Decoupling of greenhouse gas emissions from global agricultural production: 1970–2050

Since 1970 global agricultural production has more than doubled; contributing ~1/4 of total anthropogenic greenhouse gas (GHG) burden in 2010. Food production must increase to feed our growing demands, but to address climate change, GHG emissions must decrease. Using an identity approach, we estimate and analyse past trends in GHG emission intensities from global agricultural production and land‐use change and project potential future emissions. The novel Kaya–Porter identity framework deconstructs the entity of emissions from a mix of multiple sources of GHGs into attributable elements allowing not only a combined analysis of the total level of all emissions jointly with emissions per unit area and emissions per unit product. It also allows us to examine how a change in emissions from a given source contributes to the change in total emissions over time. We show that agricultural production and GHGs have been steadily decoupled over recent decades. Emissions peaked in 1991 at ~12 Pg CO₂‐eq. yr^?1 and have not exceeded this since. Since 1970 GHG emissions per unit product have declined by 39% and 44% for crop‐ and livestock‐production, respectively. Except for the energy‐use component of farming, emissions from all sources have increased less than agricultural production. Our projected business‐as‐usual range suggests that emissions may be further decoupled by 20–55% giving absolute agricultural emissions of 8.2–14.5 Pg CO₂‐eq. yr^?1 by 2050, significantly lower than many previous estimates that do not allow for decoupling. Beyond this, several additional costcompetitive mitigation measures could reduce emissions further. However, agricultural GHG emissions can only be reduced to a certain level and a simultaneous focus on other parts of the food‐system is necessary to increase food security whilst reducing emissions. The identity approach presented here could be used as a methodological framework for more holistic food systems analysis.     

中国农业系统近40年温室气体排放核算

基于排放因子法构建了包含种植业和牲畜养殖业的农业系统温室气体排放核算体系,系统核算了1980-2020年我国全国尺度上的农业系统温室气体排放总量和变化趋势,并在区县级尺度下对1980、2000、2011年的中国农业系统的温室气体排放量进行核算,对比不同阶段农业系统温室气体排放变化的时空异质性规律。研究发现：1980-2020年我国农业系统温室气体排放量呈波动增长趋势,增长了近46%。CH₄是农业系统排放贡献最大的温室气体,占总排放量的47.33%。我国农业系统温室气体排放与不同地区农业生产方式有关,CH₄排放量高的地区主要位于我国主要水稻产区以及旱地作物产区。CO₂排放量高的地区主要位于东北、西北等地区以及华东地区。N₂O排放量较高地区主要位于西北的主要畜牧养殖地区,以及我国农业经济发展水平高的中南部地区。研究有助于揭示我国农业温室气体排放的动态特征,现状规律,以及空间差异性特征,从农业减排角度为实现双碳目标提供科学参考。     

长期不施磷对稻田温室气体排放的影响

稻田磷肥的“旱重水轻”施肥策略是有效提高磷素利用率、减少磷素流失的有效技术途径,但稻季不施磷对温室气体排放的影响尚不明确。本研究监测了苏州和宜兴两块长期定位试验田中正常施磷与不施磷处理水稻生育期内CH₄和N₂O的排放通量。结果表明: 与正常施磷处理相比,长期不施磷处理均显著促进了稻田CH₄和N₂O排放,其中,苏州试验田CH₄和N₂O排放量分别增加57%和25%,宜兴试验田CH₄和N₂O排放量分别增加221%和70%。长期不施磷使土壤的速效磷、有机酸和可溶性有机碳含量下降,与CH₄排放密切相关,特别是土壤速效磷含量与CH₄排放量呈显著负相关,相关系数r=-0.987。两处试验田不施磷处理的全球增温潜势均大于施磷处理。因此,稻田长期缺磷会对土壤有机酸、可溶性有机碳和速效磷含量产生影响,进而增加稻田CH₄和N₂O的排放。     

Reducing greenhouse gas emissions and adapting agricultural management for climate change in developing countries: providing the basis for action

