【作者】 王秀斌；

【导师】 周卫； 梁国庆；

【作者基本信息】 中国农业科学院 ， 植物营养学， 2009， 博士

【摘要】 由于巨大的粮食需求,通过施肥增加作物产量同时降低对环境的负面影响,对中国尤其是华北平原的农业可持续发展十分迫切。在华北平原冬小麦/夏玉米轮作体系中,过量施氮不仅降低了氮肥利用率,还增加了硝态氮淋溶到地下水的危险。迄今为止,大量工作集中在不同氮肥用量下的氨挥发、反硝化或NO₃^-运移的单一过程研究,迫切需要全面原位定量研究化肥氮的去向和氮素循环过程,这对于提高氮肥利用率至关重要。为研究华北平原冬小麦/夏玉米轮作体系氮素循环与平衡过程,于2007年至2008年在河北省衡水试验站开展田间试验和¹⁵N示踪的微区试验,监测不同氮肥运筹下氨挥发、反硝化与N₂O排放、无机氮动态分布和¹⁵N的去向。田间试验和¹⁵N示踪的微区试验均设置4个处理,（1）习惯施氮（冬小麦和夏玉米氮肥用量分别为300 kg N/hm²和240 kg N/hm²）,（2）氮肥减量（冬小麦和夏玉米氮肥用量分别为210 kg N/hm²和168 kg N/hm²）,（3）优化施氮（基于作物阶段氮素吸收增加追肥比例和施肥次数,氮肥用量同处理2）,和（4）对照（不施氮肥）。习惯施氮和氮肥减量处理小麦季基肥和拔节肥各占1/2,玉米季基肥1/3,大喇叭口肥2/3。优化施氮处理,小麦季基肥,拔节肥和孕穗肥各占1/3;玉米季基肥占1/5,大喇叭口肥占3/5,吐丝肥占1/5。采用密闭间歇法测定氨挥发,乙炔抑制-原状土柱培育法测定反硝化速率和N₂O排放通量,连续流动注射分析仪测定土壤NO₃^--N和NH4+-N含量;同时监测大气氮素干湿沉降和灌溉水带入的氮素。基于观测值,检验脱氮-分解模型（DNDC）模拟预测氮素循环的可靠性和灵敏度。研究的主要进展概括如下:1.田间试验结果表明,三个施氮处理间冬小麦、夏玉米的籽粒产量和植株吸氮量差异不显著,优化施氮处理略高于习惯施氮处理。与习惯施氮处理相比,优化施氮冬小麦季和夏玉米季作物表观回收率分别提高了14.3和15.2个百分点。整个冬小麦和夏玉米生长季,习惯施氮、氮肥减量和优化施氮处理氮素表观损失量分别为177.6、102.9和58.4kg N/hm²,占氮素总输入量的32.8%、27.2%和15.4%。2.冬小麦和夏玉米季土壤氨挥发损失主要发生在施肥后14d内,玉米季来自肥料氮的氨挥发损失量高于小麦季。冬小麦/夏玉米轮作体系累积氨挥发量随施氮量的减少而降低。习惯施氮小麦季和玉米季氨挥发总量分别是优化施氮的2.28和2.03倍。可见,冬小麦/夏玉米轮作体系优化施氮是降低氨挥发较理想的施肥方式。3.冬小麦和夏玉米整个生育期土壤反硝化速率和N₂O排放通量均表现出明显的季节性变化,且均与土壤水分和无机氮浓度（NH4₊^-N,NO₃^--N）呈显著正相关。玉米季土壤反硝化损失量和N₂O排放量均高于小麦季,其反硝化损失量及N₂O排放量均随施肥量减少而降低。小麦季习惯施氮处理反硝化损失量和N₂O排放量是优化施氮处理的1.62和1.67倍,玉米季分别为2.01和2.00倍。优化施氮改变了土壤无机氮浓度和时间分布,从而降低了反硝化损失和N₂O排放。4.习惯施氮明显提高60 cm以下土层硝态氮含量,在成熟期大部分不能被作物利用的氮素存在淋溶到深层土壤的危险。优化施氮在小麦和玉米成熟期可提高0-20cm土层硝态氮积累量,降低20-100cm土层的积累,表观氮素损失最低。5. ¹⁵N示踪的微区试验结果表明,与习惯施肥处理相比,冬小麦季和夏玉米季优化施氮处理作物回收率分别提高了16.7和17.3个百分点,土壤残留率分别提高了约3.1和4.7个百分点,肥料¹⁵N的损失率分别降低了19.9和22.0个百分点。肥料¹⁵N的损失中,与习惯施氮处理相比,优化施氮处理冬小麦和夏玉米季的累积氨挥发量分别降低了48.4%和51.9%,反硝化损失总量分别降低了40.9%和58.1%。6.采用DNDC模型模拟的土壤氨挥发速率和N₂O排放通量与田间实测结果较为吻合,显示DNDC模型预测农田土壤氮素具有较高可信度。通过对DNDC模型进行灵敏性检验,氮肥用量、施氮肥次数、土壤初始无机氮和土壤质地的改变对土壤氨挥发、N₂O排放和硝态氮淋失均很敏感,其中氮肥用量的改变最为敏感。除不施氮肥降低了作物吸氮量外,其它变量因子的改变对作物吸氮量不敏感。综上所述,基于作物阶段氮素吸收增加追肥比例和施肥次数的优化施氮是较理想的施肥方式,有利于作物氮素吸收,提高氮肥利用率,降低氨挥发和反硝化损失量,降低肥料氮的残留量,同时获得较高的籽粒产量,优化施氮可节约氮肥30%。更多还原

【Abstract】 Due to huge food demand, increasing crop yield by fertilization and reducing negative environmental impacts from fertilization is urgent for sustaining agricultural development in China, especially in the north China plain（NCP）. Excessive N application in a winter wheat-summer corn rotation system in the NCP has been shown to led to the low N use efficiency and to increase the risk of nitrate-N leaching to groundwater. Up to date, much research work has been done in the field of ammonia volatilization, denitrification, and NO₃^- movements, but generally with only one or a few of components concerned in one experiment with different N application rates, the field measurement of the N cycling processes under optimized N application has become an essential need in the general requirement to improve the N use efficiency in agricultural soils.To gain better insight into the nitrogen cycling and balance under winter wheat-summer corn rotation system in NCP, field plot trials combined with micro-plot experiment with ¹⁵N tracing were established in Hengshui region （Hebei province） from 2007 to 2008 to monitor ammonia volatilization （AV）, denitrification and N₂O emission, NO₃^--N accumulation and ¹⁵N fate under different nitrogen application strategies. For both field trail and micro-plot experiment with ¹⁵N tracing, four