmental factor in addition to N inputs. The observed emissions were further evaluated with a newly developed growing season NO emission prediction approach for Canada. However, performance of the approach was poorer than IPCC or the current national Canadian approach. Additional tests of the new national methodology are recommended as well as consideration of non-growing season emissions.
由于土壤、管理措施和天气条件之间的复杂相互作用，一氧化二氮（NO）排放具有高度的空间和时间变异性。微气象技术可以在高时间分辨率下对大面积的排放进行综合。这使得识别 NO 排放的年内和年际变化的原因以及开发稳健的排放因子（EF）成为可能。在这里，我们研究了在加拿大安大略省一个排水不良的粉质壤土中种植的玉米和大豆的生长季和非生长季中导致 NO 排放变化的因素。我们使用通量梯度技术连续（每隔半小时至一小时测量一次）测量了 11 年的玉米和 5 年的大豆的 NO 通量，并评估了默认的 IPCC 和加拿大特定 EF 的不确定性。在生长季，施肥玉米的土壤硝态氮含量、土壤水分和温度控制着排放，而未施肥大豆的水分和温度则调节着 NO 的排放。在非生长季，作物残体中的氮（N）输入不会影响排放，这表明冻融循环是增强 NO 排放的机制。非生长季对年排放量的贡献在玉米中为 38%，在大豆中为 43%。平均而言，玉米的年排放量是大豆的 2.6 倍。观测到的平均 NO EF 分别为生长季的 0.84%（0.12-2.02%）和全年排放的 1.69%（0.29-7.32%）。从长期 NO 排放中得出的生长季 EF 为 0.9±0.14%。NO 排放和 EF 的年际变化可归因于管理措施和年度天气变化。与包括管理和环境因素以及氮输入的当前加拿大方法相比，基于总氮输入的默认 IPCC 方法在预测年度 NO 排放方面表现较差。新开发的加拿大生长季 NO 排放预测方法进一步评估了观测到的排放，但该方法的性能不如 IPCC 或当前的加拿大国家方法。建议对新的国家方法进行更多测试，并考虑非生长季排放。