Agriculture in developing countries has attracted increasing attention in international negotiations within the United Nations Framework Convention on Climate Change for both adaptation to climate change and greenhouse gas mitigation. However, there is limited understanding about potential complementarity between management practices that promote adaptation and mitigation, and limited basis to account for greenhouse gas emission reductions in this sector. The good news is that the global research community could provide the support needed to address these issues through further research linking adaptation and mitigation. In addition, a small shift in strategy by the Intergovernmental Panel on Climate Change (IPCC) and ongoing assistance from agricultural organizations could produce a framework to move the research and development from concept to reality. In turn, significant progress is possible in the near term providing the basis for UNFCCC negotiations to move beyond discussion to action for the agricultural sector in developing countries.     

Assessing greenhouse gas emissions from peatlands using vegetation as a proxy

Drained peatlands in temperate Europe are a globally important source of greenhouse gas (GHG) emissions. This article outlines a methodology to assess emissions and emission reductions from peatland rewetting projects using vegetation as a proxy. Vegetation seems well qualified for indicating GHG fluxes from peat soils as it reflects long-term water level, affects GHG emissions via assimilate supply and aerenchyma and allows fine-scaled mapping. The methodology includes mapping of vegetation types characterised by the presence and absence of species groups indicative for specific water level classes. GHG flux values are assigned to the vegetation types following a standardized protocol and using published emission values from plots with similar vegetation and water level in regions with similar climate and flora. Carbon sequestration in trees is accounted for by estimating the annual sequestration in tree biomass from forest inventory data. The method follows the criteria of the Voluntary Carbon Standard and is illustrated using the example of two Belarusian peatlands.     

Updated and harmonised greenhouse gas emissions for crop inventories

Purpose

The emission of greenhouse gases (GHG) is a key criterion in the environmental assessment of biofuels. Life cycle inventories taking into account the latest methodological developments are an essential prerequisite for this assessment. In the last years, substantial progresses in the modelling of nitrogen emissions relevant for the climate as well as in modelling the emissions from land use change (LUC) have been achieved. Therefore, the biomass production inventories in the ecoinvent database were revised to take into account these developments.

Methods

The IPCC method tier 1 has been used for the assessment of N₂O emissions. Induced emissions from NH₃ and NO₃ were included as well. Due to the importance of the latter emissions for N₂O formation, these emissions have also been updated and harmonised. The Agrammon model was used for the NH₃ emissions. The SALCA-NO₃ model has been applied in the European inventories to estimate nitrate leaching, whilst in non-European inventories the SQCB-NO₃ model has been used. The quantification of the land use change areas has been based on annualized, retrospective data of the last 20 years. All carbon pools (from aboveground biomass to soil organic carbon) were considered and differentiated on a regional level for all of the natural vegetation categories affected. Whenever possible, default values and methods from the IPCC 2006 were applied.

Results and discussion

The changes for ammonia emissions were generally very small (?5 % on average). The nitrate emissions increased on average by +13 %, but this slight trend is the result of important downward and upward changes, whilst the average N₂O emissions decreased by ?26 %. For the existing inventories of soybean, palm oil and sugarcane production, significant increases of GHG emissions resulted from LUC modelling. This was mainly due to the consistent inclusion of all carbon stocks according to the IPCC guidelines. The calculation method can also result in important C sequestration effects in certain cases like African Jatropha production.

Conclusions

The changes in greenhouse gas emissions due to the updated methodology were significant. This shows that life cycle assessment studies for biofuels using older methodological bases need to be revised and could lead to different conclusions. The implemented and cultivated superstructure for LUC modelling is modular and flexible and can be easily extended to other important crop activities. The new parameterisation functionality applied for the activities provides powerful means for the simple generation of site-specific activities.

