【作者】 黄涛；

【导师】 巨晓棠； Joachim Ingwersen； Thilo Streck；

【作者基本信息】 中国农业大学 ， 植物营养学， 2014， 博士

【摘要】 长期碳氮投入是华北平原保证粮食安全的主要措施之一,但也深刻地影响着该地区碳氮的生物地球化学循环。如何保证粮食产量、实现环境友好和提升土壤质量一直是该区重要的科学问题。本研究以四种不同的氮肥管理措施(对照不施氮、基于Nmin测试法的优化施氮、基于氮素平衡计算法的施氮和农民传统施氮)和两种不同的秸秆管理措施(秸秆还田与秸秆不还田)的长期定位试验为基础,通过田间原位观测,系统的研究了连续7年不同碳氮投入对作物产量、氮素利用、硝酸盐淋洗及N20排放的影响；通过室内培养试验,分析了长期不同碳氮投入对土壤有机碳氮库、土壤团聚体及有机碳组分、土壤N20基础排放能力及硝化-反硝化潜势的影响；并结合其他农业措施的碳排放,综合计算了长期不同碳氮投入对作物生产体系的全球净温室效应(Net-GWP)及温室气体排放强度(GHGI)的影响。对长期作物产量及氮素利用的研究表明,与农民传统施肥方式(Ncon和C+Ncon)(11.3和11.6tha-1yr-1)相比,基于Nmin测试法的优化氮肥管理方式(Nopt和C+Nopt)能够减少52-57%的氮肥投入量,且未显著降低籽粒产量(10.8和11.3t ha-1yr-1);而与农民传统施肥方式相比,基于氮素平衡计算的氮肥管理方式(C+M和C+W)既能减少45-85%的化肥氮投入,还能提高籽粒产量(12.8和12.4t ha-1yr-1)。农民传统施肥长期大量氮肥投入会导致冬小麦和夏玉米秸秆的CN比下降,降低作物对逆境和病虫害的抗性；与不施肥处理相比,碳氮投入能够增强作物产量的稳定性,而长期基于氮素平衡计算的有机肥处理更有利于作物产量的长期稳定。对0-1m氮素平衡和淋洗量的研究表明,与不施肥对照相比,农民传统施肥方式(Ncon和C+Ncon)由于长期过量氮肥投入导致大量的NO3-N累积(0-1m分别为320-896和449-699kg N ha-1;1-2m分别为265-873和323-911kg N ha-1)、表观氮损失(7年平均,分别为281和272kg N ha-1yr-1)和硝酸盐淋洗(3年平均,分别为33.7和43.9kg N ha-1yr-1)。与农民传统施肥方式相比,基于Nmin测试和平衡计算的氮素管理方式能够显著地降低0-1m和1-2m的N03-N累积量、表观氮损失量和淋洗量(P<0.05)。过量氮肥投入下,秸秆还田促进淋洗；优化氮肥投入下,秸秆还田能够降低淋洗；而有机肥投入并未增加淋洗。淋洗量与土壤剖面的硝态氮累积量具有很好的线性关系,其淋洗量分别为土壤0-1m和1-2m的硝态氮累积量的4.2%和4.3%。对土壤N20排放和Net-GWP的研究表明,与农民传统处理的N20排放量(3.4--4.5kg N20-Nha-1yr-1)相比,基于Nmin测试法的优化施氮措施能够降低46.1-46.6%。与秸秆不还田相比,秸秆还田措施能够增加26-36%的N20排放,但同时也可以提升0-20cm土壤的SOC含量(26.1vs22.4g kg-1)。传统的农民管理措施能够造成4121-3041kg CO2-eq ha-1yr-1的Net-GWP,基于Nmin测试法的管理措施可以通过减少氮肥投入而降低Net-GWP(2594-2409kg CO2-eq ha-1yr-1);而基于氮素平衡计算的管理措施既可以通过减少氮肥投入,又可以通过增加SOC含量来降低Net-GWP,而且为GWP的汇(-1939至-3330kg CO2-eq ha-1yr-1).农民传统处理的GHGI为0.24-0.35kg CO2-eqkg-1籽粒,基于Nmin测试法和氮素平衡计算法的优化氮肥管理措施分别降低了27%和141%。该地区冬小麦-夏玉米轮作体系的主要排放源是灌溉电力消耗,氮肥的生产和运输以及土壤N20排放,而土壤SOC固持则为主要汇。对土壤有机碳氮库、团聚体及有机碳组分的研究表明,与试验开始前土壤有机碳(SOC)含量相比(7.7g kg-1),6年来,除No处理下降外(6.9g kg-1),其余处理均增加了8.8-40.6%的SOC。在秸秆不还田的情况下,与不施氮对照处理相比,长期基于Nmin测试法和农民传统的氮肥管理措施对0-20cm的有机碳库无明显影响(P>0.05),却显著增加了0-20cm的土壤氮库(P<0.05)。在秸秆还田的情况下,与不施氮对照处理相比,基于Nmin测试法对0-20cm的有机碳库和氮库均无明显影响(P>0.05),农民传统仅能显著增加0-20cm的有机碳库(P<0.05),对氮库却无显著影响(P>0.05),而平衡氮素计算却均能显著增加0-20cm的有机碳库和氮库(P<0.05)。与不施氮对照处理相比,其他所有处理对20-40、40-60cm的有机碳库和氮库均无明显影响(P>0.05)。与不施氮对照处理相比,基于Nmin测试法的氮肥管理措施并未显著增加>250μm的团聚体比重(P>0.05),也并未显著增加各粒级大小团聚体的碳含量(P>0.05),但其显著增加了cPOM中的有机碳碳含量(P<0.05)。而与不施氮对照处理相比,农民传统施肥管理措施并未显著增加各粒级大小团聚体的碳含量(P>0.05),但显著增加了>250μm的团聚体比重(P<0.05),而且还显著增加了各有机碳组分的有机碳含量(P<0.05)。而与不施氮对照处理相比,平衡氮素计算法的氮肥管理由于投入了大量的有机质,既显著增加了>250μm的团聚体比重(9.4-9.5%vs6.8-7.3%)(P<0.05),也显著增加了2000-250μm团聚体中的碳含量(31.4-39.9g C kg-1vs21.4-22.2g C kg-1)(P<0.05),而且还分别增加了12.2-40.7%(iPOM_m)和8.5-30.8%(s+c_m)的稳定性碳库中的有机碳含量。土壤团聚体的碳含量基本符合团聚体层次模型,有机质是该类型土壤团聚体形成过程中主要的胶结物质。长期氮素平衡计算的管理措施不仅能够增加土壤有机碳氮库的数量,而且还能提高其质量。对土壤N2O基础排放能力和硝化-反硝化势的研究表明,与对照处理相比,除C+M处理外,长期不同碳氮投入对N20的基础排放能力无显著影响(P>0.05)。土壤N20基础排放来源既有硝化作用又有反硝化作用。采用NO3-N产生量在该类型土壤上能够较为准确的反映土壤硝化潜势的能力,土壤的硝化潜势与土壤的NH4-N具有显著的正相关关系(P<0.05)。采用气态产物(N20和N2)的产生总量能够较准确的反映土壤反硝化潜势的能力,土壤的反硝化潜势与土壤的有机碳和全氮含量具有显著的正相关关系(P<0.05)。综上所述,从合理施用氮肥、保证作物产量、降低硝酸盐淋洗和GWP来看,基于Nmin测试法的氮肥管理措施是较为优化的碳氮管理措施,但该措施不仅对土壤有机碳氮库的数量无影响,而且还有降低质量的风险。而在综合考虑氮肥合理施用、稳定作物产量、降低环境效应和提升土壤质量来看,基于氮素平衡计算的有机肥处理是该地区优化的碳氮管理措施。在优化氮肥管理的同时,实施秸秆还田,能够起到一定的增产和降低环境效应的作用。在优化碳氮管理的同时,要注意重视对水分的优化管理。但是,这些优化的碳氮水管理措施仍需长周期的进一步验证和研究。更多还原

