【作者】 王晓云；

【导师】 蔡焕杰；

【作者基本信息】 西北农林科技大学 ， 农业水土工程， 2024， 博士

【摘要】 秸秆还田和氮肥投入是农田管理的常规措施,但若施用不当,不仅会造成作物产量和土壤肥力的降低,还可能引发温室气体及氨的大量排放,给环境造成不利影响。本研究基于2020～2022年的田间试验,以陕西关中夏玉米-冬小麦轮作体系为研究对象,采用两因素随机区组设计,深入探讨了秸秆还田和氮肥管理对水氮生产力以及生态系统固碳减排潜力的影响。试验因素一为氮肥管理,设置三种施氮管理措施:当地农户传统施氮量(N_FP,夏玉米270 kg N ha^-1;冬小麦200 kg N ha^-1)、优化氮肥施用量(N_OPT,夏玉米180 kg N ha^-1;冬小麦150 kg N ha^-1)和施用高效氮肥(N_EENF,夏玉米180 kg N ha^-1;冬小麦150 kg N ha^-1);因素二为作物秸秆,设置秸秆不还田（S₀）和秸秆还田（S）2个水平。本研究分析了不同秸秆还田和氮肥管理对土壤理化生性质、作物生产力、水氮利用效率以及CO₂、N₂O和NH₃气体排放的影响,并计算了净生态系统碳收支（NECB）和净增温潜势（NGWP）,最后利用Topsis熵权法综合评价了不同处理对作物-土壤-环境效益-经济效益的影响。主要得到以下结果:（1）探明了不同秸秆还田和氮肥管理对麦玉轮作系统土壤物理、化学和生物学性质的影响。相较于单施氮肥处理,秸秆还田配施氮肥显著改善了土壤物理、化学和生物学性质。首先,秸秆还田配施氮肥通过减少土壤水分蒸发和阻碍毛细作用,使平均土壤含水量（SWC）显著增加了7.11%（P<0.05）。其次,秸秆腐解产物补充了土壤活性碳氮组分,使可溶性碳氮（DOC和DON）、微生物碳氮（MBC和MBN）以及NH₄⁺-N和NO₃^--N含量分别平均显著增加了36.37%、19.95%、29.97%、28.93%、18.61%和14.30%（P<0.05）。此外,其为土壤微生物提供丰富的碳氮源,使纤维素酶、蔗糖酶和脲酶的活性（CE、SC和UR）分别平均增加了35.75%、25.58%和20.77%。同时,使AOB-amo A、nir K、nir S和nos Z基因丰度的平均值分别增加了74.80%、37.97%、8.16%和15.04%。另外,与N_OPT处理相比,N_EENF处理使基肥和追肥第3天的UR活性平均显著降低了29.27%,使平均NH₄⁺-N和NO₃^--N含量分别下降了2.89%和5.04%,使AOB-amo A、nir K和nir S的基因丰度平均值分别显著下降了46.40%、47.91%和14.82%。（2）阐明了秸秆还田和氮肥管理对麦玉轮作系统生产力和水氮利用效率的影响。秸秆还田配施氮肥在改善土壤物理、化学和生物学性质的基础上,提升了麦玉轮作系统的生产力和水氮利用效率,提升效果在夏玉米更为显著。在夏玉米季,秸秆还田配施氮肥提高了叶面积指数（LAI）和地上部生物量（AGB）,并使产量、水分利用效率（WUE）、氮肥偏生产力（PFP_N）和氮肥表观利用率（RE_N）分别平均增加了18.12%、21.90%、14.47%和31.19%（P<0.05）。在冬小麦季,使籽粒产量、WUE、PFP_N和RE_N分别平均提高了4.65%、6.21%、5.97%和10.23%。此外,与N_FP处理相比,N_EENF处理不仅维持了夏玉米和冬小麦的籽粒产量,还使PFP_N和RE_N分别平均提高了43.56%和47.53%;此外,N_EENF和N_OPT处理在作物生长、籽粒产量以及水氮利用效率均未产生显著差异。（3）揭示了驱动麦玉轮作系统的土壤呼吸（Rs）和生态系统呼吸（Re）的非生物和生物环境因子,探究了秸秆还田和氮肥管理对Rs、Re和净碳收支（NECB）的影响。环境非生物因子（Ts、SWC、DOC和秸秆碳含量Cr）和生物因子（MBC、CE、SC和LAI）均是麦玉轮作系统的Rs排放的驱动因子。在冬小麦播种～返青期,线性模型能较好解释Re排放通量与Ts的关系,平均解释率为47.5%。在返青～抽穗期,SWC和Ts与Re的关系均可用线性模型描述（R²=0.22～0.58）。冬小麦Re通量与AGB呈显著正相关,AGB平均解释了Re通量变异的65.1%。此外,与单施氮肥相比,秸秆还田配施氮肥显著提高了年Rs和Re排放量,分别平均增加35.97%和28.42%。这归因于其显著增加了土壤呼吸底物（Cr和DOC）和SWC,提高了土壤微生物量和酶活性。此外,单施氮肥处理的年NECB为负值(-1.89～-1.19 t C ha^-1 yr^-1),而秸秆还田配施氮肥处理因有较高的碳投入使得年NECB为正值(1.41～1.94 t C ha^-1 yr^-1)。这表明,秸秆还田配施氮肥处理增加的生态系统碳输入完全补偿了增加的碳输出,实现了土壤固碳。此外,麦玉轮作系统的土壤呼吸、生态系统呼吸和NECB值均不受氮肥管理的显著影响。（4）明确了土壤NH₃和N₂O排放的控制因素,揭示了秸秆还田和氮肥调控对NH₃挥发和N₂O气体排放的影响机制。在土壤NH₃高排放期,土壤NH₃排放受SWC、NH₄⁺-N含量和UR活性调控。在夏玉米季,土壤N₂O排放主要受土壤无机氮（SIN）含量、AOB-amo A、nir K基因拷贝数以及SWC影响。在冬小麦季,调控N₂O排放的主控因子为SIN含量、Ts和SWC。此外,与单施氮肥处理相比,秸秆还田配施氮肥通过提高NH₄⁺-N含量和UR活性使土壤NH₃季节排放量平均显著增加了46.55%。在夏玉米季,其通过提高SIN含量、SWC以及AOB-amo A和nir K基因拷贝数使土壤N₂O季节排放量平均增加了69.04%。在冬小麦季,其通过提高SIN含量和SWC使N₂O季节排放量平均提高了77.22%。与N_OPT处理相比,N_EENF处理使夏玉米NH₃排放量降低了31.36%,这是因为其降低了基肥后一周内以及追肥高排放期的土壤NH₄⁺-N含量。对比N_OPT处理,N_EENF处理降低了AOB-amo A、nir K基因拷贝数以及基肥10天内和追肥高排放期的SIN含量,使夏玉米N₂O排放量降低了42.06%。N_EENF处理通过降低土壤SIN含量减少了冬小麦52.86%的NH₃排放量和36.97%的N₂O排放量。（5）计算了不同秸秆还田和氮肥管理下的净增温潜势（NGWP）,综合评价了不同处理的经济效应和环境效应,提出了本研究条件下兼顾作物、土壤和环境效益的最佳组合。本研究利用并改进了以往计算NGWP的方法,基于生态系统内固碳载体的多样性,从CO₂当量排放、土壤固碳和籽粒固碳等方面对不同处理的NGWP进行了全面评估。在两年麦玉轮作系统中,与单施氮肥处理相比,秸秆还田配施氮肥由于增加了GWP_N2O和GWP_indirect而显著增加了NGWP₁,增幅为21.24%～31.84%。然而,秸秆还田配施氮肥也增加了GWP_ΔSOC,这一积极效应有效地中和了GWP_N2O和GWP_indirect的增加,最终使NGWP₂显著降低了17.90%～38.69%。若考虑作物籽粒的固碳,全部处理的NGWP₃～NGWP₆均为负值,这表明这两年轮作系统为碳汇。Topsis熵权法综合评价结果显示秸秆还田配施氮肥优于秸秆不还田处理,以SN_EENF最优。这说明,在本研究条件下,秸秆还田配施高效氮肥(夏玉米施氮量180 kg N ha^-1;冬小麦施氮量150 kg N ha^-1)是关中夏玉米-冬小麦轮作系统维持作物生产力和促进固碳减排的较优农田管理策略。综上所述,秸秆还田配施氮肥能显著改善土壤理化生物学性质,同时提高作物生产力和土壤固碳能力,降低农田净增温潜势,有助于农田固碳减排能力的提高,其中以秸秆还田配施高效氮肥效果最为显著,其是兼顾作物、土壤和环境效益的最佳组合。更多还原