     

Livestock greenhouse gas emissions and mitigation potential in Europe

The livestock sector contributes considerably to global greenhouse gas emissions (GHG). Here, for the year 2007 we examined GHG emissions in the EU27 livestock sector and estimated GHG emissions from production and consumption of livestock products; including imports, exports and wastage. We also reviewed available mitigation options and estimated their potential. The focus of this review is on the beef and dairy sector since these contribute 60% of all livestock production emissions. Particular attention is paid to the role of land use and land use change (LULUC) and carbon sequestration in grasslands. GHG emissions of all livestock products amount to between 630 and 863 Mt CO₂e, or 12–17% of total EU27 GHG emissions in 2007. The highest emissions aside from production, originate from LULUC, followed by emissions from wasted food. The total GHG mitigation potential from the livestock sector in Europe is between 101 and 377 Mt CO₂e equivalent to between 12 and 61% of total EU27 livestock sector emissions in 2007. A reduction in food waste and consumption of livestock products linked with reduced production, are the most effective mitigation options, and if encouraged, would also deliver environmental and human health benefits. Production of beef and dairy on grassland, as opposed to intensive grain fed production, can be associated with a reduction in GHG emissions depending on actual LULUC emissions. This could be promoted on rough grazing land where appropriate.     

Current available strategies to mitigate greenhouse gas emissions in livestock systems: an animal welfare perspective

Livestock production is a major contributor to greenhouse gas (GHG) emissions, so will play a significant role in the mitigation effort. Recent literature highlights different strategies to mitigate GHG emissions in the livestock sector. Animal welfare is a criterion of sustainability and any strategy designed to reduce the carbon footprint of livestock production should consider animal welfare amongst other sustainability metrics. We discuss and tabulate the likely relationships and trade-offs between the GHG mitigation potential of mitigation strategies and their welfare consequences, focusing on ruminant species and on cattle in particular. The major livestock GHG mitigation strategies were classified according to their mitigation approach as reducing total emissions (inhibiting methane production in the rumen), or reducing emissions intensity (Ei; reducing CH₄ per output unit without directly targeting methanogenesis). Strategies classified as antimethanogenic included chemical inhibitors, electron acceptors (i.e. nitrates), ionophores (i.e. Monensin) and dietary lipids. Increasing diet digestibility, intensive housing, improving health and welfare, increasing reproductive efficiency and breeding for higher productivity were categorized as strategies that reduce Ei. Strategies that increase productivity are very promising ways to reduce the livestock carbon footprint, though in intensive systems this is likely to be achieved at the cost of welfare. Other strategies can effectively reduce GHG emissions whilst simultaneously improving animal welfare (e.g. feed supplementation or improving health). These win–win strategies should be strongly supported as they address both environmental and ethical sustainability. In order to identify the most cost-effective measures for improving environmental sustainability of livestock production, the consequences of current and future strategies for animal welfare must be scrutinized and contrasted against their effectiveness in mitigating climate change.     

Domestic water versus imported virtual blue water for agricultural production: A comparison based on energy consumption and related greenhouse gas emissions

The supply of water, food, and energy in our global economy is highly interlinked. Virtual blue water embedded into internationally traded food crops has therefore been extensively researched in recent years. This study focuses on the often neglected energy needed to supply this blue irrigation water. It provides a globally applicable and spatially explicit approach to the watershed level for water source specific quantification of energy consumption and related greenhouse gas (GHG) emissions of irrigation water supply. The approach is applied to Israel's total domestic and imported food crop supply of 105 crops by additionally including import-related transportation energy and emissions. Total energy use and related emissions of domestic crop production were much lower (551 GWh/422 kt CO₂-equivalents [CO₂e]) than those embedded into crop imports (1639 GWh/649 kt CO₂e). Domestic energy and emissions were mainly attributable to the irrigation water supply with artificial water sources (treated domestic wastewater and desalinated water, 84%). Transport accounted for 79% and 66% of virtually imported energy and emissions, respectively. Despite transport, specific GHG emissions (CO₂e per ton of crop) were significantly lower for several crops (e.g., olives, almonds, chickpeas) compared to domestic production. This could be attributed to the high share of energy-intensive artificial water supply in combination with higher irrigation water demands in Israel. In the course of an increasing demand for artificial water supply in arid and semi-arid regions, our findings point to the importance of including “energy for water” into comparative environmental assessment of crop supply to support decision-making related to the water–energy–food nexus.     

