【作者】 杨黎；

【导师】 邱建军；

【作者基本信息】 中国农业科学院 ， 农业生态学， 2013， 博士

【摘要】 氮肥在保障我国粮食安全中起着不可替代的支撑作用，氮肥施用量也在逐年持续增长，且在粮食主产区普遍偏高，对生态环境带来了安全隐患。春玉米是我国东北地区主要的粮食作物，该区春玉米农田氮肥投入通常超出氮肥推荐施用量；由于氮肥过量投入和不合理的耕作，地力呈下降趋势，也成为重要的温室气体排放源。如何优化田间管理措施在保障作物产量的同时实现固碳减排，对于该地区农业的可持续发展具有现实意义。本研究采用田间原位试验、土壤微生物测定试验和生物地球化学循环模型模拟相结合的方法，研究辽西地区春玉米农田主要温室气体（N₂O）排放和土壤呼吸特征，定量分析不同施氮措施和秸秆还田对春玉米产量、N₂O排放、土壤呼吸以及硝化和反硝化菌种群的影响，并在此基础上利用DNDC模型探讨既能保障产量又能实现固碳减排的优化管理措施。主要研究内容与结果如下：（1）2009-2012年连续4年的田间试验观测表明，在农民习惯施肥措施（FP）下，辽西地区春玉米农田土壤N₂O排放通量与高峰出现主要受施肥和降雨影响，且呈现较一致的规律性；N₂O季节排放总量均值为1.14±0.19kg N ha^-1，年际间变异系数为17%；土壤呼吸季节总量均值为2019±264kg C ha^-1，年际间变异系数为13%。进一步分析表明农田土壤N₂O排放和土壤呼吸动态与环境因子密切相关，土壤N₂O排放与土壤无机氮含量正相关（P <0.01），土壤呼吸强度与土壤温度呈指数相关，与土壤湿度显著负相关（P <0.01）。（2）不同施氮措施和秸秆还田对N₂O减排效果的田间原位观测试验结果表明，减施20%氮肥处理（OPT）与FP处理相比，2009-2012年4个春玉米生长季中农田土壤N₂O均有减排效果，且减幅在逐年增大，但减排效果不显著。而在减氮20%的基础上改施缓释肥处理（CRF）或添加硝化抑制剂处理（OPT+DCD），可在不影响春玉米产量的同时显著降低供试农田土壤N₂O排放。与FP处理相比，CRF处理下2009年和2010年春玉米生长季N₂O排放总量降低幅度分别为10%和13%，OPT+DCD处理在2011年和2012年N₂O季节排放总量降幅分别达到22%和31%，均具有较显著的减排效果。在OPT基础上加秸秆还田处理（OPTS）的4个春玉米生长季N₂O排放总量在所有处理中均为最高，秸秆还田措施明显促进了N₂O排放。（3）不同施氮措施和秸秆还田对土壤呼吸影响的田间试验结果表明，供试农田土壤呼吸季节变化与作物生长进程、土壤温度变化、秸秆还田等密切相关。在秸秆还田措施下，生长季前期土壤呼吸强度显著高于其他处理。CK、FP、OPT、OPTS处理在2009-2012年4个春玉米生长季农田土壤呼吸季节总量均值分别为1891.2±59.0kg C ha^-1、1939.3±39.6kg C ha^-1、1945.2±46.3kgC ha^-1、2096.4±156.8kg C ha^-1；CRF、OPT+DCD处理在2009-2010年和2011-2012年的结果分别为2320.8±102.5kg C ha^-1、1759.2±78.0kg C ha^-1；不同施氮措施对土壤呼吸无显著影响。（4）2012年春玉米生长季追肥前后不同处理下土壤硝化、反硝化菌群大小的微生物测定试验结果表明，CK处理下所采土壤样品中AOB和AOA amoA基因拷贝数平均值分别为0.1×105(g SDW^-1)和0.2×105(g SDW^-1)，反硝化细菌nirS基因拷贝数平均值为0.5×107(g SDW^-1)，均显著低于其它施氮处理；氮肥施用通过促进氨氧化细菌（AOB）、氨氧化古菌（AOA）和具有nirS基因的反硝化细菌种群数量增长，进而促进N₂O排放。与其他施氮处理（FP、OPT、OPTS）相比，OPT+DCD处理下供试农田土壤中AOA和AOB amoA基因拷贝数与反硝化细菌nirS基因拷贝数均为最低，可见DCD对参与硝化和反硝化反应的微生物具有抑制作用，从而实现N₂O减排。（5）利用2010和2011年实测的田间试验数据对DNDC模型的验证结果表明，DNDC模拟的不同处理下土壤呼吸季节总量、N₂O排放季节总量、春玉米产量与田间观测较一致，模拟值与观测值的均方根误差（RMSE）基本控制在8%以内；且能较准确的模拟再现土壤呼吸和N₂O排放动态。表明应用DNDC模型进一步评价春玉米农田固碳减排措施具有可靠性。（6）应用DNDC模型评价不同管理措施固碳减排长期效果的结果表明，在50年时间尺度上，优化施氮措施（OPT、CRF、OPT+DCD）不会显著影响作物产量（与FP相比），并可以不同程度降低N₂O排放（分别减少8%、13%、12%），但这些措施下土壤有机碳增加较小。在优化施氮措施基础上采取秸秆还田，能在保障产量的同时有效增加土壤固碳，大幅减少春玉米种植系统温室气体净排放，从长期看是一项有效的固碳减排措施。更多还原

