,, 郑聚锋, 程琨,, 叶仪, 庄园, 潘根兴南京农业大学农业资源与生态环境研究所/江苏省有机固体废弃物资源化协同创新中心,南京210095Quantifying Carbon Sink by Biochar Compound Fertilizer Project for Domestic Voluntary Carbon Trading in Agriculture
SUN JianFei,, ZHENG JuFeng, CHENG Kun,, YE Yi, ZHUANG Yuan, PAN GenXingInstitute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University/Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing 210095通讯作者:
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责任编辑: 李云霞
收稿日期:2018-04-19接受日期:2018-08-2网络出版日期:2018-12-01
| 基金资助: |
Received:2018-04-19Accepted:2018-08-2Online:2018-12-01
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孙建飞, 郑聚锋, 程琨, 叶仪, 庄园, 潘根兴. 面向自愿减排碳交易的生物质炭基肥固碳减排计量方法研究[J]. 中国农业科学, 2018, 51(23): 4470-4484 doi:10.3864/j.issn.0578-1752.2018.23.007
SUN JianFei, ZHENG JuFeng, CHENG Kun, YE Yi, ZHUANG Yuan, PAN GenXing.
0 引言
【研究意义】作为《京都议定书》三种灵活履约机制之一,清洁发展机制（Clean Development Mechanism,CDM）的核心内容是发达国家与发展中国家通过项目级的合作对“经核证的减排量”（Certified Emission Reductions,CERCs）进行交易（即碳交易）以履行京都议定书规定的减排义务。中国政府从2004年开始实施CDM项目,自2005年2月《京都议定书》生效以来,中国CDM项目呈现迅速增长的趋势。中国是开展和实施CDM项目最多的国家,且CERCs数量位居全球第一[1,2]。自愿减排交易是指相对《京都议定书》中CDM的发展,在市场机制下相伴形成的非强制性减排项目交易行为[3]。随着第一批环境权益平台的相继建立,2008年我国开始了自愿减排交易活动的探索和市场体系的建设。2012年6月,国家发改委印发施行了《温室气体自愿减排交易管理暂行办法》（以下简称《暂行办法》）,对温室气体减排碳交易进行管理,提高了自愿减排交易的公正性,并调动了全社会自觉参与碳减排活动的积极性。然而,在《暂行办法》施行中也存在着温室气体自愿减排交易量小、个别项目不够规范等问题[4],那么,发展合格的自愿减排项目并开发计量方法学则是进行自愿减排碳交易的重要支撑工作。【前人研究进展】农业重要的温室气体排放源,而到2030年农业减排潜力可以达到5 500—6 000 Mt二氧化碳当量[5]。未来越来越多的农业活动即将参与自愿减排碳交易,相应的农业项目方法学也逐渐被开发和应用。目前我国农业方面已经发展了畜禽业、生物质能领域以及农业碳汇（森林、农田、草原、荒漠、湿地）等项目,农业所涉及的范围广,农业的温室气体减排措施也多种多样[6]。CDM碳减排方法学的开发为我国自愿减排项目方法学的开发提供了科学参考,但我国农业经营模式的特征使得方法学研究成为当前自愿减排碳交易领域的重要课题和薄弱环节。生物质炭具有稳定的炭质、良好的孔性、高的阳离子交换量,可以改善土壤团聚结构、调节土壤pH、补充土壤养分、钝化土壤中的重金属和有机污染物[7]。许多研究表明,生物质炭在提供能源、增加土壤有机碳库、减少农田氧化亚氮排放的同时还可以提高作物产量[8,9,10,11]。作为生物质炭产业链的产品,生物质炭基肥是将生物质炭与化肥复合生产的新型的有机无机缓释肥,替代纯化学肥料[12],可以增加土壤碳库和提高肥料的使用率。已有****对炭基肥替代普通化肥施入农田固碳减排进行了研究,发现炭基肥施用和常规施肥相比,小麦生长季氧化亚氮排放降低56.01%—63.53%[13],水稻生长季的甲烷排放降低25.45%—50.58%[14],玉米生长季的土壤有机碳增加3.55%—8.17% [15]。【本研究切入点】我国在秸秆禁烧行动下,秸秆热裂解生物质炭化及炭基肥生产应用已经成为农业废弃物治理与生态农业的新产业。我国农业行政部门也已公布了炭基肥行业标准草案,生物质炭基肥生产应用早已列入我国农业关键低碳技术目录。炭基肥农业应用是潜在的自愿减排项目,但对于炭基肥的固碳减排计量方法学研究仍是空白,如何进行项目的合格性检验是需要探索的重要问题。我国农田经营模式以小户经营为主,但近年来集约化农业发展速度快,肥料工作到田间生产的一体化产业模式是现代集约化农业的新模式。【拟解决的关键问题】在计量方法学中项目边界和基准线如何定义、项目的碳库和关键排放源如何选取和用什么方法进行计量是亟待解决的技术和科学问题。基于此,本研究根据碳交易方法学架构,从项目合格性的定义、边界和基准线的确定、碳库和关键排放源的选择和计量方法、泄漏的确定等几个方面,讨论如何开发炭基肥农业固碳减排方法学,以期为炭基肥大规模农业应用自愿减排项目的开发提供科学参考。1 材料与方法
1.1 方法学开发思路
本研究主要参考《测土配方施肥固碳减排计量方法指南》[16]、《保护性耕作减排增汇方法学》[17]、CDM已颁布的方法学和相关文献[1,6,18-21],综合已发表的生物质炭和炭基肥应用的文献[7,12-14,22-24]以及炭基肥生产的国家行业标准（NY/T 3041—2016）,从项目定义-关键排放源和碳库选取-泄漏-净碳汇量计量四个方面对炭基肥项目固碳减排计量方法学的开发进行探讨（图1）。图1
新窗口打开|下载原图ZIP|生成PPT图1方法学开发思路
Fig. 1Methodology of development framework
项目合格性是指参与自愿减排碳交易的农业项目应当遵循一定的要求,包括项目的实施应符合国家、地区或行业标准,项目应当在保障粮食安全的前提下产生实在的、可测量的、长期的温室气体减排效益,以及在项目实施过程中应当遵循方法学的一些具体的要求;同时,项目还应当具有额外性。项目的额外性论证是方法学的核心问题,主要包括两个方面。首先,须要论证该项目是否是当地的普遍性做法或者国家强制实施的项目,如果不是,则该项目具有额外性;如果项目活动属于普遍性做法,但是存在技术障碍、资金障碍或者市场不普及等方面因素,依靠自身条件难以实施,则项目也具有额外性,否则,项目不具有额外性,不能作为碳交易项目实施。其次,在此基础上,还须确认该项目的实施能否带来可观的、额外的土壤碳汇及温室气体减排量[16]。
项目边界包括时间边界和空间边界。时间边界即项目期,是指项目活动以及固碳减排计量的时间长短,而空间边界是指进行项目活动时的地理范围。基准线是指一种能够合理代表在没有项目活动的情景下温室气体排放和土壤有机碳库变化量。
关键排放源是指累计温室气体源排放超过温室气体源排放总量的95%,单个温室气体排放源超过温室气体源排放总量的5%[16]。项目泄漏是指发生在项目活动边界之外,由项目活动所引起的、可测定的温室气体排放增加或者减少的情形。例如,在规模化养鸡场沼气工程CDM项目中,厌氧发酵后沼渣进行农田施用将带来温室气体排放,这部分排放发生在边界范围（养鸡场）之外,由沼气工程项目引起,属于该项目的泄漏[21]。项目净碳汇量则是基准线情景下碳库变化和温室气体排放量与项目实施过程中的碳库变化和温室气体排放量的差值,并扣除泄漏后的部分。
1.2 案例分析数据来源
本研究结合当前和未来土地利用方式的可能性,尝试对探索的不同边界情景进行案例研究。案例研究中炭基肥生产过程中的温室气体排放则采用实地调查方式进行,炭基肥田间应用农田管理、碳库变化和温室气体排放数据来源于本课题组已发表的田间试验研究。炭基肥的生产包括原料的运输、生物质炭生产排放、炭基肥生产排放。原料的运输即秸秆从农田边界运输到收储站,最后运输到工厂生产生物质炭和炭基肥。收储站到工厂的运输距离以及秸秆原料运输所带来的燃油消耗参数选取了方艳茹等[25]的研究,柴油排放参数选取BP China数据[26]。生物质炭生产排放数据则通过对本课题组合作企业进行实地调查得到[27]。根据目前生物质炭生产过程存在一些工厂未利用生物质可燃气现状,结合华东区域发电过程二氧化碳排放参数[28],计算得出未优化工艺（可燃气未被利用）和优化工艺情景下的生物质炭生产排放（可燃气被用来发电,抵消一部分煤炭发电,带来一定的温室气体减排）分别为-678和293.4 kg CO2·t-1。炭基肥生产排放数据是通过实地调查得到,调查地点位于在山东省泰安市圣元村黎明肥业公司,调查时间为2017年9月。通过调查该公司的肥料日生产能力和耗电量,我们计算出炭基肥的生产排放。该公司日生产普通复合肥料能力为40—50 t,炭基肥为20—30 t,其中炭基肥和普通复合肥的生产流程相同,需要经过配料—搅拌—粉碎—造粒—烘干—冷却—分筛—包膜,粉碎和烘干过程耗能最大,冷却和造粒耗能次之,搅拌和分筛过程耗能最小。肥料造粒采用滚筒造粒法,而炭基肥的造粒成球率要低于普通复合肥,导致炭基肥生产的产率低于普通复合肥,同时能耗要高于普通复合肥生产。整个秸秆收集、生物质炭生产、炭基肥生产的能耗参数见表1。
Table 1
表1
表1用于秸秆炭基肥固碳减排计量的秸秆收集及生产环节能耗参数
Table 1
| 原料成本参数 Feedstock cost | |||
|---|---|---|---|
| 收储到工厂 Storage to factory distance | 运输油耗[25] Fuel consumption | 柴油排放因子[26] Diesel emission factor | 电力排放因子[28] Electricity emission factor |
| 16 km | 1.60 L·t-1 | 0.00263 t CO2-eq·L-1 | 0.928 kg·kWh-1 |
| 生物质炭生产的能流[27] Energy flow with biochar production | |||
| 电力消耗 Electricity consumption | 原料消耗 Feedstock | 产率 Biochar yield | 气体发电 Syngas gas generated power |
| 1500 MWh | 30000 t | 35% | 9 GWh |
| 肥料制造能耗 Energy consumption in fertilizer manufacturing | |||
| 类型 Fertilizer type | 产量 Output | 耗电 Power consumption | 滚筒造粒功率 Drum granulation power |
| 炭基肥 Biochar-based compound fertilizer | 2.94 t·h-1 | 31.3 kWh·t-1 | 7.48 kWh·t-1 |
| 普通复合肥 Chemical Compound fertilizer | 5.29 t·h-1 | 28.0 kWh·t-1 | 4.16 kWh·t-1 |
新窗口打开|下载CSV
用于案例分析的农田试验数据来源于QIAN等[14]和李正东等研究[13]。冬小麦和水稻种植田块分别位于江苏省常熟市和安徽省池州市,炭基肥施加量分别为300 kg·hm-2和450 kg·hm-2。炭基肥的原料成分生物质炭（玉米秸秆炭）含量为24%,生物质炭含碳量为520.7 g·kg-1,案例相关肥料施用数据如表2所示。
Table 2
表2
表2案例农田肥料施用数据
Table 2
| 作物种植类型 Crop type | 基线/项目 Baseline/Project | 炭基肥料用量 Biochar compound fertilizer (kg·hm-2) | 普通肥料用量 Chemical fertilizer (kg·hm-2) |
|---|---|---|---|
| 冬小麦 Winter wheat | 基线 Baseline | 0 | N:180.75; P2O5:50.63; K2O:50 |
| 项目活动Project activity | Biochar:72; N:54; P2O5:27; K2O:30 | N:120.23; P2O5:50.63; K2O:50 | |
| 水稻 Paddy rice | 基线 Baseline | 0 | N: 208.88; P2O5:72; K2O:72 |
| 项目活动 Project activity | Biochar:108; N:81; P2O5:40.5; K2O:45 | N:186 |
新窗口打开|下载CSV
2 结果
2.1 方法学理论框架的探索
2.1.1 项目合格性的论证 根据CDM固碳减排项目方法学以及我国自愿减排项目方法学要求,参考碳交易的项目须进行项目合格性论证。关于炭基肥对作物产量影响的研究表明,施用炭基肥替代普通化肥情况下,炭基肥对普通农作物产量影响幅度为-4.0%— 35.4%[13,15,22-24]。但研究文献施用的炭基肥良莠不齐,而炭基肥制造工艺、养分配比、生物质炭含量以及生物质炭的原料类型和热裂解温度等,可能都会影响着炭基肥的效果进而影响农作物产量,所以炭基肥的制造需要遵循一定的标准以保证产品的质量。农业农村部近期已经发布了《生物炭基肥料》制造的行业标准（NY/T 3041—2016）,国际生物质炭协会（International Biochar Initiative,IBI）给出了生物质炭生产标准和产品测试指南[29]。因此,合格的炭基肥项目应当符合产量不减少且生物质炭和炭基肥产品符合政府管理部门认可或者相关国际机构的各类标准的要求。尽管农业农村部2017年将炭基肥作为秸秆十大利用模式之一[30],但秸秆热裂解生物质炭产业还面临技术和装备瓶颈以及产业政策瓶颈[31],炭基肥现阶段还未能作为普适性肥料全面推广,而且政府还未发布强制实施炭基肥项目,因此目前炭基肥项目具有额外性。已有大田试验研究显示,炭基肥替代普通化肥可减少农田氧化亚氮排放17%—64%[13-14,22],甚至减少土壤生态系统甲烷的排放[14],所以炭基肥项目可以带来额外的减排量,具有额外性。不过,由于炭基肥在不同条件下所带来的减排量和增产效果不一定,且未来是否会成为普遍性作为还需要看项目实施时的情况,所以未来在参与项目前,仍需要重新根据之前叙述进行论证。