Field application of nitrogen and phenylacetylene to mitigate greenhouse gas emissions from landfill cover soils: effects on microbial community structure

Landfills are large sources of CH₄, but a considerable amount of CH₄ can be removed in situ by methanotrophs if their activity can be stimulated through the addition of nitrogen. Nitrogen can, however, lead to increased N₂O production. To examine the effects of nitrogen and a selective inhibitor on CH₄ oxidation and N₂O production in situ, 0.5 M of NH₄Cl and 0.25 M of KNO₃, with and without 0.01% (w/v) phenylacetylene, were applied to test plots at a landfill in Kalamazoo, MI from 2007 November to 2009 July. Nitrogen amendments stimulated N₂O production but had no effect on CH₄ oxidation. The addition of phenylacetylene stimulated CH₄ oxidation while reducing N₂O production. Methanotrophs possessing particulate methane monooxygenase and archaeal ammonia-oxidizers (AOAs) were abundant. The addition of nitrogen reduced methanotrophic diversity, particularly for type I methanotrophs. The simultaneous addition of phenylacetylene increased methanotrophic diversity and the presence of type I methanotrophs. Clone libraries of the archaeal amoA gene showed that the addition of nitrogen increased AOAs affiliated with Crenarchaeal group 1.1b, while they decreased with the simultaneous addition of phenylacetylene. These results suggest that the addition of phenylacetylene with nitrogen reduces N₂O production by selectively inhibiting AOAs and/or type II methanotrophs.     

Implementing an appropriate metric for the assessment of greenhouse gas emissions from livestock production: A national case study

Livestock farming is of major economic relevance but also severely contributes to environmental impacts, especially greenhouse gas (GHG) emissions such as methane (CH₄; particularly from ruminant production) and nitrous oxide (N₂O; mainly from manure management and soil cultivated for feed production). In this study, we analyse the impact of GHG emissions from Austrian livestock production, using two metrics: a) the commonly used global warming potential (GWP) over 100 years (GWP₁₀₀ in CO₂-equivalents, CO₂-e), and b) the recently introduced metric GWP*, which describes additional warming as a function of the timeline of short-lived GHG emissions (unit CO₂ warming equivalents, CO₂-we). We first compiled the sectoral (i.e. only direct emissions without upstream processes) GWP₁₀₀ for different livestock categories with a focus on dairy cattle, beef cattle and pigs in Austria between 1990 and 2019. We also estimated product-related (i.e. per kg carcass weight or per litre of milk) GWP₁₀₀ values, including upstream processes. We then calculated the corresponding GWP* metrics, both sectoral and product-related, and compared them with the GWP₁₀₀ values. Decreasing livestock numbers and improved production efficiency were found to result in strong sectoral emission reductions from dairy production (–32 % of GWP₁₀₀ from 1990 to 2019) and from pigs (–32 % CO₂-e). This contrasts with low reductions from other livestock categories and even increases for cattle other than dairy cows (+3 % CO₂-e), mainly due to rising suckler cow numbers. Allocated results per kg milk and kg body mass show quite similar results. Using the GWP* metric, the climate impacts of Austrian livestock production are less severe. When assuming constant management and emission intensity over a period of at least 20 years, the CO₂-we (GWP*) is almost 50 % less than CO₂-e (GWP₁₀₀) per kg Austrian raw milk due to the different impacts of the short-lived CH₄. A similar trend applies to an average cattle carcass (-40 % warming impact). The emission reductions of the shrinking Austrian livestock population represent an important contribution to a climate-neutral agriculture: The CH₄ reductions of livestock production during the past 20 years reduce the current total Austrian CO₂-we by 16 %. Continuous CH₄ reduction, as we show it here for Austrian livestock, is an effective option to tackle the climate crisis in the short term. It shall be stressed that a relatively low GWP* should not be interpreted as a concession for further CH₄ emissions but as an actual reduction of (additional) warming.     

Accounting for greenhouse gas emissions from the degradation of chemicals in the environment

The International Journal of Life Cycle Assessment - The degradation of chemicals in the environment is often excluded from life cycle assessment (LCA) studies. This paper describes a method to...     

