Agricultural practices contribute significant levels of greenhouse gas (GHG) emissions. Methods to measure net global warming potential (GWP) and greenhouse gas intensity (GHGI) that account for all sources and sinks of GHG emissions in agroecosystems are still evolving. Sources of GHGs include soil CO₂, N₂O, and CH₄ emissions and CO₂ emissions associated with farm operations, N fertilization, and other chemical inputs. Sinks of GHGs include CH₄ uptake, soil C sequestration, and crop residue returned to the soil. This chapter discusses the methods of measuring net GWP and GHGI using two approaches: In the soil organic C (SOC) method, net GWP and GHGI are calculated by using N₂O and CH₄ emissions (or CH₄ uptake), as well as CO₂ emissions from farm operations, N fertilization, and other chemical inputs as GHG sources and C sequestration rate (ΔSOC) as GHG sink. In the soil respiration method, soil respiration (excluding root respiration) is included as another GHG source, and the previous year's crop residue returned to the soil instead of ΔSOC is included as GHG sink in addition to the above parameters. Advantages and drawbacks of each method of calculating net GWP and GHGI are also discussed.

中文翻译：

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净全球变暖潜能和温室气体强度

农业实践造成了大量的温室气体（GHG）排放。衡量农业生态系统中所有温室气体排放源和汇的净全球变暖潜势（GWP）和温室气体强度（GHGI）的方法仍在发展。温室气体的来源包括土壤CO ₂，N ₂ O和CH ₄排放以及与农场经营，氮肥和其他化学投入有关的CO ₂排放。温室气体汇包括CH ₄吸收，土壤固碳和农作物残渣返回土壤。本章讨论使用两种方法测量净GWP和GHGI的方法：在土壤有机碳（SOC）方法中，使用N ₂计算净GWP和GHGI。O和CH ₄排放（或CH ₄吸收），以及来自农场运营，氮肥和其他化学投入的CO ₂排放作为温室气体源，碳封存率（ΔSOC）作为温室气体汇。在土壤呼吸法中，包括土壤呼吸（不包括根系呼吸）作为另一种温室气体源，除上述参数外，还包括返回土壤的上一年农作物残渣而不是ΔSOC。还讨论了每种计算净GWP和GHGI的方法的优缺点。