2.1.2 项目边界的选择 我国农田以碎片化、小农户经营为主;而随着人类对粮食需求的不断增加,集约化生产在提高农业生产效率、增加产量方面扮演着重要的角色,是未来农业发展的趋势[2, 32-33]。因此,在当前或者未来炭基肥农业应用的过程中,项目的实施会存在两种可能性,一种是农民购买炭基肥替代普通肥料施入农田;另一种是公司或者企业通过承包规模农场,形成“工厂-农场”的生产和应用系统,即将农场收集的秸秆运输至生物质炭和炭基肥制造工厂,将工厂生产生物质炭基肥再应用到农场当中,实现农业秸秆循环利用。
基于当前和未来土地利用方式的可能性,本研究建议将炭基肥项目的空间边界设定两种情景如图2所示。情景A指农民购买炭基肥替代化肥施用,则空间边界就是农田的地理范围;情景B是集约化企业运营,即企业从其承包的农田收集秸秆,在工厂进行生物质炭和炭基肥的生产,再将生产的炭基肥施用于农田,这个空间边界则包含了企业从工厂到农田整个地理范围。
图2
新窗口打开|下载原图ZIP|生成PPT图2项目活动边界情景
Fig. 2The boundary scenarios considered in the methodology
炭基肥项目时间边界的确定应考虑监测农业温室气体和土壤碳库两个方面。对于农田温室气体监测或计量而言,时间边界可以是一个种植季或一年;而短时间内土壤碳库的变化则很难被监测到。如果土壤有机碳变化的监测采用实地监测的方法,炭基肥项目的时间边界须设置为5—10年甚至更长的时间。鉴于碳交易项目成本的有效性原则,如果能开发用于计量炭基肥施用下土壤碳库的变化因子,则计量项目土壤碳库变化量可以直接用参考系数法,避免了实地监测,不但可以降低监测成本,还可将时间边界设置为较短的期限。
2.1.3 项目基准线的确定 基准线的确定是进行项目净碳汇量计算的至关重要的一环。根据前文对系统边界的划分,炭基肥的应用不仅影响施肥方式,还可能影响秸秆处理方式。在情景A中,施用炭基肥改变了原有施肥模式,但不会改变原有秸秆处理方式。因此,情景A的基准线情景应当是当地常规施肥处理,相对于项目情景的基准线即是常规施肥处理下的温室气体排放量和有机碳变化量。而在情景B下,由于需要收集秸秆用于炭基肥的制造,原有秸秆利用方式发生了改变,例如原有利用方式为秸秆肥料化、饲料化、基料化或能源化等。那么,在考虑基准线情景时,应当把秸秆利用方式的改变造成的温室气体排放的变化也考虑进去。然而,对于某些秸秆利用方式,例如秸秆饲料化、能源化等,一般发生在前文划定的边界以外,所以炭基肥项目导致原有秸秆利用方式发生改变所带来的温室气体额外排放,应当在泄漏中予以考虑,关于泄漏的问题在后文将进行讨论。综上所述,无论是哪种系统边界,炭基肥项目的基准线都应当是该田块常规施肥管理下的温室气体排放和土壤碳库变化量。
根据项目参与方采用的基准线在项目期内是否变动,又可将基准线划分为静态基线和动态基线。静态基线是指在项目开始前对参与项目田块的温室气体排放和土壤碳库变化情况进行监测和计量,一般取3年的平均值[16]。动态基线则是在项目实施期内,同一个区域选取管理方式、种植制度、土壤性质与参与项目农田一致的田块作为样地,每年同步监测和计量该样地的温室气体排放和土壤碳库变化量作为基线。静态基线可使田块项目实施前和实施后的结果相匹配,但温室气体排放和土壤碳库变化存在较大的年际变异,选取静态基线可能对项目净碳汇量的计量带来误差;而动态基线可以避免这个问题,但样地的选取是否合理会直接影响到计量结果的准确性。因此,本研究建议项目开始前选取与参与项目田块条件一致的样地进行动态基线的监测与计量。
2.1.4 碳库选择和关键温室气体排放源 农田生态系统碳库包括土壤有机碳库、农作物地上部生物量、地下部生物量和枯落物。农作物地上部生物量包括作物籽粒和秸秆,作物籽粒将被人类或者畜禽食用,而在炭基肥项目的边界内,秸秆无论直接还田还是炭化后还田,均将通过土壤有机质矿化过程和腐殖化过程成为土壤有机碳库的一部分。而地下部生物量和枯落物通过翻耕入土,在短时间内很容易被分解,有一小部分经过微生物分解转化又转变成为土壤有机碳库的一部分。因此,在进行固碳减排计量时,由于在进行土壤有机碳库变化计量时已经包括了地上或者地下部生物量对土壤碳库带来的影响,不需要进行重复计量[16,17]。
生物质炭具有较高的稳定性,许多研究表明生物质炭的滞留时间可达551—5 448年[34,35,36,37]。生产生物质炭并通过还田将其所含稳定的有机质存储在土壤中被认为是一种通过碳封存来减缓气候变化的方法[8]。根据炭基肥的行业标准（NY/T 3041—2016）,炭基肥应当含有>6%或>9%生物质炭,那么炭基肥的施用将带来可观的土壤固碳量。近年来已经有****意识到土壤有机碳的重要性,如BOSCO在计量葡萄酒生产链碳足迹过程中,将土壤碳库项目计量在LCA方法学中[38];保护性耕作减排增汇方法学计量了项目活动引起土壤有机碳储量的变化[17]。鉴于生物质炭所含有机碳具有高稳定性,我们认为在发展炭基肥固碳减排计量方法时土壤有机碳库应该被考虑。
农田温室气体排放主要包括生态系统二氧化碳排放和甲烷排放、土壤氧化亚氮排放、农用机械燃油排放、灌溉用能发生的排放、农用生产资料生产过程的排放等。农田生态系统二氧化碳排放包括农作物生长过程中的自养呼吸、土壤异养呼吸。农作物的自养呼吸和光合碳同化作用同时发生,而光合碳同化作用所固定的碳量远高于作物自养呼吸释放的碳量。前文已讨论得出农作物碳库不须被单独计量,而且作物自养呼吸与人为管理活动关系并不密切,农作物自养呼吸过程的二氧化碳排放在碳交易固碳减排方法学中亦不须被单独计量。土壤异养呼吸在土壤碳库变化中已有体现（碳库变化量=有机质添加量-异养呼吸量）,所以生态系统二氧化碳排放在计量方法学中不作考虑。
土壤氧化亚氮主要是由土壤硝化和反硝化过程产生,而农业氮素投入是农田土壤硝化和反硝化的主要氮素来源。已有研究表明,生物质炭对农田氧化亚氮排放有很显著的抑制效果[39],炭基肥替代普通化肥施入农田将进一步提高氮素利用率和降低单位氮肥产生氧化亚氮能力[13,14]。因此,氧化亚氮减排是炭基肥项目的重要减排来源,农田氧化亚氮排放应作为关键排放源被计入。
土壤中甲烷是产甲烷菌在厌氧条件下利用土壤中的碳基质进行代谢而产生的,稻田的淹水管理为产甲烷菌提供了适宜的产甲烷条件。尽管目前关于炭基肥施用对稻田甲烷排放的影响方面还鲜有研究,但也有研究表明[14],施入炭基肥减少了稻田生态系统甲烷排放;而一些对生物质炭农田效应的研究也证实,与常规施肥相比,尽管生物质炭施用初期甲烷排放有所增加,后期甲烷排放不再增加甚至有所下降[40,41]。因此,在炭基肥项目方法学中稻田甲烷排放也应作为关键排放源被计入,而炭基肥施用对稻田甲烷排放的影响在未来研究中应当被关注。
近年来,越来越多的农田由原来的人力、畜力作业转向农用机械作业,农业机械化提高农业生产力的同时也导致了燃油使用量的增加,带来温室气体排放[42,43,44]。不过,炭基肥替代普通化肥并不会增加或者减少农田的机械活动,因此,农田机械活动所带来的温室气体排放不计入炭基肥项目方法学中。此外,机电灌溉耗能、农用生产资料生产过程也均会带来温室气体排放,但这些排放均发生在农田边界外,且炭基肥项目未影响这两个方面的排放,在方法学中不须计入在内。
炭基肥生产过程中温室气体排放主要包括：原料（秸秆、无机肥料）运输耗油、生物质炭和炭基肥生产耗能、炭基肥运输到农田耗能。在情景B中,炭基肥生产过程的温室气体排放均发生在系统边界内,属于该情景项目应当考虑的关键排放源。
2.1.5 项目泄漏 对于边界情景A而言,由于农民参与了炭基肥项目,与常规施肥项目相比,需要额外购买炭基肥,那么,购买炭基肥的运输过程将带来运输工具燃油排放。如果购买炭基肥的地点与购买常规化肥的地点一致,或者农民将炭基肥完全替代化肥施用,项目引起的泄漏可考虑为零;如果农民仅将炭基肥部分替代化肥施用,且购买炭基肥的地点与购买化肥地点不同,甚至比购买化肥地点距离更远,则需要计算项目泄漏。
在边界情景B中,农田的秸秆均被回收用于生产炭基肥,原来的秸秆利用方式会被替代。如原有秸秆利用方式是直接还田,秸秆未还田带来的土壤固碳、温室气体排放效应将在边界内关键排放源排放量计算中予以体现;而如果原有秸秆利用方式为饲料化、能源化、原料化、基料化等,改变原有利用方式可能导致工厂需要从更远的地方运输秸秆,或者导致工厂产能发生变化,这部分额外的温室气体排放由炭基肥项目直接引起并发生在边界外,应当作为泄漏予以考虑。
2.2 固碳减排计量方法开发
2.2.1 基准线计量方法 如前所述,炭基肥项目的基准线应当是田块常规施肥管理下的温室气体排放和土壤碳库变化量,如下式：GHGB=ΔSOCB×$\frac{44}{12}$+N2OB×GWPN2O+CH4B×GWPCH4 （1）
式中,GHGB为基准线,ΔSOCB为项目期代表基线情景的样地土壤碳储量变化量（kg C·hm-2）,N2OB和CH4B是项目期基线样地的氧化亚氮（kg N2O·hm-2）和甲烷排放量（适用水稻种植,kg CH4·hm-2）,GWPN2O和GWPCH4分别是100年尺度下氧化亚氮和甲烷的全球增温潜势,根据IPCC第五次评估报告分别取265和28。
碳库和温室气体排放量的计量可以采用直接监测法、参考系数法和模型模拟法[16]。直接监测法可以体现田间实际状况,但采样点能否准确代表大面积田块的情况还须论证,且采样点的增加将大幅增加监测费用,有悖于碳交易计量方法学中的成本有效性原则。参考系数法和模型模拟法是成本低、计算方便的计量方法,近年来我国****针对土壤碳库变化、温室气体排放开发了一系列排放因子和计算机模型,也对几个知名的生态系统模型（如DNDC、DAYCENT等）进行了参数化和验证,为方法学的开发奠定了方法基础[45,46,47,48,49,50,51]。我们建议在炭基肥项目方法学开发时,优先采用我国****开发或验证过的排放因子（如氧化亚氮排放因子可参考ZOU等[48],《省级温室气体清单指南》[28],甲烷排放因子可参考YAN等[47]）和生态模型（如氧化亚氮排放可采用IAP-N模型[49,50],甲烷排放可采用CH4MOD模型[45,46]）;当然,鉴于近年来发表了大量田间试验研究,为参考系数和模型的研究提供了很好的数据基础,本研究建议进一步基于我国农田实际情况,开发适用于中国的土壤碳库变化因子、氧化亚氮和甲烷排放因子,并采用试验数据对模型进行进一步的校正和验证。
2.2.2 项目温室气体排放计量方法 边界情景A下项目温室气体排放包括土壤碳库变化、农田氧化亚氮排放和稻田甲烷排放,如下式：
GHGP=ΔSOCP×$\frac{44}{12}$+N2OP×GWPN2O+CH4P×GWPCH4 （2）
式中,GHGP为项目温室气体排放量ΔSOCP为参与项目田块项目期内土壤碳储量变化量（kg C·hm-2·a-1）,N2OP和CH4P是项目田块的氧化亚氮（kg N2O·hm-2）和甲烷排放量（适用水稻种植,kg CH4·hm-2）。
截止目前,炭基肥农田应用的模型还未开发成熟,且原有生态系统模型未将炭基肥农田应用加入到模型模块中,项目温室气体排放计量可采用直接监测法和参考系数法,鉴于成本有效性原则,建议优先采用参考系数法。
IBI对生物质炭100年内的的碳的稳定性提供了三组检测方法：Alpha方法,Beta方法,Gamma方法[52]。Alpha方法是通过测定与生物质炭稳定性相关的H/C比或者挥发性物质的含量,以最小的成本对100年尺度下生物质炭稳定性进行常规评估,几分钟到几天就可以获得结果,但不能提供绝对的稳定性度量,需要Beta和Gamma进行校准;Beta方法通过控制培养条件（培养时间3—5年）,测量生物质炭损失量,通过生物质炭的分解速率（在矿化培养分解初期,新鲜生物质炭的分解速率较大,到达后期,分解速率极度缓慢）,直接计算生物质炭稳定性,可用于校准Alpha方法;Gamma方法测定了与生物质炭稳定性有关的分子性质如生物炭的芳族缩合程度,但需要高水平专业知识、专业仪器和高昂成本,很难在炭基肥项目中进行应用。在项目实际应用中,可以通过Alpha方法快速检测生物质炭的稳定性,但测定结果会有一定的误差,而用另外两种方法验证又需要一定的监测成本。生物质炭原料类型和热裂解温度影响着生物质炭的分解速率和稳定性[53],在未来研究中可基于农业分区,针对符合国际、国家或行业标准的不同原料和工艺的生物质炭进行分解速率和稳定性的研究,然后基于大数据建立生物质炭稳定性研究手册,用于项目固碳量计量。本研究中,我们根据生物质炭的稳定性或者生物质炭的半衰期分解速率,分别开发了两种方法来计量炭基肥施用带来的土壤固碳量。
方法一：根据生物质炭中所含稳定有机碳的比例进行计算,如下式：
ΔC=FBF×BFB×BC×CS （3）
式中,ΔC为项目田块项目期内有机碳增加量（kg·hm-2）,FBF为项目期炭基肥用量（kg·hm-2）,BFB为炭基肥含生物质炭比例（%）,BC为生物质炭的含碳量（%）,CS为生物质炭的稳定性指数（%）。
生物质炭的稳定性可以根据上述3种方法（Alpha方法,Beta方法,Gamma方法）进行研究。LEHMANN等[54]依据已有生物质炭稳定性研究和生物质炭由不同形态的循环碳构成,将新鲜的生物质炭的分解分为3个平均滞留周期（10年,100年,1000年）,100年尺度下仍有超过70%的初始碳未分解。应当关注的是,项目方法学的开发还应遵循保守型原则,即计算的结果应该是保守的。例如,在计算土壤固碳量或减排量时,应当就低不就高,仅计算“至少”可以固碳或者减排多少,而避免过高估计造成计量结果不实。
方法二：根据生物质炭半衰期分解速率进行计算,如下式：
ΔC=FBF×BFB×BC×$\sum\limits^{T}_{i=1}(B_{Di})$×A （4）
式中,i是项目第i年,BDi为生物质炭第i年分解残留率（%）。
BDi可以根据Beta培养法得到生物质半衰期分解速率,生物质炭进入土壤,温度、湿度、土壤属性、耕作措施和植物碳输入等因素影响其分解速率[54]。HERATH等[55]运用同位素示踪技术对添加量为7.18 t C·hm-2生物质炭进行矿化培养实验发现,黏土矿物类型为2﹕1型的淋溶土添加生物质炭后,在第510天矿化率为7.4%—7.9%,低于火山灰土的13.2%—14.1%;BRUUN等[56]通过添加5%不同炭化温度的生物质炭进行65 d土壤矿化培养发现,高温热裂解生产的生物质炭矿化速率为5.5%高于低温生物质炭矿化速率的2.9%;章明奎等[53]添加生物质炭至土壤中进行室内培养实验发现,淹水条件下比非淹水条件下生物质炭具有更高的稳定性,且75%田间持水量下,培养36周后,加入生物质炭的碳残留率在84%—93%之间。
生物质炭对土壤氧化亚氮排放的抑制作用已有诸多报道[57,58,59,60,61],整合分析显示生物质炭施用平均减少54%的氧化亚氮排放[62]。生物质炭的固定态有机质碳架起着载体的作用,实现了炭质-矿物质-化肥养分的团聚体结合,延缓了化肥的快速溶解释放,提高了养分的缓效性[63],因此炭基肥替代化肥施用所带来的氧化亚氮减排有生物质炭的抑制作用和化学氮素投入减少两方面作用。项目田块氧化亚氮排放可由下式进行计算：
N2OP=FBF×KN×EFBN （5）
