【作者】 蒋静艳；

【导师】 黄耀；

【作者基本信息】 南京农业大学 ， 生态学， 2009， 博士

【摘要】 气候变暖是当今全球性的环境问题,其主要原因是大气中温室气体浓度的不断增加。N2O是重要的温室气体之一,主要源于农业氮肥的施用。为满足未来不断增长的人口对粮食纤维的需要,氮肥使用将持续增加,其无疑将导致更多的N2O进入大气中。缓/控释氮肥作为一种新型改性氮肥,已被列为我国中长期科学与技术发展规划纲要(2006-2020)优先发展主题之一。研究其在农田生态系统上对N2O的直接和间接排放及影响因素有助于全面理解缓/控释氮肥对N2O的减排效果及未来全面推广应用的可行性,进而为后《京都议定书》时代我国温室气体减排政策提供技术支持和科学依据,具有重要意义。本研究目的是：①研究不同类型的典型缓/控释氮肥对旱地-作物系统N2O直接和间接排放的影响,探索产N20的相关微生物过程；②比较施用不同类型缓/控释氮肥的环境效益和经济效益,并在此基础上评价不同类型缓/控释氮肥对N2O减排的技术和经济可行性。本研究采用室内培养实验,盆栽试验,小区试验和大田试验相结合的方法定量研究了不同类型的缓/控释氮肥对旱地-作物系统N20的直接和间接减排效果。本研究室外试验于2006-2008年冬小麦和夏玉米4个生长季上设了7种氮肥处理。普通尿素(U)作为常规氮肥,另6种氮肥分别代表缓/控释氮肥中的三大类型。其中钙镁磷肥包膜尿素(CMCU),树脂包膜尿素(PCU)和硫磺包膜尿素(SCU)三种包膜肥料代表缓/控释氮肥中的物理型；尿甲醛(UF)代表缓/控释氮肥中的化学型；尿素添加硝化抑制剂双氰胺和脲酶抑制剂氢醌(BIHD)和尿素添加增铵一号(BIEA)代表缓/控释氮肥中的生物化学型。同时以不施肥处理作为对照(CK)。根据当地农作习惯,施肥方式为撒施；常规施氮水平冬小麦和夏玉米生长季分别为250kgN/hm2和300kgN/hm2,并于盆栽试验和大田试验增设了减施30%氮的低氮水平处理。N2O的采集和分析采用静态暗箱-气相色谱法,氨挥发采用原位通气法测定。室内实验主要是通过微生物分离纯化手段分离出自养硝化菌和异养硝化/好氧反硝化菌,并在不同土壤WFPS条件下进行无菌土反接种培养实验,以研究其对土壤内外源氮转化为N2O的作用。研究结果显示：1.冬小麦季N2O直接排放主要取决于土壤温度而不是土壤水分,玉米生长季则正好相反。玉米季N2O直接排放最适宜的土壤WFPS为55%-60%。冬小麦季累积N2O排放平均仅为玉米生长季的15%左右。不同缓/控释氮肥的N素释放特性不同决定了其施入土壤后N2O直接排放的季节性动态变化有差异。包膜肥料和尿素处理的N2O直接排放更易受施肥后首次强降雨的影响,但降雨对BIHD处理的N2O直接排放几乎不产生影响。尿甲醛和尿素添加生物抑制剂处理不论在小麦还是玉米生长季其N2O直接排放均较尿素处理为低,其减排率波动范围为15%-63%；但包膜肥料处理(CMCU, PCU和SCU)在不同的气候条件下N2O直接排放具有不同的表现特征。施肥后有强降雨,则包膜肥料处理N2O直接排放显著高于尿素处理,其增加率高达8%-99%；施肥后持续晴天则较尿素处理为低,减排率波动范围为4%-39%。2.不同生长季不同肥料处理的氨挥发速率及氨损失不同。水热条件和肥料本身的N素释放特性决定了其氨挥发的差异。在相同的田间环境条件下,冬小麦生长季不同肥料处理的氨挥发损失表现为BIEA>CMCU>SCU>UF>U>PCU;2007和2008玉米生长季不同肥料处理的氨挥发损失分别表现为U>PCU> CMCU>SCU>BIHD >UF和BIEA>U>BIHD>SCU>UF>PCU。而不同氮肥处理的间接N2O排放大小顺序与氨挥发的规律一致。总之,与尿素处理相比PCU处理无论是冬小麦季还是玉米生长季其间接N2O排放一直小于尿素处理,而BIEA则一直显著大于尿素处理。UF处理在玉米生长季间接N2O排放也一直小于尿素处理。3.与尿素相比,包膜肥料SCU和PCU无论在小麦上还是玉米生产上有明显的增产效果,且氮肥利用率较高。UF在小麦生产上表现为减产效应,但在玉米生产上表现为明显增产效应。BIEA和BIHD在玉米上也有增产效果,但增产率两者有差异。测土配方施肥是提高氮肥利用率的前提。净效益比较结果表明种植玉米对环境的影响要远远高于小麦。从不同缓/控释氮肥总N20排放来说,在小麦季上PCU,SCU,UF有较好的总N2O减排效果,而在玉米季上UF和BIHD总减排效果最好,平均减排率分别达41%和56%。结合经济效益和环境安全性可知在小麦作物上施用树脂包膜尿素和硫磺包膜尿素,在玉米作物上施用尿甲醛既能提高农民收益,又能使环境影响最小,应为肥料选择时的首选,值得政府大力推广4.在添加外源N尿素的条件下,同一假单胞菌属(Pseudomonas sp.)的两株异养硝化/好氧反硝化菌株HX2和XM1在不同水分条件下产N2O不同。在30%的土壤WFPS条件下产N2O皆高于60%WFPS条件,尤其XM1菌在60%的水分条件下几乎不产生N2O。在50%～60%土壤WFPS条件下N2O的产生有异养硝化菌的参与,土壤WFPS越低,异养硝化菌或好氧反硝化菌所起的作用越大。而较高含水量如50%WFPS条件的土壤中,N2O的产生过程主要是以自养硝化为主,其产N2O量几乎是异养硝化/好氧反硝化菌处理的2.1倍。反映在生产实践上若是低土壤水分条件,则适宜施入低C/N的肥料,有助于减少N2O的产生并达到减排的目的。本研究综合考虑了不同缓/控释氮肥氮的总损失情况,将环境效益和经济效益联系起来,为全面客观评价不同缓/控释氮肥在N2O减排上的作用提供了新的思路。更多还原

【Abstract】 Climate change and global warming continue to be subject to considerable scientific debate and public concern. Nitrous oxide (N2O) is an important trace gas that causes global warming and stratospheric ozone depletion. Nitrogen fertilization is considered as a primary source of N2O emissions from agricultural soils. The consumption of synthetic nitrogen fertilizer in agriculture has increased over the past several decades and will continue to increase to meet the food and fibre demands of the growing global population, which will no doubt result in the release of additional N2O into the atmosphere. A wise use of synthetic fertilizer N is important to mitigate N2O emissions.Slow/controlled-release N fertilizers, proposed as an