Nitrous oxide emissions from agricultural fields: Assessment, measurement and mitigation

In this paper we discuss three topics concerning N₂O emissions from agricultural systems. First, we present an appraisal of N₂O emissions from agricultural soils (Assessment). Secondly, we discuss some recent efforts to improve N₂O flux estimates in agricultural fields (Measurement), and finally, we relate recent studies which use nitrification inhibitors to decrease N₂O emissions from N-fertilized fields (Mitigation).To assess the global emission of N₂O from agricultural soils, the total flux should represent N₂O from all possible sources; native soil N, N from recent atmospheric deposition, past years fertilization, N from crop residues, N₂O from subsurface aquifers below the study area, and current N fertilization. Of these N sources only synthetic fertilizer and animal manures and the area of fields cropped with legumes have sufficient global data to estimate their input for N₂O production. The assessment of direct and indirect N₂O emissions we present was made by multiplying the amount of fertilizer N applied to agricultural lands by 2% and the area of land cropped to legumes by 4 kg N₂O-N ha^-1. No regard to method of N application, type of N, crop, climate or soil was given in these calculations, because the data are not available to include these variables in large scale assessments. Improved assessments should include these variables and should be used to drive process models for field, area, region and global scales.Several N₂O flux measurement techniques have been used in recent field studies which utilize small and ultralarge chambers and micrometeorological along with new analytical techniques to measure N₂O fluxes. These studies reveal that it is not the measurement technique that is providing much of the uncertainty in N₂O flux values found in the literature but rather the diverse combinations of physical and biological factors which control gas fluxes. A careful comparison of published literature narrows the range of observed fluxes as noted in the section on assessment. An array of careful field studies which compare a series of crops, fertilizer sources, and management techniques in controlled parallel experiments throughout the calendar year are needed to improve flux estimates and decrease uncertainty in prediction capability.There are a variety of management techniques which should conserve N and decrease the amount of N application needed to grow crops and to limit N₂O emissions. Using nitrification inhibitors is an option for decreasing fertilizer N use and additionally directly mitigating N₂O emissions. Case studies are presented which demonstrate the potential for using nitrification inhibitors to limit N₂O emissions from agricultural soils. Inhibitors may be selected for climatic conditions and type of cropping system as well as the type of nitrogen (solid mineral N, mineral N in solution, or organic waste materials) and applied with the fertilizers.     

Progress in the studies on the greenhouse gas emissions from reservoirs

The green credentials of hydroelectricity in terms of greenhouse-gas (GHG) emissions have been tarnished with the finding of the researches on GHG emissions from hydroelectric reservoirs in the last two decades. Substantial amounts of GHGs release from the tropical reservoirs, especially methane (CH₄) from Brazil’s Amazonian areas. CH₄ contributes strongly to climate change because it has a global warming potential (GWP) 24 times higher than carbon dioxide (CO₂) on a per molecule basis over a 100-year time horizon. GHGs may emit from reservoirs through four different pathways to the atmosphere: (1) diffusive flux at the reservoir surface, (2) gas bubble flux in the shallow zones of a reservoir, (3) water degassing flux at the outlet of the powerhouse downstream of turbines and spillways, and (4) flux across the air–water interface in the rivers downstream of the dams. This paper reviewed the productions and emissions of CH₄, CO₂, and N₂O in reservoirs, and the environmental variables influencing CH₄ and CO₂ emissions were also summarized. Moreover, the paper combined with the progress of GHG emissions from Three Gorges Reservoir and proposed three crucial problems to be resolved on GHG emissions from reservoirs at present, which would be benefit to estimate the total GHG emissions from Three Gorges Reservoir accurately.     