式中,KN为炭基肥含氮量（%）,EFBN为炭基肥施用的排放因子（kg N2O-N·kg-1）。炭基肥的氧化亚氮排放因子除了与土壤性质和气候条件有关,还于生物质炭原料类型、炭基肥制造工艺（掺混法、吸附法、包膜法和混合造粒法）和施入水平有密切关系[13,15,64]。目前,除了对全球文献的整合分析外,对于定量生物质炭和炭基肥施用下氧化亚氮排放因子的研究还较为有限,鉴于空间异质性和生物质炭本身的差异性,开展区域尺度不同类型生物质炭和炭基肥施用对氧化亚氮排放因子的影响定量研究将为方法学的开发提供数据支撑。
已有一些****采用整合分析讨论了生物质炭对稻田甲烷排放的影响。HE等[65]和SONG等[66]分别对全球包括田间试验、温室和室内培养试验在内的121对和31对观测值进行分析发现生物质炭施用对甲烷排放无显著影响,但是在田间试验条件下（分别为31对和24对观测值）生物质炭施用显著增加了甲烷排放;而JEFFERY等[67]则发现在淹水稻田（60对观测值）中施用生物质炭可显著降低甲烷排放。而上述3个研究所采用的数据为2014年或2015年以前发表的数据,近年来生物质炭田间应用的研究发现迅速,亟待扩充数据库进行进一步的分析。无论正效应还是负效应,本研究建议基于我国生物质炭田间应用研究数据库,细化区域和生物质炭类型及用量,发展生物质炭施用对甲烷排放的影响因子（EFCH4,无量纲）,如下式：
CH4P=CH4B×EFCH4 （6）
式中,发展影响因子EFCH4时,可基于施用生物质炭田块和对照田块甲烷排放量的比值进行确定,该值在0—1之间,说明研究区域在某种生物质炭一定用量下可减少甲烷排放,该值在1以上则说明生物质炭施用增加了甲烷排放。
边界情景B下,除边界情景A中的碳库和温室气体,还包括炭基肥生产的温室气体排放（BF,kg CO2）,如下式：
GHGP=ΔSOCP×$\frac{44}{12}$+N2OP×GWPN2O+CH4P×GWPCH4+BF （7）
炭基肥生产的温室气体排放又包括秸秆打包和运输过程中的温室气体排放（SE,kg CO2）和生产炭基肥过程的温室气体排放（BFP,kg CO2）：
BF=SE+BFP （8）
生产炭基肥过程的排放包括生物质炭生产过程和炭基肥生产过程的排放,这些排放主要通过调查工厂生产过程中的能量平衡进行计量,本研究以一个炭基肥生产公司为例,对这部分排放的计算进行示例（2.3.2）;秸秆打包一般通过机器打包和人工打包两种方式,对于规模化的承包农场来讲,一般会采用机器打包的方式,秸秆打包机打包秸秆会带来燃油排放,通过燃油量与燃油排放因子相乘进行计算。
2.2.3 项目净碳汇量计量 项目净碳汇量采用下式进行计算：
CSP= GHGB-GHGP-L （9）
式中,CSP为项目净碳汇量（kg CO2-eq·hm-2）,L为项目泄漏（kg CO2）。如前所述,在边界情景A中,如项目参与方在购置和运输炭基肥时与原来单购置化肥相比,产生显著的温室气体排放增加情况,则需要通过交通工具耗油量和燃油排放因子计算泄漏,并在项目净碳汇量计算时扣除;而在边界情景B中,如炭基肥利用替代原有秸秆利用方式导致了明显的温室气体增排的情况,则需要根据具体情况进行计算并在项目净碳汇量计算时扣除。
2.3 案例分析
基于本研究探索的炭基肥计量方法学,以炭基肥在不同作物种植（水稻和小麦）的大田试验为案例,保守性估计生物质炭的稳定性碳占到70%,对边界情景A下炭基肥项目的净碳汇量进行了估算;还根据炭基肥工厂的生产能耗调查数据,对炭基肥生产过程的温室气体排放计量进行了案例分析,进而对边界情景B下净碳汇量进行了计量。2.3.1 边界情景A 根据公式（3）计算项目活动在一个种植季所带来的固碳量,同时根据公式（9）计算了边界情景A下项目净碳汇量,计算结果如表3所示。
Table 3
表3
表3基于边界A情景的项目净碳汇量
Table 3
| 作物类型 Crop type | 基线/项目 Baseline/Project | 温室气体排放GHG emissions (kg CO2-eq·hm-2) | 净碳汇量 Net carbon sink (kg CO2-eq·hm-2) | |||
|---|---|---|---|---|---|---|
| ΔSOC | N2O | CH4 | 泄漏 Leakage | |||
| 小麦 Wheat | 基线 Baseline | 0 | 2114.70 | 0 | 0 | 1439.78 |
| 项目活动 Project activity | -96.23 | 771.15 | 0 | 0 | ||
| 水稻 Paddy rice | 基线 Baseline | 0 | 188.15 | 288.96 | 0 | 281.58 |
| 项目活动 Project activity | -144.34 | 124.55 | 215.32 | 0 | ||
新窗口打开|下载CSV
小麦种植田块项目净碳汇量为1439.78 kg CO2- eq·hm-2,而水稻种植田块的净碳汇量仅为281.58 kg CO2- eq·hm-2。其中,小麦种植季的氧化亚氮的减排量达到1 343.55 kg CO2-eq·hm-2,占净碳汇的93.32%;碳库增加的贡献仅为6.68%。而水稻种植田块碳库增加达到144.34 kg CO2-eq·hm-2,占一个水稻种植季净排放的51.26%,甲烷和氧化亚氮减排的贡献分别是22.59%和26.15%。
2.3.2 边界情景B 根据公式（8）和表1以及相关排放参数,我们计算了从原料收集到炭基肥生产整个周期的温室气体排放,如表4所示。如副产品生物质气未回收利用,炭基肥生产全生命周期的排放为102.36 kg CO2-eq·t-1,其中秸秆打包收集运输所带来的燃油排放量相对较低仅为2.89 kg CO2-eq·t-1,炭基肥生产过程排放为29.06 kg CO2-eq·t-1,占到总排放一定的比例。如优化生产工艺,对生物质气进行循环利用,则炭基肥生产全生命周期呈净碳汇效应,为-130.77 kg CO2-eq·t-1。
Table 4
表4
表4炭基肥生产过程温室气体排放
Table 4
| 排放种类 Emission sources | 排放量 GHG emissions (kg CO2-eq·t-1) |
|---|---|
| 秸秆打包收集运输 Straw packing and transportation | 2.89 |
| 生物质炭生产 Biochar production | 优化 Optimize：-162.72 未优化 Un-optimize：70.42 |
| 炭基肥生产 Biochar compound fertilizer production | 29.06 |
| 总排放 Sum of emissions | 优化Optimize：-130.77 未优化 Un-optimize：102.36 |
新窗口打开|下载CSV
由表1和表4以及公式（9）,我们可以得到B情景下项目的固碳减排量,如表5所示。对于“工厂-农场”的生产和应用系统来说,由于生产工艺不同,农田类型不同,其减排潜力差异比较大。未优化生产工艺条件下,B情景下小麦种植季带来较大的减排量,达到1 329.57 kg CO2-eq·hm-2,而一个水稻种植季项目减排量仅为235.52 kg CO2-eq·hm-2。优化生产工艺条件下,B情景下小麦种植季仍呈现较大的净碳汇效应,达1 479.1 kg CO2-eq·hm-2,而水稻仅为340.43 kg CO2-eq·hm-2。优化生产工艺条件下,炭基肥生产过程贡献了净碳汇量的3%和21%。
Table 5
表5
表5基于边界B情景的项目净碳汇量
Table 5
| 作物类型 Crop type | 基线/项目 Baseline/Project | 温室气体排放 GHG emissions (kg CO2-eq·hm-2) | 净碳汇量 Net carbon sink (kg CO2-eq·hm-2) | ||||
|---|---|---|---|---|---|---|---|
| ΔSOC | N2O | CH4 | 炭基肥 Biochar compound fertilizer | 泄漏 Leakage | |||
| 小麦 Wheat | 基线 Baseline | 0 | 2114.70 | 0 | 0 | 0 | 1479.01/1329.57 |
| 项目活动 Project activity | -96.23 | 771.15 | 0 | -39.23/30.71 | 0 | ||
| 水稻 Paddy rice | 基线 Baseline | 0 | 188.15 | 288.96 | 0 | 0 | 340.43/235.52 |
| 项目活动 Project activity | -114.34 | 124.55 | 215.32 | -58.85/40.06 | 0 | ||
新窗口打开|下载CSV
从上述案例分析可以看出,无论哪种情景,稻作的项目减排量均低于旱作约18%—23%,说明不同作物种植或种植制度下的减排效应有较大差异[68]。生物质炭生产工艺的优化程度也影响着项目的减排量（特别是水田）,加强副产品（如可燃气的利用）是生物质炭产业发展需要解决的关键问题[31],直接影响着炭基肥项目是否能通过参与碳交易获得更多的环境和经济收益。通过案例分析,我们验证了前文讨论开发的计量方法学,无论是碳库和关键排放源的确定还是计量方法的选取都适用于炭基肥项目的计量。然而,在计量土壤固碳时,我们采用了保守型估计,温室气体排放计量则直接采用试验监测结果。未来亟待进行大量的试验研究,特别是田间原位监测,获取更多的数据进行排放因子的开发,进而发展用于模拟生物质炭和炭基肥农田生态过程的模型,为炭基肥项目参与碳交易提供详实的数据支撑。
3 结论
本研究提出了以常规施肥和常规秸秆利用方式为基准线情景,并根据不同农田经营模式提出了两种空间边界情景（农民直接参与的田块模式和工厂-农田的企业集约化运营模式）,确定了以农田氧化亚氮排放和甲烷排放为关键排放源、土壤有机碳库为碳库,农民运输炭基肥导致的额外排放或原有秸秆利用方式发生改变导致的额外排放为泄漏的方法学理论框架,并对固碳减排计量方法进行了探索,提出了未来应进一步开发不同区域、不同原料类型和热裂解工艺的炭基肥氧化亚氮和甲烷排放因子,以及所含有机碳的稳定性因子和分解速率。基于本研究开发的方法学结合案例进行了分析,论证了方法学应用于炭基肥项目固碳减排计量的可行性,发现炭基肥生产过程的温室气体排放与生产工艺有直接关系,未优化生产工艺时炭基肥生产过程排放为102.36 kg CO2-eq·t-1,而优化工艺后为-130.77 kg CO2-eq·t-1。对案例进行项目净碳汇量计量发现,优化生产工艺情景下稻作农田和旱作农田的项目净碳汇量比未优化情景多104.91 和69.94 kg CO2-eq·hm-2。
参考文献 原文顺序
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Abstract Soils are subject to varying degrees of direct or indirect human disturbance, constituting a major global change driver. Factoring out natural from direct and indirect human influence is not always straightforward, but some human activities have clear impacts. These include land-use change, land management and land degradation (erosion, compaction, sealing and salinization). The intensity of land use also exerts a great impact on soils, and soils are also subject to indirect impacts arising from human activity, such as acid deposition (sulphur and nitrogen) and heavy metal pollution. In this critical review, we report the state-of-the-art understanding of these global change pressures on soils, identify knowledge gaps and research challenges and highlight actions and policies to minimize adverse environmental impacts arising from these global change drivers. Soils are central to considerations of what constitutes sustainable intensification. Therefore, ensuring that vulnerable and high environmental value soils are considered when protecting important habitats and ecosystems, will help to reduce the pressure on land from global change drivers. To ensure that soils are protected as part of wider environmental efforts, a global soil resilience programme should be considered, to monitor, recover or sustain soil fertility and function, and to enhance the ecosystem services provided by soils. Soils cannot, and should not, be considered in isolation of the ecosystems that they underpin and vice versa. The role of soils in supporting ecosystems and natural capital needs greater recognition. The lasting legacy of the International Year of Soils in 2015 should be to put soils at the centre of policy supporting environmental protection and sustainable development.
