追氮方式对夏玉米土壤N2O和NH3排放的影响

【目的】研究氮肥与硝化抑制剂撒施及条施覆土三种追施氮肥方式下土壤N2O和NH3排放规律、 O2浓度及土壤NH4+-N、 NO2--N和NO3--N的时空动态,揭示追氮方式对两种重要环境气体排放的影响及机制。【方法】试验设置3个处理: 1)农民习惯追氮方式撒施(BC); 2)撒施添加10%的硝化抑制剂(BC+DCD); 3) 条施后覆土(Band)。 3个处理均在施肥后均匀灌水20 mm。在夏玉米十叶期追施氮肥后的15天(2014年7月23日至8月8日)进行田间原位连续动态观测,并在玉米成熟期测定产量及吸氮量。采用静态箱-气相色谱法测定土壤N2O排放量,土壤气体平衡管-气相色谱法测定土壤N2O浓度,PVC管-通气法测定土壤NH3挥发,土壤气体平衡管-泵吸式O2浓度测定仪测定土壤O2浓度。【结果】农民习惯追氮方式N2O排放量为N 395 g/hm2,NH3挥发损失为N 22.9 kg/hm2,同时还导致土壤在一定程度上积累了NO2--N。与习惯追氮方式相比,添加硝化抑制剂显著减少N2O排放89.4%,使NH3挥发略有增加,未造成土壤NO2--N的累积。条施覆土使土壤N2O排放量显著增加将近1倍,但使NH3挥发显著减少69.4%,同时造成施肥后土壤局部高NO2--N累积。条施覆土的施肥条带上土壤NO2--N含量与N2O排放通量呈显著正相关。土壤气体的O2和N2O浓度受土壤含水量控制,当土壤WFPS大于60%时,020 cm土层中的O2浓度明显降低,而N2O浓度增加,土壤N2O浓度和土壤O2浓度间呈极显著负相关。各处理地上部产量及总吸氮量差异不显著。【结论】土壤NO2--N的累积与铵态氮肥施肥方式密切相关,NO2--N的累积能够促进土壤N2O的排放,且在条施覆土时达到显著水平(P0.05)。追氮方式对N2O和NH3两种气体的排放存在某种程度的此消彼长,添加硝化抑制剂在减少N2O排放的同时会增加NH3挥发,条施覆土在显著减少NH3挥发的同时会显著增加土壤N2O排放。在条施覆土基础上添加硝化抑制剂,有可能同时降低N2O排放和NH3挥发损失,此推论值得进一步研究。

Impact of fertilization method on soil nitrous oxide emissions and ammonia volatilization during summer maize growth period

[Objectives]The temporal and spatial patterns of soil NH +4 -N, NO -2 -N and NO -3 -N content variation under different nitrogen fertilization methods, and the soil air N2 O and O2 concentrations were investigated in the present study. The aim is to explore the mechanism of soil NH3 volatilization and N2 O emission. [Methods]The tested N fertilization methods were: 1) local farmers’ conventional practices in which urea is broadcasted on soil surface followed by irrigation ( BC), 2) broadcasting urea on soil surface and followed by the application of nitrification inhibitor DCD on soil surface (BC + DCD), 3) band application of urea in the middle of two adjacent maize rows and backfilled with soil (Band). Field experiment was conduct in a summer maize field from July 23 to August 8, 2014. Crop yield and nitrogen uptake were measured in the ripe period. Soil N2 O emissions were measured with static chamber-gas chromatograph ( GC) method and NH3 volatilizations with PVC tube-venting method. Soil N2 O and O2 content were measured with soil-air equilibration tube-GC and soil-air equilibration tube-pump determinator, respectively. [Results] The N2 O emission and NH3 volatilization induced by farmers’ practice was N 395 g / hm2 and N 22. 9 g / hm2 respectively, the soil NO -2 -N showed accumulation to some extend. Compared with BC, the application of DCD precluded the accumulation of soil NO -2 -N in soil, reduced N2 O emission by 89. 4% ,whereas increased NH3 volatilization by 27. 1% ; By contrast, band application of urea induced high soil NO -2 -N accumulation in the fertilizer band, doubled N2 O emission, whereas reduced NH3 volatilization by 69. 4% . O2 and N2 O concentration is soil air was regulated by WFPS. When WFPS was over 60% , O2 concentration reduced while N2 O concentration increased significantly in the 0 -20 cm soil layer. A negative relationship was observed between N2 O and O2 concentration in soil air. There was nether significant difference among the three treatments in maize yield, nor total N uptake of aboveground part. [Conclusions] The accumulation of NO -2 -N in soil induced by ammonium fertilizer relies on N management strategies. Band application of ammonium fertilizer increased NO -2 -N accumulation in soil and soil N2 O emission significantly ( P < 0. 05). There is a trade-off between the nitrogen fertilizer management strategies with different mitigation objectives. The application of DCD reduced N2 O emission while it increased NH3 volatilization on the other hand, whereas the band application of urea reduced NH3 volatilization but it increased N2 O emission. The N2 O emission and NH3 volatilization were both high in farmers’ traditional practices. Band application with DCD may reduce N2 O emission and NH3 volatilization in the same time, which needs further research.