Nitrogen deposition and greenhouse gas emissions from grasslands: uncertainties and future directions

Increases in atmospheric nitrogen deposition (N_dep) can strongly affect the greenhouse gas (GHG; CO₂, CH₄, and N₂O) sink capacity of grasslands as well as other terrestrial ecosystems. Robust predictions of the net GHG sink strength of grasslands depend on how experimental N loads compare to projected N_dep rates, and how accurately the relationship between GHG fluxes and N_dep is characterized. A literature review revealed that the vast majority of experimental N loads were higher than levels these ecosystems are predicted to experience in the future. Using a process‐based biogeochemical model, we predicted that low levels of N_dep either enhanced or reduced the net GHG sink strength of most grasslands, but as experimental N loads continued to increase, grasslands transitioned to a N saturation‐decline stage, where the sensitivity of GHG exchange to further increases in N_dep declined. Most published studies represented treatments well into the N saturation‐decline stage. Our model results predict that the responses of GHG fluxes to N are highly nonlinear and that the N saturation thresholds for GHGs varied greatly among grasslands and with fire management. We predict that during the 21st century some grasslands will be in the N limitation stage where others will transition into the N saturation‐decline stage. The linear relationship between GHG sink strength and N load assumed by most studies can overestimate or underestimate predictions of the net GHG sink strength of grasslands depending on their N baseline status. The next generation of global change experiments should be designed at multiple N loads consistent with future N_dep rates to improve our empirical understanding and predictive ability.     

京郊典型设施蔬菜地土壤N_2O排放特征

利用静态暗箱-气相色谱法对北京郊区设施蔬菜地典型种植模式(番茄-白菜-生菜)下土壤N2O排放特征进行了周年(2012年2月22日—2013年2月23日)观测,探讨了不同处理下(即不施氮肥处理(CK)、农民习惯施肥处理(FP)、减氮优化施肥处理(OPT)和减氮优化施肥+硝化抑制剂处理(OPT+DCD))N2O排放特征及土壤温度、土壤湿度、土壤无机氮含量对土壤N2O排放的影响。结果表明:每次施肥+灌溉之后设施蔬菜地会出现明显的N2O排放高峰,持续时间一般为3—5 d。不同处理N2O排放通量变化范围在-0.21—14.26 mg N2O m-2h-1,平均排放通量0.03—0.36 mg N2O m-2h-1。整个蔬菜生长季各处理N2O排放与土壤孔隙含水率(WFPS)均表现出极显著的正相关关系(P0.01);不施氮处理5 cm深度土壤温度与N2O排放通量呈现显著的正相关关系(P0.05);各处理N2O排放与土壤表层硝态氮含量具有较一致变化趋势。不同处理下N2O年度排放总量差异显著,依次顺序为FP((20.66±0.91)kg N/hm2)OPT((12.79±1.33)kg N/hm2)OPT+DCD((8.03±0.37)kg N/hm2)。与FP处理相比,OPT处理和OPT+DCD处理N2O年排放总量分别减少了38.09%和61.13%。各处理N2O排放系数介于0.36%—0.77%,低于IPCC 1.0%的推荐值。在目前的管理措施下,合理减少施氮量和添加硝化抑制剂是减少设施蔬菜地N2O排放量的有效途径。     

Microbial populations regulate greenhouse gas emissions in Sundarban mangrove ecosystem,India

Mangrove ecosystems are significant sources of greenhouse gases (GHG) that is attributed to microbial activity. However, it is still unknown how the sediment microbial populations affect GHG emissions in mangrove ecosystem. Since little is known about microbial populations of mangroves, the present study was aimed to understand the structure and function of microbial communities in the Indian part of the Sundarban mangrove ecosystem in relation to environmental variables and variation of GHG emissions during three seasons: pre-monsoon (March–June), monsoon (July–October) and post-monsoon (November–February).Seasonal variations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) gas samples were taken from the mangrove bed. Culture methods were used to detect twelve different types of microbes such as heterotrophic (Htp), N₂ fixing (Nfix), nitrifying (Ntfn), sulfur oxidizing (Soxd), Gram-negative (GMn), Gram-positive (GMp), spore forming (Sfor), denitrifying (DNtfn), anaerobic (Anrb), phosphate solubilizing (Psol), cellulose degrading (Cdeg) bacteria and actinomycetes (Actm). In the monsoon, populations of the Htp, Anrb, Psol, and Cdeg bacteria were more prevalent, whereas populations of the GMn, GMp, Ntfn, DNtfn bacteria, and Actm bacteria were more prevalent in the post-monsoon. Monsoonal CO₂ and CH₄ fluxes were larger than pre-monsoon and post-monsoon, resulting in increased microbial soil respiration and breakdown of soil organic carbon. Because of higher denitrification and soil temperature, N₂O flux was higher in the pre-monsoon period, followed by monsoon and post-monsoon periods. A univariate statistical correlation was employed to assess the relationships between environmental variables and different microbial populations. An ANN (artificial neural network) model was proposed to evaluate the relevance of microbial population contribution to GHG emissions, and it indicated that the Htp, Anrb, and Dntfn microbial populations were most relevant for CO₂, CH₄, and N₂O emissions. The suggested model would be used to assess the drivers behind GHG emission in the mangroves located at different parts of the world.     

