基施控释氮肥提高华北露地大白菜产量并减少土壤NH3和N2O排放

  【目的】  控制土壤氮素气态损失是提升菜地氮肥利用和环境效益的一个重要措施。在滴灌条件下，研究控释氮肥一次性基施和减少氮肥投入对华北地区大白菜土壤NH₃和N₂O排放及其经济效益的影响，为华北地区大白菜生产提供最优氮肥管理方案。  【方法】  在河北赵县设置田间小区试验，4个处理分别为:不施氮(CK)；常规施氮(施用尿素，总施氮量为N 400 kg/hm2，基施氮∶追肥氮=4∶6，U)；优化施氮(在常规施氮的基础上减氮10%，总施氮量为N 360 kg/hm2，基施氮∶追肥氮=4∶6，90U)；控释氮肥一次性基施(减氮10%，总施氮量为N 360 kg/hm2，90CRU) 。采用通气法和密闭式静态箱–气相色谱法，分析了不同处理下土壤NH₃和N₂O排放动态变化及大白菜产量和氮素吸收的差异。  【结果】  U、90U处理基肥期土壤NH₃排放峰出现在基施后3～6天，追肥后峰值出现在施肥后3～5天，而90CRU处理峰值延迟到基施后9～11天出现，且其峰值显著降低。与U处理相比，整个生育期90U处理土壤NH₃排放通量和总量分别降低了11.0%和10.4%，而90CRU处理其排放通量和总量分别显著降低了46.9%和27.6% (P< 0.05)。U、90U处理基肥期土壤N₂O 排放峰值出现在基施后7～9天，追肥后峰值出现在4～6天，而90CRU处理峰值出现在基施后14～17天，其峰值显著降低。施氮处理基肥期NH₃和N₂O排放峰值均高于追肥后。与U处理相比，90U处理土壤N₂O 排放通量和总量分别降低了11.1%和8.8%，90CRU处理其排放通量和总量分别显著降低了50.5%和23.2% (P<0.05)。与U处理相比，90CRU处理大白菜氮素利用率提高了5.7个百分点，产量和净经济效益分别增加了7.8%和8.0%，但差异不显著。相关分析表明，土壤温度和湿度与NH₃和N₂O排放通量成线性正相关关系，由于基肥期土壤温度和湿度高于追肥期，因此基肥期NH₃和N₂O排放通量高于追肥期。土壤脲酶活性与NH₃排放通量间呈线性正相关关系，90CRU处理通过降低其活性而显著降低了NH₃排放通量；土壤NO₃–-N含量和功能基因AOB-amoA和nirK数量与N₂O排放通量呈线性正相关关系，90CRU处理通过降低上述指标而显著降低了N₂O排放通量。  【结论】  控释氮肥一次性基施在减少氮肥和劳动力投入、提高大白菜产量、经济效益与降低土壤NH₃和N₂O排放通量方面起到积极作用，为华北地区秋季大白菜种植提供了有效的氮肥管理方式。

Basal application of controlled-release nitrogen fertilizer increases Chinese cabbage production and decreases soil NH3 and N2O emissions in Northern China

  【Objectives】  This study aimed at exploring the potential of one-time basal application of controlled-release nitrogen fertilizer (CRU) on reducing NH₃ and N₂O emission and increasing economic benefits of Chinese cabbage production in Northern China.  【Methods】  A micro-plot field experiment was conducted in Zhaoxian County, Hebei Province. Fertilization treatments included no fertilizer control (CK), routine urea N at 400 kg/hm2 and 10% less rate treatment, both applied in basal∶topdressing ratio of 4∶6 (U, 90U), and CRU in 10% less N input and totally basal applied (90CRU). Aeration methods and closed static chamber-gas chromatography methods were used to monitor and analyze soil NH₃ and N₂O emission during growing period. At harvest, the Chinese cabbage yield and N use efficiency were determined.  【Results】  The NH₃ emission peaked in U and 90U treatments 3–6 days after basal fertilization and 3–5 days after topdressing, while that in 90CRU attained its peak at 9–11 days after basal fertilization, and with significantly lower peak value than U and 90U treatment. Compared with 90U treatment, the fluxes and accumulation of soil NH₃ emission in 90CRU were decreased by 46.9% and 27.6% (P<0.05) during the whole growth period. The N₂O emission peaked in U and 90U treatments at 7–9 days after basal fertilization and 4–6 days after topdressing, while that in 90CRU was 14–17 days after basal fertilization, and with significantly lower peak value than U and 90U treatment. Compared with U, 90U treatment decreased emission flux and total N₂O emission by 11.1% and 8.8%, 90CRU treatment significantly decreased total N₂O emission by 50.5% and 23.2% during the whole growth period, increased the yield of Chinese cabbage and net economic benefit by 7.8% and 8.0% respectively, and nitrogen use efficiency by 5.7 percentage points. The relationship between NH₃ emission flux and soil urease activity was a positive linear correlation, therefore, NH₃ flux was significantly reduced by reducing soil urease activity in 90CRU treatment. Further, there was a positive linear correlation between N₂O emission flux and NO₃–-N content and the number of functional genes AOB-amoA and nirK. Therefore, N₂O emission flux was significantly reduced by the reduced indexes in 90CRU treatment.  【Conclusions】  Controlled-released nitrogen fertilizer showed significance effect in reducing nitrogenous fertilizer and labor input, improved the yield and economic benefits, reduced NH₃ and N₂O emission, and provided an effective nitrogen management mode for Chinese cabbage planting in Northern China.