黄土高原冬小麦地N2O排放

从2007年7月1日到2009年6月30日对黄土高原冬小麦地氧化亚氮(N₂O)排放采用静态箱气相色谱法进行了为期2a 的监测。设置2个处理,有小麦田(有小麦生长),无小麦田(出芽初期拔去麦苗)。研究结果表明有小麦田、无小麦田N₂O排放量年际变化不大。有小麦田年均的N₂O 排放量为2.05 kg · N₂O · hm^-2 · a^-1,无小麦田年均的N₂O 排放量为2.28 kg · N₂O · hm^-2 · a^-1 。在冻融交替期,施肥后、翻地后和降雨后无小麦田和有小麦田N₂O排放明显增加,N₂O的季节变化受到这些短期事件的显著影响;有小麦田N₂O排放与地温(P<0.01),气温(P<0.01)和WFPS(P<0.05)显著相关,而无小麦田N₂O排放与这些环境土壤因子都不相关;有小麦田和无小麦田两个处理土壤的WFPS通常都低于60%,可以推断在本地区,硝化反应是N₂O的重要生成源。

Nitrous oxide emissions from winter wheat field in the Loess Plateau

Knowledge on nitrous oxide (N₂O) emissions from agricultural soils in semiarid regions is required for better understanding global terrestrial N₂O losses. Nitrous oxide fluxes from winter wheat fields in the semi-arid Loess Plateau of China were monitored using static chambers from 1 July 2007 to 30 June 2009 at biweekly intervals. After nitrogen fertilizer application, tillage, summer rainfall and during freezing and thawing cycles, additional measurements were conducted. There were two treatments, with or without winter wheat growing (referred to as WF_in and WF_ex, respectively). The results showed that there was no significant difference between two years for both treatments (P<0.05). The annual average N₂O emissions from WF_in and WF_ex were 2.05 kg · N₂O · hm^-2 · a^-1 and 2.28 kg · N₂O · hm^-2 · a^-1, respectively. The average emission factor for WF_in and WF_ex were 0.946% and 1.05%, respectively (uncorrected for background emission). The emission factor for WF_in was about one third (32.2%) lower than the default value provided by the Intergovernmental Panel on Climate Change for the application of synthetic fertilizers to cropland(1.25%). Therefore, the amount of N₂O emissions from the semiarid wheat field may be overestimated without using regional-specific factor. Seasonal variations in N₂O emissions were mainly affected by the short-time events including freeze and thaw cycles, nitrogen fertilizer application, tillage and summer rainfall. The greatest N₂O fluxes of WF_ex occurred during the freeze and thaw cycles of 2008 (February 29) with the value of 179.58 g · N₂O · m^-2 · h^-1. In comparison, the peak values of N₂O emission from WF_in occurred after tillage, fertilization and during continuous rainfall at the beginning of October, 2007, with the value of 93.4 g · N₂O · m^-2 · h^-1. There was significant correlation between N₂O fluxes from the WF_in and soil temperature (P<0.01), ambient air temperature (P<0.01) and water field pore space (WFPS) (P<0.05). The results of stepwise multiple linear regression showed that soil temperature and WFPS could be identified as the key factors determining the temporal variability of N₂O fluxes from the WF_in and accounted for 16.9% of the temporal variation. However, for the WF_ex treatment, N₂O fluxes were not correlated with any of these environmental and soil factors. Soil WFPS in the WF_in and the WF_ex was always below 60% except for during freeze-thaw in 2008and immediately after heavy rainfall, suggesting that nitrification was the important source of N₂O in this region.