Abstract Agriculture represents about 10 % of total greenhouse gases (GHG) emission in the US, in which carbon dioxide (CO2) and nitrous oxide (N2O) can greatly contribute to global warming and climate change. Organic farming has been increasingly popular as it provides long-term environmental benefits including GHG mitigation. Judicious use of cover crops in crop rotation systems has been considered an effective approach to sustain crop productivity during organic transition period. Here, we examined effects of cover crops on soil CO2 and N2O fluxes after the first year of organic transition in corn-soybean-wheat rotation across three contrasting topographies, particularly depression, slope, and summit at Kellogg Biological Station located in Southwest Michigan, USA. Three cover cropping systems used in this study were (1) cereal rye; (2) a mixture of cold susceptible species, namely, oat, winter pea, and radish, frost-killed in winter (WK); and (3) a winter hardy mixture of cold tolerant species, namely annual ryegrass, Dwarf Essex rapeseed, and crimson clover (WH). We also examined the effect of the size of incorporated plant residue fragments on soil CO2 and N2O emissions. Soil GHG emissions were the lowest on slopes as compared to depressions and summits. Cover crop mixtures including WH and WK increased soil CO2 fluxes emitted from the soil while cereal rye decreased it. Cutting plant residues prior to incorporation tended to decrease CO2 emission, suggesting that reducing fragment size of incorporated residue has a potential to mitigate GHG emissions from agricultural soils. In contrast, differences in N2O emissions for any of the studied effects were not statistically significant, likely due to very high variability of N2O fluxes. Soil temperature, moisture and total aboveground biomass were strongly associated with soil CO2 and N2O fluxes from soil.

中文翻译：

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在玉米-大豆-小麦有机转变中，覆盖作物对地形多样的农业景观土壤 CO2 和 N2O 排放的影响

摘要 农业约占美国温室气体 (GHG) 排放总量的 10%，其中二氧化碳 (CO2) 和一氧化二氮 (N2O) 会极大地促进全球变暖和气候变化。有机农业越来越受欢迎，因为它提供了包括温室气体减排在内的长期环境效益。在轮作系统中明智地使用覆盖作物被认为是在有机过渡期间维持作物生产力的有效方法。在这里，我们在位于美国密歇根州西南部的凯洛格生物站研究了玉米 - 大豆 - 小麦轮作有机转变第一年跨越三个对比地形，特别是洼地、斜坡和山顶时，覆盖作物对土壤 CO2 和 N2O 通量的影响. 本研究中使用的三种覆盖作物系统是 (1) 谷物黑麦；(2) 冬季冻死的燕麦、冬豌豆、萝卜等易感寒种的混合物；(3) 耐寒物种的冬季耐寒混合物，即一年生黑麦草、矮埃塞克斯油菜籽和深红三叶草 (WH)。我们还研究了掺入的植物残体碎片大小对土壤 CO2 和 N2O 排放的影响。与洼地和山顶相比，斜坡上的土壤温室气体排放量最低。包括 WH 和 WK 在内的覆盖作物混合物增加了从土壤中排放的土壤 CO2 通量，而谷物黑麦则减少了它。在掺入之前切割植物残留物往往会减少 CO2 排放，这表明减少掺入残留物的碎片大小有可能减少农业土壤的温室气体排放。相比之下，对于任何研究的影响，N2O 排放的差异在统计上并不显着，这可能是由于 N2O 通量的非常高的可变性。土壤温度、水分和总地上生物量与来自土壤的土壤 CO2 和 N2O 通量密切相关。