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自愿减排交易是指相对中清洁发展机制 的发展,在市场机制下相伴形成的非强制性减排项目交易行为.伴随碳排放强度指标的分解和实施等机制的深入探讨,我国作为最大的碳排放权交易潜力市场,对自 愿减排交易中介机构、交易品种、核证标准等的研究亟待不断深入.本文通过归纳有关国内自愿减排交易的市场机理,分析自愿减排实施中存在的风险,探讨通过实 施不同的手段和方法,提出符合国情的推动国内自愿减排交易发展的政策建议.
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自愿减排交易是指相对中清洁发展机制 的发展,在市场机制下相伴形成的非强制性减排项目交易行为.伴随碳排放强度指标的分解和实施等机制的深入探讨,我国作为最大的碳排放权交易潜力市场,对自 愿减排交易中介机构、交易品种、核证标准等的研究亟待不断深入.本文通过归纳有关国内自愿减排交易的市场机理,分析自愿减排实施中存在的风险,探讨通过实 施不同的手段和方法,提出符合国情的推动国内自愿减排交易发展的政策建议.
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Agricultural lands occupy 37% of the earth's land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO60, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500-6000 Mt CO60-eq. yr6301, with economic potentials of approximately 1500-1600, 2500-2700 and 4000-4300 Mt CO60-eq. yr6301 at carbon prices of up to 20, up to 50 and up to 100 US$ t CO60-eq.6301, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000 Mt CO60-eq. yr6301 at 0-20, 0-50 and 0-100 US$ t CO60-eq.6301, respectively.
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Treatment of crop straw has been an increasingly great challenge for China's agriculture and rural environment in the past decade. To break up institutional obstacles existing in straw treatment and burning ban, industrialized treatment for commercialized products has to be developed in line with market economy. Such industrialized treatment should focus on balanced utilization of energy and nutrients recycled in agriculture. In this review, biomass pyrolysis is introduced and its merits in straw treatment are discussed in detail. Addressing the properties and functions of biochar in soils and the agro-environment, we review the development of straw pyrolysis and biochar production, focusing on soil quality improvement and safe crop production in green agriculture. Industrialization of biomass pyrolysis and biochar production offers safe treatment of crop straw as well as new resources for agricultural production as biochar can be used to improve soil fertility, providing a green and innovative way for crop straw recycling. In the context of straw burning ban, the government is suggested to establish and improve subsidy policies for straw treatment, enhance supporting services for straw collection, and encourage the emerging industrial advantages of biomass pyrolysis to solve the problem of straw treatment through marketized development of green agriculture for developing sustainable agriculture in China.
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Treatment of crop straw has been an increasingly great challenge for China's agriculture and rural environment in the past decade. To break up institutional obstacles existing in straw treatment and burning ban, industrialized treatment for commercialized products has to be developed in line with market economy. Such industrialized treatment should focus on balanced utilization of energy and nutrients recycled in agriculture. In this review, biomass pyrolysis is introduced and its merits in straw treatment are discussed in detail. Addressing the properties and functions of biochar in soils and the agro-environment, we review the development of straw pyrolysis and biochar production, focusing on soil quality improvement and safe crop production in green agriculture. Industrialization of biomass pyrolysis and biochar production offers safe treatment of crop straw as well as new resources for agricultural production as biochar can be used to improve soil fertility, providing a green and innovative way for crop straw recycling. In the context of straw burning ban, the government is suggested to establish and improve subsidy policies for straw treatment, enhance supporting services for straw collection, and encourage the emerging industrial advantages of biomass pyrolysis to solve the problem of straw treatment through marketized development of green agriculture for developing sustainable agriculture in China.
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Abstract Production of biochar (the carbon (C)-rich solid formed by pyrolysis of biomass) and its storage in soils have been suggested as a means of abating climate change by sequestering carbon, while simultaneously providing energy and increasing crop yields. Substantial uncertainties exist, however, regarding the impact, capacity and sustainability of biochar at the global level. In this paper we estimate the maximum sustainable technical potential of biochar to mitigate climate change. Annual net emissions of carbon dioxide (CO(2)), methane and nitrous oxide could be reduced by a maximum of 1.8090009Pg CO(2)-C equivalent (CO(2)-C(e)) per year (12% of current anthropogenic CO(2)-C(e) emissions; 1090009Pg=1090009Gt), and total net emissions over the course of a century by 130090009Pg CO(2)-C(e), without endangering food security, habitat or soil conservation. Biochar has a larger climate-change mitigation potential than combustion of the same sustainably procured biomass for bioenergy, except when fertile soils are amended while coal is the fuel being offset.
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A promising option to sequester carbon in agricultural soils is the inclusion of cover crops in cropping systems. The advantage of cover crops as compared to other management practices that increase soil organic carbon (SOC) is that they neither cause a decline in yields, like extensification, nor carbon losses in other systems, like organic manure applications may do. However, the effect of cover crop green manuring on SOC stocks is widely overlooked. We therefore conducted a meta-analysis to derive a carbon response function describing SOC stock changes as a function of time. Data from 139 plots at 37 different sites were compiled. In total, the cover crop treatments had a significantly higher SOC stock than the reference croplands. The time since introduction of cover crops in crop rotations was linearly correlated with SOC stock change (R2=0.19) with an annual change rate of 0.32±0.08Mgha611yr611 in a mean soil depth of 22cm and during the observed period of up to 54 years. Elevation above sea level of the plot and sampling depth could be used as explanatory variables to improve the model fit. Assuming that the observed linear SOC accumulation would not proceed indefinitely, we modeled the average SOC stock change with the carbon turnover model RothC. The predicted new steady state was reached after 155 years of cover crop cultivation with a total mean SOC stock accumulation of 16.7±1.5Mgha611 for a soil depth of 22cm. Thus, the C input driven SOC sequestration with the introduction of cover crops proved to be highly efficient. We estimated a potential global SOC sequestration of 0.12±0.03PgCyr611, which would compensate for 8% of the direct annual greenhouse gas emissions from agriculture. However, altered N2O emissions and albedo due to cover crop cultivation have not been taken into account here. Data on those processes, which are most likely species-specific, would be needed for reliable greenhouse gas budgets.
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More than two thirds of global nitrous oxide (N2O) emissions originate from soil, mainly associated with the extensive use of nitrogen (N) fertilizers in agriculture. Although the interaction of black carbon with the N cycle has been long recognized, the impact of biochar on N2O emissions has only recently been studied. Herein we reflect on proposed hypotheses to explain N2O decrease with biochar, linking them to specific mechanisms for N2O formation and consumption in soil. Moreover, to assist in elucidating key mechanisms in which biochar may act in mitigating emissions of N2O, we undertook a meta-analysis using published literature from 2007 to 2013. This quantitative analysis used 30 studies with 261 experimental treatments. Overall, we found that biochar reduced soil N2O emissions by 54% in laboratory and field studies. The biochar feedstock, pyrolysis conditions and C/N ratio were shown to be key factors influencing emissions of N2O while a direct correlation was found between the biochar application rate and N2O emission reductions. Interactions between soil texture and biochar and the chemical form of N fertilizer applied with biochar were also found to have a major influence on soil N2O emissions. While there is clear evidence that, in many cases, emissions of N2O are reduced, there is still a significant lack in understanding of the key mechanisms which result in these changed emissions. As such, we have guided readers with suggestions to address specific research gaps, which we anticipate will enhance our knowledge and understanding of biochar's N2O emission mitigation potential.
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For the last decade, there has been an increasing global interest in using biochar to mitigate climate change by storing carbon in soil. However, there is a lack of detailed knowledge on the impact of biochar on the crop productivity in different agricultural systems. The objective of this study was to quantify the effect of biochar soil amendment (BSA) on crop productivity and to analyze the dependence of responses on experimental conditions.A weighted meta-analysis was conducted based on data from 103 studies published up to April, 2013. The effect of BSA on crop productivity was quantified by characterizing experimental conditions.In the published experiments, with biochar amendment rates generally The analysis suggests a promising role for BSA in improving crop productivity especially for dry land crops, and in acid, poor-structured soils though there was wide variation with soil, crop and biochar properties. Long-term field studies are needed to elucidate the persistence of BSA's effect and the mechanisms for improving crop production in a wide range of agricultural conditions. At current prices and C-trading schemes, however, BSA would not be cost-effective unless persistent soil improvement and crop response can be demonstrated.
