黄河上游灌区稻田N2O排放特征

黄河上游灌区稻田高产区过量施肥现象十分突出,氮肥过量施用引起土壤氮素盈余,导致N₂O排放量增大,由此引起的温室效应引起广泛关注。采用静态箱-气相色谱法研究黄河上游灌区稻田不同施肥处理下N₂O排放特征。试验设置5个施肥处理,包括常规氮肥300 kg/hm²下单施尿素和有机肥配施2个处理,分别用N300和N300-OM代表;优化氮肥240 kg/hm²下单施尿素和有机肥配施2个处理,分别用N240和N240-OM代表;对照不施氮肥用N0代表。试验结果得出,灌区水稻生长季稻田土壤N₂O排放主要集中在水稻分蘖前及水稻生长的中后期,稻田氮肥施用、灌水及土壤温度的变化对N₂O排放通量影响较大,不同处理水稻各生育阶段N₂O累积排放量与稻田土壤耕层NO^-₃-N含量动态变化显著相关。稻田N₂O排放不是黄河上游灌区稻田氮素损失的主要途径,但灌区稻田N₂O排放的增温潜势较大;稻田氮肥过量施用会显著增加N₂O排放量,在相同氮素水平下,有机肥配施会显著增加稻田土壤N₂O的排放量(P＜0.01)。优化施氮能有效减少灌区稻田水稻生长季N₂O排放量。稻田不同处理的水稻整个生长季土壤N₂O排放总量为2.69-3.87 kg/hm²,肥料氮通过N₂O排放损失的百分率仅为0.43%-0.64%。在灌区习惯灌水和高氮肥300 kg/hm²时,N300-OM处理的稻田N₂O排放量达3.87 kg/hm²,在100 a时间尺度上的全球增温潜势(GWPs)为20.76×10⁷ kg CO₂/hm²;优化施氮240 kg/hm²水平下,N240和N240-OM处理的N₂O累计排放量较N300-OM处理,分别降低了1.18 kg/hm²和0.57 kg/hm²,在100 a尺度上每年由稻田N₂O排放引起的GWPs分别降低了6.33×10⁷ kg CO₂/hm²和3.06×10⁷ kg CO₂/hm²。

The feature of N2O emission from a paddy field in irrigation area of the Yellow River

Input of nitrogen (N) is essential for high crop yields, but excessive application of N fertilizer increased the loss of gaseous nitrogen. Gaseous loss of N is a main way of nitrogen loss in the paddy fields of the irrigation area. The static chamber-gas chromatograph method was used to measure the N₂O emission from the paddy field. The five N treatments of field experiment were conducted, including two treatments of the conventional N application rate (300 kg/hm²), i.e the application of only urea (N300) and the application of the organic fertilizer (manure) with the urea nitrogen (N300-OM); two treatments of the optimized N application rate (240 kg/hm²), i.e, the application of only urea (N240) and the application of the organic fertilizer (manure) with the urea nitrogen (N240-OM), and no N fertilizer application plot (CK). The results showed that N₂O emissions mainly occurred before the tiller stage or at the pre- and late- rice growth stages, and more N₂O emissions were measured after rice planting and irrigation. At different nitrogen levels, the total amount of N₂O emissions during the whole rice growing season varied among 2.69-3.87kg/hm², and the loss of fertilizer N due to N₂O emissions was only 0.43%-0.64%. N₂O emissions from the paddy field is not an important way of nitrogen loss at the Yellow River irrigation area, but the warming potential through N₂O emissions in the irrigation area is not neglectable. Excessive application of nitrogen fertilizer in the paddy field significantly increased N₂O emissions, and at the same level of nitrogen application, organic fertilizer amendment increased N₂O emissions from the paddy soil (P<0.01). Optimization of nitrogen application in the irrigated paddy field during the rice growing season reduced N₂O emissions. With the conventional irrigation practice, N₂O emissions from paddy fields in N300-OM treatment reached 3.87kg/hm². In the scales of 100a, the global warming potentials (GWPs) were 20.76×10⁷ kg CO₂/hm². Optimization of N application in the irrigated paddy field during the rice growing season reduced N₂O emissions. Compared with N300-OM treatment, cumulative N₂O emissions in N240 and N240-OM treatments decreased by 1.18 kg/hm² and 0.57 kg/hm², respectively. In the scales of 100a, GWPs caused by N₂O emissions in the paddy field decreased 6.33×10⁷ kg CO₂/hm² and 3.06×10⁷ kg CO₂/hm², respectively.