【Abstract】 Straw returning and nitrogen fertilizer inputs are routine measures for agricultural field management,but if they are not applied properly,they will not only cause a reduction in crop yield and soil fertility,but may also trigger a large amount of greenhouse gases and ammonia emissions,which will have a negative impact on the environment.In this study,based on a field trial from 2020 to 2022,the effects of straw returning and nitrogen fertilizer management on crop productivity as well as ecosystem carbon sequestration and emission reduction potentials were investigated in depth using a two-factor randomised block design with the summer maize-winter wheat rotation system in Guanzhong,Shaanxi Province,as the research object.The first factor of the experiment was N fertilizer management,and three types of N application management measures were set up:traditional N application by local farmers(NFP,270 kg N ha^-1 for summer maize and 200 kg N ha^-1 for winter wheat),optimised N fertilizer application(NOPT,180 kg N ha^-1 for summer maize and 150 kg N ha^-1 for winter wheat),and high efficiency N fertilizer application(NEENF,180 kg N ha^-1 for summer maize and 150 kg N ha^-1 for winter wheat).The second factor is crop straw,and two levels of straw not returning to the field（S0）and straw returning to the field（S）are set.In this paper,we investigated the effects of different straw returning and nitrogen fertilizer management on soil physicochemical properties,crop productivity,water and nitrogen use efficiency,and CO2,N2O and NH3 gas emissions,and calculated the net ecosystem carbon balance（NECB）and net warming potential（NGWP）,and finally evaluated the effects of different treatments on crop-soil-environmental benefits-economic benefits comprehensively by using the Topsis entropy weighting method.The following results were mainly obtained:（1）The effects of different straw returning and nitrogen fertilizer management on the physical,chemical and biological properties of soils in wheat-maize rotation system were investigated.Compared with the single N fertilizer treatment,the straw returning with N fertilizer significantly improved the physical,chemical and biological properties of the soil.Firstly,the average soil water content（SWC）was significantly increased by 7.11%（P<0.05）by reducing soil water evaporation and hindering capillary action.Secondly,straw decomposition products supplemented the soil active carbon and nitrogen fractions,which significantly increased the soluble carbon and nitrogen（DOC and DON）,microbial carbon and nitrogen（MBC and MBN）,as well as NH4⁺-N and NO3^--N contents by an average of 36.37%,19.95%,29.97%,28.93%,18.61%,and 14.30%,respectively（P<0.05）.In addition,its provision of rich carbon and nitrogen sources for soil microorganisms increased cellulase,sucrase and urease activities（CE,SC and UR）by an average of 35.75%,25.58%and 20.77%,respectively.Also,it increased the mean values of AOB-amo A,nir K,nir S and nos Z gene abundance by 74.80%,37.97%,8.16%and 15.04%,respectively.In addition,compared to NOPT treatment,NEENF treatment significantly reduced UR activity by 29.27%on average on day 3 of basal and supplementary fertilizer,decreased the average NH4⁺-N and NO3^--N content by 2.89%and5.04%,respectively,and significantly decreased the average gene abundance of AOB-amo A,nir K and nir S by 46.40%,47.91%,and 14.82%,respectively.