DOI:10.3969/j.issn.1008-0864.2011.01.12URL [本文引用: 2]
我国农田秸秆和生活垃圾等农业和农村有机废弃物面广量大,其资源化处理一直没有得到根本性解 决。开发高效低耗有机废弃物生物质碳工程转化产业化技术,以新型碳质产品就近回田回村实现农业循环,而服务于农业生产和农村生活,可能是农业和农村有机废 弃物循环利用并促进农业固碳减排的最佳解决方案。新近已经开发出不同规格和型号的中小型生物质转化工程装备,可供在农村/集镇就地集中处理秸秆、生活垃 圾,并形成可燃气、生物黑炭等原产品和生物有机肥、炭基新型肥料和调理剂等产业链产品。在农村示范建设的生物质碳化厂,可以提供农村生活能源,产出商品有 机肥和炭基肥料、调理剂等,实现低投资、低能耗（生产本身不耗能）、多产品和直接服务于当地农业增产增汇增收、新农村能源建设的新型产业化,为我国低碳农 业和循环农业以及国际农业减排技术竞争提供根本的技术支撑。同时,有望形成转化装备、转化产品和农村经营模式的一体化技术体系,向发展中国家输出。
DOI:10.3969/j.issn.1008-0864.2011.01.12URL [本文引用: 2]
我国农田秸秆和生活垃圾等农业和农村有机废弃物面广量大,其资源化处理一直没有得到根本性解 决。开发高效低耗有机废弃物生物质碳工程转化产业化技术,以新型碳质产品就近回田回村实现农业循环,而服务于农业生产和农村生活,可能是农业和农村有机废 弃物循环利用并促进农业固碳减排的最佳解决方案。新近已经开发出不同规格和型号的中小型生物质转化工程装备,可供在农村/集镇就地集中处理秸秆、生活垃 圾,并形成可燃气、生物黑炭等原产品和生物有机肥、炭基新型肥料和调理剂等产业链产品。在农村示范建设的生物质碳化厂,可以提供农村生活能源,产出商品有 机肥和炭基肥料、调理剂等,实现低投资、低能耗（生产本身不耗能）、多产品和直接服务于当地农业增产增汇增收、新农村能源建设的新型产业化,为我国低碳农 业和循环农业以及国际农业减排技术竞争提供根本的技术支撑。同时,有望形成转化装备、转化产品和农村经营模式的一体化技术体系,向发展中国家输出。
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选择了棉花秸秆(CBF)、玉米秸秆(MSF)、小麦秸秆(WSF)、稻壳(RHF)、花生壳(PHF)和生活废弃物(HWF)6种炭基复合肥,以当地常规化肥施用为对照(CF),研究田间条件下不同生物质炭复合肥对小麦产量及麦田温室气体排放的影响。小麦基肥中炭基复合肥和常规肥料的施用量分别为300 kg hm-2和356 kg hm-2,后期均追施等量的复合肥及尿素。结果表明:施用6种生物质炭复合肥均显著提高了小麦的产量,增产幅度达20%~35.4%,氮肥偏生产力也显著提高17.9%~34.4%,其中花生壳、棉花秸秆和玉米秸秆炭基复合肥处理下的小麦产量和氮肥偏生产力显著高于生活废弃物和小麦秸秆炭基复合肥。施用生物质炭复合肥均显著降低了麦田N2O的排放,减排幅度在56.0%~65.4%,但不同炭基复合肥间没有显著的差异。生物质炭复合肥对麦田CH4及CO2的排放无显著影响。麦田的全球增温潜势(GWP)和温室气体排放强度(GHGI)在施用生物质炭复合肥处理下分别降低57.5%~66.9%和68.0%~77.5%。由此可见,生物质炭复合肥在提高氮肥偏生产力和作物产量以及温室气体减排方面具有较大的应用潜力。
URL [本文引用: 6]
选择了棉花秸秆(CBF)、玉米秸秆(MSF)、小麦秸秆(WSF)、稻壳(RHF)、花生壳(PHF)和生活废弃物(HWF)6种炭基复合肥,以当地常规化肥施用为对照(CF),研究田间条件下不同生物质炭复合肥对小麦产量及麦田温室气体排放的影响。小麦基肥中炭基复合肥和常规肥料的施用量分别为300 kg hm-2和356 kg hm-2,后期均追施等量的复合肥及尿素。结果表明:施用6种生物质炭复合肥均显著提高了小麦的产量,增产幅度达20%~35.4%,氮肥偏生产力也显著提高17.9%~34.4%,其中花生壳、棉花秸秆和玉米秸秆炭基复合肥处理下的小麦产量和氮肥偏生产力显著高于生活废弃物和小麦秸秆炭基复合肥。施用生物质炭复合肥均显著降低了麦田N2O的排放,减排幅度在56.0%~65.4%,但不同炭基复合肥间没有显著的差异。生物质炭复合肥对麦田CH4及CO2的排放无显著影响。麦田的全球增温潜势(GWP)和温室气体排放强度(GHGI)在施用生物质炭复合肥处理下分别降低57.5%~66.9%和68.0%~77.5%。由此可见,生物质炭复合肥在提高氮肥偏生产力和作物产量以及温室气体减排方面具有较大的应用潜力。
DOI:10.1080/17583004.2014.912866URL [本文引用: 7]
Background: Biochar from pyrolysis of biomass amended in soils to improve nitrogen use efficiency for enhancing crop productivity and mitigate climate change in agriculture has been well documented. However, application for soil amendment of biochar at high rates could be challenged with cost-effectiveness for small-scale household farms. Results: This study, by field testing four organic/inorganic compound fertilizers of biochars pyrolysed via different biowastes compared with conventional chemical fertilizer in a rice paddy, evidenced that biochar compound fertilizer application at a much lower rate of N input ensured rice productivity by improving N use efficiency and reduced GHG emission in rice production. Conclusion: Use of biowaste-converted biochars for organic/inorganic compound fertilizer can be an option to achieve high productivity and low carbon intensity along with saving N nitrogen fertilizer use in Chinese rice agriculture.
DOI:10.1016/j.agee.2017.02.034URL [本文引用: 3]
While biochar use for soil amendment has been widely tested in world agriculture, little is known on crop production, greenhouse gases (GHG) emissions and economic performance of biochar used as compound fertilizer (BCF) combined with chemical nutrients. Using a field experiment in a low fertility Inceptisol from North China Plain, changes under different combinations with BCF in maize ( Zea mays L.) growth, in grain yield and in GHGs emission were examined, as well as economical net farm income impact was analyzed. The treatments included: No fertilizer (Blank), inorganic compound fertilizer in 100% N dose (ICF-N) as control, combination of BCF and ICF in 100% N dose (BCFj-N, 40% of N derived from BCF) and in 80% N dose (BCFj-Nr, 50% of N derived from BCF) as well as BCF in 100% N dose (BCF-N, all N derived from BFC). Soil properties, agronomic traits and grain yield were measured at harvest while soil GHG emissions monitored across the whole growing season as well as cost-benefit analysis performed using the sale prices of all fertilizer inputs and grain outputs, for a single maize production cycle. Results showed that BCF significantly increased grain yield by 10.7% and carbon efficiency by 46.2%% of maize production, compared to the ICF. Meanwhile, BCF with full N provided exerted a 43.1% increase in nitrogen agronomic use efficiency, a 12% increase in net income and in cost efficiency, over the ICF. However, the fertilization partly combined with BCF did not exert positive effects. These benefits of BCF fertilization could be attributed partly to soil improvement especially of moisture regime and phosphorus supply for maize growth, apart from its potential to slow nutrient release for prolonged supply to plant nutrition. Our findings suggest that biochar compound fertilizers can substitute chemical fertilizers for maize production in North China and allow farmers to receive higher net income via increased yields.
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DOI:10.3969/j.issn.0253-9705.2008.24.030URL [本文引用: 1]
在开发清洁发展机制(CDM)项目的过程中,项目识别是第一步也 是极其重要的一步,它关系到项目开发一系列步骤的顺利实施,更会对项目注册风险和减排量核证产生重大的影响.本文从截至2008年10月8日已得到中华人 民共和国国家发展和改革委员会批准的项目出发,对这些项目的温室气体减排类型和涉及的相关企业类型作了详细的分析和汇总,总结出识别CDM项目合格与否的 简便而有效的方法和步骤.
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DOI:10.3969/j.issn.0253-9705.2008.24.030URL [本文引用: 1]
在开发清洁发展机制(CDM)项目的过程中,项目识别是第一步也 是极其重要的一步,它关系到项目开发一系列步骤的顺利实施,更会对项目注册风险和减排量核证产生重大的影响.本文从截至2008年10月8日已得到中华人 民共和国国家发展和改革委员会批准的项目出发,对这些项目的温室气体减排类型和涉及的相关企业类型作了详细的分析和汇总,总结出识别CDM项目合格与否的 简便而有效的方法和步骤.
DOI:10.3969/j.issn.1673-1212.2007.05.009URL
随着清洁发展机制(CDM)在全球的迅速发展,在中国也有越来越多的企业投入其中.在开发CDM项目的过程中,项目合格性的识别是第一步也是极其重要的一步,它关系到项目开发一系列步骤的顺利实施,更会对项目注册风险和减排量核证产生重大的影响.在识别项目合格性时需要考虑众多因素,其中最为重要的就是额外性分析,它是CDM项目的典型特征.另外,利益相关者的意见作为单独考虑的重要方面也需要引起足够的重视.
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DOI:10.3969/j.issn.1673-1212.2007.05.009URL
随着清洁发展机制(CDM)在全球的迅速发展,在中国也有越来越多的企业投入其中.在开发CDM项目的过程中,项目合格性的识别是第一步也是极其重要的一步,它关系到项目开发一系列步骤的顺利实施,更会对项目注册风险和减排量核证产生重大的影响.在识别项目合格性时需要考虑众多因素,其中最为重要的就是额外性分析,它是CDM项目的典型特征.另外,利益相关者的意见作为单独考虑的重要方面也需要引起足够的重视.
URL [本文引用: 2]
该文以山东民和集约化养鸡场为案例,利用清洁发展机制理事会批准的方法(ACM0010),分析了沼气池处理鸡场粪便及污水、利用沼气发电替代以燃煤为主的电网电能和减少温室气体排放 的潜力.项目每年可减排温室气体为84666 t CO2-e.公司每年售电获利767万元,减排获益593万元.由于有CDM项目的额外收入,使项目的投资年限由原来的19.7 a缩短为6.0a.因此,在规模化养殖场建设沼气池并利用沼气发电,不仅减少粪便对周边环境的污染、充分利用可再生能源和减少化石燃料的使用,还能减少温 室气体的排放,获得额外的减排收益,在很大程度上提高了企业建没大型沼气工程的积极性.
URL [本文引用: 2]
该文以山东民和集约化养鸡场为案例,利用清洁发展机制理事会批准的方法(ACM0010),分析了沼气池处理鸡场粪便及污水、利用沼气发电替代以燃煤为主的电网电能和减少温室气体排放 的潜力.项目每年可减排温室气体为84666 t CO2-e.公司每年售电获利767万元,减排获益593万元.由于有CDM项目的额外收入,使项目的投资年限由原来的19.7 a缩短为6.0a.因此,在规模化养殖场建设沼气池并利用沼气发电,不仅减少粪便对周边环境的污染、充分利用可再生能源和减少化石燃料的使用,还能减少温 室气体的排放,获得额外的减排收益,在很大程度上提高了企业建没大型沼气工程的积极性.
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DOI:10.11924/j.issn.1000-6850.2014-2393URL [本文引用: 2]
炭基缓释肥是利用稻壳炭与常规尿素混合制成的长效肥料,具有肥效久,不污染环境,能够改善土壤理化性质,减少化肥农药使用量等优点。为了筛选缓释效果最好、适于玉米生长的炭基肥料,以‘华玉8号’为试材,以常规肥为对照,在施肥量均等的条件下,研究了炭粉和氮素养分配比不同的炭基缓释肥料在玉米上的施用效果。结果表明:土壤中添加稻壳炭有利于玉米的生长发育;稻壳炭基缓释肥对玉米的生长发育影响显著,能促进根系发育,使得玉米株高、茎粗增加明显。其中,施加炭粉尿素百分比为32.3%的炭基缓释肥肥效最好,与施加等量纯尿素相比可使玉米株高增加6.2%,茎粗增加10.83%,根干重增加50.7%,产量增加7.64%。
DOI:10.11924/j.issn.1000-6850.2014-2393URL [本文引用: 2]
炭基缓释肥是利用稻壳炭与常规尿素混合制成的长效肥料,具有肥效久,不污染环境,能够改善土壤理化性质,减少化肥农药使用量等优点。为了筛选缓释效果最好、适于玉米生长的炭基肥料,以‘华玉8号’为试材,以常规肥为对照,在施肥量均等的条件下,研究了炭粉和氮素养分配比不同的炭基缓释肥料在玉米上的施用效果。结果表明:土壤中添加稻壳炭有利于玉米的生长发育;稻壳炭基缓释肥对玉米的生长发育影响显著,能促进根系发育,使得玉米株高、茎粗增加明显。其中,施加炭粉尿素百分比为32.3%的炭基缓释肥肥效最好,与施加等量纯尿素相比可使玉米株高增加6.2%,茎粗增加10.83%,根干重增加50.7%,产量增加7.64%。
DOI:10.11841/j.issn.1007-4333.2014.02.05URL [本文引用: 2]
Crop residue will bring a remarkable economical,environmental and social benefits when they are utilized industrially as an important non-food biomass feedstock in large-scale.However,prior to industrial utilization,it is necessary to analyze the cost of production in order to ensure the economic viability.This present study discussed the economics of the wheat residue logistic system including collection,storage,transportation based on the field practices of Henan Tianguan enterprise group.In order to provide scientific guide to reduce the production cost,the factors which influence total cost of wheat residue logistic chain was analyzed using Monte Carlo method.The results showed that,in descending order,the highest total cost of the four investigated wheat residue supply patterns is from manual scattered mode,manual baled mode,mechanical scattered mode,mechanical baled mode,with the cost of 298,265,252,222 CNY/t,respectively.Monte Carlo simulation results showed that the influence of farmer labor price and manual collection rate on the total cost have reached significant level;whereas the effect of harvest rate and sustainable removable yield on the total cost did not show significant difference.