秸秆还田与氮肥施用对稻田温室气体排放的影响

秸秆还田与氮肥施用是农田生态系统中碳氮元素的两大主要补给途径,其在调控稻田甲烷(CH₄)和氧化亚氮(N₂O)排放以及水稻产量方面具有重要作用。以往的研究主要关注秸秆还田或氮肥施用单因素对稻田温室气体排放的影响,而双因素互作对甲烷和氧化亚氮排放的影响尚未明确。同时,在秸秆还田条件下如何进行合理的氮肥施用鲜有深入研究。本研究基于3个氮肥处理(0、180、360 kg N/hm²)和3个秸秆还田处理(0、2.25、3.75 t/hm²)进行多年水稻田间定位试验,研究结果表明:CH₄季节累积排放随秸秆还田量增加而增加,与施氮量无显著正相关关系;N₂O季节累积排放随施氮量增加而增加,与秸秆还田量无显著正相关关系;秸秆还田对于产量的影响具有不确定性,两年均在秸秆不还田+不施氮处理(S0N0)出现最低产量,2021与2022年最低产量分别为5740.64和4903.75 kg/hm²。2021与2022年最高产量分别在秸秆不还田+高氮(S0N2)和高量秸秆还田+高氮(S2N2)出现,分别为10938.48和10384.83 kg/hm²。同时,本研究发现在低量秸秆还田条件下,在碳足迹(CF, Carbon Footprint)方面,施氮量为251 kg N/hm²时碳足迹达到最低点,为1.01 kg C/kg;而在生态经济净收益(NEEB, Net Ecosystem Economic Benefits)方面,施氮量为294 kg N/hm²时生态经济净收益达到最高点,为11778.15 元/hm²。为协同生态经济净收益与碳排放,在低量秸秆还田(S1)下,配合251-294 kg N/hm²的施氮量为最优施肥方案。研究结果为指导稻田温室气体减排、实现稻田碳中和以及农田管理提供了理论支撑,为实现水稻的高产稳产与低碳生产科学依据。     

Energy balances and greenhouse gas emissions of palm oil biodiesel in Indonesia

This study presents a cradle‐to‐gate assessment of the energy balances and greenhouse gas (GHG) emissions of Indonesian palm oil biodiesel production, including the stages of land‐use change (LUC), agricultural phase, transportation, milling, biodiesel processing, and comparing the results from different farming systems, including company plantations and smallholder plantations (either out growers or independent growers) in different locations in Kalimantan and Sumatra of Indonesia. The findings demonstrate that there are considerable differences between the farming systems and the locations in net energy yields (43.6–49.2 GJ t^?1 biodiesel yr^?1) as well as GHG emissions (1969.6–5626.4 kg CO_2eq t^?1 biodiesel yr^?1). The output to input ratios are positive in all cases. The largest GHG emissions result from LUC effects, followed by the transesterification, fertilizer production, agricultural production processes, milling, and transportation. Ecosystem carbon payback times range from 11 to 42 years.     

Drivers of greenhouse gas emissions from standing dead trees in ghost forests

Biogeochemistry - Coastal freshwater forested wetlands are rapidly transitioning from forest to marsh, leaving behind many standing dead trees (snags) in areas often called ‘ghost...