（2）The effects of straw returning and nitrogen fertilizer management on the productivity and water and nitrogen use efficiency of the wheat-maize rotation system were elucidated.Based on the improvement of physical,chemical and biological properties of soil,N fertilizer with straw returning enhanced the productivity and water and N use efficiency of the wheat-maize rotation system,and the enhancement effect was more significant in summer maize.In the summer maize season,straw returning with N fertilization increased leaf area index and aboveground biomass,and increased yield,water use efficiency（WUE）,nitrogen fertilizer bias productivity（PFPN）,and nitrogen fertilizer apparent utilization（REN）by an average of 18.12%,21.90%,14.47%,and 31.19%（P<0.05）,respectively.During the winter wheat season,it resulted in an average increase of 4.65%,6.21%,5.97%,and 10.23%in yield,WUE,PFPN and REN,respectively.In addition,the NEENF treatment not only maintained yield in summer maize and winter wheat,but also increased PFPN and REN by an average of 43.56%and 47.53%,respectively,compared with the NFP treatment;furthermore,no significant differences were observed between the NEENF and NOPT treatments in terms of crop growth,yield,and water and nitrogen use efficiency.（3）Abiotic and biotic environmental factors driving soil respiration（Rs）and ecosystem respiration（Re）in the wheat-maize rotation system were revealed,and the effects of straw returning and nitrogen fertilizer management on Rs,Re and net carbon balance（NECB）were explored.Both environmental abiotic factors（Ts,SWC,DOC and straw carbon content Cr）and biotic factors（MBC,CE,SC and LAI）were the drivers of Rs emission in the wheat-maize rotation system.During the sowing～greening period of winter wheat,the linear model explained the relationship between Re emission and Ts better,with an average explanation rate of 47.5%.At the greening-tasseling stage,both SWC and Ts in relation to Re could be described by the linear model（R²=0.22-0.58）.The Re flux was significantly and positively correlated with AGB in the winter wheat season,and AGB explained 65.1%of the variation in Re flux on average.In addition,straw returning with N fertilizer significantly increased annual Rs and Re emissions by an average of 35.97%and 28.42%,respectively,compared to N fertilizer alone.This was attributed to its significant increase in soil respiratory substrates（Cr and DOC）and SWC,improved soil microbial load and enzyme activities.In addition,the annual NECB was negative(-1.89 to-1.19 t C ha^-1 yr^-1)in the N fertilizer alone treatment,while it was positive(1.41 to 1.94 t C ha^-1 yr^-1)in the straw with N fertilizer treatment due to higher carbon inputs.This indicated that the increased ecosystem carbon input of the straw-returning with N fertilizer treatment fully compensated for the increased carbon output,and soil carbon sequestration was achieved.In addition,soil respiration,ecosystem respiration and NECB values of the wheat and maize rotation system were not significantly affected by N fertilizer management.（4）The controlling factors of soil NH₃ and N₂O emissions were clarified,and the mechanisms of straw return and nitrogen fertiliser regulation on NH₃ volatilisation and N2O gas emissions were revealed.During the period of high soil NH3 emission,soil NH3 emission was regulated by SWC,NH₄⁺-N content and UR activity.In the summer maize season,soil N₂O emission was mainly affected by soil inorganic nitrogen（SIN）content,AOB-amo A,nir K gene copy number,and SWC.In the winter wheat season,the main controlling factors of N2O emission were SIN content,Ts and SWC.In addition,compared with the treatment of N fertiliser alone,the application of N fertiliser with straw returned to the field