农田温室气体净排放研究进展

农业是温室气体排放的主要排放源之一,农业温室气体减排对全球温室气体排放具有重要贡献,研究农田温室气体净排放潜力亦具有重要现实意义.本文阐述了农田温室气体净排放的涵义,并归纳总结了耕作方式、施肥、水分管理、间套作等农业措施对农田土壤有机碳(SOC)含量、农田土壤N2O和CH4、农田生产物资的使用所造成的温室气体(主要为CO2、N2O和CH4)排放的影响,结果表明:保护性耕作总体能提高表层SOC含量,减少CH4排放,但减少农田土壤N2O排放的研究尚存在一定的争议,耕作方式亦影响投入,从而影响温室气体的排放；施肥(特别是配施)能提高SOC含量.施氮肥越多,N2O排放量越大,而CH4主要受有机物料的影响较大；水分对减少N2O和CH4排放有相反作用,需综合进行平衡管理；不同的作物品种、间套作模式或促进或减少温室气体排放.此外,本文指出了国外在该领域的研究注重从系统角度考虑农田温室气体排放,而国内的研究则非常少,提出我国农田温室气体净排放可作为未来研究的一个重点,并对未来研究内容进行了初步归纳总结.     

华北集约高产农田温室气体净排放研究初探

本文以华北高产粮区山东桓台冬小麦-夏玉米轮作模式为例,借鉴LCA模型,初步探讨了华北平原通过长期大规模秸秆还田后温室气体排放的汇源问题。结果表明:综合考虑农资系统和农作系统,该模式表现为源,每各生产1 t冬小麦-夏玉米净温室气体排放量为-1 075.71kgCO2e;但具体到农作生产系统,轮作模式下农田生态系统固碳均值为+262.31 kgCO2e,能够抵消因施肥造成的-222.99 kgCO2e排放,并部分抵消机械燃油燃烧排放。因此,农作系统在坚持秸秆还田基础上,进一步改进耕作措施,具有成为温室气体排放汇的可能性。     

秸秆还田对稻田温室气体排放的影响:Meta分析——以长江中下游地区为例

全球气候变暖是人类面临的严峻挑战,稻田生态系统在全球气候变暖中起到重要的作用。目前已有许多学者通过大田试验的方法研究了不同秸秆还田方式下温室气体排放的特征,但由于试验地点等因素的不同导致最终的结果差异很大。通过整合这些结果来研究区域内不同秸秆还田方式(翻耕秸秆还田(CTS)、免耕秸秆还田(NTS)和旋耕秸秆还田(RTS))下稻田温室气体排放的特征,能够准确地反映一定区域内稻田生态系统的净减排潜力。本文基于长江中下游地区32篇关于秸秆还田对稻田温室气体排放的文献收集173组数据,利用Meta分析方法研究了3种秸秆还田方式下稻田CH_4和N_2O排放的特征,并估算出不同秸秆还田方式下稻田的全球增温潜势和净增温潜势。结果表明,CTS、NTS和RTS处理下稻田CH_4周年排放的效应值分别为0.76、0.37和0.68,稻田N_2O周年排放的效应值分别为0.44、0.36和0.52;在两熟制下,不同秸秆还田方式下稻田CH_4周年排放的效应值的大小为RTSCTSNTS,但N_2O周年排放的效应值的大小为RTSNTSCTS。在三熟制下,三种秸秆还田方式下稻田CH_4的周年排放的效应值的高低为CTSRTSNTS,而N_2O周年排放的效应值的高低为RTSNTSCTS。在相同的秸秆还田方式下,三熟制稻田温室气体周年排放的效应值都高于两熟制。此外,不同的还田秸秆种类影响稻田温室气体的排放;结合前期研究,估算出CTS、NTS和RTS处理下稻田的净增温潜势分别为12 375.55、11 232.36和15 982.87 kg CO_2-equivalent·hm~(-2)。因此,免耕秸秆还田是长江中下流地区稻田净减排条件下适宜的秸秆还田方式。     