N treatments included: （1） conventional N application （300 and 240 kg N ha-1 for winter wheat and summer corn, respectively）, （2） reduced N application （210 and 168 kg N ha-1 for winter wheat and summer corn, respectively）, （3） optimized N application （increase ratios of dress N to base N fertilizer and split application based on crop N uptake at different growth stage, same to N rate in reduced N application）, and （4） control with no nitrogen applied. For the treatments of conventional and reduced N application, 1/2 of nitrogen fertilizer applied as basal and 1/2 as topdressing at elongating stage for winter wheat, and 1/3 as basal and 2/3 as topdressing in the bell-mouthed period for summer corn. For optimized N application, 1/3 nitrogen fertilizer applied as basal, and 1/3 as topdressing at elongating stage and 1/3 at booting stage for winter wheat, and 1/5 as basal, and 3/5 as topdressing in the bell-mouthed period and 1/5 at silking stage for summer corn. After each N application, volatile NH3 and N₂O gas were collected and determined immediately, and soil were sampled for NO₃^--N and NH₄⁺-N determination. An enclosed intermittent vent method was adopted to determine AV, denitrification and N₂O emission from soil was measured using acetylene inhibition - intact soil core incubation technique, and soil NO₃^--N and NH₄⁺-N was determined by flow injection analysis. Meanwhile, dry and wet atmosphere deposition of nitrogen in the experimental site was measured as well. Based on above observation, the reliability and sensitivity of DeNitrification-DeComposition simulation model （DNDC） for forecasting nitrogen cycling and balance were tested, and influencing factors of various N cycling pathways were identified. The main findings obtained are summed up as follows:1. Field plot trials showed that grain yield and N uptake for winter wheat and summer corn in the treatment of optimized N application were slightly higher than those under conventional N application, there is no significant difference within three N fertilizer application treatments, except no N fertilizer application. Compared to conventional N fertilization, the apparent N recovery under optimized N fertilization improved by percentage points14.3 and 15.2 for winter wheat and summer corn, respectively. During whole growing season of winter wheat and summer corn, the apparent loss of N in the treatments of conventional, reduced and optimized N application were 177.6, 102.9 and 58.4kg N/hm² respectively, accounting for 32.8%, 27.2% and 15.4% of the total N fertilizer input.2. AV from soil in both winter wheat and summer corn season occurred mainly within 14 days after fertilization, and the cumulative AV amount from fertilizer N in winter wheat season was found to be less than that in summer corn season. Cumulative AV amounts from soil of winter wheat-summer corn rotation system were observed to be reduced with decreasing of N application rate. Total AV amounts under conventional N fertilization was 2.28 and 2.03 times as high as that under optimized N fertilization, showing that optimized N application is a rational and practicable N fertilization mode for reducing AV in winter wheat-summer corn rotation system.3. There were significant seasonal variations of