ABSTRACT

Estimation of the soil organic carbon (SOC) stock based on the monitoring data is important to validate the carbon model estimates and provide the initial values of SOC stock to the model. The Japanese National Greenhouse Gas Inventory Report (NIR) has applied the RothC model since 2015 to report changes in SOC in agricultural land. This study estimated soil carbon and nitrogen stocks and C:N ratio of top 30 cm arable land in Japan using the 2015–2018 database of the national soil monitoring project. Estimates based on the stationary monitoring data from the top 30 cm of the soil layer arethe first public release. We modified categorization of the soil temperature regime and soil-type classification for estimation, expecting to mitigate the underestimation and overestimation of SOC stock in the areas of soil temperature 15–17°C and more than 17°C, respectively, and to optimize the soil classification to 16 fewer types to allow an appropriate estimation even in the current situation of decreasing number of survey sites. Statistical analysis to see the effects of land use and soil temperature on SOC stock, TN stock, and C:N ratio showed that soil types other than Andosols had an inverse temperature-dependent trend for all variables, while Andosols had an unclear trend in soil temperature, supporting existing studies. Also, when Lowland soils (Fluvisols or Anthrosols in the World Reference Base) were surrounded by Andosols, redeposition of volcanic ash could affect the temperature trend in SOC stock for Lowland soils. The distribution map of the SOC stock and C:N ratio across Japan visually showed a high value in the Andosols distribution areas and a temperature-dependent trend at the distribution areas of the other soil types. The total SOC stock estimated in this study was 176±12.8 TgC in paddy field, 100±8.6 TgC in upland field, 25±1.7 TgC in orchard, 78±8.9 TgC in grassland, and 379±17.9 TgC in total, the standard deviations of which were much smaller than those of the mean values for each land use calculated by the simple average method.

摘要

根据监测数据估算土壤有机碳 (SOC) 储量对于验证碳模型估计值和为模型提供 SOC 储量的初始值非常重要。日本国家温室气体清单报告 (NIR) 自 2015 年起就应用 RothC 模型来报告农业用地 SOC 的变化。本研究利用国家土壤监测项目 2015-2018 年数据库估算了日本前 30 厘米耕地的土壤碳和氮储量和碳氮比。首次公开发布的是基于土壤层顶部 30 cm 的静态监测数据的估计值。我们修改了土壤温度状况的分类和土壤类型分类以进行估计，以期减轻土壤温度 15-17°C 和超过 17°C 地区对 SOC 储量的低估和高估，分别，并将土壤分类优化到 16 个更少的类型，以便即使在调查站点数量减少的当前情况下也能进行适当的估计。查看土地利用和土壤温度对 SOC 储量、TN 储量和 C:N 比影响的统计分析表明，除 Andosols 以外的土壤类型对所有变量都具有逆温度依赖性趋势，而 Andosols 在土壤中的趋势不明确温度，支持现有的研究。此外，当低地土壤（世界参考基准中的流质土壤或 Anthrosols）被 Andosols 包围时，火山灰的再沉积会影响低地土壤 SOC 储量的温度趋势。SOC库存和C的分布图：日本全国的氮比在 Andosols 分布区直观地显示出较高的值，而在其他土壤类型的分布区则呈现出随温度变化的趋势。本研究估计的总 SOC 储量在稻田为 176±12.8 TgC，在旱地为 100±8.6 TgC，在果园为 25±1.7 TgC，在草地为 78±8.9 TgC，总共为 379±17.9 TgC，标准差其中远小于通过简单平均法计算的每种土地利用的平均值。