土地利用变化及林业温室气体排放核算制度与方法实证

土地利用变化及林业(LUCF)活动是生态固碳最重要手段。研究确定LUCF温室气体排放核算制度和方法,对平衡碳排放、开展全国统一碳市场交易具有重要基础作用。在综述LUCF温室气体核算理论和方法基础上,借鉴IPCC指南和《省级温室气体清单编制指南(试行)》推荐的基本方法,构建了符合地域特色的LUCF温室气体排放核算制度和方法。采用2014年第九次国家森林资源清查数据,以全国低碳试点省陕西省为实证对象,初步核算了陕西省LUCF温室气体的净排放量,并从排放能力、排放结构和空间特征等角度揭示了陕西省LUCF温室气体的排放特征。结果显示:(1)2014年,陕西省LUCF温室气体净吸收量为1 698.42万t CO_2e,其中森林及其他木质生物质碳贮量净吸收1 852.67万t CO2e,森林转化净排放154.25万t CO_2e。(2)乔木林等优势树种,是陕西省LUCF温室气体排放中重要的固碳源(吸收源)。(3)陕南地区是重要固碳贡献区,陕北地区森林固碳能力较差。最后,针对LUCF温室气体排放核算制度和方法不够完善、森林固碳能力差异较大、区域固碳分化严重等问题,提出了健全温室气体核算制度、平衡森林资源空间分布、改善固碳树种结构等加强陕西省LUCF活动应对气候变化统计核算制度和能力建设的基本措施。     

土地利用变化对碳排放的影响

大气中温室气体浓度增加是人类面临的严峻挑战.土地利用变化已成为仅次于化石能源燃烧的第二大温室气体排放源.本文在界定土地利用变化碳排放作用机制及内涵的基础上,从农用地向非农用地转换、农用地内部土地利用以及非农用地内部土地利用三个方面综述了土地利用变化对碳排放的影响.农用地向非农用地的转换会增加碳排放量.农用地内部土地利用变化方面,农田转换为森林或草地能够使土壤和植被碳储量增加,但是土壤碳汇集速率存在一定的差异；农田、森林和草地管理措施对生态系统碳循环的影响目前还存在争议,但基本观点是合理的管理措施能够减少碳排放置.非农用地内部土地利用变化方面,从能源消耗角度考虑,二产用地向三产用地转换会减少碳排放量.因此合理组织土地利用对帮助我国实现碳减排承诺,发展低碳经济有重要意义.     

广东省碳源碳汇现状评估及增加碳汇潜力分析

以生态系统为研究对象,分析生态系统内部各种温室气体排放源,得到2005-2008年广东省主要排放源CO2排放量估算结果,2005年为6.19亿t,2008年达到7.4亿t。首要排放源是化石燃料燃烧,其次是土壤呼吸。两者占总排放量的77%-79%。其中土壤呼吸的排放量比较稳定,基本上保持在2.27亿t左右(或6 200万t碳),而化石燃料燃烧的排放量呈现出明显的增长趋势,从2005年的2.57亿t CO2(或7 021万t碳)增加到2008年的3.44亿t CO2(或9 375万t碳),4年增长了33.52%。其他排放源由大而小依次为:生物质转化、工业过程和人畜呼吸。2005-2008年全省主要碳汇总的CO2吸收量变化于2.53亿-2.56亿t(CO2)之间。2008年,全省最大的碳汇是林地,年固碳量达4 831万t碳,约合17 715万t CO2;其次为耕地,年固碳量为1 418万t碳,约合5 201万t CO2。这两类固碳地吸收的CO2占了全省碳汇的90%。源汇相抵后,全省净排放量从2005年的3.63亿t增加到2008年的4.86亿t。人均CO2排放量从2005年的3.95 t/人增加到2008年的5.09 t/人。单位GDP排放量则从2005年的1 625 kg/万元下降到2008年的1 361 kg/万元。在此基础上分析了增加碳汇的潜力。其中推广冬种绿肥每年可增加吸收CO22 155万t。将全省现有未成林地全部实行封山育林,约2年后每年可以增加吸收CO21 000万t。同时还建议利用海洋的生物生产力增加碳汇。     