denitrification rate and N₂O emission flux during winter wheat-summer corn growing seasons, each having a positive correlation with soil water content and inorganic nitrogen concentration （NH₄⁺-N, NO₃^--N）. Total denitrification losses and N₂O emission amounts from soil in winter wheat-summer corn rotation system were observed to be reduced with decreasing of N application rate, and which in winter wheat season were found to be less than those in summer corn season. Total denitrification losses and N₂O emission amounts under conventional N fertilization were 1.62 and 1.67 times respectively as high as those under optimized N fertilization during winter wheat growing season, and 2.01 and 2.00 times during summer corn growing season, optimizing N application could reduce denitrification losses and N₂O emission through modifying soil inorganic nitrogen concentration and its temporal distribution.4. NO₃^--N content below the 60 cm soil layer under conventional N application was significantly enhanced due to excessive N application, showing that most of nitrogen not utilized by crops under conventional N application was at the risk of leaching into deep soil. Optimizing N application improved cumulative amounts of NO₃^--N in 0-20cm soil layer at crop maturity, but reduced those in the 20-100cm soil layer, which led to the apparent N loss to be the lowest under optimizing N application.5. Micro-plot experiment with ¹⁵N tracing showed that N recovery for winter wheat and summer corn under optimizing N application was improved by percentage points 16.7 and 17.3, respectively, The residual rate in soil increased by percentage points 3.1 and 4.7, respectively, the loss rate of fertilizer ¹⁵N decreased by percentage points 19.9 and 22.0, respectively, in comparison with conventional N application. Cumulative AV amounts from fertilizer ¹⁵N under optimizing N application reduced by 48.4% and 51.9%, and denitrification losses reduced by 40.9% and 58.1% during winter wheat and summer corn growing seasons, respectively, compared to conventional N application.6. A Higher reliability was found between soil ammonia volatilization and N₂O emission simulated by DNDC model and field measured results, suggesting that the DNDC model could be used for describing N loss in soils in Hengshui under different nitrogen fertilizer management measures. According to sensitivity test on the DNDC model, soil ammonia volatilization, N₂O emission and NO₃^--N leaching were observed to be sensitive to the changes of the amount and time of N application, soil initial inorganic nitrogen and soil texture, in which the amount of N application was the most sensitive factor, while other factors except no N application were insensitive to plant N uptake.In conclusion, optimizing N application associated with increasing ratios of dress N to base N fertilizer and split application based on crop N uptake at different growth stage was a satisfactory pattern of N fertilizer application, which could enhance plant N uptake, improve N fertilizer use efficiency, reduce ammonia volatilization and denitrification, decrease residual N amounts in soils, and gain a higher grain yield as well. These results suggested that 30% of nitrogen fertilizer could be saved by optimized N fertilization.更多还原