DOI:10.11841/j.issn.1007-4333.2014.02.05URL [本文引用: 2]
Crop residue will bring a remarkable economical,environmental and social benefits when they are utilized industrially as an important non-food biomass feedstock in large-scale.However,prior to industrial utilization,it is necessary to analyze the cost of production in order to ensure the economic viability.This present study discussed the economics of the wheat residue logistic system including collection,storage,transportation based on the field practices of Henan Tianguan enterprise group.In order to provide scientific guide to reduce the production cost,the factors which influence total cost of wheat residue logistic chain was analyzed using Monte Carlo method.The results showed that,in descending order,the highest total cost of the four investigated wheat residue supply patterns is from manual scattered mode,manual baled mode,mechanical scattered mode,mechanical baled mode,with the cost of 298,265,252,222 CNY/t,respectively.Monte Carlo simulation results showed that the influence of farmer labor price and manual collection rate on the total cost have reached significant level;whereas the effect of harvest rate and sustainable removable yield on the total cost did not show significant difference.
URL [本文引用: 2]
DOI:10.1016/j.jclepro.2018.05.026URL [本文引用: 2]
Competitive utilization of straw is a challenge faced by developing countries such as China with the increase of crop production. Biochar, briquette fuel and combined heat and power generation are the three main new measures for straw utilization in recent years; however, there is still a knowledge gap for environmental and economic effects of these utilizations in China. To address this issue, combined life-cycle analysis and cost-benefit analysis was employed to assess the environmental impacts and economic benefits of biochar, briquette fuel and combined heat and power generation applications based on three cases in China. The results suggested that biochar was the most promising technology for straw utilization in China for its highest greenhouse gas mitigation potential i.e. 610.9462t CO 2 equivalent (CO 2 e) per ton straw utilized and high profit with a net present value per ton straw of 20.98 U.S. dollars with the baseline of crop straw return including carbon revenue. Briquette fuel also deserves to achieve a best net present value ratio of 5.06 and GHG abatement potential being 610.962t CO 2 t 611 straw. However, the waste of straw ash could bring some pollution risk without suitable treatment. The economic potential of the combined heat and power generation project that produces bioelectricity, is not considerable with a very low net present value ratio of 0.007 and a mitigation potential of 610.03 tCO 2 e t 611 straw due to low energy utilization efficiency of direct combustion. Biochar could be one of the most potential economic and environmental sustainable straw utilization technologies in China though the wide production and application is still a big challenge in future.
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DOI:10.3981/j.issn.1000-7857.2015.13.015URL [本文引用: 2]
Treatment of crop straw has been an increasingly great challenge for China's agriculture and rural environment in the past decade. To break up institutional obstacles existing in straw treatment and burning ban, industrialized treatment for commercialized products has to be developed in line with market economy. Such industrialized treatment should focus on balanced utilization of energy and nutrients recycled in agriculture. In this review, biomass pyrolysis is introduced and its merits in straw treatment are discussed in detail. Addressing the properties and functions of biochar in soils and the agro-environment, we review the development of straw pyrolysis and biochar production, focusing on soil quality improvement and safe crop production in green agriculture. Industrialization of biomass pyrolysis and biochar production offers safe treatment of crop straw as well as new resources for agricultural production as biochar can be used to improve soil fertility, providing a green and innovative way for crop straw recycling. In the context of straw burning ban, the government is suggested to establish and improve subsidy policies for straw treatment, enhance supporting services for straw collection, and encourage the emerging industrial advantages of biomass pyrolysis to solve the problem of straw treatment through marketized development of green agriculture for developing sustainable agriculture in China.
DOI:10.3981/j.issn.1000-7857.2015.13.015URL [本文引用: 2]
Treatment of crop straw has been an increasingly great challenge for China's agriculture and rural environment in the past decade. To break up institutional obstacles existing in straw treatment and burning ban, industrialized treatment for commercialized products has to be developed in line with market economy. Such industrialized treatment should focus on balanced utilization of energy and nutrients recycled in agriculture. In this review, biomass pyrolysis is introduced and its merits in straw treatment are discussed in detail. Addressing the properties and functions of biochar in soils and the agro-environment, we review the development of straw pyrolysis and biochar production, focusing on soil quality improvement and safe crop production in green agriculture. Industrialization of biomass pyrolysis and biochar production offers safe treatment of crop straw as well as new resources for agricultural production as biochar can be used to improve soil fertility, providing a green and innovative way for crop straw recycling. In the context of straw burning ban, the government is suggested to establish and improve subsidy policies for straw treatment, enhance supporting services for straw collection, and encourage the emerging industrial advantages of biomass pyrolysis to solve the problem of straw treatment through marketized development of green agriculture for developing sustainable agriculture in China.
DOI:10.1016/j.scitotenv.2017.04.064URLPMID:28415005 [本文引用: 1]
Global population increase will require rapid increase of food production from existing agricultural land by 2050, which will inevitably mean the increase of agricultural productivity. Due to agricultural sustainable intensification since the 1990s, crop production in Huantai County of northern China has risen to 15tha(-1)yr(-1) for the annual wheat-maize rotation system. We examined the temporal dynamics of nitrogen (N) budget, N losses, and N use efficiency (NUE) during the 35years (1980-2014) in Huantai. The results revealed that atmospheric N deposition increased 220% while reactive N losses decreased by 21.5% from 1980s to 2010s. During 1980-2002, annual N partial factor productivity (PFPN), apparent NUE and N recovery efficiency (REN) increased from 20.3 to 40.7kggrainkg(-1)Nfert, from 36.5% to 71.0%, and from 32.4% to 57.7%, respectively; meanwhile, reactive N losses intensity, land use intensity and N use intensity decreased by 69.8%, 53.4%, 50.0%, respectively, but without further significant changes after 2002. Overall increases in NUE and decreases in N losses were largely due to the introduction of optimized fertilization practice, mechanization and increased incorporation of crop straw in Huantai. Straw incorporation was also significant in soil N stock accrual and fertility improvement. By 2030, northern China may reach the lowest end of PFPN values in developed countries (>45kggrainkg(-1)Nfert). These agricultural sustainable intensification practices will be critical in maintaining high grain yields and associated decreases in environmental pollution, although water use efficiency in the region still needs to be improved. [Abstract copyright: Copyright 2017 Elsevier B.V. All rights reserved.]
DOI:10.1073/pnas.0914216107URL [本文引用: 1]
DOI:10.1111/gcb.12468URLPMID:24227744 [本文引用: 1]
Rice straw burning has accompanied paddy management for millennia, introducing black carbon (BC) into soil as the residue of incomplete combustion. This study examined the contribution of BC to soil organic matter and the rate at which it accumulates in paddy soils as a result of prolonged paddy management. Soil depth profiles were sampled along a chronosequence of 0–2000 years of rice–wheat rotation systems and adjacent non-paddy systems (50–700 years) in the Bay of Hangzhou (Zhejiang province, China). The soil BC content and its degree of condensation were assessed using benzene-polycarboxylic acids (BPCAs) as geochemical markers. The results showed that despite regular long term BC input, BC only contributed 7–11% of total soil organic carbon (SOC) in the topsoil horizons. Nevertheless, along with SOC, paddy soils accumulated BC with increasing duration of management until 297 years to reach a steady-state of 13 t BC ha611. This was 1.8 times more than in non-paddy soils. The fate of BC in paddy soils (0–1 m) could be modeled revealing an average annual input of 44 kg ha611 yr611, and a mean residence time of 303 years. The subsoils contributed at least 50% to overall BC stocks, which likely derived from periods prior to land embankment and episodic burial of ancient topsoil, as also indicated by BPCA pattern changes. We conclude that there is a significant but limited accumulation of C in charred forms upon prolonged paddy management. The final contribution of BC to total SOC in paddy soils was similar to that in other aerobic ecosystems of the world.
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DOI:10.5194/bg-9-2847-2012URL [本文引用: 1]
Pyrogenic carbon (PyC), the residue of an incomplete combustion of biomass, is considered as a carbon (C) sink due to its assumed stability in soil. PyC turnover time estimated using two modelling approaches, based on data from 16 published studies (n = 54) on PyC degradation, ranged from a decadal to centennial time scale, varying with initial biomass type, pyrolysis temperature, and incubation or field study. The average turnover time using a one-pool approach was 88 y, and the best estimate using a two-pool approach was 3 y for a fast-cycling pool and 870 y for a slow-cycling pool. Based on this meta-analysis, PyC cannot be assumed to persist in soils for thousands of years, and its use as a strategy for offsetting carbon emissions requires prudence and further research.
DOI:10.1038/ngeo358URL [本文引用: 1]
Annual emissions of carbon dioxide from soil organic carbon are an order of magnitude greater than all anthropogenic carbon dioxide emissions taken together. Global warming is likely to increase the decomposition of soil organic carbon, and thus the release of carbon dioxide from soils, creating a positive feedback. Current models of global climate change that recognize this soil carbon feedback are inaccurate if a larger fraction of soil organic carbon than postulated has a very slow decomposition rate. Here we show that by including realistic stocks of black carbon in prediction models, carbon dioxide emissions are reduced by 18.3 and 24.4% in two Australian savannah regions in response to a warming of 3C over 100 years. This reduction in temperature sensitivity, and thus the magnitude of the positive feedback, results from the long mean residence time of black carbon, which we estimate to be approximately 1,300 and 2,600 years, respectively. The inclusion of black carbon in climate models is likely to require spatially explicit information about its distribution, given that the black carbon content of soils ranged from 0 to 82% of soil organic carbon in a continental-scale analysis of Australia. We conclude that accurate information about the distribution of black carbon in soils is important for projections of future climate change.
DOI:10.1007/s11367-013-0567-3URL [本文引用: 1]
PurposeConcerns about global warming led to the calculation of the carbon footprint (CF) left by human activities. The agricultural sector is a significant source of greenhouse gas (GHG) emissions, though cropland soils can also act as sinks. So far, most LCA studies on agricultural products have not considered changes in soil organic matter (SOM). This paper aimed to: (1) integrate the Hénin–Dupuis SOM model into the CF study and (2) outline the impacts of different vineyard soil management scenarios on the overall CF.MethodsA representative wine chain in the Maremma Rural District, Tuscany (Italy), made up of a cooperative winery and nine of its associated farms, was selected to investigate the production of a non-aged, high-quality red wine. The system boundary was established from vineyard planting to waste management after use. The functional unit (FU) chosen for this study was a 0.75-L bottle of wine, and all data refer to the year 2009. The SOM balance, based on Hénin–Dupuis’ equation, was integrated and run using GaBi4 software. A sensitivity analysis was performed, and four scenarios were developed to assess the impact of vineyard soil management types with decreasing levels of organic matter inputs.Results and discussionSOM accounting reduced the overall CF of one wine bottle from 0.663 to 0.53102kg CO
DOI:10.1016/j.ecoleng.2012.01.016URL [本文引用: 1]
Approaches to reduce N2O emission from crop ecosystems deserves urgent need for climate change mitigation in world agriculture. Yet, unique ecological measures to depress N emission while conserving crop productivity have not yet been well developed for wide ranges of crop ecosystems. In order to establish an ecological engineering option to mitigate N2O emission in rice ecosystems, we conducted a field experiment with biochar amendment on N2O emission from rice paddies in three sites across South China in 2010. This experiment was performed with 6 treatments of biochar rates of 0, 20, and 40tha611 with and without N fertilization respectively. The rice ecosystem was managed with conventional crop production practices as seasonally man-managed wetlands, which were under flooding after seedling transplantation till panicling and drainage during spiking followed by a subsequent moist condition (F-D-M) till harvest across sites. Emission of N2O from rice soil was monitored with closed chambers at 7 days interval throughout the whole rice growing season (WRGS) and the gas samples analyzed with a gas chromatograph (Agilent 7890D) equipped with an electron capture detector (ECD). Total emission of N2O-N ranged from 1.5kgN2O-Nha611 to 1.9kgN2O-Nha611 without biochar, and from 0.8kgN2O-Nha611 to 1.3kgN2O-Nha611 and from 0.7kgN2O-Nha611 to 0.9kgN2O-Nha611 with biochar amendment at 20tha611 and 40tha611, respectively. Thus, biochar amendment depressed total N2O emission from chemical N fertilizer, as the calculated EF of N2O-N emission was reduced from 0.57±0.15% under chemical N fertilizer only to 0.36±0.08% and 0.22±0.04% under biochar amendment at 20tha611 and 40tha611 respectively. The value under biochar amendment at 40tha611 was found even much smaller than that of a continuously flooding rice ecosystem. As soil pH (H2O), content of soil organic carbon and total N were all upraised significantly, biochar amendment improved rice ecosystem functioning by decreasing N2O-N emission per metric ton of rice production from 0.17±0.02kgN2O-N without biochar to 0.10±0.02 and 0.07±0.03kgN2O-N under biochar respectively at 20tha611 and 40tha611. Thus, soil amendment of biochar from crop straw could be adopted as a unique ecological engineering measure to reduce N2O emission while enhancing soil fertility and sustaining rice productivity in rice ecosystems.
DOI:10.1016/j.ejsobi.2014.09.001URL [本文引用: 1]
61Biochar amendment in paddy fields reduced CH4 emissions.61N2O emissions increased by biochar amendment.61Soil Rh increased in a short period by biochar amendment.61Net GHG emission and GHG intensity reduced by biochar amendment.