【Abstract】 Long-term carbon and nitrogen inputs is one of the main solutions to ensure the food security on North China Plain (NCP), which is also deeply effect the carbon and nitrogen biogeochemical cycles in this area. How to ensure food security simultaneously achieve environmental friendly and improve soil quality is always the important scientific problem in this area. We set up a long-term field experiment, which includes eight treatments with four nitrogen managements (zero-N control, improved Nmin, calculated N balance and conventional N) and two straw managements (straw removed and straw returned). Firstly, we systematic researched the effects of long-term carbon and nitrogen inputs on crop yield, N utilization, nitrate leaching and N2O emissions by the measurements in situ. Secondly, we systematic researched the effects of long-term carbon and nitrogen inputs on quantity of soil organic carbon and nitrogen, soil aggregates, soil organic carbon fractions, soil basal N2O emissions and potential nitrification and denitrification rates by the determinations in laboratory. At last, we calculate the effects of long-term carbon and nitrogen inputs on the net global warming potential (Net-GWP) and greenhouse gas intensity (GHGI) after integrated consider all carbon resource by all agricultural managements.Compared to conventional farming practice (Ncon and C+Ncon)(11.3and11.6t ha-1yr-1), the improved Nmin tested (Nopt and C+Nopt) could reduce52-57%fertilizer N inputs, but not obviously decreased the crop yield (10.8and11.3t ha-1yr-1). However, compared to conventional farming practice, the calculated N balance (C+M and C+W) could not only decrease45-85%fertilizer N inputs, but also slightly increase the crop yield (12.8and12.4t ha-1yr-1). The long-term conventional farming practice will be decrease the straw C:N ratio of wheat or maize since the excessive nitrogen input, which also make the plants to become more susceptible to insect attack and fungal diseases and can be prone to lodging. Compared to the control, the carbon and nitrogen inputs could enhance the yield stability. The organic fertilizer inputs from the calculated N balance could more benefit for the yield stability.Compared to the zero N treatments, the conventional farming practices have a large number of soil NO3-N accumulation (320-896and449-699kg N ha-1at0-1m depth, respectively;265-873and323-911kg N ha-1at1-2m depth, respectively), the vast apparent N loss (average281and272kg N ha-1yr-1in the whole7years, respectively) and nitrate leaching (average33.7and43.9kg