【Abstract】 In China, amounts of nitrogen （N） fertilizer applied in croplands have been increasing to maintainoptimum yield. The use of N fertilizer plays an important role in ensuring food security. However,overuse of N fertilizer is widespread in crop productions, which has caused severe damages toenvironment. Spring maize is one of the most important crops in Northeastern China. To increase soilfertility and sustain high maize yield, overuse of N fertilizer is widespread in the maize fields in thisregion. The overuse of N fertilizer and intensive tillage could stimulate high emissions of greenhousegases from the maize production in Northeastern China. Therefore, it is crucial for sustaining the maizeproduction systems to reduce emissions of greenhouse gases meanwhile maintain the optimum yields byoptimizing farming management practices. In this study, we focus on mitigating emissions ofgreenhouse gases from maize fields in Western Liaoning Province through optimizing farmingmanagement practices. Field studies, soil microbiology experiments and modeling approach have beenadopted to achieve the research objectives. The results and conclusions from our study were descried asfollowing.（1） The field observations indicate that the high N₂O fluxes were mainly induced by applications ofN fertilizer or rainfall events. The means of seasonal cumulative N₂O emissions and soil respirationswere1.14±0.19kg N ha^-1and2019±264kg C ha^-1, respectively, under farmer’s conventionalfertilization practice （FP） during2009to2012. The inter-seasonal coefficient of variation of seasonalcumulative N₂O emissions and soil respirations were17%and13%, respectively. Further investigationsindicate that the N₂O fluxes were positively correlated （P <0.01） with soil mineral N contents and thesoil respirations were exponentially correlated （P <0.01） with soil temperatures and negativelycorrelated with soil moistures （P <0.01）.（2） Field studies were performed to quantify impacts of alternative N fertilization andincorporation of maize straw on emissions of greenhouse gases and maize yields. In comparison withFP, reducing N application rates by20%（OPT） didn’t significantly mitigate N₂O emissions from thetested field, although slightly reduction can be found under OPT. The treatments with slow-releasefertilizer （CRF） or nitrification inhibitor （OPT+DCD） significantly mitigated N₂O emissions from thetested field, while the crop yields remained unchanged. In comparison with FP, the seasonal cumulativeN₂O emissions in2009and2010were significantly reduced by10%and13%, respectively, under theCRF treatment; the seasonal N₂O emissions in2011and2012were significantly reduced by22%and31%, respectively, under the OPT+DCD treatment. The N₂O emissions under the treatment with maizestraw incorporation （OPTS） were highest among all the treatments in this study, indicating that theincorporation of maize straw increased N₂O emissions from the tested field.（3） The seasonal variation of soil respirations was mainly controlled by crop growth, soiltemperature and incorporation of maize straw in this study. In comparison with the treatments withoutincorporation of crop straw, OPTS obviously stimulated the rates of soil respiration during early stage of maize growing seasons. The means of seasonal cumulative soil respirations during the maize growingperiods from2009to2012were1891.2±59.0kg C ha^-1,1939.3±39.6kg C ha^-1,1945.2±46.3kg C ha^-1,and2096.4±156.8kg C ha^-1, respectively, under CK, FP, OPT, and OPTS. The mean of seasonalcumulative soil respirations was2320.8±102.5kg C ha^-1under CRF during the maize growing periodsin2009and2010. For the OPT+DCD treatment, the mean of seasonal cumulative soil respirations was1759.2±78.0kg C ha^-1during the maize growing periods in2011and2012. Our study indicates thatalternative management practices on N application didn’t obviously affect soil respirations.（4） Soil microbiology experiments were performed during the top-dressing periods in2012. Soilnitrifying and denitrifying bacteria were quantified at the field plots under different treatments toinvestigate the mechanisms resulting in different N₂O emissions among the treatments. The results fromthe soil microbiology experiments show that the average copy numbers of AOB amoA, AOA amoA, andnirS were0.1×105(g SDW^-1),0.2×105(g SDW^-1),0.5×107(g SDW^-1) under CK treatment, respectively;and these values were obviously lower than that under all the treatments with N additions. The soilmicrobiology experiments indicate that the addition of N fertilizer can stimulate the growth of AOB,AOA and nirS gene of denitrifying bacteria, and subsequently stimulate the N₂O emissions. The soilnitrifying and denitrifying microorganism under OPT+DCD were lowest among all the treatments withaddition of N fertilizer, indicating that the OPT+DCD treatment can restrict soil nitrifying anddenitrifying microorganism, and thereby mitigate N₂O emissions.（5） The DNDC model was tested against the filed observations from2010to2011. The resultsfrom the model validation indicate that the simulations of maize yields and seasonal cumulative soilrespirations and N₂O emissions are consistent with the observations. The RMSEs between thesimulations and field observations are less than14%. In addition, DNDC can generally capture thetemporal pattern of daily soil respirations and N₂O emissions. These results indicate the reliability ofusing DNDC to assess the impacts of alternative management practices on crop production andemissions of CO2and N₂O from spring maize fields.（6） We utilized the DNDC model to assess the long-term impacts of alternative managementpractices on maize production and emissions of CO2and N₂O. The modeled impacts of alternativefertilization and crop residue management practices can be summarized as follows: a) optimizing Nfertilization （OPT, CRF, and OPT+DCD） can decrease N₂O emissions （8%,13%, and12%, respectively,for OPT, CRF, and OPT+DCD） while maintain maize yields, however, only slightly increase of soilcarbon can be achieved by optimizing N fertilization; b) optimizing N fertilization in combination withcrop straw amendment may significantly increase soil carbon sequestration, and decrease emissions ofgreenhouse gases while maintain maize yields.更多还原