不同施氮量对麦田土壤水稳性团聚体和N2O排放的影响

过量施氮可破坏农田土壤结构,增加温室气体排放量。为揭示不同施氮量对土壤团聚体和N₂O排放的影响,于2018—2020年基于氮肥定位试验,设置秸秆原位还田条件下施氮 0 (N₀)、120 (N₁₂₀)、180 (N₁₈₀)、240 (N₂₄₀)、300 (N₃₀₀)、360 kg·hm^-2 (N₃₆₀) 6个处理,研究不同施氮量对麦田土壤N₂O排放、土壤充水孔隙度(WFPS)、土壤温度、硝态氮、铵态氮含量、水稳性团聚体的组成及稳定性的影响。结果表明: 土壤N₂O排放量与氮肥用量之间呈显著正相关关系,WFPS与施氮量之间无显著相关关系,0~10 cm土壤温度随氮肥施用量的增加而显著降低,土壤硝态氮、铵态氮含量与氮肥施用量间存在显著正相关关系。随氮肥施用量的增加,直径>2 mm的水稳性团聚体含量降低,直径<0.5 mm的水稳性团聚体含量增加,土壤水稳性团聚体的粒径也逐渐减小。氮肥施用量与团聚体平均重量直径(MWD)、几何平均直径之间呈显著负相关关系,但与分形维数之间并无显著相关性。MWD (x)与N₂O排放通量(y)之间的拟合方程为:y=3928.3e^-2.171x (R²=0.55,P<0.001),表明当MWD减小时,N₂O排放量将会剧烈升高。可见,麦田施氮量的增加会降低0~10 cm土壤温度,增加土壤硝态氮和铵态氮含量,减小耕层土壤水稳性团聚体的平均粒径,降低团聚体的稳定性,增加N₂O的排放量。

Effects of different nitrogen application rates on soil water stable aggregates and N2O emission in winter wheat field

Excessive nitrogen application would deteriorate soil structure and increase greenhouse gas emission. We set up six treatments, i.e., N₀, N₁₂₀, N₁₈₀, N₂₄₀, N₃₀₀and N₃₆₀(nitrogen application rates of 0, 120, 180, 240, 300 and 360 kg·hm^-2, all straws returned into the field in situ) in the nitrogen fertilizer experimental site to investigate the effects of different nitrogen application rates on soil N₂O emission, soil water-filled porosity (WFPS), soil temperature, nitrate and ammonium contents, composition and stability of water stable aggregates in winter wheat filed in 2018-2020. The results showed that there was a significant positive correlation between soil N₂O emission and nitrogen application rate. There was no correlation between WFPS and nitrogen application rate. Soil temperature in the 0-10 cm layer decreased significantly with the increases of nitrogen application rates. There was a significant positive correlation between nitrate and ammonium contents and nitrogen application rate. With the increases of nitrogen application rates, the content of water stable aggregates with diameter >2 mm decreased, while that of water-stable aggregates with diameter <0.5 mm increased. The particle size of soil water-stable aggregates also decreased gradually. There was a significant negative correlation between nitrogen application rate with mean weight diameter (MWD) and geometric mean diameter, while no correlation with fractal dimension. The fitting equation between MWD and N₂O emission flux was y=3928.3e^-2.171x (R²=0.55, P<0.001), indicating that N₂O emission increased markedly as MWD decreasing. The increases in nitrogen application rate reduced soil temperature in the 0-10 cm layer, increased nitrate and ammonium contents, decreased the average particle size of soil water stable aggregates, and the stability of soil aggregates, and increased soil N₂O emission.