N ha-1yr-1in the3years, respectively) since the N fertilizer overuse. Compared to conventional farming practice, the improved Nmin tested and calculated N balance could significantly reduce soil NO3-N accumulation at0-1m and1-2m depth, the apparent N loss, the nitrate leaching (P<0.05). On the condition of N fertilizer overuse, straw returning could stimulate nitrate leaching. On contrast, straw returning could decrease nitrate leaching under the optimum N input. Organic fertilizer input didn’t increase nitrate leaching. There is a good linear relationship between the soil profile NO3-N accumulation and nitrate leaching. The nitrate leaching is4.2%and4.3%of soil NO3-N accumulation at0-1m and1-2m, respectively, in this kind of soil climate condition on NCP.Compared to the conventional farming practice (3.4-4.5kg N20-N ha-1yr-1), the N2O emissions from the improved Nmin tested could reduce46.1-46.6%. Compared to the straw removed, straw returned could increase N2O emission by26-36%, which also could promote0-20cm SOC content (26.1vs22.4g kg-1). The Net-GWP from the conventional farming practice is4121-3041kg CO2-eq ha-1yr-1. The improved Nmin tested could decrease the Net-GWP by reducing the N fertilizer inputs, which is2594-2409kg CO2-eq ha-1yr-1. The calculated N balance could decrease the Net-GWP not only by reducing the N fertilizer inputs but also increasing the SOC content, which is-1939to-3330kg CO2-eq ha-1yr-1. The GHGI from the conventional farming practice is0.24-0.35kg CO2-eq kg-1grain. The improved Nmin tested and calculated N balance could decrease by27%and141%, respectively. The main emission sources are the power consumption for irrigation, fertilizer N production, and N2O emissions, with SOC sequestration providing the main emission sink.Compared to the initial SOC content (7.7g kg-1), all treatments increased by8.4-40.6%except No (6.9g kg-1) after6years later. On the condition of straw removed, compared to zero N treatment, the improved Nmin tested and conventional farming practice didn’t significantly increase the0-20cm SOC stocks (P>0.05), but significantly increase the0-20cm total nitrogen (TN) stocks (P<0.05). On the condition of straw returned, compared to the zero N treatment, the improved Nmin tested didn’t significantly increase the0-20cm SOC and TN stocks (P>0.05); the conventional farming practice only significantly increase the0-20cm SOC stocks (P<0.05), didn’t increase the0-20cm TN stocks (P>0.05); but the calculated N balance could significantly increase the0-20cm SOC and TN stocks (P<0.05). Compared to the zero N treatment, all treatments didn’t significantly increase the20-40and40-60cm SOC and TN stocks (P>0.05). Compared to the zero N treatment, the improved Nmin tested didn’t significantly increase the proportion of>250f.im soil aggregate and organic carbon (OC) content of all soil aggregates (P>0.05), but it significantly increase the OC content of all carbon fractions (P<0.05). Compared to the zero N treatment, the conventional farming practice didn’t significantly increase the organic carbon (OC) content of all soil aggregates (P>0.05), but it significantly increase the proportion of>250p.m soil aggregate and also significantly increase the OC content of all carbon fractions (P<0.05). However, compared to the zero N treatment, the calculated N balance not only significantly increase the proportion of>250μm soil aggregate (9.4-9.5%vs6.8-7.3%)(P<0.05) and OC content of2000-250μm soil aggregate (31.4-39.9g C kg-1vs21.4-22.2g C kg-1)(P<0.05), but also increase the OC content of iPOM_m and s+c_m by12.2-40.7%and8.5-30.8%, respectively, since a large number of organic matter input. The results of OC content of different carbon fractions support the concept of aggregate hierarchy, which also means that the organic matter is the main binding agents on the formation of soil aggregates. Long-term organic fertilizer inputs from the calculated N balance could not only increase the SOC and TN stocks, but also promote the quality of SOC.Long-term different carbon and nitrogen inputs didn’t significantly influence the soil N2O basal emissions except the C+M. The soil N2O basal emissions are not only from the nitrification but also the denitrification. It is a more precise indicator to reflect the potential nitrification rate by NO3-N generation on this kind of soil. There is a significant positive correlation between the soil potential nitrification rate and soil NH4-N content (P<0.05). Using the gaseous (N2O and N2) production to reflect the potential denitrification rate is a more accurate method on this kind of soil. There are significant positive correlations between the soil potential denitrification rate and SOC and TN content (P<0.05).In conclusion, judging from saving N fertilizer, ensuring crop yield, reducing nitrate leaching and Net-GWP, the improved Nmin tested is an optimum management. However, the improved Nmin tested not only didn’t increase SOC and TN stocks, but also risking decrease the quality of SOC. The organic fertilizer inputs from the calculated N balance is a more optimum management on NCP after integrated consider saving N fertilizer, stabling crop yield, reducing environmental effects and promoting quantity and quality of SOC and TN. Effects of optimizing nitrogen management and straw returning simultaneously would slightly on increasing crop yield and reducing environmental impacts. It is also very important to pay attention to optimum water management and concomitantly optimize carbon and nitrogen management. Nonetheless, these optimum carbon, nitrogen and water managements need to further research in the long-term field experiment.更多还原