ABSTRACT

We designed a new approach for modeling the nitrous oxide (N₂O) derived from nitrogen (N) mineralization associated with loss of soil organic matter (SOM) that meets the current IPCC guidelines (GL) because the method currently used in the National GHG Inventory Report (NIR) of Japan does not. Loss of soil carbon (C) was calculated by using the previously developed nationwide soil C calculation system for agricultural soils. We conducted a zero-C-input soil C modeling experiment, which is a one-year simulation without C input after a long-term ‘normal’ simulation with C input. Because no new organic matter was added to the system in the one-year simulation, we considered that C loss was equal to the C loss from SOM loss. Next, the amount of C loss was divided by the soil C/N ratio for each soil and agricultural land use type to calculate the amount of N mineralization. Finally, N mineralization quantity was converted to N₂O emission by using an empirical model. Because the use of this empirical model cannot be justified for paddy fields, the use of IPCC default emission factor should be recommended instead of the empirical model-derived emission. We consider that these calculated N₂O is derived from N mineralization associated with SOM loss. Our new approach, however, was not yet validated against field observation. The results are therefore only tentative and waiting for the field validation.

摘要

我们设计了一种新方法来模拟一氧化二氮 (N ₂O) 源自与土壤有机质 (SOM) 损失相关的氮 (N) 矿化，符合当前 IPCC 指南 (GL)，因为日本国家温室气体清单报告 (NIR) 目前使用的方法不符合此要求。土壤碳 (C) 损失是通过使用先前开发的全国农业土壤土壤碳计算系统来计算的。我们进行了零 C 输入土壤 C 建模实验，这是在使用 C 输入进行长期“正常”模拟之后，在没有 C 输入的情况下进行的为期一年的模拟。因为在一年的模拟中没有向系统添加新的有机物，我们认为 C 损失等于 SOM 损失的 C 损失。接下来，将碳损失量除以每种土壤和农业用地类型的土壤碳氮比，计算氮矿化量。最后，₂ O 排放使用经验模型。因为对于稻田使用这种经验模型是不合理的，所以应该推荐使用 IPCC 缺省排放因子而不是经验模型导出的排放。我们认为这些计算出的 N ₂ O 来自与 SOM 损失相关的 N 矿化。然而，我们的新方法尚未针对实地观察进行验证。因此，结果只是暂定的，正在等待现场验证。