alternative to conventional N fertilizers, have become a priority topic in the Chinese middle- and long-term science and technology development plan guidelines (2006-2020). To compare and assess the direct and indirect N2O emissions from cropland with different slow- and controlled-release nitrogen fertilizers, and thus to provide critical information for N2O mitigation in China are necessary.The objectives of this research were:1) to examine the performance of different typical slow/controlled-release nitrogen fertilizers compared to conventional urea in relation to crop N uptake and direct and indirect N2O emission under winter wheat and maize rotation system, and hence 2) to assess the technical and economical feasibility of mitigation of N2O for slow/controlled-release N fertilizers to be popularized in future.To approach the above objectives, incubaion experiments and field experiments were employed in this study. Outdoor experiments with physically altered, chemically altered and biochemically inhibited nitrogen fertilizers which represent three typical varieties of slow- and controlled-release N fertilizers were conducted during the 2006-07 and 2007-08 winter wheat growing seasons and during the 2007 and 2008 maize growing seasons to evaluate the potential of these formulations to mitigate N2O emissions. The physically altered nitrogen includes Ca-Mg-P-coated urea (CMCU), polymer-coated urea (PCU) and sulfur-coated urea (SCU). Urea formaldehyde (UF) was used as the chemically altered nitrogen. Urea with dicyandiamide and hydroquinone (BIHD) and urea with enhanced ammonium nutrition (BIEA) were used as the biochemically inhibited nitrogen. Commercial urea (U) was applied as a comparison. No fertilizer was employed as a control (CK). N2O fluxes were measured with the static chamber method. Ammonia volatilization from soil was determined by the venting method. In terms of conventional rates in this region, the total amounts of nitrogen applied in the wheat and maize growing season were 250 and 300 kgN/hm2, respectively. Some treatments with reduction nitrogen by 30% were also employed. All N fertilizers were broadcast-applied. In order to find out the main microbial processes which contribute to N2O emission, indoor incubation experiments to isolate autotrophic nitrifiers and heterotrophic nitrifiers/aerobic denitrifiers from agricultural soil were conducted.Results of this study are presented as follows:1) N2O direct emissions during the wheat growing season mainly depended on soil temperature rather than on soil WFPS. On the contrary, N2O direct emissions were greatly affected by rainfall and hence soil moisture over the maize growing season. The cumulative N2O emissions from different treatments in the winter wheat growing season was far lower (averaged only about 15%) than that in the maize growing season, and the N2O direct emission factors followed the same pattern. The optimum WFPS for high N2O emission was at 50%～65% in the field condition.The different N release characteristic of each fertilizer after application resulted in different seasonal direct emissions of