significantly increased soil NH3seasonal emission by 46.55%on average by increasing NH4⁺-N content and UR activity.In the summer maize season,it increased soil N2O seasonal emissions by an average of 69.04%by increasing SIN content,SWC,and AOB-amo A and nir K gene copy number.In winter wheat season,it increased N2O seasonal emissions by 77.22%on average by increasing SIN content and SWC.The NEENF treatment reduced summer maize NH3 emissions by 31.36%compared to the NOPT treatment due to its reduction in soil NH4⁺-N content during the week after basal fertiliser and during the high emission period of follow-up fertilizer.Compared to the NOPT treatment,the NEENF treatment reduced summer maize N2O emissions by 42.06%by lowering the AOB-amo A,nir K gene copy number,and SIN content within 10 days of basal fertiliser and during the high emission period of follow-up fertiliser.The NEENF treatment reduced winter wheat NH3 emissions by 52.86%by lowering the soil SIN content and by 36.97%by reducing N2O emissions.（5）The net greenhouse warming potential（NGWP）under different straw return and nitrogen fertilizer management was calculated,and the economic and environmental effects of the different treatments were comprehensively evaluated,and the optimal combinations that take into account crop,soil and environmental benefits were proposed under the conditions of this study.In this study,we utilised and improved the previous methods for calculating NGWP,and based on the diversity of carbon sequestration carriers in the ecosystem,we comprehensively evaluated the NGWP of different treatments in terms of CO2 equivalent emission,soil carbon sequestration and seed carbon sequestration.In the two-year wheat-yuk rotation system,straw return with N fertiliser significantly increased NGWP1 by 21.24%-31.84%due to the increase of GWPN2O and GWPindirect compared with the N fertilizer alone treatment.However,N fertilization with straw returning also increased GWPΔSOC,and this positive effect effectively neutralised the increase in GWPN2O and GWPindirect,which eventually reduced NGWP2significantly by 17.90%to 38.69%.If the carbon sequestration of crop seeds was considered,the NGWP3-NGWP6 of all treatments were negative,which indicated that the crop rotation system was a carbon sink in these two years.The results of the comprehensive evaluation of Topsis entropy weighting method showed that straw returned to the field with nitrogen fertiliser was superior to straw not returned to the field treatments,and optimal with SNEENF.This suggests that under the conditions of this study,straw returing with high efficiency N fertiliser(180 kg N ha^-1 for summer maize;150 kg N ha^-1 for winter wheat)is a better farmland management strategy to maintain crop productivity and promote carbon sequestration and emission reduction in the Guanzhong summer maize-winter wheat rotation system.In summary,the application of N fertilizers with straw returning can significantly improve the physicochemical and biological properties of the soil,simultaneously increase crop productivity and soil carbon sequestration capacity,reduce the net warming potential of the farmland,and contribute to the improvement of the carbon sequestration and emission reduction capacity of the farmland,of which the effect of straw returned to the field with high-efficiency nitrogen fertilisers was most obvious,which is the optimal combination of the benefits of the crop,the soil and the environment.更多还原