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Crop residues contribute minimally to spring-thaw nitrous oxide emissions under contrasting tillage and crop rotations
Soil Biology and Biochemistry ( IF 9.7 ) Pub Date : 2020-10-30 , DOI: 10.1016/j.soilbio.2020.108057
Pedro Vitor Ferrari Machado , Richard E. Farrell , Gordon Bell , Caio J. Taveira , Katelyn A. Congreves , R. Paul Voroney , William Deen , Claudia Wagner-Riddle

Crop residues are sources of carbon and nitrogen (N) after harvest, releasing inorganic N through mineralization or protecting soil N through immobilization. Inorganic N controls nitrous oxide (N2O) emissions, a potent greenhouse gas (GHG) from agriculture. Hence, crop residues are accounted for as N2O sources in national GHG inventories. For locations where post-harvest N2O emissions occurs due to freeze-thaw, it is not known if crop residues contribute to emissions, and if tillage or residue type impact this contribution. This is of concern since crop residue and freeze-thaw emission factors (EF) may be ‘double-counting’ N2O sources. We conducted an experiment over two non-growing seasons (NGS) in a long-term corn, soybean and winter wheat trial to (i) compare N2O emissions for different crop residues within simple or diverse crop rotations under no-tillage (NT) or conventional tillage (CT); (ii) determine the importance of above- and below-ground residue addition to spring-thaw N2O emissions as affected by rotation and tillage. A15N residue enrichment study was used to directly trace above- and below-ground residue 15N into 15N2O fluxes and derive EF. Higher N2O emissions were observed for CT than NT, regardless of rotation. Soybeans induced higher N2O emissions than corn residue and the same crop residue (e.g. corn or soybean) showed trends of higher N2O in the long-term diverse rotation. In all cases, crop residues contributed minimally to spring-thaw N2O emissions (<2%), meaning differences in N2O emissions were due to tillage and rotation effects on soil N availability, rather than by affecting crop residue N release for N2O production. The NGS 6-month EF for crop residues never surpassed 0.05%, a minimal fraction of the annual 0.6% recommended EF. Refinement in emission inventories for cold climates should focus on freeze-thaw substrate release for N2O production from other sources than crop residue.



中文翻译:

在相反的耕作和轮作条件下,农作物残留物对春季融化一氧化二氮的排放影响最小。

作物残余物是收获后的碳和氮(N)来源,通过矿化释放无机氮或通过固定化保护土壤氮。无机氮控制一氧化二氮(N 2 O)的排放,这是一种来自农业的强力温室气体(GHG)。因此,农作物残渣在国家温室气体清单中被列为N 2 O来源。对于因冰冻融化而导致收获后N 2 O排放的地区,尚不知道农作物残余物是否会造成排放,耕作或残余物类型是否会影响这一贡献。这是令人关注的,因为农作物残留物和冻融排放因子(EF)可能是“重复计算”的N 2来源。在一项长期的玉米,大豆和冬小麦试验中,我们在两个非生长季节(NGS)上进行了一项实验,以(i)比较免耕(NT)下简单或多样化轮作中不同作物残留的N 2 O排放)或常规耕作(CT);(ii)确定受旋转和耕作影响的地上和地下残留物添加对春季融化的N 2 O排放的重要性。使用15 N残留物富集研究直接将地上和地下残留15 N转化为15 N 2 O通量,并得出EF。无论旋转如何,CT观察到的N 2 O排放量均高于NT。大豆诱导较高的N 2含量在长期的不同轮作中,O排放量比玉米残渣和相同的农作物残渣(例如玉米或大豆)呈现出更高的N 2 O趋势。在所有情况下,农作物残余物对春季融化后的N 2 O排放的贡献最小(<2%),这意味着N 2 O排放量的差异是由于耕作和轮作对土壤氮素有效性的影响,而不是因为影响了土壤氮素释放量。 N 2 O生产。NGS作物残渣的6个月EF从未超过0.05%,仅为年度推荐EF的0.6%的很小一部分。应对寒冷气候下的排放清单进行细化,应着重于从作物残渣以外的其他来源生产N 2 O的冻融基质释放。

更新日期:2020-10-30
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