DOI:10.1016/j.agee.2014.03.002URL [本文引用: 1]
The amendment of biochar derived from crop residues to soil has been proposed as a potential mitigation strategy for tackling greenhouse gas (GHG) emissions in cropping systems. A field experiment was carried out to investigate GHG emissions from rice paddy fields treated with straw incorporation and straw-derived biochar amendment at various rates during two consecutive rice growing seasons in double rice cropping systems. The treatments included the following: control (no straw incorporation and no biochar amendment), low straw (rice straw incorporated at 3tha611), high straw (rice straw incorporated at 6tha611), low biochar (straw-derived biochar amended at 7.5tha611 in 2011 and adjusted to 24tha611 in 2012) and high biochar (straw-derived biochar amended at 22.5tha611 in 2011 and adjusted to 48tha611 in 2012). The results showed that straw incorporation significantly increased CH4 emissions relative to the control treatment, whereas biochar amendment significantly reduced CH4 emissions at the highest application rates (48tha611), possibly due to a biochar-induced increase in soil pH. The seasonal cumulative CH4 emissions from the low and high straw treatments were 3.0–4.1 and 6.4–8.6 times greater, respectively, in the 2011 late rice season and 7–13 and 13–23 times greater, respectively, in the 2012 early rice season than those from both biochar treatments. In contrast, N2O emissions decreased by 26–68% in comparison with the control when straw was applied to the soil, but increased by 0.13–0.80 times in the presence of biochar, possibly due to the increased availability of NH4+ or NO361 originating from the added biochar. The seasonal cumulative N2O emissions were relatively low (15–200gNha611) across all the treatments. The estimated seasonal gross global warming potentials (GWP) of CH4 plus N2O among the treatments showed a similar pattern to the seasonal cumulative CH4 emissions due to the dominance of CH4 to gross GWP (83–99% of the total). As rice straw incorporation also reduced rice grain yield, especially during the early rice season, the yield-scaled GWPs were even higher in the straw amendment treatments compared with the biochar treatments (3.2–4.0 and 7.1–8.8 times in 2011 and 9.4–13 and 18–25 times in 2012 for the low and high straw treatments, respectively). The lower gross and yield-scaled GWPs in paddy fields amended with biochar indicated that transforming straw to biochar and subsequent addition to paddy fields has potential to mitigate GHG emissions in double rice cropping systems.
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DOI:10.1016/j.agee.2011.05.012URL [本文引用: 1]
Characterizing the carbon footprint (CF) of agricultural production offers key information for pursuing low carbon agriculture and food consumption. While China has long strived for increasing food production capacity for its large and still growing population, the high emissions cost, especially from the over use of agro-chemicals, has been widely debated for the last decade. However, the CF of China's crop production has not yet been assessed. This paper reports a basic estimate of CF of crop production using national statistical data available for the period of 1993–2007. The dataset includes the amount of individual agricultural inputs (fertilizer, pesticide, diesel, plastic film, etc.), cultivation area and total of production whole crops. Using the emission factors estimated for China's agricultural features and available abroad, the mean overall CF of China's crop production was estimated to be 0.78 ± 0.08 tCE ha 611 yr 611 and 0.11 ± 0.01 tCE t 611 yr 611, for land use and bulk production respectively. For the duration the data covered, the carbon intensity under cultivation land use was seen to increase since 1993. Among the total, fertilizer induced emissions exerted the largest contribution of 6560%, being 0.45 ± 0.04 tCE per ha and 0.07 ± 0.01 tCE per ton of production, on average. Compared to the UK, the estimated overall CF of China's crop production was higher in terms of cultivation land use. While there was a significant positive correlation of carbon intensity with total production, carbon efficiency was shown in a decreasing trend during 2003-2007. Therefore, low carbon agriculture should be pursued, and the priority should be given to reducing fertilizer application in agriculture of China. However, for developing best management practices for climate change mitigation in crop production of China, further studies of crop and regional specific CFs and the variation with climate conditions and agricultural managements are needed.
DOI:10.3763/ijas.2009.0419URL [本文引用: 1]
The agriculture sector contributes significantly to global carbon emissions from diverse sources such as product and machinery manufacture, transport of materials and direct and indirect soil greenhouse gas emissions. In this article, we use farm survey data from the east of Scotland combined with published estimates of emissions for individual farm operations to quantify the relative contribution of a range of farming operations and determine the carbon footprint of different crops (e.g. legumes, winter and spring cereals, oilseed rape, potato) and farming practices (conventional, integrated and organic). Over all crops and farm types, 75% of the total emissions result from nitrogen fertilizer use (both organic and inorganic) rom production, application, and direct nitrous oxide emissions from the soil resulting from application. Once nitrogen is accounted for, there are no major differences between organic, integrated or conventional farming practices. These data highlight opportunities for carbon mitigation and will be of value for inclusion in full life cycle analyses of arable production systems and in calculations of greenhouse gas balance associated with land-use change.
DOI:10.1046/j.1365-2486.1998.00129.xURL [本文引用: 2]
Reliable regional or global estimates of methane emissions from flooded rice paddy soils depend on an examination of methodologies by which the current high variability in the estimates might be reduced. One potential way to do this is the development of predictive models. With an understanding of the processes of methane production, oxidation and emission, a semi-empirical model, focused on the contributions of rice plants to the processes and also the influence of environmental factors, was developed to predict methane emission from flooded rice fields. A simplified version of the model was also derived to predict methane emission in a more practical manner. In this study, it was hypothesized that methanogenic substrates are primarily derived from rice plants and added organic matter. Rates of methane production in flooded rice soils are determined by the availability of methanogenic substrates and the influence of environmental factors. Rice growth and development control the fraction of methane emitted. The amount of methane transported from the soil to the atmosphere is determined by the rates of production and the emitted fraction. Model validation against observations from single rice growing seasons in Texas, USA demonstrated that the seasonal variation of methane emission is regulated by rice growth and development. A further validation of the model against measurements from irrigated rice paddy soils in various regions of the world, including Italy, China, Indonesia, Philippines and the United States, suggests that methane emission can be predicted from rice net productivity, cultivar character, soil texture and temperature, and organic matter amendments.
URL [本文引用: 2]
[1] Several models have been developed over the past decade to estimate CH4 emission from rice paddies. However, few models have been validated against field measurements with various parameters of soil, climate and agricultural practice. Thus reliability of the model's performance remains questionable particularly when extrapolating the model from site microscale to regional scale. In this paper, modification to the original model focuses on the effect of water regime on CH4 production/emission and the CH4 transport via bubbles. The modified model, named as CH4MOD, was then validated against a total of 94 field observations. These observations covered main rice cultivation regions from northern (Beijing, 4000°30090005N, 11600°25090005E) to southern China (Guangzhou, 2300°08090005N, 11300°20090005E), and from eastern (Hangzhou, 3000°19090005N, 12000°12090005E) to southwestern (Tuzu, 2900°40090005N, 10300°50090005E) China. Both single rice and double rice cultivations are distributed in these regions with different irrigation patterns and various types of organic matter incorporation. The observed seasonal amount of CH4 emission ranged from 3.1 to 761.7 kg C ha0908081 with an average of 199.4 00± 187.3 kg C ha0908081. In consonance with the observations, model simulations resulted in an average value of 224.6 00± 187.0 kg C ha0908081, ranging from 13.9 to 824.3 kg C ha0908081. Comparison between the computed and the observed seasonal CH4 emission yielded a correlation coefficient r2 of 0.84 with a slope of 0.92 and an intercept of 41.1 (n = 94, p < 0.001). It was concluded that the CH4MOD can reasonably simulate CH4 emissions from irrigated rice fields with a minimal number of inputs and parameters.
URL [本文引用: 2]
[1] China is the largest rice producer in the world. Methane (CH4) emission from its rice fields has been widely measured since the late 1980s. This study collected the results of available field research, totaling 204 season-treatment measurements conducted on 23 sites. Analysis of these data shows that input of organic material, such as green manure, animal waste, and crop straw, increases CH4 emission by a factor of 2. Average CH4 flux from intermittently irrigated rice fields is 53% of that from continuously flooded rice fields; and average CH4 emission flux from late rice fields is 1.6 and 2.3 times greater than flux from early and single rice fields, respectively. There are regional differences in emission factors and a trend of decreasing emission from south to north. On the basis of earlier estimates of CH4 emission from Chinese rice fields, and recent reports on the use of crop residue and green manure, it is presumed that half of the rice fields in China receive organic input. From the frequency of various water management events indicated in the surveyed field experiments, as well as from specific statements in individual reports, it is presumed that 2/3 of irrigated rice fields have been intermittently flooded. On the basis of these assumptions, the region-specific emission factors, and 1995 data on rice cultivation area, CH4 emission from growing-season rice fields in Mainland China was estimated to be 7.67 Tg yr0908081, ranging from 5.82 to 9.57 Tg yr0908081, due to uncertainties in the areas receiving organic inputs, and intermittent irrigation. Generalized seasonal flux patterns were developed for early, late, and single rice. Monthly distributions of emission were estimated from these patterns and rice calendars. The highest emission rate occurred in August. Spatially, emission hot spots included the plains of Dongting Lake in Hunan Province, Boyang Lake in Jiangxi Province, the delta region of Qiantang River in Zhejiang Province, and the Sichuan Basin. Nearly 90% of all Mainland China CH4 emission occurred between 2300°N and 3300°N.
DOI:10.1016/j.atmosenv.2007.06.049URL [本文引用: 2]
Various water management regimes, such as continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding-moist intermittent irrigation, but without water logging (F-D-F-M), are currently practiced in paddy rice production in mainland China. These water regimes have incurred a sensitive change in direct N 2O emission from rice paddy fields. We compiled and statistically analyzed field data on N 2O emission from paddy fields during the rice growing season (71 measurements from 17 field studies) that were published in peer-reviewed Chinese and English journals. Seasonal total N 2O was, on average, equivalent to 0.02% of the nitrogen applied in the continuous flooding rice paddies. Under the water regime of F-D-F or the F-D-F-M, seasonal N 2O emissions increased with N fertilizer applied in rice paddies. An ordinary least square (OLS) linear regression model produced the emission factor (EF) of nitrogen for N 2O averaged 0.42%, but background N 2O emission was not pronounced under the water regime of F-D-F. Under the F-D-F-M water regime, N 2O EF and background emission were estimated to be 0.73% and 0.79 kg N 2O-N ha 1, respectively, during the paddy rice growing season. Based on results of the present study and national rice production data, subsequently, direct N 2O emissions during the rice growing season amounted to 29.0 Gg N 2O-N with the uncertainty of 30.1%, which accounted for 7鈥11% of the reported estimates of annual total emission from croplands in mainland China. The results of this study suggest that paddy rice relative to upland crop production could have contributed to mitigating N 2O emissions from agriculture in mainland China.
DOI:10.1639/0044-7447(2002)031[0079:TANCCS]2.0.CO;2URLPMID:12078013 [本文引用: 2]
We analyzed nitrogen budgets at national and regional levels on a timeline from 1961-2030 using a model, IAP-N 1.0. The model was designed based upon the Intergovernmental Panel on Climate Change (IPCC) methods using Asia-specific parameters and a Food and Agriculture Organization of the United Nations (FAO) database. In this paper we discuss new reactive-nitrogen and its various fates, and environmental nitrogen enrichment and its driving forces. The anthropogenic reactive nitrogen of Asia dramatically increased from 14.4 Tg N yr-1in 1961 to 67.7 Tg N yr-1in 2000 and is likely to be 105.3 Tg N yr-1by 2030. Most of the anthropogenic reactive-nitrogen has accumulated in the environment. We found that an increasing demand for food and energy supplies and the lack of effective measures to improve the efficiency of fertilizer nitrogen use, as well as effective measures for the prevention of NOxemissions from fossil-fuel combustion, are the principal drivers behind the environmental nitrogen-enrichment problem. This problem may be finally solved by substituting synthetic nitrogen fertilizers with new high-efficiency nitrogen sources, but solutions are dependent on advances in biological technology.
DOI:10.1007/s00376-008-0181-7URL [本文引用: 2]
A regional nitrogen cycle model, named IAP-N, was designed for simulating regional nitrogen (N) cycling and calculating N fluxes flowing among cultivated soils, crops, and livestock, as well as human, atmospheric and other systems. The conceptual structure and calculation methods and procedures of this model are described in detail. All equations of the model are presented. In addition, definitions of all the involved variables and parameters are given. An application of the model in China at the national scale is presented. In this example, annual surpluses of consumed synthetic N fertilizer; emissions of nitrous oxide (N 2 O), ammonia (NH 3 ) and nitrogen oxide (NO x ); N loss from agricultural lands due to leaching and runoff; and sources and sinks of anthropogenic reactive N (Nr) were estimated for the period 1961–2004. The model estimates show that surpluses of N fertilizer started to occur in the mid 1990s and amounted to 5.7 Tg N yr 611 in the early 2000s. N 2 O emissions related to agriculture were estimated as 0.69 Tg N yr 611 in 2004, of which 58% was released directly from N added to agricultural soils. Total NH 3 and NO x emissions in 2004 amounted to 4.7 and 4.9 Tg N yr 611 , respectively. About 3.9 Tg N yr 611 of N was estimated to have flowed out of the cultivated soil layer in 2004, which accounted for 33% of applied synthetic N fertilizer. Anthropogenic Nr sources changed from 2.8 (1961) to 28.1 Tg N yr 611 (2004), while removal (sinks) changed from to 2.1 to 8.4 Tg N yr 611 . The ratio of anthropogenic Nr sources to sinks was only 1.4 in 1961 but 3.3 in 2004. Further development of the IAP-N model is suggested to focus upon: (a) inter-comparison with other regional N models; (b) overcoming the limitations of the current model version, such as adaptation to other regions, high-resolution database, and so on; and (c) developing the capacity to estimate the safe threshold of anthropogenic Nr source to sink ratios.