水库温室效应研究进展与主要影响因素分析

温室气体排放导致的全球变暖成为世界各国关注的焦点。目前，关于淡水水库的温室效应在全球气候变化中的作用也成为了科学家争论的问题。已有的研究表明，世界上很多为水力发电或其他目的建造的水库，因水库蓄水所导致土壤和植被的淹没而额外增加碳基温室气体二氧化碳（CO2）和甲烷（CH4）的释放。通过对国内外关于淡水水库温室气体研究方面文献的归纳，综述分析了水库温室效应观测研究案例、〖JP2〗水库温室气体的产生机制、排放过程及其主要影响因素等方面的研究进展。为进一步从事水库温室气体研究、把握水库温室气体排放提供参考     

不同麦秸还田方式对周年稻麦轮作农田碳足迹的影响

为明确麦秸不同还田方式对稻麦轮作农田碳足迹的影响，该研究通过开展两年的大田试验，设计了3种麦秸还田方式（麦秸旋耕还田、麦秸翻耕还田和麦秸沟埋还田），并以麦秸不还田为对照，采用静态箱-气相色谱法连续两年对农田温室气体排放进行监测，并对不同麦秸还田方式的生产资料投入和生产过程碳排放及温室气体排放进行全面分析。结果表明：(1）与不还田相比，麦秸还田显著增加了稻季日均CH4排放，稻麦周年全球增温潜势95%来自稻田CH4排放；（2）在水稻季，农田CH4排放占碳足迹总量比例最大，3种麦秸还田方式中，麦秸沟埋还田处理下碳足迹最小，且能比麦秸旋耕还田处理减少4.9%；(3）在小麦季，化肥投入造成的碳足迹所占比例最大，为64.5%~77.4%，其次是土壤N2O的排放；（4）从整个稻麦周年轮作系统来看，与麦秸旋耕还田和麦秸翻耕还田处理相比，麦秸沟埋还田处理能分别减少4.6%和3.6%的周年碳足迹及8.7%和4.9%的周年单位产量的碳足迹。因此，对于稻麦轮作地区，采用麦秸沟埋还田能在一定程度上降低农业生产过程中的碳足迹。     

洞庭湖区不同利用方式下农田土壤有机碳含量特征

土地利用方式是影响土壤有机碳含量和动态的重要因子之一。其利用方式的改变必将引起土壤有机碳含量发生相应的变化。在洞庭湖腹地选取典型样区，通过调查走访和密集取样，分析了不同土地利用方式（旱地、水旱轮作地、一季稻水田和双季稻水田）下623个农田耕层土样有机碳含量。结果表明，研究区内土壤有机碳含量高低顺序为双季稻水田（28.12 g/kg） > 一季稻水田（27.03 g/kg） > 水旱轮作地（24.79 g/kg） > 旱地（17.96 g/kg），其差异均达到极显著水平（P < 0.01）。土地生产力、秸秆还田量和土壤水文状态是导致不同利用方式下耕层土壤有机碳含量差异的主要原因。进一步分析表明：加强作物秸秆还田（土）、提高土地复种指数、增加地表覆盖是维持和提高洞庭湖区耕作土壤有机碳含量的可行措施，尤其是旱作土壤。     

吉林省玉米农田保护性耕作的环境影响评价

以吉林省玉米农田4种保护性耕作为例,应用生命周期评价方法(Life Cycle Assessment,LCA)系统综合地评价吉林省玉米农田不同保护性耕作模式对环境的潜在影响。结果表明,四种保护性耕作模式的能源消耗、温室气体排放、环境酸化和富营养化的潜在环境影响分别平均比传统耕作模式减少14.62%、82.82%、15.37%和15.28%,主要由氮肥的生产及施用引起;水体毒性、土壤毒性及人体毒性则分别比传统耕作高7.40%、6.42%和7.38%,主要由农药的施用引起。综合各种环境影响类型,尽管4种保护性耕作模式较传统耕作模式能显著减缓全球变暖,但对其他环境类型的改变不明显,其中水体毒性为该种植系统中最主要的环境影响类型,富营养化次之。     

Estimation of Soil Carbon Gains Upon Improved Management within Croplands and Grasslands of Africa