N2O among the several fertilizer types. Direct emissions of N2O from the coated and urea fertilizers were easily affected by the heavy rainfall event followed by basal fertilization. However, the rainfall had no obvious effect on direct emissions of N2O for the BIHD treatment.In comparison with the U, the UF and BIEA treatments reduced direct emissions of nitrous oxide by 15%～62% for the wheat and maize growing seasons, and the BIHD treatment reduced direct emissions of N2O by 33%～63% for the maize growing season. However, the treatments with the coated nitrogen generally enhanced direct emissions of nitrous oxide by 8%～99% in comparison to U treatment when rainfall followed application, while reduced direct emissions of nitrous oxide by 4%～39% when an extended drought was experienced after application. We conclude that the application of chemically altered or biochemically inhibited nitrogen fertilizers has great potential to mitigate direct emissions of nitrous oxide, but the use of physically altered nitrogen fertilizers would enhance direct emissions of nitrous oxide under wet climate condition.2)During the winter wheat growing season, only PCU treatment reduced ammonia volatilization by 20%, while the other treatments (UF, CMCU, SCU and BIEA) enhanced ammonia volatilization by 45%～282% when compared to U treatment。However, ammonia volatilization for CMCU, BIHD, SCU, UF and PCU treatments were lower than that for urea treatment over the maize growing seasons, especially UF and PCU treatments had significant reduction effect on ammonia volatilization, averaged reduction by up to 80%. In addition, ammonia volatilization for BIEA treatment was always higher compared to urea treatment.3) There was obvious improvement in yield production and higher NUE with use of PCU and SCU in both winter wheat and maize growing seasons as compared to urea. UF treatment reduced yield of wheat but increased the maize production. To further calculate the indirect emissions of nitrous oxide suggest that PCU and SCU may be effective in reducing total N2O emission and increasing the economic benefit in wheat planting. However, the net benefit was almost negative value whatever application of any fertilizers in maize growing season. Among all treatments, UF showed priorities in reducing total N2O emissions and increasing economic benefit in maize planting.4) It is essential for mitigation N2O emission to investigate the nitrifying and denitrifying mechanisms of N2O production. In this study, two strains HX2 and XM1 as Pseudomonas sp. which could both heterotrophic nitrify and aerobic denitrify were isolated. They produced more N2O in 30% soil WFPS than that in 60% soil WFPS, especially XM1 almost produced no N2O in 60% soil WFPS. Compared to autotrophic nitrification, heterotrophic nitrification/aerobic denitrification produced fewer N2O at 50%～60% soil WFPS, and it played more important role in N2O production with soil WFPS decreasing. The results indicated that the application of low C/N fertilizer under low soil WFPS condition could depress N2O production and hence reduce N2O emission.更多还原