DOI:10.1016/j.ecolmodel.2013.04.003URL [本文引用: 1]
The prediction of methane (CH4) emissions from rice paddies could play a key role in greenhouse gas mitigation efforts associated with agriculture. We describe a methanogenesis sub-model that has been developed in the DAYCENT ecosystem model for estimating CH4 emissions and assessing mitigation potentials for rice paddies. Methanogenesis is modeled based on the simulation of soil hydrology and thermal regimes, rice plant growth, SOM decomposition, and CH4 transport from the soil to atmosphere. A total of 97 sites from China's rice paddies were used to develop and evaluate the model, in which 25 sites (91 observations) were used for parameterization and 72 sites (204 observations) were used for model evaluation. Comparison of modeled results with measurements demonstrated that CH4 emissions in rice paddies of China can be successfully simulated by the model with an overall R-2 of 0.83, and included an evaluation of CH4 emissions for a range of climates and agricultural management practices. The model was most sensitive to parameters influencing the amount of labile C available for methanogenesis. (C) 2013 Elsevier B.V. All rights reserved.
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DOI:10.1111/gcbb.2015.7.issue-3URL [本文引用: 1]
DOI:10.1016/j.soilbio.2011.11.019URL [本文引用: 1]
This study compared the effect of two principal pyrolysis methods on the chemical characteristics of biochar and the impact on C and N dynamics after soil incorporation. Biochar was produced from wheat straw that was thermally decomposed at 52502°C by slow pyrolysis (SP) in a nitrogen flushed oven and by fast pyrolysis (FP) using a Pyrolysis Centrifuge Reactor (PCR). After 65 days of soil incubation, 2.9% and 5.5% of the SP- and FP-biochar C, respectively, was lost as CO 2, significantly less than the 53% C-loss observed when un-pyrolyzed feedstock straw was incubated. Whereas the SP-biochar appeared completely pyrolyzed, an un-pyrolyzed carbohydrate fraction (8.8% as determined by acid released C6 and C5 sugars) remained in the FP-biochar. This labile fraction possibly supported the higher CO 2 emission and larger microbial biomass (SMB-C) in the FP-biochar soil. Application of fresh FP-biochar to soil immobilized mineral N (43%) during the 65 days of incubation, while application of SP-biochar led to net N mineralization (7%). In addition to the carbohydrate contents, the two pyrolysis methods resulted in different pH (10.1 and 6.8), particle sizes (113 and 2302μm), and BET surface areas (0.6 and 1.602m 202g 611) of the SP- and FP-biochars, respectively. The study showed that independently of pyrolysis method, soil application of the biochar materials had the potential to sequester C, while the pyrolysis method did have a large influence on the mineralization-immobilization of soil N.
DOI:10.1002/jsfa.5550URLPMID:22227948 [本文引用: 1]
BACKGROUND: Soil organic carbon (SOC) sequestration, methane emission, and the net carbon sink represented by rice straw incorporated into soil (RIS) were studied using long-term experimentation with rice straw incorporated into soil (LRIS) and short-term experimentation with different patterns of rice straw incorporated into soil (SPRIS).RESULTS: Soil organic carbon could be improved by RIS combined with soil ploughing. The increased rate of SOC deposition per cultivated layer was 0.10 t C ha611 for 2.625 t ha611 straw incorporated each season in LRIS and 0.36 t C ha611 for 4.5 t straw ha611 season611 incorporated in SPRIS; the apparent SOC conversion by rice straw (stubble) was reduced as the amount of incorporated straw increased. However, RIS methane emission from paddy fields also significantly exacerbated the CH4 emission flux observed during the early and late rice growing seasons, which was increased by 75.0% (P < 0.01) and 251.5% (P < 0.01), respectively, compared with combined application of nitrogen, phosphorus and potassium fertiliser (NPK). The apparent methane conversion of straw was almost uniform with a similar rice yield and soil cultivating mode. Among the patterns of RIS, methane emission was significantly reduced under straw covering untilled land, and this property led to the lowest apparent methane conversion.CONCLUSION: RIS with ploughing and tilling resulted in negative carbon sequestration because of increased methane emissions. A combined NPK application with only rice stubble incorporation may be sustainable for a higher rice yield, but this approach has a reduced rate of negative carbon sequestration in the paddy field. Straw covering with no tillage was the best measure to realise high yield and low carbon emission for RIS. Copyright 08 2012 Society of Chemical Industry
DOI:10.1021/es400554xURLPMID:23796060 [本文引用: 1]
Biochar addition to soil has been proposed to improve plant growth by increasing soil fertility, minimizing bioaccumulation of toxic metal(liod)s and mitigating climate change. Sewage sludge (SS) is an attractive, though potentially problematic, feedstock of biochar. It is attractive because of its large abundance; however, it contains elevated concentrations of metal(loid)s and other contaminants. The pyrolysis of SS to biochar (SSBC) may be a way to reduce the availability of these contaminants to the soil and plants. Using rice plant pot experiments, we investigated the influence of SSBC upon biomass yield, bioaccumulation of nutrients, and metal(loid)s, and green housegas (GHG) emissions. SSBC amendments increased soil pH, total nitrogen, soil organic carbon and available nutrients and decreased bioavailable As, Cr, Co, Ni, and Pb (but not Cd, Cu, and Zn). Regarding rice plant properties, SSBC amendments significantly (P <= 0.01) increased shoot biomass (71.3-92.2%), grain yield (148.8-175.196), and the bioaccumulation of phosphorus and sodium, though decreased the bioaccumulation of nitrogen (except in grain) and potassium. Amendments of SSBC significantly (P <= 0.05) reduced the bioaccumulation of As, Cr, Co, Cu, Ni, and Pb, but increased that of Cd and Zn, though not above limits set by Chinese regulations. Finally regarding GHG emissions, SSBC significantly (P < 0.01) reduced N2O emissions and stimulated the uptake/oxidation of CH4 enough to make both the cultivated and uncultivated paddy soil a CH4 sink. SSBC can be beneficial in rice paddy soil but the actual associated benefits will depend on site-specific conditions and source of SS; long-term effects remain a further unknown.
DOI:10.1021/es5021058URLPMID:25054835 [本文引用: 1]
Abstract Biochar has been suggested to improve acidic soils and to mitigate greenhouse gas emissions. However, little has been done on the role of biochar in ameliorating acidified soils induced by overuse of nitrogen fertilizers. In this study, we designed a pot trial with an acidic soil (pH 4.48) in a greenhouse to study the interconnections between microbial community, soil chemical property changes, and N2O emissions after biochar application. The results showed that biochar increased plant growth, soil pH, total carbon, total nitrogen, C/N ratio, and soil cation exchange capacity. The results of high-throughput sequencing showed that biochar application increased -diversity significantly and changed the relative abundances of some microbes that are related with carbon and nitrogen cycling at the family level. Biochar amendment stimulated both nitrification and denitrification processes, while reducing N2O emissions overall. Results of redundancy analysis indicated biochar could shift the soil microbial community by changing soil chemical properties, which modulate N-cycling processes and soil N2O emissions. The significantly increased nosZ transcription suggests that biochar decreased soil N2O emissions by enhancing its further reduction to N2.
DOI:10.1038/ismej.2013.160URLPMID:3930306 [本文引用: 1]
Abstract Nitrous oxide (N2O) contributes 8% to global greenhouse gas emissions. Agricultural sources represent about 60% of anthropogenic N2O emissions. Most agricultural N2O emissions are due to increased fertilizer application. A considerable fraction of nitrogen fertilizers are converted to N2O by microbiological processes (that is, nitrification and denitrification). Soil amended with biochar (charcoal created by pyrolysis of biomass) has been demonstrated to increase crop yield, improve soil quality and affect greenhouse gas emissions, for example, reduce N2O emissions. Despite several studies on variations in the general microbial community structure due to soil biochar amendment, hitherto the specific role of the nitrogen cycling microbial community in mitigating soil N2O emissions has not been subject of systematic investigation. We performed a microcosm study with a water-saturated soil amended with different amounts (0%, 2% and 10% (w/w)) of high-temperature biochar. By quantifying the abundance and activity of functional marker genes of microbial nitrogen fixation (nifH), nitrification (amoA) and denitrification (nirK, nirS and nosZ) using quantitative PCR we found that biochar addition enhanced microbial nitrous oxide reduction and increased the abundance of microorganisms capable of N2-fixation. Soil biochar amendment increased the relative gene and transcript copy numbers of the nosZ-encoded bacterial N2O reductase, suggesting a mechanistic link to the observed reduction in N2O emissions. Our findings contribute to a better understanding of the impact of biochar on the nitrogen cycling microbial community and the consequences of soil biochar amendment for microbial nitrogen transformation processes and N2O emissions from soil.
DOI:10.1016/j.agsy.2014.05.008URL [本文引用: 1]
Biochar effects on improving soil fertility, enhancing crop productivity and reducing greenhouse gases (GHGs) emission from croplands had been well addressed in numerous short-term experiments with biochar soil amendment (BSA) mostly in a single crop season/cropping year. However, the persistence of these effects, after a single biochar application, has not yet been well known due to limited long-term field studies so far. Large scale BSA in agriculture is often commented on the high cost due to large amount of biochar in a single application. Here, we try to show the persistence of biochar effects on soil fertility and crop productivity improvement as well as GHGs emission reduction, using data from a field experiment with BSA for 5-crop seasons in central North China. A single amendment of biochar was performed at rates of 0 (C0), 20 (C20) and 40tha 1 (C40) before sowing of the first crop season. Emissions of CO2, CH4 and N2O were monitored with static closed chamber method throughout the crop growing season for the 1st, 2nd and 5th cropping. Crop yield was measured and topsoil samples were collected at harvest of each crop season. BSA altered most of the soil physico-chemical properties with a significant increase over control in soil organic carbon (SOC) and available potassium (K) content. The increase in SOC and available K was consistent over the 5-crop seasons after BSA. Despite a significant yield increase in the first maize season, enhancement of crop yield was not consistent over crop seasons without corresponding to the changes in soil nutrient availability. BSA did not change seasonal total CO2 efflux but greatly reduced N2O emissions throughout the five seasons. This supported a stable nature of biochar carbon in soil, which played a consistent role in reducing N2O emission, which showed inter-annual variation with changes in temperature and soil moisture conditions. The biochar effect was much more consistent under C40 than under C20 and with GHGs emission than with soil property and crop yield. Thus, our study suggested that biochar amended in dry land could sustain a low carbon production both of maize and wheat in terms of its efficient carbon sequestration, lower GHGs emission intensity and soil improvement over 5-crop seasons after a single amendment.
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Abstract Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas (GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta???analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation.
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DOI:10.1016/j.soilbio.2016.07.021URL [本文引用: 1]
61Biochar application to soil has the potential to increase or decrease soil methane emissions.61Water management is a key factor affecting biochar's influence on the soil methane flux.61Soil pH is one of the main determinants underlying biochar's effect on soil methane fluxes.61We posit several mechanisms underlying the observed effects of biochar application on soil methane emissions.
DOI:10.1016/j.jclepro.2017.03.133URL [本文引用: 1]
Carbon dioxide and nitrous oxide are two important greenhouse gases (GHG) released from cropping systems. Their emissions can vary substantially with climate, soil, and crop management. While different methods are available to account for GHG emissions in life cycle assessments (LCA) of crop production, there are no standard procedures. In this study, the objectives were: (i) to compare several methods of estimating CO 2 and N 2 O emissions for a LCA of cropping systems and (ii) to estimate the relative contribution of soil GHG emissions to the overall global warming potential (GWP) using results from a field experiment located in Manitoba, Canada. The methods were: (A) measurements; (B) Tier I and (C) Tier II IPCC (Intergovernmental panel on Climate Change) methodology, (D) a simple carbon model combined with Intergovernmental Panel for Climate Change (IPCC) Tier II methodology for soil N 2 O emissions, and (E) the DNDC (DeNitrification DeComposition) agroecosystem model. The estimated GWPs (617.2–17Mg CO 2 eq ha 611 y 611 ;6180 to 600kg CO 2 eq GJ 611 y 611 ) were similar to previous results in North America and no statistical difference was found between GWP based on methods D and E and GWP based on observations. The five methods gave estimates of soil CO 2 emissions that were not statistically different from each other, whereas for N 2 O emissions only DNDC estimates were similar to observations. Across crop types, all methods gave comparable CO 2 and N 2 O emission estimates for perennial and legume crops, but only DNDC gave similar results with respect to observations for both annual and cereal crops. Whilst the results should be confirmed for other locations, the agroecosystem model and method D can be used, at certainly one selected site, in place of observations for estimating GHGs in agricultural LCA.