Many agro(eco)systems in Africa have been degraded as a result of past disturbances, including deforestation, overgrazing, and over exploitation. These systems can be managed to reduce carbon emissions and increase carbon sinks in vegetation and soil. The scope for soil organic carbon gains from improved management and restoration within degraded and non-degraded croplands and grasslands in Africa is estimated at 20–43 Tg C year^?1, assuming that 'best' management practices can be introduced on 20% of croplands and 10% of grasslands. Under the assumption that new steady state levels will be reached after 25 years of sustained management, this would correspond with a mitigation potential of 4–9% of annual CO₂ emissions in Africa. The mechanisms that are being put in place to implement the Kyoto Protocol - through C emission trading - and prevailing agricultural policies will largely determine whether farmers can engage in activities that enhance C sequestration in Africa. Mitigation of climate change by increased carbon sequestration in the soil appears particularly useful when addressed in combination with other pressing regional challenges that affect the livelihood of the people, such as combating land degradation and ensuring food security, while at the same time curtailing global anthropogenic emissions.     

Climate change mitigation and productivity gains in livestock supply chains: insights from regional case studies

Livestock can contribute to climate change mitigation by reducing their greenhouse gas emissions and by increasing soil carbon sequestration. Packages of mitigation techniques can bring large environmental benefits as illustrated in six case studies modeled in the Global Livestock Environmental Assessment Model developed by FAO. With feasible technical interventions in livestock production systems, the mitigation potential of each of the selected species, systems and regions ranges from 14 to 41 %. While comparably high mitigation potentials were estimated for ruminant and pig production systems in Asia, Latin America and Africa, large emission reductions can also be attained in dairy systems with already high levels of productivity, in OECD countries. Mitigation interventions can lead to a concomitant reduction in emissions and increase in production, contributing to food security. This is particularly the case for improved feeding practices and better health and herd management practices. Livestock systems also have a significant potential for sequestrating carbon in pasturelands and rangelands through improved management, as illustrated in two of the six case studies in this paper.     

Soil management practices for sustainable agro-ecosystems

A doubling of the global food demand projected for the next 50 years poses a huge challenge for the sustainability of both food production and global and local environments. Today’s agricultural technologies may be increasing productivity to meet world food demand, but they may also be threatening agricultural ecosystems. For the global environment, agricultural systems provide both sources and sinks of greenhouse gases (GHGs), which include carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). This paper addresses the importance of soil organic carbon (SOC) for agro-ecosystems and GHG uptake and emission in agriculture, especially SOC changes associated with soil management. Soil management strategies have great potential to contribute to carbon sequestration, since the carbon sink capacity of the world’s agricultural and degraded soil is 50–66% of the historic carbon loss of 42–72 Pg (1 Pg=10¹⁵ g), although the actual carbon storage in cultivated soil may be smaller if climate changes lead to increasing mineralization. The importance of SOC in agricultural soil is, however, not controversial, as SOC helps to sustain soil fertility and conserve soil and water quality, and organic carbon compounds play a variety of roles in the nutrient, water, and biological cycles. No-tillage practices, cover crop management, and manure application are recommended to enhance SOC storage and to contribute to sustainable food production, which also improves soil quality. SOC sequestration could be increased at the expense of increasing the amount of non-CO₂ GHG emissions; however, soil testing, synchronized fertilization techniques, and optimum water control for flooding paddy fields, among other things, can reduce these emissions. Since increasing SOC may also be able to mitigate some local environmental problems, it will be necessary to have integrated soil management practices that are compatible with increasing SOM management and controlling soil residual nutrients. Cover crops would be a critical tool for sustainable soil management because they can scavenge soil residual nitrogen and their ecological functions can be utilized to establish an optimal nitrogen cycle. In addition to developing soil management strategies for sustainable agro-ecosystems, some political and social approaches will be needed, based on a common understanding that soil and agro-ecosystems are essential for a sustainable society.     

