中国旱作农田一氧化氮排放及减排:Meta分析

Nitric Oxide Emissions from Chinese Upland Cropping Systems and Mitigation Strategies:A Meta-analysis

农田是大气污染物一氧化氮(NO)的主要排放源之一.与水稻田相比,旱作农田NO排放量和排放系数高,但其异质性及影响因素尚不明确.目前,我国农田NO排放和减排的研究以原位观测为主,缺乏系统的整合(Meta)分析.通过收集文献数据,定量分析玉米-冬小麦、水稻-冬小麦旱地阶段、蔬菜、茶园和果园等旱作体系NO排放量和排放系数的异质性及主要影响因素;定量评价减量施氮、有机肥替代化肥、配施新型增效氮肥和施用生物质炭等管理措施对NO排放量和排放系数的影响.收集相关文献共计49篇(发表于2006~2021年).结果表明,玉麦轮作、茶园和果园体系年排放量平均值分别为1.44、7.45和0.92 kg·hm^(-2),在这3个体系间有显著性差异(P<0.05),稻麦轮作旱地阶段和蔬菜季节排放量平均值分别为2.13 kg·hm^(-2)和2.09 kg·hm^(-2).在玉麦轮作、稻麦轮作旱地阶段和茶园体系中,NO排放量均与施氮量呈正相关关系(P<0.01),但在蔬菜和果园体系中二者无显著相关性.玉麦轮作、稻麦轮作旱地阶段、蔬菜、茶园和果园体系排放系数平均值分别为0.31%、0.71%、0.96%、1.74%和0.13%,除玉麦轮作分别与稻麦轮作旱地阶段和蔬菜体系间的差异不显著外(P>0.05),在其余体系间均有显著性差异(P<0.01).由于各体系间排放系数差异大,在编制区域或全国农田NO排放清单时,有必要对各作物体系采用不同的排放系数.减量施氮仅在减氮比例高于25%时可显著降低NO排放量(36%),但对排放系数的影响不显著.由于减氮比例过高可能会造成作物减产,尚需进一步确定既不影响作物产量又降低NO排放的减氮比例.有机肥替代化肥在土壤有机碳含量低[ω(SOC)<15 g·kg^(-1)]或酸性(pH<7)条件下以及配施新型增效氮肥在玉麦轮作农田中可显著降低NO排放量(-46%~-38%)和排放系数(-62%~-45%),施用生物质炭的影响不显著.可为不同田间条件下分别采取有效的NO减排措施提供依据.

Agroecosystems are a significant source of nitric oxide(NO),a potent atmospheric pollutant.It has been well documented that the NO emissions from upland cropping systems and their emission factors are large relative to those from paddy fields.However,a clear understanding of their uncertainty and regulating factors is still lacking.To date,various field experiments have been conducted to investigate NO emissions and mitigation,providing an opportunity for a Meta-analysis.The aims of this study were to 1 investigate the uncertainty and regulating factors of NO emissions and emission factors from maize-winter wheat rotations,non-waterlogging period in rice-winter wheat rotations,vegetable fields,tea plantations,and fruit orchards across China by extracting data from peer-reviewed publications,and 2 quantify the mitigation potential of management practices,such as reducing nitrogen fertilizer input,organic substitution with chemical fertilizers,and application of enhanced-efficiency nitrogen fertilizers or biochar by performing a pairwise Meta-analysis.A total of 49 references(published from 2006 to 2021)were collected.The results showed that annual NO emissions from the maize-winter wheat rotations,tea plantations,and fruit orchards averaged 1.44,7.45,and 0.92 kg·hm^(-2),respectively,with significant differences among the three cropping systems(P<0.05).The seasonal NO emissions from the non-waterlogging period in rice-winter wheat rotations and vegetable fields within a single growth period averaged 2.13 kg·hm^(-2)and 2.09 kg·hm^(-2),respectively.The NO emissions positively related to nitrogen inputs in the maize-winter wheat rotations,non-waterlogging period in rice-winter wheat rotations,and tea plantations(P<0.01)but not in the vegetable fields and fruit orchards.The emission factors averaged 0.31%,0.71%,0.96%,1.74%,and 0.13%in the maize-winter wheat rotations,non-waterlogging period in rice-winter wheat rotations,vegetable fields,tea plantations,and fruit orchards,respectively,with significant differences among the cropping systems(P<0.01),except between the maize-winter wheat rotations and non-waterlogging period in rice-winter wheat rotations or vegetable fields(P>0.05).Considering the substantial differences in emission factors among the cropping systems,a specific emission factor for each system should be applied when estimating an agricultural NO budget at a regional or national scale.Reducing nitrogen input only mitigated NO emissions(by 36%)at a reducing nitrogen ratio above 25%but did not impact emission factors.An optimal reducing nitrogen ratio has to be further evaluated without crop productivity penalties.Organic substitution in soils with organic carbon content<15 g·kg^(-1)or pH<7 and application of enhanced-efficiency fertilizers in the maize-winter wheat rotation simultaneously mitigated NO emissions(by-46%--38%)and emission factors(by-62%--45%).By contrast,biochar amendment had no significant effects on either NO emissions or emission factors.These findings highlight a possibility of choosing an effective NO mitigation strategy under specific field conditions.