江西省县域农业碳排放的时空动态及影响因素分析

通过构建江西省农业碳排放测算体系，采用碳转化系数法对江西省县域农业碳排放进行了估算，并分析了2000~2010年江西省农业碳排放的时空动态及其影响因素。结果表明：（1）江西省农业碳排放总量从2000年的23085万t增长到2010年的29051万t，不同年份农业碳排放均主要源于化肥施用与农业机械使用；（2）全省农业碳排放量的空间分布呈现较为明显的集聚特征，主要年份高碳排放区均集中于鄱阳湖周边地区；碳排放强度多为Ⅱ级水平，空间分布上与碳排放量相比更为均衡；（3）江西省县域间农业碳排放的相对差异与绝对差异整体上均呈明显扩大的趋势；（4）生产效率、结构、劳动力等因素对农业碳排放有抑制作用，农业经济发展则促进碳排放量增加，农业碳排放还受社会、政策等影响     

Ecosystem carbon budgeting and soil carbon sequestration in reclaimed mine soil

Global warming risks from emissions of green house gases (GHGs) by anthropogenic activities, and possible mitigation strategies of terrestrial carbon (C) sequestration have increased the need for the identification of ecosystems with high C sink capacity. Depleted soil organic C (SOC) pools of reclaimed mine soil (RMS) ecosystems can be restored through conversion to an appropriate land use and adoption of recommended management practices (RMPs). The objectives of this paper are to (1) synthesize available information on carbon dioxide (CO2) emissions from coal mining and combustion activities, (2) understand mechanisms of SOC sequestration and its protection, (3) identify factors affecting C sequestration potential in RMSs, (4) review available methods for the estimation of ecosystem C budget (ECB), and (5) identify knowledge gaps to enhance C sink capacity of RMS ecosystems and prioritize research issues. The drastic perturbations of soil by mining activities can accentuate CO2 emission through mineralization, erosion, leaching, changes in soil moisture and temperature regimes, and reduction in biomass returned to the soil. The reclamation of drastically disturbed soils leads to improvement in soil quality and development of soil pedogenic processes accruing the benefit of SOC sequestration and additional income from trading SOC credits. The SOC sequestration potential in RMS depends on amount of biomass production and return to soil, and mechanisms of C protection. The rate of SOC sequestration ranges from 0.1 to 3.1 Mg ha(-1) yr(-1) and 0.7 to 4 Mg ha(-1) yr(-1) in grass and forest RMS ecosystem, respectively. Proper land restoration alone could off-set 16 Tg CO2 in the U.S. annually. However, the factors affecting C sequestration and protection in RMS leading to increase in microbial activity, nutrient availability, soil aggregation, C build up, and soil profile development must be better understood in order to formulate guidelines for development of an holistic approach to sustainable management of these ecosystems. The ECBs of RMS ecosystems are not well understood. An ecosystem method of evaluating ECB of RMS ecosystems is proposed.     

Greenhouse Gas Fluxes in Tropical and Temperate Agriculture: The need for a Full-Cost accounting of Global Warming Potentials

Agriculture's contribution to radiative forcing is principally through its historical release of carbon in soil and vegetation to the atmosphere and through its contemporary release of nitrous oxide (N_2O) and methane (CHM₄). The sequestration of soil carbon in soils now depleted in soil organic matter is a well-known strategy for mitigating the buildup of CO₂ in the atmosphere. Less well-recognized are other mitigation potentials. A full-cost accounting of the effects of agriculture on greenhouse gas emissions is necessary to quantify the relative importance of all mitigation options. Such an analysis shows nitrogen fertilizer, agricultural liming, fuel use, N_2O emissions, and CH₄ fluxes to have additional significant potential for mitigation. By evaluating all sources in terms of their global warming potential it becomes possible to directly evaluate greenhouse policy options for agriculture. A comparison of temperate and tropical systems illustrates some of these options.     

World crop residues production and implications of its use as a biofuel

Reducing and off-setting anthropogenic emissions of CO(2) and other greenhouse gases (GHGs) are important strategies of mitigating the greenhouse effect. Thus, the need for developing carbon (C) neutral and renewable sources of energy is more than ever before. Use of crop residue as a possible source of feedstock for bioenergy production must be critically and objectively assessed because of its positive impact on soil C sequestration, soil quality maintenance and ecosystem functions. The amount of crop residue produced in the US is estimated at 367x10(6) Mg/year for 9 cereal crops, 450x10(6) Mg/year for 14 cereals and legumes, and 488x10(6) Mg/year for 21 crops. The amount of crop residue produced in the world is estimated at 2802x10(6) Mg/year for cereal crops, 3107x10(6) Mg/year for 17 cereals and legumes, and 3758x10(6) Mg/year for 27 food crops. The fuel value of the total annual residue produced is estimated at 1.5x10(15) kcal, about 1 billion barrels (bbl) of diesel equivalent, or about 8 quads for the US; and 11.3x10(15) kcal, about 7.5 billion bbl of diesel or 60 quads for the world. However, even a partial removal (30-40%) of crop residue from land can exacerbate soil erosion hazard, deplete the SOC pool, accentuate emission of CO(2) and other GHGs from soil to the atmosphere, and exacerbate the risks of global climate change. Therefore, establishing bioenergy plantations of site-specific species with potential of producing 10-15 Mg biomass/year is an option that needs to be considered. This option will require 40-60 million hectares of land in the US and about 250 million hectares worldwide to establish bioenergy plantations.     

基于IPCC方法的湖南省温室气体排放核算及动态分析

为温室气体减排提供决策参考,基于IPCC和中国《省级温室气体清单编制指南》,核算了1995~2011年湖南省温室气体排放,并对其动态作了分析。结果表明: 2011年湖南省温室气体排放总量为594.7 Mt CO₂e,主要温室气体CO₂、CH₄和N₂O的排放量分别为471.3、100.8和22.6 Mt CO₂e,占排放总量的比例依次为79.25%、16.95%和3.79%。能源消费是温室气体排放的主要来源,2011年的排放量达421.5 Mt CO₂e,占排放总量的70.87%。林业呈现为碳汇效应,2011年的值为18.2 Mt CO₂e,消解温室气体排放量的3.06%。研究时段内温室气体从241.7 Mt CO₂e增长为594.7 Mt CO₂e,年均增长率达9.12%,可分为3个阶段,其中,1995~1999年波动降低,1999~2003年缓慢上升,2003~2011年快速增长,变化率依次为-3.32%、4.69%和17.37%。能源利用效率明显提高,万元GDP温室气体排放量由10.64 t CO₂e/万元减少到2.93 t CO₂e/万元,年均减少7.75%,但人均温室气体排放量由3.65 t CO₂e增加到8.07 t CO₂e,年均增长5.08%,减排压力较大。     

The Potential of Soil Carbon Sequestration Through Improved Management Practices in Norway

The study was conducted to assess the potential of Norwegian agricultural ecosystems to sequester carbon (C) based on the data from some long-term agronomic and land use experiments. The total emission of CO₂ in Norway in 1998 was 41.4 million metric ton (MMT), of which agriculture contributed only 0.157 MMT, or <0.4% of the total emissions. With regards to methane (CH₄) and nitrous oxide (N₂O) gases, however, agricultural activities contributed 32.5% and 51.3% of their respective emissions in Norway. The soil organic carbon (SOC) losses associated with accelerated soil erosion in Norway are estimated at 0.475 MMTC yr^–1. Land use changes and soil/crop management practices with potential for SOC sequestration include conservation tillage methods, judicious use of fertilizers and manures, use of crop residues, diverse crop rotations, and erosion control measures. The potential for SOC sequestration is 0.146 MMTC yr^–1 for adopting conservation tillage, 0.011–0.035 MMTC yr^–1 for crop residue management, 0.026 MMTC yr^–1 for judicious use of mineral fertilizer, 0.016–0.135 MMTC yr^–1 for manure application, and 0.036 MMTC yr^–1 for adopting crop rotations. The overall potential of these practices for SOC sequestration ranges from 0.591 to 1.022 MMTC yr^–1 with an average value of 0.806 MMTC yr^–1. Of the total potential, 59% is due to adoption of erosion control measures, 5.8% to restoration of peat lands, 21% to conversion to conservation tillage and residue management, and 14% to adoption of improved cropping systems. Enhancing SOC sequestration and improving soil quality, through adoption of judicious land use and improved system of soil and crop management, are prudent strategies for sustainable management of soil, water and environment resources.Readers should send their comments on this paper to: bhaskarn ath@aol.com within 3 months of publication of this issue.